tekmar 264 Boiler Control - Manual (Page 8)

© 2008 D 264 - 12/08 8 of 32
Hi (3)
The Hi setting is selected if the boiler(s) that is used has a high thermal mass. This means that the boiler(s) has both a large water
content and a large metal content. A boiler that has a high thermal mass is relatively slow in coming up to temperature. This is
typical of many commercial cast iron and steel tube boilers. The Hi MASS setting stages on additional boilers at the slowest rate.
DIFFERENTIAL
An on / off heat source must be operated with a differential in order to prevent short cycling. With the control, either a fixed or an
auto differential may be selected. The boiler differential is divided around the boiler target temperature. The first stage contact
closes when the supply water temperature is ½ of the differential setting below the boiler target temperature. Additional stages
operate if the first stage is unable to bring the supply water temperature up to the boiler target temperature at a reasonable rate. As
the supply temperature reaches ½ of the differential above the boiler target temperature, stages are staged off.
Section C1
Pump
Operation
PRIMARY PUMP OPERATION
The primary pump operates under the following conditions:
• The control receives a boiler demand and is not in warm weather shut down (WWSD).
• The control receives a DHW demand when DHW MODE is set to 3 or 4.
• The control receives a setpoint demand and setpoint MODE is set to 3.
• The control receives an External Input Signal
Primary Pump Purge
After a demand is removed, the control continues to operate the primary pump for a period of time. The maximum length of time
that the primary pump continues to run is adjustable using the Purge setting. The primary pump continues to run until either the
purging time has elapsed or the boiler supply temperature drops more than a differential below the boiler minimum setting.
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Cooler T
emperature W
armer
Time
Desired temperature
160°F (71°C)
Differential
10°F (6°C) Boiler Off
Boiler On
155°F (68°C)
165°F (74°C)
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Heating Load
On
Differential
Off
Time
OR
Auto Differential
If the Auto Differential is selected, the control automatically
determines the best differential as the load changes. This
reduces potential short cycling during light load conditions.
Section C: Pump Operation
Section C1: Pump Operation
Fixed Differential
If the user desires to have a fixed differential, this is set using
the BOIL DIFF setting in the ADJUST menu.