Automatic Controls for Heating and Air Conditioning. by K. M. Letherman, N. S. Billington

By K. M. Letherman, N. S. Billington

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28 29 Applications Motor-operated valve actuators are relatively slow in operation, taking up to 2 minutes to drive over their full range. This is not a practical disadvantage for most applications. 2. Pneumatic actuators, or pneumatic motors as they are also called, consist usually of a circular diaphragm on one side of which the control pressure is applied either directly from a controller or via a positioner (see Fig. 1). The other side of T3 (c) (d) Fig. 1. Four possible arrangements of two-way valve and pneumatic motor (a) and (d) normally open, air to close, (b) and (c) normally closed, air to open.

5 SOLAR COLLECTOR SYSTEM CONTROLS In order to consume the minimum amount of energy in operation a solar collector panel should be located at a lower level than the storage tank which it feeds, so that gravity circulation can be used to provide flow through the panel. During periods when little or no solar radiation is available there would then be no tendency for heat to be extracted from the store and lost: the circulation would stop automatically as it does in a domestic boiler/cylinder arrangement with a gravity circulated primary.

An automatic constant volume regulator ensures that the total flow rate from the box remains constant, and hence the air-distribution pattern in the room. Room thermostats of the type described in Section 3Λ may be used to control the modulating motors in the mixing boxes. It is important that all the boxes in one room or conditioned space are controlled by one thermostat. Individual control, where one thermostat can be affected by a terminal unit controlled by another thermostat, will produce unsatisfactory conditions due to simultaneous heating and cooling.

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