Bryant 50YEW Design Manual page 40

Water-to-Water System Design Guide
Part III: Source Side Design / Open Loop Design
HEAT SOURCE/HEAT SINK
The heat source/heat sink for geothermal systems is determined
based upon the specifi c application. Where water quality is
good and a suffi cient quantity of water is available, an open
loop (well water) source/sink is a very cost effective solution.
Otherwise, one of the three types of closed loop applications
may be a better choice. In any case, operating costs are
very similar, since the source/sink and heat pump are sized
according to the heat loss/heat gain of the home. All residential
applications (open or closed loop) require extended range
equipment. Bryant residential series equipment is standard with
insulated water and refrigerant circuit insulation, designed for
low temperature operation.
Open Loop (Well Water)
Typical open loop piping is shown in Figure 3-3. 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 fl ushing of
the heat exchanger. Shut off valves should be positioned to allow
fl ow through the coaxial heat exchanger via the boiler drains
without allowing fl ow 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 must be plentiful and of good quality. Consult
table 3-1 for water quality guidelines. The unit can be ordered
with either a copper or cupro-nickel water heat exchanger.
Figure 3-2: Typical Open Loop Application
38
Unit Power
Disconnect
Air Pad or
Thermostat
Extruded
Wiring
polystyrene
insulation board
Bryant: Whatever It Takes.
Consult Table 3-1 for recommendations. Copper is recommended
for 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 qualifi ed technician, as acid and special pumping
equipment is required. Desuperheater (HWG) 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 fl ushing. In some cases, the
desuperheater option should not be recommended due to hard
water conditions and additional maintenance required.
Table 3-1 should be consulted for water quality requirements.
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 indices should be calculated. Use the
appropriate scaling surface temperature for the application,
150°F [66°C] for direct use (well water/open loop) and DHW
(desuperheater); 90°F [32°F] 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 be referenced in Table 3-1.
Flow
Water
Regulator
Pressure
Control
Valve
Optional
Filter
Boiler
Drains
P/T Plugs
T ank
Water Out
Water In
Shut-Off
Valve