A new PCM storage system for managing simultaneously solar and electric energy

A new hybrid thermal energy storage system (HTESS), using phase change materials, is proposed for managing simultaneously the storage of heat from solar and electric energy. Solar energy is stored during sunny days and released later at night or during cloudy days and, to smooth power demands, electric energy is stored during off-peak periods and later used during peak periods. A heat transfer model of the HTESS is developed and validated with experimental data. Simulations carried out for a period of 4 consecutive winter months indicate that, with such a system, the electricity consumption for space heating is reduced by nearly 32%. Also, more than 90% of the electric energy is consumed during off-peak hours. For electricity markets where time-of-use rate schemes are in effect, the return on the investment in such a thermal storage system is very attractive.     

Application of latent heat thermal energy storage in buildings: State-of-the-art and outlook

Latent heat thermal energy storage (LHTES) is becoming more and more attractive for space heating and cooling of buildings. The application of LHTES in buildings has the following advantages: (1) the ability to narrow the gap between the peak and off-peak loads of electricity demand; (2) the ability to save operative fees by shifting the electrical consumption from peak periods to off-peak periods since the cost of electricity at night is 1/3–1/5 of that during the day; (3) the ability to utilize solar energy continuously, storing solar energy during the day, and releasing it at night, particularly for space heating in winter by reducing diurnal temperature fluctuation thus improving the degree of thermal comfort; (4) the ability to store the natural cooling by ventilation at night in summer and to release it to decrease the room temperature during the day, thus reducing the cooling load of air conditioning. This paper investigates previous work on thermal energy storage by incorporating phase change materials (PCMs) in the building envelope. The basic principle, candidate PCMs and their thermophysical properties, incorporation methods, thermal analyses of the use of PCMs in walls, floor, ceiling and window etc. and heat transfer enhancement are discussed. We show that with suitable PCMs and a suitable incorporation method with building material, LHTES can be economically efficient for heating and cooling buildings. However, several problems need to be tackled before LHTES can reliably and practically be applied. We conclude with some suggestions for future work.     

上宏鞋业清洁能源替代工程介绍

通过对上宏鞋业有限公司用能情况进行深入分析,设计了电加热导热油蓄热供热方案替代原有燃煤锅炉蒸汽供热。以夜间低谷电加热导热油进行蓄热,白天供应生产工艺用热。在节能减排,减少投资,降低运行成本方面取得了较好的成效,该方案可以为当前清洁能源替代工程提供借鉴和参考。     

太阳能热泵相变储能复合地板辐射采暖系统

太阳能地板辐射采暖系统与相变储能技术结合使用是新能源利用的一种重要方法。介绍了一种太阳能、热泵、低谷电辅热与相变储能地板联合运行的复合地板辐射采暖系统;讨论了系统组成、运行原理以及运行流程;分析了该采暖系统在节能环保、室内热舒适性等方面的优点;展望了其良好的发展前景。     

Energetic, economic and environmental performance of a solar-thermal-assisted HVAC system

A solar-assisted HVAC system was retrofitted in 2006-2009 onto an earlier (1980) energy-efficient building. A hybrid system of flat plate and vacuum tube solar collectors heats water in a large hot storage tank that is delivered to an absorption chiller in the cooling season or directly to heating coils in the heating season. Large chilled water storage tanks are charged off-peak and discharged during the day, cooling the building in parallel with the chiller. Measurements of the seasonal performance of the system are presented. Good overall agreement between actual measurements and earlier numerical modeling results is reported for our system, with one notable discrepancy attributable to the operation of the air terminal units, which requires tuning. In cold seasons, solar thermal energy can easily displace a large fraction of traditional heating sources. In the cooling season, the conversion of heat to cooling capacity incurs several parasitic losses, which if not accounted for properly in the design stage, have the capacity to completely offset any advantage gained from the solar system. The economics of building-scale solar thermal systems are strongly dependent on the cost of energy, and electricity in particular. The economics are favorable where electricity costs are high, and vice-versa.     

电热锅炉的节能运行

电热锅炉具有很多优点，但较高的运行电费使其难以推广。结合工程实例，就如何利用峰谷电价差并通过蓄热使电热锅炉实现节能运行进行了介绍。     

蓄热式电锅炉及太阳能系统供热工程设计

采用直热式电锅炉、蓄热式电锅炉和辅助太阳能联合供热的方式。介绍了锅炉房设备选型及布置,系统设计及流程图,电锅炉、太阳能系统和集中控制系统的工作原理和设计要点。电锅炉在低谷电时段运行,太阳能系统对生活热水进行预热,节省了运行费用,达到了较高的能源利用率。     

Experimental study of under-floor electric heating system with shape-stabilized PCM plates

This paper put forward a new kind of under-floor electric heating system with shape-stabilized phase change material (PCM) plates. Different from conventional PCM, shape-stabilized PCM can keep the shape unchanged during phase change process. Therefore, the PCM leakage danger can be avoided. This system can charge heat by using cheap nighttime electricity and discharge the heat stored at daytime. In the present work, the thermal physical properties of shape-stabilized PCM developed by us were measured. A prototype room with this system was set up in Beijing to testify its thermal performance and feasibility of this heating mode. The results show that temperature of the PCM plates upper surface can be kept near the phase transition temperature in whole day and a lot of off-peak period electricity can be used for space heating in stead of using peak period electricity, which obviously lowers the electricity tariff.     

Long term operation of a solar assisted ground coupled heat pump system for space heating and domestic hot water

This paper introduces a solar-assisted ground-coupled heat pump (SAGCHP) system with heat storage for space heating and domestic hot water (DHW) supply. The simulation results of the system's detailed operating performance are presented. The optimization of the system design is carried out by the TRNSYS and a numerical simulation is performed for continuous operation of 20 years under the meteorological conditions of Beijing. Different control strategies are considered and the operational characteristics of each working mode are studied. The simulating results show that the long term yearly average space heating efficiency is improved by 26.3% compared to a traditional ground coupled heat pump (GCHP) system because the solar thermal collecting system is used to elevate the thermal energy in the soil and to provide direct space heating with heat storage. At the same time, the underground heat load imbalance problem for a heating load dominated GCHP is solved by soil recharging during non-heating periods, while extra solar energy is utilized to supply DHW. The flexibility and high efficiency of the SAGCHP system could offer an alternative for space heating and DHW supply by heat pump technology and solar energy in cold winters of northern China.     

北京地区某公司厂区太阳能低谷电接力采暖工程实例

介绍了北京的一个公司厂区太阳能低谷电接力采暖工程的成功实例。提出了该工程的设计方案和原理,并对供暖系统采集的数据进行了分析计算,这些数据对北京市目前建筑的采暖设计参数选取,以及太阳能低谷电接力供热系统的优化设计具有借鉴意义。     

Analysis and optimization of the use of CHP-ORC systems for small commercial buildings

The use of combined heating and power (CHP) systems is increasing rapidly due to their high potential of reducing primary energy consumption (PEC), cost, and carbon dioxide emissions (CDE). These reductions are mainly due to capturing the exhaust heat to satisfy the thermal demand of a building. However, when the CHP system is operated following the electric load, the recovered exhaust heat may or may not be sufficient to satisfy the thermal demand of the facility. When the recovered exhaust heat is more than the heat required, the excess is usually discarded to the atmosphere. An organic rankine cycle (ORC) can be used to recover the surplus exhaust heat to generate extra electricity. Therefore, combining the ORC system with the CHP system (CHP-ORC) reduces the electricity that has to be produced by the CHP system, thereby reducing the total PEC, cost, and CDE. The objective of this paper is to study the energetic, economical, and environmental performance of a combined CHP-ORC system and compare its performance to a standalone CHP system and a reference building for different climate zones. A comparison of a CHP-ORC system operating 24 h with a system operating during typical office hours is also performed.     

Exergy analysis for day lighting, electric lighting and space cooling systems for a room space in a tropical climate

Turning off the electric lamp during available daylight will save electricity, while at the same time thermal energy from solar radiation transmitted through the window will increase the space-cooling load. Therefore, it is necessary to evaluate the whole system that includes not only the room space with the windows and the electric lighting systems, but also the air conditioning system. For analysis of the whole system using different types of energy (i.e. electricity, solar radiation, light emitted by lamps and thermal energy), it is important to take into account the quality of these different types of energy. The concept of entropy and exergy were applied in this analysis. The purpose of this study is to show the energy use for daylighting, electric lighting, and space cooling systems as a series of exergy input, output, and consumption and reveal how a daylighting system consumes solar exergy and how electric lighting and space cooling systems consume exergy from fossil fuel. The methodology to calculate the exergy consumption of the system during a given time was developed first. This method was then applied to the lighting and cooling for a typical room. The study found that electric lighting consumes the lowest amount of exergy while the space cooling consumes the highest amount of exergy for the system.     

Optimized control strategies for solar district heating systems

Solar district heating (SDH) systems are a proven concept for the supply of space heating and/or domestic hot water using solar energy as the main heat source. SDH systems with a high solar fraction include seasonal thermal storage and various subsystems with different time scales that must be managed by the supervisory control system. This paper presents the development of optimized control strategies for the Drake Landing Solar Community in Okotoks (Alberta, Canada). The proposed strategies, based on the application of model predictive control concepts, aim to further reduce the use of auxiliary energy for heating (gas) while also reducing the pumping energy (electricity). Perfect forecasts for the weather and the SDH loads are assumed in the study and a detailed TRNSYS model is used. Results show that the primary energy consumption can be reduced by 5% by updating the supervisory control strategies.     

Analysis of feasibility on heating single family houses in rural areas by using sun and wind energy

Households in Lithuania consume about 1/3 of total final consumption of fuel energy. In order to reduce imports of fossil fuel and emissions of dangerous pollutants, solar energy could be used for the above-mentioned needs. That would require large collector areas and volumes for seasonal heat storage. In wintertime the wind speed velocity is much higher than in summertime in Lithuania. Therefore, it is advisable to study meeting the thermal needs of single family houses by combining use of wind and solar energy. To this end analytical research has been made by using deterministic method. The analysis has been carried out for the case when 1 m² of heated room area requires 0.25 m² of solar collector area and 0.5 m² working area of wind turbine rotor. Heat storage is planned for 24 h. By using such a hybrid system during the heating season 42.6–56.2% of heating needs for space and domestic hot water are satisfied. However, for individual days (especially from May to October) a surplus of generated heat is formed and it reaches about 53.6% of space heating needs per year. This relative surplus of energy could be used for transmitting wind power-plant energy to the electric network or in a household and thermal energy can be used for drying agricultural produce, heating greenhouses, open swimming pools and satisfying other needs.     

建筑一体化电热冷联产光伏组件能量特性研究

传统太阳能光伏或光热建筑一体化只能为建筑提供单一电能或热能。通过研究一种集成发电、集热、制冷3种功能的建筑一体化电热冷联产光伏组件,对其夏季工况下能量特性进行了实际检测。结果表明:白天,组件集热同时能有效降低光伏电池温度,组件工作温度高于环境温度约8~16℃,发电和集热效率分别为14.1%~13.7%和40.1%~15.7%;晴朗夜间,组件通过对流和辐射两种传热方式进行散热制冷,总制冷功率为26.0~268.5 W/m~2。电热冷联产光伏组件适合与热泵结合,为建筑提供所需能源。     

Model predictive control of a building heating system: The first experience

This paper presents model predictive controller (MPC) applied to the temperature control of real building. Conventional control strategies of a building heating system such as weather-compensated control cannot make use of the energy supplied to a building (e.g. solar gain in case of sunny day). Moreover dropout of outside temperature can lead to underheating of a building. Presented predictive controller uses both weather forecast and thermal model of a building to inside temperature control. By this, it can utilize thermal capacity of a building and minimize energy consumption. It can also maintain inside temperature at desired level independent of outside weather conditions. Nevertheless, proper identification of the building model is crucial. The models of multiple input multiple output systems (MIMO) can be identified by means of subspace methods. Oftentimes, the measured data used for identification are not satisfactory and need special treatment. During the 2009/2010 heating season, the controller was tested on a large university building and achieved savings of 17–24% compared to the present controller.     

相变材料与建筑基体复合的相变维护结构热特性探讨

将相变材料与建材基体复合，构筑成一种新型相变蓄能建筑维护结构。这种建筑维护结构可充分利用夜间低价电蓄热，供次日白天的辅助热源，降低采暖系统的投资与能耗，改善室内环境。主要探讨了相变材料与石膏等建筑基体复合后相变建筑维护结构的热特性。     

高校楼宇供暖节能控制系统研制

针对高校供暖面积大、能耗多,供热管线长、水力失调严重等特点,研制了一种楼宇供暖节能控制装置。该装置由现场控制器、温度传感器和电动调节阀组成,现场控制器完成数据的采集和处理,并根据各时段的供暖温度要求,自动调节电动阀门的开度,从而调整进入楼宇的供水流量。另外,在控制流程中还加入了节假日保证最低供暖温度的模式,避免了能源的浪费。     

Low-energy envelope design of residential building in hot summer and cold winter zone in China

With the development of the economy, the demand for energy in hot summer and cold winter zone in China is increasing very fast while the energy supply is going short. Air conditioning both for cooling and heating accounts for more than 50% of the total electricity used in the residential sector. This paper used eQUEST software to analyze envelope design on energy saving of air conditioner (AC) and the effects of energy saving strategies on AC electric consumption of different orientation rooms in hot summer and cold winter zone in China, which included exterior wall thermal insulation, solar radiation absorptance of exterior wall, area ratio of window to wall, categories of glazing and kinds of shading system, and two combined strategies. The results indicate that envelope shading and exterior wall thermal insulation are the best strategies to decrease the AC electric consumption which achieved a saving of 11.31 and 11.55%. The optimization of different strategies can decrease the annual electric consumption of AC by 25.92%, and cooling and heating electric consumption is decreased by 21.08 and 34.77%, respectively.     

Are the relative variation rates (RVRs) approximate in different cities for the same building with the same outer-window reform?

By analyzing and comparing hourly, monthly and classified cooling and heating energy consumption of Tampa and Guangzhou, it can be found that the reduction of heat transfer coefficient of outside window can obviously decrease annual heating need. Its effect is essentially similar to the reduction of outer-wall heat transfer coefficient. The reduction of outer-window heat transfer coefficient can significantly increase the heating or cooling RVRs of the hours without solar radiation (basic RVRs) and it can also increase the heating RVRs at the hours with solar radiation. However, it can just increase cooling RVRs at the hours with solar radiation limitedly. Only supplemented with restraining solar radiation effectively, it could raise the cooling RVRs significantly. Whatever any climatic conditions, the annual heating energy consumption is governed by the classification without solar radiation ($>80\%$) and annual cooling energy consumption is governed by the classification with solar radiation ($>90\%$). Therefore, in order to decrease heating energy consumption, the first choice is the improvement of envelope's thermal insulation performance while to decrease cooling need, the first measure is to restrain solar radiation and then supplemented with the improvement of envelope. It is shown by the research that under the same outer-window heat transfer coefficient (i.e., the same measure of outer-window thermal insulation is adopted for the same building), the heating RVRs are approximate and the cooling RVRs are also approximate in different cities. This paper proves at another angle the universalism of approximation of heating and cooling RVRs under different climatic conditions (or in different cities) for the same building with the same energy-efficient measure again.