Northern Heatpump NorthStar RD-WE-096 Installation & Operating Instructions Manual - page 18
08/19/2014
16
NI701
Open Loop/Well – An open system gets its name from the open discharge of water after it has been used by the
heat pump. A well must be available that can supply all of the water requirements of the heat pump along with
any other water requirements drawing off that same well. The well must be capable of supplying the heat pumps
required flow rated for up to 24 hours per day for the coldest winter day.
The discharge water is typically returned to the earth via a properly designed drain field or in a lake.
Figure 6 shows the necessary components for water piping of an open system. First a bladder type pressure tank
with a “draw down” of at least 1-1/2 to 2 times the well pump capacity must be installed on the supply side of
the heat pump to prevent short cycling the well pump. Constant pressure well pumps need to deliver the GPM
flow rate of the NHP unit and other possible consecutive demands. Shut off valves and boiler drains on the
entering and leaving water lines are necessary for future maintenance. A screen strainer is placed on the supply
line with a mesh size of 40 to 60 and enough surface area to allow for particle buildup between cleanings. Hose
kits are installed between the heat pump and ridged plumbing to reduce vibration transfer. Hose kits have
pressure temperature (P/T) plugs placed in the supply and discharge hydrant elbows so that thermometers or
pressure gauges can be inserted into the water stream. On the well water discharge side of the heat pump a flow
meter is installed to provide a visual indicator of open loop flow in GPM. The water solenoid valve must be
installed to control water flow through the unit. After the water solenoid a flow control valve is installed to
limit maximum flow through the heat pump. The ball valve installed in the leaving water line can be used to
create a small amount of back pressure to quiet the flow control valve if needed. Discharge water temperature
should not drop below 38° at any time during the units operation. Remove handle on the entering and leaving
water ball valves to prevent accidental change of flow.
A solenoid valve is then installed and wired to compressor contactor. This valve will open when the unit is
running and close when the unit stops. A visual flow meter is then installed to allow visual inspection of the
flow requirements. The flow meter can also be useful in determining when maintenance is required. Schedule
40 PVC piping, copper tubing, polyethylene or rubber hose can be used for supply and discharge water lines.
Limit rubber hose to 10ft. (3 meters) to prevent excessive pressure drop. Make sure line sizes are large enough
to supply the required flow with a reasonable pressure drop (generally 1.00” diameter). Water discharge is
generally made to a drain field, stream, pond, surface discharge, tile line, or storm sewer.
Solenoid Valve Wiring (for Open Loop
Systems)
Locate the compressor contactor in the right-hand
high-voltage side of the control panel. Wire the
solenoid valve as shown in this diagram.
CAUTION
Using a drain field requires soil conditions and adequate sizing to assure rapid percolation or the required flow rates
will not be achieved. Consult local codes and ordinances to assure compliance. Do not discharge water to a septic
system. The heat pump should never be operated with flow rates (GPM) less than specified. Operation with less than
required flow rate or no flow may result in freezing water in the water to refrigerant heat exchanger. This will cause the
unit to shut down on low-pressure lockout. If the unit locks out, verify that the unit has the required flow and reset the
unit by shutting off power to the unit for one minute. Do not continually reset the unit; if the unit locks out more than
once call your service professional. Continued reset of the unit can freeze water inside the water coil to the point of
rupturing the water coil (no warranty for frozen coils).