tekmar 157 Difference Setpoint Control - Manual (Page 6)

© 2010 D 157 - 06/10 6 of 16
MAXIMUM STORAGE TARGET
If the storage temperature rises above the maximum storage
target, the variable speed pump is turned off. This protects
the tank from overheating by stopping the transfer of heat
from the collectors. The pump remains off until the storage
temperature falls below the maximum storage target less
differential.
MINIMUM STORAGE TARGET
(Mode = 2, Heat Supplement)
This item is only available in Heat Supplement Mode 2.
The heat supplement pump will operate independently of
the variable speed pump to maintain the minimum storage
target at the storage sensor, or optional auxiliary sensor
if connected. If the temperature falls below the minimum
storage target, the heat supplement pump will turn on and
remain on until the temperature rises above the minimum
storage target plus differential. This ensures that there is
heat available in the storage tank for important loads like
domestic hot water.
CAUTION: If storage is used for domestic hot water,
anti-scald protection may be required by some local
codes.
Figure 1 shows an example of how to set up the max and
min storage targets and differentials.
MIN Storage
Target
MIN Storage
Differential
MAX Storage
Target
P1
OFF
P1
OFF
P2
OFF
P2
OFF
P1
ON
P1
ON
P2
ON
P2
ON
100
110
120
130
140
150
160
170
180
190
200
St
orag
e T
e
mperature (°F)
Supplemental Heat Operation
Time
MAX Storage
Differential
Figure 1: Turn on/off points for the variable speed pump
(P1) and the heat supplement pump (P2) in Mode 2. The
min storage target is below the max storage target. Each
have a 10°F (5.5°C) differential.
ΔT TARGET
The ΔT target is the turn on point for the variable speed
pump. Once the ΔT rises above this target the variable
speed pump will operate based on the minimum output
(%), and maximum output (minutes) settings. The control
will continue to vary the speed of the pump until the ΔT
falls below the ΔT target less differential at which point
the pump will run at the minimum output (%) for 2 minutes
before turning off.
MAX AUXILIARY TARGET
This item is only available in Heat Dump Mode 3. If the
auxiliary sensor temperature rises above the maximum
auxiliary target, the heat dump pump is turned off. The
heat dump pump remains off until the auxiliary sensor
temperature drops below the maximum auxiliary target less
differential. Using the auxiliary sensor will prevent the heat
dump, like a pool or second tank, from overheating. There
are no minimum on/off times for the heat dump pump.
MAX A
U
X
Dif
ferential
MAX AUX
Target
OFF
OFF
ON ON
MAX AUX TARGET Operation
Time
Increasing T
e
mperature
Figure 2: On and off points of the heat dump pump, using
an auxiliary sensor in heat dump mode.
FREEZE PROTECTION
If freeze protection is enabled and the source temperature
falls below 35°F (2°C), the variable speed pump will
operate at 100% output for twice as long as it takes the
source temperature to increase to 40°F (4°C). This is
limited to 20 minutes after source temperature reaches
40°F (4°C). This allows the water from the storage tank
to reach the collectors AND flow back to the storage tank
to provide freeze protection to ALL outdoor components.
This item is only available if not in Mode 4.
This item should only be turned on if:
1) other forms of freeze protection, like drain back, are
not being used
and
2) the heat transfer fluid in the collectors is 100% water
and
3) the outdoor air temperature rarely falls below 35°F
(2°C)
Section D – Control Features