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.     

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.     

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.     

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。     

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.     

Effect of storage tanks on solar-powered absorption chiller cooling system performance

Thermal storage, low power tariff at night, and low nocturnal temperature can be used in synergy to reduce the cooling costs of the solar-powered absorption chiller cooling systems. This study aims to reduce the required cooling capacity of an absorption chiller (ACH) powered by a solar parabolic trough collector (PTC) and a backup fuel boiler by integrating thermal storage tanks. The thermal performance of the system is simulated for a building that is cooled for 14 h/day. The system uses 1000 m² PTC with 1020 kW ACH. Chilled water storage (CHWS) and cooling water storage (CWS) effects on the system performance for different operation hours per day of the ACH under Izmir (Turkey) and Phoenix (USA) weather conditions are analyzed. When the ACH operates 14 h/day as the load for both systems and both locations, the variations of the solar collector efficiency and the cooling load to heat input ratio remain less than 4% after the modifications. From the addition of CHWS to the reference system, a parametric study consisting of changing the ACH operation hours per day shows that the required cooling capacity of the ACH can be reduced to 34%. The capacity factor of the ACH is improved from its reference value of 41% up to 96%.     

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.     

Solar absorption cooling plant in Seville

A solar/gas cooling plant at the Engineering School of Seville (Spain) was tested during the period 2008-2009. The system is composed of a double-effect LiBr + water absorption chiller of 174 kW nominal cooling capacity, powered by: (1) a pressurized hot water flow delivered by mean of a 352 m² solar field of a linear concentrating Fresnel collector and (2) a direct-fired natural gas burner. The objective of the project is to indentify design improvements for future plants and to serve as a guideline. We focused our attention on the solar collector size and dirtiness, climatology, piping heat losses, operation control and coupling between solar collector and chiller. The daily average Fresnel collector efficiency was 0.35 with a maximum of 0.4. The absorption chiller operated with a daily average coefficient of performance of 1.1-1.25, where the solar energy represented the 75% of generator’s total heat input, and the solar cooling ratio (quotient between useful cooling and insolation incident on the solar field) was 0.44.     

Design and transient-based analysis of a power to hydrogen (P2H2) system for an off-grid zero energy building with hydrogen energy storage

In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m² PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m² evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between ?0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.     

Modelling,simulation and warming impact assessment of a domestic-size absorption solar cooling system

In this paper the modelling, simulation and total equivalent warming impact (TEWI) of a domestic-size absorption solar cooling system is presented. The system consists of a solar collector, storage tank, a boiler and a LiBr–water absorption refrigerator. Experimentally determined heat and mass transfer coefficients were employed in the design and costing of an 11 kW cooling capacity solar driven absorption cooling machine which, from simulations, was found to have sufficient capacity to satisfy the cooling needs of a well insulated domestic dwelling. The system is modelled with the TRNSYS simulation program using appropriate equations predicting the performance of the unit. The final optimum system consists of 15 m² compound parabolic collector tilted at 30° from horizontal and 600 l hot water storage tank. The total life cycle cost of a complete system, comprising the collector and the absorption unit, for a lifetime of 20 years will be of the order of C£ 13,380. The cost of the absorption system alone was determined to be C£ 4800. Economic analysis has shown that for such a system to be economically competitive compared to conventional cooling systems its capital cost should be below C£ 2000. The system however has a lower TEWI being 1.2 times smaller compared to conventional cooling systems.     

An efficient solar-powered adsorption chiller and its application in low-temperature grain storage

A novel solar-powered adsorption cooling system for low-temperature grain storage has been built, which consists of a solar-powered water heating system, a silica gel–water adsorption chiller, a cooling tower and a fan coil unit. The adsorption chiller is composed of two identical adsorption units, each of them containing an adsorber, a condenser, and an evaporator/receiver. The two water evaporators have been incorporated into one methanol evaporator by the use of the concept of a gravity heat pipe. In order to improve the system efficiency and achieve continuous cooling production, the adsorbers are operated out-of-phase, and heat and mass recovery processes have been used. During the period from July to September of 2004, the system was put into experimental operation to cool the headspace (i.e., the air volume above the grain) of a grain bin. Three months of operation showed promising performance. The chiller had a cooling power between 66 and 90 W per m² of collector surface, with a daily solar cooling coefficient of performance (COP_solar) ranging from 0.096 to 0.13. The electric cooling COP was between 2.6 and 3.4.     

Performance analysis and optimization of a trigeneration process consisting of a proton-conducting solid oxide fuel cell and a LiBr absorption chiller

In this work, the trigeneration system, consisting of a proton-conducting solid oxide fuel cell (SOFC–H⁺) and a single-stage LiBr absorption chiller, was proposed. The SOFC–H⁺ and single-stage LiBr absorption chiller models were developed through Aspen Plus V10. From the sensitivity analysis, the results show that increases in temperature and fuel utilization can improve the performance of the SOFC–H⁺. Conversely, the air to fuel (A/F) molar ratio and pressure negatively affect the electrical efficiency and overall system efficiency. In the case of the absorption chiller, the coefficient of performance was increased and made stable according to a constant value when the generator temperature was increased from 90 to 100 °C. When the optimization was performed, it was found that the SOFC–H⁺ should be operated at 700 °C and 10 bar with fuel utilization of 0.8 and A/F molar ratio of 2 to achieve a maximum overall efficiency of 93.34%. For the energy and exergy analysis, a combined heat and power SOFC–H⁺ was found to have the highest energy and exergy efficiencies, followed by the trigeneration process. This indicates that the integration of the SOFC–H⁺ and LiBr absorption chiller is possible to efficiently produce electricity, heating and cooling.     

Dynamic simulation of hydrogen-based zero energy buildings with hydrogen energy storage for various climate conditions

Solar energy systems are an effective way to meet the needs of zone heating, cooling, electricity, and domestic hot water. However, to reach sustainability, and energy storage unit should be considered for installation. In this study, two combined cooling, heating and power (CCHP) systems are simulated and studied using TRNSYS software; both using natural gas engine generators and photovoltaics as prime movers and a hydrogen fuel cell/electrolyzer storage unit, one with absorption chiller and another with compression chiller cooling. For the study, a residential building is modeled for three major populated climate zones of the United States of America, namely, Hot-humid, mixed-humid and cold using DesignBuilder and EnergyPlus software. The energy demand for its HVAC operation and domestic electricity is obtained and used for system simulation in TRNSYS software. Due to choosing actual equipment for the CCHP arrangement, precise economic and environmental models are designed to further evaluate the possibility of execution of the system. The results show that absorption chiller-equipped CCHP has better performance both environmentally and economically. In addition, the outcome shows that the suggested systems show less favorability to be utilized in hot humid climate zones.     

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.     

Modeling and simulation of solar absorption system performance in Beirut

An analytical study is performed on solar energy utilization in space cooling of a small residential application using a solar lithium bromide absorption system. A simulation program for modeling and performance evaluation of the solar-operated absorption cycle is done for all possible climatic conditions of Beirut. The results have shown that for each ton of refrigeration it is required to have a minimum collector area of 23.3 m² with an optimal water storage tank capacity ranging from 1000 to 1500 liters for the system to operate solely on solar energy for about seven hours a day. The monthly solar fraction of total energy use in cooling is determined as a function of solar collector area and storage tank capacity.An economic assessment is performed based on current cost of conventional cooling systems. It is found that the solar cooling system is marginally competitive only when combined with domestic water heating.     

Simulation of an unglazed collector system for domestic hot water and space heating and cooling

This paper details modeling assumptions and simulation results for an unglazed collector system supplying domestic hot water, space heating, and space cooling loads. Collectors are modeled using unglazed collector test results. Variation of savings with collector area, storage volume, heat exchanger size, and wind for the Albuquerque, NM climate are shown. Over the storage-to-collector ratio range of 40–640 l/m² collector, annual savings varies only ±15%. Cooling is sensitive to heat exchanger size, and heating is sensitive to wind velocity. At a collector area of 23 m², the unglazed system meets about 56% of the annual total energy demand, saving 25.9 $/m² yr for an all-electric home. For the 23 m² area, savings for a cold/damp (Madison) and a hot/humid (Miami) climate are 64% and 56%, respectively, of the savings in Albuquerque.     

Experience with fully operational solar-driven 10-ton LiBr/H2O single-effect absorption cooling system in Thailand

A solar-driven 10-ton LiBr/H₂O single-effect absorption cooling system has been designed and installed at the School of Renewable Energy Technology (SERT), Phitsanulok, Thailand. Construction took place in 2005, after which this system became fully operational and has been supplying cooling for our main testing building's air-conditioning. Data on the system's operation were collected during 2006 and analyzed to find the extent to which solar energy replaced conventional energy sources. Here, we present these data and show that the 72 m² evacuated tube solar collector delivered a yearly average solar fraction of 81%, while the remaining 19% of thermal energy required by the chiller was supplied by a LPG-fired backup heating unit. We also show that the economics of this cooling system are dominated by the initial cost of the solar collector array and the absorption chiller, which are significantly higher than that of a similar-size conventional VCC system.     

Design and experimental testing of the performance of an outdoor LiBr/H2O solar thermal absorption cooling system with a cold store

A domestic-scale prototype experimental solar cooling system has been developed based on a LiBr/H₂O absorption system and tested during the 2007 summer and autumn months in Cardiff University, UK. The system consisted of a 12 m² vacuum tube solar collector, a 4.5 kW LiBr/H₂O absorption chiller, a 1000 l cold storage tank and a 6 kW fan coil. The system performance, as well as the performances of the individual components in the system, were evaluated based on the physical measurements of the daily solar radiation, ambient temperature, inlet and outlet fluid temperatures, mass flow rates and electrical consumption by component. The average coefficient of thermal performance (COP) of the system was 0.58, based on the thermal cooling power output per unit of available thermal solar energy from the 12 m² Thermomax DF100 vacuum tube collector on a hot sunny day with average peak insolation of 800 W/m² (between 11 and 13.30 h) and ambient temperature of 24 °C. The system produced an electrical COP of 3.6. Experimental results prove the feasibility of the new concept of cold store at this scale, with chilled water temperatures as low as 7.4 °C, demonstrating its potential use in cooling domestic scale buildings.     

Study of a novel solar adsorption cooling system and a solar absorption cooling system with new CPC collectors

One two-phase thermo-syphon silica gel-water solar adsorption chiller and LiBr-H₂O absorption chiller with new medium CPC (Compound Parabolic Concentrator) solar collectors were investigated. The reliability of adsorption chiller can be improved, because there is only one vacuum valve in this innovative design. Medium temperature evacuated-tube CPC solar collectors were firstly utilized in the LiBr-H₂O air conditioning system. The former system was applied in north of China at Latitude 37.45° (Dezhou city, China), the latter system was applied at Latitude 36.65° (Jinan city, China). Experimental results showed that the adsorption chiller can be powered by 55 °C of hot water. The adsorption chiller can provide 15 °C of chilled water from 9:30 to 17:00, the average solar COP (COPs) of the system is 0.16. In the absorption cooling system, the efficiency of the medium temperature evacuated-tube CPC solar collector can reach 0.5 when the hot water temperature is 125 °C. The absorption chiller can provide 15 °C of chilled water from 11:00 to 15:30, and the average solar COPs of absorption system is 0.19.     

Modelling and simulation of an absorption solar cooling system for Cyprus

In this paper a modelling and simulation of an absorption solar cooling system is presented. The system is modelled with the TRNSYS simulation program and the typical meteorological year file containing the weather parameters of Nicosia, Cyprus. Initially a system optimisation is carried out in order to select the appropriate type of collector, the optimum size of storage tank, the optimum collector slope and area, and the optimum thermostat setting of the auxiliary boiler. The final optimised system consists of a 15-m² compound parabolic collector tilted 30° from the horizontal and a 600-l hot water storage tank. The collector area is determined by performing the life cycle analysis of the system. The optimum solar system selected gives life cycle savings of C£1376 when a nonsubsidized fuel cost is considered. The system operates with maximum performance when the auxiliary boiler thermostat is set at 87°C. The system long-term integrated performance shows that 84,240 MJ required for cooling and 41,263 MJ for hot water production are supplied with solar energy.