DRAWING THREE SYSTEM AS WE FOUND IT Another contractor altered the control logic, as illustrated in drawing three. The control contractor attempted to address two problems regarding the original design. (1) They allowed the return air controller access to the mixed air loop. The conservation intent was correct, but the application made no difference. The two mistakes occurred when they selected the biasing relay and commissioned that relay. The first error was selecting a biasing relay with a 1:1 ratio that can not squeeze the ten pound damper function between the heating and cooling valves where there is only a one pound span available. The second error observed caused the biasing relay signal to be advanced to the dampers rather than retarding the signal. In theory the changes caused a greater over-lap of free cooling and heating; however, at a practical level the system performed exactly as the original design. (2) The second alteration performed was installing a gradual switch in the occupied space, allowing the occupants the option of raising or lowering the return air set point. This caused problems as the gradual switch had a blind dial with only six dots. The set point impact range was 42F° (7F° per dot) while the occupants thought each dot represented 1F°. The two intended improvements were both valid points; however, the implementation of both actually had an over-all negative impact on control of the occupied space. Graph one, at the back of this report, illustrates the system's energy performance as we found it. Graph two, at the back of this report illustrates the system's energy performance after we corrected the over-sights in logic. Attempting to equalize the load, we deliberately chose time slots for both graphs that were at night, eliminating solar impact and human activity variation. The times chosen experienced identical average outside air temperatures. Other unknown factors caused the space to require 81.6°F supply air during data collection for the first graph and 70.66°F for the second graph. During the period of the first graph, the system would have required 49.75% less heat attaining the 81.6°F supply air temperature if it employed the logic present for the second graph. The system, as we found it, brought in an average of 74.86% fresh air, causing the return air controller to open the heating valve an average of 41.4%. In comparison the system as it now stands brought in an average of 27.4% fresh air, causing the return air controller to open the heating valve an average of 3.4%. The old system over-cooled the mixed air and then activated the heating coil to compensate for the unwanted cooling. The new system logic allows the controls variable use of heat in the return air that has already been purchased. 8.72
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