Electrical equipments when operated over long hours produce heat, which must be removed to prevent the equipment from getting damaged. Sizing a cooling system requires an understanding of the amount of heat produced by the equipment contained along with the heat produced by the other heat sources.
The total heat output of a system is the sum of the heat outputs of the individual components. The complete system includes the UPS, Power Distribution, Air Conditioning Units, Lighting, and People. Fortunately, the heat output rates of these devices can be easily determined through simple and standardized rules.
The heat output of UPS and Power Distribution systems consists of a fixed loss and a loss proportional to operating power. Heat generated by lighting and people can also be readily estimated using standard values. The only information needed to determine the cooling load for the complete system are a few readily available values, such as the floor area in square feet, and the rated electrical system power.
A quick estimate using simple rules gives results that are within the typical margin of error of the more complicated analysis. The quick estimate also has the advantage that it can be performed by anyone without specialized knowledge or training.
The prior analysis ignores sources of environmental heat such as sunlight through windows and heat conducted in from outside walls. Many small data centers and do not have walls or windows to the outside, so there is no error resulting from this assumption. However, for large data centers with walls or a roof exposed to the outdoors, additional heat enters the data center which must be removed by the air conditioning system.
If the data center room is located within the confines of an air-conditioned facility, the other heat sources may be ignored. If the data center has significant wall or ceiling exposure to the outside, then a HVAC consultant will need to assess the maximum thermal load and it must be added to the thermal requirement of the complete system determined in the previous section.
The determination of cooling requirements for IT systems can be reduced to a simple process that can be done by anyone without special training. Expressing all measures of power and cooling in Watts simplifies the process.
For larger data centers, the cooling requirements alone are typically not sufficient to select an air conditioner. Typically, the effects of other heat sources such as walls and roof, along with recirculation, are significant and must be examined for a particular installation. The design of the air handling duct work or raised floor has a significant effect on the overall system performance, and also greatly affects the uniformity of temperature within the data center. The adoption of simple, standardized and modular air distribution system architecture, combined with the simple heat load estimation method could significantly reduce the engineering requirements for data center design.
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