tekmar 420 Boiler Reset Module User Manual
Page 20
© 2007
D 420 - 08/07
20 of 24
Setpoint Mode 3 – Setpoint in Primary / Secondary
Whenever a setpoint demand is present, the primary pump
(P1) is turned on and the boiler is operated to maintain the
setpoint target.
Setpoint Mode 4 - Setpoint in Primary / Secondary
with Priority
Whenever a Setpoint Demand is present, the primary pump
(P1) is turned on and the boiler is operated to maintain the
setpoint target. Space heating zones will be shut off using
zone load shedding if the boiler is unable to maintain the
boiler target temperature.
Primary
Pump
Setpoint
Mode = 3
Setpoint
Primary
Pump
OFF
Mode = 4
Setpoint Priority Override
Setpoint Priority Override applies to SETPOINT MODE
2 and MODE 4. To prevent the building from cooling off
too much or the possibility of a potential freeze up during
setpoint priority, the control limits the amount of time for
setpoint priority. As the outdoor air temperature becomes
colder, the length of time the control provides setpoint
priority is reduced. Once the allowed time for priority has
elapsed, the control overrides the setpoint priority and
resumes space heating.
Conditional Setpoint Priority
If the boiler supply temperature is maintained at or above
the required temperature during setpoint generation, this
indicates that the boiler has enough capacity for setpoint
and possibly heating as well. As long as the boiler target
temperature is maintained, setpoint and heating occur at
the same time.
Pump Operation
Section I
Primary Pump
The primary pump is switched on in the following
situations:
•
• There is a Boiler Demand and that zone’s thermostat
has H1 Pump set to On.
•
• There is a DHW Demand and the control is set to DHW
Mode 3 or 4.
•
• The control is completing a DHW Purge.
•
• There is a Setpoint Demand and the control is set to
Setpoint Mode 3 or Mode 4.
DHW Pump
The DHW Pump operates whenever there is a DHW Demand
and the control is not in DHW Priority Override.
DHW Valve
The DHW Valve operates whenever there is a DHW Demand
and the control is not in DHW Priority Override.
Primary
Pump
DHW
Pump
Pump Exercising
Section J
The system control will exercise all pumps, mixing valves and hydronic zones (zone valves and zone pumps) for 10 seconds
every three days to prevent seizure.