Subject to change without prior notice Revised
05-12
6 720 220 045
12 cP/BP series
Once the thermostat reaches set point
temperature and the humidity is above set point
the unit will operate in the hot gas reheat mode
first by cooling and dehumidifying then reheating
the air using hot refrigerant gas before delivering it
to the space usually 2°F to 5°F below room
temperature. The unit is operating as a
dehumidifier. By reheating the air along a constant
sensible heat line the relative humidity of the
supply air is reduced.
The moisture removal capacity of a specific heat
pump is determined by the unit latent capacity
rating. A heat pump’s latent capacity can be
determined by reviewing the heat pump specification
data sheets. Depending upon the entering water and
air conditions a total and sensible capacity can be
interpolated from the data sheets. Subtracting
sensible capacity from total capacity yields latent
capacity. Dividing the latent capacity by 1069 (BTU/
LB of water vapor at 80° DB and 67° WB) yields the
amount of moisture removal in pounds per hour.
sequence of operation - on/off
control
The sequence of operation in the cooling and
heating mode is the same as a regular heat pump.
In the reheat mode on a call from the humidistat the
reheat relay coil is energized through the “H” circuit.
The blower relay, reversing valve and compressor
contactor are energized through the contacts of the
reheat relay. See typical wiring diagrams at the end
of the manual. The cooling relay remains de-
energized enabling the reheat solenoid (Note: The
reheat mode always operates in the cooling mode.)
Should the temperature in the space increase above
set point the compressor terminal Y is energized
which will de-energize the reheat valve putting the
unit into the straight cooling mode. A call for cooling
or heating will always take precedence over hot gas
reheat.
Hot Gas reheat controllers
There are several ways to control heat pumps with hot
gas reheat. You should choose the means that best
suits your specific application. See typical wiring
diagrams and the end of the manual for some possible
control sequences. Most heat pump compatible
thermostats in conjunction with a humidistat are
acceptable for use, (Note: “O” output for reversing
valve energized in cooling mode is required.)
Combination thermostats/humidistat are also
available.
special considerations
Some applications require special consideration to
maximize the performance of the hot gas reheat
function:
• Low Temperature Well Water
• Indoor Pool Dehumidifying During Winter Months
Consult the factory for special application
considerations.
low temperature Well Water
When low temperature well water is utilized as the
water source (below 55°F), a means of establishing two
flow rates, one for the cooling/reheat mode and one for
heating mode is recommended. In the cooling mode at
low entering water temperatures and standard flow
rates discharge pressures and corresponding discharge
gas temperatures are relatively low. At these conditions
when the reheat mode is initiated the low temperature
discharge gas can reduce reheat capacity. A means to
reduce the water flow rate and elevate the discharge
pressure/ temperature in cooling/reheat mode should
be provided. Conversely, at low entering water
temperatures in the heating mode system suction
pressure is reduced causing a loss in heating capacity. A
means of providing higher flow in the heating mode
should be provided. The simplest way to accomplish the
above is to install water regulating valves.
indoor Pool dehumidifying during
Winter Months
It is important to remember that when in the reheat
mode the heat pump is cooling and reheating. A
secondary means of heating the space during the
dehumidification mode should be provided. The
indoor space temperature should be kept at least
2°F above the pool water temperature. If this is not
done the warm pool water attempts to heat the
space and the humidity levels increase
exponentially. The heat pump is normally sized to
handle the design latent load moisture removal. A
sequence of operation
