Solar district heating and cooling: A review

Both district heating and solar collector systems have been known and implemented for many years. However, the combination of the two, with solar collectors supplying heat to the district heating network, is relatively new, and no comprehensive review of scientific publications on this topic could be found. Thus, this paper summarizes the literature available on solar district heating and presents the state of the art and real experiences in this field. Given the lack of a generally accepted convention on the classification of solar district heating systems, this paper distinguishes centralized and decentralized solar district heating as well as block heating. For the different technologies, the paper describes commonly adopted control strategies, system configurations, types of installation, and integration. Real‐world examples are also given to provide a more detailed insight into how solar thermal technology can be integrated with district heating. Solar thermal technology combined with thermally driven chillers to provide cooling for cooling networks is also included in this paper. In order for a technology to spread successfully, not only technical but also economic issues need to be tackled. Hence, the paper identifies and describes different types of ownership and financing schemes currently used in this field.     

Reduction of carbon dioxide emissions by solar water heating systems and passive technologies in social housing

Growing global concern regarding climate change motivates technological studies to minimize environmental impacts. In this context, solar water heating (SWH) systems are notably prominent in Brazil, primarily because of the abundance of solar energy in the country. However, SWH designs have not always been perfectly developed. In most projects, the installation option of the solar system only considers the electric power economy aspects and not the particular characteristics of each climatic zone. Thus, the primary objective of this paper is to assess the potential of carbon dioxide reduction with the use of SWH in comparison with electric showers in social housing in several Brazilian climatic zones. The Brazilian government authorities have created public policies to encourage the use of these technologies primarily among the low-income population. The results of this paper indicate that hot climactic regions demonstrate a low reduction of CO₂ emissions with SWH installations. Thus, solar radiation is not useful for water heating in those regions, but it does lead to a large fraction of household cooling loads, implying a demand for electrical energy for air conditioning or requiring the adoption of passive techniques to maintain indoor temperatures below threshold values.     

家用太阳热水器与太阳热水系统的技术经济比较

分析了户用太阳热水器和太阳热水系统工程的经济技术特点,对两者成本构成、项目财务净现值、投入回收期和财务内部收益率等有关指标进行了经济技术比较.分析比较表明,太阳热水系统与家用热水器相比,节省安装占地,与建筑相结合得好,在降低成本,缩短投资回收期,提高经济效益方面有明显的优势.     

Analysis of natural circulation solar water heating systems

This paper presents an analysis of the performance of a solar water heating system with natural thermosyphon circulation between the collector and the storage tank. The analysis is based on the formulation by Ong except that provision for withdrawal of hot water from the tank (for domestic/ industrial use) has been made in the energy balance equation; further in contrast to the use of the finite difference method by Ong, explicit expressions have been obtained. The results of the present analysis (in the absence of withdrawal of hot water from the tank) are seen to be in better agreement with experiments than the corresponding results of Ong, obtained by use of the finite difference method.

Numerical results, corresponding to hot water retrieved from the storage tank, have been presented for two modes of hot water withdrawal viz. the constant flow rate and constant mean storage tank water temperature.     

空气-水复合平板型太阳能集热器

提出了一种适用于太阳能供热采暖工程的新型太阳能空气-水复合平板集热器。该集热器可以单独使用空气、水或同时以空气和水作为集热工质。测试显示,该集热器空气循环集热效率为55%～65%,水循环集热效率为32%～34%,能够满足太阳能供热采暖工程的要求。该集热器成本不高,适用于在我国北方广大农村地区推广使用。     

Optimum glazing combination for solar space heating

A study is made for comparing the maximum seasonal energy yield obtainable by solar collectors for space heating application. Different glazing combinations with glass and plastic as glazing materials are considered. The study is made for four different locations. The performance of eight glazing combinations with covers ranging in number from one to three is compared to obtain the optimum combination for each location. The results show that selecting the optimum glazing combination improves the performance significantly. In general, plastic covers give higher yield. The study confirmed that the use of two covers is justified in cold, cloudy climates while a single cover is suitable for temperate climates. In most cases three covers lead to a significant reduction in the yield. Replacing plastic by glass as a top cover for longer life results in a small yield reduction. Some of the other conclusions are that the ratio of average to normal transmittance-absorptance product changes significantly with location and month of the year. However, the seasonal average value of this ratio is almost constant for any number of covers but changes with location.     

太阳能热水系统结合地板采暖在高层住宅中的应用

介绍太阳能热水系统结合低温热水地板采暖系统的工作原理,以上海地区为例,在高层住宅中应用壁挂式太阳能集热器,可以实现太阳能与建筑一体化。对该太阳能系统进行节能效益分析,结果表明,系统的动态回收期为3.98年。     

太阳能低温地板辐射采暖系统的效益分析与评价

介绍太阳能低温地板辐射采暖系统的工作原理和形式,结合某一顶层复式住宅用能源价格法对太阳能地板采暖与常规热源进行经济性分析,并从节能效益、环保效益和投资回收期等3个方面进一步分析太阳能地板采暖系统的优势,对各方案进行综合评价,对该系统的普遍应用进行了展望。     

Transient analysis of parallel plate forced circulation solar water heating system

In this paper, a transient analysis of a forced circulation solar water heating system with and without heat exchangers in the collector loop and storage tank has been presented for a parallel flat plate collector. The effect of various water heating system parameters on its performance have been studied. Numerical calculations have been made for a typical cold day viz. 26 January 1980 in Delhi.     

燃气炉与太阳能联合供热系统的研究

阐述了燃气炉与太阳能联合供热系统的设计、制造和控制方法,在令人舒适满意的基础上确保经济性。     

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.     

Fuzzy model representation of thermosyphon solar water heating system

The aim of this paper is to focus on improvement in prediction accuracy of model for thermosyphon solar water heating (SWH) system. The work employs grey-box modeling approach based on fuzzy system to predict the outlet water temperature of the said system. The prediction performance results are compared with neural network technique, which has been suggested by various researchers in the last one decade. The outlet water temperature prediction by fuzzy modeling technique is analyzed by using 3 models, one with three inputs (inlet water temperature, ambient temperature, solar irradiance), next with two inputs (inlet water temperature, solar irradiance) and last one with single input (solar irradiance/inlet water temperature). An improved prediction performance is observed with three inputs fuzzy model.     

Optimization of parabolic trough solar collector system

Process heat produced by solar collectors can contribute significantly in the conservation of conventional energy resources, reducing CO₂ emission, and delaying global warming. One of the major problems associated with solar process heat application is fluctuation in system temperature during unsteady state radiation conditions which may cause significant thermal and operation problems. In this paper a transient simulation model is developed for analysing the performance of industrial water heating systems using parabolic trough solar collectors. The results showed that to prevent dramatic change and instability in process heat during transient radiation periods thermal storage tank size should not be lower than 14.5 l m^?2 of collector area. Small periods of radiation instability lower than 30 min do not have significant effect on system operation. During these periods when water flow rate of collector loop is doubled the time required to restore system normal operating condition increased by a ratio of 1.5. Copyright © 2005 John Wiley & Sons, Ltd.     

太阳能低温热水地板辐射供暖系统的研究

低温地板辐射供暖具有舒适、节能、清洁等许多优点，这种供暖方式已在我国北方得到广泛的应用。研究、开发廉价和清洁的辐射供暖的低温热源－太阳能，对于大面积推广低温辐射供暖系统具有十分重要的意义。     

Thermal modelling of a few novel solar collector-cum-storage units for passive heating

Analytical models have been put forward to predict the thermal performance of passive heating systems, which have previously been suggested. The systems consist of a water vessel for heat storage and a structure positioned on its outside wall, which act as a solar collector and a thermal insulation for the storage, respectively. Four different variations of structures have been considered and numerical calculations performed corresponding to the physical parameters of an earlier reported experimental study. The analysis is able to predict the experimental results fairly satisfactorily.     

Potential for large-scale solar collector system to offset carbon-based heating in the Ontario greenhouse sector

In the Ontario greenhouse sector the misalignment of available solar radiation during the summer months and large heating demand during the winter months makes solar thermal collector systems an unviable option without some form of seasonal energy storage. Information obtained from Ontario greenhouse operators has shown that over 20% of annual natural gas usage occurs during the summer months for greenhouse pre-heating prior to sunrise. A transient model of the greenhouse microclimate and indoor conditioning systems is carried out using TRNSYS software and validated with actual natural gas usage data. A large-scale solar thermal collector system is then incorporated and found to reduce the annual heating energy demand by approximately 35%. The inclusion of the collector system correlates to a reduction of about 120 tonnes of CO₂ equivalent emissions per acre of greenhouse per year. System payback period is discussed considering the benefits of a future Ontario carbon tax.     

Design,fabrication and performance evaluation of natural circulation rectangular box-type solar domestic water heating system

This study includes design and experimental analysis of a solar domestic water heating system. Water heating systems with glazed and unglazed collectors were constructed and tested at Dhaka, Bangladesh, at a latitude of 23.7 °N. Collector thermal efficiency and capability of raising water temperature were considered as performance evaluation measures. A typical day analysis showed that collector efficiency varied with time and touched its peak at around 12:00 h. During testing, the efficiency of the glazed collector increased by about 70.3% when compared with the unglazed collector. Average collector efficiency over the whole test period was also estimated to be 57.3% and 33.7% for glazed and unglazed collectors, respectively. Maximum water temperatures measured at daytime user outlets were, respectively, 82.4 °C and 65.5 °C for domestic water heating systems with glazed and unglazed collectors and approximated to be 49 °C and 32 °C higher than the ambient temperature. The glazed collector eventually offered significantly higher performances over the unglazed collector in improving system performance.     

家用太阳热水系统标准探讨

家用太阳热水系统性能检测的国家标准主要有GB/T 18708-2002、GB/T 19141-2003,因测试目的不同,两个标准之间以及与其他各相关标准之间存在一些差异,针对热性能测量系数对各相关的国内外标准进行对比分析,对家用太阳热水系统某些参数测量提出改进建议。     

Towards zero carbon design in offices: Integrating smart facades,ventilation, and surface heating and cooling

This paper discusses an overall strategy for reducing energy demand in non-domestic buildings, mainly focusing on office developments. It considers four areas: reducing internal heat loads; addressing passive design through the building construction; using efficient and responsive HVAC systems and focusing on chilled (heated) surface systems; integrating renewable energy supply systems into the building design. The impact on energy use and carbon dioxide emissions will be discussed. The paper will draw from a range of design projects carried out in Europe, where this integrated approach has been applied, and then explore the benefits in relation to applications in the Middle East and China. Energy modeling results, to inform the design process will be presented, using energy simulation for three case study locations, in Zurich, the Chongqing and Abu Dhabi.     

基于能量梯级利用的太阳能冷热联供系统

从能量梯级利用的角度出发，提出了一种新型太阳能冷热联供复合系统。该复合系统可根据太阳辐射强度在不同的季节分别用作单一的太阳能热水器、热泵热水器或太阳能吸附式冷热联供复合系统。建立了相应的数学模型，计算了该系统在不同季节各种典型工况下的性能指标。计算结果表明，该系统不仅可实现冷热联供的双重功能，而且具有较大的节能潜力。