Comparative analysis of active and passive solar heating systems with transparent insulation

The objective of this research is to achieve a high solar fraction in social housing, for which investment costs are strictly limited. Six houses have been built in the east of France: two with active (solar collectors) and four with passive (Trombe walls) solar heating systems. Two types of transparent covers are compared: a capillary structure and a simpler polycarbonate plate. The project was monitored during 1 year. Experimental measurements as well as simulation results are presented in this article. The use of simulation allowed a comparison of the various systems on a common basis, i.e., minimizing the effect of different occupants behaviour. Compared to the less expensive cover, transparent insulation increased the productivity of the air collectors 25% and doubled the gain of the Trombe wall. Thanks to passive or active controls, the thermal comfort was not reduced by the solar systems in summer nor in mid-season.     

Selective coatings in passive solar heating

A recently-developed analytic model for predicting passive solar heating performance is applied to the case of selective coatings on storage walls. Comparisons of theoretical predictions with recent experimental measurements are presented and found to be in good agreement. The theoretical predictions are found to be in good agreement with the experimental findings for non-selectively coated storage walls as well. The value of the analytic model in making general predictions on the value of selective coatings in passive solar heating and in predicting the performance of yet untested configurations is also discussed.     

Review of passive solar heating and cooling technologies

Heating, ventilating, and air-conditioning (HVAC) are parts of the major energy consumption in a building. Conventional heating and cooling systems are having an impact on carbon dioxide emissions, as well as on security of energy supply. In this regard, one of the attempts taken by researchers is the development of solar heating and cooling technologies. The objective of this paper is to review the passive solar technologies for space heating and cooling. The reviews were discussed according to the working mechanisms, i.e. buoyancy and evaporative effects. The advantages, limitations and challenges of the technologies have been highlighted and the future research needs in these areas have also been suggested.     

Optical efficiency of a reflector-window system for passive insolating systems of solar heating

The optical efficiency of a reflector-window system for solar passive heating systems with flat reflectors placed at the south and north sides of a building is determined.     

Characteristics, design implications, and applicability of passive solar heating systems for buildings

The paper reviews the performance characteristics of various passive solar heating systems for buildings, the main design factors affecting their performance, the relative advantages and main problems associated with them, and their applicability to different building types and climatic regions. Emphasis is placed on the architectural design issues associated with the different passive solar heating systems and to the problems that may be encountered when passive solar heating is applied in regions with hot summers.     

Transient response of the Trombe wall temperature distribution applicable to passive solar heating systems

The unsteady temperature distribution and heat loss history of a Trombe wall, applicable to passive solar heating, were obtained from both analytical and numerical approaches to investigate the transient performance of the Trombe wall. A one-dimensional exact solution was obtained by the Duhamel superposition technique for the time dependent boundary, and for a comparison, the numerical result was calculated through an implicit finite difference scheme. Data was obtained and discussed for the influence of solar radiation and Trombe wall thickness on the transient performance of the Trombe wall. The data may provide the thermal design basis for Trombe wall solar heating systems.     

太阳空气加热系统漫谈

近十年来,我国太阳热水系统的研究、开发和推广应用已经取得举世瞩目的进展,成为全球太阳热水器产量最大的国家。并且,为适应不同用户的需求,各种类型的热水器,包括全玻璃真空管型、带肋片的热管—玻璃直接封接真空管型、铜铝复合和全铜平板型,以及ICS(整体式集热—贮热)型全面开花,形势大好。相比之下,太阳空气集热器及空气加热系统的研究和开发却冷冷清清,几乎处于无人问津的状态。在20世纪80年代,北京市太阳能研究所、中国科学院广州能源研究所、上海市能源研究所、清华大学和中国科学技术大学等单位都开展了太阳空气加热器的研究,有些…     

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.     

The optimization of solar heating systems

The optimization of a solar system with a limited number of discrete collection areas available has been discussed. This optimization is based on an exponential relationship between the auxiliary energy required and collector area. In most cases, the optimum area is that area formed by an array of collector panels which is closest to but greater than A_op. In many cases, an even larger collection area can be used without a severe economic penalty since the cost curve changes slowly as collector area is increased. Larger collector areas are also preferable from the standpoint of reducing our dependence on non-renewable fuels.     

Honeycomb roof cover system for passive solar space heating

This paper presents an analysis of the passive space heating characteristics of an air-filled honeycomb placed on the concrete roof-top of a building. In particular, the solar transmittance and heat losses through the honeycomb cover system have been investigated to estimate the solar collection efficiency and heat retention duration of the system. Numerical calculations are carried out for a typical winter day in New Delhi (28°N). and a relatively colder day in Boulder (40°N). It is found that the honeycomb cover system considerably increases the heat collection efficiency of the roof. It also reduces the nocturnal heat losses to enable longer heat retention. The system is more effective in colder climates.     

Optimal heating control in a passive solar commercial building

A smart heating controller has a twofold objective: to save as much energy as possible while maintaining an acceptable comfort level in the building. Due to very large time constants in the building response, it has to anticipate internal and external disturbances. In the case of a passive solar commercial building, the need for anticipation is reinforced by important solar and internal gains. Indeed, large solar gains increase the energy savings potential but also the overheating risk. Optimal control theory presents an ideal formalism to solve this problem: its principle is to anticipate the building behaviour using a model and a forecasting of the disturbances in order to compute the control sequence that minimises a given cost function over the optimisation horizon. This cost function can combine comfort level and energy consumption. This paper presents the application of optimal control to auxiliary heating of a passive solar commercial building. Simulation-based and experimental results show that it can lead to significant energy savings while maintaining or improving the comfort level in this type of building.     

Incentives for solar water heating systems

Life-cycle costing has been used in an economic analysis of three solar domestic hot water installations. These are in operation in Las Palmas (Canary Islands) and are backed by conventional installations consuming either fuel-oil (GG), butane (BB) or electricity (EE). The cumulative cost flows (CCF), including expenditures for purchase, recovery, maintenance, fuel and operating costs, are calculated over the useful life of the installations for expected annual fuel-increment rates. Twenty-seven comparisons are made between the solar (SAS) and conventional systems (CS). Total savings are found over the lifetime and the repayment periods are obtained as a function of discount rate. The SAS and CS are examined with respect to economic incentives such as subvention, tax deduction, loans and their combinations. Finally, the variations of the payback periods and rates of return on investment (IRR) are plotted against the fuel price, annual fuel increment rate and initial investment in the SAS for a wide range of economic parameters.     

Energy savings for solar heating systems

In this paper the realistic behaviour and efficiency of heating systems were analysed, based on long term monitoring projects. Based on the measurements a boiler model used to calculate the boiler efficiency on a monthly basis was evaluated. Comparisons of measured and calculated fuel consumptions showed a good degree of similarity. With the boiler model, various simulations of solar domestic hot water heating systems were done for different hot water demands and collector sizes. The result shows that the potential of fuel reduction can be much higher than the solar gain of the solar thermal system. For some conditions the fuel reduction can be up to the double of the solar gain due to a strong increase of the system efficiency. As the monitored boilers were not older than 3 years, it can be assumed that the saving potential with older boilers could be even higher than calculated in this paper.     

一种开孔被动式太阳能集热器热效率的研究

对一种具有多孔折线型的被动式太阳能集热器的热性能进行实验研究,探讨在受迫奈件下集热器热效率的计算公式。实测过渡季集热器出口温度、进口风速和太阳辐射强度3个参数。通过实验分析,这种折线型太阳能集热器的热效率可达59．4％,并且热效率随进口风速和太阳辐射强度的增加而提高。此外,集热器效率要先于太阳辐射强度达到当天最大值。     

The evaluation of heat capacity and choice of materials for short-term storage of diurnal solar heat surplus in passive solar heating systems

The results of numerical studies aimed to evaluate the heat capacity of short-term phase change heat accumulators applied in passive solar heating systems (PSHS) with a three-layer energy active translucent enclosure (TE) are presented. An example is given of calculation of specific (per unit of TE surface area) weight of heat accumulator using dimethyl sulfoxide, (СН₃)₂SO, with melting temperature 18.6°C and latent heat of phase transition 173 kJ/kg, as the heat storage agent.     

Numerical simulation and sensitivity analysis of lattice passive solar heating walls

A lattice passive solar heating wall (LPSHW) can remarkably improve the heating performance of passive solar heated buildings. Many parameters affect the thermal performance of the LPSHW so that it is not realistic to scrutinize the thermal performance of the LPSHW experimentally. This paper develops a three-dimensional transient heat transfer model of the LPSHW, based on which a computer simulation program is developed in language. The model predictions agree quite well with experimental data. The program can be used to simulate and evaluate the transient thermal performance, to analyze the sensitivity and the effect of climate, and to optimize LPSHW structural parameters. Hour-by-hour computer simulations are run with the program to analyze the sensitivity of a variety of parameters of the LPSHW. The calculations are rerun many times with structural parameters changed one at a time so that the effect of the changed structural parameter on the thermal performance of the LPSHW can be assessed. From the sensitivity analysis, the optimum configuration is thus obtained. The comparison between the LPSHW and the Trombe wall is made thereafter. Under the chosen conditions, thermal efficiency is 30.2% for the LPSHW and 22.6% for the Trombe wall.     

Economic evaluation and optimization of solar heating systems

A procedure is developed for assessing the economic viability of a solar heating system in terms of the life cycle savings of a solar heating system over a conventional heating system. The life cycle savings is expressed in a generalized formby introducing two economic parameters, P₁ and P₂, which relate all life cycle cost considerations to the first year fuel cost or the initial solar system investment cost. Using the generalized life cycle savings equation, a method is developed for calculating the solar heating system design which maximizes the life cycle savings. A similar method is developed for determining the set of economic conditions at which the optimal solar heating system design is just competitive with the conventional heating system. The results of these optimization methods can be presented in tabular or graphical form. The sensitivity of the economic evaluation and optimization calculations to uncertainties in constituent thermal and economic variables is also investigated.     

Operational modes of solar heating and cooling systems

This paper emphasizes factors associated with the subsystems that are required to extract heat from solar collectors, store this heat, and deliver it to the loads upon demand. While minimum use of auxiliary energy is the general objective, it must be sought with due regard to safety, convenience and cost. Subsystem alterations that improve energy efficiency typically come at added cost in terms of installation and maintenance. In some cases, the advantages of a specified component or arrangement of components are immediately evident. In other cases, such options are less decisive and will require longer periods of comparative operation to arrive at accurate assessments. The Colorado State University Solar House I allows for such comparative operation in several experimental modes. These selected modes of operation provide for different methods of solar heat transfer and employ different arrangements of system components and control functions. The principles underlying these modes as well as results of these studies are presented. In addition, the methods of operation found necessary for efficient and reliable performance are discussed. While this evaluation is an ongoing process, the initial “start up” and “break in” periods have been experienced and serve as a basis for several recommendations concerning subsystem components and component arrangements.     

Heat efficiency of complex translucent barrier with partially absorbing layer and airway in passive solar insolation heating systems

The results of numerical and experimental investigations to determine the heat efficiency of a complex translucent barrier with partially radiation absorbing layer and airway in passive solar insolation heating systems are presented.