Prior art digital thermostats for such systems have the capability of adjusting the temperature set point for the room or other enclosed area which the thermostats are intended to control, and the thermostats normally operate to provide a controlled pressure in a pneumatic line which is connected to control elements such as dampers, valves and the like and such thermostats operate to admit increased pressure from a pneumatic supply line for the purpose of increasing the temperature and to decrease the pressure in the control line when the temperature is to be reduced. It should be understood by those of ordinary skill in the art that the system can be reverse acting, in that decreasing the pressure can increase the controlled temperature fan coil unit.
The controlled pneumatic pressure typically adjusts the position of the valves, dampers and the like to regulate the temperature in the controlled area. Additionally, there are many buildings which are controlled by pneumatic thermostats which control the operation of unit ventilators, such as are often used in schools. Such unit ventilators are typically stand-alone units and have a fan for circulating air, a heating coil through which steam or hot water may circulate with the amount of flow therethrough being regulated by a valve. While such mechanical pneumatic thermostats adequately control the temperature in the area which they are located, they are generally stand-alone units from a system standpoint, except for the capability of being switched between day/night operation by changing the pressure in the supply pneumatic lines, as is well known in the art.