Solar-assisted System Research Articles

Comparison of the Performance of a Forced-Air and a Radiant Floor Residential Heating System Connected to Solar Collectors

A detailed building energy analysis tool is used to model the performance of a forced-air system and a radiant floor system. These two systems use a low-temperature tank to store solar energy from a solar collector array. An electrically heated tank at a higher temperature is used to provide any additional heat needed to meet the space heating load. The simulation models developed are then used to compare the performance of the forced-air and radiant floor systems based on maintaining the same operative temperature inside the space. It is found that the portion of the heating load that comes from solar energy is higher in the case of the radiant system. This portion from solar energy increases even further when the operating temperature of the radiant floor is lowered. The results also show that the energy performance of the radiant floor relative to the forced-air system improves for houses with higher envelope R-values and infiltration rates. Given the many different interacting factors that influence the performance of the solar-assisted systems studied, it is very important to use detailed simulation models to help assess which system is more energy efficient for a particular application.

Energy simulation of solar assisted absorption system and examination of clearness index effects on auxiliary heating

Abstract The smog and pollutants in the atmospheric air of heavily populated urban areas are anticipated to have substantial adverse effects on the collection of solar energy and the performance of solar energy systems. The objectives of this study are (a) to develop a simulation model for analyzing the performance of a water–LiBr solar assisted absorption system with an auxiliary heating source and (b) to examine the effects of clearness index on the auxiliary heating requirements. To achieve the objectives, a numerical model for a water–LiBr solar assisted absorption system is developed, and the influence of a reduction in the clearness index, based on actual recorded data, is investigated for constant and time varying cooling loads. Under the condition of peak solar gain on July 21, when a 1000 m 2 solar collector is designed to provide 70% of the heating energy required for a constant cooling load of 1265 MJ/h (=100 refrigeration tons), as the system coefficient of performance decreases due to higher ambient temperatures, it is found that a reduction in the clearness index from 0.63 to 0.52 results in a 67% increase in auxiliary heating required of the boiler. It is concluded that accounting for clearness index data is necessary for accurate prediction of solar energy collection.

Development of advanced solar assisted drying systems

The Solar Energy Research Group in the Universiti Kebangsaan Malaysia has been set-up more than two decades ago. One of the activities is in the field of solar thermal process, particularly in development of solar assisted drying systems. Solar drying systems technical development can proceed in two directions. Firstly simple, low power, short life, and comparatively low efficiency-drying system. Secondly, the development of high efficiency, high power, long life expensive solar drying system. The group has developed four solar assisted drying systems namely (a) the V-groove solar collector, (b) the double-pass solar collector with integrated storage system, (c) the solar assisted dehumidification system for medicinal herbs and (d) the photovoltaic thermal (PVT) collector system. The common problems associated with the intermittent nature of solar radiation and the low intensities of solar radiation in solar thermal systems can be remedied using these types of solar drying systems. These drying systems have the advantages of heat storage, auxiliary energy source, integrated structure control system and can be use for a wide range of agricultural produce.

05/01803 Solar assisted heat pump desalination system: Hawlader, M.N.A. et al. Desalination, 2004, 168, (15), 49–54

05/01803 Solar assisted heat pump desalination system: Hawlader, M.N.A. et al. Desalination, 2004, 168, (15), 49–54

Solar assisted heat pump desalination system

This paper describes a novel system of solar assisted heat pump desalination. A single effect desalination unit has been designed and fabricated, and it is connected to an existing solar assisted heat pump. The system consists of a compressor, condenser, evaporator, solar evaporator-collector, desalination chamber, feed tank, vacuum pump and distillate collection unit. A vacuum pump is connected to the desalination chamber. A spray nozzle has been used to generate droplets of feed water in the desalination unit. The feed water has been preheated before being sprayed by the nozzle. The desalination unit incorporates both falling film evaporation and flash distillation concepts. A series of experiment has been conducted on the system under different operating and meteorological conditions of Singapore. The effects of feed temperature and flashing have been investigated. The performance ratio and the coefficient of performance (COP) have been evaluated. The performance ratio (PR) obtained from the experiments ranges from 0.77 to 1.15 and COP of the system was found to vary between 5.0 and 7.0.

Prospects for utilisation of solar driven ejector-absorption cooling system in Turkey

Solar assisted refrigeration appears to be a promising alternative to the conventional electrical driven units. The main advantages of solar assisted refrigeration systems concern the reduction of peak loads for electricity utilities, the use of zero ozone depletion impact refrigerants, the decreased primary energy consumption and decreased global warming impact. The main focus of this study is to investigate usage possibility of ejector-absorption cooling system (EACS) in Turkey. This study determines whether or not required heat for generator of EACS can be obtained from solar energy in Turkey. There are two important reasons for the utilisation of EACSs in Turkey. One of them is that the production and use of the CFCs and HCFCs will be phased out in a few years according to Montreal Protocol, adopted in 1987. The other is that Turkey has high solar energy potential because of its location in the northern hemisphere with latitudes 36–42 °N and longitudes 26–45 °E and the yearly average solar radiation is 3.6 kWh/m2 day, and the total yearly radiation period is ∼2610 h. For analysis, 17 cities were selected in different regions of Turkey in which the radiation data and sunshine duration information have been collected since 2000. By using the meteorological data, it was aimed that required optimum collector surface area for maximum coefficient of performance (COPmax) conditions of EACSs operated with aqua-ammonia was defined. In addition, required minimum energy for auxiliary heater was calculated so that the system can be used throughout the year. It was found that the heat gain factor (HGF) varies in the range from 0.5 to 2.68 for the all the seasons in the selected cities. The maximum HGF of about 2.68 was obtained for Van in July. This study shows that there is a great potential for utilisation of solar cooling system for domestic heating/cooling applications in Turkey.

The economic feasibility of small solar MED seawater desalination plants for remote arid areas

The objective of this paper is to compare the economics of using solar energy to operate small multiple effect seawater distillation systems in remote areas with the conventional method of using fossil fuels. The particular multiple effect system used is an advanced horizontal tube, falling film system called “multiple effect stack”, MES, in which the pumping energy requirement is relatively low compared with the horizontal in-line system. Three system configurations were investigated: (1) conventional system using a steam generator to provide steam for the MES evaporator and a diesel generator to provide pumping power, (2) solar-assisted system which uses solar thermal collectors to provide hot water (instead of steam) for the evaporator and a diesel generator for pumping power, and (3) solar stand-alone system which uses solar thermal collectors for the evaporator heat requirement and a solar PV array to provide electrical energy for pumping. At the present time, solar energy cannot compete favorably with fossil energy particularly under the present international market prices of crude oil. However, in many remote sunny areas of the world where the real cost of fossil energy can be very high, the use of solar energy can be an attractive alternative. Two important cost parameters affect the relative economics of solar energy vis-à-vis conventional (fossil) energy: the collector cost in $ per square meter and the cost of diesel oil in $ per Giga Joule. Solar energy becomes more competitive as the local cost of procuring conventional fuel increases and as the collector cost decreases. The water cost from a solar thermal-diesel-MES system (Configuration #2) can be seen to approach the water cost from a steam generator-diesel-MES system (Configuration #1) when the collector cost drops to 200 $/m 2 and diesel oil cost at the remote site reaches 50 $/GJ. Using a 100% solar system (Configuration #3) with solar thermal and solar PV collectors being utilized, the economics was seen to improve in favor of the solar system. Even when diesel fuel can be procured at 10 $/GJ at the remote site, the cost of water from the solar system can be seen to approach that from a conventional plant when thermal collectors costing 200 $/m 2 are used. The cost of water from the solar system was shown to be always less than that from a conventional system which uses diesel oil procured at the high price of 50 $/GJ but always higher than water produced from a conventional system using diesel oil at the low price of 10 $/GJ.

Economics of small solar-assisted multiple-effect stack distillation plants

The objective of this paper is to compare the economics of using solar energy to operate small, multiple-effect seawater distillation systems in remote areas with the conventional method of using fossil fuels. The particular multiple-effect system used is an advanced horizontal-tube, falling-film system called “multiple-effect stack” (MES) in which the pumping energy requirement is relatively low compared with the horizontal in-line system. Three system configurations were investigated: (1) a conventional system using a steam generator to provide steam for the MES evaporator and a diesel generator to provide pumping power, (2) a solar-assisted system which uses solar thermal collectors to provide hot water (instead of steam) for the evaporator and a diesel generator for pumping power, and (3) a solar stand-alone system which uses solar thermal collectors for the evaporator heat requirement and a solar PV array to provide electrical energy for pumping. At the present time, solar energy cannot compete favorably with fossil energy, particularly under the present international market prices of crude oil. However, in many remote sunny areas of the world where the real cost of fossil energy can be very high, the use of solar energy can be an attractive alternative. Two important cost parameters affect the relative economics of solar energy vis-à-vis conventional (fossil) energy: the collector cost in dollars per square meter and the cost of diesel oil in dollars per giga Joule. Solar energy becomes more competitive as the local cost of procuring conventional fuel increases and as the collector cost decreases. The water cost from a solar thermal-diesel-MES system (configuration #2) can be seen to approach the water cost from a steam generator-diesel-MES system (configuration #1) when the collector cost drops to $200/m 2 and diesel oil cost at the remote site reaches $50/GJ. Using a 100% solar system (configuration #3) with solar thermal and solar PV collectors, the economics was seen to improve in favor of the solar system. Even when diesel fuel can be procured at $10/GJ at the remote site, the cost of water from the solar system can be seen to approach that from a conventional plant when thermal collectors costing $200/m 2 are used. The cost of water from the solar system was shown to be always less than that from a conventional system which uses diesel oil procured at the high price of $50/GJ, but always higher than water produced from a conventional system using diesel oil at the low price of $10/GJ.

Optimization of irreversible solar assisted ejector-vapor compression cascaded systems

The technique of energetic optimization is employed to investigate the optimal performance of focusing collector driven, irreversible Carnot ejector-vapor compression cascaded cooling and heating systems. The optimal operating temperature of the solar collector and the maximum overall coefficient of performance of the cooling and heating modes of the combined system are derived. The results obtained here may serve as a good guide for the evaluation of existing real solar assisted hybrid systems.

Utilization of Solar Energy and Waste Heat

A heat pump and thermal energy storage unit were combined in an experimental setup to utilize solar energy and waste heat efficiently at low temperatures (10-50 C). The calcium chloride hexahydrate was used as the thermal energy storage medium and water was used as the working liquid between storage tank and collectors. The performance of the experimental setup at different heat source temperatures for space heating in a laboratory building in Trabzon, Turkey, were investigated both experimentally and theoretically. The fraction of the space heating load that was supplied by the solar-assisted system was determined as a function of collector area and storage volume from a developed numerical method and results were compared with experimental results.

Exergy analysis of solar assisted double effect absorption refrigeration system

Exergy or the available energy is based on the second law of thermodynamics and goes back to Maxwell and Gibbs. It is the exergy content and not the energy content, that truly represents the potential of the substance to cause change. Exergy is the only rational basis for evaluating the system performance. The aim of this project is to study in detail the exergy variation in the solar assisted absorption system. The influence of the cycle parameters are analysed on the basis of first law and second law effectiveness and the results indicated various ways of improving system performance by better design. Also a better quality of the evaporator has more effect on the system performance than the better quality of other components. It was shown that second law analysis quantitatively visualizes losses within a system and gives clear trends for optimization.

Supply of cooling and heating with solar assisted absorption heat pumps: an energetic approach

The primary energy consumption of two kinds of solar assisted absorption systems (solar assisted absorption chiller during summertime and heat pump during wintertime or solar assisted absorption chiller with direct gas combustion for heating during wintertime) is compared with the primary energy consumption of a compression chiller which can work as a heat pump during wintertime. For the absorption systems three technical options were considered: a single effect machine; a double effect machine with the solar energy delivered to the lower temperature desorber and combustion heat of a gas burner delivered to the higher temperature desorber; a double effect machine with both solar energy and combustion heat delivered to the higher temperature desorber. The analysis performed in this article shows that solar assisted absorption chillers, absorption heat pumps and direct solar heating systems even with low and intermediate solar fractions can operate with considerably less primary energy consumption than compression systems. Further, the necessary solar collector area to achieve that goal is compatible with roof area available in buildings. It was also verified that, for the double effect absorption machines, there is no advantage in delivering the solar energy to the higher temperature desorber, thus establishing as preferable the solution in which it is delivered to the lower temperature desorber.

Ammonia-Water Low-Temperature Thermal Storage System

An analysis of a low-temperature thermal storage system using an ammonia-water solution both as a refrigerant and as a low-temperature thermal storage material is considered. The thermal storage is useable at a temperature of −27°C and higher. The proposed system is designed to shift electric demand from high to low-demand periods. The system utilizes a heat-operated absorption refrigeration system; however, the generator heat is supplied by a self-contained vapor compression heat pump. The heat pump is operated during the off-peak period to recover the low-temperature thermal storage by reprocessing the stored ammonia-water solution to a lower ammonia-water concentration. The ammonia vapor liberated from solution in the dephlegmator is used in the compressor to produce the generator heat. Three different configurations are considered, including a solar-assisted system. The results are compared to an eutectic salt storage system.

Economic analysis of a solar assisted desalination system

This paper deals with an economic analysis of a solar assisted desalination system. The analysis is carried out for four types of applications, two domestic, a hotel and a village. It is shown that solar desalination is viable for the two bigger installations (hotel and village) with water prices below C£0.89/m 3. It is also shown that the water cost is insensitive to the changes in method of payment or to small variations in direct costs. It is not worth operating the desalination system solely on solar energy due to the high cost of the desalination system and the diurnal nature of the solar input which implies high percentage of inactive time.

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.

A study of solar chimney assisted wind tower system for natural ventilation in buildings

The concept of a solar chimney coupled with a wind tower to induce natural ventilation has been studied analytically in this paper. It is estimated that the effect of a solar chimney is relatively much higher for lower wind speeds. For ambient wind speed of 1.0 m/s, for example, the wind tower alone creates a mass flow rate of 0.75 kg/s only, while the solar chimney assisted system is able to create an air flow up to 1.4 kg/s at 700 W/m 2 incident solar radiation.

Performance of a solar assisted heat pump system

In this study, a series solar heat pump system which uses solar energy storage as a heat source was simulated. The simulation was performed for a house in Istanbul, Turkey for space heating. The fraction of the space heating load that was supplied by the solar assisted system was determined as a function of collector area and thermal storage volume. The heat pump, solar panels, storage tank and thermal response of the house were dynamically analyzed, and a computer model was obtained for each one. The whole system was simulated by varying panel area and tank size. Also, a detailed parametric study was performed for only the heat pump by changing the inlet water temperatures of the heat exchangers. The computer program includes design and off-design parts. First, four major components in the vapor compression cycle were sized. Once the system has been defined, the program is able to compute the performance of the system at all possible combinations of inlet flow stream conditions.

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.

Testing domestic solar water heaters—The New Zealand experience

A procedure is described for measuring the thermal performance of solar water-heating systems. The basis of the method is a comparison between the electrical energy used by a conventional electrically heated tank and the electrical energy used by the solar-assisted systems to bring the energy delivered to the same value. Measurements were made on 25 systems at three different rates of water consumption over a period of 1 yr, thus providing comprehensive data for a variety of systems over a full range of weather conditions. Measurements included electrical energy input, solar radiation, water quantity delivered, temperature of water delivered, ambient temperatures and wind speed. It was concluded that the measurements were repeatable and that the technique could be used for establishing the rating of systems with considerable accuracy. Study of the data obtained has shown that it would be possible to obtain a useful thermal rating at a mean value of insolation and three different water draw-off rates in 3–4 weeks of testing. This would require, however, that certain conditions were satisfied, in particular that a range of insolation levels was experienced.

Calculating the solar contribution to solar assisted systems

After summarizing the methods for calculating the solar contribution for systems without thermal storage, this paper extends a previously proposed method which is based on using a frequency distribution of insolation data. This extension allows rapid hand calculation of solar contribution for most collector types and for any specified collector inlet and outlet temperatures. Typical results are shown to be accurate to within 1 per cent relative to dynamic computer simulation methods. The effect on the method of collector orientation and tilt is discussed, and a simple method of determining the maximum possible (i.e. infinite collector area) solar contribution for a given collector system is described.