Raypak MVB 503-2003 - Manual (Page 14)

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longer than 7 minutes or where cold water operation is
continuous, provisions must be made to mix higher
temperature 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 to control the bypass, should be used.
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 to 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 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.