Open Loop - Ground Water Systems
Shut off valves should be included for ease of servicing. Boiler
drains or other valves should be “tee’d” into the lines to allow
acid flushing of the heat exchanger. Shut off valves should be
positioned to allow flow through the coaxial heat exchanger
via the boiler drains without allowing flow into the piping
system. P/T plugs should be used so that pressure drop and
temperature can be measured. Piping materials should be
limited to copper or PVC SCH80. Note: Due to the pressure
and temperature extremes, PVC SCH40 is not recommended.
Water quantity should be plentiful and of good quality. Consult
water quality table for guidelines. The unit can be ordered with
either a copper or cupro-nickel water heat exchanger. Consult
table 3 for recommendations. Copper is recommended for
closed loop systems and open loop ground water systems
that are not high in mineral content or corrosiveness. In
conditions anticipating heavy scale formation or in brackish
water, a cupro-nickel heat exchanger is recommended. In
ground water situations where scaling could be heavy or
where biological growth such as iron bacteria will be present,
an open loop system is not recommended. Heat exchanger
coils may over time lose heat exchange capabilities due to
build up of mineral deposits. Heat exchangers must only
be serviced by a qualified technician, as acid and special
pumping equipment is required. Desuperheater coils can
likewise become scaled and possibly plugged. In areas with
extremely hard water, the owner should be informed that the
heat exchanger may require occasional acid flushing. In some
cases, the desuperheater option should not be recommended
due to hard water conditions and additional maintenance
required.
Water Quality Standards
Scaling potential should be assessed using the pH/
Calcium hardness method. If the pH <7.5 and the Calcium
hardness is less than 100 ppm, scaling potential is low. If
this method yields numbers out of range of those listed, the
Ryznar Stability and Langelier Saturation indecies should be
calculated. Use the appropriate scaling surface temperature
for the application, 150°F [66°C] for direct use (well water/
open loop) and HWG (desuperheater); 85°F [29°C] for indirect
use. A monitoring plan should be implemented in these
probable scaling situations. Other water quality issues such
as iron fouling, corrosion prevention and erosion and clogging
should also be considered.
Expansion Tank and Pump
Use a closed, bladder-type expansion tank to minimize
mineral formation due to air exposure. The expansion tank
should be sized to provide at least one minute continuous
run time of the pump using its drawdown capacity rating to
prevent pump short cycling. Discharge water from the unit
is not contaminated in any manner and can be disposed
of in various ways, depending on local building codes (e.g.
recharge well, storm sewer, drain field, adjacent stream
or pond, etc.). Most local codes forbid the use of sanitary
sewer for disposal. Consult your local building and zoning
department to assure compliance in your area.
The pump should be sized to handle the home’s domestic
water load (typically 5-9 gpm [23-41 l/m]) plus the flow rate
required for the heat pump. Pump sizing and expansion
tank must be chosen as complimentary items. For example,
an expansion tank that is too small can causing premature
pump failure due to short cycling. Variable speed pumping
applications should be considered for the inherent energy
savings and smaller expansion tank requirements.
Water Control Valve
Always maintain water pressure in the heat exchanger by
placing the water control valve(s) on the discharge line
to prevent mineral precipitation during the off-cycle. Pilot
operated slow closing valves are recommended to reduce
water hammer. If water hammer persists, a mini-expansion
tank can be mounted on the piping to help absorb the excess
hammer shock. Insure that the total ‘VA’ draw of the valve
can be supplied by the unit transformer. For instance, a slow
closing valve can draw up to 35VA. This can overload smaller
40 or 50 VA transformers depending on the other controls
in the circuit. A typical pilot operated solenoid valve draws
approximately 15VA. Note the special wiring diagrams later in
this manual for slow closing valves.
Flow Regulation
Flow regulation can be accomplished by two methods. One
method of flow regulation involves simply adjusting the ball
valve or water control valve on the discharge line. Measure the
pressure drop through the unit heat exchanger, and determine
flow rate from tables located later in this manual. Since the
pressure is constantly varying, two pressure gauges may be
needed. Adjust the valve until the desired flow of 1.5 to 2 gpm
per ton [2.0 to 2.6 l/m per kW] is achieved. A second method
of flow control requires a flow control device mounted on
the outlet of the water control valve. The device is typically
a brass fitting with an orifice of rubber or plastic material
that is designed to allow a specified flow rate. On occasion,
flow control devices may produce velocity noise that can be
reduced by applying some back pressure from the ball valve
located on the discharge line. Slightly closing the valve will
spread the pressure drop over both devices, lessening the
velocity noise.
NOTE: When EWT is below 50°F [10°C], a
minimum of 2 gpm per ton (2.6 l/m per kW) is required.
Water Coil Low Temperature Limit Setting
For all open loop systems the 30°F [-1.1°C] FP1 setting
(factory setting-water) should be used to avoid freeze
damage to the unit. See “Low Water Temperature Cutout
Selection” in this manual for details on the low limit setting.
Ground-Water Heat Pump Applications
11
Wa t e r- t o - Wa t e r ( 5 0 Y E R ) S e r i e s - P u r o n
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R e v. : 1 J u l y, 2 0 1 0
