1 Basic Principle of Heat Transfer Hot Cold Summer Conditions 90 F 72 F Summer Conditions Heat flow Indoor air temperature Summer Conditions Heat flow Indoor air temperature Remove heat from indoor air Finned-Tube Heat Exchanger (Indoor coil) Indoor Air Refrigerant Indoor Coil 72 F 55 F 2 Warm indoor air (72 F) Cold refrigerant (40 F) Heat transferred from the air to the refrigerant Refrigerant The fluid used for energy exchanges in an air conditioning, refrigeration or heat pump system. Usually the refrigerant absorbs heat while undergoing a liquid to vapor phase change (evaporation) and releases heat while undergoing a vapor to liquid phase change (condensation). Heat Evaporation liquid vapor Heat Condensation Refrigerant liquid Refrigerant vapor Indoor Coil (Evaporator) System Components Outdoor coil Expansion valve Compressor Indoor coil Reversing valve Low pressure & temperatureHigh pressure & temperature System Pressures and Temperatures Outdoor coil Expansion valve Compressor Indoor coil Refrigerant flow 3 Outdoor coil (Condenser) Outdoor Air Refrigerant vapor Refrigerant liquid Air Conditioning Cycle Outdoor air 72 F 55 F 90 F low temperature high temperature Indoor air 110 F Residential Air-Conditioning System Outdoor Unit ? Outdoor coil ? Compressor ?Fan Indoor Unit ? Indoor coil ?Valve ?Fan System Performance Work Heat Heat Coefficient of Performance Energy Efficiency Ratio COP = Desired heat transfer effect (units) Work required (units) COP = Heat transfer rate FROM indoor air Power input to the compressor and fans EER = Heat transfer rate (Btu/hr) Electrical power (Watts) 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80 85 90 95 100 105 110 115 Outdoor air temperature (F) C O P (d i m en si o n l e s s ) Indoor air temperature = 72 F Maximum COP for an Air-Conditioning Cycle as a Function of Outdoor Air Temperature 4 Winter Conditions 25 F 72 F Winter Conditions 25 F 72 F Indoor air temperature Winter Conditions 25 F 72 F Add heat to the indoor air Indoor air temperature Beware of the snowman Reverse the operation of the air conditioning system Low pressure & temperature High pressure & temperature Outdoor coil Expansion valve Compressor Indoor coil Direction of refrigerant flow is reversed in all components except the compressor. 5 Compare to the air conditioning cycle. Heat Pump Cycle Outdoor air 20 F 10 F 72 F low temperature high temperature Indoor air 90 F System Performance Work Heat Heat Coefficient of Performance Energy Efficiency Ratio COP = Desired heat transfer effect (units) Work required (units) COP = Heat transfer rate TO indoor air Power input to the compressor and fans EER = Heat transfer rate (Btu/hr) Electrical power (Watts) 0.0 10.0 20.0 30.0 40.0 50.0 -10 0 10 20 30 40 50 60 Outdoor air temperature (F) CO P ( d imen sio n les s ) Indoor air temperature = 72 F Maximum COP for a Heat-Pump Cycle as a Function of Outdoor Air Temperature Geothermal Heat Pumps 6 Determining the performance parameters of a refrigeration and heat pump system. COP = Heat transfer rate TO/FROM indoor air Power input to the compressor and fans EER = Heat transfer rate (Btu/hr) Electrical power (Watts) ?Measure the electrical power. ?Calculate the heat transfer rate to/from the air. Energy Systems 2.0 Outdoor coil Indoor coil Compressor Digital thermometer Power meter Exp. valve Rev. valve Duct 4-inch Nozzle Atmospheric Air Nitrogen (78.08) Oxygen (20.95) Argon (0.93) Carbon dioxide (0.03) other gases (0.01) + Water vaporDry air Moist air Ideal gas mixture Calculating the heat transfer rate to the air. in T out T Temperature of the moist air increases while water vapor content of the air remains constant. Only sensible heat transfer is present. Duct Heating coil Calculating the heat transfer rate from the air. in T out T Depending on the temperature of the coil, water vapor condenses on the coil surface and is removed from the air stream. The air is cooled and dehumidified. In this case both sensible and latent heat transfer effects are present. Duct Cooling coil Condensate removed 7 Calculate the heat transfer rates assuming DRY AIR (no water vapor is present). () rate flow volume Q heat specificc volumespecific TTc Q q p inoutp = = = ?=    v v Ideal Gas (R) atureair temper T Rlb lbft 352.53R airfor constant gasR pressure catmospheriP TRP m f a a a = ? ? = = = =v Duct 4-inch Nozzle Calculating the volume flow rate of air. )(ft area sectional crossA (ft/min) velocity averageV min)/(ftA VQ 2 3 = = =  V Velocity probe is used to measure the air velocity ? A summary. ? A diagram of the system. ? The basic principles involved. ? A clear discussion of how the system works. ? How you determined the performance parameters. ? Your experimental results. ? Your calculations of the performance parameters. Assignment Write a 3-6 page technical paper discussing the refrigeration unit and your experiment. This report should include: