Comparison of analytical and numerical modeling approaches for sizing of seasonal storage solar heating systems

Analytical and numerical approaches for the predesign of central solar heating plants with seasonal storage (CSHPSS) systems are compared. The results indicate that the analytical approach employed in SOLCHIPS predesign tool is significantly faster and more powerful than the traditional numerical methods for predesign of high solar fraction seasonal storage solar heating systems.     

Verification of a CSHPSS simulation program with emphasis on system control

A comparison between one-year measured and simulated thermal performance of a full-scale seasonal storage solar heating system (CSHPSS) is presented: To minimize simulation inaccuracies, special attention has been paid to the system control and operational strategies. Then the discrepancies on monthly basis are less than 15% and the predicted yearly energy flows differ only by a few percent.     

High temperature water pit storage projects for the seasonal storage of solar energy

Central solar heating plants with seasonal storage (CSHPSS) are capable of covering more than 75% of the annual heat demand of housing areas if appropriate storage technologies are available. The maximum design temperature should be 90–95° and the long term cost goal is 100 DM m⁻³ for a storage volume larger than 10 000 m³ water equivalent. Three pilot projects are presently under construction and planning in Germany with 600, 4500 and 12 000 m³ volume. The storage medium in all three cases is water.A first pilot heat storage with about 600 m³ volume is being built in Rottweil. This small scale project will be applied as short term storage in connection with a combined heat and power (CHP) plant. The storage container is made of concrete, water tightness is achieved by a stainless steel linear and mineral wool is used as insulation. The aim of this project is to demonstrate the feasibility of the technology and to gain practical experience for the construction of larger stores.During 1995/96 two full scale central solar heating plants with seasonal storage (CSHPSS) of this type will be built in Hamburg, North Germany and Friedrichshafen, South Germany, with 4500 and 12 000 m³ storage volume, respectively.     

Central solar heating plants with seasonal storage in Germany

In the house building sector, central solar heating plants presently offer the most cost-favourable application of all possibilities of solar-thermal systems. By the integration of seasonal heat storage, more than 50% of the annual heating demand for space heating and domestic hot water can be supplied by solar energy. Since 1995, eight central solar heating plants with seasonal heat storage have been built in Germany within the governmental R&D-programme ‘Solarthermie-2000’. This report describes the technology of central solar heating plants and gives advice about planning and costs. The pilot and demonstration plants for seasonal heat storage already built in Germany are described in detail to give an idea about possible system design and applications of central solar heating plants.     

Effect of climate on major CSHPSS design parameters

The effects of site location on the sizing of the main components of a central solar heating system with seasonal storage (CSHPSS) are discussed. Results for optimum storage volume, collector area, and cost of produced energy versus latitude are shown for a generic CSHPSS type. The study indicates a decrease in the storage capacity requirement per unit collector area (V/A_c-ratio) when moving towards north though showing simultaneously a declining system cost-effectiveness.     

Experimental and numerical analysis of seasonal solar‐energy storage in buildings

This paper presents seasonal‐energy storage of solar energy for the heating of buildings. We distinguish several types of seasonal storage, such as latent, sensible, and chemical storage, among which the thermochemical storage is used and analysed in this research. In the first part, a laboratory heat‐storage tank, which was made in the laboratory for heating, sanitary, and solar technology and air conditioning from the Faculty of Mechanical Engineering, University of Ljubljana, Slovenia, was presented. The experimental model was tested for charging and discharging mode. Two types of numerical models for sorption thermal‐energy storage exist, which are microscale and macroscale (integral). For microscale analysis, the analysis system (ANSYS) model can be used to simulate the behaviour in the adsorption reactor. On macroscale or integral scale, TRaNsient SYStem (TRNSYS) model was used to perform the operation of the storages on the yearly basis. In the second part the simulation of the underfloor heating system operation with a built‐in storage tank was carried out for two locations, Ljubljana and Portoro?. Furthermore, the comparison between a thermochemical and sensible‐heat storage was performed with TRNSYS and Excel software. In this comparison, the focus was on the surface parameters of the SCs and volume of the thermal‐storage tank for the coverage of the energy demand for selected building. With this analysis, we would like to show the advantage of the thermochemical storage system, to provide greater coverage of the energy demand for the operation of the building, compared with the seasonal sensible‐heat storage (SSHS). Such a heat‐storage technology could, in the future, be a key contributor to the more environmentally friendly and more sustainable way of delivering energy needs for buildings.     

The use of floor panel energy storage in a heat pump heated dwelling

A method of improving the performance of heat pumps for domestic space heating has been investigated. The study focuses on the short-term storage of heat pump output energy in concrete floor panels. This paper describes the dynamic computer simulation of an air to water heat pump, a floor panel energy store and energy flowpaths in a dwelling. The heating plant, controls and building thermal behaviour, were simulated as a complete energy system to enable the study of interactions between the subsystems. The model heating system comprised a number of under floor water heated panels installed in ground floor rooms of a two storey dwelling. Supplementary energy was supplied by direct electric heaters situated in most rooms. Heat pump operating periods were controlled as a function of the external air temperature within two prescribed occupancy intervals per day. Results of the investigation indicate that a heat pump system using floor panel storage and emission may be efficiently managed to provide nearly continuous heating with little supplementary energy input. The short-term storage of energy in thick floor panels allowed the heat pump to be operated for extended periods without cycling. Because of this, the seasonal loss in heat pump performance resulting from intermittent operation was less than 1 per cent. Attempting to supply the total space heating load with the heat pump and floor panel system resulted in severe overheating during periods of high solar or casual gain. Under these conditions the simple control strategy based on the measurement of external air temperature was ineffective. This problem was eliminated by reducing the heat pump energy input to the dwelling and supplying about 10 per cent of the seasonal energy demand by direct electric heaters. The influence of floor panel energy storage capacity on the performance of the heating system was investigated. Concrete panel depths of between 25 and 150 mm were considered. The seasonal system efficiency was found to increase with floor panel thickness, although not significantly with panel depths beyond 100 mm. The extensive use of floor slabs to store energy caused mean floor temperatures to be higher than when using direct electric air heaters only. However, with the depth of under floor insulation considered in the study (75 mm), heating the floor slab increased the seasonal energy loss of the building by only 4 per cent.     

太阳能季节性地下水池蓄热供热系统的模拟研究

分析了太阳能季节性地下水池蓄热供热系统的运行原理,建立了蓄热水池的数学模型,以哈尔滨一栋采用该供热模式的别墅建筑为实例,以满足太阳能保证率为目标、地下水池中水温为约束,通过改变集热器面积和地下水池的体积及其他相关参数,模拟计算得到太阳集热器面积和地下水池半径的最佳匹配、系统集热量与热损失量和水温与集热效率的关系.     

A simulation study on a solar heat pump heating system with seasonal latent heat storage

Solar heating systems with seasonal energy storage have attracted an increasing attention over the past decades. However, studies of such systems using a phase change material (PCM) as seasonal storage medium have not been found in the open literature. In this paper a solar heat pump heating system with seasonal latent heat thermal storage (SHPH–SLHTS) is firstly described. This is followed by reporting the development of a simplified mathematical model for a SHPH–SLHTS system. Using the model developed, the operational performances of a SHPH–SLHTS system which provided space heating to a villa building have been investigated by simulation, and simulation results are reported in this paper.     

Solar multi-mode heating system based on latent heat thermal energy storage and its application

为克服太阳能间断性和不稳定性的缺点进而实现太阳能集热与采暖的能量供需调节和全天候连续供热,提出了基于相变储热的太阳能多模式采暖方法（太阳能集热直接采暖、太阳能集热采暖+相变储热、太阳能相变储热采暖）,并在西藏林芝市某建筑搭建了太阳能与相变储热相结合的采暖系统,该系统可根据太阳能集热温度和外界供热需求实现太阳能多模式采暖的自动控制和自动运行。实验研究表明：在西藏地区采用真空管太阳能集热器可以和中低温相变储热器很好地结合,白天储热器在储热过程中平均储热功率为10.63 kW,储热量达到92.67 kW·h,相变平台明显;晚上储热器在放热过程中供热量达85.23 kW·h,放热功率和放热温度平稳,储放热效率达92%,其储热密度是传统水箱的3.6倍,可连续供热时间长达10 h,从而实现了基于相变储热的太阳能全天候连续供热,相关研究结果对我国西藏地区实施太阳能采暖具有一定的指导作用。     

Investigation of a combined solar–heat pump system for residential heating. Part 1: experimental results

In order to investigate the performance of the combined solar–heat pump system with energy storage in encapsulated phase change material (PCM) packings for residential heating in Trabzon, Turkey, an experimental set‐up was constructed. The experimental results were obtained from November to May during the heating season for two heating systems. These systems are a series of heat pump system, and a parallel heat pump system. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load meet by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. Copyright © 1999 John Wiley & Sons, Ltd.     

Modeling, design and thermal performance of a BIPV/T system thermally coupled with a ventilated concrete slab in a low energy solar house: Part 1, BIPV/T system and house energy concept

This paper is the first of two papers that describe the modeling, design, and performance assessment based on monitored data of a building-integrated photovoltaic-thermal (BIPV/T) system thermally coupled with a ventilated concrete slab (VCS) in a prefabricated, two-storey detached, low energy solar house. This house, with a design goal of near net-zero annual energy consumption, was constructed in 2007 in Eastman, Québec, Canada - a cold climate area. Several novel solar technologies are integrated into the house and with passive solar design to reach this goal. An air-based open-loop BIPV/T system produces electricity and collects heat simultaneously. Building-integrated thermal mass is utilized both in passive and active forms. Distributed thermal mass in the direct gain area and relatively large south facing triple-glazed windows (about 9% of floor area) are employed to collect and store passive solar gains. An active thermal energy storage system (TES) stores part of the collected thermal energy from the BIPV/T system, thus reducing the energy consumption of the house ground source heat pump heating system. This paper focuses on the BIPV/T system and the integrated energy concept of the house. Monitored data indicate that the BIPV/T system has a typical efficiency of about 20% for thermal energy collection, and the annual space heating energy consumption of the house is about 5% of the national average. A thermal model of the BIPV/T system suitable for preliminary design and control of the airflow is developed and verified with monitored data.     

Simulation studies of the expected performance of Kerava solar village

The Kerava solar village is the first regional building complex in Finland with a combined solar heating and heat pump system using seasonal heat storage. The village will be completed at the beginning of 1983. In this study we describe the heating system of Kerava solar village. The heat demand was estimated by computer simulations. Different weather conditions and operational situations were considered. Under normal weather and operating conditions approximately 60 percent of the total heat demand of the Kerava solar village is estimated to be obtained from solar energy.     

A REVIEW OF LARGE-SCALE SOLAR HEATING SYSTEMS IN EUROPE

Large-scale solar applications benefit from the effect of scale. Compared to small solar domestic hot water (DHW) systems for single-family houses, the solar heat cost can be cut at least in third. The most interesting projects for replacing fossil fuels and the reduction of CO₂-emissions are solar systems with seasonal storage in combination with gas or biomass boilers. In the framework of the EU–APAS project “Large-scale Solar Heating Systems”, thirteen existing plants in six European countries have been evaluated. The yearly solar gains of the systems are between 300 and 550 kWh per m² collector area. The investment cost of solar plants with short-term storage varies from 300 up to 600 ECU per m². Systems with seasonal storage show investment costs twice as high. Results of studies concerning the market potential for solar heating plants, taking new collector concepts and industrial production into account, are presented. Site specific studies and predesign of large-scale solar heating plants in six European countries for housing developments show a 50% cost reduction compared to existing projects. The cost–benefit-ratio for the planned systems with long-term storage is between 0.7 and 1.5 ECU per kWh per year.     

SOLCHIPS—A fast predesign and optimization tool for solar heating with seasonal storage

A new version of the SOLCHIPS predesign and optimization tool for solar heating systems with seasonal storage is described. The tool is based on analytical solution of the energy balance equations describing the system performance. It comprises a user-friendly interface with a minimum input requirement and is intended for preliminary system sizing and optimization purposes. The tool is here applied to the redesign of an existing solar heating installation and to the predesign of a completely new solar plant. The evaluation and dimensioning of one CSHPSS configuration can now be done in 10–20 s thus enabling fast optimization in respect to several parameters. A case study of an existing CSHPSS plant shows a 50% decrease in the annual energy price when the system is redesigned using the SOLCHIPS tool.     

Investigation of thermal performance of a ground coupled heat pump system with a cylindrical energy storage tank

An analytical and computational model for a solar assisted heat pump heating system with an underground seasonal cylindrical storage tank is developed. The heating system consists of flat plate solar collectors, an underground cylindrical storage tank, a heat pump and a house to be heated during winter season. Analytical solution of transient field problem outside the storage tank is obtained by the application of complex finite Fourier transform and finite integral transform techniques. Three expressions for the heat pump, space heat requirement during the winter season and available solar energy are coupled with the solution of the transient temperature field problem. The analytical solution presented can be utilized to determine the annual variation of water temperature in the cylindrical store, transient earth temperature field surrounding the store and annual periodic performance of the heating system. A computer simulation program is developed to evaluate the annual periodic water and earth temperatures and system performance parameters based on the analytical solution. Copyright © 2003 John Wiley & Sons, Ltd.     

Validation of a computer model for solar assisted district heating systems with seasonal hot water heat store

The TRNSYS XST-model for the calculation of the thermal behaviour of ground buried hot water heat stores was validated. For the validation procedure measured data of the seasonal hot water heat store in Hannover (Germany) were used. In contrast to previous investigations the temperatures of the surrounding ground were also taken into consideration. The determination of the heat store parameters was carried out using TRNSYS in combination with the parameter identification software DF. The deviation between measured and calculated temperatures is less than ±3%. The measured and calculated heat quantities are also in good agreement (annual deviation less than 2%). The validated XST-model was integrated into a TRNSYS model to calculate the thermal behaviour of the solar assisted district heating system in Hannover in 2002. The deviations between measured and calculated heat quantities do not exceed 5%.     

Experimental and theoretical investigation of a solar heating system with heat pump

In this study, the performance of a solar heating system with a heat pump was investigated both experimentally and theoretically. The experimental results were obtained from November to April during the heating season. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load met by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. The average seasonal heating performance values are 4.0 and 3.0 for series and parallel heat pump systems, respectively. A mathematical model was also developed for the analysis of the solar heating system. The model consists of dynamic and heat transfer relations concerning the fundamental components in the system such as solar collector, latent heat thermal energy storage tank, compressor, condenser, evaporator and meteorological data. Some model parameters of the system such as COP, theoretical collector numbers (N_c), collector efficiency, heating capacity, compressor power, and temperatures (T₁, T₂, T₃, T_T) in the storage tank were calculated by using the experimental results. It is concluded that the theoretical model agreed well with the experimental results.     

Swedish solar heated residential area with seasonal storage in rock: Initial evaluation

A partly solar heated building area comprising 50 residential units has been built in Anneberg, Sweden. The system includes low-temperature space heating with seasonal ground storage of solar heat. Heating is supplied by 2400 m² solar collectors and individual electrical heaters for supplementary heating. The ground storage comprises about 60,000 m³ of crystalline rock with 100 boreholes drilled to 65 m depth and fitted with double U-pipes. The collectors will have favourable working conditions but the store is rather small, the estimated heat loss from the heat store is about 40% of stored solar heat and the average solar fraction is estimated to 70% after 3–5 years of operation. An initial evaluation after 2 years of operation shows that, although problems have occurred and several parts seem to work less efficient than expected, the overall system idea works as intended.     

A review on thermal energy storage systems in solar air heaters

The drying needs of agricultural, industrial process heat requirements and for space heating, solar energy is one of the prime sources which is renewable and pollution free. As the solar energy is inconsistent and nature dependent, more often there is a mismatch between the solar thermal energy availability and requirement. This drawback could be addressed to an extent with the help of thermal energy storage systems combined with solar air heaters. This review article focuses on solar air heaters with integrated and separate thermal energy storage systems as well as greenhouses with thermal storage units. A comprehensive study was carried out in solar thermal storage units consisting of sensible heat storage materials and latent heat storage materials. As the phase change heat storage materials offer many advantages over the sensible heat storage materials, the researchers are more interested in this system. The charging and discharging characteristics of thermal storage materials with various operational parameters have been reported. All the possible solar air heater applications with storage units have also been discussed.