tekmar 157 Difference Setpoint Control - Manual (Page 5)

5 of 16 © 2010 D 157 - 06/10
Mode 3 Heat Dump is for applications where an
alternative heat sink can be utilized when the storage tank
and collector are both above their maximum target. The
variable speed pump turns off when the tank exceeds its
max setpoint. The heat dump pump turns on when both
the tank and collectors exceed their max setpoints. If
during a heat dump the storage temperature falls below
its maximum targets less differential, the heat dump pump
relay is turned off and the variable speed pump is allowed
to operate normally. The auxiliary sensor is optional in this
mode. Install the auxiliary sensor in the heat dump. Refer
to application A157-4.
Heat
Storage
Variable
Speed Pump
Heat Dump
Pump
Mode 4 Booster Pump is for drain back applications
where a booster pump is used to overcome high head upon
system startup. When the ΔT rises above the ΔT target,
the control turns on the booster pump and operates the
variable speed pump at 100% output. After an adjustable
time, the control turns off the booster pump and operates
the variable speed pump above the minimum pump speed
setting. Refer to application A157-5.
Booster
Pump
Variable
Speed
Pump Heat
Storage
Table 2: Second Pump Mode Summary
MODE NAME DESCRIPTION APPLICATION
Off Off Only the variable speed pump is operational. A157-1
1
Heat
Exchanger
Heat exchanger pump operates together with the variable speed pump. A157-2
2
Heat
Supplement Heat supplement pump operates independently of the variable speed pump
to maintain the storage tank at the minimum storage target.
A157-3
3 Heat Dump
Heat dump pump operates when the storage and source temperatures rise
above their max targets to dump excess heat from the collectors.
A157-4
4
Booster
Pump Booster pump operates together with the variable speed pump at start up for
an adjustable amount of time to overcome high head in drain back systems.
A157-5
MAXIMUM SOURCE TARGET
(Mode = off, 1, 2, and 4)
If the source temperature rises above the maximum source
target, the variable speed pump is turned off. In a drain
back system, turning off the pump allows the fluid to drain
back into a separate tank which protects the collectors from
overheating. Ceasing operation may also protect equipment
like the pump impeller from damage. The pump remains
off until the source temperature falls below the maximum
source target less differential.
(Mode = 3, Heat Dump)
In order for the heat dump pump to turn on, the storage
temperature must be above the Maximum Storage Setpoint
and the source temperature must be above the Maximum
Source Setpoint. If the source or storage temperatures
fall below their maximum targets less differential, the heat
dump pump is turned off. The variable speed pump operates
normally whenever the storage temperature falls below its
maximum setpoint less differential. This setting ensures
that the water being supplied to the heat dump is at least
the Maximum Source Target temperature.
Table 3: Outlines when the variable speed pump and heat
dump pump are allowed to operate normally in mode 3.
Table 3 Scenario
1 2 3 4
Max Storage Setpoint below above above below
Max Source Setpoint below below above above
Variable Speed Pump on off off on
Heat Dump Pump off off on off
MINIMUM SOURCE TARGET
If the source temperature drops below the minimum source
target, the variable speed pump is turned off. In a drain
back system, turning off the pump allows the fluid to drain
back into a separate tank which protects the collectors from
freezing. The pump remains off until the source temperature
rises above the minimum source target plus differential. This
item is only available if freeze protection is turned off.
Section C: Targets and Differentials