Adsorption cooling driven by solar collector: A case study for Tokyo solar data

An analytical investigation has been performed to study the possibility of application of solar cooling for the climatic condition of Tokyo, Japan. Silica gel–water adsorption cooling system has been taken into consideration for the present study and lumped parameter model is used to investigate the performance of the system. Based on the solar radiation data it is found that at least 15 collector (each of 2.415 m²) is required to achieve the required heat source temperature (around 85 °C) to run the cooling unit. It is also observed that the solar powered adsorption cooling unit provides cooling capacity around 10 kW at noon with base run conditions, while the system provides solar COP around 0.3, however, the solar collector size can be reduced by optimizing the cycle time.     

Performance assessment of an integrated free cooling and solar powered single-effect lithium bromide-water absorption chiller

In this study, performance assessment of an integrated cooling plant having both free cooling system and solar powered single-effect lithium bromide–water absorption chiller in operation since August 2002 in Oberhausen, Germany, was performed. A floor space of 270 m² is air-conditioned by the plant. The plant includes 35.17 kW cooling (10-RT) absorption chiller, vacuum tube collectors’ aperture area of 108 m², hot water storage capacity of 6.8 m³, cold water storage capacity of 1.5 m³ and a 134 kW cooling tower. The results show that free cooling in some cooling months can be up to 70% while it is about 25% during the 5 years period of the plant operation. For sunny clear sky days with equal incident solar radiation, the daily solar heat fraction ranged from 0.33 to 0.41, collectors’ field efficiency ranged from 0.352 to 0.492 and chiller COP varies from 0.37 to 0.81, respectively. The monthly average value of solar heat fraction varies from 31.1% up to 100% and the five years average value of about 60%. The monthly average collectors’ field efficiency value varies from 34.1% up 41.8% and the five-year average value amounts about 28.3%. Based on the obtained results, the specific collector area is 4.23 (m²/kW_cold) and the solar energy system support of the institute heating system for the duration from August 2002 to November 2007 is 8124 kWh.     

The effects of operation parameter on the performance of a solar-powered adsorption chiller

A solar-powered adsorption chiller with heat and mass recovery cycle was designed and constructed. It consists of a solar water heating unit, a silica gel-water adsorption chiller, a cooling tower and a fan coil unit. The adsorption chiller includes two identical adsorption units and a second stage evaporator with methanol working fluid. The effects of operation parameter on system performance were tested successfully. Test results indicated that the COP (coefficient of performance) and cooling power of the solar-powered adsorption chiller could be improved greatly by optimizing the key operation parameters, such as solar hot water temperature, heating/cooling time, mass recovery time, and chilled water temperature. Under the climatic conditions of daily solar radiation being about 16–21 MJ/m², this solar-powered adsorption chiller can produce a cooling capacity about 66–90 W per m² collector area, its daily solar cooling COP is about 0.1–0.13.     

Design and test results of a low-capacity solar cooling system in Alicante (Spain)

Despite its attractiveness, solar cooling technology is still in an early stage of development. Most installations currently in operation show differences in the collector area per kilowatt of cooling capacity that cannot be explained only by project-specific circumstances. The purpose of this paper was twofold. First, to answer some questions that came up during the design process of the plant by using a TRNSYS system model and statistical tools. Second, to gain knowledge about the plant operation and validate the TRNSYS model through measured data. The system was equipped with a flat-plate collector field of 38.4 m². A lithium bromide-water single-effect absorption chiller (17.6 kW) was selected in order to provide chilled water to fan-coils. Performance data were registered at the solar plant working with a 1000-l heat storage tank and a required temperature of 80 °C to drive the absorption machine. An average of 29% of the solar energy incident on the solar collectors’ surface was transferred to the hot water storage. The registered average COP of the absorption chiller was 0.691. The performance data were compared with the values predicted by the TRNSYS plant model and a high level of agreement was obtained.     

Design and performance of a solar-powered heating and cooling system using silica gel/water adsorption chiller

In this paper, a solar-powered compound system for heating and cooling was designed and constructed in a golf course in Taiwan. An integrated, two-bed, closed-type adsorption chiller was developed in the Industrial Technology Research Institute in Taiwan. Plate fin and tube heat exchangers were adopted as an adsorber and evaporator/condenser. Some test runs have been conducted in the laboratory. Under the test conditions of 80 °C hot water, 30 °C cooling water, and 14 °C chilled water inlet temperatures, a cooling power of 9 kW and a COP (coefficient of performance for cooling) of 0.37 can be achieved. It has provided a SCP (specific cooling power) of about 72 W/(kg adsorbent). Some field tests have been performed from July to October 2006 for providing air-conditioning and hot water. The efficiency of the collector field lies in 18.5–32.4%, with an average value of 27.3%. The daily average COP of the adsorption chiller lies in 33.8–49.7%, with an average COP of 40.3% and an average cooling power of 7.79 kW. A typical daily operation shows that the efficiency of the solar heating system, the adsorption cooling and the entirely solar cooling system is 28.4%, 45.2%, and 12.8%, respectively.     

Experimental study of the performance of a circular tube solar collector with closed-loop oscillating heat-pipe with check valve (CLOHP/CV)

This paper describes the performance of a circular glass tube solar collector with a set of closed-loop oscillating heat-pipes with check valves (CLOHP/CV). The assembly was divided into three sections, i.e. circular glass tube, adiabatic gap and condenser water tank. A circular 10-set glass tube solar collector of 0.058 m diameter and 1.50 m length was housed on a collecting plate. The inside circular glass tube consisted of a CLOHP/CV and collecting plate. The adiabatic gap was 0.05 m. The condenser water tank was made from a 0.03 × 0.05 m² zinc sheet. The CLOHP/CV consisted of the collecting plate cover with inner diameter of 0.003 m and 26.40 m total length per set, and it contained two check valves with evaporator 1.50 m long, adiabatic gap 0.05 m and condenser 0.30 m long. R-134a was used as the working fluid with filling ratio of 50%. The CLOHP/CV arrangement was aligned at an inclination angle of 18 degrees from the horizontal plane, with 6 turns per set. A 0.001 m thick aluminum sheet was used to make a collecting plate with 0.10 × 1.50 m² test area. Efficiency evaluations were conducted during daylight hours over a 2-month period and included extensive monitoring and recording of temperatures with type-K thermocouples placed at key locations throughout the system. The results confirmed the anticipated fluctuation in collector efficiency dependent on the time of day, solar energy irradiation, ambient temperature and circular tube surface mean temperature. An efficiency of approximately 76% was achieved, which correlates with the efficiency of the more expensive heat-pipe system. The CLOHP/CV system offers the additional benefits of corrosion-free operation and absence of freezing during winter months.     

Experimental study of the performance of a solar collector by closed-end oscillating heat pipe (CEOHP)

An experimental flat plate solar collector operating in conjunction with a closed-end oscillating heat pipe (CEOHP) offers a reasonably efficient and cost effective alternative to conventional solar collector system that use heat pipes. The CEOHP system described in this study relies on the natural forces of gravity and capillary action and dose not require an external power source. The flat plate collector consisted of a 1 mm thick sheet of black zinc covered by a glass enclosure with a collecting area of 2.00 × 0.97 m² , an evaporator located on the collecting plate, and a condenser inserted into a water tank. A length of 0.003 ID copper tubing was bent into multiple turns at critical points along its path and used to channel the working fluid throughout the system. R134a was used as the working fluid. Efficiency evaluations were conducted during daylight hours over a two month period and included extensive monitoring and recording of temperatures with type-K thermocouples placed at key locations throughout the system. The results confirmed the anticipated fluctuation in collector efficiency dependant on the time of day, solar energy irradiation, ambient temperature and flat plate mean temperature. An efficiency of approximately 62% was achieved, which correlates with the efficiency of the more expensive heat pipe system. The CEOHP system offers the additional benefits of corrosion free operation and absence of freezing during winter months.     

Development of the high concentration III-V photovoltaic system at INER,Taiwan

The 100 kW high concentration photovoltaic (HCPV) system has been constructed in October 2007 at the Institute of Nuclear Energy Research (INER), Taiwan. The maximum module efficiency with a geometrical concentration ratio of 476× is about 26.1% under 850 W/m² DNI and passive cooling conditions [Cherng-Tsong Kuo. The project of demonstrating MW high concentration photovoltaic (HCPV) system. Science and technology yearbook of Taiwan. ROC; 2008]. The 100 kW HCPV system consists of 14 sets of pillar-stand 5 kW systems and 21 sets of roof-top 1.5 kW systems. Each 5 kW system and 1.5 kW are comprised of 40 modules and 12 modules respectively. Each module was integrated with 40 solar cells with 35% conversion efficiency each, manufactured by Spectrolab Company, the highest III-V solar cell conversion efficiency record keeper. This project is the pioneer for the establishment of one MW HCPV demonstration system in 2008.     

A comparison of solar absorption system configurations

Solar thermal driven cooling systems for residential applications are a promising alternative to electric compression chillers, although its market introduction still represents a challenge, mainly due to the higher investment costs. The most common system configuration is an absorption chiller driven by a solar thermal system, backed up by a secondary heating source, normally a gas boiler. Heat storage in the primary (solar) circuit is mandatory to stabilize and extend the operation of the chiller, whereas a cold storage tank is not so common.This paper deals with the selection of the most suitable configuration for residential cooling systems with solar energy. In Spain, where cooling needs are usually higher than heating needs, the interest of a reversible heat pump as auxiliary system and a secondary cooling storage are analyzed.A complete TRNSYS model has been developed to compare a configuration with just hot storage (of typical capacity 40 L/m² of solar collector surface) and a configuration with both, hot and cool storages. The most suitable configuration is very sensible to the solar collector area. As the collector area increases, the advantages of a cool storage vanish. Increasing the collector area tends to increase the temperature of the hot storage, leading to higher thermal losses in both the collector and the tank. When the storage volume is concentrated in one tank, these effects are mitigated. The effect of other variables on the optimal configuration are also analyzed: collector efficiency curve, COP of the absorption chiller, storage size, and temperature set-points of the chillers.     

Performance of a solar ejector cooling-system in the southern region of Turkey

Performance variations of a solar-powered ejector cooling-system (SECS) using an evacuated-tube collector are presented for Antalya, Aydin, Konya and Urfa cities located in the southern region of Turkey by means of hourly and monthly average ambient temperature and solar radiation meteorological data. A SECS, based on a constant-area ejector flow model and using R-123, was considered. The cooling season and period were taken into account for the 6 months (May–October) and the hours 8:00–17:00, respectively. It was found that the evacuated-tube collector efficiency depending upon the ambient temperature and solar radiation within the day was remarkably varied. However, for all the cities, the cooling capacities of the SECS were very similar. When generator, condenser, and evaporator temperatures were taken, namely, 85 °C, 30 °C and 12 °C, the maximum overall coefficient of performance and the cooling capacity were obtained as 0.197 and 178.26 W/m², respectively, at 12:00 in August for Aydin. The evacuated-tube collector area per ton cooling was found to be around 21 m² at noontime in August for all the cities. Furthermore, at the off-design conditions, a performance map of the system was derived and discussed. It was determined that the SECS could be used for office-cooling purposes during the hours (8:00–15:00) in the southern region of Turkey.     

Field test of a solar seawater desalination unit with triple-effect falling film regeneration in northern China

Based on the mechanism of falling film evaporation condensation, a new four-stage distillation unit with triple-effect regeneration has been designed, constructed and field tested. The seawater desalination system is driven by 80 m² all-glass vacuum tube solar collection system with an additional 1 kW wind power system to provide electricity for pumps. The field testing and monitoring of the system had been carried out under the real weather condition for 2 years. The results show that the water production of the system for per unit of solar collector area could reach up to more than 12 kg/m²/day under the fine weather conditions. Water production of the system was stable in long period and the annual production could reach to 250 tons in northern China. The economic performance of the system is also discussed. The cost of water production is estimated approximately 4.6 Dollar/ton for the 15-year service life.     

Performance of a dual-purpose solar continuous adsorption system

A conceptual design and performance of a dual-purpose solar continuous adsorption system for domestic refrigeration and water heating is described. Malaysian activated carbon and methanol are used as the adsorbent–adsorbate pair. The heat rejected by the adsorber beds and condensers during the cooling process of the refrigeration part is recovered and used to heat water for the purpose of domestic consumption. In a continuous 24-h cycle, 16.9 MJ/day of heat can be recovered for heating of water in the storage tanks. In the single-purpose intermittent solar adsorption system, this heat is wasted. The total energy input to the dual-purpose system during a 24-h operation is 61.2 MJ/day and the total energy output is 50 MJ/day. The latter is made up of 44.7 MJ/day for water heating and 5.3 MJ/day for ice making. The amount of ice that can be produced is 12 kg/day. Using typical value for the efficiency of evacuated tube collector of water heating system of 65%, the following coefficient of performances (COP's) are obtained: 44% for adsorption refrigeration cycle, 73% for dual-purpose solar water heater, 9.1% for dual-purpose solar adsorption refrigeration and 82.1% for dual-purpose of both solar water heater and refrigerator.     

Experimental study of a solid adsorption cooling system using flat-tube heat exchangers as adsorption bed

In this paper, a solid adsorption cooling system with silica gel as the adsorbent and water as the adsorbate was experimentally studied. To reduce the manufacturing costs and simplify the construction of the adsorption chiller, a vacuum tank was designed to contain the adsorption bed and evaporator/condenser. Flat-tube type heat exchangers were used for adsorption beds in order to increase the heat transfer area and improve the heat transfer ability between the adsorbent and heat exchanger fins. Under the standard test conditions of 80 °C hot water, 30 °C cooling water, and 14 °C chilled water inlet temperatures, a cooling power of 4.3 kW and a coefficient of performance (COP) for cooling of 0.45 can be achieved. It has provided a specific cooling power (SCP) of about 176 W/(kg adsorbent). With lower hot water flow rates, a higher COP of 0.53 can be achieved.     

Modelling and analysis of air-cooled reciprocating chiller and demand energy savings using passive cooling

The study presents modelling and analysis of air-cooled chiller system in an office building at Central Queensland University in Rockhampton, Australia. EnergyPlus, building energy simulation software, has been used to model and to simulate the energy savings. Base case cooling energy has been compared with measured data. The simulated results show a reasonable agreement with the measured data. As a passive cooling means, the effect of economiser usages and pre-cooling have been simulated and analysed to assess annual demand savings for an energy intensive office building at Rockhampton, Australia. It was found that implementation of the pre-cooling and economiser system could save 115 kW/m²/month and 72 kW/m²/month total cooling energy and 26 kW/m²/month and 42 kW/m²/month chiller energy, respectively.     

Analysis of solar desiccant cooling system for an institutional building in subtropical Queensland,Australia

Institutional buildings contain different types of functional spaces which require different types of heating, ventilating and air conditioning (HVAC) systems. In addition, institutional buildings should be designed to maintain an optimal indoor comfort condition with minimal energy consumption and minimal negative environmental impact. Recently there has been a significant interest in implementing desiccant cooling technologies within institutional buildings. Solar desiccant cooling systems are reliable in performance, environmentally friendly and capable of improving indoor air quality at a lower cost. In this study, a solar desiccant cooling system for an institutional building in subtropical Queensland (Australia) is assessed using TRNSYS 16 software. This system has been designed and installed at the Rockhampton campus of Central Queensland University. The system's technical performance, economic analysis, energy savings, and avoided gas emission are quantified in reference to a conventional HVAC system under the influence of Rockhampton's typical meteorological year. The technical and economic parameters that are used to assess the system's viability are: coefficient of performance (COP), solar fraction, life cycle analysis, payback period, present worth factor and the avoided gas emission. Results showed that, the installed cooling system at Central Queensland University which consists of 10 m² of solar collectors and a 0.400 m³ of hot water storage tank, achieved a 0.7 COP and 22% of solar fraction during the cooling season. These values can be boosted to 1.2 COP and 69% respectively if 20 m² of evacuated tube collector's area and 1.5 m³ of solar hot water storage volume are installed.     

A solar-powered traveling-wave thermoacoustic electricity generator

Traveling-wave thermoacoustic electricity generator is a new external-combustion type device capable of converting heat such as solar energy into electric power. In this paper, a 1 kW solar-powered traveling-wave thermoacoustic electricity generation system is designed and fabricated. The system consists of a traveling-wave thermoacoustic electricity generator, a solar dish collector and a heat receiver. In the preliminary tests, using electric cartridge heaters to simulate the solar energy, a maximum electric power of 481 W and a maximum thermal-to-electric efficiency of 15.0% were achieved with 3.5 MPa pressurized helium and 74 Hz working frequency. Then, after integrating the traveling-wave thermoacoustic electricity generator with the solar dish collector and the heat receiver, the solar-powered experiments were performed. In the experiments, a maximum electric power of about 200 W was obtained. However, due to the solar dish collector problems, the heating temperature of the receiver was much lower than expected. Optimizations of the collector and the heat receiver are under way.     

Numerical investigation of a two-stage air-cooled absorption refrigeration system for solar cooling: Cycle analysis and absorption cooling performances

Two-stage air-cooled ammonia–water absorption refrigeration system could make good use of low-grade solar thermal energy to produce cooling effect. The system simulation results show that thermal COP is 0.34 and electrical COP is 26 under a typical summer condition with 85 °C hot water supplied from solar collector. System performances under variable working conditions are also analyzed. Circular finned tube bundles are selected to build the air-cooled equipment. The condenser should be arranged in the front to get an optimum system performance. The mathematical model of the two-stage air-cooled absorber considering simultaneous heat and mass transfer processes is developed. Low pressure absorber should be arranged in front of middle pressure absorber to minimize the absorption length. Configuration of the air-cooled equipment is suggested for a 5 kW cooling capacity system. Temperature and concentration profiles along the finned tube length show that mass transfer resistance mainly exists in liquid phase while heat transfer resistance mainly exists in cooling air side. The impacts on system refrigeration capacities related to absorption behaviors under variable working conditions are also investigated. Both cycle analysis and absorption performances show that two-stage air-cooled ammonia–water absorption chiller is technically feasible in practical solar cooling applications.     

Analysis of ground source heat pumps with horizontal ground heat exchangers for northern Japan

Computer simulation and analysis of a ground source heat pump system with horizontal ground heat exchangers operating in heating (max 5.5 kW) and cooling (max 3.3 kW) mode was carried out for a typical residential house, with 200 m² of living space, located in Sapporo (Japan). In spite of high electricity rate, the ground source heat pump system is more beneficial alternative for space heating than an oil furnace and an electric resistance system. Besides, the heat pump technology offers relatively low thermal degradation of the ground environment, lower cost of heating and cooling, higher operating efficiency than electric resistance heating or air-source heat pump and is environmentally clean, i.e. without greenhouse gas emission, if the electricity is generated from renewable energy resources, such as wind and solar. The use of the cooling mode can provide further benefits like a shorter investment payback and human thermal comfort in summer. As a result, application of horizontal loops for new and retrofit residential and commercial use in northern Japan is feasible particularly in farmland areas.     

A thermo-economical optimization of a domestic solar heating plant with seasonal storage

In this study, the thermo-economic optimization analysis to determinate economically optimal dimensions of collector area and storage volume in domestic solar heating systems with seasonal storage is presented. For this purpose, a formulation based on the simplified P₁ and P₂ method is developed and solved by using MATLAB optimization Toolbox for five climatically different locations of Turkey. The results showed that the required optimum collector area in Adana (37 °N) for reaching maximum savings is 36 m²/house and 65 m²/house in Erzurum (39 °N) for same storage volume (1000 m³). The effects of collector efficiency on solar fraction and savings are investigated. The simulation results showed that the solar fraction and savings of the selective flat plate collector systems are higher than the other black paint flat plate collector systems.     

Waste heat driven silica gel/water adsorption cooling in trigeneration

A low-grade waste heat driven solid/vapour adsorption chiller has been successfully designed and tested. A simple model was developed to aid the design and predict the performances. The system comprised two identical sorption reactors operating out of phase in order to ensure continuous cold production. One sorption reactor consisted of six commercially available automotive plate/fin heat exchangers in which silica gel grains were accommodated between the fins. The system was tested as to the power delivered at 12 °C and the power density. The average cooling power was 3.6 kW. This is only 72% of the design value and can be largely attributed to the lower heat transfer fluid flow rate through the sorbent reactor. The thermal efficiency, COP, was 0.62 and the power density was 17 kW/m³ for the system as a whole. Higher power densities are possible. At present, the adsorption chiller is integrated in a prototype trigeneration system, which is tested at CRF’s Eco-building in Turin.