Cooling systemFor process cooling (based on process )

1. Use outside air if the outside air temperature is low enough (Fan..)

2. Use direct evaporative cooling

3. Use Indirect evaporative cooling(Cooling Tower, Swamp Cooler…)

4. Most plants use chiller for cooling purpose• Chillers consist of a compressor, an evaporator, an expansion valve, and a

condenser. The evaporator is a tube-and-shell heat exchanger used to transfer heat to evaporate the refrigerant. The expansion valve is usually some form of regulating valve (such as a pressure, temperature, or liquid-level regulator), according to the type of control used. The condenser is most often a tube-and-shell heat exchanger that transfers heat from the system to the atmosphere or to cooling water.

Major equipment and methods for cooling purpose

• Chiller

• Cooling Tower

• Insulation

• Air conditioning

Energy consumption and waste generation

• Power equipment by electricity usually (low pressure steam or hot water)

• Waste generation: – Energy loss due to heat transfer from high

temperature to low temperature

– Inappropriate usage(temperature setpoint)

– Efficiency of each equipment (Motor)

– Maintenance(frost, lubrication, refrigerating liquid, filters )

Insulation

• Thermal insulation is the reduction of heat transfer between objects in thermal contact or in range of radiative influence.

• Important part of every plant or building where any transfer of fluids or gases takes place and their temperature is required to be different then that of ambient air.

• Properly insulated pipes, tanks and other equipment can save thousands of dollars

Types of insulation• Insulation of pipe (steam, hot water, cold water…)

• Insulation of tanks(hot media, cold media…)Example: DA Tank ( Unit Forging, Inc. )

Save $ 1,800/yr

• Build Insulation (dock doors…)Example: insulate wind tunnel ( Modine, Inc.)

Save $ 8,800/yr

How to calculate energy saving

• First of all, heat transfer direction should be determined. During the heat transfer process, what kind of thermal resistance influences heat transfer.

1. Conduction

2. Convection

3. Radiation

Thermal resistance for conduction

L: wall thickness

k: wall conductivity

Thermal resistance for convection

k: flow heat transfer coefficient

Two convection:1. Natural convection2. Forced convection

For the natural convection, h could be obtained from books directly.For the forced convection, h should be obtained from your calculation.

Forced convection by a fan

Natural convection

Thermal resistance for radiation

The annual heat loss

• The annual heat loss (Q) is given by:• Q = U Aw (Ta – To) Hh

– U = overall heat transfer coefficient (Btu/hr –ft2 oF)

– Aw = area of the wall (ft2)– Ta = ambient temperature (oF)– To = average surrounding area (oF)– Hh = Operation hours (h)

U= 1/R

The annual energy savings

The annual cost savings

• The annual cost savings (ACS) is given by:

• ACS = AES RGa C2

• where,

• RGa = Average electricity rate C2 = energy conversion factor

AR sample

Chiller

• A chiller is a machine that removes heat from a liquid via a compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.

In industrial application• In industrial application, chilled water or other liquid from

the chiller is pumped through process or laboratory equipment. Industrial chillers are used for controlled cooling of products, mechanisms and factory machinery in a wide range of industries.

Compression Chiller

• The mechanical compression refrigeration system consistsof four basic parts; compressor, condenser, expansiondevice, and evaporator.

Operation principle

2

1

Cooling tower water, river water, city

water, or outdoor air

Absorption refrigeration chiller

• Absorption chiller use heat rather than electricity as their energy source. Because natural gas is the most common heat source for absorption cooling, it is also referred to as gas-fired cooling. Other potential heat sources include propane, solar-heated water, or geothermal-heated water.

• Mainly used in industrial or commercial settings

• Relatively small work input compared to compression chiller

Operation principle

• 2 chemicals (water and lithium bromide brine commonly)

• Driven by heat

Two stage absorption chiller

Methods to Reduce Costs

• 1. Use refrigeration efficiently.

• 2. Operate at the lowest possible condenser temperature/pressure (lowest entering condenser water temperature).

• 3. Operate at the highest possible evaporator temperature/pressure (highest leaving chilled-water temperature); do not overcool.

• 4. Operate multiple compressors economically.

• 5. Recover heat rejected in the condenser.

Relevant Calculation of condenser1. Condenser heat load = Q x T x Cp

Parameter Details Unit

Q Water flow rate Kg/h

T Average CW temperature rise oC

Cp Specific heat kcal/kg oC

2. Calculated condenser vacuum =

Atmospheric pressure – Condenser back-pressure

3. Deviation in condenser vacuum =

Expected condenser vacuum - Measured condenser vacuum

4. Condenser TTD =

Saturation temperature – Cooling water outlet temperature

Relevant Calculation of condenser (cont.)

5. Condenser Effectiveness =Rise in cooling water temperature

Saturation temperature - Cooling water inlet temperature

6. Condenser heat duty in kcal/h =Heat added by main steam + heat added by reheater + heat added by SH attemperation + heat added by RH attemperation + heat added by BFP - 860 x (Pgen + Pgen losses + heat loss due to radiation)

7. Condenser tube velocity (m/s) = Cooling water flow rate (m3/h) x 106

3600 x tube area (mm2) x ( no. of tubes per pass - no. of tubes plugged per pass )

Relevant Calculation of condenser (cont.)8. Determination of actual LMTD

Tsat - ToutLn

LMTD =Tout - Tin

Tsat -Tin

9. LMTD expected = LMTD test x ft x fw x fq

(Saturation Temperature during test – LMTD during test

Saturation Temperature design – LMTD design)ft =

0.25

fw =Tube velocity during test

Tube velocity design( )0.50

fq =Condenser design duty

Condenser duty during test( )

fw: correction for

water flow rate

fq: correction for

cooling water heat load

ft: Correction for cooling water inlet temperature

Relevant Calculation of cooling tower1. C.T. Range = Water inlet temperature – Water

outlet temp.

2. C.T. Approach = Water outlet temperature – Wet bulb temp.

3. Effectiveness % =Range x 100

( range + approach )

Fan actual airflow (Nm3) / cell =

Fan rated airflow (Nm3) / h x ( Fan input kW actual )

( Fan input rated )

1/3

1/3

4.

5. Air mass flow / cell = flow x density of air

Relevant Calculation of cooling tower (cont.)

5. Evaporation losses =CW flow (m3/ h) x CT range in 0C

675

6. Makeup water consumption =Evaporation losses

(COC – 1)

The above readings may be taken on daily basis for three days on different

atmospheric conditions say during mid summer, winter & monsoon period. Once

in the mid day and once in the mid night time and a record duly maintained.

Collect unit load (MW), frequency, and condenser vacuum condition while

taking the cooling tower measurement

Condenser

• Possibility of Improvement in condenser vacuum

• Turbine heat rate Reduction possibilities

• Improving the effectiveness of condenser and TTD

• Cooling water flow adequacy and flow optimization

• Air ingress

• Increasing the TTD of the condenser

• Fouling of tubes

Exploration of Energy

Conservation Possibilities

Water pumping and cooling tower• Improvement of systems and drives• Use of energy efficient pumps• Correcting inaccuracies of the Pump sizing / Trimming of impellers• Use of high efficiency motors• Integration of variable speed drives into pumps: The integration of

adjustable speed drives (VFD) into compressors could lead to energy efficiency improvements, depending on load characteristics

• High Performance Lubricants: The low temperature fluidity and high temperature stability of high performance lubricants can increase energy efficiency by reducing frictional losses

• Improvements in condenser performance• Improvement in cooling tower performance• Application potential for energy efficient fans for cooling tower fans• Measuring and tracking system performance

Exploration of Energy

Conservation Possibilities (cont.)

• Measuring water use and energy consumption is essential in determining whether changes in maintenance practices or investment in equipment could be cost effective

• In this case it is advised to monitor the water flow rate and condenser parameters, cooling tower parameters periodically i.e. at least once in a three months and energy consumption on daily basis. This will help in identifying the -

- Deviations in water flow rates

- Heat duty of condenser and cooling towers

- Measures to up keep the performance

System Effect Factors

• Equipment cannot perform at its optimum capacity if fans, pumps, and blowers have poor inlet and outlet conditions

• Correction of system effect factors (SEFs) can have a significant effect on performance and energy savings

• Elimination of cavitation: Flow, pressure, and efficiency are reduced in pumps operating under cavitation. Performance can be restored to manufacturer’s specifications through modifications. This usually involves inlet alterations and may involve elevation of a supply tank

Exploration of Energy Conservation Possibilities (cont.)

Exploration of Energy Conservation Possibilities (cont.)

• Internal Running Clearances: The internal running clearances between rotating and non-rotating elements strongly influence the turbo machine's ability to meet rated performance. Proper set-up reduces the amount of leakage (re-circulation) from the discharge to the suction side of the impeller

• Reducing work load of pumping: Reducing of obstructions in the suction / delivery pipes thereby reduction in frictional losses. This includes removal of unnecessary valves of the system due to changes. Even system and layout changes may help in this including increased pipe diameter. Replacement of components deteriorated due to wear and tear during operation, modifications in piping system

Assessment Recommendation Code of Cooling Systems

• 2.2121 INCREASE AMOUNT OF CONDENSATE RETURNED

• 2.2122 INSTALL / REPAIR INSULATION ON CONDENSATE LINES

• 2.2123 INSULATE FEEDWATER TANK

• 2.2124 INSTALL DE-AERATOR IN PLACE OF CONDENSATE TANK

• 2.2125 REPLACE BAROMETRIC CONDENSERS WITH SURFACE CONDENSERS

• 2.2126 LOWER OPERATING PRESSURE OF CONDENSER (STEAM)

• 2.2127 FLASH CONDENSATE TO PRODUCE LOWER PRESSURE STEAM

• 2.2128 USE STEAM CONDENSATE FOR HOT WATER SUPPLY (NON-POTABLE)

• 2.2131 INSULATE STEAM / HOT WATER LINES

• 2.2132 REPAIR FAULTY INSULATION ON STEAM LINES

Assessment Recommendation Code of Cooling Systems (cont.)

• 2.2611 MODERATE COOLING TOWER OUTLET TEMPERATURE

• 2.2612 USE COOLING TOWER WATER INSTEAD OF REFRIGERATION

• 2.2613 USE ANTIFREEZE IN COOLING TOWERS TO ALLOW WINTER USE

• 2.2614 USE COOLING TOWER OR ECONOMIZER TO REPLACE CHILLER COOLING

• 2.2615 CLEAN CONDENSER TUBES

• 2.2621 MODIFY REFRIGERATION SYSTEM TO OPERATE AT A LOWER PRESSURE

• 2.2622 REPLACE EXISTING CHILLER WITH HIGH EFFICIENCY MODEL

• 2.2623 MINIMIZE CONDENSER COOLING WATER TEMPERATURE

• 2.2624 USE COLD WASTE WATER TO COOL CHILLER FEED WATER

• 2.2625 CHILL WATER TO THE HIGHEST TEMPERATURE POSSIBLE

• 2.2626 AVOID FROST FORMATION ON EVAPORATORS

• 2.2627 USE MULTIPLE-EFFECT EVAPORATORS

• 2.2628 UTILIZE A LESS EXPENSIVE COOLING METHOD

• 2.2691 SHUT OFF COOLING IF COLD OUTSIDE AIR WILL COOL PROCESS

• 2.2692 USE OUTSIDE COLD WATER SOURCE AS A SUPPLY OF COOLING WATER

• 2.2693 USE WASTE HEAT STEAM FOR ABSORPTION REFRIGERATION

• 2.2694 USE HIGHEST TEMPERATURE FOR CHILLING OR COLD STORAGE

• 2.2695 USE CASCADE SYSTEM OF RECIRCULATING DURING COLD WEATHER TO AVOID SUB-COOLING

• 2.2696 USE EXCESS COLD PROCESS FLUID FOR INDUSTRIAL COOLING NEEDS

• 2.7232 REPLACE EXISTING HVAC UNIT WITH HIGH EFFICIENCY MODEL

• 2.7233 USE PROPERLY DESIGNED AND SIZED HVAC EQUIPMENT

• 2.7234 USE HEAT PUMP FOR SPACE CONDITIONING

• 2.7251 REDUCE AIR CONDITIONING LOAD BY EVAPORATING WATER FROM ROOF

• 2.7252 UTILIZE AN EVAPORATIVE AIR PRE-COOLER OR OTHER HEAT EXCHANGER IN AC SYSTEM

Assessment Recommendation Code of Cooling Systems (cont.)