Installation and piping of solar thermal systems
Solar systems for hot water generation are usually used to provide hot water in the household, for swimming pool heating, for heating support and for process heat generation. They thus offer a sensible alternative to conventional water heating. Today, two-circuit systems are predominantly installed.
In the first circuit, a heat transfer medium (water-antifreeze mixture) is pumped through the collector and the absorbed heat is transferred to the drinking water via a heat exchanger in the hot water tank. In the second circuit, the heated drinking water is led to the consumer.
In single-circuit systems, the water is fed directly through the collector and heated. This system is sometimes used to heat swimming pool water without the risk of frost. Single-circuit systems in countries where there is a risk of frost must be able to be shut off and drained by means of an appropriate control system.
The correct dimensioning of the system is the requirement for satisfactory operation. For small systems in one/two-family houses, one can assume a water consumption of around 50 l of hot water per person per day. With a temperature specification of 50 °C and the necessary reserves for days with less radiation, the collector area should be about 2 m² per person.
Materials for the piping
Suitable materials for the pipes of the solar circuit offer:
- sufficient temperature resistance
- glycol resistance
- high pressure resistance
- the necessary weathering and corrosion resistance for outdoor use (no galvanised pipes).
Hot water tank
The hot water storage tank should have a volume of 1.5 to 2 times the daily consumption of hot water per person, i.e. about 100 litres per person, to store hot water for days with less radiation.
Storage tanks should have a slim, cylindrical shape to ensure good temperature stratification. The storage tank should have at least 10 cm of close-fitting and gap-free thermal insulation to minimise heat loss.
The solar circuit serves to transport heat between the collector and the heat exchanger in the hot water tank. The circuit should be as short as possible; for systems in one/two-family houses, a pipe diameter of 15 mm or 18 mm is usually sufficient. The high temperatures of over 110 °C in the collector and in the collector circuit also require matched thermal insulation of the pipes. Outdoors, the thermal insulation must also withstand UV radiation, weathering and bird damage. Therefore, UV-resistant and / or leaded materials with corresponding temperature resistance must be used there. Frequently used foam materials, which are only designed for heating systems up to 90 °C, often fail here after only a few days.
Special foamed materials are available on the market for the requirements of the collector circuit. In addition, there is the possibility of thermal insulation using rock or glass wool as well as melamine resin. The pipes must be insulated against heat loss in accordance with the insulation thicknesses of the heating system ordinance. In smaller systems for one/two-family houses, the common flow rate is 30 to 50 litres per m² collector area. The pressure test must be carried out according to the solar system manufacturer's instructions.
The supply and return lines must be laid with a gradient so that the system can be drained if necessary. For the solar circuit, special attention must be paid to the change in length of the pipes. Due to the high temperature differences to be expected, the copper or stainless steel pipes expand several times compared to a conventional hot water installation. This expansion in length must be taken into account through appropriate fastening (compensators) and the installation of expansion bends or bendable joints in the pipe. Solar pipes are dimensioned in the same way as heating pipes.