Northern Heatpump NorthStar RD-WE-096 Installation & Operating Instructions Manual - page 20
08/19/2014
18
NI701
Desuperheater, Domestic Hot Water
General
All NHP Series units can be equipped with a desuperheater and an integrated circulating pump that can provide
Supplemental Domestic hot Water (SDW). This is done by stripping heat from the superheated gas leaving the
compressor.
Fuses – 3-amp fuses are installed in series with the desuperheater pump. The fuses are located in the line
voltage control box, upper right. Remove the fuses (turn 230 power source off) to disable the pump whenever
the system is not in operation.
Dual Compressor Models – contain two desuperheater heat exchangers, one for each refrigeration circuit. The
water side of these exchangers is piped in series. These models still utilize one circulating pump.
General Plumbing and Installation Suggestions
1.
Insulated ½” copper piping should be used from the hot water tank to the desuperheater connections on the
left side of the unit. The copper tubing should be straight to maintain good water velocity and prevent
pockets from forming at the pump inlet.
CAUTION
Due to high water temperatures generated by the desuperheater, PEX or poly pipe may rupture
if coupled directly to heat pump outlet.
2.
Shut off valves should also be used to service the desuperheater pump without draining the entire hot water
tank. Note: Always be sure these valves are open when pump is running.
3.
Pump problems develop by running the pump dry or with air in the system. All air must be purged from the
desuperheater plumbing before the pump is engaged.
4.
To purge air from the lines, loosen the desuperheater pump from its housing by turning the brass collar. Let
water drip out of the housing until flow is established and re-tighten the brass collar.
5.
Never operate the system without the high temperature switch (normally factory installed) otherwise tank
temperatures could become dangerously high.
6.
Poor water quality may restrict the effectiveness of using the desuperheater pump and will not allow the
pump to circulate.
7.
Desuperheater maintenance includes periodically opening the drain on the hot water tank to remove any
deposits. Hard water may cause scale buildup in the desuperheater coil reducing its effectiveness.
8.
The temperature difference between the water entering and leaving the desuperheater should be 5°F to
15°F. The water flow should be approximately 0.4 GPM per ton of nominal cooling.
9.
Northern Heat Pump strongly suggests a water heater buffer tank, Figure 7, for the maximum efficiency
from the provided desuperheater module. The Figure 7A single tank plumbing and application is shown for
information only.
There are a number of ways the desuperheater/pump can be plumbed with and into the building/household
water heater tank. However, many common methods used are not very effective because they simply circulate
already heated water from the water heater tank through the desuperheater. The heat pump desuperheater
cannot effectively produce hot water energy if the temperature of the water entering the desuperheater is close
to or beyond the compressor gas capability to transfer energy into this circulated water – typically 110° F (43°
C) to 130° F (54° C). Note: Health code requires 130° F (54° C) minimum.
Example – if the water heater electric element thermostat is set at 140° F (60° C), it will maintain the tank
at 140° F (60° C). There is no point in circulating 140° F (60° C) water through the desuperheater because it
is picking up very little or no energy from the compressor hot gas.
In fact, the energy flow may even be negative if the Geo HP loop temperature is too low, it is possible for a
single tank hot water heater to actually flow energy into the Geo HP system with very bad system
efficiency.