Collector cum storage solar water heaters with and without transparent insulation material

The integrated collector–storage solar water heaters are less expensive and can offer the best alternative for domestic applications particularly to small families to meet hot water requirements. The top heat losses of such solar water heaters are quite high during the night and the temperature of stored hot water is considerably reduced unless covered with extra insulating cover in the evening which is a cumbersome job. The transparent insulation material widely used in Europe for space heating can also minimize top heat losses, if used in such solar water heaters. For this purpose, two units of solar collector cum storage water heaters have been designed to study the relative effect of TI for retaining solar heated hot water for a night duration. Both units were identical in all respects except one of them was covered with TIM. The theoretical exercise was carried out to evaluate design parameters of ISC which revealed total heat loss factor (U_L) 1.03 W/m² K with TIM glazed against 7.06 W/m² K with glass glazed. The TIM glazed has been found to be quite effective as compared to glass glazed SWH and yielded hot water at higher temperature by 8.5 to 9.5°C the next morning. The storage efficiency of such solar water heaters has been found to be 39.8% with TIM glazed as compared to 15.1% without TIM. The TIM glazing means not having to cover the ISC solar water heater with a separate insulator cover in the evening and thus makes its operation much simpler.     

Status and prospects of local solar heating and cooling systems

In this paper, a state-of-the-art of solar heating and cooling systems is presented. Solar air heaters and different types of solar water collectors are discussed in detail. Storage systems including water, rocks, and heat-of-fusion salts are described as are space heating systems employing solar air heaters, in conjunction with rock or heat-of-fusion salt storage, and the use of water collectors plus hot water storage for space heating and domestic hot water. An indication of the commercialization of various space-heating systems and broad economic projections are presented. The three major solar cooling methods—absorption cooling, solar mechanical systems, and those involving humidification-dehumidification cycles—are also discussed in detail. Finally, an overview of solar heating and cooling activities in Kuwait is also given.     

Economics of a solar-assisted heating/cooling system for an aquatic centre in a tropical environment

The paper reports on a feasibility study of a solar-powered heating/cooling system for a swimming pool/space combination in a tropical environment. The system employs an absorption chiller and a cooling tower to meet the locker-room load. The heating is accomplished by employing hot water generated by heat exchange with the solar collector working fluid. Two thermal storage tanks are employed for the collector and domestic use. The absorption chiller utilizes hot water to regenerate the LiBr solution. The proposed system will enable the swimming season to be extended from 16 weeks to 52 weeks. The economic analysis is performed based on the life-cycle-cost method. The effects of discount rate, fuel prices, and the fuel inflation rate are discussed. The analysis shows, with the present level of fuel prices, that the solarassisted system is not economical enough over a life cycle of 10 years. The study presents different scenarios for which the solar-assisted system is, however, economical.     

ICS solar systems with two water tanks

Integrated collector storage (ICS) systems are compact solar water heaters, simple in construction, installation and operation. They are cheaper than flat plate thermosiphonic units, but their higher thermal losses make them suitable mainly for application in locations with favourable weather conditions. Aiming to the achievement of low system height and satisfactory water temperature stratification, new types of ICS systems with two horizontal cylindrical storage tanks, properly mounted in stationary CPC reflector troughs are suggested. The non-uniform distribution of solar radiation on the two absorbing surfaces is combined with the seasonal sun elevation, resulting to effective water heating. In addition, the inverted absorber concept design can be applied to ICS systems with two storage tanks. In this paper, we present the design and performance of double tank ICS solar systems, which are based on the combination of symmetric and asymmetric CPC reflectors with water storage tanks. The analytical equations of the collector geometry of all models are calculated with respect to the radius of the cylindrical water storage tank and the reflector rim angles. Experimental results for the variation of the water temperature inside storage tanks, the mean daily efficiency and the coefficient of thermal losses during night are given for all experimental models. The tests were performed without water draining and the results show that the double tank ICS systems are efficient in water temperature rise during day and satisfactory preservation of the hot water temperature during night, with the upper storage tank being more effective in performance in most of the studied models.     

Performance and economics of annual storage solar heating systems

Annual storage is used with active solar heating systems to permit storage of summer-time solar heat for winter use. This paper presents the results of a comprehensive computer simulation study of the performance of active solar heating systems with long-term hot water storage. A unique feature of this study is the investigation of systems used to supply backup heat to passive solar and energy-conserving buildings, as well as to meet standard heating and hot water loads.

Findings show that system performance increases linearly as storage volume increases, up to the point where the storage tank is large enough to store all heat collected in summer. This point, the point of “unconstrained operation”, is the likely economic optimum. In contrast to diurnal storage systems, systems with annual storage show only slightly diminishing returns as system size increases. Annual storage systems providing nearly 100% solar space heat may cost the same or less per unit heat delivered as a 50 per cent diurnal solar system. Also in contrast to diurnal systems, annual storage systems perform efficiently in meeting the load of a passive or energy-efficient building. A breakeven cost 4¢–10¢/kWh is estimated for optimal 100 per cent solar heating in the U.S.A.     

The marginal cost of solar backup

The long-run marginal cost of providing electricity for solar heating and hot water systems is estimated for three utilities and compared with the cost of providing electricity to electric-only systems. All investment, fuel, and operating costs are accounted for. Hot water systems and combined heating and hot water systems are analyzed separately. It is found that the marginal cost for solar backup is no more than the marginal cost of electricity used for purely electric heating and hot water devices and also no more than the incremental cost of normal load growth. For the three utilities studied, there appears to be little basis for rate distinctions between solar devices using electric backup and electric-only heating and hot water devices. “Off-peak storage” heating and hot water devices have a much lower marginal cost than the standard systems; again, there appears to be no basis for distinguishing between solar and electric off-peak devices. Compared with average cost pricing, marginal cost pricing offers benefits to customers using solar and electric heat and hot water, especially if a separate lower rate is adopted for off-peak storage devices; these benefits can amount to several hundred dollars a year. Substantial savings in the use of oil and gas fuels can be achieved if residences using these fuels convert to solar systems, savings not necessarily achievable by a shift, instead, to electric systems.     

Solar ICS systems with two cylindrical storage tanks

Two types of ICS solar water heaters designed, constructed and tested. The systems consist of two cylindrical storage tanks, which are connected in series and are horizontally incorporated in a stationary asymmetric CPC type mirror. The efficient operation of the system is due to the thermal losses suppression of the two inverted cylindrical surfaces and the effective use of the two tanks during sunshine period. Low cost and durable materials are used to construct the systems. The mean daily efficiency and the thermal performance of the hot water storage during night are calculated from outdoor experimental data. The results show that the proposed ICS systems are efficient and suitable for practical use as DHW systems.     

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.     

Simulation of a solar heating and cooling system

This paper presents thermal and economic analyses of a solar heated and air conditioned house in the Albuquerque climate. The system includes the following components: water heating collector, a water storage unit, a service hot water facility, a lithium bromide-water air conditioner (with cooling tower), an auxiliary energy source, and associated controls. The analysis of the thermal performance indicates the dependence of output on collector area (considered as the primary design variable) and shows, for example, the manner in which annual system efficiency decreases as collector area increases. Based on the computed thermal performance, cost estimates are made which show variations in annual cost as functions of collector area and costs of collector and fuel.     

The marginal cost of electricity used as backup for solar hot water systems: A case study

In this study, a method is developed for estimating the long run marginal cost to electric utilities of providing backup service for solar residential heating and hot water (HHW) systems. This method accounts for all investment, fuel, and operating costs required to provide the added electric service for HHW. From the information produced using this method, the impacts of various rate design philosophies and of government tax and regulatory policies on annual homeowner costs, fuel consumption patterns, environmental pollutants, and the net social cost of providing HHW service can be computed. Also, the differences in these parameters among solar, electric, and conventional HHW systems can be compared.In an initial study, it was found that for one Northeastern utility the estimated marginal cost of electricity for backup to solar hot water (HW) systems was less than that for comparable electric HW systems for the period of the mid to late 1990s. Load management (shifting all electricity use to off-peak periods) substantially reduced marginal costs for both electric and solar systems and essentially eliminated any difference between them. In all cases, the marginal cost was lower than the average cost of all electricity generated for market penetration rates that can realistically be expected to be experienced. The impact on total annual costs to homeowners of various electricity rate schemes and the impacts of Federal tax credits and property tax exemptions were computed. Net changes in resource consumption patterns due to the use of solar systems were estimated.     

太阳能吸收式空调及供热系统的设计和性能

一套太阳能吸收式空调及供热综合系统已在山东省乳山市建成。该系统由热管式真空管集热器、溴化锂吸收式制冷机、储水箱、循环、冷却塔、空调箱、辅助燃油锅炉和自动控制系统等内部分组成,具有夏季制冷、冬季供热和全年提供生活用热水等功能。太阳能集热器总采光面积540m∧2,制冷、供热功率100kW,空调、采暖建筑面积1000m∧2供生活用热水量32m∧3／d。文中着重介绍了系统的设计特点和测试性能。     

A solar-assisted heat pump system for heating and cooling residences

A significant impact of solar energy applications on the total energy demand requires systems or devices which can be retrofitted to existing energy users. The all-electric residence unit, which includes about 10 per cent of all such units in the U.S.A. and constitutes over half of those completed in 1973, seems particularly suited to a solar modification. It is proposed that heating and cooling of the all-electric residence unit be accomplished by using a solar-assisted heat-pump system. The proposed system makes use of a conventional air-conditioning unit which would be modified by fitting controls to reverse the flow of refrigerant for the heating mode and by changing the outdoor heat exchanger from refrigerant-to-air to refrigerant-to-water. In addition, there would be provided a solar collector and two insulated water-storage tanks. Water from one tank would be circulated through the refrigerant-to-water heat exchanger when needed and then returned to the other tank, so that essentially a source of heat of constant temperature would be maintained, thus decreasing the temperature interval for the heat pump and thereby saving energy. In the cooling mode the stored water would be cooled by exposure of the solar collector to the night sky to decrease the temperature interval for the heat pump, thereby reducing energy consumption. Calculations were made for an existing residence unit for which the total energy input is known and to which the proposed solar-assisted heat-pump system is applied. An estimated cost of equipment and of its operation is compared with the cost of owning and operating fuel and electrically heated systems. It is concluded that the solar-assisted heat-pump system with current fuel prices can provide immediate economic benefit over the all-electric home and is possibly on par with residences using fuel oil or liquefied petroleum gas, but it yields higher cost over systems using natural gas. The effect of a two-phase expander to replace the expansion valve in the refrigerant circuit has been theoretically investigated. It shows a significant energy saving worthy of further economic and practical consideration.     

Solar and geothermal heating and cooling of the European Centre for Public Law building in Greece

The European Centre for Public Law in Legraina near Athens in Greece is heated and cooled by a combined solar and geothermal system. The main components of the system are a saline groundwater supplying well, water storage tank for 6 h autonomy, inverter for regulating geothermal flow, heat exchanger, two electrical water source heat pumps placed in cascade, fan coils, air handling units, as well as solar air collectors for air preheating in winter. In addition, hot water is supplied to the building hostel by solar water heaters. Monitoring of the energy system during heating showed excellent energy efficiency and performance.     

Performance of hot water systems with tanks in series

It is usual to extract hot water from a storage tank, using displacement by cold water from the mains; this causes the temperature of the outgoing hot water to decrease with time. In order to alleviate this undesirable feature a number of tanks in series may be employed. In this communication the effect of number of tanks on the outlet temperature of hot water, has been analytically investigated; it has been assumed that the only heat exchange, taking place in the tanks is on account of flow of water. The considerations in this analysis are similar to those made by Rabinovich and Fert [1] and Rabinovich [2], for a system of tanks in a solar collector loop without any outflow of water. Thus the analysis is best applicable when hot water is extracted at a fast rate, so that the gain or loss of heat by other mechanisms is negligible, compared to that due to the flow of water. The analysis should also be applicable to shallow solar ponds, Sodha et al. [3], and built in storage water heaters, Sodha et al. [4].     

小高层学生公寓太阳能中央热水系统方案分析

针对小高层学生公寓太阳能中央热水系统储热水箱、管网和辅助加热系统,叙述了适合小高层学生公寓的最优太阳能中央热水系统设计方案及运行控制系统的边界条件。     

Performance analysis of a solar-assisted swimming pool heating system

This paper deals with feasibility studies for a solar-assisted heating system for the University of Miami's Aquatic Center using the simulation program TRNSYS. The Aquatic Center is composed of an outdoor olympic size swimming pool and locker room building. The solar heating is accomplished by employing hot water generated by heat exchange with the solar collector working fluid. Two thermal storage tanks are employed for the collector and domestic use. The performance of the system is analyzed from both thermodynamic and economic standpoints and general conclusions are reached.     

Economics of solar heating with homeowner-type financing

A feasibility study of the present-day economics of solar space and hot water heating is presented for a region with Tennessee's climate and geographic latitude. The economics of solar systems are considered for typical cities across the state representing different weather conditions. Financing is considered for conditions likely to be encountered by a homeowner. These costs are compared to current fossil fuels and electric power systems, with graphs presented to aid in economic decisions.     

太阳能生活热水系统相变储能研究进展

该文阐述了太阳能生活热水（SDHW）系统用相变材料的选择与封装情况,综述了相变材料在SDHW系统水箱、太阳能集热器和SDHW系统循环中的储能及其改进与强化换热研究进展情况,并对今后SDHW系统相变材料应用发展方向提出建议和展望。研究表明,石蜡与三水醋酸钠应用于SDHW系统水箱和集热器的研究较为广泛,其封装形式主要是的塑料、铝、不锈钢的宏封装,形状为管、柱体、球等,且相变材料加入到传统的SDHW系统中均能提高太阳能生活热水器的储热性能,其储热性能还有较大的提升与改进空间。     

Solar energy for the Australian food processing industry

Since the cost effectiveness of solar heat generating systems decreases as the temperature increases, the potential for large-scale use of solar energy for industrial processes is very dependent on the operating temperature of the process. Examination of a sample of the Australian food processing industry has shown that 70 per cent of the heat is used at temperatures below 100°C and there is no significant usage above 150°C. A feasibility study of a typical plant in Melbourne shows that it is technically practicable to phase solar energy heating systems into existing processes, and that using known techniques over 30 per cent of the annual heat requirements could be provided by solar collectors. The roof area is adequate for the mounting of collectors but space must be found for insulated hot water tanks to provide thermal storage. Since the gross return on investment in the solar installation is the value of the fuel saved, this directly related to fuel prices. In a situation where energy prices are changing rapidly, recommendations on cost effectiveness have no lasting significance. The paper describes simple methods of making accurate predictions for specific situations so that plant owners and operators can make their own judgements on cost effectiveness.     

Thermoeconomics of seasonal latent heat storage system

A simple thermoeconomic analysis is performed for a seasonal latent heat storage system for heating a greenhouse. The system consists of three units that are a set of 18 packed‐bed solar air heaters, a latent heat storage tank with 6000 kg of technical grade paraffin wax as phase‐changing material, and a greenhouse of 180 m². The cost rate balance for the output of a unit is used to estimate the specific cost of exergy for a yearly operation. Based on the cost rate of exergy, fixed capital investment, operating cost, and economic data, approximate cash‐flow diagrams have been prepared. The systems feasibility depends on the cost rate of exergy, operating cost, internal interest rate, and rate of taxation strongly. A cash‐flow diagram based on exergy considerations may enhance the impact of thermoeconomic analysis in feasibility studies of thermal systems. Copyright © 2006 John Wiley & Sons, Ltd.