Northern Heatpump NorthStar RD-WE-096 Installation & Operating Instructions Manual - page 22
08/19/2014
20
NI701
Hydronic (Load), Space Water Heating, Installation
Plumbing
The Geo unit load circuit is basically a heat exchanger with piping ports for out and in flow. There are no
pumps within the unit. Use standard water heating loop parts/components and piping/plumbing best practices
as if this Geo unit is a “boiler”. The minimum GPM flow requirement and pressure drop within the Geo unit
heat exchanger is shown on the page 3 specification chart, for the appropriate model size. The internal feet of
head resistance or pumping requirement is at the nominal GPM shown.
Depending upon the installation/heating zone concept, plumbing will depend upon decision for closed loop
pressure or non-pressure system. If the vertical lift is less than approximately 15 feet (4.5 meters), a buffer tank
with non-pressure concept is recommended.
Load Distribution/Zones Pumping, Pressurized
If the design involves a pressure system, expansion tank is required with an external safety valve ASME stamp
and rated for 30 psi maximum. The necessary air relief and air separation components are strongly
recommended for long-term continuous operations.
Call for aquastat heating (HW terminal) assumes the minimum, continuous, flow through the Geo unit heat
exchanger is always greater than the minimum GPM shown on the mechanical specification chart, for the
appropriate model. This Geo unit does not include a flow switch for the load circuit, if the flow is less than the
specified minimum GPM or if there is no flow due to air locks, pump failure or load water circuit issues, the
compressor will immediately lock out with high pressure. After the second reset compressor cycle, the
compressor will be on permanent lockout with no further action until service or troubleshooting takes place.
If an external flow switch is added, wire it in series with the internal loop flow switch.
Load Heating Zones
If there are small zones or zones which cannot handle the Btu/h capacity of the appropriate installed model
(specification chart Btu/h) or if these zones reduce the GPM water flow, there must be external controls or a
buffer tank within the system to make sure the compressor does not short cycle or the system does not overheat.
For a Geo water to water unit the most effective and easiest method of handling multiple zones is with a buffer
tank system.
WARNING
THE SYSTEM MUST BE DESIGNED FOR A MINIMUM 10 TO 15 MINUTE COMPRESSOR RUN
TIME ON EACH AQUASTAT CALL. IF, DURING THE LIFE OF THE WARRANTY, THERE ARE
COMPRESSOR FAILURE ISSUES AND AN EVALUATION OF THE INSTALLATION
DETERMINES THERE WAS NO PROVISION FOR TAKING CARE OF COMPRESSOR SHORT
CYCLING OR COMPRESSOR HIGH DISCHARGE PRESSURE REPEATED OPERATION,
WARRANTY MAY BE REJECTED.
Hydronic Buffer Tank Consideration
Inclusion of a buffer tank is ideal for non-pressure concept and is the simplest pumping/plumbing approach.
The number and size of heating zones has no immediate consideration, the Geo unit has its own external main
pump which simply “pumps into” a buffer tank circulating loop. If all pumps are installed below the lower half
of the buffer tank, a non-pressure tank is the ideal solution. No purging or air lock issue will develop in this
situation.
Each heating zone pump has its own thermostat control device which simply causes its pump to pull energy
from the buffer tank as required. An aquastat type device on the buffer tank controls or determines the Geo unit
HW call.
Buffer tank sizing is typically 6 to 10 gallons per ton. If it is a heating only installation, a larger buffer tank is
suggested and should be considered.