A.O. Smith SGS-28, Installation, User And Service Manual

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6.3.3 Protection for the solar heating system
6.3.3.1 Drain-back tank
The solar heating system may optionally be equipped with a drain-back tank. The tank fills
itself with the heating fluid when there is no heat demand. This avoids overheating of the
solar heating system. The high insulation factor of the tank also protects the system
against freezing of the fluid. The use of the drain–back tank also serves to extend the
useful life of the fluid.
The existence of a drain-back tank is set during the installation (see section 9.2.8.1).
Refer to the solar heating system manual for more details.
6.3.3.2 Fluid temperature
The heat exchanger of the solar heating system is filled with glycol. If the temperature of
the heating fluid is too high, a signal is sent to the controller of the solar collector and the
pump of the solar collector is switched off. This signal is passed to the controller by
temperature sensor S
1
.
Safety Description
Maximum temperature:
- S
1
> 130 ºC
The pump of the solar heating system switches off
when the temperature of the heating fluid at S
1
exceeds the maximum value. The solar heating
system enters error mode. The error is also visible
on the display of the water heater.
6.3.4 Safety of the solar heating system
6.3.4.1 Expansion vessel
The solar heating system must be equipped with an expansion vessel. An expansion vessel
serves to limit pressure variations in the system. The expansion vessel in the solar heating
system can withstand a maximum pressure of 600 kPa (6 bar). The supply pressure to the
expansion vessel depends on the static head of the system.
The system is protected from overpressure by an expansion valve (see section 6.3.4.2) as
well as the expansion vessel.
6.3.4.2 Expansion valve
The solar heating system is equipped with an expansion valve. The expansion valve
monitors the pressure in the solar heating system. Should the pressure become higher
than 600 kPa (6 bar), the valve will open. The hot water can now flow out of the
installation. The valve remains open until the unsafe situation has passed, i.e. until the
pressure has fallen back to below 600 kPa (6 bar).
Note
Because a closed system is pressurized and is not filled automatically, the system will
have to be filled (see section 7.9.1) again when the expansion valve has been activated.
A system with a drain-back tank is not pressurized and does not have an expansion valve.
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