A.O. Smith 400 - 2100 Installation & Operation Manual page 37

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Water connections
Pump minimum delta T (T)
A pump minimum T feature is provided in addition to the
pump delay. After a call for heat, the unit will shut down and
the pump will continue to run as long as the T is above the
preset value. The minimum T can be set to ON, 1 to 20°F or
OFF. If set to ON, the pump will run continuously whether or
not there is a call for heat. If set to a value of 1 to 20°F, the pump
will run until the T drops below the set value plus the pump
delay time. Factory default is 5°F. If set to OFF, the pump will
run for 30 seconds after the call for heat.
Maximum delta T (T)
A maximum T feature is provided. If enabled, this will allow
the controller to monitor the water heater's T to allow it to
display a Max T error and enable the alarm circuit should the
programmed value be exceeded. The maximum T can be set
to a value from 80°F to 20°F or OFF. If set to OFF it will disable
this feature. This can be useful to alert the user to either poor
flow or hard water issues. Factory default is OFF.
Pump installation and maintenance
For installation and maintenance information on the circulator
pump, refer to the pump manufacturer's instructions provided
in the instruction package.
Water heater flow rate
The maximum flow rate for Models 400 - 750
CAUTION
is 55 GPM and 90 GPM on Models 1000 -
2100. Do not exceed the maximum flow rate
of the water heater.
If higher flow rates are required through
the water heater, an optional Cupro-Nickel
heat exchanger is available. When using a
Cupro-Nickel heat exchanger, GPM can be
increased by 30 percent. Consult the factory
for specific application requirements.
Flow rate can be determined by measuring the temperature rise
through the water heater.
Minimum water temperatures
Inlet water temperatures below the specified minimum of
140°F (60°C) can excessively cool the products of combustion
resulting in condensation on the heat exchanger. Condensation
on the heat exchanger can cause operational problems, bad
combustion, sooting, flue gas spillage and reduced service life of
the related components.
A water heater allowed to operate at setpoint
CAUTION
temperatures below the specified minimum
settings
problems with the operating controls
and safety switches, obstruction of the
flue gas passages on the heat exchanger,
incomplete combustion and possible flue gas
spillage. Operation at lower than specified
water temperatures may cause hazardous
conditions that result in non-warrantable
damage to the appliance.
(continued)
may experience operational
Installation & Operation Manual
TABLE - 4A
MAXIMUM FLOW FOR HEATING WATER HEATER
The maximum flow rate through the water heater with a
copper heat exchanger must not exceed the following:
Model
400 - 750
1000 - 2100
If higher flow rates are required through the water heater, an
optional Cupro-Nickel heat exchanger is available. Consult the
factory for specific application requirements.
Low system water volume
System run time is very important to the overall operating
efficiency of the unit. Short cycling of the unit creates problems
with condensation in the vent stack, condensation on the
heat exchanger, system temperature spikes, and mechanical
component failures. To prevent short cycling of the water
heater, it is important to limit the cycles to six or fewer per hour.
TABLE - 4B
WATER HEATER TEMPERATURE RISE AT MAXIMUM FLOW
Temperature Rise at Full Rate Fire, 55 and 90 GPM
Maximum Flow
Model
400
500
650
750
1000
1250
1450
1800
2100
Typical water heater installations
General plumbing rules:
1. Check all local codes.
2. For serviceability of the water heater, always install unions.
3. Always pipe pressure relief valve to an open drain.
4. Locate system air vents at highest point of system.
5. Support all water piping.
Maximum Flow
55 GPM
90 GPM
Temperature Rise
12°F (6.7°C) @ 55 GPM
15°F (8.3°C) @ 55 GPM
20°F (11.1°C) @ 55 GPM
23°F (12.8°C) @ 55 GPM
19°F (10.6°C) @ 90 GPM
24°F (13.3°C) @ 90 GPM
27°F (15°C) @ 90 GPM
34°F (18.9°C) @ 90 GPM
39°F (21.7°C) @ 90 GPM
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