تجزیه و تحلیل شبیه سازی برای سیستم گرمایش خورشیدی فعال از یک منفعل خانه

The active solar heating system consists of the following sub-systems: (1) a solar thermal collector area, (2) a water storage tank, (3) a secondary water circuit, (4) a domestic hot water (DHW) preparation system and (5) an air ventilation/heating system. An improved model for the secondary water circuit is proposed and two interconnection schemes for sub-systems (4) and (5) are analyzed. The integrated model was implemented to Pirmasens passive house (Rhineland Palatinate, Germany). Both interconnection schemes show that (almost all) the solar energy collected is not used for space heating but for domestic hot water preparation. The classical water heater operates all over the year and the classical air heater operates mainly during the nights from November to April. The yearly amount of heat required by the DHW preparation system is about 77% of the yearly total heat demand of the passive house and the classical water heater provides about 20% of the yearly heat required by the DHW preparation system. The solar fraction lies between 0.247 in January and 0.930 in August, with a yearly average of 0.597.

In residential buildings, a large proportion of the energy is used for space heating—on average about three quarters of the final energy consumption in the existing building stock in central Europe. In 80s, the low energy house standard arose after the oil crises, with a space heat load about 75 kW h/(m2 y). First passive houses (PH) were built in the north European countries while the first German passive house was constructed in the year 1992. Passive houses need about 80% less heating energy than new buildings designed to the standards of the 1995 German Thermal Insulation Ordinance [1]. The Passive House Energy Standard is now the leading standard for energy efficient design and construction [2]. The main prerequisite of being a passive house is that the building annual space heating demand does not exceed 15 kW h/(m2 y). Furthermore, the building annual primary energy consumption for space heating, hot water and building services must not exceed 60 kW h/(m2 y). A set of yearly measures showed that these goals may be achieved) by using standard building material and technology with additional costs of about 5% upper the same implementation but according to the current building regulation. It could be useful to remind a few basic facts about previous international efforts on passive houses. Research on the physics and technology of passive house is performed all over Europe [3] and [4] and an International Conference on Passive Houses is regularly held with its 9th event in 2005. The leading authority in the field is the Darmstadt Passivhaus Institut founded in 1996 as an independent research institution employing physicists, mathematicians and civil, mechanical and environmental engineers [5]. Another important research center is at Fraunhofer Institute for Solar Energy in Freiburg. There it has been proven that in solar passive buildings the remaining heating demand can be met with compact heating and ventilation units [6]. The CEPHEUS project was an important step to spreading across Europe previous knowledge on passive house technology [1]. Its aim was construction of about 250 housing units to Passive House Standards in five European countries, with in-process scientific back-up and with evaluation of building operation through systematic measurement programs. Up to 2001 about 1000 passive house units have been built in Germany and this amount sensibly doubles every year [7]. In Europe already more than 5000 passive house units have been successfully built and completed. Positive feedback from inhabitants has confirmed what had been projected: not only utility costs can be reduced drastically, but also the comfort of living increases significantly through energy efficient construction [8], [9] and [10]. The extended thermal insulation and enhanced air-tightness of a passive house removes the need for heating sources temperature higher than 50 °C. This makes renewable energy sources particularly suitable for heating and domestic hot water production. The domestic hot water (DHW) turns out to be the major energy consumer in a passive house (with 50–80% of the total heat demand) [7] and [11]. In two previous papers [12] and [13] (later on referred to as paper I and paper II, respectively) we proposed an integrated model to evaluate the contribution of renewable energy sources to meet the heating demand of a three-zone passive house. In paper I we showed the main input data required during modeling the thermal behavior of a passive house. Details about Pirmasens PH (Rhineland Palatinate, Germany) were given. A model to evaluate the building thermal load was developed and applied to Pirmasens PH in paper II. The space heating thermal load of that passive house is almost completely covered by the warm air of a central ventilation system with a ground heat exchanger (GHE), a heat-recovery unit and an air post-heater. A solar thermal system is optionally used to assist the space heating system. Several simplifying hypotheses were adopted in paper II when the interconnection between various elements of the heating/ventilation system was considered. Some of these hypotheses were relaxed in [14] (later on referred to as paper III) where detailed models were developed for both the heat recovery unit and the active solar system. The new models were integrated into the existing theoretical approach and implemented within the computer code used to simulate the heating system operation in Pirmasens PH [14]. In this paper an improved model for the secondary water circuit is proposed. This new model is used to analyse two different interconnection schemes for the main users of the thermal energy provided by the solar energy conversion system (i.e. the space heating system and the DHW preparation system). The structure of the article is as follows. For reader convenience, in Section 2 we give a brief description of Pirmasens PH. In Section 3 the models previously developed are listed and the new model of the secondary water circuit is shortly presented. Preliminary results are reported in Section 4 and conclusions are outlined in Section 5.

Two series interconnection schemes were analyzed for the water-to-air and water-to-water heat exchangers, respectively (see Fig. 2). Rather similar results were obtained in both cases (see Table 2). The main conclusion is that the series interconnection is unfavorable for the water-to-air heat exchanger. To save space just results for one of the scheme (i.e. the water-to-water heat exchanger near the water storage tank as in Fig. 2(a)) are reminded below. The collected solar energy finally used for DHW preparation is more than 10 times larger than that used for space heating. Therefore, almost all space heating load is covered by using the classical air heater, which operates mainly during the nights from November to April. The yearly amount of heat required by the DHW preparation system is about 77% of the yearly total heat demand of the passive house (i.e. the heat necessary for both hot water preparation and space heating). This is in agreement with previous knowledge. Despite the rather strong contribution of the active solar system, there is still a need for the classical water heater to operate all over the year. The classical water heater provides about 20% of the yearly heat required by the DHW preparation system. The end user solar energy conversion efficiency lies between 0.096 in July and 0.328 in December, with an average of 0.214 while the solar fraction lies between 0.247 in January and 0.930 in August, with an average of 0.597. These values are in rather good concordance with common practice. It is expected, however, that a stratified water tank would improve the performance.