TEC Zoning Control System for Stand-Alone and BACnet® MS/TP ...

Table 9: Maximum Heat Flow Adjustment (Part 2 of 2)Reheat Stage(RehtConfParameter)(2): On/Off DuctReheat Only(3): On/OffPeripheral ReheatOnly(4): Analog DuctReheat and On/OffPeripheral ReheatTime Base forReheat Output(BO5 TimeParameter)(0): 15 Minutes(Four Cycles perHour)(1): 10 Seconds(Six Cycles perHour) for SolidState Relays(0): 15 Minutes(Four Cycles perHour)(1): 10 Seconds(Six Cycles perHour) for SolidState RelaysN/AMaximum Heat Flow Adjustment(MaxHTPos Parameter)Adjust the maximum heat flow to any value higher thanthe current selected minimum position.Example: The minimum airflow is set at 25% and themaximum heat flow is set at 75%. If the primary air iscold, when the BO5 output is energized on a call forheat, the zone damper moves directly from 25% opento 75% open. As soon as the BO5 output isde-energized, the zone damper returns to 25% open.Adjust the maximum heat flow to any value higher thanthe current selected minimum position.Example: The minimum airflow is set at 25% and themaximum heat flow is set at 75%. If the primary air iscold, when the BO5 output is energized on a call forheat, the zone damper moves directly from 25% opento 75% open. As soon as the BO5 output isde-energized, the zone damper returns to 25% open.Leave the maximum heat flow at its default setting of30%, or adjust it to any other setting. The maximumheat flow adjustment is not used in this scenario.Leave the maximum heat flow at its default setting of30%, or adjust it to any other setting. The maximumheat flow adjustment is not used in this scenario.Adjust the maximum heat flow to any value higher thanthe current selected minimum position.Example: The minimum airflow is set at 25% and themaximum heat flow is set at 75%. If the primary air iscold, when the PI heating loop (and analog output)goes from 0 to 100%, the zone damper moves linearlyfrom 25 to 75% open.The selected minimum position of the zone damper has a direct impact on thetemperature stability within certain zones. Having a minimum position selectedcan produce an overcooling and/or overheating effect. This effect is created by theminimum position, when the primary air temperature is in the opposite mode thanwhat the zone currently requires (for example, an internal zone that is calling forcooling in the winter, while the rooftop controller is supplying hot air for theexternal zones).Depending on the application, setting a minimum position for a zone damper maybe mandatory. Eliminating this minimum position, or at least lowering it to a valuebelow the standard, may resolve certain system design issues. A good example ofthis is an internal zone with a grossly oversized VAV unit.Balancing the Minimum, Maximum, and Heat Flow ValuesTo balance the minimum airflow:1. Set the outside heating lockout value (H lock parameter) at the rooftopcontroller to ensure that local system heating is allowed.TEC Zoning Control System for Stand-Alone and BACnet® MS/TP Networked ApplicationsTechnical Bulletin29