A solar water heater with a built-in latent heat storage

In this paper, we have investigated the performance of a novel built-in storage type water heater containing a layer of PCM-filled capsules at the bottom. The PCM layer is introduced with a view of getting hot water during off-sunshine hours. The moving solid-liquid boundary layer problem for the PCM material is simplified to a stationary boundary layer problem, and the effect of latent heat is included in the specific heat by replacing the semi-melted PCM by a fictitious solid. The performance of the water heater is then predicted analytically for two depths of PCM and for different flow rates, both constant and intermittent. The case of sudden withdrawal of water over very short periods is also studied.     

Year round performance studies on a built-in storage type solar water heater at Jodhpur, India

An improved solar water heater (capacity 901) made up of a 112×80×10 cm rectangular tank which performs the dual function of absorbing heat and storing the heated water has been designed and a prototype tested in Jodhpur. The performance tests carried out at the Central Arid Zone Research Institute, Jodhpur, indicate an efficiency factor reaching as high as 70 per cent. The year-round performance tests show that this heater can supply 901 of water at a mean temperature of 50 to 60°C in winter and 60 to 75°C in summer (measured at 4:00 p.m.). The performance tests also indicate that sufficient hot water can be obtained in the early morning if the heater is covered with an insulation blanket overnight or if the hot water is stored in an insulated tank.A performance equation for this type of heater, where the inputs are the solar intensity, ambient air temperature and geometry and material specifications of the heater, has also been developed. With this performance equation the optimum gap depth, i.e. the distance between upper and lower plate of the heater, has been found to be 10·0 cm.     

Long-term performance of an n built-in storage water heater

In this paper, an experiment has been performed to validate the theoretical results obtained for the n built-in storage water heater. The long-term performance of the system has also been studied in detail. It was found that (i) there is good agreement between theoretical and experimental observations and (ii) the condition of quasi-steady state is achieved only after 3–4 days.     

Performance of a solar collector/storage water heater

This paper presents a general analytical model of a solar collector/storage water heater in which water is flowing at a constant rate between the glass cover and the absorbing plate. The effects of the variations of the depth of water, its flow velocity and the length of the absorbing plate on the performance of the collector have been studied.     

Thermal performance of integrated collector storage solar water heater with corrugated absorber surface

An investigation is reported of the thermal performance of an integrated solar water heater with a corrugated absorber surface. The thermal performance of the rectangular collector/storage solar water heater depends significantly on the heat transfer rate between the absorber surface and the water, and on the amount of solar radiation incident on the absorber surface. In this investigation, the surface of the absorber is considered to be corrugated, with small indentation depths, instead of plane. The modified surface has a higher characteristic length for convective heat transfer from the absorber to the water, in addition to having more surface area exposed to solar radiation. The corrugated surface based solar water heater is determined to have a higher operating temperature for longer time than the plane surface. It means during the operation of water heater, more solar energy is converted into useful heat. However, this modification has reduces the efficiency of the system marginally.     

Integrated collector storage solar water heater: Temperature stratification

An analysis of the temperature stratification inside an Integrated Collector Storage Solar Water Heater (ICS-SWH) was carried out. The system takes the form of a rectangular-shaped box incorporating the solar collector and storage tank into a single unit and was optimised for simulation in Scottish weather conditions. A 3-month experimental study on the ICS-SWH was undertaken in order to provide empirical data for comparison with the computed results. Using a previously developed macro model; a number of improvements were made. The initial macro model was able to generate corresponding water bulk temperature in the collector with a given hourly incident solar radiation, ambient temperature and inlet water temperature and therefore able to predict ICS-SWH performance. The new model was able to compute the bulk water temperature variation in different SWH collectors for a given aspect ratio and the water temperature along the height of the collector (temperature stratification). Computed longitudinal temperature stratification results obtained were found to be in close agreement with the experimental data.     

Performance of a non-metallic unglazed solar water heater with integrated storage system

The performance of a new design of non-metallic unglazed solar water heater integrated with a storage system has been studied. In this system, the collector and storage were installed in one unit. All parts of the system have been fabricated from fiberglass reinforced polyester (GFRP) using a special resin composition that provides good thermal conductivity and absorptivity. The storage tank has a capacity of 329 l. The design of the storage system was sandwich construction, with the core material made out of polyurethane foam, which combines stiffness and lightness of structure with very good thermal insulation. The width and length of the absorber plat were 1.4 and 1.8 m, respectively. The performance of the system has been investigated by two methods. In the first method, the storage tank was filled up with water the night before the test. The tank was then drained during the night, refilled and made ready for the next day’s test. The tests were repeated under varied environmental conditions for several days. The maximum water temperature in the storage tank of 63 °C has been achieved for a clear day operation at an average solar radiation level of 700 W m⁻² and ambient temperature of 30 °C. The decrease of water temperature with and without the thermal diode is 10 and 20 °C, respectively. In the second method, the testing was of the same way, but in this case without draw-off or draining of the hot water from the storage tank. All data readings were recorded from sunrise to sunset over the same period. The temperature was recorded for several days and ranges of 60–63 °C were obtained in the storage tank. A system efficiency of 45% was achieved at an average solar radiation level of 635 W m⁻² and ambient temperature of 31 °C.     

Experimental investigation of a domestic solar water heater with solar collector coupled phase-change energy storage

Phase change materials (PCMs) have good properties such as high thermal capacity and constant phase change temperature. Their potential use in solar energy storage is promising. Tests of exposure and constant flow rate are performed to investigate the thermal performance of a domestic solar water heater with solar collector coupled phase-change energy storage (DSWHSCPHES). Due to the low thermal conductivity and high viscosity of PCM, heat transfer in the PCM module is repressed. The thermal performance of the DSWHSCPHES under exposure is inferior to that of traditional water-in-glass evacuated tube solar water heaters (TWGETSWH) with an identical collector area. DSWHSCPHES also performs more efficiently with a constant flow rate than under the condition of exposure. Radiation and initial water temperature have impacts on system performance; with the increase of proportion of diffuse to global radiation and/or initial water temperature, system performance deteriorates and vice versa.     

新型整体式太阳能热水器的优化设计和实验研究

本文的新型焖晒式热水器主要有两个特点 :一是水箱采用倒三角形且水平横向长纵向短的设计方式 ,以减少水箱中的死水和承压问题 ;二是在玻璃盖板和吸热面之间覆盖透明V形槽或透明蜂窝 ,该种透明隔热构件既有较高的太阳透过率又有较好的隔热性能 ,虽然减少了到达吸热面上的太阳辐射能 ,但保温性能提高了 1～ 2倍。该种热水器热效率接近真空管热水器 ,但成本低 ,且不怕冻冰 ,是我国大部分地区全年可用的低成本高效率的热水器。     

Analysis of a flat plate solar collector/storage water heater with evaporation

We analyse the performance of a flat-plate collector with a constant rate of evaporation of flowing water between a glass cover and an absorbing plate. The effects of fluid-flow velocity, depth of fluid and length of the absorbing surface are discussed. We have allowed for periodic variation of the solar intensity and ambient air temperature during a typical day in New Delhi.     

Thermal performance of n built-in storage water heaters (or shallow solar ponds) in series

This note presents an analysis of the thermal performance of n built-in storage water heaters (or shallowsolar ponds), connected in series. It is seen that for typical parameters, three or four built in storage tanks may be connected in series for significantly better performance. Numerical calculations have been made for two typical days, viz. 26 May 1978 and 28 April 1979 at Delhi.     

Techno-economic appraisal of an integrated collector/storage solar water heater

Integrated collector/storage solar water heaters, due to their simple compact structure and inherent freeze protection, offer a promising approach for solar water heating in colder climates. Such a system, designed specifically for application at a Northern latitude, has been developed incorporating a heat retaining storage vessel mounted within a concentrating cusp reflector supported by a novel exo-skeleton framework. The performance was determined experimentally under real operational conditions in the Northern Irish climate. A detailed cost analysis is presented and payback periods, substituting different local fuel/power sources, determined.     

Thermal performance of a solar still coupled with an inexpensive ground water heater

This paper presents the results of investigations carried out over a solar still coupled with an inexpensive solar ground water heater. The explicit expressions for water temperature at the outlet of water heater, glass and water temperatures in the case of a solar still in which the hot water is flowing at a constant rate, have been derived. To appreciate the enhancement in the still productivity, numerical calculations have also been carried out for two typical days at Delhi, India.     

“看不见”的太阳能热水器

太阳能热水器已经走进千家万户,但其市场仍主要在农村和小城镇,城市市场的份额相对较小。其原因在于在城市高楼大厦上安装太阳能热水器被安装场地和城市建筑美观要求所局限。随着我国城市现代化、农村城镇化进程的加快,住宅建筑形式也向多样化发展,普通落水式太阳能热水器的安装局限性开始显现,甚至有的小区楼顶已经不允许安装,这对太阳能热水器与建筑的结合提出了更高要求。因而,太阳能与建筑一体化成为打破这一瓶颈的有效解决方案。     

太阳热水器技术讲座(三)家用太阳热水器

太阳热水器(或称太阳热水装置)根据用途可分为家用热水器和太阳热水系统(或称太阳热水工程)。严格来说，应按国标GB／18713—2002规定来区分，即水箱容水量在0．6t以下的太阳热水器称之为家用太阳热水器．而水箱容量大于0．6t的太阳热水器称之为太阳热水系统。     

Thermal performance of a new solar air heater

A solar air heater, part of a food drying system using solar energy as a renewable energy source for heat, was developed and tested for several agricultural products (i.e., sultana grapes, green beans, sweet peppers, chilli peppers). Drying processes were conducted in the chamber with forced natural air heated partly by solar energy. Solar air heater performances were discussed along with estimates of energy efficiency of the system. The obtained results indicate that the present system is efficient and effective.     

Thermal analysis of compact solar water heater under local climatic conditions

Extensive experimental studies on a compact solar water heater were carried out, in order to evaluate the performance of the heater and determine the optimal depth of the storage tank. The experiments were conducted for tank depths of 5, 10 and 15 cm with single and double glazing. Experimental results show that a temperature rise of about 68 °C during the month of July at storage tank depth of 10 cm can be achieved by the heater. The 10 cm depth of the tank is optimum which can supply hot water for 24 h. The rise of water temperature is slightly higher in the case of single glazing than the double glazed system, while the double glazed system is more effective in retaining higher temperatures during night hours.