tekmar 263 Boiler Control - Manual (Page 16)

© 2009 D 263 - 03/09 16 of 36
CONDITIONAL DHW PRIORITY
The Conditional DHW Priority Override applies to DHW MODE 2 and 4. 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 control performs a purge on the boiler(s). The control shuts off the boiler(s) and continues
to operate either the DHW pump or the DHW valve and the system and boiler pump if applicable. This purges the residual heat
from the boiler(s) into the DHW tank. The control continues this purge for a maximum of four minutes or until the boiler supply water
temperature drops 20°F (11°C) below the boiler target temperature during the DHW operation. The control also stops the purge if
the boiler supply temperature drops below the current boiler target 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 in
parallel with priority (DHW MODE 2), the control shuts off the boiler(s),
but continues to operate the DHW pump 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.
DHW DURING UNOCCUPIED
The DHW operation during an unoccupied period (UNOCC) depends on the type of DHW Demand that the control is receiving. For
this function to operate, the control must have the Setback / None DIP switch set to Setback.
External Demand (DHW Sensor DIP Switch = Off)
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 (DHW Sensor DIP Switch = DHW Sensor)
If an internal DHW Demand is used, a DHW UNOCC temperature can be set. This is the temperature that the tank maintains as
long as the control is in an unoccupied mode. The DHW UNOCC can also be set to Off so that a call for DHW is ignored as long
as the control is in an unoccupied mode.
NUMBER OF BOILERS USED FOR DHW GENERATION
The number of boilers used for DHW generation can be selected to either one or two. This setting is only available when the control
is operating in Mode 1 - Two ON / OFF Stages.
Section E2: DHW with Low Temperature Boilers
If DHW is to be incorporated into a low temperature system such as a
radiant heating system, a mixing device is often installed to isolate the high
DHW supply temperature from the lower system temperature. If a mixing
device is not installed, high temperature water could be supplied to the
low temperature system while trying to satisfy the DHW demand. This may
result in damage to the low temperature heating system. The control is
capable of providing DHW in such a system while maximizing the chance
that the temperature in the heating system does not exceed its allowed
Boiler Maximum
setting.
To prevent high temperature water from being introduced into the heating
system, the primary pump (Prim P1) must be turned off during a call for
DHW. To do this, the control must be set to DHW MODE 2 or DHW MODE 4
and Boil MIN must be set to OFF.
DHW MODE 2 OPERATION
On a call for DHW, the control provides DHW priority by shutting off the primary pump (Prim P1) for a period of time. This time
is based on the outdoor air temperature as described in the DHW Priority Override section. However, if the DHW Demand is not
satisfied within the allotted time, the boiler(s) shuts off and the heat of the boiler is purged into the DHW tank.
Once the boiler supply temperature is sufficiently reduced, the DHW Pmp / Vlv contact shuts off. The heating system is turned on
for a period of time to prevent the building from cooling off. After a period of heating, and if the DHW Demand is still present, the
control shuts off the heating system and provides heat to the DHW tank once again.
DHW
Pump
Primary
Pump Boiler
Pump
DHW
Pump
Primary
Pump Boiler
Pump