GENERAL On any heating system where the level of heat is to be determined by the actual requirement of the space, it is imperative that the control point which sends a signal to the main plant to demand heating levels also controls the local device which regulates the heat into the local area. It is a very common error to have computer points in several classrooms to scan the building for the greatest demand for heat while having local thermostats controlling the flow of heat to the rooms. This can create a situation where the computer is demanding full heat to satisfy a room where the thermostat is set to not allow the heat to enter the room. The system can be controlled equally well with either completely computer logic or completely pneumatic logic. If you choose to use computer logic, each of the room thermostats in the sample rooms has to be replaced with a transducer to control the valve (or the valve can be replaced with an electronic modulating valve) and the software has to be able to determine the room with the greatest requirement for heating. The software then has to coordinate the supply of heat with the position of the local control valve in the coldest room. If you choose to use pneumatic logic, you will tee into the existing branch lines of the sample room thermostats and often run them to a multi-low selector. A biasing relay will likely be used to establish an Energy Conservation Demand Temperature Signal. The safety of the building occupants, the mechanical equipment and the building must be the first concern to a designer making changes to save energy. It is the responsibility of the designer to know every potential problem area for each system and address each one in a logical manner. No two buildings are exactly the same; therefore, no two conservation circuits are exactly the same. 8.143
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