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Note 14. Control Signal Polling

When optimizing the efficiency of a system, a common control function is selecting the highest or lowest signal from a number of inputs. This function is needed in a variety of the energy saving measures of the Energy Efficiency Manual, especially in larger HVAC systems.

A typical application is chilled air temperature reset. Signals from all the thermostats served by an air handling system are routed to a control device, typically called a discriminator, that picks out the signal calling for the greatest cooling load. This signal is used by the control system to adjust the supply air temperature of the air handling unit.

This Note explains concisely the methods used to perform this control function. It can be done with standard control components designed for the purpose, or it can be done using an energy management computer system.