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© 2010 D 265 - 07/10
Section D1
Domestic Hot
Water (DHW)
Section D2
DHW w/ Low
Temp Boilers
Section D: Domestic Hot Water Operation
Section D1: Domestic Hot Water (DHW)
DHW operation is available during Boiler Reset (Stand Alone) and External Input operation.
The DHW operation requires the use of the
Boiler 3
/
DHW
contact; therefore, only 2 boilers can be connected to the control. The
BOIL 3 setting must be set to
OFF
before the DHW MODE item will be available.
DHW DEMAND
A
DHW Demand
is required in order for the control to provide heat to the DHW system. A
DHW aquastat or setpoint control is used as a switch in the DHW demand circuit. Once
the control detects a DHW demand, the
DHW Demand
pointer turns on in the LCD and the
control operates the boiler to provide a sufficient boiler supply water temperature to the
DHW tank. The control operates the pumps as described below.
The control registers a
DHW
Demand
when a voltage between 24 and 230 V (ac) is applied
across the
Setp
/
DHW
and
Com
Dem
terminals (31 and 30).
BOILER TARGET DURING DHW GENERATION
The boiler target temperature is at least as hot as the DHW exchange setting
(DHW
XCHG
). The DHW demand overrides the boiler
reset target temperature, except when the boiler reset target is higher than the DHW Exchange setting.
DHW MODE AND PRIORITY OPERATION
The control has five different settings available for DHW MODE. The required DHW MODE setting will depend on the piping
arrangement of the DHW tank.
It is often desirable to have a priority for the DHW allowing for quick recovery of the DHW tank temperature. This is achieved by
limiting or even stopping the flow of heat to the heating system when the DHW tank calls for heat.
DHW Mode Off – No DHW
The DHW feature is not selected.
30 31
Com
Dem
Setp/
DHW
24 to 230 V (ac)
Aquastat
DHW
Pump
Primary
Pump
Boiler
Pump
DHW
Pump
Primary
Pump
Boiler
Pump
DHW MODE 1 - DHW in Parallel no Priority
When a DHW Demand is present, the
Boiler
3
/
DHW
contact
(terminals 21 and 22) closes with the DHW demand. The primary
pump contact does not turn on, but may operate based on a Boiler
Demand, or an External Input Signal.
It is assumed that the DHW pump will provide adequate flow
through the heat exchanger and the boiler.
DHW MODE 2 - DHW in Parallel with Priority
When a
DHW Demand
is present, the Boiler 3 /
DHW
contact (terminals
21 and 22) closes and the primary pump contact is opened.
It is assumed that the DHW pump will provide adequate flow
through the heat exchanger and the boiler.
