ASHRAE Journal - February 2009 - 22

• Low-temperature carbon dioxide secondary coolant system with single suction group; and • Low-temperature carbon dioxide direct expansion cascade system with two suction groups. Basic piping diagrams for the three systems are shown in Figure 3. In the DX baseline system and the CO2 secondary system, the HFC component is a low-temperature system, which can be subcooled by another medium-temperature system installed nearby. Subcooling of low-temperature systems using a system operating at higher saturated suction temperature is an important energy saving feature that is considered in the following analysis. Circuiting and line sizing for the low-temperature HFC DX baseline system was based on the existing circuited system configuration that is currently manufactured. Line sizes for the various CO2 systems were selected specifically for this analysis based on current practice, which dictates a loop-type of installation for both systems as control valves are located at the individual evaporator coils rather than having common valving for multiple coils (evaporator pressure regulators) as is the case with most HFC systems. It was assumed that all lines would be copper piping, of the thickness required for the specific applications. In several instances, the CO2 piping required Type-K copper pipe. All lines were assumed to run inside the building envelope and in air-conditioned space with a constant ambient temperature of 24°C (75°F). With system configurations established, the analysis for each system type was carried out. The bar graph in Figure 5 shows the results of the analysis of distribution piping heat gain for the three different low-temperature systems. The analysis indicates that although the line temperatures are lower for the CO2 secondary coolant system, the HFC direct expansion system has significantly higher heat gain due to the larger pipe diameters and installed lengths of copper piping. The smaller lines and somewhat warmer pipe temperatures in the CO2 cascade system lead to further reductions in heat gain. In addition to heat gain, it is interesting to look at how the different system types compare with each other in terms of installed feet and weight of copper. This gives some indication of potential differences in installation cost between the various system types. Table 1 summarizes the installed copper length and weight of copper pipe for each of the system 22 ASHRAE Journal Low-Temperature Loads Medium-Temperature Loads Refrigeration System Figure 4: Representative store layout. Low-Temperature Heat Gain, % of Total Low-Temperature Load 16% 14% 12% 12.29% 10% 8% 6% 4% 2% 0% 6.06% Insulation: Low-Temperature HFC DX: 0.75 in. Supply, 1.0 in. Return Low-Temperature CO2 SC: 1.0 in. Supply, 1.0 in. Return Low-Temperature CO2 DX: 0.75 in. Supply, 1.0 in. Return 9.12% Low-Temperature HFC DX Baseline Low-Temperature CO2 Secondary Low-Temperature CO2 DX Cascade Figure 5: Low-temperature system heat gain into distribution piping. 2,400 2,200 2,000 1,800 1,600 1,400 1,200 1,000 800 600 400 200 0 –17.7 (0) –12.2 (10) –6.7 (20) –1.1 (30) 4.4 (40) 10 (50) 15.6 (60) 21.1 (70) Atlanta Los Angeles Boston Hours Per Year 26.7 (80) 32.2 (90) 37.8 (100) Ambient Temperature, °C (°F) Figure 6: Bin weather data for selected cities. ashrae.org February 2009

ASHRAE Journal - February 2009

Table of Contents for the Digital Edition of ASHRAE Journal - February 2009

ASHRAE Journal - February 2009
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
     Carbon Dioxide in North American Supermarkets
     Frost on Air-Cooling Evaporators
     Electronic Expansion Valves Versus Thermal Expansion Valves
     Anniversary Feature: Air Handling Unit Design for Energy Conservation
     Redundancy for Data Centers
Building Sciences
Washington Report
InfoCenter
Special Products
Emerging Technologies
People
Products
Classified Advertising
Advertising Index
ASHRAE Journal - February 2009 - ASHRAE Journal - February 2009
ASHRAE Journal - February 2009 - Cover2
ASHRAE Journal - February 2009 - 1
ASHRAE Journal - February 2009 - 2
ASHRAE Journal - February 2009 - Contents
ASHRAE Journal - February 2009 - 4
ASHRAE Journal - February 2009 - Commentary
ASHRAE Journal - February 2009 - Industry News
ASHRAE Journal - February 2009 - 7
ASHRAE Journal - February 2009 - 8
ASHRAE Journal - February 2009 - 9
ASHRAE Journal - February 2009 - 10
ASHRAE Journal - February 2009 - 11
ASHRAE Journal - February 2009 - 12
ASHRAE Journal - February 2009 - 13
ASHRAE Journal - February 2009 - Letters
ASHRAE Journal - February 2009 - 15
ASHRAE Journal - February 2009 - 16
ASHRAE Journal - February 2009 - A1
ASHRAE Journal - February 2009 - A2
ASHRAE Journal - February 2009 - A3
ASHRAE Journal - February 2009 - A4
ASHRAE Journal - February 2009 - A5
ASHRAE Journal - February 2009 - A6
ASHRAE Journal - February 2009 - A7
ASHRAE Journal - February 2009 - A8
ASHRAE Journal - February 2009 - A9
ASHRAE Journal - February 2009 - A10
ASHRAE Journal - February 2009 - A11
ASHRAE Journal - February 2009 - A12
ASHRAE Journal - February 2009 - A13
ASHRAE Journal - February 2009 - A14
ASHRAE Journal - February 2009 - A15
ASHRAE Journal - February 2009 - A16
ASHRAE Journal - February 2009 - A17
ASHRAE Journal - February 2009 - A18
ASHRAE Journal - February 2009 - A19
ASHRAE Journal - February 2009 - A20
ASHRAE Journal - February 2009 - A21
ASHRAE Journal - February 2009 - A22
ASHRAE Journal - February 2009 - A23
ASHRAE Journal - February 2009 - A24
ASHRAE Journal - February 2009 - A25
ASHRAE Journal - February 2009 - A26
ASHRAE Journal - February 2009 - A27
ASHRAE Journal - February 2009 - A28
ASHRAE Journal - February 2009 - A29
ASHRAE Journal - February 2009 - A30
ASHRAE Journal - February 2009 - A31
ASHRAE Journal - February 2009 - A32
ASHRAE Journal - February 2009 - A33
ASHRAE Journal - February 2009 - A34
ASHRAE Journal - February 2009 - A35
ASHRAE Journal - February 2009 - A36
ASHRAE Journal - February 2009 - A37
ASHRAE Journal - February 2009 - A38
ASHRAE Journal - February 2009 - A39
ASHRAE Journal - February 2009 - A40
ASHRAE Journal - February 2009 - Meetings and Shows
ASHRAE Journal - February 2009 -      Carbon Dioxide in North American Supermarkets
ASHRAE Journal - February 2009 - 19
ASHRAE Journal - February 2009 - 20
ASHRAE Journal - February 2009 - 21
ASHRAE Journal - February 2009 - 22
ASHRAE Journal - February 2009 - 23
ASHRAE Journal - February 2009 - 24
ASHRAE Journal - February 2009 - 25
ASHRAE Journal - February 2009 - 26
ASHRAE Journal - February 2009 -      Frost on Air-Cooling Evaporators
ASHRAE Journal - February 2009 - 28
ASHRAE Journal - February 2009 - 29
ASHRAE Journal - February 2009 - 30
ASHRAE Journal - February 2009 - 31
ASHRAE Journal - February 2009 - 32
ASHRAE Journal - February 2009 - 33
ASHRAE Journal - February 2009 -      Electronic Expansion Valves Versus Thermal Expansion Valves
ASHRAE Journal - February 2009 - 35
ASHRAE Journal - February 2009 - 36
ASHRAE Journal - February 2009 - 37
ASHRAE Journal - February 2009 - 38
ASHRAE Journal - February 2009 - 39
ASHRAE Journal - February 2009 -      Anniversary Feature: Air Handling Unit Design for Energy Conservation
ASHRAE Journal - February 2009 - 41
ASHRAE Journal - February 2009 - 42
ASHRAE Journal - February 2009 - 43
ASHRAE Journal - February 2009 - 44
ASHRAE Journal - February 2009 - 45
ASHRAE Journal - February 2009 - 46
ASHRAE Journal - February 2009 - 47
ASHRAE Journal - February 2009 - 48
ASHRAE Journal - February 2009 - 49
ASHRAE Journal - February 2009 - 50
ASHRAE Journal - February 2009 - 51
ASHRAE Journal - February 2009 -      Redundancy for Data Centers
ASHRAE Journal - February 2009 - 53
ASHRAE Journal - February 2009 - 54
ASHRAE Journal - February 2009 - 55
ASHRAE Journal - February 2009 - Building Sciences
ASHRAE Journal - February 2009 - 57
ASHRAE Journal - February 2009 - 58
ASHRAE Journal - February 2009 - 59
ASHRAE Journal - February 2009 - Washington Report
ASHRAE Journal - February 2009 - 61
ASHRAE Journal - February 2009 - InfoCenter
ASHRAE Journal - February 2009 - 63
ASHRAE Journal - February 2009 - 64
ASHRAE Journal - February 2009 - 65
ASHRAE Journal - February 2009 - 66
ASHRAE Journal - February 2009 - 67
ASHRAE Journal - February 2009 - Special Products
ASHRAE Journal - February 2009 - Emerging Technologies
ASHRAE Journal - February 2009 - 70
ASHRAE Journal - February 2009 - 71
ASHRAE Journal - February 2009 - 72
ASHRAE Journal - February 2009 - People
ASHRAE Journal - February 2009 - Products
ASHRAE Journal - February 2009 - 75
ASHRAE Journal - February 2009 - 76
ASHRAE Journal - February 2009 - Classified Advertising
ASHRAE Journal - February 2009 - 78
ASHRAE Journal - February 2009 - 79
ASHRAE Journal - February 2009 - Advertising Index
ASHRAE Journal - February 2009 - Cover3
ASHRAE Journal - February 2009 - Cover4
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