John Wood Commercial - AJWS - Manual (Page 11)

Closed System/Thermal Expansion
Periodic discharge of the temperature and pressure relief
valve may be due to thermal expansion in a closed water
supply system. The water utility supply meter may contain a
check valve, backflow preventer or water pressure reducing
valve. This will create a closed water system. During the
heating cycle of the water heater, the water expands caus-
ing pressure inside the water heater to increase. This may
cause the temperature and pressure relief valve to dis-
charge small quantities of hot water. To prevent this, it is
recommended that a diaphragm-type expansion tank (suit-
able for potable water) be installed on the cold water supply
line. The expansion tank must be properly sized for the
application. Contact the local water supplier or plumbing
inspector for information on other methods to control this sit-
uation.
Important: Do not plug or remove the temperature and
pressure relief valve.
11
1 1/2” Cold
water supply
Pressure
Reducing
Valve
Thermometer
Temperature and
Pressure Relief Valve
Hot Water
to Fixtures
Pre-Heater
Pre-Heated
Water to
the Booster
Outlet
Boosted
Temperature
Temperature and
Pressure Relief Valve
Typical
Booster
Heater
Shut-off valve
Thermometer
Thermal
Expansion
Tank
Shut-off
valve Check valve
Figure 8: Commercial Unit with Auxiliary Storage Heater - Forced Circulation With or Without Building Recirculation
- Top Inlet/Outlet Connections
Note: Install a vacuum
relief valve if required
by local codes.
45mm (1 1/2
in) Cold water
supply