Engineered Systems - April 2008 - (Page 62)

It’s The Humidity use at which temperature. This may be complicated by the fact that most cooling and humidification equipment is controlled by rh, and most operators have a better feel for rh vs. grains/lb as an operating parameter. Changes in how equipment is specified and controlled will be needed to fully use dewpoint or humidity ratio as a means for measurement and control. So what impact does this have on data center operations? The main impact comes in the form of increased energy use, equipment cycling, and quite often, simultaneous cooling/dehumidification and reheating/ humidification. Discharging air at 55° from the coils in an AHU is common practice in HVAC industry, especially in legacy data centers. Go ahead, get more green this year. Sure, Carlyle compressors are green, but did you know using Carlyle can also lead to more green in your pocket—as much as $15,000 per store? Carlyle’s reliability means more than just a longer lasting compressor (a recent study of supermarket refrigeration racks showed our average life span is 9.9 years versus 5.2 years for the leading competitor), it means reduced downtime, less scrap waste going into the environment, and significant savings in repair and replacement costs. And for supermarket applications Carlyle offers our Compound Cooling compressor, the most energy efficient low temperature compressor in the industry. So why not consider the option that allows you to save time, money and the environment? There’s never been a better time to go green. For more information regarding Carlyle’s reliability data and the cost savings per store, visit www.CarlyleCompressor.com. 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°F air vs. 75° air. F 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. Why? Because typical room conditions for comfort cooling during the summer months are generally around 75° and 50% rh. The dewpoint at these conditions is 55°, so the air will be delivered to the conditioned space at 55°. The air warms up (typically 20°) due to the sensible heat load in the conditioned space and is returned to the AHU. It will then be mixed with warmer, more humid outside air and sent back to flow over the cooling coil. The air is then cooled and dried to a comfortable level for human occupants and supplied back to the conditioned space. While this works pretty well for office buildings, it does not transfer as well to data center design. Using this same process description for an efficient data center cooling application, it would be modified as follows: Since the air being supplied to the computer equipment needs to be (as an example) 78° and 40% rh, the air being delivered to the conditioned space would be able to range from 68° to 73°, accounting for safety margins due to unexpected mixing of air resulting from improper air management techniques. (The air temperature could be higher with strict airflow management, using enclosed cold aisles or cabinets that have provisions for internal thermal management). The air warms up (typically 20° to 25°), due to the sensible heat load in the conditioned space and is returned to the AHU. (Although the discharge temperature of the computer is not of concern to the computer’s performance, high discharge temperatures need to be carefully analyzed to prevent thermal runaway during a loss of cooling as well as the effects of the high temperatures on the data center operators when working behind the equipment). It will then be mixed with warmer, more humid outside air and is sent back to flow over the cooling coil (or there is a FREE INFO: 132 62 En gi neer ed S y stem s April 2008 http://www.CarlyleCompressor.com http://www.CarlyleCompressor.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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