Refrigeration and air conditioning

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1 Training Session on Energy Equipment Refrigeration & Air Conditioning Presentation from the “Energy Efficiency Guide for Industry in Asia” www.energyefficiencyasia.org © UNEP 2006 Electrical Equipment/ Refrigeration & AC

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2 © UNEP 2006 Training Agenda: Refrigeration & Air Conditioning Introduction Type of refrigeration Assessment of refrigeration and AC Energy efficiency opportunities Electrical Equipment/ Refrigeration & AC

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3 © UNEP 2006 Introduction How does it work? Electrical Equipment/ Refrigeration & AC High Temperature Reservoir Low Temperature Reservoir R Work Input Heat Absorbed Heat Rejected

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4 © UNEP 2006 Introduction Thermal energy moves from left to right through five loops of heat transfer: How does it work? Electrical Equipment/ Refrigeration & AC (Bureau of Energy Efficiency, 2004) 1) Indoor air loop 2) Chilled water loop 3) Refrigerant loop 4) Condenser water loop 5) Cooling water loop

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5 © UNEP 2006 Introduction AC options / combinations: AC Systems Electrical Equipment/ Refrigeration & AC Air Conditioning (for comfort / machine) Split air conditioners Fan coil units in a larger system Air handling units in a larger system

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6 © UNEP 2006 Introduction Small capacity modular units of direct expansion type (50 Tons of Refrigeration) Centralized chilled water plants with chilled water as a secondary coolant (50 – 250 TR) Brine plants with brines as lower temperature, secondary coolant (>250 TR) Refrigeration systems for industrial processes Electrical Equipment/ Refrigeration & AC

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7 © UNEP 2006 Introduction Bank of units off-site with common Chilled water pumps Condenser water pumps Cooling towers More levels of refrigeration/AC, e.g. Comfort air conditioning (20-25 o C) Chilled water system (8 – 10 o C) Brine system (< 0 o C) Refrigeration at large companies Electrical Equipment/ Refrigeration & AC

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8 © UNEP 2006 Training Agenda: Refrigeration & Air Conditioning Introduction Type of refrigeration Assessment of refrigeration and AC Energy efficiency opportunities Electrical Equipment/ Refrigeration & AC

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9 © UNEP 2006 Types of Refrigeration Vapour Compression Refrigeration (VCR): uses mechanical energy Vapour Absorption Refrigeration (VAR): uses thermal energy Refrigeration systems Electrical Equipment/ Refrigeration & AC

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10 © UNEP 2006 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC Highly compressed fluids tend to get colder when allowed to expand If pressure high enough Compressed air hotter than source of cooling Expanded gas cooler than desired cold temperature

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11 © UNEP 2006 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC Two advantages Lot of heat can be removed (lot of thermal energy to change liquid to vapour) Heat transfer rate remains high (temperature of working fluid much lower than what is being cooled)

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12 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC © UNEP 2006 Refrigeration cycle Condenser Evaporator High Pressure Side Low Pressure Side Compressor Expansion Device 1 2 3 4

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13 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC © UNEP 2006 Refrigeration cycle Low pressure liquid refrigerant in evaporator absorbs heat and changes to a gas Condenser Evaporator High Pressure Side Low Pressure Side Compressor Expansion Device 1 2 3 4

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14 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC © UNEP 2006 Refrigeration cycle The superheated vapour enters the compressor where its pressure is raised Condenser Evaporator High Pressure Side Low Pressure Side Compressor Expansion Device 1 2 3 4

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15 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC © UNEP 2006 Refrigeration cycle The high pressure superheated gas is cooled in several stages in the condenser Condenser Evaporator High Pressure Side Low Pressure Side Compressor Expansion Device 1 2 3 4

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16 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC © UNEP 2006 Refrigeration cycle Liquid passes through expansion device, which reduces its pressure and controls the flow into the evaporator Condenser Evaporator High Pressure Side Low Pressure Side Compressor Expansion Device 1 2 3 4

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17 © UNEP 2006 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC Type of refrigerant Refrigerant determined by the required cooling temperature Chlorinated fluorocarbons (CFCs) or freons: R-11, R-12, R-21, R-22 and R-502

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18 © UNEP 2006 Type of Refrigeration Vapour Compression Refrigeration Electrical Equipment/ Refrigeration & AC Choice of compressor, design of condenser, evaporator determined by Refrigerant Required cooling Load Ease of maintenance Physical space requirements Availability of utilities (water, power)

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19 © UNEP 2006 Type of Refrigeration Vapour Absorption Refrigeration Electrical Equipment/ Refrigeration & AC Condenser Generator Evaporator Absorber Cold Side Hot Side

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20 © UNEP 2006 Type of Refrigeration Vapour Absorption Refrigeration Electrical Equipment/ Refrigeration & AC Evaporator

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21 © UNEP 2006 Type of Refrigeration Vapour Absorption Refrigeration Electrical Equipment/ Refrigeration & AC Absorber

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22 © UNEP 2006 Type of Refrigeration Vapour Absorption Refrigeration Electrical Equipment/ Refrigeration & AC High pressure generator

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23 © UNEP 2006 Type of Refrigeration Vapour Absorption Refrigeration Electrical Equipment/ Refrigeration & AC Condenser

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24 © UNEP 2006 Type of Refrigeration Evaporative Cooling Electrical Equipment/ Refrigeration & AC (Adapted from Munters, 2001) Cold Air Hot Air Sprinkling Water Air in contact with water to cool it close to ‘wet bulb temperature’ Advantage: efficient cooling at low cost Disadvantage: air is rich in moisture

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25 © UNEP 2006 Training Agenda: Refrigeration & Air Conditioning Introduction Type of refrigeration Assessment of refrigeration and AC Energy efficiency opportunities Electrical Equipment/ Refrigeration & AC

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26 Assessment of Refrigeration and AC Cooling effect: Tons of Refrigeration TR is assessed as: Assessment of Refrigeration Electrical Equipment/ Refrigeration & AC 1 TR = 3024 kCal/hr heat rejected TR = Q x  Cp x  (Ti – To) / 3024 Q = mass flow rate of coolant in kg/hr Cp = is coolant specific heat in kCal /kg deg C Ti = inlet, temperature of coolant to evaporator (chiller) in 0C To = outlet temperature of coolant from evaporator (chiller) in 0C © UNEP 2006

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27 © UNEP 2006 Specific Power Consumption (kW/TR) Indicator of refrigeration system’s performance kW/TR of centralized chilled water system is sum of Compressor kW/TR Chilled water pump kW/TR Condenser water pump kW/TR Cooling tower fan kW/TR Electrical Equipment/ Refrigeration & AC Assessment of Refrigeration and AC Assessment of Refrigeration

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28 © UNEP 2006 Coefficient of Performance (COP Carnot ) Standard measure of refrigeration efficiency Depends on evaporator temperature Te and condensing temperature Tc: COP in industry calculated for type of compressor: Electrical Equipment/ Refrigeration & AC COP Carnot = Te / (Tc - Te) Assessment of Refrigeration and AC Assessment of Refrigeration

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29 © UNEP 2006 Electrical Equipment/ Refrigeration & AC COP increases with rising evaporator temperature (Te) COP increases with decreasing condensing temperature (Tc) Assessment of Refrigeration and AC Assessment of Refrigeration

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30 © UNEP 2006 Measure Airflow Q (m3/s) at Fan Coil Units (FCU) or Air Handling Units (AHU): anemometer Air density  (kg/m3) Dry bulb and wet bulb temperature: psychrometer Enthalpy (kCal/kg) of inlet air (h in ) and outlet air (H out ): psychrometric charts Calculate TR Electrical Equipment/ Refrigeration & AC Assessment of Refrigeration and AC Assessment of Air Conditioning

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31 © UNEP 2006 Indicative TR load profile Small office cabins : 0.1 TR/m2 Medium size office (10 – 30 people occupancy) with central A/C: 0.06 TR/m2 Large multistoried office complexes with central A/C: 0.04 TR/m2 Assessment of Air Conditioning Electrical Equipment/ Refrigeration & AC Assessment of Refrigeration and AC

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32 © UNEP 2006 Accuracy of measurements Inlet/outlet temp of chilled and condenser water Flow of chilled and condenser water Integrated Part Load Value (IPLV) kW/TR for 100% load but most equipment operate between 50-75% of full load IPLV calculates kW/TR with partial loads Four points in cycle: 100%, 75%, 50%, 25% Considerations for Assessment Electrical Equipment/ Refrigeration & AC Assessment of Refrigeration and AC

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33 © UNEP 2006 Training Agenda: Refrigeration & Air Conditioning Introduction Type of refrigeration Assessment of refrigeration and AC Energy efficiency opportunities Electrical Equipment/ Refrigeration & AC

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34 © UNEP 2006 Optimize process heat exchange Maintain heat exchanger surfaces Multi-staging systems Matching capacity to system load Capacity control of compressors Multi-level refrigeration for plant needs Chilled water storage System design features Electrical Equipment/ Refrigeration & AC Energy Efficiency Opportunities

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35 © UNEP 2006 Energy Efficiency Opportunities High compressor safety margins: energy loss Proper sizing heat transfer areas of heat exchangers and evaporators Heat transfer coefficient on refrigerant side: 1400 – 2800 Watt/m2K Heat transfer area refrigerant side: >0.5 m2/TR Optimum driving force (difference Te and Tc): 1 o C raise in Te = 3% power savings 1. Optimize Process Heat Exchange Electrical Equipment/ Refrigeration & AC

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36 © UNEP 2006 Energy Efficiency Opportunities Electrical Equipment/ Refrigeration & AC Evaporator Temperature ( 0 C) Refrigeration Capacity * (tons) Specific Power Consumption (kW/TR) Increase kW/TR (%) 5.0 67.58 0.81 - 0.0 56.07 0.94 16.0 -5.0 45.98 1.08 33.0 -10.0 37.20 1.25 54.0 -20.0 23.12 1.67 106.0 (National Productivity Council) Condenser temperature 40 ◦ C 1. Optimize Process Heat Exchange Condensing Temperature ( 0 C) Refrigeration Capacity (tons) Specific Power Consumption (kW /TR) Increase kW/TR (%) 26.7 31.5 1.17 - 35.0 21.4 1.27 8.5 40.0 20.0 1.41 20.5 *Reciprocating compressor using R-22 refrigerant. Evaporator temperature.-10 ◦ C

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37 © UNEP 2006 Energy Efficiency Opportunities 3. Selection of condensers Options: Air cooled condensers Air-cooled with water spray condensers Shell & tube condensers with water-cooling Water-cooled shell & tube condenser Lower discharge pressure Higher TR Lower power consumption 1. Optimize Process Heat Exchange Electrical Equipment/ Refrigeration & AC

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38 © UNEP 2006 Energy Efficiency Opportunities Poor maintenance = increased power consumption Maintain condensers and evaporators Separation of lubricating oil and refrigerant Timely defrosting of coils Increased velocity of secondary coolant Maintain cooling towers 0.55 ◦ C reduction in returning water from cooling tower = 3.0 % reduced power 2. Maintain Heat Exchanger Surfaces Electrical Equipment/ Refrigeration & AC

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39 © UNEP 2006 Energy Efficiency Opportunities Effect of poor maintenance on compressor power consumption 2. Maintain Heat Exchanger Surfaces Electrical Equipment/ Refrigeration & AC (National Productivity Council) Condition Te ( 0 C) Tc ( 0 C) Refrigeration Capacity * (TR) Specific Power Consumption (kW/TR) Increase kW/TR (%) Normal 7.2 40.5 17.0 0.69 - Dirty condenser 7.2 46.1 15.6 0.84 20.4 Dirty evaporator 1.7 40.5 13.8 0.82 18.3 Dirty condenser and evaporator 1.7 46.1 12.7 0.96 38.7

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40 © UNEP 2006 Energy Efficiency Opportunities Suited for Low temp applications with high compression Wide temperature range Two types for all compressor types Compound Cascade 3. Multi-Staging Systems Electrical Equipment/ Refrigeration & AC

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41 © UNEP 2006 Energy Efficiency Opportunities a. Compound Two low compression ratios = 1 high First stage compressor meets cooling load Second stage compressor meets load evaporator and flash gas Single refrigerant b. Cascade Preferred for -46 oC to -101oC Two systems with different refrigerants 3. Multi-Stage Systems Electrical Equipment/ Refrigeration & AC

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42 © UNEP 2006 Energy Efficiency Opportunities Most applications have varying loads Consequence of part-load operation COP increases but lower efficiency Match refrigeration capacity to load requires knowledge of Compressor performance Variations in ambient conditions Cooling load 4. Matching Capacity to Load System Electrical Equipment/ Refrigeration & AC

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43 © UNEP 2006 Energy Efficiency Opportunities 5. Capacity Control of Compressors Electrical Equipment/ Refrigeration & AC Cylinder unloading, vanes, valves Reciprocating compressors: step-by-step through cylinder unloading: Centrifugal compressors: c ontinuous modulation through vane control Screw compressors: sliding valves Speed control Reciprocating compressors: ensure lubrication system is not affected Centrifugal compressors: >50% of capacity

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44 © UNEP 2006 Energy Efficiency Opportunities 5. Capacity Control of Compressors Electrical Equipment/ Refrigeration & AC Temperature monitoring Reciprocating compressors: return water (if varying loads), water leaving chiller (constant loads) Centrifugal compressors: outgoing water temperature Screw compressors: outgoing water temperature Part load applications: screw compressors more efficient

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45 © UNEP 2006 Energy Efficiency Opportunities Bank of compressors at central plant Monitor cooling and chiller load: 1 chiller full load more efficient than 2 chillers at part-load Distribution system: individual chillers feed all branch lines; Isolation valves; Valves to isolate sections Load individual compressors to full capacity before operating second compressor Provide smaller capacity chiller to meet peak demands 6. Multi-Level Refrigeration Electrical Equipment/ Refrigeration & AC

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46 © UNEP 2006 Energy Efficiency Opportunities Packaged units (instead of central plant) Diverse applications with wide temp range and long distance Benefits: economical, flexible and reliable Disadvantage: central plants use less power Flow control Reduced flow Operation at normal flow with shut-off periods 6. Multi-Level Refrigeration Electrical Equipment/ Refrigeration & AC

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47 © UNEP 2006 Energy Efficiency Opportunities Chilled water storage facility with insulation Suited only if temp variations are acceptable Economical because Chillers operate during low peak demand hours: reduced peak demand charges Chillers operate at nighttime: reduced tariffs and improved COP 7. Chilled Water Storage Electrical Equipment/ Refrigeration & AC

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48 © UNEP 2006 Energy Efficiency Opportunities FRP impellers, film fills, PVC drift eliminators Softened water for condensers Economic insulation thickness Roof coatings and false ceilings Energy efficient heat recovery devices Variable air volume systems Sun film application for heat reflection Optimizing lighting loads 8. System Design Features Electrical Equipment/ Refrigeration & AC

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49 Training Session on Energy Equipment Refrigeration & Air Conditioning Systems THANK YOU FOR YOUR ATTENTION © UNEP 2006 Electrical Equipment/ Refrigeration & AC

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50 © UNEP 2006 Disclaimer and References Electrical Equipment/ Refrigeration & AC This PowerPoint training session was prepared as part of the project “Greenhouse Gas Emission Reduction from Industry in Asia and the Pacific” (GERIAP). While reasonable efforts have been made to ensure that the contents of this publication are factually correct and properly referenced, UNEP does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication. © UNEP, 2006. The GERIAP project was funded by the Swedish International Development Cooperation Agency (Sida) Full references are included in the textbook chapter that is available on www.energyefficiencyasia.org