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R e s i d e n t i a l H & V - 6 0 H z H F C - 4 1 0 A

R e v. : 7 A u g . , 2 0 1 1 B

G e o t h e r m a l H e a t P u m p S y s t e m s

Electric water heaters are recommended. If a gas, propane,
or oil water heater is used, a second preheat tank must be
installed (Figure 15). If the electric water heater has only a
single center element, the dual tank system is recommended
to insure a usable entering water temperature for the HWG.

Typically a single tank of at least 52 gallons (235 liters) is
used to limit installation costs and space. However, a dual
tank, as shown in Figure 15, is the most effi cient system,
providing the maximum storage and temperate source water
to the HWG.

It is always advisable to use water softening equipment on
domestic water systems to reduce the scaling potential and
lengthen equipment life. In extreme water conditions, it may
be necessary to avoid the use of the HWG option since the
potential cost of frequent maintenance may offset or exceed
any savings. Consult Table 3 for scaling potential tests.

Hot Water Generator

The HWG (Hot Water Generator) or desuperheater option
provides considerable operating cost savings by utilizing
excess heat energy from the heat pump to help satisfy
domestic hot water requirements. The HWG is active
throughout the year, providing virtually free hot water when
the heat pump operates in the cooling mode or hot water at
the COP of the heat pump during operation in the heating
mode. Actual HWG water heating capacities are provided in
the appropriate heat pump performance data.

Heat pumps equipped with the HWG option include a built-
in water to refrigerant heat exchanger that eliminates the
need to tie into the heat pump refrigerant circuit in the fi eld.
The control circuit and pump are also built in for residential
equipment. Figure 14 shows a typical example of HWG water
piping connections on a unit with built-in circulating pump.
This piping layout reduces scaling potential.

The temperature set point of the HWG is fi eld selectable
to 125°F or 150°F . The 150°F set point allows more heat
storage from the HWG. For example, consider the amount
of heat that can be generated by the HWG when using the
125°F set point, versus the amount of heat that can be
generated by the HWG when using the 150°F set point.

In a typical 50 gallon two-element electric water heater
the lower element should be turned down to 100°F, or the
lowest setting, to get the most from the HWG. The tank will
eventually stratify so that the lower 80% of the tank, or 40
gallons, becomes 100°F (controlled by the lower element).
The upper 20% of the tank, or 10 gallons, will be maintained
at 125°F (controlled by the upper element).

Using a 125°F set point, the HWG can heat the lower 40
gallons of water from 100°F to 125°F, providing up to 8,330
btu’s of heat. Using the 150°F set point, the HWG can heat
the same 40 gallons of water from 100°F to 150°F and the
remaining 10 gallons of water from 125°F to 150°F, providing
a total of up to 18,743 btu’s of heat, or more than twice as
much heat as when using the 125°F set point.

This example ignored standby losses of the tank. When
those losses are considered the additional savings are even
greater.

Figure 14: Typical HWG Installation

Figure 15: HWG Double Tank In stal la tion

WARNING!

WARNING! A 150°F SETPOINT MAY LEAD TO
SCALDING OR BURNS. THE 150°F SET POINT MUST
ONLY BE USED ON SYSTEMS THAT EMPLOY AN
APPROVED ANTI-SCALD VALVE.

Upper

element to

120 - 130°F

[49 - 54°C]

Cold Inlet From

Domestic Supply

Hot Outlet