Instruction manual

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P/N HN-IOM-1 82-0331 Copyright 2009 Mestek, Inc.
Finned copper tube gas boilers & water heaters – Control manual
Table 9 Setup menus — parameter explanations (continued)
Menu item Under . . . Explanation
OP LIM BAND
SETPOINTS
If the boiler outlet water temperature rises
toward the OPERATE LIMIT setting, the
HeatNet control will begin to reduce the
boiler’s firing rate when the temperature gets
within the limit band degrees F below the
operating limit setting. At the lower end of the
limit band, the boiler can fire up to maximum
input (100%). By the time the temperature
reaches the upper end of the band (the OP
LIMIT setting), the boiler is limited to minimum
input (20%). Example: If OPERATE LIMIT is set to 220°F and OP LIM BAND is set to 30°F, the
boiler will begin to reduce firing rate when the SUPPLY temperature in the boiler exceeds
220° – 30° = 190°F. The boiler firing rate will be reduced to minimum when SUPPLY
temperature reaches 220°F. The boiler will shut off if the SUPPLY temperature rises above
220°F.
Restart — The boiler will not fire again until the SUPPLY temperature drops below the bottom
of the OP LIM BAND. For the example above, the boiler will be allowed to come on again
below 190°F.
The limit band reduces the likelihood of short cycling on boilers controlled by a master
control or a remote control by reducing boiler maximum allowable firing rate as the
temperature rises toward the limit setting. Make sure the lower end of the limit band is above
the upper end of the heat band.
SETPOINT SOURCE
SETPOINTS
Specifies where the space heating setpoint temperature comes from:
AUTO:
With AUTO selected, the HeatNet control determines the setpoint (using local setpoint,
outdoor reset or SYS/DHW HEADER temperature setpoint).
4-20mA:
If 4-20mA is selected, the HeatNet control determines setpoint based on the signal it receives
at the 4-20ma terminals on the connection board.
There must be a contact closure across the 4-20mA ENABLE terminals (J12A) for the boiler to
respond to the 4-20mA signal.
The temperature and boiler start settings are set in the ADVANCED SETUP | 4-20mA INPUT
menus. (The menu will automatically transfer to the 4-20mA INPUT menus if 4-20mA is
selected for SETPOINT SOURCE.)
If the HEAT DEMAND input is closed, the H-NET control will use the SYSTEM SETPT or LOCAL
SETPT temperature to control the boiler(s) if the 4-20ma signal is below 5ma. Once the
current exceeds 5ma, the setpoint is determined from the ma signal value. (This method may
be thought of as a backup in the event the 4-20ma signal is lost.)
If the HEAT DEMAND input is open, the 4-20ma signal will start the H-NET system once the
current exceeds 5ma. Temperature is controlled to the setpoint determined by the milliamp
signal value.
OA RESET
OUTDOOR AIR
Set to “ON” to enable resetting the SUPPLY temperature (or SYSTEM HEADER temperature)
based on outside air temperature. This requires an outdoor sensor when enabled.
Set to “OFF” to disable outdoor reset.
WARM WEATHER SD
OUTDOOR AIR
When this setting is YES, the boiler will shut down when outdoor temperature is at or above
WWS SETPOINT. The outside temperature must drop at least 2°F below the WWS SETPOINT
for the boiler to come on again.
Set to NO to disable.
Control menus and adjustments (continued)
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