Variations in the Capacity of the System
Conditions of operation and cooling capacity to change the heat load of the process changes. Good practice encourages cooling system designers size of the system, so it has a capacity that is slightly larger than the expected loads. This is done so that the system will have sufficient capacity to maintain the temperature and humidity near the correct level in the periods of peak load. On the basis of this design practice, most systems become oversized as their cooling load is reduced.
In a typical system, die operating conditions are highest at the beginning of the business cycle, when the temperature in its highest value. Conversely, the thermal load on its low cost, at the end of the cycle, when the temperature of outer space at a low cost. Thus, cooling system seldom works on design capacity, temperature difference, differential pressure set point or the pressure of condensation. Instead, these variables change from their design values whenever the load or ambient temperatures differ from the design values.
In those cases, when the heat load is usually fluctuates within a small circle around the design conditions, performance management adequately achieved by Cycling the power on and off, as described in the previous section.
Relative lengdi on and off cycles will vary with the application's diermal load and capacity. For systems in which diere is the biggest change to die load under normal cycles, more aggressive means of changing the capacity is required. These measures are in addition to Cycling the power on and off widi two-position controller.
When developing the strategy, which will differ in the ability of the system in response to large changes in load, some applications may require only one or two steps of capacity management, while others may require a few more steps or the use of smooth adjustment of the strategy. There are strategies that give an artificial load on the evaporator to get the right balance between reasonable (temperature reduction) and latent (humidity reduction) loads. Others reduce the pumping capacity of the compressor. It is important to remember that the method of capacity control the operating conditions of the process, and change the performance of the compressor changes.
Where required, to vary the capacity of the system, without changing the temperature Ana humidity die space, it is necessary to vary the power evaporator die with compressor capacity. Frequendy, some methods work together to get the desired flexibility. These techniques are also used in large systems, where the size of equipment has a circular system on and off two-position controller impractical. Some die more General methods of struggle with the evaporator and the compressor capacity are discussed in the following sections...
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