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Water-to-Water System Design Guide
Part II: Load Side Design / System Design & Selection
Drawing 2-6 – 50PSW/GSW Typical Load Piping - Chilled Water
Cooling / Single Buffer Tank / No DHW Heating or Separate
DHW System: System #6 uses one or more water-to-water
units and a buffer tank for each unit. Drawing 2-6 shows a
typical piping arrangement for this system. Two aqua-stats (well-
mounted if possible) sense tank temperature, one for heating and
one for cooling, which allows the water-to-water unit to engage
the compressor, load pump and source pump(s) when the tank
temperature drops below the set point (typically 120°F [49°C]
or less] in the heating mode, or when the tank temperature rises
above the set point [typically 45-50°F [7-10°C]) in the cooling
mode. The radiant fl oor (or baseboard, radiator, fan coil, etc.)
heating system and the chilled water cooling system (typically
fan coil units) therefore are completely isolated from the water-
to-water unit. The controls for the hydronic distribution system
energize pumps and/or zone valves to allow heated/chilled water
Drawing 2-6: 50PSW / GSW Typical Load Piping -
Chilled Water Cooling System / Single Buffer Tank
- No DHW Heating or Separate DHW System
Cold Water Supply
To/From
Fan Coil Units
To/From
Radiant Floor
18
P.R.V.
Air Vent
Note 1
M
H
C
Cooling
Aqua-stat
Heating / Chilling
Buffer Tank
Notes 2,3
Heating
Aqua-stat
Bryant: Whatever It Takes.
in the buffer tank to fl ow through the heating/cooling distribution
systems. The motorized valves are used to switch between the
two distribution systems (and aqua-stats) based upon heating or
cooling season. Due to the complexity of the controls, a manual
seasonal changeover switch is the best way to determine heated
or chilled water operation. The switch (typically a light switch)
switches the unit reversing valve, motorized valves, and aqua-stats
(additional relays are required for determining heating/cooling
logic). A reversible unit is required for this application (50YEW
is heating only – 50PSW/GSW units are reversible). When using
one tank for both heated and chilled water, a buffer tank (not an
electric water heater) is recommended, since water heaters do not
have enough connections to facilitate all of the water connections
and the two well-mounted aqua-stats. Potable water is heated
with a separate system.
Note 4
Exp
Tank
P/T port (50PSW / GSW only)
See drawings in section 3 for Source connections
IN
OUT
OUT
50PSW
or GSW
Unit
Load HX
Source HX
(coaxial)
(coaxial)
IN
NOTES:
1. Motorized valves to be activated by unit RV solenoid
coil (24VAC).
2. Aqua-stat should be installed in an immersion well.
Locate heating aqua-stat in the bottom half of the tank.
Locate cooling aqua-stat in the top half of the tank.
3. Chilled water tank must be insulated to avoid condensation.
4. Place air vent at the highest point in the system.
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
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