This invention, relates to a heating, ventilating, air conditioning (HVAC) system and in particular to an HVAC system having a plurality of zones supplied by air handling equipment (as opposed to systems using hot/cold water or electric baseboard heaters, for example).
It is known to use a single heating and/or cooling unit to supply a plurality of zones in a building. Each zone may be provided with a thermostat and a motor driven damper. A control system monitors the thermostats and controls the various dampers and the heating and cooling units. A variety of different systems are known in the prior art.
For example, in the system according to the Clark, et al U.S. Pat. No. 4,533,090, fan volume control is achieved as a result of temperature sensing using a plurality of sensors. Binary signals from thermostatic transducers indicate if zones ("terminals") are satisfied or not. Transducer signals are fed to a controller which acts to increase, decrease, or maintain fan speed.
The Weatherston U.S. Pat. No. 3,677,335 discloses a staged heating and cooling system. Thermostat signals are clocked at intervals, e.g. two minutes, to a binary up-down counter, the output of which is decoded to feed different amounts of current to progressively open or close a valve for heating or, for cooling, operate a modulating motor which can open dampers to allow cooling air to be brought into the building and, if a lot of cooling is called for, turn on refrigeration units.
The Coon U.S. Pat. No. 3,814,173 discloses a system in which an air fan associated with a furnace or cooling coils has its speed changed by digital increments in response to the total demand heat heated air or cooled air, as sensed by the individual thermostats.
U.S. Pat. No. 3,724,534 of Weatherston discloses a multiple zone control system with priority of service. The system may have 16 zones or more. Signals from thermostats are scanned and summed to see whether, over a given time period, the net change from all zones is toward more cooling air or more heating. A thermostat can be connected to more than one scanner input to give it more "weight".