ASHRAE Journal - August 2008 - (Page 57)

system, with a 90% saturation efﬁciency, would provide cold aisle inlet conditions of 65°F (18°C) DB and 90% RH for San Francisco, 64.4°F (18°C) DB and 85% RH for Reno, 65.4°F (19°C) DB and 85% RH for Salt Lake City, 63.3°F (18°C) DB and 85% RH for Denver and 63.6°F (18°C) DB and 84% RH for Albuquerque. Although these cold aisle inlet conditions are not within the Table 2.1 recommended levels for Class I and II data centers, they would allow continuous operation of the electronics during a refrigeration failure and prevent a costly data center shut down. The hot aisle resultant return air conditions produced by the electronics, assuming a 20°F (7°C) temperature rise, are all within Class I through IV operating limits, and the room dew point does not exceed the 63°F (17°C) maximum limit either at sea level or at 5,000 ft (1524 m) elevation for the ﬁve cities listed. By submitting the internal cooling load directly to an adiabatic WBE, the space may be held within acceptable limits using 100% outdoor air. This would not be true with either an air-side economizer or a water-side economizer. Filtration Redundancy Best Practices Cold Aisle Inlet Conditions 55°F DP 3 2 1 40°F 35° FW B 55° FW 4 5 B 55°F 68.5°F 75°F 95°F 1. Outdoor air at 40°F DB and 35F WB. 3. Dew-point supply air at 55°F DP and 55°F DB. 2. Mixed air at 68.5°F DB and 55°F WB. 4. Reheated air to cold aisle at 75°F DB and 55°F DP . 5. Hot aisle return air at 95°F DB, 69°F WB and 55°F DP . Figure 5: The psychrometric conditions are shown for each state point at the locations indicated in Figure 4. Fan heat not included. Resultant Room Condition With Ventilation Only °F DB/% RH Resultant Room Condition With Evaporative Cooling °F DB/% RH Location ASHRAE 0.4% Summer Design °F DB/WB Air contamination in the data center San Francisco 83/63 103°F at 18% 85.0°F at 45% is a valid concern which needs to be addressed. Consistent with the LBNL 95/61 Reno, Nev. 115°F at 7% 84.4°F at 43% study4 recommendations, air side econo96/62 Salt Lake City 116°F at 8% 85.4°F at 44% mizers which introduce large amounts of outdoor air need to be equipped with bet93/60 Denver 113°F at 7% 83.3°F at 43% ter ﬁltration than data center systems that 96/60 Albuquerque, N.M. 116°F at 7% 83.6°F at 42% use 100% recirculation. With 100% recirculation systems, ﬁlters with a MERV rat- Table 2: Direct evaporative cooling as refrigeration backup. ing of 8 or 9 (ANSI/ASHRAE Standard 52.2-1999, Method of Testing General Ventilation Air-Cleaning dampers are open to outdoor air. Tests run in 1988 and 1991 at Devices for Removal Efﬁciency by Particle Size; equivalent to the Air Filter Testing Laboratories in Louisville, Ky.,6 show a 40% efﬁcient based on the older “dust spot” efﬁciency rat- dust spot efﬁciency of 16% at 500 ft/min (2.5 L/s) face velocity ing of ANSI/ASHRAE Standard 52.1-1992, Gravimetric and with 1.5 gpm/ft2 (1.0 L/[s·m2]) water recirculation through the Dust-Spot Procedures for Testing Air-Cleaning Devices Used in media.* General Ventilation for Removing Particulate Matter) are used. Although a direct evaporative cooler/humidiﬁer should not When outdoor air is introduced, it is necessary to increase the be used as the primary source for data center contamination MERV rating to 10 or 11 (equivalent to 85% efﬁciency based removal, it provides a valuable redundancy to the principal on the duct spot method).5 ﬁltration system in an air-handling unit. The WBE uses a 12 in. (305 mm) deep wetted media pad that Makeup water and recirculation water furnished to the rigid acts as an air scrubber that will further reduce gaseous and par- media pad should be treated to reduce the risk of airborne miticulate contaminants from the airstream when the economizer crobial or particulate contamination of the supply air. A new, nonchemical, water treatment system that uses a pulse-power * The 12 in. wetted media demonstrates a 90% removal effectiveness for some technology is recommended for the DEC sump recirculation gaseous contaminants such as ammonia, urea, oxides of nitrogen, formaldewater ﬂow.8 hyde, radon, and chlorine, as well as 60% removal of ozone.7,10 August 2008 ASHRAE Journal 57

Table of Contents Feed for the Digital Edition of ASHRAE Journal - August 2008

ASHRAE Journal - August 2008 Contents Commentary Industry News Letters Meetings and Shows Maintain to Sustain—Delivering ASHRAE’s Sustainability Promise Ultraviolet Germicidal Irradiation: Current Best Practices Improving Humidity Control With Energy Recovery Ventilation Single- or Two-Stage Compression Data Center Cooling: Using Wet-Bulb Economizers Building Sciences InfoCenter Practical Pointers Products Emerging Technologies Washington Report People Special Products Classified Advertising Advertising Index

ASHRAE Journal - August 2008

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