ASHRAE Journal - February 2010 - 15

–13°C) and a return gas temperature to the compressor suction header around 50°F (10°C). The heat available for recovery from a refrigeration system comes from the high-pressure, high-temperature refrigerant gas discharge of the compressors. The return gas temperature at the compressor suction header impacts the temperature of the discharge gas from the compressors, which impacts the heat available for recovery. Therefore, the documentation of the basis of design and the proper physical adjustment of the refrigeration systems are vital for effective and consistent heat recovery performance. The information in Tables 1 and 2 illustrate the relative design temperatures, refrigerant properties and heat energy available for refrigerants R-407A and R-404A. The quality of heat available from desuperheating is dependent on the temperature of the compressor discharge at a given condensing temperature. This “desuperheated” energy can be applied to a variety of heat recovery schemes, as it has higher heat quality. The amount of superheat available at a given condensing temperature is equal to the mass flow rate times the difference of the vapor enthalpies. The mass flow rate for a given refrigeration load varies by refrigerant and is based on the difference in the latent heat of vaporization (difference in enthalpies from saturated liquid to saturated vapor) for the refrigerant and the inlet quality to the evaporator coil. The condensing temperature is the measure of the liquid refrigerant. The compressor discharge temperature is the temperature of the superheated refrigerant at the exit of the compressor. As the condensing temperature of the system moves from design maximum to design minimum, the mass flow of the system adjusts to a relatively stable minimum based on the refrigerated case load. The electrical energy consumption of a refrigeration system is proportional to the mass flow rate of the refrigerant. The refrigerant mass flow required to meet the system load is the sum of the evaporator load plus the system condition loads, such as the condensing temperature, subcooler load, and parasitic piping losses. As the refrigerant temperature approaches R-404A Properties – Low Temperature – Desuperheating1 Superheated Condensing Condensing Compressor Vapor Enthalpy Temp. Pressure Discharge Condenser (°F) (psia) (°F) Inlet (Btu/lbm) Saturated Vapor Condenser (Btu/lbm) Liquid Enthalpy (Btu/lbm) Mass Flow (lbm/h) Load (Btu/h) Heat Recovery Percent of Available Design Day (Desuperheating) Load (Btu/h) 65 75 85 95 105 115 151.1 175.7 203.2 233.8 267.8 305.4 157.0 167.0 179.0 192.0 205.0 218.0 184.3 185.9 188.1 190.4 192.8 195.1 161.0 161.9 162.6 163.3 163.7 163.9 97.2 100.8 104.5 108.3 112.2 116.3 5,791 6,412 7,140 8,008 9,061 10,397 320,875 332,200 343,525 354,850 366,175 377,500 85% 88% 91% 94% 97% 100% 135,182 154,400 181,509 217,454 263,331 324,283 Based on a low temperature system with a 378 MBh refrigeration load at –20°F saturated suction temperature and a medium temperature system with a 889 MBh refrigeration load at +20°F saturated suction temperature. One MBh is equal to 1,000 Btu/h. No natural subcooling or useful superheat included. Table 2: Desuperheating heat recovery for a R-404A system. February 2010 ASHRAE Journal 15

ASHRAE Journal - February 2010

Table of Contents for the Digital Edition of ASHRAE Journal - February 2010

ASHRAE Journal - February 2010
Contents
Commentary
Industry News
Letters
Meetings and Shows
Heat Recovery In Retail Refrigeration
Using CO2 in Supermarkets
Demand-Based Control Of Lab Air Change Rates
Anniversary Feature: Improved Zoning Betters Department Store Air Conditioning
History of Radiant Heating & Cooling Systems, Part 2
Save Chiller Plant Energy With Guideline 22-2008
Building Sciences
ACREX 2010 Show Guide
Washington Report
InfoCenter
People
Technical Topics
Emerging Technologies
Special Products
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - February 2010 - ASHRAE Journal - February 2010
ASHRAE Journal - February 2010 - Cover2
ASHRAE Journal - February 2010 - 1
ASHRAE Journal - February 2010 - 2
ASHRAE Journal - February 2010 - Contents
ASHRAE Journal - February 2010 - 4
ASHRAE Journal - February 2010 - Commentary
ASHRAE Journal - February 2010 - Industry News
ASHRAE Journal - February 2010 - 7
ASHRAE Journal - February 2010 - 8
ASHRAE Journal - February 2010 - 9
ASHRAE Journal - February 2010 - Letters
ASHRAE Journal - February 2010 - 11
ASHRAE Journal - February 2010 - Meetings and Shows
ASHRAE Journal - February 2010 - 13
ASHRAE Journal - February 2010 - Heat Recovery In Retail Refrigeration
ASHRAE Journal - February 2010 - 15
ASHRAE Journal - February 2010 - 16
ASHRAE Journal - February 2010 - 17
ASHRAE Journal - February 2010 - 18
ASHRAE Journal - February 2010 - 19
ASHRAE Journal - February 2010 - 20
ASHRAE Journal - February 2010 - 21
ASHRAE Journal - February 2010 - 22
ASHRAE Journal - February 2010 - 23
ASHRAE Journal - February 2010 - Using CO2 in Supermarkets
ASHRAE Journal - February 2010 - 25
ASHRAE Journal - February 2010 - 26
ASHRAE Journal - February 2010 - 27
ASHRAE Journal - February 2010 - 28
ASHRAE Journal - February 2010 - 29
ASHRAE Journal - February 2010 - Demand-Based Control Of Lab Air Change Rates
ASHRAE Journal - February 2010 - 31
ASHRAE Journal - February 2010 - 32
ASHRAE Journal - February 2010 - Insert1
ASHRAE Journal - February 2010 - Insert2
ASHRAE Journal - February 2010 - 33
ASHRAE Journal - February 2010 - 34
ASHRAE Journal - February 2010 - 35
ASHRAE Journal - February 2010 - 36
ASHRAE Journal - February 2010 - 37
ASHRAE Journal - February 2010 - 38
ASHRAE Journal - February 2010 - 39
ASHRAE Journal - February 2010 - 40
ASHRAE Journal - February 2010 - 41
ASHRAE Journal - February 2010 - Anniversary Feature: Improved Zoning Betters Department Store Air Conditioning
ASHRAE Journal - February 2010 - 43
ASHRAE Journal - February 2010 - 44
ASHRAE Journal - February 2010 - 45
ASHRAE Journal - February 2010 - 46
ASHRAE Journal - February 2010 - 47
ASHRAE Journal - February 2010 - 48
ASHRAE Journal - February 2010 - 49
ASHRAE Journal - February 2010 - History of Radiant Heating & Cooling Systems, Part 2
ASHRAE Journal - February 2010 - 51
ASHRAE Journal - February 2010 - 52
ASHRAE Journal - February 2010 - 53
ASHRAE Journal - February 2010 - 54
ASHRAE Journal - February 2010 - 55
ASHRAE Journal - February 2010 - Save Chiller Plant Energy With Guideline 22-2008
ASHRAE Journal - February 2010 - 57
ASHRAE Journal - February 2010 - 58
ASHRAE Journal - February 2010 - 59
ASHRAE Journal - February 2010 - Building Sciences
ASHRAE Journal - February 2010 - 61
ASHRAE Journal - February 2010 - 62
ASHRAE Journal - February 2010 - 63
ASHRAE Journal - February 2010 - 64
ASHRAE Journal - February 2010 - ACREX 2010 Show Guide
ASHRAE Journal - February 2010 - S2
ASHRAE Journal - February 2010 - S3
ASHRAE Journal - February 2010 - S4
ASHRAE Journal - February 2010 - S5
ASHRAE Journal - February 2010 - S6
ASHRAE Journal - February 2010 - S7
ASHRAE Journal - February 2010 - S8
ASHRAE Journal - February 2010 - S9
ASHRAE Journal - February 2010 - S10
ASHRAE Journal - February 2010 - S11
ASHRAE Journal - February 2010 - S12
ASHRAE Journal - February 2010 - S13
ASHRAE Journal - February 2010 - S14
ASHRAE Journal - February 2010 - S15
ASHRAE Journal - February 2010 - S16
ASHRAE Journal - February 2010 - S17
ASHRAE Journal - February 2010 - S18
ASHRAE Journal - February 2010 - S19
ASHRAE Journal - February 2010 - S20
ASHRAE Journal - February 2010 - S21
ASHRAE Journal - February 2010 - S22
ASHRAE Journal - February 2010 - S23
ASHRAE Journal - February 2010 - S24
ASHRAE Journal - February 2010 - S25
ASHRAE Journal - February 2010 - S26
ASHRAE Journal - February 2010 - S27
ASHRAE Journal - February 2010 - S28
ASHRAE Journal - February 2010 - S29
ASHRAE Journal - February 2010 - S30
ASHRAE Journal - February 2010 - S31
ASHRAE Journal - February 2010 - S32
ASHRAE Journal - February 2010 - Washington Report
ASHRAE Journal - February 2010 - InfoCenter
ASHRAE Journal - February 2010 - 67
ASHRAE Journal - February 2010 - 68
ASHRAE Journal - February 2010 - 69
ASHRAE Journal - February 2010 - 70
ASHRAE Journal - February 2010 - 71
ASHRAE Journal - February 2010 - 72
ASHRAE Journal - February 2010 - People
ASHRAE Journal - February 2010 - Technical Topics
ASHRAE Journal - February 2010 - 75
ASHRAE Journal - February 2010 - 76
ASHRAE Journal - February 2010 - 77
ASHRAE Journal - February 2010 - Emerging Technologies
ASHRAE Journal - February 2010 - 79
ASHRAE Journal - February 2010 - 80
ASHRAE Journal - February 2010 - 81
ASHRAE Journal - February 2010 - 82
ASHRAE Journal - February 2010 - Special Products
ASHRAE Journal - February 2010 - Products
ASHRAE Journal - February 2010 - Classified Advertising
ASHRAE Journal - February 2010 - 86
ASHRAE Journal - February 2010 - 87
ASHRAE Journal - February 2010 - Advertisers Index
ASHRAE Journal - February 2010 - Cover3
ASHRAE Journal - February 2010 - Cover4
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