tekmar 363 Universal Reset Control Installation User Manual
Page 10
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Copyright © D 363 -
12/08
Section C2 —DHW Priority
DHW PRIORITY
It is often desirable to limit or even stop the flow of heat to the heating system when the DHW tank calls for heat. This allows faster recovery
of the DHW tank. The 363 has a number of features that it can use when dealing with DHW priority. The features available depend on
the type of DHW device that is being used and the type of
DHW Demand the control receives.
Mixing Priority (DHW PRI = MIX)
It can be selected that the DHW tank has priority over the mixing zones.
If this option is chosen, the mixing device is throttled back on a call for
DHW. The
Mix P2 pump continues to operate based on the Mix Demand.
By reducing the mixing device output, more heat is directed to the DHW
tank. The boiler zones continue to operate without change. This setting
is available if DHW THRU
is set to PUMP or VALV.
Boiler and Mixing Priority (DHW PRI = B+M)
It can be selected that the DHW tank has priority over the boiler and
mixing zones. If this option is chosen, the mixing device is throttled back
and the boiler pump (P1) turns off on a call for DHW. This setting is
available only if a pump is selected as the DHW device (DHW THRU set
to PUMP). Ensure that the flow rate of the DHW pump is adequate for both
the DHW heat exchanger and the boiler.
DHW PRIORITY OVERRIDE
To prevent the building from cooling off too much or the possibility of a potential freeze up
during DHW priority, the 363 limits the amount of time for DHW priority. As the outdoor air
temperature becomes colder, the length of time that the 363 provides DHW priority is reduced.
Once the allowed time for priority has elapsed, the 363 overrides the DHW priority and
operates DHW and heating simultaneously.
CONDITIONAL DHW PRIORITY
If the boiler supply temperature is maintained at or above the required temperature during
DHW generation, this indicates that the boiler has enough capacity for DHW and possibly
heating as well. As long as the boiler supply temperature is maintained near its target, DHW
and heating occurs simultaneously.
DHW POST PURGE
After the
DHW Demand is removed, the 363 performs a purge on the boiler. The 363 shuts
off the boiler and continues to operate either the DHW pump or the DHW valve and the boiler
pump. This purges the residual heat from the boiler into the DHW tank. The 363 continues this
purge for a maximum of four minutes or until the boiler supply temperature drops 20˚F (11˚C)
below the DHW Boil TRG temperature. The 363 also stops the purge if the boiler supply
temperature drops below the current Boil TRG temperature.
DHW MIXING PURGE
After DHW operation, the boiler is extremely hot. At the same time, the heating zones may
have cooled off considerably after being off for a period of time. To avoid thermally shocking
the boiler after DHW priority, the 363 shuts off the boiler, but continues to operate the DHW
while restarting the heating system. This allows some of the DHW return water to mix with the
cool return water from the zones and temper the boiler return water.
External Demand (Aquastat)
If an external
DHW Demand is used, the control can either continue operation of the DHW system as it would during the Occupied
period or the control can ignore a call for DHW as long as the control is in an
UnOccupied mode.
Internal Demand (Sensor)
If an internal
DHW Demand is used, a DHW TANK Unocc temperature can be set. This is the temperature that the tank maintains
as long as the control is in an
UnOccupied mode.
Away
If the AWAY setting is made in the
Schd menu, any DHW Demand is ignored and the tank cools off. Note: AWAY does not require
the DIP switch =
Setback.
Outdoor air temperature
Increasing Air Temperature
Increasing T
ime
DHW priority demand time limit
P
P1
P2
DHW
P
P
P
P2
P1