Carrier AQUAZONE PSV User Manual
Page 34
34
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
*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.
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
Fig. 34 — HWR Schematic
Water Out
(To Water Loop)
Water In
(From Water Loop)
Mixing Valve
COAX
Evaporator Coil
Reheat
Coil
Refrigerant Out
(Cooling)
Refrigerant In
(Cooling)
Entering Air
Leaving
Air
Internal Pump
NOTE: All components shown are
internal to the heat pump unit.
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