©
2012 274_D
-
11/12
10
of
44
DHW Differential Setting in Adjust Menu
Due to large differences between the heating load and the
DHW load, a separate DHW differential should be used
whenever a DHW Demand is present. This will improve
staging and boiler cycling. When using a DHW Sensor, a
DHW Demand is registered when the DHW sensor drops 1/2
of the DHW Differential setting below the DHW setting. The
DHW Demand is satisfied once the DHW Sensor rises 1/2
of the DHW Differential setting above the DHW setting.
DHW
Differential
DHW Target
ON
OFF
Boiler Target Temperature during a DHW Demand
If a Powered DHW Demand is present, the boilers are
operated to maintain the DHW Exchange temperature. If a
DHW sensor demand is present, the boilers are operated
to maintain a temperature 40°F above the DHW tank
temperature. If a tN4 demand is present, the primary
pump is turned on according to the device’s reported
requirements and the boilers are operated to maintain the
devices requested target on the bus. The DHW Demand
overrides the boiler reset target temperature, except when
the boiler reset target is higher than the DHW target.
Regardless of DHW settings and requested targets, the
boilers will maintain a supply temperature no higher than
the Boil MAX setting.
DHW During UnOccupied
When using a Powered DHW Demand, the control has a
DHW Exchange UnOccupied setting that allows the installer
to select On or Off. When set to On, and the control receives
a DHW Demand during an UnOccupied or Sleep period,
the control continues operation of the DHW system as it
would during the Occupied and Wake periods. When set to
Off, the control will ignore a DHW Demand for the duration
of the UnOccupied and Sleep periods.
When using a DHW Sensor, a second DHW temperature
setting is available for the UnOccupied or Sleep period.
DIP Switch must be set to Setback to view UnOccupied
items.
During the Away Scene, DHW demands are ignored.
DHW Mode Setting in the Adjust Menu
The control has six different DHW Modes that affect pump
operation. The required DHW Mode setting will depend on
the piping arrangement of the DHW tank and whether or
not priority for DHW is necessary. DHW Priority stops or
limits the delivery of heat to the building heating system
while the DHW tank calls for heat. This allows for quick
recovery of the DHW tank.
Mode OFF / No DHW Generation
All DHW demands are ignored. If this mode is selected while
DHW generation is underway, all DHW operation stops.
Mode 1 - DHW in Parallel with No Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) turns on. The primary pump can operate
when a Boiler Demand is present. It is assumed that the
DHW pump will provide adequate flow through the heat
exchanger and the boiler. Heating zones are unaffected
by DHW operation.
Mode = 1
DHW
Pump
Primary
Pump
Mode 2 - DHW in Parallel with Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) turns on. The primary pump can operate
when a Boiler Demand is present. If the boilers are unable
to maintain the boiler target temperature, space heating
zones are shut off sequentially using tN4 communication
in order to provide priority to the DHW tank. For non-tN4
systems, the primary pump shuts off to provide priority. It
is assumed that the DHW pump will provide adequate flow
through the heat exchanger and the boiler.
Mode = 2
DHW
Pump
Primary
Pump
OFF