Carrier PSV, PSD006-070, 50PSH instruction manual HWR Operating Modes, A50-8145

HWR APPLICATION CONSIDERATIONS — Unlike most hot gas reheat options, the HWR option will operate over a wide range of entering-water temperatures (EWTs). Special flow regulation (water regulating valve) is not required for low EWT conditions. However, below 55 F, supply-air temperatures cannot be maintained at 72 F because the cooling capacity exceeds the reheat coil capac- ity at low water temperatures. Below 55 F, essentially all water is diverted to the reheat coil (no heat of rejection to the building loop). Although the HWR option will work fine with low EWTs, overcooling of the space may result with well water systems or, on rare occasions, with ground loop (geothermal) systems (NOTE: Extended range units are required for well water and ground loop systems). Since dehumidification is generally only required in cooling, most ground loop systems will not experience overcooling of the supply-air temperature. If overcooling of the space is a con- cern (e.g., computer room well water application), auxiliary heating may be required to maintain space temperature when the unit is operating in the dehumidification mode. Water source heat pumps with HWR should not be used as makeup air units. These applications should use equipment specifically designed for makeup air.

HWR COMPONENT FUNCTIONS — The proportional controller operates on 24 VAC power supply and automatically adjusts the water valve based on the supply-air sensor. The supply-air sensor senses supply-air temperature at the blower inlet, providing the input signal necessary for the proportional control to drive the motorized valve during the reheat mode of operation. The motorized valve is a proportional actuator/three- way valve combination used to divert the condenser water from the coax to the hydronic reheat coil during the reheat mode of operation. The proportional controller sends a signal to the motorized valve based on the supply-air temperature reading from the supply air sensor.

The loop pump circulates condenser water through the hy- dronic reheat coil during the reheat mode of operation (refer to Fig. 34). In this application, the loop pump is only energized during the reheat mode of operation. The hydronic coil is uti- lized during the reheat mode of operation to reheat the air to the set point of the proportional controller. Condenser water is di- verted by the motorized valve and pumped through the hydron- ic coil by the loop pump in proportion to the control set point. The amount of reheating is dependent on the set point and how far from the set point the supply air temperature is. The factory set point is 70 to 75 F, generally considered "neutral" air.

Table 17 — HWR Operating Modes

MODE			INPUT					OUTPUT
	O	G	Y1	Y2*	H	O	G	Y1	Y2*	Reheat
No Demand	On/Off	Off	Off	Off	Off	On/Off	Off	Off	Off	Off
Fan Only	On/Off	On	Off	Off	Off	On/Off	On	Off	Off	Off
Cooling Stage 1	On	On	On	Off	Off	On	On	On	Off	Off
Cooling Stage 2	On	On	On	On	Off	On	On	On	On	Off
Cooling and Dehumidistat†	On	On	On	On/Off	On	On	On	On	On/Off	Off
Dehumidistat Only	On/Off	Off	Off	Off	On	On	On	On	On	On
Heating Stage 1	Off	On	On	Off	Off	Off	On	On	Off	Off
Heating Stage 2	Off	On	On	On	Off	Off	On	On	On	Off
Heating and Dehumidistat**	Off	On	On	On/Off	On	Off	On	On	On/Off	Off

*Not applicable for single stage units; Full load operation for dual capacity units.

†Cooling input takes priority over dehumidify input.

**Deluxe D is programmed to ignore the H demand when the unit is in heating mode.

NOTE: On/Off is either on or off.

Water Out					Refrigerant In
(To Water Loop)	Mixing Valve				(Cooling)
Water In		Internal Pump
					COAX
(From Water Loop)
			Refrigerant Out
				(Cooling)		Entering Air

NOTE: All components shown are	Evaporator Coil
internal to the heat pump unit.

a50-8145

Leaving

Air

Reheat

Coil

Fig. 34 — HWR Schematic

34