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Bosch Geothermal Heat Pumps
Bosch Thermotechnology Corp.
Data subject to change
Applications Manual
All hot water piping should be a minimum of 3/8 inch O.D.
copper tubing to a maximum distance of fteen (15) feet.
For longer distances but not exceeding sixty (60) feet, use
½ inch O.D. copper tubing. Insulate all exposed surfaces
of both the connecting water lines with 3/8 inch minimum
wall closed cell insulation. Install isolation valves on the
supply and return lines to the HRP.
To re ll the existing water heater tank, open the cold
water supply to the tank. Open a hot water faucet to vent
air from the system until water ows from the faucet then
closed the faucet. Depress the hot water tank pressure
relief valve handle to ensure there is no air remaining in
the water heater tank. Carefully inspect all plumbing for
any water leaks and correct as necessary. Purge all air
from the HRP by depressing the Schrader valve on the HRP
unit heat exchanger. Allow all air to bleed out until water
appears at the Schrader valve.
Before restoring power or the fossil fuel source, adjust
the temperature setting on the water heater tank
thermostat(s) to ensure the maximum utilization of
the heat available from the refrigeration system and
to conserve the most energy. With water heater tanks
equipped with both upper and lower electric heating
elements and two thermostats, the lower element should
be adjusted to 100ºF, while the upper element should be
adjusted to 120ºF. Depending on the speci c needs of
the customer, the upper element may need to be adjusted
accordingly. On water heater tanks with a single heating
element and one thermostat, lower the thermostat setting
to 120ºF or the “Low” position. After the thermostat
adjustment, replace the access cover and restore electrical
or the fossil fuel supply to the water heater.
Assure that all valves in the HRP piping system are open.
Never operate the HRP pump dry. Turn on the Bosch
geothermal heat pump. The HRP pump will not run unless
the Bosch geothermal heat pump compressor is energized
(the HRP pump should never run if the compressor is not
running). Press the HRP switch on the face of the Bosch
geothermal heat pump to the “On” position. The HRP
pump will operate if the entering water temperature to the
HRP is below 120ºF. The HRP pump will not operate if the
“On/Off” switch is in the “Off” position.
The temperature difference between the water entering
and leaving the HRP should be between approximately 5ºF
and 15ºF.
Allow the Bosch geothermal heat pump and the HRP
to operate for 20 to 30 minutes to ensure the HRP is
functioning properly. The HRP pump will de-energize
automatically when the water temperature entering it
reaches 120ºF.
The Bosch HRP is typically equipped with a low gas limit
which closes at approximately 125°F, and a hot water
temperature limit that opens at approximately 140ºF.
17.3 Bosch Hot Gas Reheat (HGR)
The Bosch Hot Gas Reheat (HGR) option is often utilized
to maintain a speci ed humidity level within a conditioned
space. When in the reheat mode the return air from the
space is cooled, dehumidi ed 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 satis ed.
The amount of moisture removal capacity of a speci c
Bosch geothermal heat pump is determined by the
unit latent capacity rating. A Bosch geothermal heat
pump’s latent capacity can be determined by reviewing
the speci c Bosch geothermal heat pump speci cation
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 1,069 (BTU/LB of water vapor at 80°
DB and 67° WB moist air enthalpy) yields the amount of
moisture removal in pounds per hour.
Typical residential reheat applications for the Bosch HGR
include:
f
Rooms with larger than normal latent loads
f
Locations where humidity infiltration is a problem
17.3.1 Refrigerant Flow Path with HGR
In the cooling and heating modes, the refrigerant ow path
is identical to standard Bosch geothermal heat pumps.
In the reheat the compressor discharge gas is diverted
through a reheat valve (Fig. 129) to a reheat coil (Fig. 130)
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
two (2) check valves to prevent refrigerant ow into the
reheat coil during standard cooling and/or 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 and/or heating
cycles.
Fig. 129 Reheat valve
