Analysis of natural circulation solar water heating systems

This paper presents an analysis of the performance of a solar water heating system with natural thermosyphon circulation between the collector and the storage tank. The analysis is based on the formulation by Ong except that provision for withdrawal of hot water from the tank (for domestic/ industrial use) has been made in the energy balance equation; further in contrast to the use of the finite difference method by Ong, explicit expressions have been obtained. The results of the present analysis (in the absence of withdrawal of hot water from the tank) are seen to be in better agreement with experiments than the corresponding results of Ong, obtained by use of the finite difference method.

Numerical results, corresponding to hot water retrieved from the storage tank, have been presented for two modes of hot water withdrawal viz. the constant flow rate and constant mean storage tank water temperature.     

Design,fabrication and performance evaluation of natural circulation rectangular box-type solar domestic water heating system

This study includes design and experimental analysis of a solar domestic water heating system. Water heating systems with glazed and unglazed collectors were constructed and tested at Dhaka, Bangladesh, at a latitude of 23.7 °N. Collector thermal efficiency and capability of raising water temperature were considered as performance evaluation measures. A typical day analysis showed that collector efficiency varied with time and touched its peak at around 12:00 h. During testing, the efficiency of the glazed collector increased by about 70.3% when compared with the unglazed collector. Average collector efficiency over the whole test period was also estimated to be 57.3% and 33.7% for glazed and unglazed collectors, respectively. Maximum water temperatures measured at daytime user outlets were, respectively, 82.4 °C and 65.5 °C for domestic water heating systems with glazed and unglazed collectors and approximated to be 49 °C and 32 °C higher than the ambient temperature. The glazed collector eventually offered significantly higher performances over the unglazed collector in improving system performance.     

Energetic and exergetic evaluation of flat plate solar collectors

Energy efficiency is generally used as one of the most important parameters in order to introduce and compare thermal systems including flat plate solar collectors despite of the fact that the first law of thermodynamics is not solely capable of demonstrating quantitative and qualitative performance of such systems. In this paper, a theoretical and comprehensive model for energy and exergy analysis of flat plate solar collectors is presented through which the effect of the entire design parameters on performance can be examined. Upon the verification and confirmation of the model based on the experimental data, effect of parameters such as fluid flow rate and temperature, type of working fluid and thickness of the back insulation on the energy and exergy efficiency of the collector has been examined and based on the analysis and comparison of results, the optimal working condition of the system has been determined. According to the results, designing the system with inlet water temperature approximately 40° more than the ambient temperature as well as a lower flow rate will enhance the overall performance.     

Long term performance of large scale solar water heating systems: Forced circulation mode

This paper presents a mathematical model of a solar water-heating system. The model is duly supported by experiment. The solar water heating system, comprised of 12 collectors and a storage tank for both natural and forced circulation with and without withdrawal of hot water from the storage tank, has been studied. The analysis has also been made for various configurations of the system viz. series, parallel and a combination. It is concluded that, under thermosyphon, true parallel, and in forced circulation, true series combinations perform better.     

Design and performance of large low-cost solar water heating systems

An analysis is presented for the monthly performance evaluation of a simple design low cost solar water heating systems. A sample of typical results is presented which confirms their suitability as solar heating systems for summer peacking or as solar preheaters for year around loads.     

连接方式对自然循环太阳能热水系统的影响

以国标GB／T18708—2002《家用太阳热水系统热性能试验方法》为依据,针对自然循环平板式太阳能热水系统在连接方式不同的情况下,其热性能的差异进行了对比试验,并从自然循环系统循环动力——热虹吸压力的角度分析了两种连接方式下热性能差异的原因。     

Techno-economic evaluation of domestic solar water heating systems in India

The most wide spread thermal use of solar energy, so far, has been for water heating. Solar water heating systems have been commercialized in many counties in the world. Though the technical feasibility of domestic solar water heating systems (DSWHS) has long been established, their financial viability needs to be carefully examined, particularly in tropical countries with relatively lower annual capacity utilization and poor purchasing power of potential users.The potential number of Indian households who can invest in DSWHS have been estimated based on the income distribution in the country, the capital cost of solar water heating systems, interest rate charged on the loan provided for the purchase of DSWHS etc. Using the seasonal and diurnal variation of ambient temperatures at many locations in the country, the periods with annual hot water requirement have been identified. A simple framework for financial evaluation of DSWHS has also been presented. The results of some typical exemplifying calculations have been presented and discussed.     

Energetic and exergetic performance evaluation of the quadruple-effect evaporator unit in tomato paste production

Quadruple-effect evaporator units are commonly used in food focus area in sector is evaporative unit. It consumes about 60% of total energy input. The present study evaluates the performance of quadruple-effect evaporator unit (QEEU) by using exergy analysis based on actual operational data. A tomato paste factory is chosen for the analysis. The highest exergy destruction/loss occurs in the first effect with 158.2 kW, 52.7% of exergy input in first effect. Steam temperature should be decreased in order to decrease exergy destruction in first effect. Also, third effect achieves the highest exergy efficiency with 93.3%. Exergetic improvement potential of each effect varies between 0.3 kW and 83.6 kW. The highest and lowest exergetic improvement potential occurs in first and third effect of QEEU system, respectively. Exergetic improvement potential is equals to 52.80%, 11.10%, 6.73% and 69.8% of exergy loss/destruction from the first effect to the last effect, respectively. Total exergetic improvement potential is achieved as 128 kW (55% of total exergy loss/destruction) in QEEU system. It is expected that analyses result provide important information for designer and/or resources of multiple effect evaporator unit.     

Energy conservation and field performance of a natural circulation type solar water heater

A natural circulation type solar water heater has been fabricated and installed at the CAZRI Guest House. Its field performance has been evaluated. The heater provides 2001 of hot water at 50–60 °C at all times. This solar water heater is economical.     

Incentives for solar water heating systems

Life-cycle costing has been used in an economic analysis of three solar domestic hot water installations. These are in operation in Las Palmas (Canary Islands) and are backed by conventional installations consuming either fuel-oil (GG), butane (BB) or electricity (EE). The cumulative cost flows (CCF), including expenditures for purchase, recovery, maintenance, fuel and operating costs, are calculated over the useful life of the installations for expected annual fuel-increment rates. Twenty-seven comparisons are made between the solar (SAS) and conventional systems (CS). Total savings are found over the lifetime and the repayment periods are obtained as a function of discount rate. The SAS and CS are examined with respect to economic incentives such as subvention, tax deduction, loans and their combinations. Finally, the variations of the payback periods and rates of return on investment (IRR) are plotted against the fuel price, annual fuel increment rate and initial investment in the SAS for a wide range of economic parameters.     

Economic evaluation and optimization of solar systems for space and domestic water heating

Solar energy will be utilized only if it proves to be economical. In this paper, we evaluate the economic feasibility of the use of solar energy for space and domestic water heating systems for a house in Benghazi, Libya. A comprehensive evaluation considerering 324 cases representing the proper ranges of economic and load factors and based on the annual equivalent cost approach is given. The optimum collector area for each case is determined. The results obtained and relationships developed permit generalizations that can be applicable in other locations.     

Forced versus natural circulation solar water heaters: A comparative performance study

An experimental study has been carried out to compare the performance of natural and forced circulation domestic solar water heaters. Several measurments have been made for the two cases which included; the collector water inlet and outlet temperatures, the mass flow rate, the tank temperature, the ambient temperature and the solar insolation. The main parameters for the solar collector are calculated for the natural and forced circulation systems. These included; the top, back, and overall loss coefficients, the heat removal factor, the efficiency factor, the useful energy gain and the instantaneous efficiency. The comparison showed that the efficiency of the forced circulation system could be 35 to 80% higher.     

Integrated performance of liquid-based solar heating systems

A closed form model for the integrated performance of liquid-based solar heating systems is presented. The model is general enough to be used for most liquid-based systems. It can be used for systems with either flat plate or concentrating collectors and the load is not restricted to space heating applications. Three new system parameter are introduced by this model. These are the system heat storage factor, the solar distribution factor and the load distribution factor. These three factors respectively account for the reduction in system performancev which results from finite storage, non-uniform solar flux and non-uniform load. These factors are discussed in detail and closed form mathematical expressions, from which numerical values can be calculated, as persented.     

Thermal characteristics of a building-integrated dual-function solar collector in water heating mode with natural circulation

As a modified building-integrated solar thermal system, building-integrated dual-function solar collector here proposed is able to provide passive space heating in cold winter, and water heating in warm seasons. In this study, evaluations were made on this modified collector system for the warm period operation under the water heating mode with natural circulation of flow. A dynamic numerical model has been developed and validated by experimental data. Based on practical air-conditioned room design conditions, numerical analysis was performed to study the water heating performance, as well as to compare the solar transmission through building facade in different seasons with or without its presence. The results show that when working in the water heating mode, the system performs well in providing services hot water in the warm seasons without bringing in summer overheating problem.     

Transient analysis of forced circulation solar water heating system

This paper presents a transient analysis of a solar water heating system with forced circulation. Two modes of hot water retrieval have been taken into account viz direct from the tank and through a heat exchanger placed in the tank. Analysis has been presented both for constant flow and constant collection temperature modes. Effects of heat exchanger length and time of starting hot water retrieval on the system performance have also been studied. Numerical calculations have been made for a typical cold day (26 January, 1980) at Delhi.     

太阳能热水系统技术方案

图1凡是使用过接触过或关注过太阳热水器(或系统)的人都会得出这样的认识:尽管太阳热水器有着其它热水器(油、电、气)无可比拟的节能、环保、安全等优点,但它也确实存在着其它热水器所不存在的令人头疼的难题,诸如:防冻、抗冻问题;一年四季24小时供应热水问题;与建筑物有机结合问题以及恒温,恒压出水问题。这些问题中任何一个问题的根本解决,都会对太阳能热利用起到很大的推动作用。如果能全部加以解决,那将对目前3种热水器的市场格局产生决定性的影响。能不能找到一种技术方案,把这所有的难题一下子全部加以解决呢?通过多年摸索与工程实践,…     

Economic evaluation and optimization of solar heating systems

A procedure is developed for assessing the economic viability of a solar heating system in terms of the life cycle savings of a solar heating system over a conventional heating system. The life cycle savings is expressed in a generalized formby introducing two economic parameters, P₁ and P₂, which relate all life cycle cost considerations to the first year fuel cost or the initial solar system investment cost. Using the generalized life cycle savings equation, a method is developed for calculating the solar heating system design which maximizes the life cycle savings. A similar method is developed for determining the set of economic conditions at which the optimal solar heating system design is just competitive with the conventional heating system. The results of these optimization methods can be presented in tabular or graphical form. The sensitivity of the economic evaluation and optimization calculations to uncertainties in constituent thermal and economic variables is also investigated.     

家用太阳热水器与太阳热水系统的技术经济比较

分析了户用太阳热水器和太阳热水系统工程的经济技术特点,对两者成本构成、项目财务净现值、投入回收期和财务内部收益率等有关指标进行了经济技术比较.分析比较表明,太阳热水系统与家用热水器相比,节省安装占地,与建筑相结合得好,在降低成本,缩短投资回收期,提高经济效益方面有明显的优势.