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Section C: Pump Operation
PRIMARY PUMP OPERATION
The primary pump operates under the following conditions:
• • A boiler demand is present and the control is not in Warm Weather
Shut Down (WWSD).
• • A DHW demand is present and DHW MODE is set to 3 or 4.
Primary Pump Purge
After a demand is removed, the control continues to operate the primary
pump for a period of time. The maximum length of time that the primary
pump continues to run is adjustable using the Primary Pump Purge
setting. The primary pump continues to run until either the purging
time has elapsed or the boiler supply temperature drops more than a
differential below the Boiler Minimum setting.
BOILER PUMP OPERATION
The boiler pump turns on prior to the boiler firing (pre-purge) and continues to run after the boiler is turned off (post-purge). The
boiler pump pre-purge time is determined by the Boiler Mass setting. As the Boiler Mass setting is increased, the boiler pump pre-
purge time of the boiler also increases.
Boiler Pump Purge
The amount of time that the boiler pump continues to run after the boiler turns off is adjustable using the Boiler Pump Purge setting.
Section D: Boiler Reset Operation
BOILER DEMAND
A boiler demand is required in order for the control to provide heat to
the heating system. A boiler demand is generated by applying a voltage
between 24 and 230 V (ac) across the Boiler Demand terminals (1 and
2). Once voltage is applied, the Boiler Demand pointer is displayed in
the LCD. If the control is not in Warm Weather Shut Down (WWSD), the
control closes the primary pump contact. The control calculates a boiler
target supply temperature based on the outdoor air temperature and the
characterized heating curve settings. The control then fires the boiler, if
required, to maintain the target supply temperature.
OUTDOOR DESIGN TEMPERATURE
The outdoor design temperature is the outdoor air temperature that is the typical coldest temperature of the year where the building
is located. This temperature is used when doing the heat loss calculations for the building. If a cold outdoor design temperature is
selected, the boiler supply temperature rises gradually as the outdoor temperature drops. If a warm outdoor design temperature is
selected, the boiler supply temperature rises rapidly as the outdoor temperature drops.
© 2010
D 270 - 08/10
8 of 24
24 to 230 V (ac)
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