Bosch BSS250E-2 Installation And User Manual page 33

Your SolaStat-Eco is pre-programmed in the factory as per below:
Pump ON Pump OFF Top Out Frost
12 °c 6°c 75°c 4°c
Your SolaStat-Eco has a microcomputer at its core that intelligently and automatically controls
your solar hot water system at greater efficiency. The SolaStat-Eco measures water
temperatures at 2 different places in the system and turns on a water pump at the optimum
time.
The pump moves hot water from the solar collector into the hot water tank.
The SolaStat-Eco has advanced features that; protect the system from damage, run self
diagnostics, self correction of some problems and will keep you informed as to what the
SolaStat-Eco is measuring and what decisions it is making.
Principle of operation:
The solar hot water panel sensor is called „ROOF‟
The lower hot water tank sensor is called „INLET‟
The SolaStat-Eco is a differential solar hot water controller. The controller measures the
temperature at the „Roof‟ sensor and compares this to the „Tank‟ sensor. If the difference
between the roof and the tank is greater than the programmed upper limit (typically 12C) then
the pump turns on and transfers heated water from the solar collector to the tank and replaces
this with cooler water from the bottom of the tank. When this happens the tank heats up and
the collector tends to cool down.
The heat difference is reduced to a point where the lower limit (typically 6C) is reached and the
pump turns off. This cycle repeats as long as the sun shines and there is a difference in
temperature, the tank heats up progressively this way.
There is a huge amount of energy in sunshine, as high as 1000 watts per square metre. This
can lead to water temperatures present in the hot water tank beyond what it is designed to
handle (close to boiling). This is especially true of „ceramic‟ lined tanks. Also pressure can
build which can cause other plumbing problems. To protect the hot water tank and stop
pressure problems a maximum temperature can be set called „Topout‟. This will prevent the
pump from moving any more water from the collector until the tank has cooled to a safe level.
To protect the solar collector from freezing in mild frost areas the „Frost‟ function can be
enabled.
This will turn the pump on to move a small amount of water through the collector. Heavy frost
areas may need other solutions such as glycol based systems or drain down.
The SolaStat-Eco has other special features to those mentioned above.
· Pump Timer: This is an optional factory setting to assist in pump cavitation recovery. After
the pump has run continuously for approximately ten minutes, it will turn off for one minute.
This cycle is repeated as long as the pump is required to run and will not affect normal
operation in a standard hot water collector and cylinder installation. The one minute turn off
period helps any accumulated air to escape from the pump and has been effective as a
backup in exceptional conditions. This feature can help prevent the pump running for hours in
a „locked up‟ state, increasing the installation reliability. Also refer „Plumbing Issues, Cavitation‟
· 20°C lockout: If the collector is less than 20°C it will not contribute any useful heat, even to
cold water. Therefore the controller will not turn the pump on under differential conditions
(„frost‟ protection still works).
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