21
Alpha SolarSmart 90 - System Operation
6.2
OPERATION OF THE SOLARSMART SYSTEM - Fig.21
Control
When the controls detect a collector sensor temperature that is at least 10°C higher than the lower cylinder sensor and
the solar cylinder temperature is less than 65°C, the drain back unit pump will start. The pump will run at full speed for
250 seconds and then modulate between 30 and 50% of full speed to circulate water around the collector. The speed of
the pump is dependent upon the difference in the temperature between the collector sensor and the lower cylinder
sensor.
At the same time that the drain back unit pump starts the cylinder pump will start at 10% of full speed to circulate the
cylinder water through the drain back unit heat exchanger. The drain back unit pump will stop when the temperature
difference between the collector sensor and the lower cylinder sensor falls to 3.5°C or the cylinder temperature reaches
70°C. The cylinder pump will continue to run for 120 seconds to collect any excess heat from the drain back unit then it
will also stop.
When both pumps are operating, a flashing dot will be visible in the right hand corner of the display (Fig. 20). If only the
cylinder pump is running, a flashing dot will be visible in the middle of the display.
If a fault occurs, a fault code will be visible in the display. Refer to Section 7 for a list of fault codes and possible
solutions.
Temperature display
The display (see Fig. 20) will display the solar cylinder temperature (10 - 70°C) for 4 seconds followed by the operating
mode (o
n
or oF) for 2 seconds, after which the sequence will be continually repeated.
Domestic hot water circuit
When a hot tap is opened, cold mains water enters the solar cylinder at the bottom forcing hot water out from the top to
go to the solar valve where it either goes directly to the tap or to the boiler for further heating. The cylinder pump passes
the cool water from the bottom of the cylinder through the drain back unit heat exchanger and warm water back to the
centre of the cylinder.
Collector water circuit
The drain back unit pump (See Fig. 21) is controlled by the controls. The collector water is circulated in a closed loop
through the collector panel where it is heated then through the heat exchanger in the drain back unit where heat is
passed to the domestic water from the cylinder.
Frost protection
If the collector sensor registers a temperature less than 3°C, the temperature difference required to start the drain back
unit pump (normally 10°C) will be increased by 15° to 25°C. This will ensure that the unit will not operate in frosty
conditions (with the possibility of freezing). When the temperature rises above 3°C this temperature difference of 25°C
will remain for a further 24 hours when it returns to normal.
Pumps
If the electrical supply is on and the solar system has not operated for 24 hours, the pumps will operate automatically
every 24 hours, providing the collector temperature is above 10°C.
