Product Overview

T
Key to symbols
Safety relief valve
Check valve
Isolation valve
Expansion vessel
Filter
Pump
Domestic water system with recirculation connected to tank
MI
N
M
A
X
7
1
2
Globe Valve
STORAGE
HOT WATER
HEATER
2
1
For domestic recirculating systems that include a single ASSE 1017 point-
of-distribution thermostatic mixing valve, such as the Caleffi 5231 series
thermostatic mixing valves, the piping installation below is recommended.
In any reciculating hot water distribution system there will be times when
the circulator is operating, but no hot water is being drawn at the fixtures.
Under this condition, heat continually dissipates from the piping forming
the recirculation loop. If the loop is relatively short, and well insulated, the
rate of heat loss should be very small. If the loop is long, and uninsulated,
the rate of heat loss could be substantially greater.
To maintain the recirculating water at the desired delivery temperature the
heat lost from the loop must be replaced. This requires some water flow
between the loop and the hot water source. Ideally, this flow is adjusted so
that the rate of heat trasfer from the hot water source to the loop exactly
balances the rate of heat loss from the loop's piping.
The figure (below right) shows a "bypass valve" (1), and "return valve"
(2), which regulates how much warm water from the return side of
the recirculating loop flows back to the storage tank. When there
is no demand for hot water at the fixtures, the flow of return water
to the tank will equal the rate of hot water flow from the tank to the
inlet port of the mixing valve. Ideally, this flow should be adjusted
so that the rate of heat transfer from the tank to the recirculating
loop exactly balances the rate of heat loss from the recirculating loop. This
allows the water temperature leaving the mixing valve to remain stable.
The bypass valve (1) and possibly the return valve (2) must be adjusted
when there is no domestic water draw on the recirculating loop (when all
the fixtures are off). Begin with the bypass valve (1) fully closed, and the
return valve (2) fully open. Turn on the recirculating circulator and let it run
for several minutes. The supply water temperature leaving the mixing valve
will likely be lower than the setting of the valve, since there is no return
flow to the tank.
Slowly open the bypass valve (1) and monitor the temperature leaving the
mixing valve. It will likely begin rising as some water returns to the tank,
and an equal flow of hot water moves from the tank to the hot port of
the mixing valve. When the temperature leaving the mixing valve remains
stable, and is at or very close to the temperature set on the mixing valve,
the bypass valve is correctly set.
The return valve (2) can remain fully open unless a situation occurs where
the bypass valve (1) is fully open, but the temperature leaving the mixing
valve is still too low. If this occurs, partially close the return valve (2) to
add flow resistance. This forces more flow through the bypass valve (1).
Repeat the previously described procedure of slowly opening the bypass
valve (1) until the water temperature leaving the mixing valve is stable.
Recirculation with point-of-distribution thermostatic mixing valves