In the construction sector, the central solar heating systems are the most cost-effective among all the potential of solar thermal systems. Through the integration of the seasonal heat accumulator can be covered by more than 50% of energy costs for heating and hot water supply. Table 1 shows the large-scale solar heating systems in Europe, built before 2002.
Table 1. The ten largest solar central heating systems in Europe, which were put into operation before 2000. (Click for larger image).
In central and northern Europe since 1995 have become popular seasonal batteries to store solar thermal energy stored in the warm season, and its utilization in the cold.
The figure below shows the 4 types of seasonal solar batteries, but this article will speak directly to the battery of the dirt (duct heat store).
Types of seasonal thermal solar energy battery. (Click for larger image).
For the construction and successful operation of the battery ground must be met such conditions as the corresponding part of the soil and plenty of free space.
The concept of this system is to store solar thermal energy directly into the ground. Suitable geological formations for its use may be, for example, mountain / rocky soil, or water-saturated soil. Charging and discharging the battery ground by means of vertical heat exchangers placed in the boreholes to a depth of 30 - 100 m. On the surface of the battery is a layer of insulation, preventing heat loss into the environment. During charging, the heat flow is directed from the center to the periphery, to result in a higher temperature at the center and lower at the border. During discharge the reverse direction of heat flow. The advantage of this system is a modular design that allows you to expand. Additional drill holes with vertical heat exchangers can easily be added, for example, in the case of increasing the number of homes heated in a residential area. [Schmidt T. , Mangold D. , Müller-Steinhagen H. , July 2003. Central Solar Heating Plants with Seasonal Storage in Germany. Solar Energy, 76: 165-174. ].
At the end of 2002 in a residential area close to Stockholm - Anneberge was put into operation solar thermal systems with seasonal groundwater battery without the use of heat pump. The development of the solar thermal system with a battery pack dirt in Sweden was part of a project of the European Union EU THERMIE, whose goal was to research and development of large-scale solar heating systems for housing. Preliminary modeling and calculation of the system have been implemented in computer software TRNSYS and MINSUN and on the basis of the results was chosen as the optimal system configuration. [Nordell B. , Hellström G. , 2000. High Temperature Solar Heated Seasonal Storage System for Low Temperature Heating of Buildings. Solar Energy, 69 ( 6): 511-523 ].
One of the requirements of the local municipality was to create a residential area, which would be environmentally friendly. Place for this was well chosen - the whole residential area surrounded by pine forest and at the same time is just 10 km north of Stockholm. In the course of construction were used such materials as hard wood, water-soluble paint, insulation and environmental m. Dr.. One of the rooms in each apartment can be completely electrically isolated in the late 90's it was considered beneficial to health. Every resident of every day makes a contribution to preserving and improving the environment by complying with the rules of waste management, as well as caring for the natural environment.
This solar thermal system consists of 2400 square meters. meters of solar collectors placed on the roofs of 50 private houses, ground battery capacity 60 000 cubic. m, 13 sabyunitov with water tanks, batteries, hot water, low temperature heating system ( floor heating ), and additional electric heaters for heating and hot water supply. Heating homes through a system of floor heating with an estimated temperature of 27/32 degrees Celsius. The total heating area - 5444 sq.. m. The annual energy consumption for heating - 565 MW * h. Roofs of houses are oriented in a southeasterly direction with the angles of inclination 15 degrees. , 31 oz. , 37 oz. On the roofs of installed solar collectors with propylene glycol as a coolant. The contour is separated from the solar collector loop heat accumulator and heating systems with heat exchangers. Solar radiation is not constant, so in order to ensure year-round hot water and heating needs seasonal heat accumulator. Accordingly, this battery was designed capacity of 60,000 cubic. 99 m deep boreholes 65 m and the distance between them is 3 m. About 60 % of the annual consumption of energy spent on heating is provided by solar thermal system. However, residents Anneberga dissatisfied with the solar system, which, according to preliminary assessment and calculations had to work much more efficiently. In 2007 two studies were conducted to identify the reasons for the low efficiency of the system. Studies have shown that.
1) drum battery has not yet reached a steady state temperature;.
2) energy consumption by tenants on heating and hot water supply exceeds the set parameters in the simulation system;.
3) losses in the distribution network is much higher than expected, while the level of the received solar energy below.
The expected time during which the heat storage is expected to reach a steady state was determined at the design stage as 7-8 years. After this period, in 2010 - 2011 years was carried out new research on the effectiveness of solar systems, the results of which read the next article in this series.
Anna Ponomareva, design engineer, the company Rentehno.
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