AC&R 4-1 June 1996

Refrigeration, Air Conditioning, andElectronics Cooling Water Systems

Chapter Four

References◊ NSTM Chapter 510, Heating, Ventilation and Air Conditioning for Surface Ships

◊ NSTM Chapter 516, Refrigeration Systems

◊ NSTM Chapter 532, Liquid Cooling Systems for Electronic Equipment

◊ Chapters 22 and 23, Volume 3, DD-963 Propulsion Plant Manual, S9234-AL-GTP-030

◊ Chapters 22 and 23, Volume 3, FFG-7 Propulsion Plant Manual, S9234-BL-GTP-030

◊ 150-Ton Air Conditioning Plant Technical Manual for DD-963’s, NAVSEA S9514-CF-MMA-010

◊ 1.5-Ton Ship’s Stores Refrigeration Plant Technical Manual for DD-963’s, NAVSEA 0959-LP-047-4010

◊ Ship’s Stores Refrigeration Plant for AE-26/27 Class Ships, NAVSEA 0959-LP-022-5010

◊ 80-Ton Air Conditioning Plant (HFC-134a) Technical Manual for FFG-7’s, NAVSEA S9514-DL-MMO-A10

◊ Volume 2, Parts 2 and 3, Ship’s Information Book for DD-985, 9DD0-64-SIB-030/DD-985 andS9DD0-64-SIB-040/DD-985

◊ COMNAVSEASYSCOM WASHINGTON DC 201128Z OCT 94, Alarms for Electronic CoolingWater Loops No. 1 and 2 for DD-963 Class

◊ Management of Ozone Depleting Substances, Chapter 6, OPNAVINST 5090.1B of 1 November1994, Environmental and Natural Resources Program Manual

ObjectivesYou should be able to satisfy the following objectives once you’ve waded through this tome on air

conditioning and refrigeration:

• Understand the basic thermodynamic cycle for air conditioning and refrigeration (AC&R) systems.

• Describe major refrigeration system components paying particular attention to their purpose andfunction for proper and safe system operation. Familiarity with the following specific componentsand subsystems shall be gained:

◊ Thermostatic Expansion Valve (TXV) and Hand Expansion Valve (HXV).

◊ Compressor and its safety features.

◊ Capacity Control System and Loading and Unloading feature.

◊ Condenser, Water Regulating Valve (WRV), and Receiver.

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◊ Dehydrator and Heat Exchanger.

◊ King, or Liquid Line, Solenoid Valve and Thermostat.

◊ Evaporator Pressure Regulating Valve (EPRV).

• Understand AC&R operational modes and typical problems associated with normal system operation:

◊ Pulldown.

◊ Normal, or Temperature Holding, Operation.

◊ Hot Gas Bypass.

◊ Purging.

◊ Effects of moisture in refrigerant piping.

◊ Miscibility of lubricating oil and refrigerant.

• Describe air conditioning and chill water system components and their operational features, such as:

◊ Water Chiller.

◊ Low Temperature Switch.

◊ Chill Water Circulating Pump.

◊ Expansion Tank.

◊ Cooling Coils and Drip Pans.

◊ Thermostat and Solenoid Valve.

◊ Orifice.

• Understand the purposes and functions of the electronics cooling system and its major components insupport of combat systems operation.

• Understand the provisions of the Clean Air Act of 1990 and its impact on shipboard operation,maintenance, and training in support of AC&R systems. The Navy’s program to convert shipboardAC&R systems to replace Freon (R-12) with HFC-134a will be presented. The requirements forfamiliarity with the following shall be understood:

◊ EPA certification of all AC&R technicians.

◊ EPA record keeping and AC&R leak repair criteria.

◊ Navy’s program to manage Ozone Depleting Substances (ODSs).

• Be familiar with the requirements to utilize Refrigerant Recovery Units (RRUs) and Purge and PumpOut (PPO) units.

You will also be introduced to some (real) basic troubleshooting for some typical (and recurring) problemswith AC&R systems in the fleet. Try and develop an understanding of some of these deficiencies. Application ofthis knowledge will help to make your plants operate effectively and efficiently.

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Introduction

Recent Inspection ResultsRecent INSURV inspections and SOSMRC underway training periods have shown material deficiencies

in air conditioning and refrigeration (AC&R) systems indicating that these systems are not being maintained andoperated in accordance with the requirements. One of the principle reasons for this is a lack of understanding ofthe fundamentals of refrigeration. Inspections show a recurring problem: inoperative and/or bypassed automaticcontrol devices and switches. Sample inspection results are:

⇒ The No. 1 and 2 refrigeration plant water regulating valves were inoperative and bypassed.

⇒ The No. 1 refrigeration plant low pressure switch was inoperative.

⇒ The No. 3 A/C plant water failure switch was inoperative.

⇒ The A/C system was significantly degraded due to missing valves, inoperative thermostats, dirty ventducting, and modified vent ducting.

⇒ Five of eight A/C units were inoperative.

⇒ The refrigeration system was contaminated with dirt.

⇒ Thermostatic expansion valves were inoperative and hand expansion valves were being used.

⇒ Water regulating valves were bypassed.

⇒ Freeze box temperatures were out of specification.

⇒ Both refrigeration compressors were receiving Freon in a liquid state due to failure of the thermostaticexpansion valves.

⇒ No. 1 and 2 refrigeration compressors’ safety switches improperly set.

⇒ No. 1 A/C plant sea water strainer and condenser headers heavily fouled with marine growth. Zincswere significantly degraded.

⇒ Chill water (CW) imbalance and insufficient CW to support 4 CIWS when only 2 A/C plantsoperating.

⇒ All NTDS console electronics cooling water low flow switches inoperative.

⇒ Halocarbon monitors inoperative.

Basic Principles of RefrigerationThe purpose of refrigeration is to cool spaces, objects, or materials and to maintain them at a temperature

below the temperature of the surrounding atmosphere. In order to produce a refrigeration effect, it is merelynecessary to expose the material to be cooled to a colder object or environment and allow heat to flow in its"natural" direction, that is, from the warmer material to the colder material. So, the heat we do not want will beremoved, cooling the space or equipment. For example, a pan of hot water placed on a block of ice will be cooledby the flow of heat from the hot water to the ice. This refrigeration effect can be maintained as long as thetemperature differential exists between the ice and the hot water, or until their temperatures have equalized. Butno matter how much ice there is, the water cannot be cooled below 32°F.

The ice absorbs the latent heat of vaporization when it melts. Latent heat transfer is important torefrigeration because of the significant amount of heat required to transform liquid water to a vapor. Recall fromthermodynamics that one pint of water (1 lb) absorbs 970 BTUs when it boils from water to steam at a constant

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temperature and pressure. Under these saturation conditions where the temperature does not change, the heattransferred is called latent heat of vaporization. If that same pint of water stayed a liquid, you would have toraise its temperature by 970°F to absorb the same 970 BTUs! Likewise, to transform 1 pint of liquid water (1 lb) toice at 32°F requires that 144 BTUs be removed from the liquid. This form of heat transferred is called the latentheat of fusion. (No relation to nuclear fusion!)

In refrigeration, the key has always been finding a "refrigerant" that changes phase (boils) at atemperature cold enough to maintain the temperature of the space or equipment below a particular setting. Forexample, if you want to make ice and store it at 0°F, you need a refrigerant that boils below 0°F, so that the heat isremoved or transferred from the warmer liquid water to the colder refrigerant. Once the 144 BTUs for every poundof water has been removed, ice is formed. At atmospheric pressure, water boils at 212°F (not a good refrigerant),but R-12 boils at -21°F and ammonia boils at -28°F.

When the temperature of the working fluid (the refrigerant) is below that of the body being cooled, heatflows from the body to the working fluid and, when the temperature of the working fluid is greater than that of thesurrounding atmosphere, heat is given up to the atmosphere. In many refrigeration systems, this change oftemperature of the working substance is effected by the expenditure of mechanical energy, i.e., by doing work uponthe working fluid, commonly with a compressor.

The capacity of any refrigerating system is the rate at which it will remove heat from the refrigeratedspace and is usually stated either in BTU/hour or in tons of refrigeration.

Basic Thermodynamic DefinitionsReviewing some of the basic thermodynamic concepts will assist in establishing a frame work in

understanding and the discussing refrigeration both as a thermodynamic process and as a shipboard system.

Heat and Temperature. Heat is the thermal energy a body contains. Temperature is the measure of theamount of heat, or thermal energy, of a body. Temperature is familiar to us all as degrees of Fahrenheit or Celsius.The quantity or amount of heat measured in terms of a standard unit is called a British Thermal Unit (BTU).

British Thermal Unit (BTU). The amount of heat needed to raise one pound of water 1°F at atmosphericpressure.

Sensible Heat. Sensible heat is that heat given off or absorbed by a substance which does not cause thesubstance to change phase. Sensible heat changes are observed as changes in temperature and are measured by athermometer.

Latent Heat. Latent heat is given off or absorbed by a substance that is changing phase (e.g., liquid to gasor solid to liquid or vice versa). The temperature and pressure remain constant during the phase change until allthe substance has been transformed. These temperature and pressure conditions are unique and are calledsaturation conditions. The latent heat of vaporization (LHV) is the heat required to transform a liquid to a gasat constant temperature and pressure (i.e., saturation). The latent heat of condensation (LHC) is equivalent inmagnitude to the LHV for the substance, but now we are going in the opposite direction in transforming the gas toa liquid. When a liquid is transformed to a solid as in the ice-making process, the liquid gives off its latent heat offusion (LHF) to form the solid. The LHF to transform a pint of water to 1 lb of ice at 32°F is 144 BTUs. Wewould have to add 144 BTUs to every pound of ice to melt it.

Specific Heat. Specific heat is the amount of heat required to raise one pound of a substance 1°F atatmospheric pressure. (Notice the difference with the definition of the BTU: the BTU is the heat required to raisethe temperature of water, whereas specific heat is for any substance.)

Flow of heat. Heat flow may take place by radiation, convection and conduction. Heat always flows fromthe hotter substance to the colder one. Total heat is the combination of sensible and latent heat.

Ton. The refrigeration ton is based on the cooling effect of one ton (2000 pounds at 144 BTU/lb) of ice at32°F melting in 24 hours. The refrigeration ton is the standard unit of measure used to designate the heat removal

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capacity of a refrigeration unit as measured in the space being refrigerated, i.e., freeze box heat transfer rate. Onerefrigeration ton removes 12,000 BTU’s per hour, the same as a mid-sized portable room A/C unit.

Pressure and Temperature. The boiling point of any liquid varies according to the pressure on the liquid:the higher the pressure, the higher the boiling point. We select refrigerants that boil at low pressures and lowtemperatures, so that, the latent heat of vaporization can be removed at low temperatures. For example, R-12 boilsat -21°F at atmospheric pressure. R-12 boils in the cooling coils in the freeze box as it absorbs latent heat.Compressing a gas raises its temperature. This is known as the heat of compression. Conversely, expanding agas lowers its temperature. And, this is called the cold of expansion. These concepts are very important in therefrigeration cycle.

Types of RefrigerantsRefrigerants are a broad class of substances used to cool air, equipment, and spaces. They are classified

by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) using a prefix (theletter "R" for refrigerant) and a numbering system. Some examples are: air (R-729), nitrogen (R-728), ammonia(R-717), and water (R-718). The largest and most common refrigerants used commercially (and in the Navy) arein the Freon family. These substances contain fluorine, chlorine, and hydrocarbons in their molecular structures,i.e., fluoro-chloro-hydrocarbons. Freon refrigerants have boiling points in the range of -41°F to 74°F. Thistemperature range gives them a wide variety of uses. The following table shows the primary members of the Freonfamily today with their uses in the US Navy:

Freon ChemicalComposition

ASHRAEDesignator

Use Aboard Ship

Freon 12 CF2Cl2 R-12 Reciprocating AC&R Plants

Freon 114 C2F4Cl2 R-114 Centrifugal A/C Plants

Freon 113 C2F3Cl3 R-113 Grease Cleaning Solvent

Freon 11 CFCl3 R-11 Older A/C Plants

Freon 22 HCF2Cl R-22 Sealed Package Units

Unfortunately, it has been found that Freons also belong to a group of substances which, when released tothe atmosphere, react to reduce the ozone layer above the earth. The primary element in the Freon molecularstructure which is the culprit is chlorine and this group is called chlorofluorocarbons, or CFC’s. Since CFC’sdeplete the ozone layer, they are called ozone depleting substances (ODS). Halon 1211 and 1301 which are used infirefighting systems aboard ship are also CFC’s and ODSs.

R-22 is not a CFC. It is an HCFC. The hydrogen atom tends to prevent the chlorine atom fromdisassociating from the rest of the molecule and thus has minimal, if any, harmful effects on the ozone layer. It isnot considered an ODS, but has an ozone depleting potential (ODP) of 0.05. (The reference for ODP is R-11 witha baseline value of 1.0.)

There are some other refrigerants which are mixtures of two. R-502 is used in ice making machines andis a mixture of R-22 and R-115, or CFC-115.

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Thermodynamics of the Refrigeration CycleFigure 4-1 shows the temperature-entropy (T-S) and the pressure-enthalpy (P-h) diagrams for a simple

closed-loop refrigeration cycle. As an introduction to the system, it will be helpful to trace the refrigerant throughthe entire cycle, noting especially the points at which the refrigerant changes from liquid to vapor and from vaporto liquid. Particular attention should also be paid in noting the accompanying flow of heat from the space to therefrigerant, how the refrigerant’s energy is changed, and where the heat removed from the cooled space goes.

Recall from our Thermodynamics Course the dome-like curve represents saturated conditions for therefrigerant. On the left half of the dome, the refrigerant exists as a saturated liquid and on the right as saturatedvapor. Both liquid and gaseous refrigerant coexist inside the dome in saturation. To the left of the dome, therefrigerant is a subcooled liquid and to the right of the dome, it is a superheated vapor.

The numbers (1 through 4) represent significant points in the flow of refrigerant as it makes its circuit inthe cycle. The refrigerant working fluid undergoes thermodynamic changes between these points. Tracing thesystem from point 1 to point 4, we find:

♦ Point 1-2 (Evaporation): Since this is inside the dome, constant pressure (21.5 psia) and temperature(-5°F) are maintained, i.e., saturation. When heat is transferred at saturation, the result is a changein phase. Here the Freon evaporates, or boils, changing from a liquid to a gas. It absorbs its latentheat of vaporization (LHV) as the freeze or reefer box gives up heat to the Freon. Notice that thisheat transfer process does not end at the dome but slightly up and to the right. This follows theconstant pressure line into the superheated region of the refrigerant’s T-S (or P-h) diagram.Superheating the Freon guarantees all the refrigerant is converted into a vapor. This will prevent anypossibility of liquid Freon flowing to the next portion of our cycle.

♦ Point 2-3 (Compression): Compressing the gaseous Freon from 21.5 to 141 psia (6.5 to 126 psig)produces a concomitant increase in thermal energy represented by a rise in the enthalpy and thetemperature of the Freon from 5° to 125°F. This is the heat of compression resulting from the addedenergy to the Freon vapor. Compression provides the thermal driving head to sustain the flow ofFreon through the cycle.

♦ Point 3-4 (Condensation): In passing through the dome from the right side to the left, the refrigerantcools from 125° to 105°F and changes phase from a superheated vapor to a slightly subcooled liquid.

Figure 4- 1: Refrigeration Cycle

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While at 105°F it condenses to a liquid under saturation conditions at a constant pressure of 141 psia.The unwanted heat from cooling the freeze box and from the compression process is removed fromthe Freon and disposed.

♦ Point 4-1 (Expansion): The refrigerant is expanded by passing through an expansion valve where itspressure is reduced from 141 psia to 21.5 psia. In the process of expanding, the Freon cools from105° to -5°F (cold of expansion) and crosses into the dome where both saturated liquid and gaseousFreon can coexist. About 25% of the fluid vaporizes into a gas during the process. The Freon hasnow returned to start the cycle again.

Each of these points and the paths between them are important and correspond to major components in allrefrigeration systems.

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Basic Refrigeration SystemThe basic refrigeration system is classified as a mechanical system of the vapor-compression type. It is a

mechanical system because the energy input is in the form of mechanical energy, or work. The compressionprocess adds work or energy by compressing the refrigerant as a vapor allowing the refrigerant to discharge heat ata relatively high temperature.

A simplified refrigeration system is shown in Figure 4-2. All refrigeration systems are closed-loop andhave the same basic components: evaporator (or chiller coils), compressor, condenser, and expansion valve. Eachof these components correspond to the flow paths on Figure 4-1 from 1 to 2 for the evaporator, from 2 to 3 for thecompressor, and so on. The basic refrigeration cycle has two pressure sides. The low pressure side extends fromthe orifice of the expansion valve up to and including the intake side of the compressor. The high pressure sideextends from the discharge side of the compressor to the expansion valve.

Figure 4- 2: Basic Refrigeration System

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ExpansionLiquid Freon enters the expansion valve at high pressure. The refrigerant leaves the outlet of the

expansion valve at a much lower pressure and enters the low pressure side of the system. Because the pressurerelease has decreased the refrigerant’s potential energy, the liquid refrigerant manifests this energy conversion bybeginning to boil and to flash into vapor. The Freon is still saturated and at a very low temperature of -5°Fentering the evaporator, or chiller, coils. It is now a mixture of liquid and vapor refrigerant. This temperaturegives us a thermal differential to cool, or keep cool, a freeze box which must be maintained at 0°F. Therefrigerant is now ready to absorb the unnecessary heat from the freeze box by entering the evaporator coils locatedin the space to be cooled (freeze box).

EvaporationFrom the expansion valve, Freon as a saturated mixture of liquid and vapor passes into the cooling coil, or

evaporator, located in the freeze box to be cooled. The cooling coil acts as a heat exchanger. The boiling point ofthe refrigerant under the low pressure in the evaporator is extremely low - much lower than the temperature of thespaces in which the cooling coils are installed. The temperature differential between the -5°F refrigerant in thecoils and the air in the freeze box slightly above 0°F causes heat to be transferred from the freeze box to therefrigerant. It absorbs its latent heat of vaporization from the surroundings, thereby cooling the space. Therefrigerant continues to absorb heat until all the liquid has boiled and vaporized. To ensure all the refrigerantchanges phase to vapor, the Freon must be slightly superheated. As a rule, 6° to 10°F of superheat is added to theFreon. The refrigerant leaves the evaporator as a low pressure superheated vapor, having cooled the freeze box byabsorbing its unwanted heat. The remainder of the cycle is concerned with disposing of this heat and getting therefrigerant back into a liquid state so that it can again vaporize in the evaporator and thus again absorb heat fromthe freeze box.

CompressionThe low pressure, superheated Freon vapor is discharged from the evaporator to the suction side of the

compressor. The compressor is the mechanical unit which keeps the refrigerant circulating through the system byincreasing the fluid’s pressure and thermal potential energies. In the compressor (either reciprocating orcentrifugal), the refrigerant is compressed from a low pressure vapor to a high pressure vapor, and its temperaturerises accordingly from the heat of compression. This increase in energy provides the driving force to allow theFreon to flow through the system.

CondensationThe refrigerant must be thermodynamically returned to its starting point as a high pressure (141 psia) and

high temperature (105°F) subcooled liquid from a higher temperature (125°F) superheated vapor. There is asignificant amount of heat to extract in transforming the Freon from a gas to a liquid in the form of latent heat ofcondensation (LHC). Since this extraneous heat must be disposed, a sea water heat exchanger is used to absorbthe LHC and discharge it overboard. The heat removal from the refrigerant causes it to condense into a liquid at aconstant pressure of 141 psia. The refrigerant, still at a high pressure, is now a subcooled liquid ready tocommence the process again. From the condenser, the refrigerant flows into a receiver, which serves as a storageplace for the liquid refrigerant and as a seal between the high and low pressure sides of the Freon loop. From thereceiver, the refrigerant returns to the expansion valve and the cycle begins again.

All refrigeration and air conditioning systems follow this simple process no matter what type ofrefrigerant is used. The operating parameters will change, but it still is the same basic cycle.

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Shipboard Refrigeration System and ComponentsA basic R-12 vapor compression refrigeration plant, similar to that used in many naval ship applications,

is shown in Figure 4-3. This diagram shows the major components in a single refrigerant closed-loop system andwill be used for the remaining discussion of refrigeration plant components. Figure 4-4 shows a schematic of atypical shipboard refrigeration system where two (2) refrigeration units (each consisting of a compressor,condenser, receiver, dehydrator, and solenoid valve) can supply three (3) refrigeration loads. These loads are theship’s freeze and chill rooms, or boxes, used to store foods aboard ship. Freeze boxes are maintained at 0°F, whilechill boxes are maintained at 33°F. There’s an exception to this rule for freeze boxes, though…DDG-51 classships have the setpoints for their freeze boxes at -10°F instead of 0°F. We are still going to use the 0°F as thestandard box, but remember that the refrigerant in a DDG-51 reefer plant flows at lower saturation conditionsthrough its coils. The plants can be cross-connected so that one may supply Freon to all the boxes simultaneously.

Figure 4- 3: Basic Refrigeration Plant

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The thermostatic expansion valve (TXV) shown in Figure 4-5 is probably the most importantcomponent in the entire system. Many problems or symptoms can be traced to an improperly set TXV. It shouldalways be the first component checked during any troubleshooting.The valve is located at the inlet to the evaporator and has a thermalbulb which senses the temperature at the outlet of the evaporator. TheTXV throttles, or meters, the amount of liquid R-12 entering theevaporator coil. It is designed to regulate the rate at which therefrigerant enters the cooling coil in proportion to the rate ofevaporation of the liquid Freon in the coil. The flow rate of the Freondepends on the amount of heat being removed from the refrigeratedspace. The TXV prevents liquid R-12 from flooding back to thecompressor. Pressure in the thermal bulb is transmitted through thecapillary tubing to the diaphragm at the top of the valve. A spring isinstalled acting upward against the diaphragm tending to close thevalve. This is called the superheat spring and determines the amountof superheat added to the Freon vapor exiting the evaporator coils.The TXV in Figure 4-5 also has an external equalizing connection.If our refrigeration systems were designed to only heat the Freon tosaturation, then the TXV would only need two (2) inputs to operatethe valve. Saturation conditions are unique in that, if the temperatureis known, then the pressure is known. The converse holds true also.However, superheat is not a unique state in determining temperaturesand pressures of fluids. We are outside the dome. Therefore, since

Figure 4- 4: Shipboard Refrigeration System

Figure 4- 5: Thermostatic ExpansionValve (TXV)

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our refrigeration systems are designed to ensure the Freon in the coils becomes slightly superheated, three inputsare needed to control the valve operation. The additional input comes from directly sensing the Freon linepressure from the evaporator coil outlet. An increase in evaporator coil outlet temperature will cause the pressureof the Freon in the capillary tube to increase causing the TXV to open. Spring pressure and evaporator pressuretends to close the TXV. Superheat at the outlet of the evaporator coil should usually be 6° to 10°F above theboiling point of the refrigerant. The degree of superheat is controlled by the spring pressure. A temperature rangeof 6° to 10°F of superheat is considered desirable because it increases the efficiency of the plant and it evaporatesall of the liquid, thus preventing liquid carryover into the compressor. Some TXV’s have internal pressureequalization. An external connection will be used where the refrigerant pressure loss through the evaporator coilsis greater than 2.5 psig for mid-sized refrigeration systems and for frozen food applications with a 0.5 psig drop inpressure in the coils. (FFG-7’s and larger fall within this criteria.)

The TXV transforms the Freon into a mixture of liquid and vapor under saturation conditions at a lowtemperature and pressure (-5°F at 21.5 psia). At this state any additional heat absorbed will further boil the Freoninto 100% vapor. The Freon from the TXV flows to the evaporator coils located inside the space to be cooled, i.e.,freeze and chill boxes. These coils are simply a large heat exchanger with the Freon contained in the tubes whichline the periphery of the boxes. Heat istransferred from the warmer space to theFreon inside the coils increasing therefrigerant’s thermal energy sufficiently bya latent heat transfer (no temperature orpressure change) that all the Freonbecomes saturated vapor. (The latent heatof vaporization for R-12 is 70.4 BTU/lb at-5°F. Recall from Thermodynamics itrequires 970 BTU/lb of latent heat to boilwater at 212°F.)

The compressor (Figure 4-6)provides the motive force to circulate therefrigerant through the entire system. Itcompresses the low pressure, lowtemperature gas to a high pressure, hightemperature gas, raising the boiling pointof the refrigerant gas so it can becondensed. The reciprocating compressoris similar to an air compressor in thatpiston-cylinder configurations are thecompression method. However, AC&Rsystems use only single stage compressionunits.

Figure 4- 6: Refrigeration Compressor

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Refrigeration compressors have a forced lubrication system as shown in Figure 4-7. Notice high pressurelube oil is supplied to a component called the capacity control valve (and system).

The capacity control system serves a similar function as the loading/unloading feature on LP aircompressors and is integrally connected to the pressure regulating valve. Figure 4-8 shows a cross section of thepressure regulating andcapacity control valves whichare mounted on thecompressor crankcase wall.This arrangement allows forthe unloaded starting of acompressor until lube oilpressure is established. Notall cylinders are unloaded inreciprocating compressors -some refrigerant flow isrequired to minimize startingtorque and to preventoverheating. (For example,the refrigeration compressorsin DD-963’s arereciprocating with threecylinders in a "W"arrangement. Only two ofthe three have unloading devicesinstalled. The refrigerationcompressors on the AE-27 have 6cylinders with controlled, unloadedoperation on 4.)

When the compressor isstarted, the plunger is in the extremeright hand position such that no oil issupplied to the compressor unloaderpower elements. With this oil flowpath, the unloading element ensuresthat the unloading sleeve around thecylinders hold the suction valvesopen with six lifting pins preventingthem from seating (Figure 4-9).Once oil pressure reaches aminimum limit (above low lube oilshutdown pressure), oil is ported tothe unloader power elementsallowing the unloading sleeve tolower, seating the suction valves, andloading the pistons. The compressorthen pressurizes the refrigerant forsystem operation.

Figure 4- 7: Forced Lubrication System

Figure 4- 8

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The pressure regulating portion of the assemblyallows for unloading the pistons when the refrigeratingload is light or when less refrigerant is required. Whencompressor suction pressure is high indicating morerefrigerant is needed, the cage valve opens allowing oil todrain to the crankcase. This causes the plunger to shift tothe left causing oil to be ported to the unloading powerelements. Oil to these elements will seat the suction valvesloading down the pistons to pressurize Freon for theincreased need. With a decreasing compressor suctionpressure, the reverse occurs such that the pressureregulating cage valve moves to the right restricting oil flowthrough the plunger. The pressure imbalance between theoil and spring forces the plunger to the right until the firstpower element oil port is allowed to drain unloading thefirst cylinder. Continued decrease in suction pressure willsequentially cause the second piston to unload by drainingthe oil from the second unloader power element. These areset so all cylinders are unloaded prior to operation of thelow lube oil pressure switch which shuts the compressor down. Sequential unloading reduces the refrigeratingcapacity proportionally, as in the case of a plant in AE-27, one unloaded cylinder results in 83 1/3% capacity, twoin 66 2/3% capacity, three down to 50%, and so on.

The compressor has several safety devices to protect itself and the system from damage.

◊ The oil failure switch shuts the compressor down if there is insufficient oil pressure. It measures thedifferential pressure between the lube oil pump discharge pressure and the crankcase pressure. If theoil pressure drops below a safe minimum above crankcase pressure or fails to build up to asatisfactory minimum upon start up, the switch deactivates the relays in the motor controller to stopthe compressor. These two values are not the same nor are they same from compressor tocompressor. On a DD-963, these values are 15 psig for the safe minimum operating pressure and 20psig for a minimum start up pressure, whereas, on an AE-27, the pressures are 12 and 18 psig,respectively. This oil safety feature for the refrigeration compressors on an FFG-7 occur at 10 and 16psig, respectively. The oil failure switch also has an interlock with a 10-15-second time delay toallow oil pressure to build up when it is started. This switch is automatically reset after thecompressor is shut down.

◊ The low suction pressure switch protects the compressor from operating needlessly under norefrigerant flow conditions. If the freeze box is at the desired temperature, the solenoid valve willclose stopping refrigerant flow. Continued operation will simply cause the compressor to run for noapparent reason. The low suction pressure switch will shut down the compressor if the compressorsuction line pressure falls below a minimum level. For AE-27, DD-963, and FFG-7 ships, this valueis 5" Hg vacuum. Should suction pressure rise above this value, the compressor will automatically berestarted when the cut in value is reached. For all of our examples, the refrigeration compressors willrestart when suction line pressure reaches 8 psig.

◊ The compressor will be shut down on high discharge pressure. For a DD-963, this switch shutsdown the compressor when the pressure reaches 150 psig as it is increasing and will restart thecompressor at 125 psig as the pressure falls. For a refrigeration compressor on both the AE-27 andthe FFG-7 classes, the shutdown also occurs at 150 psig with a restart at 125 psig.

◊ All compressors have an internal relief valve which lifts at some high discharge pressure valuerelieving to the suction side of the compressor. For a DD-963, the relief valve setting is 300 psig andon an AE-27 the valve lifts at 350 psig.

Figure 4- 9: Unloader Power Element

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◊ A water failure switch stops the compressor if sea water flow to the condenser is interrupted or ifwater pressure falls to a low limit. The operating band for a DD-963’s compressor will open thecontacts in the motor controller at 5 psig and automatically close the contacts at 15 psig restarting thecompressor. The water failure switch on an AE-27’s refrigeration compressor operates in the samefashion with settings of 5 psig and 15 psig. FFG-7’s have the water failure shutdown featureoccurring at 15 psig and restarting the compressor when water pressure returns to at least 30 psig.

The condenser is a two-pass heat exchanger which uses sea water as the cooling medium to remove thesuperheat and the latent heat of condensation from the refrigerant and return the Freon to a subcooled liquid(105°F and 141 psia). The water may be supplied by its own pump or from the firemain. The compressordischarges the high temperature (125°F), high pressure (141 psia) gas to the shell side of the condenser. Sea waterflows through the inside of the tubes. The R-12 vapor is cooled and condensed to a high pressure, hightemperature liquid. The refrigerant is subcooled slightly below its boiling point to ensure that it will not flash intovapor.

A water regulating valve (WRV) (Figure 4-10)is located in the sea water outlet piping from the condenserand controls pressure in the high pressure side of thesystem by regulating the amount of cooling water suppliedto the condenser. Its function is to maintain saturationconditions for the gaseous Freon to condense (about 141psia and 105°F). An actuating line connects the waterregulating valve bellows assembly with the condenser shellpressure (saturation pressure that the Freon is condensingat). If the refrigerant condenser pressure increases, thevalve opens to increase water flow, thereby providing morecooling. This increased cooling effect will reduce thecondensing temperature of the Freon and, because theprocess occurs at saturation, the Freon pressure willdecrease. Conversely, a decrease in condensing pressurewill admit less water to the condenser, decreasing thecooling effect of the water and thereby increasing thetemperature at which condensation of the Freon isoccurring. Thus, the Freon pressure will concomitantly increase. On compressor shutdown, the refrigerantpressure decreases in the condenser shell to the saturated vapor conditions at ambient temperature. This decreasein pressure is sufficient to shut the water regulating valve stopping the flow of water.

The receiver acts as a storage and surge tank for the liquid refrigerant which flows from the condenser.The receiver also serves as a seal between the vapor in the condenser and the flow of liquid refrigerant to theexpansion valve. It has a level indicator which shows the amount of refrigerant in the system. There is a systemrelief valve on the receiver set at 225 psig for all installations to protect the receiver when the system is fullycharged and secured. The relief discharges to the condenser and acts as an equalizing line.

The dehydrator (Figure 4-11) contains a desiccant cartridge which adsorbs water in the system, similarto the Type II dehydrator in the dry air system. Without this feature, water in the refrigerant would freeze in thecomponents in the low pressure side after passing through the TXV. The dehydrator has a moisture indicator onthe end (left side of Figure 4-11) which will beblue for an acceptable moisture level in theFreon. It will change to pink when thedesiccant requires replacing. It is virtuallyimpossible to replace the desiccant cartridge inthe dehydrator without releasing very smallamounts of refrigerant into the atmosphere.The MRC is written as such that some minoramounts will be vented. The replacement could

Figure 4- 10: Water Regulating Valve

Figure 4- 11: Dehydrator

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June 1996 4-16

be accomplished without venting any refrigerant, but air would be introduced into the refrigerant which eventuallywould result in changes to the saturation conditions in the condenser due to the presence of the air. The airaccumulates in the condenser as a noncondensible gas. The condenser would then need to be purged of thistrapped air to return the plant to its proper operating parameters. If no replacement desiccant cartridges areavailable, the existing cartridge can be reactivated sufficiently for temporary use by heating it at 300°F for 12hours.

This hot liquid refrigerant then passes through the shell side of a horizontal heat exchanger which hascold Freon vapor in the tubes. Here in the heat exchanger the liquid Freon is cooled and the vapor is warmed.Cooling the liquid reduces the presence of flash gas to the TXV and enables the Freon to absorb a greater amountof heat per pound of flow in the evaporator. Heating the gaseous Freon returning to the compressor evaporates anytrace amounts of liquid prior to entering the compressor suction. Even small amounts of liquid in the compressorcan dilute its lube oil and reduce the net refrigeration effect when the liquid expands to a gas during thecompression process. Excessive amounts of Freon in a liquid form will damage the compressor.

The liquid line solenoid valve starts andstops the flow of liquid refrigerant to theexpansion valve. It is located in the liquid linebefore the thermostatic expansion valve (TXV).When the coil is energized, the magnetic field liftsthe plunger, opening the valve. Whendeenergized, the plunger will close, stopping theflow of refrigerant. The thermostatic switch isdesigned to energize and deenergize the solenoidvalve. Both are shown in Figure 4-12. It islocated outside the refrigerated space. A thermalbulb (or helix unit) connected to the switch by acapillary tube is located in the air stream of therefrigerated space where it will come in contactwith the average air temperature. As the spacetemperature rises, the pressure in the bulb willincrease, closing the switch, and energizing thesolenoid valve. The thermostat works inconjunction with the solenoid valve to control thetemperature of the refrigerated space. In largesystems, the valve may be called a king solenoidvalve installed just after the receiver. An undervoltage (UV) relay in the compressor motorcontroller will deenergize the solenoid valve if anyof the following occur: "STOP" button pushed,loss of voltage, overload relay trips, low lube oilpressure (oil failure shutdown), high compressordischarge pressure shutdown, or sea water failureshutdown.

Figure 4- 12

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The liquid line strainer (Figure 4-13) protects the solenoid valve and thermostatic expansion valve fromscale and foreign matter. It is located in the liquidline before the solenoid valve.

A hand expansion valve (HXV) isavailable as a bypass valve for the TXV. Extremecare should be taken when operating this valvebecause of the danger of liquid flood back to thecompressor. Every effort should be made to repairthe TXV as soon as possible due to the higherprobability of allowing insufficiently superheatedor, even saturated, Freon from entering thecompressor. Because the TXV is located usuallyin a ship’s passageway, it have ice accumulate onthe valve’s exterior. This is normal in highhumidity environments because of the rapidpressure losses (i.e. energy changes) as therefrigerant passes through the TXV. However, no ice should accumulate on the exterior of the HXV whennormally aligned. If the HXV is iced over, the valve is leaking by and too much refrigerant is flowing through theevaporator coils. The TXV will cycle too much to compensate for refrigerant flow it cannot control.

The evaporator pressure regulating valve(EPRV), shown in Figure 4-14, is also called a suctionpressure regulator and a backpressure regulator. Itspurpose is to control evaporator coil pressure when oneset of compressors is used to cool multiple boxes. Noticeon Figure 4-4 the boxes at the discharges of each chillbox. These are indicated as typical suction controls.This is the location for the EPRV’s. They are onlyinstalled at the outlet of chill box evaporator coils, notfreeze boxes. This valve regulates the suction pressureto the compressor by increasing back pressure in theevaporator. In doing this, the boiling point of the liquidR-12 inside the chill box evaporator is increased, whichreduces the temperature difference between the Freonand the air in the chill box. This will reduce theamount of moisture removed from the produce stored inthe chill boxes. Increasing the operating temperature ofthese boxes raises the dew point temperature andincreases the relative humidity. By this process, ourproduce will not wilt as it would in temperatures withlower dew points. It also means that the evaporator heatexchanger surfaces must be larger (less temperaturedifference means more area for heat transfer). The EPRV’s also give us the flexibility to operate chill boxes asfreeze boxes, if necessary, by operating the plant with the EPRV bypassed.

Figure 4- 13: Strainer

Figure 4- 14: Evaporator Pressure Regulating Valve(EPRV)

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June 1996 4-18

Refrigeration Systems Operation

PulldownPulldown is the process of bringing all three refrigerated spaces from ambient temperature to their

operating temperatures for freezing and chilling foods. Both refrigeration units would be operated to reduce thechilled space temperatures to 0°F and 33°F, respectively. One unit would serve the freeze box and the second unitthe two chill boxes. The systems would be operated in a split plant mode with the suction and liquid cross-connectvalves closed between the two plants.

The pulldown operation normally takes about two days of continuous operation to establish thenormal refrigeration temperatures for each type of box. If frost builds up sufficiently during pulldown thatdefrosting is required, the operation should be shifted to single-plant cross-connected operation. A hot gas bypassshould be conducted to defrost the coils. Following this, pulldown should be recommenced.

Normal OperationThis may also be called temperature holding operation to maintain the operating temperatures required

for each box. After temperatures have stabilized during pulldown, the plant is shifted from split plant to singleplant operation. One refrigeration unit serves both functions for maintaining the freeze and chill boxes at normaloperating temperatures. The units should not be cross-connected to prevent refrigerant from one plantcontaminating the other.

A plant’s operational parameters as found in a technical manual are based on a worst case scenario - fullload with a sea water inlet temperature of 85°F. Operating the ship in warmer waters where sea watertemperatures of 95°F could be experienced will cause the refrigerant condensing temperature to rise between 5°Fand 10°F above the 85°F readings. The sea water regulating valve will open fully such that the velocity of the seawater through the condenser will be 6 feet per second (fps). Compressor discharge pressure may rise as much as20 psi from about 125 psi to 145. A new system balance will be created where suction and evaporator temperaturesand pressures will increase. This will cause the refrigeration plant’s ability to maintain 0°F and 32°F in the freezeand chill boxes, respectively, to decrease and the compressor will work harder. Similar effects will occur in the airconditioning plant where chill water temperatures out of the water chiller will increase.

Hot Gas Bypass OperationHot gas bypass is a manual defrosting process. Hot refrigerant gas from the compressor discharge is

routed to the inlet of the evaporator coils of any affected space by bypassing the condenser. The hot gas will meltany accumulated ice which is then collected in drip pans and drained away. Only one condensing unit (or,refrigeration unit) is utilized for this technique, while all other units are secured. This is done to minimize thepossibility of contaminating the refrigerant from one unit to another.

Any frost that accumulates on piping and other components will reduce the thermal efficiency of the plantoverall and the heat transfer characteristics of the coils in specific. Ice will form on those components in the lowpressure side of the refrigeration system from the TXV and downstream through the evaporator coils. This is theregion where the refrigerant undergoes an almost instantaneous pressure and temperature drop in flashing to avapor at temperatures about 5° below 0°F.

Evaporator coils are usually made from copper (Cu). If ice starts to form on the coils in a freeze box, theice acts as an insulator retarding or resisting heat transfer. You can see the differences between the heat transfercoefficients (k in BTU per hr per ft per °F) of Cu and of ice. Cu has a heat transfer coefficient with a value of 232BTUs per hr per ft per °F, while ice’s is 1.26 BTUs per hr per ft per °F. What does that mean? Well, in one sense

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it means that Cu transfers 184 times more heat than the same amount of ice in the same period of time. Or, icetransfers 184 times less. Take your pick. In either case, your freeze box will be less efficient if ice develops on itscoils. The box temperature will rise and probably stabilize at some value greater than the design temperature of0°F. The refrigeration compressor will work harder and longer. Compressors are designed to unload if lessrefrigerant is needed or even shutdown if the compressor’s suction pressure falls off. With ice on the box’s coils,the box temperature will never get low enough to allow the system components to work together to unload andshutdown the compressor. The result is the compressor will operate continuously trying to get the temperaturedown to the 0°F setpoint.

Consider this: If 1/4” of ice develops on your coils, the coils will transfer over 90% less heat than ifthey are frost-free.

Ice formation on evaporator coils is a normal occurrence since all air contains some moisture. As the airin the freeze boxes is cooled, the water moisture in the air condenses and freezes on the coils. Each time the boxesare entered the old air is replaced with new moisture-containing air. Moisture can also enter the freeze boxthrough leaking door seals.

It is good practice to defrost the freeze box evaporator coils whenever the average ice thickness reaches3/16 inch. If a box is operated near 32°F, a minimal amount of ice will form, if any. Every time the compressor issecured or each time the king solenoid valve secures refrigerant to that box, the ice will melt away. Therefore, iceaccumulation on the coils in a chill box should not be a problem unless the box is being used as a freeze box.

Here’s another exception…DDG-51’s again!!! Here, instead of having a manual defrosting system, thehot gas process in DDG-51’s is automatic. In the ship’s stores handling area is located the Defrost Panel whereelectric heaters can be controlled to energize and defrost the coils anywhere between 1 and 12 times per day.Normal set-up is for automatic defrosting once per day. The automatic feature causes the king solenoid valve to beshut and the circulation fans to be secured before the heaters are energized. The defrosting process is automaticallystopped when the Defrost Termination Thermostat (DTT) senses an evaporator temperature of 40°F. When the40°-shutdown temperature is achieved, the reverse process occurs to return the system to normal temperatureholding operations - heaters deenergized, fans started, and king solenoid valve opens. The defrost system in DDG-51 ships includes two safety shutdown features: (1) defrost timer fails safe after 16 minutes and (2) storeroomtemperature reaches 40°F.

PurgingWhenever a refrigeration system is opened for maintenance (like replacing the dehydrator or cleaning the

strainer) or repairs, the potential exists that air will be introduced into the refrigerant piping. Maintenanceprocedures are written to minimize air introduction to refrigerant piping. As long as no vacuum exists in thesystem or section of the system to be worked on, then no air will enter the refrigerant portion of the system.Additionally, following the procedures in NSTM Chapter 516 by establishing a refrigerant pressure between 1 and2 psig (note “gage pressure”) before breaking piping fasteners will ensure that air is kept out. Lastly, maintenancepersonnel should ensure that procedures returning the system to operation to prevent air from entering the repairedpiping sections are followed. Cleaning, flushing and evacuating piping should be strictly adhered to.

The presence of air is not good, not only because all air contains moisture, but air will degrade theoptimum conditions of the plant. Air (and other noncondensible gases) will collect in the plant’s condenser. Itcannot pass through the condenser to the receiver because of the existence of liquid refrigerant which acts as a sealand also because the conditions for refrigerant to condense are not low enough in temperature for the air tocondense to a liquid state at 125 psi. The presence of air in the condenser will increase the pressure on the shell-side of the condenser. With this increase in pressure, the temperature will increase also since saturation conditionsfor the condensing refrigerant must be maintained. The sea water regulating valve will respond to return thecondenser to the saturation temperature and pressure by throttling open to allow more sea water flow to remove theexcess heat from the condenser.

However, so much air may be entrained in the condenser that the water regulating valve may not be ableto return and maintain the normal condenser operational parameters. Purging, or venting the condenser shell to

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the atmosphere, is a PMS action which is an authorized release of refrigerant. A NAVSSES thumbrule is when theactual temperature in the condenser is about 6°F (“degrees of air”) greater than the saturation temperaturecorresponding to the compressor discharge then it’s time to purge, or vent, the condenser shell. The purgeprocedures vary by plant and should be checked in the particular technical manual. For example, the refrigerationsystem in a DD-963 has a criterion for a temperature difference of 5°F, while an AE-27 class ship has a criterion of10 psi for comparing the saturation conditions. The air conditioning plants in DD-963 class ships use a 3°Fdifferential to in order to use the Purge and Pump Out (PPO) Unit, which will be discussed later.

Purging of the condenser will release some refrigerant though should be minimized as much as possiblesince not only are Freons hazardous to the atmosphere, but also all refrigerants are heavier than air and theirrelease to the atmosphere can become hazardous in a compartment by creating locally high concentrations.Purging additionally may not remove all noncondensible gases. After purging, the continued existence of atemperature difference will probably indicate a fouled sea water side and the need to clean the condenser and itstubes.

MoistureAt 80°F, R-12 Freon can hold 98 ppm of water. If the temperature of the R-12 were to fall to 0°F, it can

now only hold 8.3 ppm. Where does this water come from and where does it go?

The air we breathe is never without moisture. Without it, we would find it very uncomfortable. But,moisture trapped in air is not good for machinery. Our refrigeration systems are designed to operate in contactwith some (very little) air. That’s the reason that designers have put dehydrators in the liquid refrigerant lineupstream of the TXV. But, if moisture-laden air gets into our refrigeration systems, it can create havoc to the foodswe are trying to keep cold and the machinery and equipment trying to do that!

As discussed above, we run the risk of air intrusion into our refrigerant lines whenever they are opened formaintenance or repairs. And, with air comes moisture. So, whenever systems require purging for excessive airbuild up in the condenser, good engineering practice dictates that the dehydrator should also be checked and mayrequire replacing.

Where do those 90 ppm of water go during a drop in refrigerant temperature to 0°F? In air conditioningsystems where we maintain chill water at 44°F, this excess moisture becomes free water in the vicinity anddownstream of the system’s TXV. Recall that as refrigerant passes through the TXV the pressure and temperaturedrop so dramatically that some of the refrigerant flashes to vapor because we are so close to the refrigerant’s“dome”. During this temperature drop the excess moisture is freed from the refrigerant and condenses as it passesthrough the TXV. It will accumulate in low areas downstream of the TXV in the water chiller. If the temperatureof the refrigerant hovers around or even drops below 32°F, the trapped water will freeze in the refrigerant pipingblocking its flow. It may cause an intermittent freezing/thawing cycle of the chiller causing erratic compressoroperation.

If refrigeration systems free up excess moisture through the TXV, ice will definitely form since therefrigerant temperature is at about -5°F. The TXV will become blocked with ice restricting or even stoppingrefrigerant flow completely. The heat transfer characteristics and rate of cooling the freeze box will be adverselyaffected. The TXV will not operate properly or may operate erratically (sticking). According to NSTM Chapter516, moisture is the most common form of refrigeration system contamination. This manifests itself as:

⇒ A shortage in refrigerant,

⇒ Compressor short-cycling on low suction pressure,

⇒ High freeze box and chill box temperatures,

⇒ Bubbling in the liquid line sight glass,

⇒ Hissing sounds in refrigerant piping, and

⇒ General unsatisfactory plant performance.

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Water has another debilitating effect. Water and refrigerants (at least, the Freons) don’t mix! What Ireally mean is they do and, when they do, we get the formation of two acids: hydrochloric acid (HCl) andhydrofluoric acid (HF). Both are highly corrosive to metal components and will cause copper to be plated out inthe high temperature regions at the discharge from the compressor, especially at the discharge valve plate. This isobservable as a decided discoloration or dark sludge forming inside the refrigerant piping. This dark sludge is alsocalled “copper plating”. In fact, the more water present, the more rapid the rate of copper plating.

Lubricating OilCopper plating can also manifest itself in high metal content in the compressor’s lubricating oil which

will be detected during spectrographic analysis of the oil. Freon refrigerants are highly miscible with lube oil. Inother words they mix quite well. Actually, whenever a refrigeration compressor is operating, there will always besome oil vapor present in the Freon and other refrigerants as it is circulated throughout the system. This has itsgood side because small amounts of oil are necessary to lubricate valves and other components in the refrigerantpiping system.

However, this “mix-ability” depends on oil temperature and refrigerant pressure. High refrigerantpressure and low oil temperature will permit more absorption of refrigerant in the oil than a refrigerant at a lowerpressure and an oil at a higher temperature. When the compressor is stopped, the lubricating oil temperature willdecrease and the refrigerant back pressure in the low side of the system (including the crankcase) graduallyincreases. Thus, these conditions permit the refrigerant vapor to be absorbed in the crankcase by the oil. When thecompressor is started again, the refrigerant-oil mixture will heat up such that the refrigerant will tend to boilcausing the oil to foam. This is normal on start up and should eventually disappear since the refrigerant isreturned to a vapor state. If oil foaming is excessive, it indicates that there is excessive oil dilution withrefrigerant. The compressor could be damaged because of the loss of lubricating properties of the oil. Theexcessive foaming can be caused by possible refrigerant floodback, overcharge in refrigerant, or leaky valves. Toeliminate or reduce the miscibility problem, therefore, some units, especially air conditioning units, will have anoil heating system installed and operating when the compressors are shut down keeping the oil temperature atabout 140°-145°F.

The compressor’s oil may become emulsified with excessive amounts of water and acid. If thediscoloration discussed above is found on components in high temperature regions of the refrigerant piping, thenexcessive moisture is indicated. If the oil crankcase and oil passages contain a dark sludge, then moisture is againindicative. High metal content is determined during spectrographic analysis of the oil. This comes from high acidconcentration which is caused by excessive moisture in the refrigerant. NSTM Chapter 516 states that, if the watercontent of refrigeration compressor oil is less than 100 ppm water, then the refrigerant in the system is dry.Should it be discovered that the system’s oil requires changing for water content, the dehydrator should also bereplaced.

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June 1996 4-22

Self-Contained Refrigeration and Freezing UnitsSelf-contained equipment are sealed refrigerating or freezing systems within a cabinet or housing to

perform a specific function or service. These are sometimes referred to as package units. The following areexamples of self-contained equipment in use on Navy ships:

◊ reach-in refrigerators

◊ frozen food cabinets

◊ drinking coolers

◊ ice making machines

◊ air conditioning units

◊ soft ice cream freezers

◊ canned juice dispensers

◊ dehumidifiers

◊ soft drink vending machines

◊ refrigerated salad and dessert counters

◊ milk and beverage dispensers

These units are similar to their counterparts used ashore with the exception of certain added requirementssuch as the requirement to withstand pitch, roll, vibration, shock, and to operate continuously in high ambienttemperatures.

Most self-contained equipment use R-12, though some ice makers and ice cream machines use R-22. R-502 is also used which is simply a mixture of R-22 and CFC-115. Newer scuttlebutts are being manufactured withHFC-134a, but there has been no wholesale conversion of these small refrigeration units to environmentally-saferalternatives. R-22 is not an ozone-depleting substance (ODS). It is an HCFC with a composition of CHClF2 andhas an ozone-depleting potential (ODP) of 0.05. There is substitute for R-22 yet, but it shall be phased out by2020.

NAVSUP has the responsibility in the Navy to identify shipboard replacement models for the above list ofpackage units. All in all it may be more cost effective to simply replace defective units than to repair them.

It should also be remembered that Type I dehydrators used in low pressure air systems contain R-12 as therefrigerant.

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June 19964-23

Air Conditioning

IntroductionAir conditioning plants are installed in Naval ships to cool certain spaces where operation of equipment,

personnel efficiency, health, or safety, would be adversely affected by high temperatures or high humidity. Typicalspaces include ammunition storage and handling rooms, electronic equipment and control spaces, hospital areas,and living, messing, and office spaces. In air conditioning plants, fresh water in a closed loop replaces the freezebox as the medium to be cooled in a refrigeration system. It is now called chilled water. It flows in a closed loopcircuit to transfer its cooling effect to the equipment and spaces requiring air conditioning. Chill water is not onlyused to cool spaces and people, but it is also used to transfer its cooling effect to the electronics cooling watersystems. Since air conditioning is a refrigeration process, we shall examine the differences between the twosystems.

Air Conditioning DefinitionsA review of air conditioning terminology is in order.

Humidity. The moisture content of the atmosphere is called humidity . Both insufficient and excessivemoisture in the air can cause discomfort and lowered efficiency. When air contains the maximum amount of waterpossible, it is saturated, and the temperature is the same as the dew point. When temperature of saturated air isreduced below its saturation temperature (or, below its dew point), water vapor will condense into water. Examplesof this process include dew that forms in the early morning, the fog that forms when a cold air mass lowers thelocal air temperature, and the sweat that forms on cold water pipes. Recall from the Compressed Air chapter that,since compressed air is saturated, the addition of moisture separators (inter- and aftercoolers) to a compressorcauses water vapor to condense due to the cooling effect of the sea water. This cooling lowers the dew point of thecompressed air.

Relative Humidity. When air is saturated with water, it is at the dew point and the relative humidity is100%. When it is half saturated, it contains half as much water as it is capable of holding and the relativehumidity is 50%. Relative humidity is defined as the ratio of the weight of moisture in the air to the weight ofmoisture that would be in the air at the dew point at the same temperature. Relative humidity affects comfort sinceit controls the evaporation rate at these conditions. At 100% relative humidity there is no evaporation. If you cansee your perspiration then it is not evaporating - that’s sensible heat transfer. If your perspiration evaporates, itpulls with it the latent heat of vaporization and you feel more comfortable. With conditions of high relativehumidity that occurs on the East Coast during the summer, relief is difficult to find (if you do not have an airconditioned home). It is even possible to improve comfort by raising the temperature, if it reduces the relativehumidity.

Foggy Windshields. One of the easiest ways to understand dew point and relative humidity is the exampleof a foggy automobile windshield. You enter your car on a cool, humid summer morning. The windshield is clear.As you breathe moist air into the car’s interior, the relative humidity increases. The warm, moist air hits the coldwindshield and fogs the inside of the glass. This happens because the temperature of the glass is below thedewpoint, causing water to precipitate out of the air. Either of two actions will correct the problem:

Turn on the defroster: Heating the windshield removes the cold surface which has caused thecondensation.

Turn on the air conditioner: Cooling the air in the air conditioner removes moisture - that’s why airconditioners always drip water. By removing moisture from the air, there is not enough water to condense onto thestill cold windshield. In effect, you have lowered the dew point of the air in the car below the temperature of thewindshield.

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Temperature. Two temperature measurements are normally used with air conditioning. These are thedry-bulb and wet-bulb temperatures. Dry-bulb temperature is measured with an ordinary thermometer andrepresents the sensible heat in the air. The wet-bulb thermometer has a woven cloth sleeve wetted with waterplaced over the bulb. High velocity air causes the water to evaporate, depending on the relative humidity of the air.At 100% relative humidity, there is no evaporation. The wet-bulb, dry-bulb temperatures, and the dew point are allthe same. Wet and dry bulb temperature readings are used to find the amount of water in the air, and therefore, thepercent humidity using a psychrometric chart, which is shown in Figure 4-15.

Sensation of Comfort. Temperature, relative humidity, and air motion are the principal factors incomfort. The impact of air motion can be drawn from the effect wind chill factors can produce in hot, humidenvironments. The extremes of wind chill can also have very uncomfortable personal results in cold weather. Thenet effect of these three factors is called the effective temperature. Figure 4-16 displays a comfort index chart.For health and comfort reasons, the bestcomfort zone is realized when relativehumidity is 40-50% in cold weather and 50-60% in warm weather. An overall range of30-70% is generally considered comfortable.

Figure 4- 15: Comfort Index Chart

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Shipboard Air Conditioning System and ComponentsAir conditioning equipment on board Naval ships are of the mechanical type using reciprocating or

centrifugal compressors. Air conditioning systems are cross-connected in the chilled water piping, but not in therefrigerant piping. Plants using reciprocating compressors are installed with a capacity up to 80 tons at not lessthan 35°F suction temperatures and use R-12 as the refrigerant. Where higher loads are involved, centrifugalcompressors are used starting at about 100-ton capacity. These plants generally use centrifugal compressors withR-114, though some older plants may use R-11. R-12 is being phased out by a suitable non-ozone-depletingrefrigerant called HFC-134a. Its physical properties will be discussed later, but, since it is being used aboard shipstoday, HFC-134a’s functional applicability in air conditioning systems should be examined. Figure 4-17represents the thermodynamic cycle associated with an HFC-134a air conditioning plant in a FFG-7 class ship.Recall that the choice of refrigerant is based on a boiling point lower than the temperature we need to cool thespace or equipment. So, the characteristics of the R-12 refrigeration cycle in Figure 4-1 would be totallyinappropriate for chilling water for air conditioning and electronics cooling. The temperature is too low at -5°F foruse in air conditioning units. By changing the operating characteristics of the plant and, possibly, choosing adifferent refrigerant, we now have a system providing the refrigerant parameters shown on the T-s and P-hdiagrams of Figure 4-17. Similar parameters would be encountered if R-12’s or R-114’s were plotted instead.The system components would require modification to accept a different refrigerant for the same job.

Figure 4- 16: Psychrometric Chart

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Figure 4-18 shows a simple air conditioning system arrangement. Most shipboard air conditioning plantsare of the indirect type. That is, the refrigerant is circulated to a heat exchanger or water chiller that cools freshwater. The water chiller acts as the load for the refrigerant and replaces the evaporator coils in a refrigerationsystem. Water is cooled to a design temperature of 44°F by the primary refrigerant through a water chiller locatedwithin the refrigeration machinery room. The cooled water is then circulated in parallel flow paths to coolingcoils in remote areas of the ship for air conditioning and electronics cooling services. The water in passingthrough the cooling coil picks up heat from the space and returns it to the chiller for cooling. Water leaving thechiller is maintained at a constant temperature by controls that actuate the refrigeration machinery. For safety, acontrol is included to prevent freezing of the water chiller. The temperature of the conditioned space is regulatedby a thermostatically-operated on-off solenoid valve controlling the flow of chilled water through cooling coils.The quantity of chilled water flowing through the cooling coil is throttled by an orifice. Never remove this orificewith the intent that more cooling can be obtained. The opposite effect can occur with the added detrimental effecton adjacent coils, which would receive reduced chill water flow.

Figure 4- 17: Air Conditioning Cycle with HFC-134a

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Figures 4-19 and 4-20 show schematics of the chill water (CW) distribution systems for DD-963 andFFG-7 class ships, respectively. All ships have multiple air conditioning plants with their respective interfacessupplying CW to supply loops or risers to the ship’s CW loads (i.e., cooling coils and electronics cooling waterheat exchangers).

The CW distribution system is divided into zones which allows the plants to be cross connected for highCW usage. An FFG-7’s air conditioning system has three (3) zones: Zone No. 1 is forward of frame 150 and isnormally supplied by No. 1 A/C unit located in the A/C Machinery Room (3-84-0-E). Zone No. 2 encompasses themiddle portion of the ship between frames 150 and 212. Chill water for Zone 2 is normally supplied by the No. 2A/C unit in AMR 2 (5-212-0-E). Similarly, No. 3 A/C unit, which is also located in AMR 2, provides chill waterto the after part of the ship from frame 212. A DD-963’s air conditioning system is also divided into three zonessupplied by three A/C units. Two of the plants are located in AMR 1 (5-220-0-E) with the third unit in No. 2Pump Room (3-398-0-Q). Each plant has a 150-ton cooling capacity.

Figure 4- 18: Basic Air Conditioning System

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After the chill water has absorbed the heat from the cooling coils and heat exchangers, this warmer waterreturns to the on-line air conditioning plant(s) to be re-cooled by the refrigerant in the water chiller(s).

An air conditioning plant is a self-contained unit such that all components associated with the refrigerantthermodynamic cycle are essentiallymounted on the same bedplate.

Figure 4- 19: DD-963 Chill Water Distribution System

Figure 4- 20: FFG-7 Chill Water Distribution System

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Systems with Reciprocating CompressorsAll air conditioning compressors serve the same functions as those in refrigeration plants. They provide

the motive force to circulate the refrigerant in the closed loop system by increasing the refrigerant’s energypotential due to its pressure.

Let’s examine the FFG-7’s system with a reciprocating compressor first, followed by a review of thecentrifugal compressor on the DD-963 class ship. The FFG-7 compressor is shown in Figure 4-21. It is motor-driven and has 12 cylinders arranged in a “W” pattern which compresses the refrigerant R-12 vapor in a singlestage due to the reciprocating action of the pistons as the crankshaft rotates. The reciprocating compressorsprovide enough energy for 80 tons of cooling capacity each.

As with refrigeration compressors, A/C compressors have capacity control systems integral to the unitsto allow the compressors to respond to load changes. This also provides for reduced power consumption andeliminates cyclic operation of the compressors as the load varies. Thus, we can expect a longer operational life.The capacity control system for a FFG-7 R-12 reciprocating compressor is shown in Figure 4-22. This system useslubricating oil as the control fluid and operates similarly to the capacity control system for a reciprocatingrefrigeration compressor as discussed on Pages 4-12 through 4-14. Its design allows for unloaded start up of thecompressor. An increase in load requirements results in an increase in crankcase oil pressure. Based on thesetting of the capacity control valve, the increased oil pressure flows through the valve via an orifice to thehydraulic relay assembly. The spring setting in the hydraulic relay allows oil to be ported to one or more unloaderpower elements. The rise in oil pressure to the unloader power element causes the piston in the element tocompress the spring pivoting the lifting fork to seat the suction valves on the cylinder being loaded by lowering theunloader sleeve. This affords the compressor the ability to sequentially load (and unload) designated cylinders in

Figure 4- 21: FFG-7 Reciprocating A/C Compressor

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pairs, or steps, in response to the needs of the system. The table below shows the loading sequence for the variouscapacity control settings for the air conditioning units on FFG-7’s. These values are the same for both types ofrefrigerants in use onboard FFG-7’s, R-12 and HFC-134a. The suction valve lifting arrangement is the same asshown in Figure 4-9.

Figure 4- 22: FFG-7 A/C Capacity Control System (R-12)

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Capacity Control Setting Unloaded Cylinders Loaded Cylinders Capacity(%)

Full 0 12 100

Step I 2 10 83 1/3

Step II 4 8 66 2/3

Step III 6 6 50

Step IV 8 4 33 1/3

The capacity control system for an FFG-7 compressor which uses HFC-134a for its refrigerant is shown inFigure 4-23. With the change to HFC-134a, the capacity controls operate in the same fashion, however,externally-mounted solenoid valves now control the porting of oil to the unloader power elements for the controlledcylinders. The original (R-12 refrigerant) components of capacity control valve, strainer, and hydraulic relay areno longer used to control oil flow to the power elements and are sealed off and isolated. In the new arrangement,a capacity control thermostat senses the temperature of the chill water at the CW outlet from the water chiller.This signal is sent to the unloader controller which electrically controls the operation of the unloader solenoidvalves. Energizing the solenoids based on a falling CW outlet temperature will cause control oil to be dumpedfrom the unloader power element back tothe crankcase raising the lifting fork andunseating the cylinder’s suction valves.Thus, the compressor unloads. With anincrease in CW temperature, the capacitycontrol thermostat sends the risingtemperature signal to the unloadercontroller de-energizing the requiredsolenoids to increase oil pressure to theunloading element. The increased oilpressure will adjust the unloader liftingfork to lower the unloader sleeve. Thesuction valves will re-seat allowing thecylinder to load.

Figure 4- 23: Capacity Control System for an HFC-134a A/C Unit

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Reciprocating air conditioning compressors have safety features to protect themselves and their systemsfrom damage. They are similar to those on refrigeration compressors and are described below:

◊ The oil failure switch stops the compressor when oil pressure is insufficient. The switch disconnectscontacts in the motor controller if the oil pressure drops below a safe minimum of 12 psig abovecrankcase pressure or if oil pressure fails to develop on start up to a safe minimum of 18 psig. Thisswitch is interlocked to a time delay relay in the controller to allow oil pressure to develop for a shortperiod (10-15 seconds) on start up below the 18-psig minimum. Should the compressor be stopped bythe action of this switch, it must be manually restarted once the low oil pressure condition has beencorrected.

◊ The low suction pressure switch operates in the same fashion as on a refrigeration compressor. Inthis case, the compressor cut out point occurs when refrigerant suction pressure falls to 20 psig andwill restart automatically when the pressure returns to 40 psig.

◊ A high discharge pressure switch shuts down the compressor when the compressor discharge risesabove 150 psig. As the outlet pressure drops to 125 psig, the contacts in the switch will closerestarting the compressor.

◊ An internal relief valve will cause high compressor discharge pressure to relieve to the suction side ifthis differential pressure exceeds 225 psi.

◊ Two switches will stop the compressor if either sea water is lost to the condenser or fresh water islost to the water chiller. The sea water failure switch secures the compressor if sea water pressurefalls to 5 psig and restarts the compressor when the pressure rises to 15 psig. The fresh water failureswitch accomplishes the same for the compressor at chill water pressures of 30 and 45 psig,respectively.

◊ Lubricating oil pressure control is vital for proper compressor operation and for satisfactory operationof the unloading feature of the capacity control system. An oil pressure regulator, or relief valve, isinstalled on the side of the crankcase near the shaft seal housing to maintain oil pressure between 45and 55 psig above oil suction pressure.

◊ The chill water system is designed to be operated with a temperature of 44°F. To prevent freezing, achill water low limit thermostat is installed to secure the refrigerant compressor if the chill watertemperature in the water chiller falls to 36°F. As the temperature rises to 40°F, the compressor willrestart.

◊ As part of the oil temperature control system, the compressor has two electric heaters installed to heatthe oil in the crankcase when the compressor is not running. A crankcase temperature safety switchdeenergizes the heaters at 140°F and will secure the compressor if it is running.

◊ Compressor oil temperature should be maintained between 100°F and 120°F. A lubricating oil cooleris installed as the second half of the oil temperature control system which uses chill water from thewater chiller outlet to cool the oil. To control the temperature of the oil going to the compressor, anoil cooler water regulating valve is located at the outlet to the chiller and is actuated by atemperature sensing bulb in the oil outlet piping of the oil cooler.

Following the compression process, the refrigerant flows to the condenser where the heat absorbed fromthe chill water and the heat of compression is removed from the refrigerant and transferred to the sea watercoolant. It is then discharged overboard.

The remainder of the refrigerant loop in an air conditioning plant with a reciprocating compressor like theFFG-7’s contains the same components as the refrigeration system we discussed in the first part of this chapter. Areceiver will be installed downstream from the condenser. It serves the same functions as the one discussed onPage 4-18 for refrigeration systems. It has a relief valve set at 225 psig to equalize the pressure with thecondenser. The receiver also acts as the point to collect refrigerant during pump down operations or whencharging the system. Next in line comes the liquid line solenoid valve followed by the heat exchanger and drier(or, dehydrator). A solenoid valve is installed upstream of the thermal expansion valve (TXV) and is controlled by

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the chill water thermostat. The chill water thermostat monitors chill water outlet temperature from the chiller tocontrol the solenoid valve in the liquid refrigerant line to the TXV. The TXV performs the same functions as inrefrigeration systems to throttle refrigerant flow to the chiller by measuring and maintaining the 8°-10°F ofsuperheat at the chiller outlet. This arrangement and operation is exactly the same as the refrigeration system.The warm refrigerant vapor then flows back to the reciprocating compressor suction valves, completing the circuit.

Systems with Centrifugal CompressorsDD-963 class ships utilize R-114 as the refrigerant for their air conditioning systems in plants designed

with a 150-ton capacity. These plants have centrifugal compressors providing the pressure potential energy tocirculate the refrigerant to cool the chill water. CG-47, DDG-51, and DDG-993 classes all have similar systems asthe SPRUANCE class except their capacities are 200-ton. Additionally, LSD-44 and -45 have four 125-ton R-114centrifugal compressors,while LSD-46 and on have 1250-ton unit and 2 125-tonunits. Figure 4-24 showsthe arrangement of a DD-963’s air conditioning unit.These centrifugalcompressors are powered bya 194-HP motor operating at3600 RPM. The speed of themotor is stepped up througha reduction gear with a3.38:1 ratio such that thecompressor runs at over12,000 RPM. The otherclasses have the similararrangements, for example,the 200-ton compressorsoperate at about 9800 RPMvia a 2.7:1 gear ratio.

The SPRUANCE class destroyers have three (3) air conditioning plants which use centrifugal compressorsand R-114 as the refrigerant. There are four plants for each of the other twin-screw gas turbine ship classes.Notice that all parts which comprise the air conditioning system are compactly co-located in the same unit. Theflow of refrigerant is shown in Figure 4-25 for the same DD-963 air conditioning plant.

Figure 4- 24: DD-963 Centrifugal Air Conditioning Plant

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The capacity control system performs the same functions (to maintain desired CW temperature and toprevent motor overloading) as other compressors, but, now with a centrifugal compressor, a different system isrequired to vary refrigerant load without changing compressor speed or cycling the compressor. Note theprerotation vanes at the compressor suction in Figure 4-25. Control of these vanes provides capacity control forthe centrifugal compressor. A schematic of the capacity control system is shown in Figure 4-26. They serve threefunctions:

⇒ Maintain desired chill water temperature.

⇒ Limit motor loading to a preset maximum current.

⇒ Restrict refrigerant backflow by closing on shutdown.

Figure 4- 25: DD-963 Centrifugal Compressor Refrigerant Flow

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The incorporation ofthe prerotation vanes increasescompressor efficiency at start upby reducing the time required fortemperature pulldown andminimizing oil foaming in thecompressor oil reservoir. Theposition of the vanes iscontrolled by a pneumatic vaneoperator which receives acontrol air signal from the pilotpositioner. The positioner actsas an amplifier to move the vaneoperator proportionally to the airpilot signal received. The airsignal to the pilot positioner canbe controlled by one of threepneumatic devices: a currentlimiter transducer, a chill waterthermostat, or a manual loadingvalve. Under normal operating conditions, the chill water thermostat is used.

The current limiter transducer senses the load on the motor and prevents overloading by moving thevanes to the closed position. A 240-amp (341 amps for 200-ton plants) full-load limit is set to prevent overload byclosing the prerotation vanes. This situation can occur under three conditions: on start up, when high CWtemperatures prevail, or when the cooling load exceeds the capacity of the unit. Based on the desired load setting,the current limiter monitors the current driving the compressor motor. When this setting is exceeded, the currentlimiter will override the normal response of the vane operator to limit the air signal sent by the CW thermostat orthe manual loading valve. It will then reduce the air signal to the vane operator to partially close the prerotationvanes until the motor loading condition reduces. Use of the current limiter transducer results in the shortesttemperature pulldown time from warm conditions since the prerotation vanes are permitted to open quickly afterthe motor is started. This prevents the oil reservoir pressure from decreasing rapidly, thus minimizing thepossibility of oil foaming. This feature, however, is only effective when the manual loading valve is maintained inthe open position. This allows the pilot signal pressure to pilot positioner to be established by the chill waterthermostat. The motor current limiter includes a load limiting controller and a transducer. The controller is anelectronic device that converts the AC motor current inversely proportional to a DC output voltage. This DCsignal is sent to the transducer to control the primary air signal to the vane operator. As long as the motor isoperating below the controller current setpoint, the DC output voltage is 16 volts. Thus, the transducer will passthe maximum amount of air to operate the vanes. If the current to the motor exceeds the setpoint, the signal fromthe load limiting controller decreases toward 0 volts DC. This reduces the air signal from the transducer limitingair to the vane operator. When the compressor motor is stopped, the transducer’s air signal to the vane operatorwill be zero to close the vanes. The vanes will also close if a loss of electrical power occurs.

A chill water thermostat (or, a T-8000 chill water thermostat) senses the CW temperature at the outletto the water chiller and controls the air signal sent to the pilot positioner to maintain the CW temperature bymoving the vanes. An 8 psig pilot air signal corresponds to 44°F chill water temperature. When the temperatureof the chill water decreases, the thermostat decreases the air pilot signal to the pilot positioner whichproportionately closes the blades via the vane operator. The opposite will occur as the chill water temperaturereturns to 44°F.

When maintenance is required, a manual loading valve is used. It is normally fully open (clockwise) inits non-operative position. Manual adjustment of the prerotation vanes is needed during initial start up until theautomatic controls are adjusted. The manual loading valve can also be used temporarily if the automatic controlsare inoperative or out of adjustment. Any use of the manual loading valve requires close attention to avoid motoroverload conditions and to maintain correct CW temperature. Counterclockwise movement of the valve will

Figure 4- 26: Capacity Control System for DD-963 A/C Unit

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increase the amount of air bled off from pilot signal circuit causing the vanes to close. Automatic controlspermitting, clockwise movement of the manual loading valve will cause the vanes to open, increasing compressorcapacity. Since the manual loading valve is in series with the chill water thermostat, the manual valve can alwaysbe used to reposition the prerotation vanes toward a closed position. However, it can open the vanes only as far asthe thermostat and current limiter settings permit.

Any of these devices can override the others to decrease the air signal to the pilot positioner which willreduce the capacity of the compressor.

Note the "hot gas switch" in the pilot air signal line on the right side of Figure 4-26. This is a pressureswitch which senses pilot air pressure and will open the hot gas bypass solenoid valve under low load signals. Thisreleases sufficient high temperature and high pressure refrigerant vapor from the condenser (compressor discharge)back to the water chiller to simulate an increase in water chiller loading. This device maintains a minimumsuction head to the compressor during low load conditions to prevent cycling or surging of the compressor. Thehot gas bypass solenoid provides a minimum refrigerant flow through the compressor even when the prerotationvanes are closed. This feature will maintain stable compressor operation.

Centrifugal Compressor Oil SystemA lube oil system is a lube oil system is a lube oil system! No big deal! Well, not exactly.

The lubricating oil system for centrifugal air conditioning compressors like those in DD-963’s is shown inFigure 4-27. Oil must be supplied to the compressor impeller bearing, but also to the bearings on the high speedshaft that drives it, the low speed shaft and the reduction gear. This system has four (4) pumps. Two oil pumpsare attached, one to each shaft. The third is an auxiliary oil pump (AOP) and the last is a jet oil pump (Figure 4-28).

The attached oil pumps arecentrifugal and provide oil to thehigh and low speed portions of thecompressor while the compressor isoperating at speed. The low speedpump discharges to the high speedsuction. The high speed pump’sdischarge is then passed through dualoil filters and the oil cooler to supplylubricating oil throughout the system.Part of its discharge makes up thesupply for an internal jet pump whichworks similar to an eductor.(Bernoulli triumphs in other areasthan just getting rid of bilge water!)This jet pump draws a suction fromthe oil reservoir, or sump, and is thesupply oil to the low speed (main) oilpump.

The AOP is a rotary,positive displacement pump andlubricates the compressor on start upwhile the attached pumps come up to speed and on shutdown while the compressor coasts to a stop. It is externalto the compressor and is electrically-operated. When its controller is selected for "AUTO", the AOP will operateautomatically during start up and shutdown. It may be operated manually by choosing "MANUAL" on the selectorswitch. When the "START" button is pressed with the AOP in automatic, the AOP will start to build up oilpressure in the system for a 25-second period. If lubrication is adequate, the compressor motor will start.

Figure 4- 27: Centrifugal Compressor Oil System

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The AOP will continue to supply oil onstart up for 60 seconds after the compressor starts.It will start up on shutdown and remain on line fora 45-second period while the compressor coastsdown.

Three 450-watt electric heaters areinstalled in the oil sump to ensure the oil is keptwarm during periods of shutdown by maintainingthe oil at 145°F. This temperature is sufficient toensure the oil does not absorb any refrigerant and,therefore, reduces oil foaming. During prolongedshutdown periods, the oil in the sump tends toabsorb oil, depending on the oil’s temperature andthe pressure of the refrigerant that may be present.As the oil temperature is lowered, the amount ofrefrigerant the oil can absorb will increase. If therefrigerant content in the oil becomes excessive,foaming of the oil may become violent as the oilpressure in the sump is reduced on start up. Therefrigerant vapor may carry away oil droplets into

the compressor suction. Since the oil pumps are centrifugal, the vapor entrained in the oil can cause oil pressurefluctuations due to vapor binding and can reduce lubrication of mechanical components. Therefore, one of theseheaters is continuously energized while the compressor is idle. The other two are controlled thermostatically tomaintain the 145°F oil temperature requirement. Under normal start up procedures, the electric heating systemmust be operated for 12 hours prior to system light off. However, the air conditioning compressor may be startedwithin 1 hour of oil replacement without energizing the oil heating system. As long as a unit will be shutdown for1 hour or less prior to being restarted, the heaters may be disconnected electrically.

Like all other compressors and rotating machinery, safety devices cannot be ignored:

◊ The chill water flow switch senses the differential pressure between the chill water flowing into andout of the water chiller. The switch closes when the chill water pressure differential increases above 7psid. If the pressure differential drops below 4 psi, the switch will open stopping the compressor. Analarm will sound. When the differential pressure of 7 psid is restored, the switch will close. The"COMPRESSOR RESET" button must be pressed to reactivate the relays in the motor controller.Once all other operational checks have been satisfactorily completed, the compressor may berestarted.

◊ The oil pressure failure switch senses the differential oil pressure at the pump discharge against thecrankcase pressure. The switch will close when the pressure is above 32 psid and will secure thecompressor if the pressure differential drops to 27 psi. Its operation is similar to the oil failure switchon other types of compressors, however, on restoration of oil pressure, the compressor does notautomatically restart the compressor. It must be reset and restarted manually.

◊ A high refrigerant pressure switch will secure the compressor if the compressor discharge pressurerises above 50 psig. If the pressure drops to 40 psig, the switch’s contacts will close the relays in thecontroller, but the compressor must be manually reset and started.

◊ On DD-963 centrifugal compressors, a hot gas bypass switch automatically routes high temperatureand pressure vapor from the compressor discharge to the water chiller under light loading conditions.This artificially stabilizes compressor operation. This was discussed above as part of the capacitycontrol system. If the pilot air signal falls to 6.5 psig, the hot gas bypass switch will open thesolenoid valve to send the hot vapor back to the chiller. When system demand returns and the airpressure rises to 8.5 psig, the switch closes the valve securing the bypass operation.

Figure 4- 28: Oil Jet Pump

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◊ The sea water flow switch will secure the compressor if sea water through the condenser falls below5 psig. The switch will re-energize when the pressure rises to 14 psig. But, again like those switchesabove, the compressor must be reset and restarted manually.

◊ Should the temperature of the chill water fall sufficiently below the 44°F design setting, it couldfreeze. The low water temperature switch will stop the compressor when the chill watertemperature discharging from the chiller falls to 40°F. The compressor can be manually reset andstarted when the temperature returns to 44°F.

◊ A high oil temperature switch monitors the compressor lubricating oil discharge temperature. If thetemperature rises to 175°F, the switch will stop the compressor or prevent it from being started. Oncethe oil temperature falls to 165°F, the compressor can be reset and started.

◊ The oil heater thermostat switch was discussed above and controls the operation of three electricheaters installed in the compressor’s oil sump. When the system is secured, one of the heaters is usedto ensure the oil temperature is maintained at 145°F. If the temperature falls below 145°F, the switchenergizes the two supplemental heaters. The switch automatically de-energizes all three heaters if a155°F temperature is reached. The switch will also secure the heaters electrically once thecompressor is started.

◊ The compressor will be stopped if the refrigerant temperature in the chiller falls below 32°F by thelow refrigerant temperature switch. Once the refrigerant’s temperature increases to 38°F, theswitch closes relays to allow the compressor to be started after being reset.

◊ The compressor is protected from high refrigerant discharge temperature by the high dischargetemperature switch which will secure the compressor if the temperature increases above 235°F.When the refrigerant temperature falls to 225°F, the switch’s contacts are energized allowing thecompressor to be reset and restarted.

Systems utilizing centrifugal compressors (i.e., R-114 systems over 150 tons in capacity...DD-963, CG-47,DDG-51, DDG-993, LSD-44) do not have a receiver between the condenser and the rest of the high pressurecomponents. They don’t need one! These systems have Purge and Pump Out (PPO) units which will be discussedbelow for refrigerant charging and evacuation processes, but they inherently produce no pulsations likereciprocating compressors. Following the phase change from a hot vapor to a subcooled liquid in the condenser,the refrigerant flows directly to the water chiller. The chiller is a shell and tube heat exchanger. The warmer chillwater flows through the tubes as the refrigerant enters through two passages at diagonally opposite ends of thewater chiller. Like all heat transfer processes, the chill water gives up its heat, cooling it down to 44°F, andboiling the refrigerant in the shell side of the chiller. The liquid refrigerant flows from each end of the chillerthrough a passage and then merges in the bottom. It rises upward through a distributor plate across the tubebundle containing the chill water. (See Figure 4-25.) It absorbs its latent heat of vaporization from the chill waterbecoming vapor and is carried upward by the compressor suction.

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Purge and Pump Out (PPO) UnitFigure 4-29 shows the Purge and Pump Out (PPO) Unit installed on air conditioning units aboard DD-

963 class ships. Similar units are also aboard CG-47, DDG-51 and DDG-993 classes and LSD-44 and on. PPOunits serve three functions:

◊ To separate and remove noncondensible gases from the main system,

◊ To remove refrigerant vapor from the main system prior to opening for maintenance and repairs, and

◊ To assist in transferring refrigerant between the main system and remote receivers.

Purging is required when the temperature difference between the saturation temperature associated withthe compressor discharge pressure and the condenser refrigerant thermometer exceeds 3°F. This conditionindicates the presence of excessive noncondensible gases in the condenser which can modify the characteristics ofthe condensing action of the gaseous refrigerant. During purging operations, the plant’s main compressor must berunning to establish system head which sends liquid refrigerant from the condenser into the PPO unit. The liquidrefrigerant flows through the finned tubes of the purger, where it will absorb the heat from the "foul",noncondensible gases collecting at the top of the purger during the condensing process. Once refrigerant flow isestablished through the purger, the PPO compressor is started. It is a two-cylinder, reciprocating compressor drivenby a 2-HP motor and draws a suction of the "foul" gases at the top of the plant’s main condenser through the PPOdehydrator and concentrator. This dehydrator is similar to those in refrigeration systems (see Figure 4-11) and isused to remove moisture from the refrigerant. The concentrator and purger are identical tube-and-shell heatexchangers with a spirally-wound fin surrounding the single-pass tube. The condensed liquid refrigerant thatforms in the purger shell collects at the bottom and flows through a liquid strainer up to the tube-side of theconcentrator. Here it absorbs heat from the "foul" gas in the shell side which condenses to separate the

Figure 4- 29: DD-963 Purge and Pump Out (PPO) Unit

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noncondensibles from the refrigerant. The liquid refrigerant that forms flows through the capillary tubes to joinwith the liquid refrigerant from the tube-side of the concentrator to return to the main plant’s water chiller. Thenoncondensible gases at the top of the concentrator are removed by the suction from the PPO compressor to bereturned to the shell-side of the purger heat exchanger.

Venting the noncondensible gases from the top of the purger is an automatic function performed by asolenoid-operated purge control valve. The solenoid valve is electrically connected to a high pressure switchlocated in PPO compressor discharge line. As compressor discharge pressure develops to exceed 60 psig, thesolenoid valve opens and simultaneously stops the PPO compressor. As the pressure in the discharge line reducesto 30 psig, the solenoid valve will close automatically restarting the PPO compressor.

Once the 3°F (or less) temperature differential for saturation conditions in the main condenser is reached,the purging operation may be secured.

Refrigerant Recovery Units (RRUs)Since Freons are being eliminated, Defense Logistics Agency (DLA), along with NAVSUP, has

established defense reserves of Freon based on the mission criticality of the equipment and systems to carry DODthrough the transition period during conversion to non-ODSs. Refrigerant recovery units (RRUs) have been issuedto all ships (with a few exceptions) to utilize during maintenance to evacuate and recover refrigerants which areozone depleting substances. These may also be used to reclaim and turn the refrigerants in to the Supply System.

Navy standard issue RRUs are the ST-100A and ST-1000 for shipboard use. They are semi-portable andare capable of recovering all Freons except R-114. All ships have them with the exception of MCMs and shipswith plants using R-114 as the refrigerant. These vessels (CG-47, DD-963, DDG-993, DDG-51, and LSD-44)have R-114 air conditioning plants which have Purge and Pump Out (PPO) units for the same purpose.

SIMAs and Naval shipyards have RRUs available for loan and are portably transported through the use ofa trailer. These units are capable of recovering all Navy refrigerants: R-11, R-12, R-22, R-114, and HFC-134a.

Freon Leak DetectionGeneral Specifications for Ships (GENSPECS) requires halocarbon monitors permanently be installed to

continuously monitor and detect refrigerant leakage in spaces containing air conditioning and refrigerationequipment. Installation of halocarbon monitoring systems aboard ships started in 1989. Stringency of therequirements were relaxed somewhat and now monitors are required to be installed in compartments withrefrigerant-charged equipment, except for the following (SEA-56Y1 memorandum of 21 August 1991 andCOMNAVSEASYSCOM 011128Z FEB 95 refer):

⇒ Main and auxiliary machinery rooms as originally designed.

⇒ Compartments with ventilation rate of change of 2 minutes or less for the lowest fan speed andserved by either W or circle W DC vent systems. One third of the exhaust quantity must be fromterminals located 9 inches above the deck and near the plant machinery.

⇒ Compartments with self-contained units containing less than 20 pounds of refrigerant, such asice-makers, water coolers and most galley equipment.

This convoluted criteria for permanent monitor installations has led NAVSEA to clarify the requirementsby ship type. Therefore, FFG-7 class ships are only required to have the monitor installed in the AC MachineryRoom. DD-963 and DDG-993 classes required a monitor to be installed in Refrigeration Machinery Room.Installations in CG-47’s and DDG-51’s are adequate and no changes are necessary. A review of remaining surfaceships is underway and is expected to be promulgated by March 1995. For those ships which have a resultantreduction in monitors installed, NAVSEA will Alterations Equivalent to Repair (AERs) to remove and dispose ofthe excess monitors.

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The Foxboro Corporation is the primary supplier of permanently installed halocarbon monitors in ships.Their Foxboro-Miran models 984/101-GA2S have been installed in all ships. Yet, to date, many units havebecome inoperable within about 6 months of installation. Supply support for the Foxboro monitors has been aparticular problem. Additionally, with the conversion to HFC-134a, those monitors currently installed are notcapable of sensing the new refrigerant. Foxboro will be developing the Miran 984/101-GA2T to monitor HFC-134a leakage to replace their earlier model. These new models will be installed as part of the conversionalteration, which will be discussed later.

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Chill Water LoopChill water (CW) cooled to an operating temperature between 40°F and 44°F is piped in a closed-loop

system throughout the ship for air conditioning and for electronics cooling to combat systems equipment andspaces. On DD-963 class ships there are three zones for chill water distribution as shown in Figure 4-19. Eachzone can be fed from its own air conditioning unit in a split plant arrangement or can be cross-connected with anyof the other two units. Normally vital CW loads are supplied via the starboard main and non-vital via the portmain.

There are three (3) chill water pumps in DD-963’s which provide the energy to circulate the chill waterthrough the loops to the loads in the zone(s) being supplied. Each pump is driven by a 40-HP motor to supply 540GPM of chill water at 75 psig shut off head pressure. The chill water pump is of the centrifugal-type that takes asuction on the water chiller and circulates the chilled water through the entire system. The pump runscontinuously when the plant is in operation.

Since the chill water system is a closed system, an expansion tank is installed to allow for expansion,leakage, surge during high usage, and evaporation of the chilled water. The tank is filled with fresh water bymeans of a hose connection from the fresh water system. On DD-963’s, CG-47’s, DDG-51’s and DDG-993’s, theexpansion tanks have a 60-gallon capacity, while in FFG-7 class, they contain 20 gallons. FFG-7 and DD-963class ships have three expansion tanks, one tank for each air conditioning unit, while the others have four. The fillhose is temporary and should never be left installed as it is possible to contaminate the potable water system withchill water. The expansion tank acts as an inventory point and is kept charged with 35-psig air pressure. Thisprovides the required suction pressure for proper pump operation.

Cooling coils are located in vent ducting and are of the finned-type. Chill water passes through the tubesof the coil, while air passes over the finned coil tubes. The chill water passing through absorbs the heat from theair passing over the coil, thus cooling the space. It is very important to keep the coils clean and free of dust. A0.004 inch layer of dust can reduce cooling efficiency by 30%. Drip pans are installed to collect condensationfrom the air cooling action. This condensation is drained off to the ship’s drain system. The drain lines sometimeshave loop seals to ensure proper drainage of the drip tray. The loops seal separates two different pressure regions:atmospheric at the end of the drain line with a slight vacuum in the drip pan created by the velocity of the airflowing through the coils.

Thermostats are located in the space being cooled which control the solenoid valves to start and stop theflow of chill water to the coils based on space temperature. The solenoid valve is electromagnetically operated bythe thermostat, controlling the flow of chill water to the coil. It does not regulate or throttle the flow. The valve iseither fully open or fully closed.

An orifice is usually installed in the chill water line downstream of the cooling coil. The orifice is sizedto allow for the correct flow of water to the coil. Imbalances in the air conditioning system will result if theseorifices are removed or become eroded over time.

Filters are installed to keep cooling coils free of dirt and dust. As with a dirty cooling coil, a dirty orclogged vent filter will reduce air flow and therefore reduce cooling.

Electronics Cooling Water SystemsElectronics systems generate sufficient heat that they require their own cooling water systems to remove

this unwanted heat to prevent component burn out. Electronics cooling is supplied by two subsystems of coolingwater: primary and secondary. The primary system is either a closed loop system of chill water or coolingprovided by the open loop of sea water from the firemain or its own sea water suction. Heat is removed by either ofthese as it is transferred from the secondary loop which removes the unwanted heat from the electronic component.Cooling water for the secondary loop is always supplied by distilled water in a closed loop subsystem. This fresh

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water is demineralized for strict compliance with conductivity requirements which is discussed in detail in theChemistry portion of SOSMRC.

NSTM 532 describes in general shipboard electronics cooling water systems. All cooling systems havetwo loops to ensure supporting water to combat systems suites. One loop is for normal operation and the other actsas a standby during maintenance or for high heat removal situations.

Types of Electronics Cooling Water SystemsElectronics cooling water systems are divided into three types categorized on the combination of water for

the primary loop (sea and/or chill) and the water combination for the normal and standby heat exchangers betweenprimary and secondary loops. (Remember, secondary loop water removes the heat directly from the electronicscomponents.)

Type I systems deliver demineralized water (DW) in the secondary loop at temperatures of 100°F andabove. Both normal and standby heat exchangers utilize sea water-to-demineralized water (SW-DW) heatexchangers.

Type II systems provide DW between 80°F and 99°F for secondary loop heat removal. The normal heatexchanger is SW-DW, while the standby one utilizes a combination of chill water-to-demineralized water (CW-DW).

A Type III system is designed with CW-DW heat exchangers for both normal and standby systemalignment delivering DW to electronics components at 80°F and below.

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DD-963 Shipboard Electronic Cooling Water SystemThe DD-963 class has two electronics cooling water subsystems. One system is for electronics equipment

in the sonar suite (Loop 1) and superstructure (Loop 2) of the ship shown in Figure 4-30. It has two loops both ofwhich are of the Type III variety. Both normal and standby heat exchangers use CW in the primary loop and DWin the secondary loop. The primary CW loop is a closed-loop system which returns the warm CW back to the airconditioning unit supplying it. DW is supplied through DW circulating pumps and two demineralizers. Twopumps are normally operated with the third in standby. This equipment is located in the Electronics CoolingWater Room (01-206-01-Q). Each loop supplies DW at 75°F and has a 20-gallon expansion tank to allow for highusage and to maintain a positive head through the chillers to the CW pumps. Each tank is charged with lowpressure air to 15 psig and is equipped with a 26-psig relief valve.

The second subsystem supports cooling the sonar power supplies in the Sonar Equipment Rooms. Thisconfiguration is a single loop of the Type I variety using a SW-DW heat exchanger and is shown in Figure 4-31.The secondary closed loop consists of two DW circulating pumps and one demineralizer. This equipment islocated in No. 2 Sonar Equipment Room (2-28-01-Q). One pump supplying DW circulation with the other in

Figure 4- 30: DD-963 Sonar and Superstructure Cooling System

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standby is the normal line up. The primary loop is open returning the warm sea water overboard.

Both subsystems’ secondary loops must have demineralized water of high quality, i.e., low conductivity.Conductivity is monitored locally at the DW Control Panels.

Five fault switches in each of the two loops for the sonar (Loop 1) and superstructure (Loop 2) equipmentmonitor the following parameters:

◊ DW Water Low Level (10% of total or below sight glass).

◊ DW High Temperature (80°F).

◊ DW High Conductivity (2 micromhos).

◊ DW Low Temperature (65°F). Low DW temperature causes condensation which can damageelectronic equipment.

◊ DW Low Flow (100 GPM for Loop 1 or 65 GPM for Loop 2).

Any of these alarm conditions electrically actuates a summary signal at a module in an IC/SM AlarmPanel in CIC (2-139-0-C) and in CCS (2-227-0-C). Ship’s personnel must monitor all DW parameters in thepump room if this summary alarm is actuated in attempting to clear the alarm condition. The summary alarmmust be cleared in CCS first before attempting to clear CIC’s alarm since this is supervisory alarm.

Responsibility for Operation and MaintenanceCOMNAVSURFLANT has explicitly defined responsibilities for operation and maintenance of a

LANTFLT ship’s electronic cooling water system. CSIP Advisory No. 55 (CNSL 040449Z APR 90) states that theoperation and preventive maintenance of both primary and secondary loops are the responsibility of combatsystems or electronics ratings. All gages in the electronics cooling water system are critical gages. Engineering

Figure 4- 31: DD-963 Sonar Power Supply Cooling System

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department personnel shall assist in corrective maintenance and in ensuring topside personnel are trained properly.Commanding Officers are allowed to deviate from this requirement as the command situation dictates. However,any such deviation must be documented by the Commanding Officer.

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The Clean Air Act of 1990

Effects of the ActThe Clean Air Act was passed in 1990 and amended in 1992 in response to the Montreal Convention and

the growing concerns on the hazardous effects the atmospheric release certain chemicals have had in reducing theozone layer of the earth. This deleterious effect increases the amount of ultraviolet radiation reaching the earth’ssurface. It has been found that chlorine (Cl) is a major contributor to this dangerous phenomenon. Chlorine wasdeclared an ozone depleting substance (ODS) and is a major constituent in the chemical structure of all the Freonrefrigerants in use commercially and in the Navy’s refrigeration and air conditioning plants. As much as 15% ofozone depleting substances come from Freons in A/C&R plants. The Freons fall into a category of chemicalcompounds known as CFC’s, or chlorofluorocarbons.

The Clean Air Act of 1990 banned atmospheric release of CFC’s as of 1 July 1992. Their manufacturewill cease after 31 December 1995. Unfortunately, the Navy also uses CFC’s widely in firefighting systems in theforms of Halon 1211 and 1301.

To minimize the potential release of Freons, all ships (with some exceptions) have been fitted out withRefrigerant Recovery Units (RRUs) to reclaim Freon when maintenance is required. The Navy’s policy is to ceaseprocurement of new Freon by recovering and re-using existing stocks. DLA and NAVSUP has been tasked withthe responsibility to maintain reserves of Freon (and Halons) for mission critical requirements until suitablesubstitutes are found for all the Navy’s ODSs. The RRU is a vacuum pump and receiver, similar in operation tothe Purge and Pump Out (PPO) Units installed in centrifugal R-114 A/C plants (DD-963 and other twin screw gasturbine ships). Recovered Freons are pumped into orange cylinders which have yellow stripes around the top.These are then turned into the supply system for reclamation.

There are provisions in the Clean Air Act for personal liability and levying fines for violations. The Actallows fines of up to $25,000 per incident per day for intentional releases of ODSs into the atmosphere. Also,approved but not in use yet are rewards which may be given by the Environmental Protection Agency (EPA) toinformants. These can be as high as $10,000 based on the magnitude of the violation.

Replacement RefrigerantsNAVSEA is working with commercial vendors to develop new refrigerants which are not CFC’s. The

Navy primarily uses R-12 and R-114 for AC&R units. Both industry and the Navy are searching for suitablereplacements for Freons. Refrigeration is taken for granted to such a degree that you have to think just howpervasive and wide spread the Clean Air Act will affect all of us. A/C units in the home and office, yourrefrigerator at home, water fountains (scuttlebutts), soda machines, and the A/C in your car are just a few.

The Freon R-12 has probably the biggest impact and is the first refrigerant the Navy and private industryhave tackled to find an acceptable alternative. Dow Chemical has developed HFC-134a as a replacement for R-12and the Navy has selected it as the refrigerant of choice to convert all R-12 AC&R plants onboard ships. It wassuccessfully tested aboard USS DEWERT (FFG-45) and USS MOUNT HOOD (AE-29) as a replacement for R-12and, now, these two ships are completely free of R-12.

HFC-134a is a hydrofluorocarbon, HFC, (not a chlorofluorocarbon). This refrigerant is already beingmarketed in commercial refrigerators and as the refrigerant in use in the air conditioning systems of 1995 new carmodels on the market. The major car manufacturers will be coming out with conversion kits for pre-1995 cars, butlocal dealers have not been able to provide distribution or cost data for these conversions. It is estimated that an airconditioning conversion from Freon to HFC-134a may cost about $800 per unit. The replacement of a complete airconditioning system with a Freon-free refrigerant like HFC-134a will cost more than $1000. Even the cost ofcontinuing to use R-12 instead of converting will rise from about $1.50 per pound to $1.00 an ounce.

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HFC-134a has similar physical and heat transfer properties as the Freon R-12, yet it has an ozonedepleting potential (ODP) of zero since it does not contain chlorine. It has a composition of CH2FCF3 with amolecular weight of 102 grams per mole as compared to R-12’s weight of 120.9 grams per mole. It boils at -15°Fand requires 93.4 BTU/lb of latent heat to vaporize. R-12, on the other hand, has a boiling point of -21.6°F andit’s latent heat of vaporization is 71 BTU/lb. HFC-134a requires a compression ratio of 4.7, while R-12 needs 4.1.

HFC-134a has low toxicity. At ambient temperature and pressure it is nonflammable. However, in thepresence of 60% air content, it becomes combustible at pressures greater than 5.5 psig and temperatures above350°F. Yet, as long as it is at ambient temperatures with pressures less than 15 psig, any concentration of HFC-134a is safe in air. HFC-134a is still heavier than air and has the potential to kill by displacing air. Like Freon, itdecomposes at high temperatures from flames or electric heaters. It becomes toxic under these conditions andproduces irritating compounds like hydrogen fluoride (HF) gas. These may manifest themselves as pungent odorsthat irritate the nose and throat.

A replacement for R-114 has recently been identified. HFC-236fa appears to present the best suitabilityand is very similar in chemical and physical characteristics. York is in the process of developing a conversion kitfor the centrifugal air conditioning compressors and systems. It is anticipated that a target of FY-98 has beenestablished to commence R-114 conversion to HFC-236fa in CG-47 class ships with a completion about FY-08.

Other Freons used in the Navy will be phased out with decommissionings as is the case with R-11 or willbe replaced with commercially available equipment as with sealed package units. For example, R-113 is used as asolvent and, currently, two possible alternatives are being tested: HCFC-225 and HCFC-141b.

Equipment and System ModificationsHFC-134a testing has identified specific changes to modify R-12 refrigeration plants. These are

necessitated because HFC-134a has slightly different physical and heat transfer characteristics. The followingmodifications are required to accept HFC-134a aboard ship:

• Replace the TXV.

• Add a crankcase oil cooler and control devices.

• Change lubrication oil to polyolester (POE).

• A molecular-sieve dehydrator (vice alumina) must be used.

• Larger fans must be added and some valves replaced.

• Some compressors may need to be replaced or to have their speeds changed.

Air conditioning plants require similar changes as refrigeration plants and are summarized below:

• Change the lubrication oil to POE.

• Add a lube oil cooler and control devices.

• Add crankcase heaters.

• Modify capacity controls and oil filter.

• Install vibration eliminators.

The conversion to synthetic POE oils requires different JOAP/NOAP testing criteria than the currentlyutilized VV-L-825 oils in R-12 plants. Synthetic POE (Castrol SW68) has a higher initial acidity than VV-L-825oils. POE oils are hygroscopic in nature. (Hygroscopic substances tend to absorb or attract water from air.) [SeeNSWC SSES PHILA 091940Z JUN 94]

NSWC SSES PHILA 171600Z NOV 93 announced that current refrigerant leak detectors are notcompatible with HFC-134a. The Yokogawa Model H10N has been identified as a suitable portable, hand-held

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monitoring device for not only HFC-134a, but additionally detects R-12 and R-22. The Yokogawa detector isauthorized for earliest replacement. Its stock number is 4940-01-368-6535 and its APL is under development.

Efforts at upgrading permanently-installed halocarbon monitors aboard ship were discussed on Page 4-41as promulgated in COMNAVSEASYSCOM 011128Z FEB 95.

HFC-134a Conversion PlanCarderock Division NSWC SSES Philadelphia is the lead activity in scheduling and performing a ship’s

conversion from R-12 AC&R systems to HFC-134a. These conversions are being done as alteration installationteams (AITs). All conversions are performed coincident with a ship’s depot-level availabilities, usually duringSRA’s. No ships which are scheduled for decommissioning shall be converted.

There are 495 refrigeration plants on surface ships to be converted. About one week is required to converteach refrigeration plant. The current R-12-to-HFC-134a conversion plan for refrigeration systems is divided intofour groups:

⇒ Group I are minor changes on surface ships.

⇒ Group II consists of surface ships with major modifications to the compressor and condenser.

⇒ Submarine conversion beginning in FY-97 consists of Group III.

⇒ The scheduling of MSC ships is still under negotiation as part of Group IV.

328 R-12 air conditioning units on surface ships require conversion to HFC-134a. Each A/C unitconversion consists of primarily mechanical modifications and will take between one and three weeks. The surfaceship conversion plan is broken down into four parts as follows:

⇒ LSD-41’s and some FFG-7’s.

⇒ AE’s, AOE-1’s, CVN-65, and LSD-36’s.

⇒ AO-177’s, ARS-50’s, and LPD’s.

⇒ Group of special requirements including MCM’s and MHC’s.

AC&R Technician TrainingThe Environmental Protection Agency (EPA) has been tasked with coordinating compliance with the

Clean Air Act. One of these requirements is that, as of 14 November 1994, all personnel who performmaintenance on AC&R equipment must be EPA-certified.

Two CNET messages discussed the Navy’s plan to train the Navy’s AC&R maintenance personnel tomeet compliance with the EPA’s certification requirements. (See CNET 271400Z APR 94 and CNET 021402ZMAY 94) These established a two-day certification course with testing at 10 sites throughout CONUS usingCNET’s video teleconferencing system. The sites were Dam Neck, Norfolk, Newport, Charleston, Mayport,Ingleside, San Diego, Treasure Island, Bangor, and Great Lakes. Priority was given to operational units to certifytheir AC&R personnel currently onboard at these sites.

CNET then added a technician CERTEST Program to allow shipboard training and testing of AC&Rpersonnel to meet EPA certification. It was authorized for all who desired to be certified, but mandatory forpreviously trained AC&R technicians but not EPA-certified. CERTEST’ing was ceased by CNET 2112300Z NOV94, but is still available on a case basis from CNET. In fact, all SURFPAC ships, MCMRON 3, CV-62, CV-64,and AS-33 have exemptions.

CERTEST’s are provided on encrypted discs which generate and grade the examinations. Multiple testsmay be taken without request. A ship must establish security for these CERTEST’s similar to enlisted ratingexaminations. Strict "to-the-letter" compliance is required. A maximum of three examination proctors can be

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assigned with data base access. Requests for the CERTEST package should be submitted to the TYCOM via theship’s ISIC. CNET will provide a VTT training file on disc upon request.

There are three levels or types of certification based on the amount and pressure of the refrigerant charge:

• Type 1 - For servicing high pressure systems with less than 5 lbs of refrigerant charge asmeasured at the evaporator or water chiller. Small package units fall in this category.

• Type 2 - For servicing high pressure systems with greater than 5 lbs of charge. Shipboard AC&Rsystems using R-12, R-114, and HFC-134a refrigerants require Type 2 technician certification.

• Type 3 - For servicing low pressure (R-11) air conditioning systems.

All graduates of the Navy’s AC&R schools must be EPA-certified. Those students attending AC&Rschool having trouble becoming certified receive remedial instruction until they achieve EPA-certification. Theyare not allowed to execute their orders to their ultimate duty station and nor are they awarded the NEC. AC&Rschool graduates with NEC 4291 for surface AC&R technicians are awarded universal EPA-certification to workon all three types of equipments. Submariners with NEC 424X are certified to work on Type 1 and 2 equipment.

Management of ODSsThe CNO has promulgated the Navy’s Environmental and Natural Resources Program Manual

(OPNAVINST 5090.1B of 1 November 1994). Chapter 6 establishes the Navy’s management policy to controlozone depleting substances (ODSs) until the Navy is CFC-free. It superseded OPNAVINST 5090.2A of 14 July1994 and reiterates all previously provided information on CFC’s and requires specific actions for all commandlevels in the Navy. For Commanding Officers afloat it requires:

♦ Reporting ODSs procured outside the Navy Stock System annually to NAVSUP.

♦ Implementing ODS procurement guidance.

♦ Ensuring ODSs are on the "authorized HM use list".

♦ Establishing procedures to reduce ODS emissions.

♦ Providing resources to train personnel.

♦ Submitting waiver requests to CNO (N-4) via the chain of command.

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ODS AdvisoriesIn order to support the CNO’s policy on ODS management and for consistent promulgation of issues and

procedures, COMNAVSEASYSCOM (SEA-03V2) has commenced an advisory system which are coordinated withEchelon II commands and approved by CNO (N-45). Here is a list of active ODS Advisories thus far:

Advisory No. Date Subject95-01 2 Oct 95 Mission Critical Applications of Class I ODSs

96-01A 6 May 96 ODS Supply Support

96-02 8 Feb 96 Refrigerant Leak Repair and Record Keeping

ODS Advisory 96-02 is not applicable to ships, only to shore facilities. However, with the release of CNO051558Z JUN 96, N-45 has directed NAVSEA develop procedures for ships consistent with EPA requirements tominimize leaks, expedite repairs to systems in excess of leak criteria, and develop a record management system todocument repairs and inadvertent discharges. Even though the CNO has declared Naval vessels to fall within theexempting conditions for military uniqueness, we will continue to manage our systems and control refrigerants tothe spirit of 40 CFR Part 82.

The message says two other important things: (1) Even if your ship’s AC&R systems have been convertedto a non-ODS refrigerant, like HFC-134a, you are required to comply with the same procedures as ships with ODSrefrigerants. (2) If your ship is approached by federal, state, or local governmental officials to inspect yourequipment or records, they are to be denied access. A routine message report must be sent to CNO (N-45)informing the chain of command of the request.

You can expect some record keeping and leak repair procedures to be promulgated similar to theguidelines listed in the paragraphs below:

• Naval personnel receiving EPA-certified training must have proof of technician certification. Thisshall take the form of certificates entered into the individual’s training folder. Technicians shallcarry wallet-sized cards of certification. Page 13 entries shall suffice for enlisted AC&R technicianscompleting EPA-certification.

• Specific records shall be maintained when service is performed on AC&R systems which containgreater than 50 lbs of refrigerant. IMA and shipyard personnel shall provide the ship’s EngineerOfficer with proof of their certification prior to performing any maintenance. Maintenancedocumentation shall include the date and type of service and the amount of refrigerant added orremoved from the system.

• Technicians servicing their own command’s systems shall record date and type of service, the amountof refrigerant added or removed, and the quantity of refrigerant drawn from supply.

• These maintenance records shall be reviewed and inspected monthly by a designated engineeringdepartment officer. All of these records shall be retained for a minimum of three (3) years.

• All attempts to eliminate refrigerant leaks on systems containing greater than 50 lbs of refrigerantwithin 30 days of discovery is mandatory. For A/C systems, repairs must be made when the annualleakage rate exceeds 15% of the total system charge. Leaks in refrigeration systems must be repairedwhen the annual rate is greater than 35% of the total charge. If the leaks cannot be corrected within30 days, the command must develop a plan to retrofit or retire the affected system within one year.The leakage rate is based on an annual criteria, not on the amount which leaks in one year. If a 100-lb A/C system leaks 1.5 lbs of the refrigerant in 1 month, this equates to an 18% annual rate. It,therefore, must be repaired in 30 days according to this leak repair policy.

Some examples of refrigerant charges in A/C systems are:

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◊ A CG-47 200-ton A/C plant has a charge of 775 lbs of refrigerant.

◊ Each of the four DDG-51 plants is charged with 560 lbs of refrigerant.

◊ There are 950 lbs of refrigerant in one of the 300-ton A/C plants in LHD-1 class ships.

In comparison, a DD-963’s refrigeration system has a capacity of 1.5 tons. It has a refrigerant charge of130 lbs.

Navy Points of ContactTo assist senior level managers, some points of contact are provided below.

♦ Overall CFC Program Management: CNO (N-45), Ms Catherine Cyr, DSN 332-5335.

♦ Technical Issues: NAVSEA (SEA-03V24), Mr. Joe Thill, DSN 332-0928 (X242).

♦ HFC-134a MACHALT Installation Scheduling: NSWC SSES Phila (Code 1651), Mr. VincentCancila, DSN 443-1417.

♦ HFC-134a Technical Issues: NSWC SSES Phila (Code 9213), Mr. Mike McGovern or Mr. V.DiFillipo, DSN 443-7211.

♦ HFC-134a Leak Detectors: NSWC SSES Phila (Code 9533), Mr. J. Winard, DSN 443-8783.

♦ Training: CNET (Code 3213), LT K. Searles, DSN 922-3084.

♦ Course Quota Control: CNSL (N-434A1), LT Martin, DSN 564-5319 and CNSP (N-821A),OSC(SW) Allvord, DSN 577-3120.

♦ General CFC and Halon Information: Navy Clearinghouse, Mr. Peter Mullenhard, (703) 769-1889and FAX (703) 769-1885.

TroubleshootingThe most common AC&R problems with remedies are described below.

High compartment temperature◊ Ice buildup around the evaporator coils will reduce heat transfer from the space to the Freon. Defrosting

(hot gas bypass) may be necessary when the compressors are lightly loaded and the box temperatures arerising. The checklist in Appendix K to NAVSUP Publication 486 contains an area for inspection thatno ice is allowed to accumulate more than 1/4” in thickness on the interior surfaces of the freeze boxor on coils.

◊ There needs to be adequate movement of air past the cold coils throughout the space. If boxes are piled infront of the coils, you may get food spoilage in a distant corner. Supply Department personnel shouldmaintain proper food stowage to optimize air circulation in the boxes.

◊ Any one of four inoperative automatic controls can stop Freon flow in a refrigeration system: thermostat,liquid line or king solenoid valve, TXV, and evaporator pressure regulator valve.

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High compressor discharge pressure (short-cycling on the highpressure switch)

◊ Air in the system can raise system pressure. Check for leaks.

◊ Insufficient sea water flow raises the temperature in the condenser, which raises the pressure because ofsaturation conditions. Check the water regulating valve (WRV) setting and check the sea strainer forclogging.

◊ Dirty condenser tubes reduce heat transfer and raise temperature and pressure in the condenser. Clean thecondenser tubes.

◊ An overcharge of Freon in the system will increase system pressure.

Low compressor discharge pressure◊ Excessive cooling water flow will lower temperature and therefore pressure in the condenser. Check the

WRV.

◊ Liquid refrigerant flooding back to the compressor will reduce discharge pressure (it could also damagethe compressor). Liquid floodback is caused by either a faulty TXV or a leaking hand expansion valve(HXV). If your TXV is bypassed and the HXV is being used, then operators must closely monitor thesystem to ensure there is no floodback. The amount of superheat (which controls floodback) is anadjustment that must be set on the TXV.

◊ Worn compressor valves and piston rings will also reduce output. This may also result in refrigerantcontamination of lubricating oil.

High compressor suction pressure◊ Too much refrigerant being passed by the TXV will raise suction pressure. The solution is again, checking

the TXV setpoint.

◊ Low compressor suction pressure (short-cycling on the low pressure switch)

◊ Low refrigerant charge will cause low suction pressure.

◊ A restricted flow of Freon will also cause low suction pressure. Restrictions can be caused by incorrectlyset TXV’s, malfunctioning solenoid valves and clogged Freon filters.

Dehydration◊ Wilted lettuce is caused by dehydration. Dehydration is caused by low dew points. Low dew points are

caused by using Freon which is too cold. Using Freon which is too cold for the particular application willmaintain box temperatures satisfactorily, but will lower humidity. The most common cause of thiscondition is an incorrectly adjusted evaporator pressure regulator valve (EPRV). By increasing thepressure of the Freon, the boiling point is raised, which in turn raises the dew point in the space.

Food storage◊ Ice accumulation will retard the heat transfer characteristics of the coils in the freeze box resulting in

higher than normal freeze box temperatures (i.e., greater than 0°F). This will cause the refrigerationcompressor to operate harder and longer to try and reduce the temperature to where it is supposed to be.

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Hot gas defrosting will eliminate ice, but any rapid return of the ice may be symptomatic of other causeslike too frequent box entry raising air humidity or leaking door seals allowing humid air entry even withthe door closed.

◊ “Overstuffing”, or overstocking freeze and chill boxes with food will inhibit air flow within the boxreducing the capability to keep the box temperature at set point. NAVSUP Publication 486, Volume I,entitled Food Service Management, and NAVMED P-5010-1 stipulate that no less than 4 inches shallbe allowed between food stacks and the bulkheads or evaporator coils. NAVMED P-5010-1 alsostates that there shall a minimum vertical distance of 6 inches between the top of food stacks and theventilation ducting. NAVSUP Publication 421, Food Service Operations, requires a 2-inchseparation or space between the box deck and the bottom of the stack in which is installed floorgrating. All of these measures are used to guarantee minimum required air flow for proper heat transferto occur. Checklists for inspection of food service and storage areas are contained in Appendix K toNAVSUP Publication 486.

◊ Foods in chill boxes can be made to deteriorate (“ripen”) more slowly by using ethylene absorber blankets.Attaching these 10-lb blankets to ventilation ducts in the chill boxes will remove the ethylene gas thatfresh fruits and vegetables (FFV) emit as they ripen and decay. These blankets are available through thestock system (NSN 6850-01-303-1336) at a cost of between $70 and $123 per bag. Use of these bags canprolong FFV life by a factor of two or three times. Some submarines have experienced significantincreases in lettuce “life expectancy” by as much as 70 days!

High temperatures in electronics spaces and systems◊ Insufficient CW or DW flow will reduce the amount of heat removed from the electronics systems being

served.

◊ Cavitating CW or DW circulating pumps will reduce heat removal capacity. This can be the result of aninsufficient positive suction head upstream from the pumps. The expansion tanks may not have enoughwater charge in the system. The air charge in the tanks may be low. Open vent lines on the expansiontanks will eliminate whatever head is required to maintain pump head and also introduce air.

Troubleshooting summaryObviously, there are many more possible problems and their associated troubleshooting steps that could be

listed here. A complete review of system troubleshooting shows that many problems can be solved with thefollowing five actions:

1. Check the TXV superheat setting. This is the single most common solution to a wide variety ofAC&R problems. The TXV controls the amount of superheat out of the evaporator or waterchiller and, thus, eliminates the possibility of liquid floodback to the compressor.

2. Check for ice buildup and defrost the coils, if necessary.

3. Check the WRV setting. The water regulating valve controls the temperature of condensationand, therefore, the pressure in the condenser.

4. Check refrigerant level in the system...too much or too little will cause problems.

5. Check filters and strainers for clogging.

Final ExamSatisfactory completion of the following will put you in good stead with your A Gang:

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June 19964-55

1.) Probably the most important component of any AC&R system is the thermostatic expansion valve, orTXV. Explain its operation.

2.) Describe the two modes of operation of refrigeration systems - pulldown and normal, or temperatureholding.

3.) Explain the operation of the water regulating valve (WRV)?

4.) Refrigeration systems are designed to operate with sea water supplied ranging in temperature from28°F to 85°F. How will your refrigeration system react if your sea water injection temperature isgreater than 85°F but less than or equal to 95°F? What would happen if the sea water temperaturerose above 95°F?

5.) What is a hot gas bypass? R-114 centrifugal A/C compressors have a hot gas switch in their capacitycontrol systems. Does it perform the same function? What is different?

6.) Ice accumulates on the evaporator coils inside your freeze box. Why? What some operational factorsthat too much ice will affect? How do you get rid of it? Why is ice bad? How much can you allow toaccumulate before you should be concerned? If ice accumulates in your chill boxes, should you beconcerned?

7.) Whenever maintenance is performed on your AC&R systems where the system integrity is broken, airwill enter the refrigerant loop. Is this satisfactory? What about too much air? What happens to yoursystem operation if too much air enters your refrigerant loop? How do you get rid of the air? Arethere any thumbrules or operating criteria to check?

8.) If you get air in your refrigeration system, you will get moisture along with it. Fact. Is moisture inthe refrigerant harmful? Are there any components installed to minimize the effects of moistureentrained in your refrigerant? Explain the consequences of too much moisture? How do you know ifyou have too much moisture?

9.) AC&R compressor lube oil and refrigerants mix quite well. In fact, we want some oil vapor/dropletsto be carried throughout our refrigerant loop to help lubricate valves and other moving components.Too much of a good thing can be bad. What are the effects of too much oil in your refrigerant?

10.) What do the NAVMED and NAVSUP manuals say about how food should be stowed in freeze andchill boxes?

11.) A/C and refrigeration system are very similar; in fact, their refrigerant loops are the same - almost.A/C systems have a component called a low temperature cut-out switch or thermostat. What is itsfunction? Why do we need it?

12.) Who are the only people authorized to perform maintenance on your AC&R systems?

13.) Your A/C system has an expansion tank installed in the chill water (CW) loop. Why? What functionand purpose does it perform? What would happen to the CW circulating pump if the expansion tankwere not charged with LP air to about 35-45 psig? What would happen to the cooling effect of theCW if this occurred?

Commanding Officer Interest Items

Refrigerants◊ Freons and the new HFC-134a displace oxygen, so they can (and have been) deadly. Being 4 to 6

times heavier than air, they will concentrate in the bilge. In high concentrations, the vaporsthemselves have an anesthetic effect, causing lack of coordination, shortness of breath, and irregularheart beat.

AC&R

June 1996 4-56

◊ Freons and HFC-134a will freeze the skin, or eyes, or any other part of the body that they come intocontact with, so personnel protective equipment is necessary when handling them.

◊ Open flames will decompose both the Freons and HFC-134a to a toxic gas (like phosgene).

◊ All bottles used to store refrigerants should be stored in racks with proper fitting metal collars (as allcompressed bottles should be stowed). Manila line used to secure bottles or having a single metal barsecuring more than one bottle is not authorized.

Refrigerated and air conditioned spaces◊ Ripe fruit will generate carbon dioxide, which is colorless and odorless. Concentrations of 6-8% CO2

will cause heart palpitations. Entering a space daily should be sufficient to clear it of CO2.

◊ Spaces maintained in the extremes of temperature (too hot or too cold) can have adverse impacts oncrew morale and well-being. These conditions can also impact watchstanding responsiveness.

◊ Air conditioning boundaries should be maintained at all times. Propping doors open will overworkcompressors making routine maintenance more frequent. This also increases likelihood of correctivemaintenance. All that’s being done is trying to air condition the atmosphere that wasn’t designed tobe supported by your equipment!

HFC-134a Conversion and ODS management◊ All your AC&R technicians should be certified through the new EPA guidelines.

◊ If your systems have not been converted yet, every attempt should be made to be ready for itsinstallation when it comes. Training, coordination with NSWC SSES Philadelphia and FTSC, ILSsupport for modified systems, HFC-134a leak detector, etc.

◊ Are your Engineer Officer and Supply Officer in compliance with OPNAVINST 5090.2B and otherguidance (like ODS Advisories) to manage ODSs?

◊ What procedures have your Engineer Officer and A Division Officer implemented to document allmaintenance actions on AC&R systems? What about repairing leaks?

◊ What training has the Engineer Officer incorporated for these new requirements?

◊ Is there a well-defined line of responsibility for maintenance of these systems?

AC&R

June 19964-57

Remember the old SOSMRCadage...

Keep it clean.Keep it cool.

Keep it forever!