Engineered Systems - October 2008 - (Page 57)

Controlling humidity in IT environments is essential to achieving high availability. This article explains how humidity affects equipment, and why humidity control is required. The author offers quantitative design guidelines for existing and new computing installations, and he also explains the hidden costs associated with over-humidification. BY TONY EVANS very piece of electronic equipment, data center, and person on earth is located at the bottom of an ocean of air. This fact is taken for granted to be a good thing, but there are instances when the air surrounding IT equipment can directly lead to its failure. The water vapor contained in air protects IT equipment from dangerous static electrical discharge. Reliance on precision cooling solutions to maintain the proper humidity level in a computer room or data center does not always ensure proper humidity levels at the IT equipment air intake. Let’s look at the nature of humidity, its effects, and its management in computer rooms and data centers. EFFECTS OF HUMIDITY IN THE IT ENVIRONMENT Humidity in the computer room or data center provides beneficial effects when it is maintained at proper levels and potential problems when it is at a level that’s too high or too low. The primary benefit of maintaining proper humidity levels is a reduction in the “charging” effect that can lead to static electrical discharge by making the air itself just a little more electrically conductive and the surfaces it touches just slightly “wet.” Because of the air’s slight increase in conductivity, the imbalance of positive and negative charges that create static electricity are less likely to result in electrical discharges (10,000+ volt sparks) that can damage computing equipment.1 The low-humidity cooling air mov- E ing throughout the data center itself can be a source of static electricity every time it moves across an ungrounded insulated surface and must be guarded against by maintaining proper humidity levels. The effects of varied rh levels on everyday activities that generate static electricity are shown in Table 1. The values of 250 and 1,500V seem high, but as static electricity are not real threats to computing equipment. The 12,000 and 35,000V values can discharge as sparks and can cause damage. High rh levels in the IT environment further reduce the chance of static discharge but are not desirable due to the increased likelihood of corrosion of metal components. High humidity levels can also increase the risk of water damage to equipment. This is why most IT equipment specifications show the acceptable humidity range in terms of non-condensing humidity. In essence, equipment manufactures are stating that their equipment will operate normally within a humidity range (typically 20% to 80% rh) as long as the temperature of the equipment itself and everything around it remains above the dewpoint. This is the temperature at which water vapor in the air starts “condensing” on the equipment just like in the formerly described cold drink example. Environments with high rh and fast changes in temperature are most likely to experience condensing humidity. When upper humidity limits are exceeded in IT environments with high-speed printing, paper stock may swell and increase its thickness, resulting in jams, and process downtime. w w w. esmag a zin e. c o m 57 http://www.esmagazine.com

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Engineered Systems - October 2008 Contents Editor’s Note Letters Back2Basics HVAC Challenge Case in Point Commissioning Building Automation HydroTech HVACR Designer Tips Special Insert: Engineer's Technical Library Fall 2008 Living Wild! Chilled Beams in Chicago Phoenix Convention Center: On The Rise Cold-Climate HVAC Challenges Humidification Strategies For Data Centers & Network Rooms Special Advertising Supplement: Tabb Talk Computers & Software Issues & Events Products Literature & Catalogs Glossary Classifieds Advertiser Index Tomorrow’s Environment

Engineered Systems - October 2008

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