HEATING INPUT Many control systems determine the main building supply heating temperature based only on the outside air temperature. This similar to allowing your furnace to run for varying number of minutes per hour based on the outside air temperature. This might sound logical, but consider these scenarios. SCENARIO OSA TEMP. FURNACE RUN WIND OCCUPANCY SUN CONDITION ROOM TEMP. ONE 30°F 15 MIN./HR STILL 25 (GATHERING) BRIGHT NOON SUN ? TWO 30°F 15 MIN./HR BLIZZARD YOU ALONE NIGHT ? If the fifteen minute run time per hour, based on the 30°F outside air temperature is enough to keep you warm in scenario two’s conditions, the gathering will over-heat under the conditions of scenario one with the same run time based only on the outside air temperature. The graph on page 5.36 illustrates a comparison of actual heating water requirements of the coolest area of the building to heating water determined by only outside air temperature. CO-ORDINATING THE HEATING AND COOLING WHICH ARRANGEMENT SEEMS BETTER? SYSTEM HEAT INPUT 100,000 BTU (HEAT REQUIRED) SYSTEM COOLING AND VENTILATION INPUT 50,000 BTU (HEAT LOSS) ROOM HEAT LOSS 50,000 BTU (HEAT LOSS) ROOM TEMPERATURE 70°F SYSTEM HEAT INPUT 55,000 BTU (HEAT REQUIRED) SYSTEM VENTILATION INPUT 5,000 BTU (HEAT LOSS) ROOM TEMPERATURE 70°F ROOM HEAT LOSS 50,000 BTU (HEAT LOSS) 5.35
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