tekmar 422 Universal Reset Module User Manual

Page 26

D 422 - 08/07

26 of 32

Boiler Target During Setpoint

The boiler target temperature during a Setpoint Demand is
increased to at least the Setpoint setting. This temperature is
maintained as long as the control has a setpoint demand.

Setpoint During UnOccupied

The control has a Setpoint UnOccupied setting that allows
the installer to select On or Off. When set to On, and the
control receives a Setpoint Demand during an UnOccupied or
Sleep period, the control continues operation of the Setpoint
system as it would during Occupied and Wake periods. When
set to Off, the control can ignore a Setpoint Demand for the
duration of the UnOccupied and Sleep periods.

Setpoint Modes

The Setpoint Mode determines the operation of the primary pump.
The Setpoint Mode setting is found in the Adjust menu.

Setpoint Mode 1 - Setpoint in Parallel
Whenever a setpoint demand is present, the boiler is
operated to maintain the setpoint target. The primary pump
(P1) does not turn on, but may operate based on either a
Boiler, Mixing or a DHW Demand.

It is assumed that the Setpoint pump will provide adequate
flow through the heat exchanger and the boiler.

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 2 - Setpoint in Parallel with Priority
When a Setpoint Demand is present, the boiler is operated
to maintain the setpoint target. The primary pump (P1) can
operate when a boiler demand is present. If the boiler is
unable to maintain the boiler target temperature, space heating
zones are shut off sequentially using tN4 communication in
order to provide priority for the setpoint load. This is known
as zone load shedding.

It is assumed that the setpoint pump will provide adequate
flow through the heat exchanger and the boiler.

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.

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.

Primary

Pump

Setpoint

Mode = 3

Setpoint

Primary

Pump

OFF

Mode = 4