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Finned copper tube gas boilers & water heaters – Boiler Manual
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Variable Water Flows
Figure 5 shows a typical primary/secondary piping system. A
dedicated pump is used to maintain a constant water fl ow through
the boiler. Th is boiler pump is sized to overcome the head loss of
the boiler and near piping while supplying the fl ow rate required
to maintain the desired temperature rise across the boiler heat
exchanger. Th e system pump is sized to provide the required fl ow
to the heating system.
Low Return Water Temperatures
To prevent the problems associated with condensation of the
products of combustion due to low return water temperatures a
primary/secondary piping system with a bypass and bypass valve
must be installed, see Figures 6 and 6A. Th e bypass and bypass
valve must be sized the same as the secondary piping. A balancing
valve must also be installed in the supply side of the secondary
piping downstream of the bypass. Th e balancing valve should be
adjusted to divert some of the heated discharge water into the return
water until the required inlet water temperature is achieved. Th e
primary and secondary pumps should be sized to provide the required
fl ow through each system.
Multiple Boiler Systems
Systems using multiple boilers can also be installed using a primary/
secondary manifold system, Figure 7.
Piping For Use With Cooling Units
Th e boiler, when used in connection with a refrigeration system,
must be installed so the chilled medium is piped in parallel with
the boiler. Appropriate valves must be used to prevent the chilled
water from entering the boiler.
When a boiler is connected to a heating coil that may
be exposed to refrigerated air from an air handling device, the piping
system must be equipped with fl ow-control valves or some other
automatic means of preventing gravity circulation of the boiler water
during the cooling cycle.
DOMESTIC WATER SUPPLY PIPING
Proper controls must be used to prevent water
supplied for domestic use from exceeding
130°F
,
54°C
or a scald injury will occur! When higher
water temperatures are required for appliances such
as a dishwasher, a mixing valve or some other
tempering means must be installed. Households with
small children may require water temperatures less
than
120°F
,
49°C
. Local codes must be complied with!
General Piping Requirements
Ensure that the water heater is equipped with bronze headers. Piping
and components connected to the water heater must be suitable for
use with potable water. Th e water heater must not be connected to
any heating system piping or components previously used with a
non-potable water heating appliance. No toxic chemicals, such as
those used for boiler treatment, are to be introduced into any potable
water used for space heating. If a hot water storage tank is used in the
system, it must be equipped with a temperature and pressure relief
valve that complies with ANSI Z21.22 or CAN-4.4 and CAN-4.6.
Th e storage tank must be located as close to the water
heater as possible to prevent excessive head loss which
will reduce fl ow.
Water Chemistry
Th e required temperature rise across the water heater is based on
water having a hardness between 5 and 25 grains per gallon with
a level of dissolved solids not exceeding 350 ppm. Water having a
hardness less than 5 grains can cause excessive corrosion of the
heat exchanger. Water that has a hardness greater than 25
grains per gallon and/or a level of dissolved solids exceeding 350
ppm will require a recalculation of the pump size and temperature
rise.
A cupro-nickel heat exchanger may also be required. Th e
manufacturer should be consulted when these water conditions
are encountered. See Table 9A.
RBI water heaters are designed to run scale free. Due to the extreme
variables of water conditions world wide it is necessary to consider
pH values and water hardness in relationship to scaling. It is crucial
to consider these two variables when making heat exchanger and
pump selections. If local water conditions are extreme follow the
guidelines in the Heat Exchanger Selection Table (Table 9A) and
the Pumping Performance Table (Table 9B). Scale free operation
can be achieved by using water with a hardness between 8
and 18 and by maintaining the pH between 5 and 9. Follow the
conditions listed under NORMAL in the table. In some areas of
the country additional precautions must be observed due to unusual
characteristics of the local water supply. Call the nearest RBI
representative for details.
To properly size the pump a grain hardness and pH test
must be taken at the installation site before the order is
placed. Proper pump sizing will improve heater performance and
help ensure heater longevity.
Expansion Tank
An expansion tank or other means to control thermal expansion
must be installed in the water heating system if back fl ow prevention
devices are installed.
