Hydronic Heating - Raypak 503A Installation & Operating Instructions Manual

Cold Water Starts
Cold water starts, where the inlet water temperature
remains below 120°F (49°C) must have cold water
start protection. Known protection 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 outlet temperature may
continue to climb and trip the high limit, thereby shut-
ting down the heater. Thus an automatic valve system,
such as a three-way proportional valve to control the
bypass, should be used.
*Maximum 4 times the pipe diameter or 12", whichever is less.
Fig. 9: Cold Water Start
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
water source heat pump applications as well as some
others. An injector pump arrangement may be used 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 automatically to changes in the system
water coming back to the heater.
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Hydronic Heating

*Maximum 4 times the pipe diameter or 12", whichever is less.
Fig. 10: Cold Water Run
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
16°F to 39°F (9°C to 22°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.
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