BUILDING SERVICES - VI

PACKAGE AIR CONDITIONERS

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Air - Conditioning

Non Ducted systemsNon Ducted systems

Window A.C. Split A.C.

Ducted systemsDucted systems

Packaged A.C.Packaged A.C. Central air conditionersCentral air conditioners

Types of Units Commonly Used in IndiaTypes of Units Commonly Used in India

• The first packaged air conditioners made in India appeared in the market in the early 1950s with water-cooled condensers and semi-hermetic compressors. Availability of water was not a problem in those days and semi-hermetic compressors were considered more reliable than hermetic (airtight closure) and easily repairable in case of a burnout, which was fairly common at that time with undependable power supply in most parts of the country.

• As the market grew, water became scarcer by the year, power supply improved, hermetic compressors became more reliable and today air cooled units with hermetic compressors dominate the scene. India companies have gained more confidence and today produce a wider variety of units but still import the newer designs such as the VRF unit. Some other designs and capacities not made in India are covered in another article. Most of the units are designed for normal comfort applications with indoor conditions of 27°C, 19°C and 35°C ambient.

• A mini central plant neatly assembled in one compact sheet metal enclosure is a packaged air conditioner (PAC) and when assembled in two separate enclosures is a split air conditioner. What distinguishes these packaged / split ACs from the more common room ACs such as window units / mini splits is their capability of being connected to a ducted air distribution system with a fresh air intake.

• The design of the packaged AC and all its components is capacity matched to enable it to perform at optimum operating conditions with pre-determined ratios of airflow/ton, sensible heat / latent heat removal capacity and kW/ton.

• The capacity range of packaged ACs commonly manufactured in India is 3 ton to 16.5 ton. Air-cooled units are more commonly used because of water shortage all over the country and the hermetic scroll compressor is more popular than the reciprocating type.

A battery of air-cooled condensers on the terrace of a building, connected to indoor vertical ducted PACs with scroll compressors.

Growing Popularity of PACs

• With a low installed price per ton, short delivery schedule, dependable performance and reputed manufacturers recommending their use, more and more users are opting for the packaged unit alternative rather than a central chilled water plant with recip/screw chillers. The central plant market size is gradually being eroded by the PAC market.

• The PAC market, in turn, is being eroded, but to a smaller extent, by the ductless splits.

Applications of PACs

Originally conceived and manufactured for the small to medium size commercial sector comprising restaurants, retails shops, banks and offices, manufacturers and their dealers have penetrated a much wider market with great success. Larger capacities and specially designed units, both made in India and imported, have helped to grow the market substantially.

Comparison of the benefits and limitations of packaged air Comparison of the benefits and limitations of packaged air conditioners, designed for the mass comfort sector.conditioners, designed for the mass comfort sector.

BENEFITS LIMITATIONS

•Low installation cost •Precise control of room conditions is not possible

•Readily and easily available •Limitations on air flow and filtration levels

•Being totally factory built, ensures better quality and reliability

•Smaller compressor and hence higher kW/ton consumption

•Less plant room space required •Operating sound levels can be quite high

•Simple operation – trained man power is not required

•Limitations on the amount of fresh air intake

•Modularity permits phase wise air conditioning

•Variations in the room temperature due to on/off cycles

•Metering of consumed power by individual customers is very easy

•Must be greatly over sized for high sensible load applications

•Possible to switch off units catering to unoccupied spaces thereby avoiding wastage.

•Average life span of about 10 years.

ResidentialResidential

Most homes in India are not fully air conditioned and hence ducted splits are not commonly used. During the past few years, with dropping prices, aggressive marketing and rise in disposable incomes, window AC's and ductless splits are becoming common place in many bedrooms and living rooms in multi-storey apartment buildings as well as in single family and joint family bungalows. The VRF unit imported from China or Japan is being installed in several large multi-room mansions. The installed price of such units is much higher than regular ductless splits but some of the benefits, quite often overrule the price factor.

Small CommercialSmall Commercial The packaged / ducted split AC is ideally suited for the thousands of restaurants, sari

shops, jewellery shops, small food stores, car showrooms, bowling alleys, banks and offices spread out in all urban areas of the country. Installed as a single unit or in multiples, depending on the area and cooling load, these units are connected to an air distribution ductwork to evenly spread the cooling effect. Outside air is introduced in the return air path to provide a feeling of freshness for customers and staff unlike window and mini-split ACs which are not designed to provide such a facility.

Large CommercialLarge Commercial

• Even though the largest capacity PAC manufactured in the country is only 16.5 tons, which can handle a small office building floor area of approximately 3000 ft, multiple units have been installed in many larger office buildings, adding upto 700 or 800 tons.

Similarly, several shopping malls designed for central chilled water systems have installed PACs with total capacities of anywhere around 750 tons, mainly for economic considerations.

• Such large installations of PACs suffer from increased maintenance costs because of the large number of units involved, and inconvenience to occupants in case of breakdowns, since it is not possible to have a standby for each unit. To a major extent the problem of not having a standby is taken care of by having multiple refrigeration circuits in a single unit.

Since the lifespan of PACs is about 10-12 years against 18-20 years for a central plant, the owner must take this factor into account before taking a final decision in his choice of the AC system.

Water-Cooled Floor Standing Ductable PackageWater-Cooled Floor Standing Ductable Package

• This is the first and oldest design and is produced by only two companies since the demand is quite small. Shell-and-tube condensers are used because they are easier to clean and maintain. They are available in capacities of 5 ton to 16.5 ton and external static pressure of 6-10 mm.

Air-Cooled, Floor Standing, Ductable Split

With the same sheet metal enclosure as the water-cooled model shown, the S&T condenser is replaced by a remote mounted air-cooled condenser with propeller fans, to be installed in an open space with free air discharge.

11 ton Floor-Mounted Package Unit11 ton Floor-Mounted Package Unit

Air-Cooled, Ceiling Suspended, Ductable Split.Air-Cooled, Ceiling Suspended, Ductable Split.

• The DX evaporator with blower, motor and filters are part of the “indoor unit” while the “outdoor unit” consists of the hermetic compressor and condenser with propeller fan or the "condensing unit"as it is called in refrigeration parlance. Free air discharge is recommended for best results. Should it be necessary to mount the condensing unit indoors, a centrifugal blower and discharge air ductwork can replace the propeller fans. The manufacturer's guidance and approval must be obtained before making such a change.

• Capacities available are 3 ton to 16.5 ton with external static pressure of 5to12 mm wg.

Air-Cooled, Floor Standing, Free Air DischargeAir-Cooled, Floor Standing, Free Air Discharge Available in capacities of 2 to 4.5 tons with

aesthetically designed indoor units, such ACs are ideal for small commercial establishments, with no need of ductwork. The indoor unit is left exposed and is unobtrusive in performance while the outdoor unit is mounted where there is plenty of cool outside air available. See Photo 4.

Water-Cooled, Ductable SplitsWater-Cooled, Ductable Splits

Where water supply is not problem these units, available with both floor mounted or ceiling suspended ductable indoor units are available in capacities of 3 ton to 11 ton. A large 360 ton installation was recently completed in Ahmedabad, with the condensing units installed on the terrace, alongside the cooling tower and the indoor units installed in a loft directly below, with conditioned air supplied to a large open shopping area.

Precision Air ConditionersPrecision Air Conditioners

• The IT revolution has paved the way for a totally new concept — equipment cooling. If the room temperature gets too high or too low, data integrity and system reliability suffer. Very high and very low humidity can also be a major problem. It can cause data alteration, oxide shedding and loss of data in the magnetic media.

• Manufacturers recommend set tolerances for conditions to be maintained in the equipment rooms. Typically these are 22±1°C and 50±5% RH.

• Moreover, the sensible load in equipment rooms is very high – almost 90-95% of the total load component. Therefore the air conditioning system has to be designed with very high air quantity to remove that much sensible heat.

• Dust is the worst enemy of electronic equipment and filtration levels have to be strictly quantified and maintained. Last but not least, an air conditioning system catering to an electronic equipment room has to be rugged enough to be in operation 24x7.

Precision air conditionersPrecision air conditioners

They are stand-alone units with scroll / reciprocating compressors. The evaporators could be single circuit or dual circuit (to operate on chilled water when a central plant is operational). It is provided with either top discharge or floor discharge as per the equipment requirements. The microprocessor controller is designed to cater to precision tolerances of temperature and humidity. They are provided with an integral humidifier / heater to add moisture / heat as required. They are also equipped with filters conforming to required filtration levels.

Durable constructionDurable construction• Durable full metal jacket protects the coil • Compressor Cycle Protection prevents unnecessary wear and tear • Heavy Gauge galvanized steel cabinet • Powder-paint finish provides durability and long lasting protection • Unit is finished in a 500-hour salt spray treatment • High and low pressure switches provide an unusually high level of protection

Flexible installation DesignFlexible installation Design• Any qualified air conditioning technician can easily install this equipment in

your home or office. It has been designed to be extremely easy to install. It will normally require about 4-6 hours to replace an existing similar type system. For you do-it-yourselfers replacing an existing package unit, simply connect your existing supply and return ducts and the electrical, and the installation is complete. The electrical connections should be made by a qualified electrician.

• This unit is designed for ground level or roof-top installation and features a side-by-side supply and return duct configuration. It can be installed in mobile or modular homes, on flat rooftops, or any home with an open crawl space.

Advantages of Packaged units Advantages of Packaged units

Energy Efficient and Quiet: Reliably Keeps Home Cool

When you want reliable, efficient air conditioning and a variable speed blower with the right mix of cooling efficiency (at least 14 SEER and 12 EER) and quiet operation (as low as 71 dB), ask for Performance.

Ratings

•  Energy Efficiency 7 of 7

•  Humidity Control 6 of 7

•  Durability 6 of 7

CEE UNITARY AIR-CONDITIONING SPECIFICATION

PAT Series Specifications Cooling Only Package PAT Series Specifications Cooling Only Package UnitUnit

EXPLOSION PROOF AIR CONDITIONERS - INDUSTRYEXPLOSION PROOF AIR CONDITIONERS - INDUSTRY

• Applications include explosion proof air conditioning, heating, and pressurization systems for Switchgear Buildings, Motor Control Centers, Control Rooms, Analyzer Shelters, Driller's Cabins, and many others.

• Manufactured for the Chemical, Petrochemical, Refining, and Offshore Oil & Gas industries, both domestic and international.

Dual air conditioning, heating, and pressurization unit with gas-phase air filtration

Quick Notes• A single-package unit contains all the components and

generally mounts through the wall or on the roof. Ducting to and from the unit conveys air to and from the rooms. This type is not commonly used in residential applications.

• These can be installed in office buildings, schools, banquet halls etc. where 5-50 tons load of air conditioning is required.

• It consumes more amount of energy than split of same load.• It is cheaper than central air conditioning system.• Moreover, no special operational team is required.• These are available in minimum 5 ton load; which is

available for approx. 1 lakh Rupees.• The c/c distance at which the diffusers are installed in a

room is generally 10 feet.

SPECIFICATIONS FOR AIRCONDITIONING PACKAGE UNIT

• These specifications set out the basis of design of self contained packaged air conditioner units with air cooled condensers to meet the environmental needs of electronic equipments in Telephone Exchanges.

• The firms who are interested to supply such units to the Department should get prototype unit approved by the Department.

CABINET:1. The Cabinet should be constructed from best quality GI sheet steel of

thickness not less than 16 gauge for top, bottom and side panels & 20 gauge for front and back panels suitably treated for weather protection, corrosion and shall be powder coated.

2. Coil and blower sections should be insulated internally for both acoustics and thermal purposes with 12 mm thick resin bonded Fibre Glass of density 48 Kg/m3 glass wool covered with glass cloth of fire retardant grade.

3. Suitable arrangement shall be provided for lifting/easy handling of machines.

DESIGN CRITERIA FOR AIR CONDITIONING PACKAGE UNIT OF 7 TR & 14 TR CAPACITY

The air-cooled AC Pkg unit should be designed as per following conditions:

1. Rated capacity : 7 TR & 14 TR (Sensible cooling capacity)2. Flow direction : Upward flow/Downward flow3. Air inlet temp. : 25 deg C (DB) at 50% RH (Return Air)4. Saturated Suction Temp. : Between 9 deg C and 10 deg. C5. Minimum Super heat : 2 deg. C6. Saturated discharge Temperature : Maximum 53 deg. C (at ambient

of 43 deg. C)7. Ambient air design temperature : 43 deg. C (However the system

should be (Entering the condenser) able to work with ambient temp. up to 50 deg. C)

8. Air Quantity : Air quantity : >550 CFM/TR9. Total static pressure : 35 mm of WG between inlet and outlet of

Blower i.e. across the blower.

• 10. No. of refrigerant circuits : Two• 11. Filters : 1) Filter to be provided on the Package unit• having 95% efficiency down to 5 microns,• EU-3 type and EU-2 filter having efficiency• of 90% down to 20 microns.• 12. Face velocity across the : < 2.5 m/sec• Cooling coil• 13. Type of load : The exchanges are having high sensible heat• Load (Sensible Heat factor > 0.95)• 14. Minimum C.O.P. : 2.90

– Twin refrigerant circuits are to be provided for both 7 TR & 14 TR capacity.

•Separate auto / manual switch for each circuit is to be provided for bypassing the controller. However manual mode should not be made effective through control card i. e. it should be independent of the control card. All the safeties such as HP / LP, overload, thermostat etc. plus the starting sequence of blower, condenser, compressor and the interlocking of blower with condenser & compressor should be functional in manual mode also.

Design Safety Measures

Types Of Package Units

• Glycol cooled system

• Water cooled system

Glycol cooled system

Basic FunctioningBasic Functioning

• This type of system locates all refrigeration cycle components in one enclosure (like a self-contained system) but replaces the bulky condensing coil with a much smaller heat exchanger shown in Figure.

• The heat exchanger uses flowing glycol (a mixture of water and ethylene glycol, similar to automobile anti-freeze) to collect heat from the refrigerant and transport it away from the IT environment.

• Heat exchangers and glycol pipes are always smaller than condensing coils (2-piece air cooled systems) and condenser air ducts (self-contained air cooled systems) because the glycol mixture has the capability to collect and transport much more heat than air does.

• The glycol flows via pipes to an outdoor-mounted device called a fluid cooler. Heat is rejected to the outside atmosphere as fans force outdoor air through the warm glycol-filled coil in the fluid cooler.

• A pump package (pump, motor and protective enclosure) is used to circulate the glycol in its loop to and from the computer room air conditioner and fluid cooler.

Advantages

• The entire refrigeration cycle is contained inside the computer room air conditioning unit as a factory-sealed and tested system for highest reliability with the same floor space requirement as a two piece air cooled system.

• Glycol pipes can run much longer distances than refrigerant lines (air cooled system) and can service several computer room air conditioning units from one fluid cooler and pump package.

• In cold locations, the glycol within the fluid cooler can be cooled so much (below 50°F [10°C]) that it can bypass the heat exchanger in the CRAC unit and flow directly to a specially installed economizer coil. Under these conditions, the refrigeration cycle is turned off and the air that flows through the economizer coil, now filled with cold flowing glycol, cools the IT environment. This process is known as “free cooling” and provides excellent operating cost reductions when used.

Disadvantages:– Additional required components (pump package,

valves) raise capital and installation costs when compared with air cooled DX systems.

– Maintenance of glycol volume and quality within the system is required.

– Introduces an additional source of liquid into the IT environment.

Usually Used:– In computer rooms and small-to-medium data centers

with moderate availability requirements.

Water Cooled System

Water Cooled System• Water cooled systems are similar to glycol cooled systems in that all

refrigeration cycle components are located inside the computer room air conditioner. However, there are two important differences between a glycol cooled system and a water cooled system:

• A water (also called condenser water) loop is used instead of glycol to collect and transport heat away from the IT environment

• Heat is rejected to the outside atmosphere via a cooling tower instead of a fluid cooler.

• A cooling tower rejects heat from the IT room to the outdoor environment by spraying warm condenser water onto sponge-like material (called fill) at the top of the tower.

• The water spreads out and some of it evaporates away as it drips and flows to the bottom of the cooling tower (a fan is used to help speed up the evaporation by drawing air through the fill material).

• In the same manner as the human body is cooled by the evaporation of sweat, the small amount of water that evaporates from the cooling tower serves to lower the temperature of the remaining water.

• The cooler water at the bottom of the tower is collected and sent back into the condenser water loop via a pump package.

• Condenser water loops and cooling towers are usually not installed solely for the use of water cooled computer room air conditioning systems.

• They are usually part of a larger system and may also be used to reject heat from the building’s comfort air conditioning system (for cooling people) and water chillers.

All refrigeration cycle components are contained inside the computer room air conditioning unit as a factory-sealed and tested system for highest reliability.Condenser water piping loops are easily run long distances and almost always service many computer room air conditioning units and other devices from one cooling tower.In leased IT environments, usage of the building’s condenser water is generally less expensive than chilled water.

Advantages

Disadvantages– High initial cost for cooling tower, pump, and piping

systems.– Very high maintenance costs due to frequent cleaning and

water treatment requirements.– Introduces an additional source of liquid into the IT

environment.– A non-dedicated cooling tower (one used to cool the entire

building) may be less reliable then a cooling tower dedicated to the Computer Room Air Conditioner.

Usually Used:– In conjunction with other building systems in small,

medium and large data centers with moderate to high availability Requirements.

CASE - STUDY

Eicher Factory

Sector – 2, Parwanoo

A Package Unit has been

installed outside the

building.

Design Considerations• For high sensible-load jobs, such as homes, offices etc., where

occupancy is relatively low, air quantities are usually too low for the installed tonnage. Latent capacity, on the other hand, may be higher than desired.

• Thus, if we have a total load of 5 tons—41⁄2 tons sensible and 1⁄2 ton latent—and we have available a 5 - ton unit with a capacity of 4 tons sensible and 1 ton latent, it is obvious that during extreme weather the unit will not be able to hold the dry-bulb temperature down, but the relative humidity will be well below design value. Under such conditions, these units may be satisfactory.

• In the cases in which the latent capacity is too low and we have more than enough sensible capacity, we can set the thermostat below design indoor dry-bulb temperature and maintain a lower dry-bulb temperature and higher relative humidity to obtain satisfactory comfort conditions.

• Where we have insufficient sensible capacity, we have to leave the thermostat at the design setting. This will automatically yield a highe dry-bulb temperature and lower relative humidity— and the premises will b comfortable if the total installed capacity is not less than the total load.

CEI

L

ING

MOUNTED

DIFFUSERS

CASE - STUDY

Spice ‘N’ Flavours

Multi-Cuisine Food Court

Crown Interiorz Mall, Faridabad

Multi – Cuisine Food Court

For restaurants, bars, etc., where high latent loads are encountered, the unit handles more than enough air; also, the sensible capacity is greater than required. However, the latent capacity may be lower than desired. This will result in a somewhat higher relative humidity in the premises.

Ducted System above the False Ceiling

Diffusers installed at 8 feet c/c

Ducts above the False Ceiling

COOLING EQUIPMENT—CENTRAL PLANTPACKAGED UNITS

• For an economical installation, the air-handling units should be chosen to handle the least amount of air without danger of sweating ducts and grilles. In most comfort cooling, an 18F discharge temperature below room temperature will be satisfactory.

• If a fresh-air duct is used, the required fresh air is mixed with the return air, and the mix is sent through the cooling coil; i.e., the fresh-air load is taken care of in the coil, and discharge air must take care of the internal load only. Then, the amount of air to be handled is

Q = qs/1.08 ΔTwhere qs internal sensible load

T - temperature difference between room and air leaving coil (usually18 deg. F).

• If a fresh-air duct is not installed, and the outside air is allowed to infiltrate into the premises, we use Eq. (13.30) with the sensible part of the load of the infiltration air added to qs , because the outside air infiltrating becomes part of the internal load.

• Once the amount of air to be handled is determined, choose a coil of face area such that the coil-face velocity V would be not much more than 500 ft /min. Some coil manufacturers recommend cooling-coil-face velocities as high as 700 ft /min.

• But there is danger of moisture from the cooling coil being carried along the air stream at such high velocities.

V = Q/Ac

where Q air flow, ft3 /minAc coil face area, ft2

V air velocity, ft /min

• To meet the great demand for cheaper air-conditioning installations, manufacturers produce packaged, or preassembled, units.

• These vary from 4000 to 30,000 Btu/ hr for window units and 9000 Btu/hr and up for commercial units.

• Less field labor is required to install them than for custom-designed installations.

First-floor store (load 7.25 tons)

In as much as a 5-ton unit is too small, we must choose the next larger size—a 71⁄2-ton packaged unit.This unit has a greater capacity than needed to maintain design conditions.However, many people would like a somewhat lower temperature than 80F dry bulb, and this unit will be capable of maintaining such conditions.Also, if there are periods when more than 50 occupants will be in the store, extra capacity will be available.

First-floor store (load 7.25 tons)

• In as much as a 5-ton unit is too small, we must choose the next larger size—a 71⁄2-ton packaged unit.

• This unit has a greater capacity than needed to maintain design conditions.

• However, many people would like a somewhat lower temperature than 80F dry bulb, and this unit will be capable of maintaining such conditions.

• Also, if there are periods when more than 50 occupants will be in the store, extra capacity will be available.

Second-floor offices (No. 1, load 3.50 tons; No. 2, load 1.13 tons)

• A 5-ton unit is required for the two offices. But it will be necessary to provide a fresh-air connection to eliminate the fresh-air load from the internal load, to reduce air requirements to the rated flow of the unit.

• Then, the 2000 ft3 /min rating of the 5-ton packaged unit will be close enough to the 2236 ft3 /min required for the two offices.

• In as much as the total tonnage is slightly above that required, we will balance out at a slightly lower relative humidity than 50%, if the particular packaged unit selected is rated at a sensible capacity equal to the total sensible load.

Water Air – Conditioning Cycle

• Roof-type packaged units are available for a variety of applications. These units contain a complete cooling cycle (usually with an air-cooled condenser) and a furnace. All controls are factory pre-wired, and the refrigeration cycle is completely installed at the factory.

• Necessary ductwork, wiring, and gas piping are supplied in the field.

• A combination packaged unit including an evaporative condenser is also available.

• Most packaged units are standardized to handle about 400 ft3 /min of air per ton of refrigeration. This is a good average air quantity for most installations.

Designing of Ducts

• In designing a duct system for air conditioning, we must first determine air-outlet locations. If wall grilles are used, they should be spaced about 10 ft apart to avoid dead spots. Round ceiling outlets should be placed in the center of a zone. Rectangular ceiling outlets are available that blow in either one, two, three, or four directions.

• Manufacturers’ catalog ratings should be checked for sizing grilles and outlets.

• These catalogs give the recommended maximum amount of air to be handled by an outlet for the various ceiling heights. They also give grille sizes for various lengths of blows.

Some of the more elaborate heating and air-conditioning installations consist ofa high-pressure warm-air duct system and a high-pressure cold-air duct system.Each air outlet is mounted in a sound attenuation box with pressure-reducing valvesand branches from the warm- and cold-air systems.Room temperatureis controlled by a thermostat actuating two motorized volume dampers.When coolingis required, the thermostat activates the motor to shift the warm-air damper tothe closed or throttled position and the cold-air damper to the open position.

Duct Calculation for 7 ½ - ton Packaged Unit for Store

• Smaller Ducts installed hence lower cost.• Higher power consumption for operation of the system.

If a 71⁄2-ton packaged unit is used, for example, the ducts should have a capacity at least equal to the 3000 ft3 /min at which this unit is rated.

Future TrendsFuture Trends• The largest capacity PAC available today is 16.5 tons with three hermetic scroll

compressors of 5.5 ton each operating at 50Hz and an ambient temperature of 35°C. With an 11 ton scroll compressor already available in the market, the maximum capacity of packaged units will increase to 22/33 tons. This increase is necessary to cope with the larger buildings being built today and the ever growing popularity of PACs.

• Fully packaged, air-cooled, outdoor units similar to the rooftop type in the US market will appear on the scene to cater to the needs of smaller towns where low height buildings spread out over a larger land area are common. Such units can also be used in industrial buildings which are usually single storey.

• VRF units with digital scroll compressors are in the development phase with Indian manufactures at this time and will be in the market shortly to compete with the imported variety.

• Reverse cycle heat pumps for both cooling and heating will gradually appear on the scene in central and north India to cater to the needs of the extreme climates in these areas.

ConclusionConclusion

• The market for packaged air conditioners is expected to grow annually at a rate of 20% to 25% and the growing variety and capacity will help cater to a larger range of applications.