Finned copper tube gas boilers & water heaters – Boiler Manual
18
DOMESTIC WATER SUPPLY PIPING
Proper control settings 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. The 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 the 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.
The storage tank must be located as close to the water
heater as possible to prevent excessive head loss which
will reduce flow.
Water Chemistry
The required temperature rise across the water heater is based on
water having a hardness between 8 and 18 grains per gallon with a
level of dissolved solids not exceeding 350 ppm. Water having a
hardness less than 8 grains can cause excessive errosion of the heat
exchanger. Water that has a hardness greater than 18 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. The manufacturer
should be consulted when these water conditions are encountered.
See Table 8A.
The maximum allowable flow rate through a Dominator
water heater with copper heat exchanger is
105 GPM
,
6.6 L/s
. The cupro-nickel heat exchanger allows for
120 GPM
,
7.6 L/s
, see Table 8B.
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 selection. If local water conditions are extreme follow the
guidelines in the Heat Exchanger Selection Table (Table 8A) and the
Pumping Performance Table (Table 8B). 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 flow preven-
tion devices are installed.
Cold Water Supply
The cold water supply must be piped to the water heater's outlet piping
between the water heater and the hot water storage tank. This will
prevent untempered water from entering the water heater, see the
Temperature Rise Control section below. A typical water heating
system is shown in Figure 14 and 15.
Pump Requirements
This low-mass water heater requires a continuous mini-mum water
flow for proper operation. The low water flow switch provided for this
unit will shut down the water heater if flow falls below the required
minimum level. Table 8B provides the heat exchanger pressure drop
chart and temperature rise table.
The temperature rise across
the water heater must never exceed 35°F, 19°C.
Temperature Rise Control
Water returned to the water heater inlet must not be less than
125°F
,
52°C
or excessive condensation of the products of combustion will
damage the water heater voiding the warranty. The method outlined
below can be employed to prevent this condition from occurring.
A balancing valve should be installed on the outlet side of the water
heater for purposes of adjusting the flow rate through the heat
exchanger. Thermometers are installed on both the inlet and outlet
of the water heater for determining the temperature rise through the
unit. The proper velocity through the water heater must be maintained
in accordance with Table 8B for efficient operation and long life. If
the temperature rise through the water heater is lower than
recommended the water velocity is too high. Premature erosion of
the heat exchanger will occur. Conversely, if the temperature rise is
higher than recommended in Table 8B the flow rate is too low. Scaling
and softening of the heat exchanger will occur.
Thermostatic Mixing Valve -
Water Above 140°F, 60°C
Water can be stored at temperatures above
140°F
,
60°C
provided
that a thermostatically controlled mixing valve is used to temper
the hot water to an acceptable temperature before it's supplied for
domestic use.
The mixing valve MUST be set to prevent a scald injury from
occurring, see the caution against scalding above.
Storage of water for domestic use above
140°F
,
60°C
will provide
an increased quantity of tempered water and help prevent the growth
of water born bacteria.
