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Drawing 2-2 – 50YEW Typical Load Piping Water Heater with
Secondary Heat Exchanger / No Cooling or Separate Cooling
System: System #2 uses one or more water-to-water units
and a buffer tank for each unit. Drawing 2-2 shows a typical
piping arrangement for this system. A thermistor mounted in
an immersion well senses tank temperature, which allows the
internal controls (50YEW units only) to engage the water-to-water
unit compressor, load pump and source pump(s) when the tank
temperature drops below the set point, typically 120°F [49°C]
or less. The radiant fl oor (or baseboard, radiator, fan coil, etc.)
system therefore is completely isolated from the water-to-water
unit. The controls for the hydronic distribution system energize
pumps and/or zone valves to allow heated water in the buffer
tank to fl ow through the heating distribution system. Potable
water is heated via a direct water heater (typically an electric
water heater) and a secondary heat exchanger (typically a brazed
plate heat exchanger), so that heating system water and potable
water do not mix. The 50YEW unit has an internal motorized
valve, which allows the load pump to send heated water to the
buffer tank or the secondary heat exchanger for heating potable
water. A thermistor mounted in an immersion well senses tank
Drawing 2-2: 50YEW Typical Load Piping -
Water Heater with Secondary Heat Exchanger /
No Cooling or Separate Cooling System
H
C
Direct
Secondary
Water Heater
Note 2
Thermistor
To/From
Radiant Floor,
Radiator,
Baseboard,
or Fan Coil
Heating System
H
Heating
Buffer Tank
Note 3
Bryant Geothermal Heat Pump Systems
Part II: Load Side Design / System Design & Selection
P.R.V.
Pump
Air Vent
Plate Heat
Exchanger
Exp
Tank
C
Thermistor
Note 2
Water-to-Water System Design Guide
temperature, which allows the internal controls (50YEW units
only) to engage the water-to-water unit compressor, load pump
and source pump(s) when the tank temperature drops below
the set point, typically 130°F [54°C]. The use of a direct water
heat and secondary heat exchanger requires a pump between
the secondary heat exchanger and the water heater. The addition
of a pump contactor near the water heater will be necessary to
energize the pump any time the 50YEW load pump is energized
for potable water heating. If desired, the 50YEW controls allow
emergency water heating via electric elements if the 50YEW unit
is locked out. This requires a contactor at the water heater to
energize the electric elements when the heat pump is locked out.
Cooling is accomplished with a separate system.
Secondary Heat Exchanger Sizing: Due to the
lower water temperatures associated with heat
pumps (as compared to 180-200°F [82-93°C] boiler
temperatures), heat exchanger sizing is critical.
Bryant recommends the use of sizing software
provided by the heat exchanger manufacturer. An
example is shown in fi gure 2-5. NOTE: Even though
the maximum leaving water temperature of the
50YEW series equipment is 145°F [63°C], some
room for piping changes, pump performance, and/
or pressure switch tolerance, should be considered
via slightly lower design temperatures (143°F [62°C]
is shown in fi gure 2-5 example). Refrigerant high
pressure switches typically have a tolerance of ± 15
psi [±1 Bar], potentially resulting in nuisance faults if
the switch tolerance is on the lower side of the range.
The compressor is rated for 145-149°F [63-65°C]
operation, but if the switch is marginal, a slightly
conservative design temperature will help avoid
nuisance faults.
Note 2
See drawings in section 3 for Source connections
IN
IN
OUT
OUT
OUT
IN
HTG
DHW
HTG
DHW
M
50YEW
Unit
Load HX
Source HX
(brz plt)
(coaxial)
NOTES:
1. Place air vent at the highest point in the system. If
internal expansion tanks are installed, only an air
vent is required.
2. Thermistors should be installed in an immersion well.
Locate thermistor in the bottom half of the tank.
3. If electric water heat is used instead of buffer tank, see
drawing 7.
4. P/T (pressure/temperature) ports are internal for
50YEW units on load and source connections.
5. Other components (additional ball valves, unions, etc.)
may be required for ease of service. This drawing
shows only minimum requirements. Your specific
installation will dictate final component selections.
6. Buffer tank must be approved as a heating vessel.
7. Local code supercedes any piping arrangements or
components shown on this drawing.
03Oct07
13
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