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Table D-1
ΔP Should include typical piping To/From a single tank as well as bypass piping.
NOTE: gpm flow rates limited by maximum
acceptable velocity through heat exchanger tubes.
May be increased by 10% for closed heating
systems. Pressure drop would increase by 21%.
HYDRONIC HEATING
Pump Selection
In order to ensure proper performance of your boiler
system, you must install a properly sized pump.
Raypak recommends using a 20°F ΔT as design ΔT.
(ΔT is the temperature difference between the inlet
and outlet water when the boiler is firing at full rate). If
a ΔT larger than 20°F is necessary, the bypass must
be installed and adjusted to ensure proper hydraulics
through the boiler while still allowing minimum flow to
satisfy the safety flow switch. See Table E for flow rate
requirements.
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 — Heating Boilers
All high points should be vented. Purge valves and a
bypass valve should be installed. A boiler installed
above radiation level must be provided with a low
water cutoff device. The boiler, when used in connec-
tion with a refrigeration system, must be installed so
the chilled medium is piped in parallel with the boiler
with appropriate valves to prevent the chilled medium
from entering the boiler.
Table E: Rate of Flow and Pressure Drop
The boiler piping system of a hot water heating boiler
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
boiler water during the cooling cycle. It is highly recom-
mended that the piping be insulated.
Air-Separation/Expansion Tank
All boilers should be equipped with a properly sized
expansion tank with an air separation fitting as shown
in the following diagrams.
Three-Way Valves
Valves designed to blend water temperatures or
reduce water circulation through the boiler should not
be used. Raypak heaters are high recovery low mass
heaters not subject to thermal shock. Raypak offers a
full line of electric sequencers that produce direct reset
of boiler water temperature. Refer to the Controls
Section in our Complete Catalog.
13
40°F
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