Raypak 302B-902B - Manual (Page 17)

17
Pressure Drop in Feet of Head
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. Purge valves and a
bypass valve should be installed. A heater installed
above radiation level must be provided with a low wa-
ter cut-off device (sales order option F-10). The 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
equipped with flow control valves or other automatic
means to prevent gravity circulation of the heater
water during the cooling cycle. It is highly recommend-
ed that the piping be insulated.
Air-Separation/Expansion Tank
All heaters should be equipped with a properly sized
expansion tank and air separator fitting as shown in
Fig. 10.
Three-Way Valves
Valves designed to blend water temperatures or
reduce water circulation through the heater should not
be used. Raypak heaters are high-recovery, low-mass
Fig. 10: Air-Separation/Expansion Tank
heaters which are not subject to thermal shock.
Raypak offers a full line of electronic sequencers that
produce direct reset of heater water temperature.
(Refer to the Controls section of the Raypak Catalog.)
Domestic Hot Water
When designing the water piping system for domestic
hot water applications, water hardness should be con-
sidered. Table I indicates the suggested flow rates for
soft, medium and hard water. Water hardness is ex-
pressed in grains per gallon.
NOTE: BYPASS FOR
LOW TEMP SYSTEMS ONLY
SYSTEM SENSOR
12” MAX
OR MIN FEASIBLE
5’ MAX
Fig. 11: Single Heater - For Hydronic or Heat Pump
Primary/Secondary Piping
12” MAX
OR MIN FEASIBLE
SYSTEM SENSOR
(LESS THAN
4:1 TURNDOWN)
5’ MAX
5’ MAX
SYSTEM SENSOR
(4:1 TURNDOWN
OR GREATER)
Fig. 12: Dual Heaters (Reverse/Return)
with Primary/Secondary Piping