Coldest reset

The coldest reset strategy is used in dual duct systems to reset the setpoint temperature of the air in the heating supply duct. Usually it is used in conjunction with a warmest reset strategy resetting the temperature of the air in the cooling supply duct. For each zone in the system at each system timestep, the control logic calculates a supply air temperature that will meet the zone heating load at the maximum zone supply air flow rate. The highest of the possible supply air temperatures becomes the new supply air temperature setpoint, subject to minimum and maximum supply air temperature constraints. The resulting temperature setpoint is the lowest supply air temperature that will meet the heating requirements of all the zones. When compared to a fixed heating supply air temperature setpoint, this strategy minimises central boiler energy consumption (if the hot water temperature is also reset or there are variable speed pumps) at the cost of possible increased fan energy (if there is variable volume control in the air system).