German central solar heating plants with seasonal heat storage

Central solar heating plants contribute to the reduction of CO₂-emissions and global warming. The combination of central solar heating plants with seasonal heat storage enables high solar fractions of 50% and more. Several pilot central solar heating plants with seasonal heat storage (CSHPSS) built in Germany since 1996 have proven the appropriate operation of these systems and confirmed the high solar fractions.Four different types of seasonal thermal energy stores have been developed, tested and monitored under realistic operation conditions: Hot-water thermal energy store (e.g. in Friedrichshafen), gravel-water thermal energy store (e.g. in Steinfurt-Borghorst), borehole thermal energy store (in Neckarsulm) and aquifer thermal energy store (in Rostock). In this paper, measured heat balances of several German CSHPSS are presented. The different types of thermal energy stores and the affiliated central solar heating plants and district heating systems are described. Their operational characteristics are compared using measured data gained from an extensive monitoring program. Thus long-term operational experiences such as the influence of net return temperatures are shown.     

Experimental investigation of a two-phase closed thermosyphon solar water heater

In this study, experiments were performed to find out how the thermal performance of a two-phase thermosyphon solar collector was affected by using different refrigerants. Three identical small-scale solar water heating systems, using refrigerants R-134a, R407C, and R410A, were constructed and tested side-by-side under various environmental and load conditions. The performance of the system under clear-sky conditions has been investigated with and without water load. Detailed temperature distributions and cumulative collection efficiencies were determined and presented. The experimental results were compared to the results found in the literature and they showed good agreement.     

Thermal characteristics of a building-integrated dual-function solar collector in water heating mode with natural circulation

As a modified building-integrated solar thermal system, building-integrated dual-function solar collector here proposed is able to provide passive space heating in cold winter, and water heating in warm seasons. In this study, evaluations were made on this modified collector system for the warm period operation under the water heating mode with natural circulation of flow. A dynamic numerical model has been developed and validated by experimental data. Based on practical air-conditioned room design conditions, numerical analysis was performed to study the water heating performance, as well as to compare the solar transmission through building facade in different seasons with or without its presence. The results show that when working in the water heating mode, the system performs well in providing services hot water in the warm seasons without bringing in summer overheating problem.     

光照资源富集区太阳能集中供热系统容量配置及热网管径协同设计优化研究

针对常规太阳能供热系统优化设计中太阳集热供热站设计与供热管网设计相互分离,供热管网热传输过程中热损失难以精准计算的问题,建立太阳能集中供热系统容量配置及热网管径协同优化模型,以系统全生命周期成本最小为优化目标,采用遗传算法求解,并通过具体算例与常规优化方法以及工程设计方法的计算结果进行对比分析。结果表明,利用协同优化模型进行太阳能集中供热系统设计,能够有效避免设计系统太阳能保证率偏小以及供热管网比摩阻不满足规范要求的现象。针对具体算例,当太阳能保证率由50%增至100%时,系统最优最低供水温度从60℃降至45℃;随着太阳能保证率的升高,系统单位太阳集热器面积所匹配的储热水箱体积增大,而系统供热管网管径保持不变。     

A state-of-the-art review of solar passive building system for heating or cooling purpose

The major portion of energy in a building is consumed by heating, ventilating, and air-conditioning (HVAC). The traditional heating and cooling systems contribute greatly to the emission of greenhouse gases, especially carbon dioxide. Four different ways, i.e., Trombe wall, solar chimney, unglazed transpired solar façade, and solar roof, are adopted for solar heating. Similarly, two major ways, i.e., evaporative cooling and building integrated evaporative cooling are adopted for cooling of the building. Therefore, an attempt has been made in this paper to compile the developments of solar heating and cooling technologies in a building.     

A solar thermal cooling and heating system for a building: Experimental and model based performance analysis and design

A solar thermal cooling and heating system at Carnegie Mellon University was studied through its design, installation, modeling, and evaluation to deal with the question of how solar energy might most effectively be used in supplying energy for the operation of a building. This solar cooling and heating system incorporates 52 m² of linear parabolic trough solar collectors; a 16 kW double effect, water-lithium bromide (LiBr) absorption chiller, and a heat recovery heat exchanger with their circulation pumps and control valves. It generates chilled and heated water, dependent on the season, for space cooling and heating. This system is the smallest high temperature solar cooling system in the world. Till now, only this system of the kind has been successfully operated for more than one year. Performance of the system has been tested and the measured data were used to verify system performance models developed in the TRaNsient SYstem Simulation program (TRNSYS). On the basis of the installed solar system, base case performance models were programmed; and then they were modified and extended to investigate measures for improving system performance. The measures included changes in the area and orientation of the solar collectors, the inclusion of thermal storage in the system, changes in the pipe diameter and length, and various system operational control strategies. It was found that this solar thermal system could potentially supply 39% of cooling and 20% of heating energy for this building space in Pittsburgh, PA, if it included a properly sized storage tank and short, low diameter connecting pipes. Guidelines for the design and operation of an efficient and effective solar cooling and heating system for a given building space have been provided.     

Hybrid photovoltaic–thermal systems for domestic heating and cooling—A theoretical approach

Hybrid photovoltaic–thermal (PV/T) collectors consist of a thermal collector in which a photovoltaic laminate is attached as a thermal absorber. In addition to their improved electrical efficiency, due to the decrease of the photovoltaic temperature, PV/T collectors have also thermal efficiency, which is the main issue of this research. The theoretical study of a photovoltaic–thermal system for domestic heating and cooling has led to the result that the system can cover a remarkable percentage of the domestic heating and cooling demands. Furthermore, the performance of the PV/T collector with respect to the variation of geographical region as well as to different total surface areas of the system was also investigated. According to the results in both cases, the variation of the above-mentioned parameters has notably affected the solar coverage percentage of the system. As a conclusion it could be claimed that the photovoltaic–thermal technology offers a remarkable solution to the problem of domestic heating and cooling, hence contributing to the reduction of energy consumption in houses.     

Development of advanced solar assisted drying systems

The Solar Energy Research Group in the Universiti Kebangsaan Malaysia has been set-up more than two decades ago. One of the activities is in the field of solar thermal process, particularly in development of solar assisted drying systems. Solar drying systems technical development can proceed in two directions. Firstly simple, low power, short life, and comparatively low efficiency-drying system. Secondly, the development of high efficiency, high power, long life expensive solar drying system. The group has developed four solar assisted drying systems namely (a) the V-groove solar collector, (b) the double-pass solar collector with integrated storage system, (c) the solar assisted dehumidification system for medicinal herbs and (d) the photovoltaic thermal (PVT) collector system. The common problems associated with the intermittent nature of solar radiation and the low intensities of solar radiation in solar thermal systems can be remedied using these types of solar drying systems. These drying systems have the advantages of heat storage, auxiliary energy source, integrated structure control system and can be use for a wide range of agricultural produce.     

Energy and economic analysis of an integrated solar absorption cooling and heating system in different building types and climates

The use of solar energy in buildings is an important contribution for the reduction of fossil fuel consumption and harmful emissions to the environment. Solar thermal cooling systems are still in their infancy regarding practical applications, although the technology is sufficiently developed for a number of years. In many cases, their application has been conditioned by the lack of integration between cooling and heating systems. This study aims to evaluate the potential of integrated solar absorption cooling and heating systems for building applications. The TRNSYS software tool was used as a basis for assessment. Different building types were considered: residential, office and hotel. The TRNSYS models are able to run for a whole year (365 days), according to control rules (self-deciding whether to operate in heating or cooling modes), and with the possibility of combining cooling, heating and DHW applications. Three different locations and climates were considered: Berlin (Germany), Lisbon (Portugal), and Rome (Italy). Both energy and economic results are presented for all cases. The different local costs for energy (gas, electricity and water) were taken into account. Savings in CO₂ emissions were also assessed. An optimization of solar collector size and other system parameters was also analysed.     

屋顶集热式太阳房供暖系统研究

研制了一种屋顶集热式太阳房供暖系统,对该系统进行了结构设计优化和试验测试,结果表明,在冬季晴朗的白天,对于保温较差的试验平房（热负荷约为120W／m^2）,利用1／2的屋顶面积集热,室内温度最高达到20℃,平均温度约18℃,比对照房温度高约6℃;对于保温较好的建筑物（采暖期热负荷约为20W／m^2）,太阳能供暖系统在冬季白天可有效地为房间供热,多余的热量利用储热装置储存以满足夜间供暖的需要,从而实现冬季24小时为建筑物供热的目标。     

On the effects of solar radiation variations on solar heating system performances

The effect of solar radiation availability on the performance of different solar heating systems has been studied. The systems include a solar water heater, passive solar houses and district solar heating systems with seasonal heat storage. Also, different collector orientations and collector types have been investigated. The hourly radiation data were generated by a simple computational simulation procedure. It was found that district solar heating systems with concentrating collectors and passive solar houses showed the largest variations for the given conditions.     

太阳能吸收式空调系统的经济性分析

针对一个特定的对象,进行了太阳能吸收式空调系统寿命周期内的模拟计算及影响因素的分析,结果表明：（1）单纯太阳能空调（无采暖与热水供应）的经济性很差,太阳能空调与供热的复合系统的经济性要优于单纯的太阳能空调系统;（2）太阳能采暖与空调的复合系统,采暖与供冷的负荷比对系统的经济性有很大影响,即使在最佳的负荷比时仍无法和常规的系统竞争;（3）太阳能与生活热水系统的负荷系统中,热水负荷所占比重越大,经济性越好,当太阳能空调使用生活热水系统夏季多余的热量时,太阳能空调系统经济上可以和天然气锅炉＋电动制冷机竞争,并具有很好的节能性和环境效益。     

Performance evaluation of a passive solar building in Western Himalayas

Under the Passive Solar Building Programme, more than 100 buildings have been constructed in the high altitude region of the Indian State of Himachal Pradesh. A policy decision has been taken by the State that all government/semi-government buildings are to be designed and constructed as per passive solar housing technology. The evaluation studies of some of these buildings have been carried out by our group. In the present study, the thermal performance of a passive solar bank building at Shimla, has been evaluated. This solar building incorporates a heat-collecting wall and a roof-top solar air heater with an electric heating backup, sunspaces and double-glazed windows. The monitoring of the building shows that the solar passive features in the building results in comfortable living conditions. The study shows that the high cost central electric/gas/wood-fired heating systems can be replaced by a low cost solar heating system with backup heaters. This will result not only in reducing higher installation costs of these systems but also the annual running and maintenance costs. It is shown that the solar passive features save electricity required for space heating and reduce the heat losses in the building by about 35%. The strategy to be followed for the propagation of passive solar technology on large scale in this Himalayan State or in any other cold hilly region is also presented.     

Enhancement of the yield of solar still with the use of solar pond: A review

A solar pond (SP) is a remarkable growth of renewable energy technology that has stored solar energy for storage purposes and is used in many solar thermal applications. It is also utilized for many purposes, such as heating, cooling, space heating, air conditioning, and many more. The present paper shows the use of an SP to improve the yield of solar still (SS) by providing hot water through the heat energy stored in it. It also reveals the use of shallow and mini SPs with SS to improve yield. Various future research works on SS using SPs have also been included in this paper. From the current review paper, it was concluded that the SP increases the yield of the SS.     

泰安地区利用太阳能采暖的技术经济分析

从泰安地区气候条件、可采用的采暖系统形式、集热器选择及面积计算、蓄热水箱容量计算等几个方面对太阳能采暖系统的技术性分析,又通过对几种方案的年计算费用的比较对系统的经济性分析,论证了太阳能采暖在泰安地区是切实可行的。为泰安地区今后在建筑中推广利用太阳能采暖工作提供参考。     

吸收式热泵在燃气采暖冷凝热回收中的应用

作者建立了一种利用吸收式热泵回收燃气锅炉冷凝热的系统，解决了供热回水温度高而难以回收烟气冷凝热问题，比现有的锅炉烟气冷凝热回收技术提高效率5％以上。计算分析结果表明，这一工艺的应用可产生显著的经济、节能和环保效益。     

Numerical simulation and performance assessment of a low capacity solar assisted absorption heat pump coupled with a sub-floor system

A prototype low capacity (10 kW) single stage Li–Br absorption heat pump (AHP), suitable for residential and small building applications has been developed as a collaborative result between various European research institutes and industries. The primary heat source for the AHP is supplied from flat plate solar collectors and the hot/chilled water from the unit is delivered to a floor heating/cooling system. In this paper we present the simulation results and an overview of the performance assessment of the complete system. The calculations were performed for two building types (high and low thermal mass), three climatic conditions, with different types of solar collectors and hot water storage tank sizes and different control systems for the operation of the installation. The simulations were performed using the thermal simulation code TRNSYS. The estimated energy savings against a conventional cooling system using a compression type heat pump was found to be in the range of 20–27%.     

Net energy analysis of domestic solar water heating installations in operation

The potential of solar water heating systems to reduce domestic energy use is frequently acknowledged. However there are two factors that are rarely discussed when studying this technology. Firstly the real performance of the installed systems in operation, and secondly a life cycle perspective of its energy use. These two issues are reviewed in this paper, and a field study in Ireland is also presented. In the review, some studies show that measured real performance of domestic solar water heating systems can be lower than expectations. Concerning their life cycle energy performance, existing studies show that the initial energy investment for the systems (their embodied energy) is a small portion of the energy savings over their lifetime with calculation paybacks generally lower than 2 years. On the field study carried in Ireland, representative of a maritime north European climate, the ‘energy payback’ based on the expected energy savings is between 1.2 and 3.5 years, values comparable to previous studies considering the less favourable climate and installation characteristics. However the measured energy savings generally worsened the life cycle energy performance of this technology and thus increased the energy payback period. The study concludes that while there is a real potential for life cycle energy savings through domestic solar water heating installations, devising mechanisms to ensure proper design, installation and operation of systems is essential for this technology.     

Evaluation of a solar thermal system using building louvre shading devices

External louvres are increasingly used to provide solar protection for building glazed surfaces. The integration of collectors into the external louvres of buildings offers a means of reducing system cost as well as providing architects with more freedom to integrate the technology into their designs. This work concerns the modification of existing louvre designs to integrate a solar collector in the shading device. The evaluation of a thermal solar system for water heating is assessed in this paper. A numerical model for the integrated solar collector was developed for different configurations and the collector efficiency is quantified for each configuration. System thermal performance was obtained for the climatic conditions of Lisbon (Portugal) and Tenerife (Spain). Economic and environmental viability of the system is assessed.