30079_64b

30079_64b - and light commercial cooling equipment operates...

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and light commercial cooling equipment operates with a coil SHF of 0.75-0.8 with the air entering the coil at about 8O 0 F or 27 0 C dry bulb and 67 0 F or 19 0 C wet bulb temperature. This equipment usually has a capacity of less than 10 tons or 35 kW. When the peak cooling load and latent heat requirements are appropriate, this less expensive type of equipment is used. In this case the air quantity is determined in a different way. The peak cooling load is first computed as 1.3 times the peak sensible cooling load for the structure to match the coil SHF. The equipment is then selected to match the peak cooling load as closely as possible. The air quantity is specified by the manufacturer for each unit and is about 400 cfm/ton or 0.0537 m 3 /sec • kW. The total air quantity is then divided among the various rooms according to the cooling load of each room. 64.3.5 Fuel Requirements The only reliable methods available for estimating cooling equipment energy requirements require hour by hour predictions of the cooling load and must be done using a computer and representative weather data. This is mainly because of the great importance of thermal energy storage in the structure and the complexity of the equipment used. This approach is becoming much easier due to the development of personal computers. This complex problem is discussed in Ref. 3. There has been recent work related to residential and light commercial applications that is adapt- able to hand calculations. The analysis assumes a correctly sized system. Figure 64.15 summarizes the results of the study of compressor operating time for all locations inside the contiguous 48 states. With the compressor operating time it is possible to make an estimate of the energy consumed by the equipment for an average cooling season. The Air-Conditioning and Refrigeration Institute (ARI) publishes data concerning the power requirements of cooling and dehumidifying equipment and most manufacturers can furnish the same data. For residential systems it is generally best to cycle the circulating fan with the compressor. In this case fans and compressors operate at the same time. However, for light commercial applications the circulating fan will probably operate continuously, and this should be taken into account. 64.4 AIR-CONDITIONING EQUIPMENT 64.4.1 Central Systems When the requirements of the system have been determined, the designer can select and arrange the various components. It is important that equipment be adequate, accessible for easy maintenance, and no more complex in arrangement and control than necessary to produce the conditions required. Figure 64.16 shows the air-handling components of a central system for year-round conditioning. It is a built-up system, but most of the components are available in subassembled sections ready for
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30079_64b - and light commercial cooling equipment operates...

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