Methods of control
There are three methods of control in common use in air conditioning: two-position, proportional and, to a lesser extent, floating. All are capable of sophistication, aimed at improvement, whereby offset is reduced or stability enhanced.
The form of control chosen must suit the application. For example, one essential feature of floating control is that it works best with a system having a small thermal storage and a predictable response. If it is misapplied, the system may hunt as a result of excessive lag and may be difficult to set up if the response is not well known. It is also essential that any method of control chosen should be as simple as is consistent with the results desired. Elaboration may result in some controls being redundant, the system becoming temperamental and wearisome to commission. There is more to commissioning an air conditioning installation than setting 21°C on a thermostat and switching the plant on.
Posted in Engineering Fifth Edition