ASHRAE Journal - April 2010 - 68

the air circulation fan power is deducted Entering WLHP GWHP GLHP GLHP from the total before EER is computed. Liquid and Air Water Loop Groundwater Ground Loop (Part Load) The combined influence of minimal fan power and lower ELT (68°F [20°C]) will ELT (Sink – Cooling) 86°F (30°C) 59°F (15°C) 77°F (25°C) 68°F (20°C) generate an optimistic value for cooling ELT (Source – Heating) 68°F (20°C) 50°F (10°C) 32°F (0°C) 41°F (5°C) efficiency. Table 3 provides a more meaningEAT (db/wb, Cooling) 80.6/66.2°F (27/19°C) ful comparison taken directly from EAT (Heating) 68°F (20°C) the manufacturer’s performance data, which includes some impact of fan Values for TC, EER, HC and COP do not include fan power to circulate air through duct and filters and power to pump water through heat pumps and piping loop. power (although no fan static pressures are provided) and can include air and Table 1: ISO 13256-1 conditions used to rate water-to-air heat pumps for total cooling, water flow rates appropriate for good energy efficiency ratio, heating capacity and coefficient of performance. dehumidification in cooling and comfort in heating (<400 cfm/ton [54 L/ Ground Loop Ground Loop Water Loop Groundwater (s·m)] and 3 gpm/ton [0.05 L/(s·m)]). (Part Load) (Full Load) The comparison assumes the full-load loop entering liquid temperature is 90°F Dual Single Dual Single Dual Single Dual Single (32°C) in cooling and 40°F (4°C) in EER 15.8 17.5 22.7 26.1 18 19.7 25.1 NA heating. The single-speed heat pump is 6% more efficient than the dual5.1 5.5 4.7 4.8 4.1 4.0 4.7 NA COP capacity machine in cooling and 2% Table 2: Dual and single capacity water-to-air heat pump rated EERs and COPs. improved in heating. At part-load, the ground loop temperature will moderate so cooling ELT is Full-Load Part-Load reduced to 80°F (27°C) and the heating (3 gpm/ton) (3 gpm/ton) ELT increased to 50°F (10°C). It should Dual Single Dual Single also be recognized that part-load con390 cfm/ton 375 cfm/ton 370 cfm/ton 325 cfm/ton ditions are typically accompanied by a reduction in load sensible heat ratio. TC (Btu/h) TC (Btu/h) 47,800 47,300 37,900 49,000 EER EER To better match this condition, airflows 14.5 15.4 18.6 18.6 (90°F ELT) (80°F ELT) can be reduced to improve latent performance. Data for the single-capacity HC HC (Btu/h) 42,900 43,000 33,200 47,400 (Btu/h) machine is provided at 325 cfm/ton COP 4.1 4.2 4.2 4.4 COP (44 L/[s·m]) while the lowest flow (50°F ELT) (40°F ELT) data for the dual-capacity heat pump is 370 cfm/ton (50 L/[s·m]). At these Table 3: Corrected total cooling (TC), EER, heating capacity (HC) and COP. conditions the heat pump efficiencies are equal in cooling and the single-capacity machine is 5% One method of attaining dual- or variable-capacity is to improved in heating. Additionally, the reduction in capac- use an electronic inverter drive similar to the motor drives ity of the dual-capacity unit from full- to part-load is only for pumps and fans. Air-to-air heat pump manufacturers 22%. So the enhanced part-load dehumidification due to the marketed this technology for unitary compressors in the reduction in on-off cycles is minimal. 1990s but abandoned it several years ago. One compressor manufacturer developed a technology that reversed the Equipment Needed for Dual-Capacity Heat Pumps direction of rotation of a reciprocating compressor to attain A past emphasis by utility and government incentive programs dual-capacity by unloading one of the two cylinders. The upon seasonal efficiency unfortunately has served to obscure the predecessor to the dual-capacity product line used for the importance of full-load performance, the true driver of electric- previous examples incorporated this technology. However, ity demand. Part-load and seasonal efficiency metrics are not the product line was also abandoned in favor of a dualrestricted by the constraints necessary to provide adequate dehu- capacity scroll compressor technology. The dual-capacity midification in cooling and comfortable air delivery temperature scroll compressor is also used to replace the reversing in heating. This has driven manufacturers of all heat pump types compressor for warranty repairs. to increase their efforts to improve advertised efficiency often at The modulating scroll compressor is currently the technolthe expense of full-load efficiency and simplicity. ogy of choice. Two ports and a modulating ring are added to
68	 ASHRAE	Journal	 ashrae.org	 	 April	 2010



ASHRAE Journal - April 2010

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

ASHRAE Journal - April 2010
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
The Science of Evaporation is Key to Defense in Murder Trial
Selecting DOAS Equipment with Reserve Capacity
Technology Award Case Studies: Greening Hospitals
Technology Award Case Studies: Sustainable Remedy for Hospital
Building Sciences
Emerging Technologies
Technical Topics: Selecting Efficient Fans
Technical Topics: Dual-Capacity Heat Pumps
IAQ Applications
International Column
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2010 - Intro
ASHRAE Journal - April 2010 - ASHRAE Journal - April 2010
ASHRAE Journal - April 2010 - Cover2
ASHRAE Journal - April 2010 - 1
ASHRAE Journal - April 2010 - 2
ASHRAE Journal - April 2010 - Contents
ASHRAE Journal - April 2010 - Commentary
ASHRAE Journal - April 2010 - 5
ASHRAE Journal - April 2010 - Industry News
ASHRAE Journal - April 2010 - 7
ASHRAE Journal - April 2010 - 8
ASHRAE Journal - April 2010 - 9
ASHRAE Journal - April 2010 - 10
ASHRAE Journal - April 2010 - 11
ASHRAE Journal - April 2010 - 12
ASHRAE Journal - April 2010 - 13
ASHRAE Journal - April 2010 - 14
ASHRAE Journal - April 2010 - 15
ASHRAE Journal - April 2010 - 16
ASHRAE Journal - April 2010 - 17
ASHRAE Journal - April 2010 - Letters
ASHRAE Journal - April 2010 - 19
ASHRAE Journal - April 2010 - Meetings and Shows
ASHRAE Journal - April 2010 - 21
ASHRAE Journal - April 2010 - The Science of Evaporation is Key to Defense in Murder Trial
ASHRAE Journal - April 2010 - 23
ASHRAE Journal - April 2010 - 24
ASHRAE Journal - April 2010 - 25
ASHRAE Journal - April 2010 - 26
ASHRAE Journal - April 2010 - 27
ASHRAE Journal - April 2010 - 28
ASHRAE Journal - April 2010 - 29
ASHRAE Journal - April 2010 - Selecting DOAS Equipment with Reserve Capacity
ASHRAE Journal - April 2010 - 31
ASHRAE Journal - April 2010 - 32
ASHRAE Journal - April 2010 - BRC1
ASHRAE Journal - April 2010 - BRC2
ASHRAE Journal - April 2010 - 33
ASHRAE Journal - April 2010 - 34
ASHRAE Journal - April 2010 - 35
ASHRAE Journal - April 2010 - 36
ASHRAE Journal - April 2010 - 37
ASHRAE Journal - April 2010 - 38
ASHRAE Journal - April 2010 - 39
ASHRAE Journal - April 2010 - 40
ASHRAE Journal - April 2010 - 41
ASHRAE Journal - April 2010 - Technology Award Case Studies: Greening Hospitals
ASHRAE Journal - April 2010 - 43
ASHRAE Journal - April 2010 - 44
ASHRAE Journal - April 2010 - 45
ASHRAE Journal - April 2010 - 46
ASHRAE Journal - April 2010 - 47
ASHRAE Journal - April 2010 - 48
ASHRAE Journal - April 2010 - 49
ASHRAE Journal - April 2010 - Technology Award Case Studies: Sustainable Remedy for Hospital
ASHRAE Journal - April 2010 - 51
ASHRAE Journal - April 2010 - 52
ASHRAE Journal - April 2010 - 53
ASHRAE Journal - April 2010 - Building Sciences
ASHRAE Journal - April 2010 - 55
ASHRAE Journal - April 2010 - 56
ASHRAE Journal - April 2010 - AP1
ASHRAE Journal - April 2010 - AP2
ASHRAE Journal - April 2010 - AP3
ASHRAE Journal - April 2010 - AP4
ASHRAE Journal - April 2010 - 57
ASHRAE Journal - April 2010 - 58
ASHRAE Journal - April 2010 - 59
ASHRAE Journal - April 2010 - Emerging Technologies
ASHRAE Journal - April 2010 - 61
ASHRAE Journal - April 2010 - 62
ASHRAE Journal - April 2010 - 63
ASHRAE Journal - April 2010 - Technical Topics: Selecting Efficient Fans
ASHRAE Journal - April 2010 - 65
ASHRAE Journal - April 2010 - Technical Topics: Dual-Capacity Heat Pumps
ASHRAE Journal - April 2010 - 67
ASHRAE Journal - April 2010 - 68
ASHRAE Journal - April 2010 - 69
ASHRAE Journal - April 2010 - IAQ Applications
ASHRAE Journal - April 2010 - 71
ASHRAE Journal - April 2010 - 72
ASHRAE Journal - April 2010 - 73
ASHRAE Journal - April 2010 - International Column
ASHRAE Journal - April 2010 - 75
ASHRAE Journal - April 2010 - 76
ASHRAE Journal - April 2010 - 77
ASHRAE Journal - April 2010 - 78
ASHRAE Journal - April 2010 - 79
ASHRAE Journal - April 2010 - 80
ASHRAE Journal - April 2010 - 81
ASHRAE Journal - April 2010 - 82
ASHRAE Journal - April 2010 - 83
ASHRAE Journal - April 2010 - 84
ASHRAE Journal - April 2010 - 85
ASHRAE Journal - April 2010 - Classified Advertising
ASHRAE Journal - April 2010 - 87
ASHRAE Journal - April 2010 - Advertisers Index
ASHRAE Journal - April 2010 - Cover3
ASHRAE Journal - April 2010 - Cover4
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