W A T E R - S O U R C E H E A T P U M P S
JRE-Series
R e v. : A u g u s t 1 9 , 2 0 2 0
I n s t a l l a t i o n , O p e r a t i o n , M a i n t e n a n c e
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Condenser Hot Water Reheat – Benefits and Applications
Figure 9: Condenser Hot Water Reheat Schematic
Modulating Reheat Option -
Johnson Controls’
condenser hot water reheat provides an innovative
solution to dehumidification without complicated
refrigerant controls. Condenser water reheat utilizes one
of the biggest advantages of a Water-Source Heat Pump
(WSHP), the transfer of energy through the water piping
system. Condenser Hot Water Reheat simply diverts
condenser water through a water-to-air coil that is placed
after the evaporator coil. If condenser water is not warm
enough, the internal “run-around” loop increases the
water temperature with each pass through the condenser
coil (see figure 9, below).
Benefits -
Proportional reheat is controlled to the
desired leaving air temperature set point (factory set
point of 72°F, 22°C), no matter what the water loop
temperature is. Since dehumidification operation will
occur under less than full load cooling conditions a
good percentage of the time, it is important to have
a reheat function that provides 100% reheat in the
spring and fall when the water loop is cool. Supply air
temperature is field adjustable to +/- 3°F [+/- 1.7°C] for
even greater flexibility with the optional potentiometer. It
is recommended that the reheat supply air temperature
be set to match the space cooling setpoint so that reheat
does not impact room temperature. Competitors without
hydronic reheat typically use an on/off (non-modulating)
refrigeration based reheat circuit, typically referred to as
“Hot gas reheat” (HGR). HGR needs higher condensing
temperatures to work well, typically 85°F [29°C] entering
water temperature (EWT).
With HGR, cooler water temperatures produce cooler
supply air temperatures, which could overcool the space,
requiring additional space heating from another source
or a special auto-change-over relay to allow the unit to
switch back and forth between reheat and heating. Rarely
does HGR provide 100% reheat, like condenser water
reheat. Condenser water reheat has a simple and easy
to troubleshoot refrigerant circuit. No switching valves
or hard to diagnose leaky check valves are utilized. No
unusual refrigerant pressures occur during the reheat
mode. Condenser Hot Water Reheat technology does
not alter the refrigerant circuit from a standard unit
without reheat (no complicated reheat refrigerant circuit to
diagnose if problems occur). Plus, the water loop portion of
the condenser water reheat option is easy to understand
and diagnose..
Applications -
Condenser water reheat can be applied to
a number of common applications, such as:
• Classrooms.
• Condominiums.
• Apartments.
• Computer rooms.
• Spaces with high latent loads like auditoriums,
theaters, convention centers, etc.
• Most applications where humidity is a problem.
(Note: Condenser water reheat is not for use in high
fraction outdoor air applications or in applications
with corrosive atmospheres, such as pool rooms.)
NOTE:
Brazed plate heat exchanger is used when connecting to a loop with no antifreeze.
