Engineered Systems - April 2008 - (Page 63)

It’s The Humidity separate AHU for supplying outside air). The air is then cooled down and returned to the conditioned space. What is the difference in these two examples? All else being equal, the total air conditioning load in the two examples will be the same. However, the power used by the central cooling equipment in the first case will be close to 50% greater than that of the second. This is due to the fact that much more energy is needed to produce 55° air vs. 75° air (Figure 2). Also, if higher supply air temperatures are used, the hours for using outdoor air for either air economizer or water economizer can be extended significantly. This includes the use of more humid air that would normally be below the dewpoint of the coil using 55° discharge air. Similarly, if the rh or humidity ratio requirements were lowered in cool and dry climates that are ideal for using outside air for cooling, more hours of the year could be used to reduce the load on the central cooling system without having to add moisture to the airstream. CONCLUSION Understanding the psychrometric processes that underpin HVAC system performance is critically important in developing successful system design and control strategies for data centers. Continual refinement of standards and best practices specific to data centers is needed to make advancements in optimizing design and operation. Education of data center designers and operators, as well as close collaboration of the computer manufacturers will be required, however, to fully realize the benefits of these advancements. ES CITED WORKS 1. Kaveh, A. “The History of Power Dissipation.” Electronics Cooling Magazine. January, 2000. 2. Schmidt, R. R. and B. D. Notohardjono. “High End Server Low Temperature Cooling.” IBM Research and Development Magazine. November, 2002. 3. Woolfold, Allen. “Specifying Filters for Forced Convection Cooling.” Electronics Cooling Magazine. October, 1995. 4. Parry, John, Jukka Rantala, and Clemens Lasance. “Temperature and Reliability in Electronics Systems - The Missing Link.” Electronics Cooling Magazine, November, 2001. Kosik is a managing principal at EYP Mission Critical Facilities (EYP MCF), and a member of the firm’s Technology Council, EYP MCF’s R&D organization. He is the leader of “Moving Towards Sustainability,” one of eight corporate pillars at EYP MCF, which is focused on the research, development, and implementation of sustainable, energy-efficient, and environmentally responsible design strategies for data centers and other high-performance building types. His projects have earned 19 ASHRAE Awards. FREE INFO: 20 w w w. esmag a zin e. c o m 63 http://www.vaisala.com/HMT330 http://www.vaisala.com http://www.vaisala.com http://www.esmagazine.com

Table of Contents Feed for the Digital Edition of Engineered Systems - April 2008

Engineered Systems - April 2008 Contents Editor’s Note Back2Basics HVAC Challenge Case In Point Commissioning Building Automation Energy Wiz HVACR Designer Tips This Time, Water Cooled Was All Wet Cleanroom Design In 10 Easy Steps It's Not The Heat, It's The Humidity Issues & Events Computers and Software Products Glossary Classifieds Advertiser Index Tomorrow’s Engineer

Engineered Systems - April 2008

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