19.01-4
SolaStat-Plus Users Guide.
Your SolaStat-Plus has a microcomputer at its core that intelligently and automatically controls your solar
hot water system at greater efficiency. The SolaStat-Plus measures water temperatures at three 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-Plus-2 (with the addition of the SolaStat-Rly) allows intelligent control of the electric element
used in the hot water tank (HWC control). The SolaStat-Plus-2 can prevent the electric element coming on
for a programmed time interval when Solar Hot Water is already being transferred into the hot water tank
(Holdoff Timer). While making sure you don’t run out of hot water (Reheat) and being vigilant that safe
water conditions are maintained (BioSafe). These controls should save a considerable amount of electricity.
The SolaStat-Plus 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-Plus is measuring and
what decisions it is making.
Principle of operation.
The solar hot water collector sensor is called: ‘ROOF’
The upper hot water tank sensor is called: ‘TANK’
The lower hot water tank sensor is called: ‘INLET’
The SolaStat-Plus is a differential solar hot water controller. The controller measures the temperature at the
‘ROOF’ sensor and compares this to the ‘Inlet’ sensor. If the difference between the roof and the inlet 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-Plus 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 DegC lockout: If the collector is less than 20C 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).
· Sensor diagnostics: The SolaStat-Plus constantly checks the sensors. If a sensor is below -20C the
display reads ‘Lo’. If a sensor is above 140C the display reads ‘Hi’. If the roof sensor reads ‘Hi’, the pump is
disabled. If a sensor is outside the specified temperature range of -40C to 150C then the Display reads
‘SSd’ and the controller enters Smart Shutdown mode. When the display reads ‘SSd’ the sensor has either
a steady light for a temperature above 150C (possibly shorted sensor or wire) or a flashing light for a
temperature below -40C (possibly open sensor or broken wire). For example if the ‘Roof’ sensor wire is cut
during some building work then the SolaStat-Plus display reads ‘SSd’, the ‘Roof’ light flashes and the
controller enters Smart Shutdown mode until the wire is repaired.
· Smart Shutdown (SSd): In Smart Shutdown mode, the Display reads ‘SSd’ and the pump is dis-
abled except for ‘Frost’ protection when the Roof sensor is working. During Smart Shutdown for the SolaStat-
Plus-2, the HWC output is activated and the Hot Water Tank Temperature will be controlled by the Hot
Water Tank Thermostat for the electric element.
· Pump override: For added flexibility you can make the pump operate manually. The pump will turn
on as long as the ‘Pump’ button is held down unless of course the pump is already on in normal operation.
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