tekmar 156 Difference Setpoint Control - Manual (Page 4)

© 2010 D 156 - 06/10 4 of 12
MAXIMUM STORAGE SETPOINT
If the measured storage temperature rises above the Maximum Storage Setpoint, the relay is turned off. The relay remains
off until the storage temperature drops below the Maximum Storage Setpoint less the Maximum Storage Differential.
The Maximum Storage Setpoint stops the transfer of heat when the storage temperature rises above the Maximum
Storage Setpoint, which prevents the storage tank from over heating. Turning off the relay allows heat to be drawn out of
the tank to satisfy any heating loads without heat being returned to the tank from the heat source, thus lowering the tank
temperature.
Relay operation showing the
turn on and turn off points with
respect to the Max Storage
Setpoint and Differential.
Relay operation showing the
turn on and turn off points with
respect to the Min Source
Setpoint and Differential.
Min Source
Differential
Min Source
Setpoint
ON ON
OFF OFF
OFF
Increasing Time
Increasing T
e
mper
ature
Increasing Time
MINIMUM SOURCE SETPOINT
If the measured source temperature drops below the Minimum Source Setpoint, the relay is turned off. The relay remains
off until the source temperature rises above the Minimum Source Setpoint plus the Minimum Source Differential.
The Source Minimum Setpoint does not provide freeze protection; it only stops the transfer of heat when the source
temperature falls below the Minimum Source Setpoint. The heat source is still susceptible to freezing. Turning off the relay
allows the heat source to gain heat by stopping the heat transfer to the storage tank.
Max Storage
Differential
Max Storage
Setpoint
ON
ON
ON
OFF
OFF
Increasing Time
Increasing T
e
mper
ature
Increasing Time
ΔT SETPOINT
The control measures the difference between the source and the storage temperatures (ΔT). When the measured ΔT is
greater than the ΔT setpoint, the relay is turned on to transfer heat from the source to the storage. If the ΔT drops below
the ΔT Setpoint less the ΔT Differential, the relay is turned off.
ΔT Differential
ΔT
Setpoint
ON ON
OFF OFF
OFF
Increasing Time
Increasing ΔT
Relay operation showing
the turn on and turn off
points with respect to the ΔT
Setpoint and ΔT Differential.
Typical Settings ΔT Setpoint Differential
With a heat exchanger 15 to 25°F (8 to 14°C) 10 to 15°F
(6 to 8°C) Without a heat exchanger 13 to 21°F (7 to 12°C)