tekmar 401 House Control Installation - Manual (Page 21)

21 of 28 © 2011 D 401 - 07/11
DHW Mode 5 - DHW in Near Boiler Piping with
Priority
DHW Mode 5 requires that a DHW sensor be located on
the boiler outlet pipe and a DHW call from an aquastat
inside the DHW tank. The aquastat operates the DHW
tank temperature while the DHW sensor is used to control
the boiler temperature delivered to the DHW indirect heat
exchanger.
When a DHW Call is present, the DHW pump is activated.
All boiler temperature zones are shut off through tekmarNet
®
communication to achieve DHW priority.
It is assumed that the DHW pump will provide adequate
flow through the 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 control limits the amount of time for DHW priority
during cold weather. During warm weather the DHW
priority is 120 minutes. During cold weather the DHW
priority is 15 minutes. Once the allowed time for priority
has elapsed, the control overrides the DHW priority and
resumes space heating for 15 minutes. It will then revert
back to DHW Priority and repeat.
DHW Post Purge ------------------------------ ------------------------------
After the DHW Call is removed, the control performs a purge
on the boiler. The control shuts off the boiler and continues
to operate the DHW pump. This purges the residual heat
from the boiler into the DHW tank. The control continues
this purge for a maximum of two minutes. The control also
stops the purge if the boiler supply temperature drops
below the current boiler target temperature.
ON
DHW
Sensor
OFF
DHW
Pump Zone
Pump
Boiler
Pump
Boiler
Sensor
DHW Mode = 5
DHW Priority Override Time
Increasing Time
Decreasing Outdoor Air Temperature