Often, it is desirable to limit or stop the flow of heat to the
heating system when the DHW tank calls for heat. This allows
for faster recovery of the DHW tank. The control has several
features that it can use when dealing with DHW priority. The
features available depend on the type of DHW device being
used and the type of DHW demand the control receives.
Mixing Priority (DHW PRI = MIX) (See fig. e)
It can be set up so the DHW tank has priority over mixing
zones. In this case:
• The mixing device is throttled back on a call for DHW
• The mixing system pump (P1) continues to operate based on
the mix demand
• The reduction of the mixing device's output directs more
heat to the DHW tank
NOTE: Boiler zones will continue
to operate without change.
DHW PRIORITY OVERRIDE
To prevent the building from cooling off too much or from a
potential freeze up during DHW priority, the control limits the
amount of time for DHW priority.
• As the outdoor air temperature becomes colder, the length of
time that the control provides DHW priority is reduced
• Once the allowed time for priority has elapsed, the control
overrides the DHW priority and operates DHW and heating
simultaneously
CONDITIONAL DHW PRIORITY
During DHW generation, if the boiler supply temperature
holds at or above the required temperature the boiler has
enough capacity for DHW and possibly the heating system.
• DHW and heating occurs simultaneously as long as the
boiler supply temperature is maintained near its target
Section C2: DHW Priority
65
CONTROL FUNCTION
OVERVIEW
CONTROL FUNCTION OVERVIEW - Section C - Domestic Hot Water
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