System information

42
Geothermal Applications
Carrier: Turn to the Experts.
Rarely does HGR provide 100% reheat, like the Whole House
Dehumidifi cation option.
It is simple to troubleshoot the Whole House dehumidifi cation
circuit. No switching valves or hard to diagnose leaky check valves
are utilized. No unusual refrigerant pressures occur during the
reheat mode. The Whole House Dehumidifi cation refrigerant
circuit is like every other Carrier Geothermal unit (without
reheat), so everything the technician already knows applies to
troubleshooting the Whole House Dehumidifi cation refrigeration
circuit. Plus, the water loop portion of the Whole House
Dehumidifi cation option is easy to understand and diagnose.
Features Include:
• Modulating reheat for precise control of supply
air temperatures
• 100% reheat (operates as a dehumidifi er)
• “Neutral” supply air temperature even at part load (non-
design) conditions
• Supply air temperature adjustment, +/- 3°F [+/-1.7°C] from
72°F [22°C] factory setpoint with optional potentiometer
• Integrated reheat controls – simply attach a humidistat
or dehumidistat
• Microprocessor (DXM) controls standard
• Ultra simple refrigeration circuit
• All water system eliminates refrigeration circuit modifi cations
(same refrigeration circuit as units without Whole House
Dehumidifi cation)
• Stable refrigeration pressures, even at low EWTs
• All components located inside the cabinet
• Moves heat of rejection from ground loop to supply air stream
Availability
The Whole House Dehumidifi cation option is currently available
on Carrier Geothermal residential GT-PX (50YD) and GT-PG
(50YE) series units.
Whole House Dehumidifi cation Applications
With the Whole House Dehumidifi cation option, return air from
the space is conditioned by the air-to-refrigerant (evaporator) coil,
then reheated by the water-to-air (reheat) coil to dehumidify the
air, but maintain the same space temperature (thus operating as a
dehumidifi er). The moisture removal capability of the heat pump
is determined by the unit’s latent capacity rating. Latent Capacity
(LC) equals Total Capacity (TC) minus Sensible Capacity (SC). For
example, at 85°F [29°C] EWT, the moisture removal capability
(latent capacity) of a Carrier Geothermal size 030 heat pump is 9.6
MBtuh [2.8kW] as shown in Table 4.
Dividing the latent capacity by 1,069 BTU/LB of water vapor at
80°F DB and 67°F WB [26.7°C DB and 19.4°C WB] moist air
enthalpy, converts the amount of moisture removal to pounds
per hour (multiply pounds per hour by 0.4536 to obtain kg/hr).
Calculations are shown in fi gure 22. Most Carrier Geothermal
heat pumps have a sensible-to-total (S/T) ratio of 0.72 to 0.76.
Therefore, approximately, 25% of the cooling capacity is dedicated
to latent cooling capacity (moisture removal). When selecting a
unit with Whole House Dehumidifi cation, the space sensible and
latent loads should be calculated. If the unit will be used for space
cooling, a unit with at least enough capacity to satisfy the building
sensible load should be selected. If the latent cooling load is not
satisfi ed by the selection, a larger unit with enough latent capacity
will be required. The Whole House Dehumidifi cation option can
be used for the additional moisture load. If the unit will be used
for dehumidifi cation purposes only, the latent capacity is the only
consideration necessary. In this case, sensible load is immaterial.
Example latent capacities for a typical Carrier Geothermal heat
pump are shown in table 4.
Whole House Dehumidifi cation is especially useful in
Northern Climates, where the heat pump may be oversized in
cooling to provide enough heating. Units with Whole House
Dehumidifi cation will compensate for these applications by
operating as a whole house dehumidifi er when necessary to
maintain space RH.
Since the Whole House Dehumidifi cation option is internal to
the unit, installation is much easier than a separate whole house
dehumidifi er. Plus, an additional compressor and controls can be
eliminated, simplifying the system and lowering operating and
installation costs.
Table 4: Typical Unit Latent capacity
Latent Capacity at 85°F [29.4°C] EWT
Size MBtuh lbs/hr kW kg/hr
18 4.7 4.4 1.4 2.0
24 6.1 5.7 1.8 2.6
30 6.8 6.4 2.0 2.9
36 9.6 9.0 2.8 4.1
42 11.0 10.3 3.2 4.7
48 12.7 11.9 3.7 5.4
60 15.2 14.2 4.5 6.4
70 16.9 15.8 5.0 7.2
Whole House Dehumidification