tekmar 262 Boiler Control Installation User Manual

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Sequence, Section C2

Internal Demand (DHW SENS = DHW)

If the control receives a

DHW demand from a DHW sensor attached to the Com Sen and the DHW 10K terminals (19 and 20), the

Boil TRG temperature is at least as hot as the DHW TANK setting plus 40˚F (22˚C).

DHW DURING UNOCCUPIED

The DHW operation during an

UnOccupied period depends on the type of DHW demand that the 262 is receiving and the type of setback

that is being used. For this function to operate, the control must have the

Setback / None DIP switch set to Setback.

External Demand (Aquastat )

If an external

DHW Demand is used, the control can either continue operation of the DHW system as it would during the Occupied

period or the control can ignore a call for DHW as long as the control is in an

UnOccupied mode.

Internal Demand (Sensor)

If an internal

DHW Demand is used, a DHW TANK Unocc temperature can be set. This is the temperature that the tank maintains

as long as the control is in an

UnOccupied mode.

Away

If the AWAY setting is made in the

Schd menu, any DHW Demand is ignored and the tank cools off. Note: AWAY does not require

the DIP switch =

Setback.

Section C2 —DHW Priority (Mode = —1—)

DHW PRIORITY (DHW PRI = BOIL)

It is often desirable to limit or even stop the flow of heat to the heating
system when the DHW tank calls for heat. This allows for a faster recovery
of the DHW tank. If DHW PRI is set to Boil, the boiler pump (P1) is turned
off on a call for DHW. This setting is available only if DHW THRU = PUMP
has been selected as the DHW device. If a valve is used as the DHW
device, DHW priority can not be used. Caution should be taken to ensure
that the flow rate of the DHW pump is adequate for both the DHW tank and
the boiler(s), as this will be the only pump providing flow through the
boiler(s).

DHW PRIORITY OVERRIDE

To prevent the building from cooling off too much or the possibility of a
potential freeze up during DHW priority, the 262 limits the amount of time
for DHW priority. As the outdoor air temperature becomes colder, the
length of time that the 262 provides DHW priority is reduced. Once the
allowed time for priority has elapsed, the 262 overrides the DHW priority
and operates DHW and heating simultaneously.

CONDITIONAL DHW PRIORITY

If the boiler supply temperature is maintained at or above the required
temperature during DHW generation, this indicates that the boiler(s) has
enough capacity for DHW and possibly heating as well. As long as the
boiler supply temperature is maintained near its target, DHW and heating
occurs simultaneously.

DHW POST PURGE

After the

DHW Demand is removed, the 262 performs a purge on the boiler(s). The 262 shuts off the boiler(s) and continues to operate

either the DHW pump or the DHW valve and the boiler pump. This purges the residual heat from the boiler(s) into the DHW tank. The
262 continues this purge for a maximum of four minutes or until the boiler supply water temperature drops 20˚F (11˚C) below the DHW
Boil TRG temperature. The 262 also stops the purge if the boiler supply temperature drops below the current Boil TRG temperature.

DHW MIXING PURGE

After DHW operation, the boiler(s) is extremely hot. At the same time, the heating zones may
have cooled off considerably after being off for a period of time. To avoid thermally shocking
the boiler(s) after DHW priority, the 262 shuts off the boiler(s), but continues to operate the
DHW while restarting the heating system. This allows some of the DHW return water to mix
with the cool return water from the zones and temper the boiler return water.

Outdoor air temperature

Increasing Air Temperature

Increasing T

ime

DHW priority demand time limit

DHW