BAS BAS BAS BAS LOCAL STAT LOCAL STAT LOCAL STAT VALVE VALVE LOCAL STAT LOCAL STAT VALVE VALVE VALVE VALVE WILD CONVECTORS AND FAN COILS WILD CONVECTORS AND FAN COILS MIXING VALVE MIXING VALVE SECONDARY PUMP PRIMARY PUMP BOILER SECONDARY PUMP PRIMARY PUMP BOILER ROOM ONE ROOM TWO ROOM THREE ROOM FOUR ROOM ONE ROOM TWO ROOM THREE ROOM FOUR ENERGY LOSS VIA CO-ORDINATION LACK , REGARDING LOCAL AND BAS CONTROL ROOM FOUR LOCAL CONTROL SET AT 68°F. BAS ATTEMPTING BUILDING CONTROL AT 71°F, BASED ON ROOM FOUR TEMPERATURE. Scenario “A” presents a very common problem where a Building Automation System (BAS) over-lays an existing building control system. The new BAS scans sample rooms, determining the greatest requirement for heat. Room four (one of several sample rooms) is the coldest room with a temperature of 69.5°F. The local thermostat is set at 68°F; therefore, the valve controlling heat entry to the room is closed. The BAS attempts to control the coldest room to 71°F; therefore, raises the secondary water temperature. The increased water temperature can not correct the cool condition in room four, as the local thermostat disallows flow to the room. At higher water temperatures, increased heat is lost in the main heating distribution piping and in areas where wild convectors or fan coils exist. In locations with local thermostat control, other than room four, the valves have an increased risk of damage to their seats and discs, as they are forced to modulate their valves at a more closed position. Scenario “B” presents one solution regarding the problem of scenario “A”. The BAS takes local control of the valves regulating the hot water flow into the sample rooms. The BAS opens the local control valve completely, assuring full water flow into the room before the BAS starts to raise the secondary hot water temperature in response to that room’s temperature set point. The average cooler water temperature causes less heat loss regarding the main hot water piping, as well as in areas with wild convectors or fan coils. The average cooler water temperature causes valves in other areas to be modulated in a more open position, reducing the risk of disc or seat damage in the valves. The same logic is attainable leaving local pneumatic thermostats controlling their individual valves. The sample rooms’ signals are tapped and the coolest room’s signal is determined via a multi-low selector. The lowest signal (coolest room signal) is tubed to a transducer, which produces a voltage or ma signal used by the BAS to control the secondary water temperature. “A” “B” 5.38
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