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longer than 7 minutes or where cold water operation is
continuous, provisions must be made to mix higher
t
emperature outlet water with the colder inlet water
and thereby raise the inlet temperature to at least
120°F (49°C) within the 7-minute time limit.
Cold Water Starts
Cold water starts, where the inlet water temperature
remains below 120°F (49°C) for more than 7 minutes,
must
have cold water start protection. Known pro-
tection methods consist of mixing heated outlet water
with the inlet water using a bypass to raise the inlet to
120°F (49°C) or higher. Once the system is heated up
and has return water temperatures of 120°F (49°C) or
higher, the mixing of outlet water with inlet water is no
longer needed and the bypass can be shut off. If the
bypass is not shut off as the system heats up, the out-
let temperature may continue to climb and trip the high
limit, thereby shutting down the heater. Thus an auto-
matic valve system, such as a three-way proportional
valve or a modulating two-way valve to control the
bypass, should be utilized.
Cold Water Run
Cold water run differs from cold water start in that the
system water entering the heater remains below
120°F (49°C) continuously. Typically, this is the case in
swimming pool heating. If the system water is kept in
a narrow temperature range of no more than 10°F
(5°C), a permanent manual bypass can be employed
and manually adjusted to achieve an inlet temperature
of 120°F (49°C) or higher as adjusted at the minimum
t
emperature in this narrow temperature range (i.e.
Range 75°F to 85°F – adjust bypass with temperature
at 75°F (24°C)) so that when temperature is 85°F
(29°C), minimum inlet temperature would be 130°F
(
54°C). An injector pump arrangement may also be uti-
lized to keep the heater loop at or above 120°F (49°C).
An injector pump approach has the added value of
being able to adjust to changes in the system water
coming back to the heater take-off.
Hydronic Heating
Pump Selection
In order to ensure proper performance of your heater
system, you must install a correctly-sized pump. Ray-
pak requires designing for a ∆T within the range of
10°F to 40°F (5°C to 20°C). See Table F for accept-
able flow rates for each model (∆T is the temperature
difference between the inlet and outlet water when the
heater is firing at full rate).
Feedwater Regulator
Raypak recommends that a feedwater regulator be in-
stalled and set at 12 psi minimum pressure at the
highest point of the system. Install a check valve or
back flow device upstream of the regulator, with a
manual shut-off valve as required by local codes.
*
Fig. 9: Cold Water Start
*
Fig. 10: Cold Water Run
*Maximum 4 times the pipe diameter or 12”, whichever is less.
*Maximum 4 times the pipe diameter or 12”, whichever is less.