tekmar 274 Boiler Control User Manual

Page 13

13 of 44

Setpoint Operation

Section F

Setpoint operation is only available when DHW Mode is
set to Off.
The control can operate to satisfy the requirements of a
setpoint load in addition to a space heating load. A setpoint
load overrides the current outdoor reset temperature in
order to provide heat to the setpoint load.

Setpoint Demand
Setpoint Demands come from one of two sources: a
Powered Setpoint Demand, or a tN4 Setpoint Control.

Powered Setpoint Demand
The control registers a Setpoint Demand when a voltage
between 20 and 260 V (ac) is applied across the Setpoint
Demand terminals 23 and 24. An aquastat or setpoint
control is used to switch the Setpoint Demand circuit.
Program a Setpoint target for the Occupied and UnOccupied
events in the Adjust Menu.
• DHW Mode must be set to Off.

tN4 Setpoint Control
The control can register a Setpoint Demand when a tN4
Setpoint Control is wired to terminals 1 and 2. The Setpoint
Demand is sent over the tN4 communication bus when
the Setpoint Control calls for heat. Program a Setpoint
temperature for the Occupied and UnOccupied events and
the desired supply water temperature required on the tN4
bus in the Adjust Menu of the tN4 Setpoint Control.

• DHW Mode must be set to Off.

A demand from a tN4 Setpoint Control can coexist with another
setpoint demand without generating an error message. The
274 will then use the higher of the two targets.

Boiler Target Temperature during a Setpoint Demand
If a Powered Setpoint Demand is present, the boilers are
operated to maintain the Setpoint target. If a tN4 demand
is present, the primary pump is turned on according to
the device’s reported requirements and the boilers are
operated to maintain the devices requested target on the
bus. The Setpoint Demand overrides the boiler reset target
temperature, except when the boiler reset target is higher
than the Setpoint target. Regardless of Setpoint settings
and requested targets, the boilers will maintain a supply
temperature no higher than the Boil MAX setting.

Setpoint During UnOccupied
When using a Powered Setpoint Demand, 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 the Occupied and Wake periods. When set
to Off, the control will ignore a Setpoint Demand for the
duration of the UnOccupied and Sleep periods.

DIP Switch must be set to Setback to view UnOccupied
items.
During the Away Scene, Setpoint demands are ignored.

Setpoint Mode Setting in the Adjust Menu
The control has four different Setpoint Modes that affect
pump operation. The required Setpoint Mode setting will
depend on the piping arrangement and whether or not
priority is necessary. Setpoint Priority stops or limits the
delivery of heat to the building heating system while the
Setpoint load calls for heat. This allows for quick recovery
of the Setpoint load.

Mode OFF

No Setpoint Operation

All Setpoint demands are ignored. If this mode is selected
while Setpoint operation is underway, all Setpoint operation
ceases.

Mode 1

Setpoint in Parallel with No Priority

Whenever a Setpoint Demand is present, the boilers are
operated to maintain the setpoint target. The primary
pump does not turn on, but may operate based on a Boiler
Demand. It is assumed that the Setpoint pump will provide
adequate flow through the heat exchanger and the boiler.

Primary

Pump

Setpoint

Mode = 1

Mode 2

Setpoint in Parallel with Priority

When a Setpoint Demand is present, the boilers are
operated to maintain the setpoint target. The primary
pump can operate when a Boiler Demand is present. If the
boilers are unable to maintain the boiler target temperature,
space heating zones are shut off sequentially using tN4
communication in order to provide priority to the Setpoint
Load. For non-tN4 systems, the primary pump shuts off to
provide priority. It is assumed that the Setpoint pump will
provide adequate flow through the heat exchanger and
the boiler.

Setpoint

Primary

Pump

OFF

Mode = 2