FHP heat pump Application manual

HOT GAS REHEAT OPTION
Are uncontrollable humidity problems
costing you a bundle?
Why put up with humidity problems
when you can have true climate control
with the installation of an FHP water
source heat pump with the Hot Gas
Reheat Option (Humidimiser option).
When your FHP unit contains this
Underwriters Laboratory (UL) approved
optional feature...your normal air conditioning
cycle converts, as required, to an air drying operation.
Your FHP unit with the Humidimiser option will
provide cooling, heating, and dehumidification by
setting our combination thermostat/humidistat control.**
This option is available on the full range of FHP products.
This option is ideal for any application where a high level
of dehumidification is required. Typical applications are:
Indoor Pool Areas*
Outside/Make-Up Air Applications**
Computer Rooms
Hotel rooms during non-occupancy
* Note: Special coil and/or cabinet coating may be necessary
** Note: Cooling always takes priority over dehumidification.
ISO 9001: 2000 Certified
FHP MANUFACTURING COMPANY
601 N.W. 65TH COURT • FT. LAUDERDALE, FL 33309 • PHONE: (954) 776-5471 • FAX: (800) 776-5529
http://www.fhp-mfg.com
heat pumps
970-196 Rev. 10/04
HOT GAS REHEAT
HOT GAS REHEAT
FHP MANUFACTURING COMPANY
601 N.W. 65th Court • Fort Lauderdale, FL 33309
Phone: 954/776-5471 • Fax: 800/776-5529
http://www.fhp-mfg.com
TABLE OF CONTENTS
Safety Approvals....................................................................1
Common Reheat Applications ...............................................1
Reheat Functions...................................................................1
Refrigerant Flow.....................................................................2
Sequence of Operation..........................................................2
Front End Controllers.............................................................3
Special Considerations ..........................................................3
Typical Wiring Diagram ..........................................................4
Operating Pressure Temperatures..........................................4
Heat Pump Cabinet Dimensions ............................................4
SAFETY APPROVALS:
This factory installed option is Underwriter Laboratories (UL), (CUL) and
The City of New York Materials Equipment Acceptance Division (MEA)
safety listed.
COMMON REHEAT APPLICATIONS:
APPLICATION MANUAL
HUMIDIMISER
ENERGY WISE
HVAC EQUIPMENT
Below are a list of common reheat applications:
• Indoor swimming pool space conditioning.
• Computer room space conditioning.
• Auditoriums, theaters, etc... with large latent load requirements.
• Outside air units delivering air directly to the space.
• Any location where humidity infiltration is a problem.
REHEAT FUNCTION:
The reheat function is utilized to maintain a specified humidity level
within the conditioned space. When in the reheat mode the return air
from the space is cooled, dehumidified and reheated. By reheating the
air along a constant sensible heat line the relative humidity of the leaving
air is reduced. The leaving air dry bulb temperature is usually 2 to 5
degrees F. cooler than the return air temperature. This will vary model
by model. This cycle will continue until the humidistat is satisfied.
HOT GAS REHEAT
2
AIR FLOW
REHEAT COIL
EVAPORATOR
COIL
HOT GAS LINE
REVERSING
VALVE
CONDENSER
COIL
WATER
CHECK
LIQUID
LINE
VALVE
DISTRIBUTOR
CHECK
VALVE
EQUALIZER LINE
EXPANSION VALVE
CHECK
VALVE
BYPASS REGULATOR*
SOLENOID
REHEAT
VALVE
EQUALIZER LINE
PILOT Coil
COMPRESSOR
SUCT. IN
DISCH.
OUT
HOT GAS LINE
*Optional
( Figure #1 )
The amount of moisture removal capacity of a specific
heat pump is determined by the the unit latent
capacity rating. A heat pumps 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 moist air enthalpy) yields
the amount of moisture removal in pounds per hour.
REFRIGERANT FLOW PATH:
In the cooling and heating modes the refrigerant flow
path is identical to standard heat pumps. In the reheat
mode the compressor discharge gas is diverted
through the reheat valve to the reheat coil which is
located behind the primary air coil. The hot gas then
passes though the water to refrigerant coil. At this
point the rest of the cooling cycle is completed. There
are (2) check valves to prevent refrigerant flow into the
reheat coil during standard cooling/heating cycles. A
small copper bleeder line is connected to the outlet
line of the reheat coil and between the expansion valve
outlet and distributor to the air coil. This line is
necessary to let any liquid that may have migrated to
the reheat coil during reheat to escape during
standard cooling/heating modes. (See Figure #1)
SEQUENCE OF OPERATION:
Three modes of operation are available with heat
pumps equipped with hot gas reheat. They are as
follow:
• Cooling mode only
• Heating mode only
• Cooling mode in conjunction with hot gas
reheat mode
COOLING MODE:
On a call from the front end controller for cooling the
blower relay is energized through the "G" circuit run
through the normally closed contacts on the reheat
relay. The reversing valve is energized through the "O"
circuit. The compressor contactor is energized through
the "Y" circuit which energizes the cooling relay coil
closing the cooling relay normally open contacts and
energizing the compressor contactor from the "R" side
of the transformer. At the same time the reheat
solenoid valve is disabled by opening the normally
closed contacts of the cooling relay. (Note: On most
front end controllers the "O" terminal is constantly
energized when the system’s switch is in the cooling
position or the auto position.)
HOT GAS REHEAT
HEATING MODE:
On a call from the front end controller for heating the
blower relay is energized through the "G" circuit run
through the normally closed contacts of the reheat
relay. The reversing valve is de-energized by the
absence of the "O" circuit signal. The rest of the
sequence is identical to that of cooling. (Note: The
compressor contactor is still energized through the
cooling relay contacts.)
REHEAT MODE:
On a call from the front end controller (humidistat
signal) the reheat relay coil is energized through the
"H" circuit. The blower relay is energized through the
"R" side of the transformer run through the normally
open contacts of the reheat relay coil. The "O" circuit
is energized thus energizing the reversing valve. The
compressor contactor is energized though the"R" side
of the transformer run through normally open contacts
on the reheat relay. The cooling relay remains deenergized thus the reheat solenoid is enabled. (Note:
The reheat mode always operates simultaneously with
the cooling mode.)
FRONT END CONTROLLERS:
(THERMOSTATS & HUMIDISTAT)
There are many ways to control heat pumps with hot
gas reheat. You should choose the means that best
fits your specific application.
(Figure #2) illustrates one possible control sequence.
Most other heat pump compatible thermostats in
conjunction with a humidistat is acceptable for use,
(Note: "O" output for reversing valve energized in
cooling mode required.)
SPECIAL CONSIDERATIONS:
Some applications require special attention to
maximize the performance of the hot gas reheat
function:
• Low Temperature Well Water
• Indoor Pool Dehumidifying During Winter Months
(Re: Heating Mode)
• Heating To Reheat Circuit
Consult the factory for special application
considerations.
LOW TEMPERATURE WELL WATER:
When low temperature well water is utilized as the
water source (below 55 degrees F), a means of
establishing (2) two flow rates, (1) one for the
cooling/reheat mode and (1) 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
3
temperatures are relatively low. At these conditions
when the reheat mode is initiated the low temperature
discharge gas can condense in the reheat coil thus
yielding minimal 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
(RE: HEATING MODE):
It is important to remember that when in the
reheat/dehumidification 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) degrees 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 second heat pump or resistance heat
should be provided to handle the structures shell loss
load. A water to water heat pump pool heater can be
provided to heat the pool.
If questions arise on an indoor pool space conditioning
application, please consult the factory for engineering
assistance.
NOTE: BRONZ-GLOW COATING IS HIGHLY
RECOMMENDED FOR ALL POOL APPLICATIONS
DUE TO THE HIGHLY CORROSIVE CHEMICAL
ENVIRONMENT.
Cabinet and coil fins are warranted for 1 year. FHP will
not warrant cabinets or coils from corrosion unless
BRONZ-GLOW coatings are factory supplied.
HEATING TO REHEAT CIRCUIT:
An automatic change over relay and corresponding
control circuit is available as an optional feature. An
example of this type of application would be a school
locker room where latent loads would be high during
the occupied mode. This circuit allows the unit to shift
from heating to reheat without changing the system
switch on the front end controller. Another application
that this has been used on is indoor swimming pool
applications where additional heating means have not
been provided. This application is only successful
where structure shell loss is minimal. This is not
recommended in large enclosed pool areas where
structure heating loads are substantial.
HOT GAS REHEAT
4
OPERATING PRESSURES AND
TEMPERATURES: (REHEAT MODE)
Operating pressures and temperatures in the reheat
mode vary slightly from standard cooling mode
operating characteristics. The variations are as follows:
CONTROLS BY OTHERS:
Please consult the factory for engineering assistance if
any controller other than the Climatouch CT03TSHB
FHP Part Number 641-186 is being used to control
the heat pump with this hot gas reheat option.
UNIT DIMENSIONS:
Discharge Pressure: (-) 5 to 20 PSIG
Discharge Gas Temperature: (-) 5 to 15 Degrees F.
Suction Pressure: (+) 5 to 10 PSIG
Suction Gas Temperature: (+) 5 to 10 Degrees F.
All models except the EM007, EM009 and EM012
horizontals remain the same. The EM007, EM009 and
EM012 will have the same cabinet footprint as the
EM015 HZ and EM007, EM009 and EM012 height
remains the same.
( Figure #2 )
Rev. 11/06