Heat Controller HTH, HTV, HTD manual Hot Water Generator, Typical HWG Installation

Installation, Operation & Maintenance HTV/HTD/HTH SERIES Heat Controller, Inc.

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 field. 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 field 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.

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 efficient 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.

Figure 14: Typical HWG Installation

	Hot Outlet	Cold
		Inlet
	to home
			Shut Off
			Valve #1
			Shut Off
			Valve #4
			Upper
			element to
			120 - 130°F
			[49 - 54°C]
			Lower
	Powered		element to
	Water		100 - 110°F
Shut-off	Heater		[38 - 43°C]

Valve #3

Shut Off

Valve #2

Field supplied 3/4’ brass nipple and ‘T’

Insulated water lines -

5/8” OD, 50 ft maximum (one way) [16mm OD, 15 meters maximum]

Figure 15: HWG Double Tank Installation

Hot Outlet to

house

Cold Inlet from

Domestic supply

Hot Outlet

Cold Inlet

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.

	Shut-off	Upper element to 130°F [54°C]
	Valve #1	(or owner preference)
	Shut-off
	Valve #4
	Powered
	Water Heater	Lower element to 120°F [49°C]
	Unpowered
Shut-off	Water Heater
Valve #3
Shut Off
Valve #2
	Field Supplied 3/4” brass nipple and “T”
Insulated water lines - 5/8” OD, 50 ft maximum (one way)
	[16mm OD, 15 meters maximum]

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