Revision history [back]
General Advice for Sizing Problems with VAV Systems
- Make sure
Zone Heating Design Supply Air TemperatureinSizing:Zonematches theMaximum Reheat Air Temperaturein theAirTerminal:SingleDuct:VAV:Reheatassigned to this zone. If the sizing temperature is higher than the maximum reheat temperature, then during operation the terminal isn't allowed to operate at the temperature it was designed for, meaning that it can't provide the designed heating capacity. - Make sure that the
Design Loop Exit Temperaturein theSizing:Plantfor the Hot WaterPlantLoopmatches theWinter Design Day Schedulein theSetpointManager:Scheduledassigned to your Hot WaterPlantLoop. If everything is sized for high temperature water but then operated at a lower temperature, sometimes the equipment can't meet the load. - Make sure that the
Rated Inlet Water TemperatureandRated Outlet Water Temperatureof theCoil:Heating:WaterReheat Coils match theDesign Loop Exit TemperatureandLoop Design Temperature Differencein theSizing:Plantfor the Hot WaterPlantLoop. This ensures that the coils and their plant loop are sized with the same temperature and delta-T.
So for your particular IDF:
- Change
Zone Heating Design Supply Air Temperaturefrom 40C to 35C to match max reheat - Change
Design Loop Exit Temperaturefor Hot Water Loop from 82.2C to 67C to match HW setpoint - Change
Rated Inlet Water Temperaturefor Reheat Coils from 82.2C to 67C to match HW setpoint - Change
Rated Outlet Water Temperaturefor Reheat Coils from 71.1C to 55.9C to match HW delta-T
Result: Time Setpoint Not Met During Occupied Heating drops from 1145.00 to 234.33