Raypak 503-2003 - Manual (Page 14)

14
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 and water source heat pump
applications as well as some others. 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 adjust-
ed at the minimum temperature in this narrow
temperature range (i.e. Range 75°F – 85°F – adjust
bypass with temperature at 75°F (24°C)) so that when
temperature is 85°F (29°C), minimum inlet tempera-
ture would be 130°F (54°C). An injector pump
arrangement may also be utilized 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 recommends designing for a ΔT 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 (ΔT 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.
Piping
All high points should be vented. A heater installed
above radiation level must be provided with a low wa-
ter cut-off device (sales order option F-10). This
heater, when used in connection with a refrigeration
system, must be installed so that the chilled medium is
piped in parallel with the heater with appropriate
valves to pre-vent the chilled medium from entering
the heater.
The piping system of a hot water heater connected to
heating coils located in air handling units where they
may be exposed to circulating refrigerated air, must be
*
Fig. 7: Cold Water Start
*
Fig. 8: 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.