Product Overview

SUPPLY
MIX
3
2
4
WATER
HEATER
Safety relief valve
Check valve
Isolation valve
Expansion vessel
Filter
Pump
Globe valve
SUPPLY
MIX
3
2
4
WATER
HEATER
Safety relief valve
Check valve
Isolation valve
Expansion vessel
Filter
Pump
Globe valve
Keys to symbols
Domestic hot water system with recirculation
1
2
Recirculation with point-of-distribution thermostatic mixing valves
For domestic recirculating water systems that include a single ASSE
1017 point-of-distribution thermostatic mixing valve, such as the Caleffi
MixCal
™
521 series, the piping installation below is recommended.
In any recirculating 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 transfer from the hot water source to
the loop exactly balances the rate of heat loss from the loop’s piping.
The figure (below) shows a “bypass valve” (1), and “return valve” (2),
which regulate 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 thus, no hot water to the hot port of the
mixing valve.
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.