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.     

Energy and economic analysis of an integrated solar absorption cooling and heating system in different building types and climates

The use of solar energy in buildings is an important contribution for the reduction of fossil fuel consumption and harmful emissions to the environment. Solar thermal cooling systems are still in their infancy regarding practical applications, although the technology is sufficiently developed for a number of years. In many cases, their application has been conditioned by the lack of integration between cooling and heating systems. This study aims to evaluate the potential of integrated solar absorption cooling and heating systems for building applications. The TRNSYS software tool was used as a basis for assessment. Different building types were considered: residential, office and hotel. The TRNSYS models are able to run for a whole year (365 days), according to control rules (self-deciding whether to operate in heating or cooling modes), and with the possibility of combining cooling, heating and DHW applications. Three different locations and climates were considered: Berlin (Germany), Lisbon (Portugal), and Rome (Italy). Both energy and economic results are presented for all cases. The different local costs for energy (gas, electricity and water) were taken into account. Savings in CO₂ emissions were also assessed. An optimization of solar collector size and other system parameters was also analysed.     

Techno-economic performance analysis of solar cooling systems

Vapour absorption cooling systems, powered by solar thermal energy, are now commercially manufactured in sizes ranging from 1.5 to over 20 RT (one refrigeration ton = 3.51 kW of cooling). The needed thermal energy at appropriate temperature potential can either be provided by solar thermal collectors or else from a solar pond. The paper gives the assessment criteria and results for technical and economic evaluation of the performance of absorption chiller using a solar pond. These results, based on Kuwait's environmental data and costs, have been compared with three alternate cooling systems, namely:

• 1 Solar thermal collector absorption cooling system.
• 2 Solar photovoltaic cooling system.
• 3 Standard vapour compression cooling system.

The criteria, used for performance evaluation of the solar cooling systems on a technical basis, consists of assessing the extent to which such systems can make a positive contribution in a conserving fossil fuel. This is done by first estimating the total electrical energy needed by the standard system (defined in para. 3 above) to produce one unit of cooling output. Solar cooling systems are then analysed and compared with a standard system to establish their electrical energy saving or generation capability, after accounting for the parasitic electrical energy used in pump/fan motors and equivalent energy needed for the production of soft water (used-up in the cooling tower) from seawater desalination. The economic analysis considers the cost and life of subsystems and that of the electrical and water desalination plants to arrive at the unit cooling cost. The unit cooling is defined as the ratio of amortized capital investments plus operation and maintenance costs over the year and the total yearly cooling production by the system. The results show that the solar pond absorption cooling system is the closest competitor to the conventional cooling system.     

An exergy analysis of a solar-driven ejector refrigeration system

Exergy analysis is used as a tool to analyse the performance of an ejector refrigeration cycle driven by solar energy. The analysis is based on the following conditions: a solar radiation of 700 W/m², an evaporator temperature of 10 °C, a cooling capacity of 5 kW, butane as the refrigerant in the refrigeration cycle and ambient temperature of 30 °C as the reference temperature. Irreversibilities occur among components and depend on the operating temperatures. The most significant losses in the system are in the solar collector and the ejector. The latter decreases inversely proportional to the evaporation temperature and dominates the total losses within the system. The optimum generating temperature for a specific evaporation temperature is obtained when the total losses in the system are minimized. For the above operating conditions, the optimum generating temperature is about 80 °C.     

Experimental investigations of a small-scale solar-assisted absorption cooling system

The present study deals with a small-scale solar-assisted absorption cooling system having a cooling capacity of 3.52 kW and was investigated experimentally under the climatic conditions of Taxila, Pakistan. Initially, a mathematical model was developed for LiBr/H₂O vapor absorption system alongside flat-plate solar thermal collectors to achieve the required operating temperature range of 75°C. Following this, a parametric analysis of the whole system was performed, including various design and climate parameters, such as the working temperatures of the generator, evaporator, condenser, absorber, mass flow rate, and coefficient of performance (COP) of the system. An experimental setup was coupled with solar collectors and instruments to get hot water using solar energy and measurements of main parameters for real-time performance assessment. From the results obtained, it was revealed that the maximum average COP of the system achieved was 0.70, and the maximum outlet temperature from solar thermal collectors was 75°C. A sensitivity analysis was performed to validate the potential of the absorption machine in the seasonal cooling demand. An economic valuation was accomplished based on the current cost of conventional cooling systems. It was established that the solar cooling system is economical only when shared with domestic water heating.     

Transient simulation and parametric study of solar-assisted heating and cooling absorption systems: An energetic,economic and environmental (3E) assessment

This paper presents energetic, economic, and environmental (3E) analyses of four configurations of solar heating and cooling (SHC) systems based on coupling evacuated tube collectors with a single-effect LiBr–H₂O absorption chiller. In the first configuration (SHC1), a gas-fired heater is used as the back-up system, while a mechanical compression chiller is employed as the auxiliary cooling system in the second configuration (SHC2). The capacity of the absorption chiller is designed based on the maximum building cooling load in these configurations. The third and fourth configurations (SHC3 and SHC4) are similar to SHC2, but the absorption chiller size is reduced to 50% and 20%, respectively. The results show that the highest primary energy saving is achieved by SHC2, leading to a solar fraction of 71.8% and saving 54.51% primary energy as compared to a reference conventional HVAC system. The economic performance of all configurations is still unsatisfactory (without subsidies) due to their high capital costs. However, if a government subsidy of 50% is considered, the results suggest that SHC4 can be economically feasible, achieving a payback period of 4.1 years, net present value of 568,700 AUD and solar fraction of 43%, contributing to 27.16% decrease in the plant primary energy consumption.     

A solar thermal cooling and heating system for a building: Experimental and model based performance analysis and design

A solar thermal cooling and heating system at Carnegie Mellon University was studied through its design, installation, modeling, and evaluation to deal with the question of how solar energy might most effectively be used in supplying energy for the operation of a building. This solar cooling and heating system incorporates 52 m² of linear parabolic trough solar collectors; a 16 kW double effect, water-lithium bromide (LiBr) absorption chiller, and a heat recovery heat exchanger with their circulation pumps and control valves. It generates chilled and heated water, dependent on the season, for space cooling and heating. This system is the smallest high temperature solar cooling system in the world. Till now, only this system of the kind has been successfully operated for more than one year. Performance of the system has been tested and the measured data were used to verify system performance models developed in the TRaNsient SYstem Simulation program (TRNSYS). On the basis of the installed solar system, base case performance models were programmed; and then they were modified and extended to investigate measures for improving system performance. The measures included changes in the area and orientation of the solar collectors, the inclusion of thermal storage in the system, changes in the pipe diameter and length, and various system operational control strategies. It was found that this solar thermal system could potentially supply 39% of cooling and 20% of heating energy for this building space in Pittsburgh, PA, if it included a properly sized storage tank and short, low diameter connecting pipes. Guidelines for the design and operation of an efficient and effective solar cooling and heating system for a given building space have been provided.     

A new combined cooling, heating and power system driven by solar energy

A new combined cooling, heating and power (CCHP) system is proposed. This system is driven by solar energy, which is different from the current CCHP systems with gas turbine or engine as prime movers. This system combines a Rankine cycle and an ejector refrigeration cycle, which could produce cooling output, heating output and power output simultaneously. The effects of hour angle and the slope angle of the aperture plane for the solar collectors on the system performance are examined. Parametric optimization is conducted by means of genetic algorithm (GA) to find the maximum exergy efficiency. It is shown that the optimal slope angle of the aperture plane for the solar collectors is 60° at 10 a.m. on June 12, and the CCHP system can reach its optimal performance with the slope angle of 45° for the aperture plane at midday. It is also shown that the system can reach the maximum exergy efficiency of 60.33% under the conditions of the optimal slope angle and hour angle.     

Feasibility study of a solar-assisted heating/cooling system for an aquatic centre in hot and humid climates

This 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 utilizes an absorption chiller and a cooling tower to meet the facilities and 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 were employed for the collector and domestic use. The absorption chiller utilizes hot water to regenerate the LiBr solution. The proposed system enables the swimming season to be extended from sixteen weeks to fifty-two weeks. Simulation results indicate that a combination of a double glazed collector area of 600–4800 m² and a storage tank volume of 11·36 m³ results in a 25–37% reduction in the consumption of natural gas. Economic analysis is performed based on the life-cycle-cost method and takes into account the effects of discount rate, fuel price and fuel inflation rate. Different scenarios for which the solar-assisted system is economical are presented and analysed. © 1997 John Wiley & Sons, Ltd.     

太阳能喷射/压缩复合制冷循环性能研究

研究了一种太阳能喷射/压缩复合制冷循环,由太阳能集热子系统、喷射制冷子系统及压缩制冷子系统组成,系统充分利用热电两种能源以及两种制冷方法各自的优点,优化喷射制冷子系统工作性能的同时,改善压缩式子系统的工作条件,从而提高复合制冷循环性能的同时节约高品位电能。采用性能较好的高蒸发温度式喷射制冷带走压缩机排气余热具有实际意义。通过数值模拟的手段分析系统性能及其主要影响因素,并优化工作条件。研究表明,与相同工作条件下的单压缩制冷循环相比,复合制冷循环工作日全天候运行时电力性能系数提升约为31.5%,节电优势显著。存在一个最佳的喷射子系统蒸发温度使得复合制冷循环性能系数达到运行工况的最大值。     

Performance analysis on a building-integrated solar heating and cooling panel

The solar heating and nocturnal radiant cooling techniques are combined aiming at a novel solar heating and cooling panel (termed as SHCP) to be easily assembled as construction components for building roofing or envelope and also compatible with surroundings for its versatile coating colors, which can remove the double-skin mode from conventional solar equipment. SHCP has two functions for heating and cooling collecting. In this paper, the heating and cooling performances were analyzed in detail based on a small scale experimental system and effects of air gap and coatings were investigated. The results show that in sunny day of extreme cold January in Tianjin, China, the daily average heat-collecting efficiency is 39% with the maximum of 65%, while in sunny night during hot seasons the average cooling capacity can reach 87 W/m². When two different coatings were sprayed on SHCP without air gap, its heating and cooling performances were all analyzed, the daily average heat-collecting efficiency was 39% and 27% with the maximum points of 65% and 49%, respectively, and the cooling capacity was almost the same of 30 W/m² in January.     

Technical performance analysis of a micro-combined cooling,heating and power system based on solar energy and high temperature PEMFC

A solar energy and high temperature proton exchange membrane fuel cell (PEMFC)-based micro-combined cooling, heating and power (CCHP) system (named system I) is proposed in this work. This system mainly consists of a PEMFC subsystem, an organic Rankine cycle (ORC) subsystem and a vapor compression cycle (VCC) subsystem. System I would reduce to a high temperature PEMFC-based CCHP system (named system II) if there was no solar energy. With the technical performance analysis models developed, the effects of the current density, operating temperature, solar radiation intensity and ambient temperature on the thermal, economic and environmental performances of the systems are theoretically analyzed. The results show that the current density and solar radiation intensity are the main impact factors that can significantly affect the thermal, economic and environmental performances, while the operating temperature and ambient temperature only have remarkable influences on the thermal performance. The coefficient of performance (COP) of system II is approximately 1.19 in summer and 1.42 in winter, which is always higher than that of system I under the same working conditions. The exergy efficiency of system I and system II are approximately 49.7% and 47.4%, respectively. The primary energy saving rates (PESRs) of system I and system II are 64.9% and 31.8% in summer, and 60.0% and 36.2% in winter, respectively. The payback periods of system I and system II are 9.6 yr and 6.0 yr without government subsidy, respectively. Compared with system II, the pollutant emission reduction rates (ERRs) of system I can be increased by approximately 8.4%–23.5% with the addition of solar energy, which indicates that the development and utilization of clean and renewable energy such as solar energy can significantly reduce pollutant emissions.     

Solar refrigeration and cooling

In this paper a review of solar cooling and refrigeration technologies is presented. A discussion on the main reasons why these technologies are not presently economically feasible is carried out. and two installations in Mexico are analysed.     

Experimental investigation and performance analysis on a solar adsorption cooling system with/without heat storage

A solar adsorption cooling system which can be switched between a system with heat storage and a system without heat storage was designed. In the system with heat storage, a heat storage water tank was employed as the link between the solar collector circulation and the hot water circulation for the adsorption chillers. However, the heat storage water tank was isolated in the system without heat storage, and the hot water was directly circulated between the solar collector arrays and the adsorption chillers. It was found that the inlet and outlet temperatures for the solar collector arrays and the adsorption chillers in the system without heat storage were more fluctuant than those of the system with heat storage. Also found was that the system with heat storage operated stably because of the regulating effect by the heat storage water tank. However, under otherwise similar conditions, the cooling effect of the system without heat storage was similar to that of the system with heat storage. Compared with the system with heat storage, the system without heat storage has the advantages of higher solar collecting efficiency as well as higher electrical COP.     

New design of solar roof for household heating and cooling

A new design of solar roof is presented. It is a roof-integrated solar collector that is configurable by water redistribution. This way, this active system can provide household heating and cooling. Its thermal performance and cost were studied. It is found that total cost is similar to standard roofs and significant energy savings could be achieved.     

Very low temperature radiant heating/cooling indoor end system for efficient use of renewable energies

Solar or solar-assisted space heating systems are becoming more and more popular. The solar energy utilization efficiency is high when the collector is coupled with indoor radiant heating suppliers, since in principle, lower supply temperature means lower demand temperature and then the system heat loss is less. A new type radiant end system is put forward for even lower supply temperature compared to the conventional radiant floor heating systems. A three dimensional model was established to investigate its energy supply capacities. Simulation results show that 50 W per meter length tube can be achieved with the medium temperature of 30 °C for heating and 15 °C for cooling. The predicted results agree well with the actual data from a demonstration building. Furthermore, it is demonstrated that a supply temperature of 22 °C in winter and of 17 °C in summer already met the indoor requirements. The new end system has good prospects for effective use of local renewable resources.     

Thermodynamic analysis of a lithium bromide/water absorption system for cooling and heating applications

Absorption systems have the potential of employing thermal energy such as waste heat to produce both chilled water and hot water for building cooling and heating applications. In the present study, a lithium bromide/water (LiBr/H₂O) absorption system for cooling and heating applications was analysed on the basis of the first and second laws of thermodynamics. Simulation was employed to determine the coefficient of performance (COP) and the exergetic efficiency of the absorption system under different operating conditions such as the heat source, cooling water, chilled water, and supply hot water temperatures. Copyright © 2001 John Wiley & Sons, Ltd.     

A novel approach to improve the performance of solar-driven Stirling engine using solar-driven ejector cooling cycle

In this paper, a novel system to enhance the performance of a solar-driven finite speed alpha-type Stirling engine is proposed and evaluated. Part of the concentrated solar energy is used to drive an ejector refrigeration system. The cooling produced in the ejector cooling cycle is used to cool the Stirling engine to enhance its efficiency. Model equations to describe the systems are proposed and solved numerically. The results indicate that the new system produces averagely 3.3 times electrical power more than the conventional one. Moreover, the proposed system improves the Stirling engine efficiency by up to 46% in comparison with 19.15% for the conventional Stirling engine under solar radiation intensity of (1 kW/m²). Also, the results showed that the solar radiation intensity and wind speed are the most influential parameters that affect the proposed system efficiency. The new system is recommended to use in desert climates where high average daily solar radiation intensity, low wind speeds, and water shortage exist. Economic analysis is carried out to determine the feasibility of the proposed system under different economic parameters. It is found that, for instance, the simple payback period is 4.64 years for the new system when the selling price of electricity is 0.35 $/kWh.     

Optimal control and performance test of solar-assisted cooling system

The solar-assisted cooling system (SACH) was developed in the present study. The ejector cooling system (ECS) is driven by solar heat and connected in parallel with an inverter-type air conditioner (A/C). The cooling load can be supplied by the ECS when solar energy is available and the input power of the A/C can be reduced. In variable weather, the ECS will probably operate at off-design condition of ejector and the cooling capability of the ECS can be lost completely. In order to make the ejector operate at critical or non-critical double-choking condition to obtain a better performance, an electronic expansion valve was installed in the suction line of the ejector to regulate the opening of the expansion valve to control the evaporator temperature. This will make the SACH always produce cooling effect even at lower solar radiation periods while the ejector performs at off-design conditions. The energy saving of A/C is experimentally shown 50–70% due to the cooling performance of ECS. The long-term performance test results show that the daily energy saving is around 30–70% as compared to the energy consumption of A/C alone (without solar-driven ECS). The total energy saving of A/C is 52% over the entire test period.     

风冷太阳能双级水喷射制冷空调系统性能分析

对额定制冷量为12.3 kW的风冷太阳能双级水喷射制冷空调系统进行了变工况性能分析。该系统的制冷量随室内温度升高而增大,随环境温度升高而减小,随太阳辐照度增强而增大;COP的变化与制冷量的变化类似,所不同的是COP随着太阳辐照度的增强先迅速增大,当太阳辐照度增大到一定程度后,COP基本保持稳定。在室内温度不低于27℃,室外温度不高于38℃,太阳辐照度不低于500 W/m2的条件下,系统的制冷量为7.7~32 kW,COP为0.082~0.107。