There is generally agreement among the HVAC (Heating Ventilating and Air Conditioning) community that one of the main issues impeding solar thermal technologies from achieving their full potential for space heating and domestic hot water (DHW) production applications is the development of economically competitive and reliable means for seasonal storage of thermal energy. This is particularly true at high latitude locations, where seasonal variations of solar radiation are significant, and in cold climates, where seasonally varying space heating loads dominate residential energy consumption. This review presents the principal methods available for seasonal storage of solar thermal energy. It concentrates on residential scale systems, and particularly those currently used in practice which mostly store energy in the form of sensible heat. Some newer methods that exhibit promise, like chemical and latent storage, are also briefly discussed and pertinent reviews are referenced.

A review of available methods for seasonal storage of solar thermal energy in residential applications

To sufficiently store and use high-quality heat energy, thermal stratification is gradually applied in many kinds of energy storage fields such as solar thermal utilization system. Because of the unsteady characteristics of solar radiation, thermal storage becomes very essential in long-term operation of heating load. The wide application of thermal stratification lies in the minimization of the mixing effect by use of the thermal stratification, which is caused by the thermal buoyancy because of the difference of temperature between cold and hot water. According to the review, the conception of thermal stratification allows a wide variety of different design embodiments, which essentially extends the fields of practical application of these devices. In this paper a survey of the various types of thermal stratification tanks and research methods is presented, and reasons of energy storage with efficiency problems related to the applications are introduced and benefits offered by thermal stratification are outlined. The structure designs based on theoretical prediction of thermal-stratified water tank performed at many organizations are introduced and are compared with their experimental results. Finally, the development of the tank with thermal stratification in the future application is predicted.

Thermal stratification within the water tank

Rotary desiccant air conditioning system, which combines the technologies of desiccant dehumidification and evaporative cooling, is advantageous in being free from CFCs, using low grade thermal energy and controlling humidity and temperature separately. Compared with conventional vapor compression air conditioning system, it preserves the merits of environment-friendly, energy saving, healthy, comfortable, etc. Ongoing research and development works suggest that new desiccant materials and novel system configurations have significant potential for improving the performance and reliability and reducing the cost and size of rotary desiccant dehumidification and air conditioning system, thereby increasing its market competitiveness and breaking out the current fairly small niche market. For the purpose of providing an overview of recent efforts on these issues and showing how rotary desiccant air conditioning systems can be designed and coupled to available thermal energy, this paper presents and analyzes the status of rotary desiccant dehumidification and air conditioning in the following three aspects: the development of advanced desiccant materials, the optimization of system configuration and the utilization of solar energy and other low grade heat sources, such as solar energy, district heating, waste heat and bioenergy. Some key problems to further push forward the research and development of this technology are also summarized.

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Technical development of rotary desiccant dehumidification and air conditioning: A review

Solar water heating (SWH) systems have a widespread usage and applications in both domestic and industrial sectors. According to Renewable Energy Policy Network data (2010), 70 million houses worldwide were reported to be using SWH systems. Solar water heating is not only environmentally friendly but requires minimal maintenance and operation cost compared to other solar energy applications. SWH systems are cost effective with an attractive payback period of 2–4 years depending on the type and size of the system. Extensive research has been performed to further improve the thermal efficiency of solar water heating. This paper presents a detailed review exclusively on the design aspects of SWH systems. The first part of the paper provides a consolidated summary on the development of various system components that includes the collector, storage tank and heat exchanger. The later part of this paper covers the alternative refrigerant technology and technological advancements in improving the performance as well as the cost effectiveness of the SWH system.

Recent advances in the solar water heating systems: A review

Power shortage and unstable power supply remain serious problems Conventional cooling technologies that utilize harmful refrigerants consume more energy and cause peak loads leading to negative environmental impacts As the world grapples with the energy and environmental crisis, there is an urgent need to develop and promote environmentally benign sustainable cooling technologies Solar cooling is one such promising technology, given the fact that solar energy is the cheapest and widely available renewable energy that matches the cooling load requirements Thermal storage systems are essential to overcome the disadvantage of the intermittent nature of solar energy and variation in cooling demand The enhanced utilization of solar energy and other consequences of thermal storage integrated systems have gained the attention of researchers in the recent years This paper reviews research articles in the field of solar cooling techniques, solar collectors, storage methods and their integration, along with performance improvement studies reported using thermal stratification and cascaded thermal storage systems

Review of solar cooling methods and thermal storage options

Effect of obstacles on thermal stratification in hot water storage tanks

Heat transfer enhancement in a tube using circular cross sectional rings separated from wall

Improved thermal stratification with obstacles placed inside the vertical mantled hot water tanks

Effect of ambient conditions on the first and second law performance of an open desiccant cooling process

Thermal stratification in a mantled hot water storage tank is analysed numerically for different water inlet velocities. The aim is to obtain higher thermal stratification and supply hot water for usage as long as possible. Twelve different water inlet velocities to the hot water storage tank are considered. The numerical method is validated by comparing its results against experimental and numerical results from the literature. It turned out that the results obtained from the numerical analysis have shown very good agreements with the results from previous works. As a result, the water temperature in the tank increases with the increase of the water inlet velocities to the mantle but this increment is not proportional. After a period of operation of 7.2 h, which corresponds to the average sunshine duration in Turkey, temperature increments of 6.5 and 35 K have been estimated for the hot water inlet velocities of 0.01 and 0.3 m s−1, respectively, at a radial distance of 0.1 m and a height of 1 m inside the storage tank. Copyright © 2005 John Wiley & Sons, Ltd.

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Papers

Effect of obstacles on thermal stratification in hot water storage tanks

Heat transfer enhancement in a tube using circular cross sectional rings separated from wall

Improved thermal stratification with obstacles placed inside the vertical mantled hot water tanks

Effect of ambient conditions on the first and second law performance of an open desiccant cooling process

Effect of water inlet velocity on thermal stratification in a mantled hot water storage tank