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The image shows the test building with the new heat supply concept shortly after completion.
© ISFH
Using solar thermal heat directly for space heating
10.05.2016

The system concept was put into practice in the experimental building according to this energy flow diagram.
© ISFH

Here, the building element activation pipes are being laid on the ground floor of the building shell.
© ISFH

Here, the heating system of the experimental building can be seen during commissioning.
© ISFH

The building serves as a heat storage tank

Buildings with high solar shares of fraction require large water tanks to store heat. Researchers have developed a space-saving alternative: excess heat is stored in the ceilings of the building via building element activation. Scientists are currently testing the concept in an experimental building near Hanover. They now have the results of the first year of operation.

Buildings which have a good thermal insulation standard and which cover more than 50 per cent of their heating requirements through solar thermal energy are known as solar houses. Surplus heat is usually stored in the water tank inside the building. Scientists at the Institute for Solar Energy Research in Hamelin (ISFH) are testing an alternative approach in order to achieve high solar shares of fraction. They are combining a small heat storage tank with building element activation (BEA) driven directly by solar thermal energy in solid slabs in the building. Instead of using a wood-burning stove, as is standard in solar houses, they have opted for a heat pump as backup heating for days where there are low levels of sunlight. “The large heat storage tanks used to date, which hold several cubic metres of water, can be reduced to around one cubic metre,” explains Jan Steinweg, the project manager responsible at ISFH. “That saves on costs and requires less space. There are far fewer cases of storage losses during the summer leading to overheating.” Building element activation is designed to cover the basic heat load. With its small size, it comes at a relatively low cost. There is large layout spacing, no sub-distributor circuits and simple control.

The researchers are currently examining how this concept proves its worth in practice in an experimental building near Hanover. 32 square metres of solar collectors have been installed on the roof of the house, which has 270 square metres of living space. The average U-value of the building envelope amounts to 0.27 W/m2K. A brine-water heat pump is used, the source of which is a small geothermal heat collector close to the surface.

The first year of operation with stress tests

The first annual results with measurement data from April 2015 to March 2016 are now available. The balance period includes the commissioning of the building, during which several control strategies still needed to be optimised and when the system was not yet running at maximum efficiency. Around 60 per cent of the solar yield are directly used for space heating in the building element activation driven directly by solar thermal energy. As a result, the solar energy plant directly covered 43 per cent of space heating requirements. The solar share of fraction for heating and hot water amounts to 52 per cent in total, while the final energy requirements (electricity) for the building are 8 kWh/m2. The building concept has proven to be highly robust.

During the measuring period, the scientists used so-called stress tests to examine the durability of the system. These tests also contribute to the fact that the energy consumption in the annual results is higher than during normal operation. One new insight obtained from the tests is that the geothermal heat collectors, which are already designed to be small in size (170 square metres) and which can be regenerated using solar energy could even have been made considerably smaller. If the plant had been designed in the classic way in accordance with the Association of German Engineers (VDI), the geothermal heat collector area would have had to correspond to around twice the size of the living space. According to Mr. Steinweg: “We assume that on this site and due to the solar heat, a geothermal collector with a size of around half the living space would have been entirely adequate. As a result, geothermal collectors are also possible on smaller plots of land.”

Since building element activation can be controlled in a targeted way, it does not contribute to overheating, unlike storage tanks installed inside the house. Technically speaking, cooling via the BEA would also be possible, although this was not put into practice in the test building. Shading systems and night ventilation are sufficient in order to prevent overheating during the summer.
Since the plant operation has now been optimised, the scientists assume that during the forthcoming measurement year, the level of system efficiency in the experimental building will continue to rise. The German Federal Ministry for Economic Affairs and Energy will fund the project until the spring of 2017.

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Scientific project management
ISFH GmbH

Realisation experimental building
HELMA Eigenheimbau AG

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