ASHRAE Journal - March 2011 - 47
Polymer-Tube Indirect Air-Side Economizer
Another type of IASE uses a horizontal polymer-tube heat exchanger5 (Figure 3). With this design, outdoor scavenger air is drawn across the exterior of elliptical tubes, which are wetted by a recirculation water pump. The elliptical shape of the heat exchanger tubes maximizes the allowable surface area for heat rejection and is sufficiently elastic such that its subtle expansion and contractions, resulting from normal operation, aid in the shedding of residual solids that are a by-product of evaporation. With scavenger air flowing over the wet exterior tube surfaces, evaporative heat transfer efficiently cools the data center hot aisle air flowing through the inside of the tubes. Although only 45% to 51% effective when operating dry, when the outside of the polymer-tube HX (Figure 3) is wetted, the HX is able to provide 70% to 80% wet-bulb depression effectiveness (WBDE), as an indirect evaporative cooler. WBDE is a measure of the approach of the hot-aisle dry-bulb temperature to the outdoor air wet-bulb temperature. Using a 75% WBDE HX design, 100% of data center heat may be rejected solely using indirect evaporative cooling (IEC) whenever the ambient wet-bulb temperature is 66.2°F (19°C) or lower, based on a hot aisle temperature, after recirculation fan heat, of 101.5°F (38.6°C) cooling to a target cold-aisle temperature of 75°F (23.9°C). Figure 4 shows the scavenger-side pressure drop and WBDE as a function of the HX’s rated flow for the condition of recirculation air entering at 101.5°F (38.6°C) dry bulb at 55°F (12.8°C) dew point and with scavenger air entering at 73°F (22.8°C) dry bulb at 65°F (18.3°C) wet bulb (HX designed for a target 70% WBDE). When the HX operates with recirculation and scavenger air flowing at design (1 times rated value), the scavenger-side pressure drop is 0.33 in. w.c. (82.1 Pa), and the WBDE is 70.2%. Holding the recirculation flow constant at design, if the scavenger airflow is reduced to 0.4 times design, the resulting scavenger-side pressure drop will be just over 0.06 in. w.c. (14.9 Pa), and the WBDE will be just over 52.5%. Because the WBDE declines slowly as scavenger flow is reduced, the scavenMarch 2011
ger fan flow and corresponding power consumption rapidly drop as the ambient wet-bulb temperature falls. The scavenger fans operate at low capacity for most operating hours. To better quantify this statement, consider an IASE system operating in Chicago, with a hot-aisle condition (after supply fan heat) of 101.5°F (38.6°C) dry bulb at 55°F (12.8°C) dew point, and with a target cold-aisle deliv-
www.info.hotims.com/33862-32
ASHRAE Journal
47
ASHRAE Journal - March 2011
Table of Contents for the Digital Edition of ASHRAE Journal - March 2011
ASHRAE Journal - March 2011
Contents
Commentary
Industry News
Meetings and Shows
Feature Articles
ASHRAE’s Best: 2011 Technology Awards
Technology Award Case Studies: Hospital Retrofit
Energy Savings for Quick Service Restaurants
Affinity Laws: Why They Work & When They Don’t
Data Center Heat Rejection: Indirect Air-Side Economizer Cycle
Health Care Standard Update
Building Sciences
Solar NZEB Project
HVAC Mythbuster
Washington Report
Emerging Technologies
IAQ Applications
Special Products
People
Classified Advertising
Advertisers Index
ASHRAE Journal - March 2011 - Intro
ASHRAE Journal - March 2011 - ASHRAE Journal - March 2011
ASHRAE Journal - March 2011 - Cover2
ASHRAE Journal - March 2011 - 1
ASHRAE Journal - March 2011 - 2
ASHRAE Journal - March 2011 - Contents
ASHRAE Journal - March 2011 - Commentary
ASHRAE Journal - March 2011 - 5
ASHRAE Journal - March 2011 - Industry News
ASHRAE Journal - March 2011 - 7
ASHRAE Journal - March 2011 - 8
ASHRAE Journal - March 2011 - 9
ASHRAE Journal - March 2011 - 10
ASHRAE Journal - March 2011 - 11
ASHRAE Journal - March 2011 - 12
ASHRAE Journal - March 2011 - 13
ASHRAE Journal - March 2011 - 14
ASHRAE Journal - March 2011 - 15
ASHRAE Journal - March 2011 - 16
ASHRAE Journal - March 2011 - 17
ASHRAE Journal - March 2011 - 18
ASHRAE Journal - March 2011 - 19
ASHRAE Journal - March 2011 - Meetings and Shows
ASHRAE Journal - March 2011 - 21
ASHRAE Journal - March 2011 - ASHRAE’s Best: 2011 Technology Awards
ASHRAE Journal - March 2011 - 23
ASHRAE Journal - March 2011 - 24
ASHRAE Journal - March 2011 - 25
ASHRAE Journal - March 2011 - 26
ASHRAE Journal - March 2011 - 27
ASHRAE Journal - March 2011 - 28
ASHRAE Journal - March 2011 - 29
ASHRAE Journal - March 2011 - 30
ASHRAE Journal - March 2011 - 31
ASHRAE Journal - March 2011 - Technology Award Case Studies: Hospital Retrofit
ASHRAE Journal - March 2011 - 33
ASHRAE Journal - March 2011 - 34
ASHRAE Journal - March 2011 - 35
ASHRAE Journal - March 2011 - Energy Savings for Quick Service Restaurants
ASHRAE Journal - March 2011 - 37
ASHRAE Journal - March 2011 - 38
ASHRAE Journal - March 2011 - 39
ASHRAE Journal - March 2011 - 40
ASHRAE Journal - March 2011 - 41
ASHRAE Journal - March 2011 - Affinity Laws: Why They Work & When They Don’t
ASHRAE Journal - March 2011 - 43
ASHRAE Journal - March 2011 - Data Center Heat Rejection: Indirect Air-Side Economizer Cycle
ASHRAE Journal - March 2011 - 45
ASHRAE Journal - March 2011 - 46
ASHRAE Journal - March 2011 - 47
ASHRAE Journal - March 2011 - 48
ASHRAE Journal - March 2011 - 49
ASHRAE Journal - March 2011 - 50
ASHRAE Journal - March 2011 - 51
ASHRAE Journal - March 2011 - 52
ASHRAE Journal - March 2011 - 53
ASHRAE Journal - March 2011 - 54
ASHRAE Journal - March 2011 - 55
ASHRAE Journal - March 2011 - Health Care Standard Update
ASHRAE Journal - March 2011 - 57
ASHRAE Journal - March 2011 - 58
ASHRAE Journal - March 2011 - 59
ASHRAE Journal - March 2011 - 60
ASHRAE Journal - March 2011 - 61
ASHRAE Journal - March 2011 - Building Sciences
ASHRAE Journal - March 2011 - 63
ASHRAE Journal - March 2011 - 64
ASHRAE Journal - March 2011 - 65
ASHRAE Journal - March 2011 - 66
ASHRAE Journal - March 2011 - 67
ASHRAE Journal - March 2011 - 68
ASHRAE Journal - March 2011 - 69
ASHRAE Journal - March 2011 - Solar NZEB Project
ASHRAE Journal - March 2011 - 71
ASHRAE Journal - March 2011 - 72
ASHRAE Journal - March 2011 - 73
ASHRAE Journal - March 2011 - 74
ASHRAE Journal - March 2011 - 75
ASHRAE Journal - March 2011 - 76
ASHRAE Journal - March 2011 - 77
ASHRAE Journal - March 2011 - HVAC Mythbuster
ASHRAE Journal - March 2011 - 79
ASHRAE Journal - March 2011 - Washington Report
ASHRAE Journal - March 2011 - 81
ASHRAE Journal - March 2011 - Emerging Technologies
ASHRAE Journal - March 2011 - 83
ASHRAE Journal - March 2011 - 84
ASHRAE Journal - March 2011 - 85
ASHRAE Journal - March 2011 - IAQ Applications
ASHRAE Journal - March 2011 - 87
ASHRAE Journal - March 2011 - 88
ASHRAE Journal - March 2011 - 89
ASHRAE Journal - March 2011 - Special Products
ASHRAE Journal - March 2011 - People
ASHRAE Journal - March 2011 - 92
ASHRAE Journal - March 2011 - 93
ASHRAE Journal - March 2011 - 94
ASHRAE Journal - March 2011 - 95
ASHRAE Journal - March 2011 - 96
ASHRAE Journal - March 2011 - 97
ASHRAE Journal - March 2011 - 98
ASHRAE Journal - March 2011 - 99
ASHRAE Journal - March 2011 - 100
ASHRAE Journal - March 2011 - 101
ASHRAE Journal - March 2011 - Classified Advertising
ASHRAE Journal - March 2011 - 103
ASHRAE Journal - March 2011 - Advertisers Index
ASHRAE Journal - March 2011 - Cover3
ASHRAE Journal - March 2011 - Cover4
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