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This concept can provide comfortable living conditions with heat sources of temper-ature in range from 8 to 25^◦C. According to low temperatures needed to implement this heating technique, it is possible to apply a very simple and low-performance solar energy collection system and a very-low-temperature seasonal HS system.

A schematic presentation (Fig. 3.24) of TB with the low-performance solar col-lector as the energy supplying system and multi-zone GHS system clearly shows the layout of each component and its role in the operating process. The solar collector absorbs the solar radiation energy, converts into the heat, and transfers the heat to the fluid that flows through polypropylene pipes. Next, the collected solar energy is transmitted down through a pipe system located in the core layer of external walls to the GHS system located underneath the building basement. Transmission heat losses are reduced to a minimum due to highly-effective insulation layers on both sides of the core layer and operating features of TB. The temperature distribution in ground naturally divides the GHS system into three temperature zones:

• high temperature zone with the temperature not less than 20^◦C,

• medium temperature zone with the temperature not less than 15^◦C,

• low temperature zone with the temperature not higher than 8^◦C.

Figure 3.24: Location of Thermal Barrier components [103]

The performance of this multi-zone GHS system can be easily improved with the use of PCM, which changes between a liquid and a solid at temperatures typically between 15^◦C and 45^◦C [18]. The GHS system can be also used to preheat the ventilation air supplied to buildings.

3.4 Summary

The use of passive solar energy systems, undoubtedly, provides environmental and financial benefits since it reduces the energy consumption from non-renewable en-ergy sources for the space-heating in residential buildings. The application of a solar design, however, has several limitations and might not be sufficient to provide the indoor thermal comfort, particularly in regions having extreme climates [31].

Moreover, the implementation of a solar design does not provide the DHW demand.

Therefore, passive solar energy systems should be implemented together with active solar energy systems.

The active solar technology, whose main component is a solar collector, is an effective way to use the solar energy for residential buildings. Basically, three types of solar collectors including a flat plate, compound parabolic and evacuated tube collectors can be installed in residential buildings. These devices, characterized by efficiency values higher than 0.5 [−] [9], can be roof-mounted or installed separately outside the building. Therefore, they are not aesthetically acceptable in many cases [25, 168]. This is a great disadvantage of conventional solar collectors, which may often limit the implementation of active solar energy systems in residential buildings.

The most common applications of active solar technologies are water- and space-heating systems.

In the case of the solar water-heating application, the efficiency of the active solar energy system is limited due to the type and size of the system, and climate conditions. Nevertheless, it is estimated that small scale SDHW systems indicate an annual share of the solar energy in the range of 50–70 % [41].

In the case of the space-heating application, the efficiency of the active solar energy system is mainly limited due to the nature of its source. The need for long-term storing of the collected energy, due to a significant discrepancy between peaks of the maximum demand and availability of the solar energy, makes the seasonal HS system a key technology in the efficient operation of the active solar energy system. It was reported [146] that by the integration of seasonal HS, more than 50 % of the annual heating demand for the space-heating in residential buildings and DHW can be supplied by the solar energy. When the energy from the collector or storage unit is not sufficient to meet current heating requirements, the auxiliary heat source must be applied. In general, a source of the problem refers to the operating temperature of conventional heating systems, such as floor heating and radiators, whose operating temperatures are 35^◦C and 60^◦C, respectively. The maintenance of such temperatures in the seasonal HS system during the winter season is hardly impossible. Hence, conventional active solar space-heating systems

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have to be supported by auxiliary electrical heaters that may increase the total building energy consumption.

An alternative to auxiliary electrical heaters is the use of the heat pumps tech-nology. This technology can be used to increase the performance of SDHW systems as well as operates as an auxiliary heat source to carry space-heating loads when the solar energy is not available. Such a combination contributes to the maximization of the solar energy use for the purpose of the space-heating in residential buildings. On the other hand, it does not agree with the general idea of the energy consumption reduction in residential buildings, since pumps are powered by electricity increasing the total energy consumption.

An attractive solution for problems of active solar space-heating systems, includ-ing the interference of solar collector into buildinclud-ing aesthetics as well as high opera-tional temperatures of heating devices, is the Thermal Barrier technology [103]. It is a representative of techniques of the indirect heating and cooling driven by the solar energy stored in the GHS system of a very-low-temperature but not smaller than 25^◦C. Such a temperature in the seasonal HS system can be successfully main-tained during the whole year operation, when the solar energy is collected with the use of conventional solar collectors. On the other hand, it enables to develop and implement new, very cheap and of simple structure solar collectors characterized by the lower performance than classic ones, which do not affect the building aesthetics.

Chapter 4