tekmar 157 Difference Setpoint Control User Manual

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MINIMUM OUTPUT, %

This item selects the minimum speed the variable speed
pump will run in order to avoid unwanted drain back when
the pump is running at low speeds in a drain back system.
At low speeds, some pumps stall and provide no flow. It is
important to set the minimum pump speed above this stall
point. This setting is adjustable between 0% and 100%.
At 100% output the variable speed pump operates as an
on/off pump.

MAXIMUM OUTPUT, minutes

When the variable speed pump turns on, it will operate at
100% output for this adjustable amount of time to overcome
high head when filling a drain back system. If the control
is in booster pump mode 4, the variable speed pump and
the booster pump will operate together at 100% output for
this adjustable amount of time.

This item can be used in drainback applications with or
without a booster pump. Set this item to the time it takes
the fluid to circulate through the collectors and into the
drainback tank.

This item can also be used to prevent short cycling of
the pump upon startup in non-drain back applications.
When the variable speed pump turns on, the warm water
in the collector passes by the source sensor causing its
temperature to rise. Once all this water has passed, the
cooler water in the pipe before the collector will pass by the
source sensor causing the temperature to drop; potentially
enough to loose the delta T and thus turn off the pump.

This sequence could happen a number of times before
the system stabilizes and the variable speed pump runs
continuously.

Setting the maximum pump speed (minutes) to the time it
takes the fluid in the storage tank to reach the collectors
will force the system to stabilize and thus reduce any short
cycling of the pump at startup. This is especially important
when the ambient outdoor temperature is very cool.

MONITORING TEMPERATURES

The control includes monitoring of minimum and maximum
Source, Storage, and Auxiliary temperatures in the view
menu. These items may be reset to their respective current
sensor temperature by pressing and holding the ▲ and
▼ buttons simultaneously for 1 second while viewing the
selected item. ‘Clr’ will then be displayed followed by
the value being reset to its respective current sensor
temperature when the buttons are released.

PUMP 2 RUNNING HOURS

The control includes monitoring of the second pump’s
running hours in the view menu where 1 count equals 1
hour. This item may be reset to zero by pressing and holding
the ▲ and ▼ buttons simultaneously for 1 second while
viewing this item. ‘Clr’ will then be displayed followed by the
value being reset to zero when the buttons are released.

Section E – Energy Calculation

To calculate the amount of heat the system has transferred
from the solar collectors to the storage tank, the control
uses the following equation and displays ENERGY in the
view menu in BTU’s or kWh:

Total Heat Transferred = (%ΔT hours) x (Flow) x K

Where:

%ΔT hours is calculated by the control.
Flow is the amount of fluid the variable speed pump moves

through the system in US Gallons per minute.

K is a fluid constant to be programmed in the adjust menu.

K is a constant calculated by multiplying the properties of the
fluid; specific heat (BTU/lbm°F) by density (lbm/USGal) by
60 (min/hr). For example, 100% water has a specific heat of
1 BTU/lbm°F and a density of 8.33 lbm/USGal. Therefore
the value of K in this case is 1 x 8.33 x 60 = 500.

The value of K depends on the percent of glycol added to
the heat transfer fluid. Select an appropriate K value from
table 1 and program it into the adjust menu. If 100% water
is used, select K = 500.

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•

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Table 4: K values for different heat transfer solutions based
on % glycol.

Ethylene Glycol Solution

Propylene Glycol Solution

Freezing

Point (°F)

K @

40°F

Freezing

Point (°F)

K @

40°F

500

492

495

483

489

471

480

-13

453

-8

463

-36

433

-29

443

-70

412

-55

422

FLOW

In the adjust menu, enter the actual flow rate of the variable
speed pump operating at 100% output in US Gallons per
minute (GPM).
Note:

BTU

= British Thermal Unit

lbm =

Pound

Mass

USGal

Gallon

GPM

= Gallon Per Minute