2013 was a very good solar year for the housing developer of 8-19 Kastenienplatz in Querfurt, a city in the east of Germany. The solar thermal system of the developer’s multi-family houses with 95 flats along 8-19 Kastanienplatz yielded a whopping 586 kWh/m2 of collector area. Last year’s monitored solar yield, which was produced by a field of 50 m2 of flat plate collector area, was as high as 29,557 kWh. Kastanienplatz is just one of several reference projects by German engineering company and system developer Parabel Energiesysteme to reach specific yields of more than 500 kWh/m²a (see the chart on the left). Usually, solar hot water systems in multi-family houses only allow specific solar yields between 200 and 400 kWh.
Another project is the building with 72 flats at 8 Gerberstraße in Halberstadt, just 90 km north of Querfurt. Here, the specific annual yield in the solar thermal circuit even reaches 539 kWh/m². The key figures of both projects are listed in the following table.
8 Gerberstraße, Halberstadt
8-19 Kastanienplatz, Querfurt
Heated floor space
Backup heat source
Collector area per flat
Solar yield in 2013
Specific solar yield in 2013
Solar share of hot water and space heating demand
Volume of solar buffer tank
What is most noticeable is the relatively low solar share, which is one of the key factors for the high specific yield. The second one is the solar heating control system Juri Maxx, which provides the link between the conventional heating system and the solar circuit. This prefabricated and fully wired hydraulic grid is equipped with a DDC controller and a modem, enabling the Parabel team to gain access to the Juri Maxx either through a phone or an internet connection. The online monitoring system detects any defects immediately. “The most important alarm settings are a drop in collector circuit flow or a drop in temperature, either in the hot water or in the space heating circuit,” company founder and Managing Director Bernhard Jurisch explains. Daily logs allow the company to evaluate the performance of the control system.
Heart of the heat supply: The Solar Heating Manager (SEZ in the graphic), for example, type Juri Maxx, controls the different hydraulic circuits.
Figure: Parabel Energiesysteme
Parabel started with Solar Heating Manager Juri Maxx back in 2007. Today, the company has a staff of 10 and operates and monitors around 400 solar thermal systems across Germany, four in Luxembourg, one in Spain, 12 in Austria, one in the Ukraine and one in Brazil. Since 2008, the company has had a collaboration agreement with German boiler manufacturer Bosch Thermotechnik.