Solar thermal energy still has an enormous potential in buildings. Although energy collectors are widely used on the eastern Mediterranean coast, and although Spain has now launched an ambitious programme to install them, the technology, research and practice of solar thermal energy are much more middle and north European issues. In those countries with temperate climates, solar systems make a partial contribution to the overall heat supply of buildings. In southern European countries with higher radiation rates, the sun can provide nearly all the energy to produce domestic hot water and a share of space heating. But there is a certain paradox in the fact that sun shines strongest when less heat is needed. The performance of these systems must therefore be reduced in the hot summer and energy stored for the winter periods. But storing energy from summer to winter is difficult.

 

Atika has an innovative system, with the solar collectors supplying energy not only for heating but also for cooling purposes. They can accumulate about 70 % of the hot water supply and up to 30 % of the energy for space heating. When cooling is needed, the solar collectors provide energy for the house’s air conditioning system.

Eleven VELUX solar collectors, with a total surface of approximately 10 m2, are installed in south-facing roof slopes, with angles varying between 15° and 60°. A mixture of glycol and water circulates through the solar collectors. Glycol is an antifreeze fluid that eliminates the problem of ice in the system and burst pipes. The glycol flows in a closed loop system from the collectors into the 700-litre accumulation tank which is hereby heated up to a maximum of 90°C.

(However, in some parts of the Mediterranean area, e.g. Bilbao, the climate in winter is so mild that glycol is needless.)

 

An additional source of heat, an electrically powered boiler, supports the production of hot water. This hot water is used for domestic purposes, for room heating and for feeding the absorption chiller unit that converts heat into cold water used for air conditioning via the fan coils.

 

The compact single-effect absorption chiller functions in much the same way as an electric air-conditioning appliance but uses hot water to power a thermo-dynamic cooling cycle – instead of a compressor that consumes electricity.

The machine installed in Atika makes use of rotation techniques to increase the efficiency of this cycle, thereby reducing the size of the appliance and allowing it to be installed without the need for a cooling tower. By using water instead of other common refrigerants, it does not harm the ozone layer.