GRAPH #6 Graph #6 was prepared to illustrate the increased energy loss in the unitventilator and the loss of control in the room as the supply water temperature rises. All the readings for the graph were taken in a classroom from sensing points shown on FIGURE #1. The thermostat branch pressure was obtained at (C); the low limit branch signal was obtained at (D); the supply air temperature was obtained at (E); the supply water temperature was obtained at (A) and the return water temperature was obtained at (B). The supply water temperature was provided at three different modes of operation: 1. The first was based on the Energy Conservation Demand Signal logic with an average supply water temperature of 92.3°F. 2. The second was based on actual outside air temperature reset with an average supply temperature of 121.7°F. 3. And the third was based on boiler supply water at an average supply temperature of 171.5°F. We ran the thermostat on full cooling with a fifteen pound branch pressure and on full heating with a zero pound branch pressure as shown by the green line. We observed two characteristics of the unitventilator’s response. One was the energy use based on the differential of the supply and return water temperatures and the second was the ability to maintain comfort based on the supply air temperature. The coil always had the same rate of water flow; therefore, the differential temperature was a direct indication of the relative amount of heat escaping into the room when on cooling under the three different supply water temperatures. The following chart indicates the supply water temperature, the water differential temperature, the discharge air temperature and the low limit branch pressure when the thermostat was demanding full cooling. SUPPLY DIFFERENTIAL DISCHARGE AIR LOW LIMIT TEMPERATURE TEMPERATURE TEMPERATURE PRESSURE 92.3°F 1.3F° 55.8°F 7.8 PSIG 121.7°F 3.12F° 57.5°F 8.3 PSIG 171.5°F 7.1F° 64.9°F 11.8 PSIG 8.141
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