tekmar 402 House Control Installation - Manual (Page 27)

27 of 32 © 2010 D 402 - 09/10
Auto Differential -------------------------------- --------------------------------
Both on-off and modulating boilers are operated with
a differential. In some cases, a modulating boiler must
be operated with a differential while operating at low
fire because this indicates the load is smaller than
the minimum modulation of the boiler. For modulating
boilers, the differential no longer applies once operating
the boiler above low fire.
The differential operates by closing the boiler contact
when the boiler supply water temperature is 1/2 of the
differential below the boiler target temperature. As the
supply temperature reaches 1/2 of the differential above
the boiler target temperature, the boiler is shut off.
+1/2 Differential
- 1/2 Differential
Boiler Target
Boiler On
Boiler Off
In order to decrease temperature swings and increase boiler
efficiency, the Auto Differential feature automatically adjusts
the operating differential of the boiler based on the heating
load. As the load increases, the differential will decrease
to minimize temperature swings. As the load decreases,
the differential will increase to prevent short cycling. This
can significantly improve operating efficiency and prevent
equipment failures through excessive cycling.
Off
Differential
Time
Heating Load
On
Domestic Hot Water Heat Source Section G
The 402 can use a high-efficiency water heater as a source
of heat for space heating zones in addition to providing
domestic hot water. This is an open-loop system in which
potable water is circulated through the zones. When the
flushing feature is set to on, the mixing valve is moved to the
fully open position, all four zone valves are opened, and the
mix system pump is turned on for 5 minutes each day. This
prevents stagnation of the water in the heating system.
402
070
Pump Operation Section H
Mix System Pump ------------------------------ ------------------------------
The mix system pump operates whenever all the
following conditions are met:
A Mix Call is present.
The thermostat calling for heat has the Heat 1 pump
setting set to On.
The heating system is not in Warm Weather Shut Down.
Boiler System Pump ---------------------------- ----------------------------
The boiler system pump operates whenever all the
following conditions are met:
A Mix or a Boiler Call is present.
The thermostat calling for heat has the Heat 1 pump
setting set to On.
There is no DHW priority.
The heating system is not in Warm Weather Shut Down.
DHW Pump ------------------------------------- -------------------------------------
The DHW pump operates whenever all the following
conditions are met:
A DHW Call is present.
The heating system is not in DHW priority override.
DHW post purge.
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Variable Speed Injection Pump ----------------- -----------------
The variable speed pump operates whenever the
following conditions are met:
A Mix Call is present.
The heating system is not in Warm Weather Shut
Down.
Note: The variable speed pump operates at minimum
speed whenever the boiler supply temperature falls below
the boiler minimum setting and whenever there is a DHW
Call and DHW priority has been selected.
Pump Exercising ------------------------------ ------------------------------
The control operates each pump every three days for 10
seconds to help prevent corrosion and / or precipitate build
up on the pump components that can lead to pump seizure.
The control ensures that no heat is supplied to the zones
during exercising.
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