• Energy Research

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.

Abstract The objective of this study is to present a comparison between the measured and the calculated energy performance of dwellings. For this purpose, the energy consumption of ten dwellings is measured for one year. The added value of this work is that it is performed in a summer dominant environment. The energy needs of the same dwellings are also calculated by means of the methodology based on European Standards described in the CEN/TR 15615:2008 technical report. According to the findings of this study, a large gap exists between the calculated and the measured energy consumption of the examined dwellings. In order to evaluate the reasons for this deviation, a detailed analysis of the heating and cooling loads of the dwellings is performed. The intermittent heating of the building is found to be simulated accurately by the employed methodology, whereas the comparison between the calculated and the measured cooling loads reveals a large deviation of about 150%. Based on the findings of this study, a factor of 0.6 should be adopted in the case of cooling schedule, compared to the heating operation of the building.

Abstract A ground heat exchanger can be used for the injection or extraction of thermal energy into/from the ground. The line source model is an easy method of evaluating the characteristics of the borehole and does not need expensive equipment. This method is presented and a test is performed in order to determine a borehole’s characteristics in layers consisting of clay, silt and sand at various analogies. For the borehole under test the ground thermal conductivity ( λ ) was found to be 1.605 W/(m K) and the effective borehole thermal resistance ( R b ) to be 0.257 K/(W/m). The accuracy of the collected data could be affected mainly by two factors. The first factor is the daily flux penetration through the ground which gradually increases the temperature of the top layers and the second factor is a variation of the heating coil injection rate per active length of borehole. As it was observed this combined effect has a negligible result on the mean fluid temperature during the test hours of 280–400, when the system was operating at steady state. The steady state conditions yield values of borehole thermal resistance which deviates about 25% from the values given by the line source method. The ground thermal conductivity deviates only about 5%. This method however is not suitable for estimating the above values because of the uncertainty that exists in the estimation of the mean ground temperature, which is not constant throughout the borehole length nor is it constant at different points in a cross section of the grout. Also this method takes a lot of time until the steady state is reached.

This study describes the evolution of domestic dwellings in Cyprus during the twentieth century with respect to their heating and cooling requirements. The methods of construction employed and materials used are also presented. TRNSYS is used for modelling and simulation of the energy flows of various types of houses. For the calculations, a typical meteorological year for the Nicosia area and a typical model plan of a house are used. The inside house temperature, for the various construction methods, when no air-conditioning is used, is estimated. The temperature inside the traditional house varies in a similar manner with a well-insulated modern house. This variation is 16–20°C for winter and between 25–35°C for summer compared to 11–20°C for winter and 33–46°C for summer for a non-insulated house with a flat roof. The summer temperatures drop considerably, by about 5°C, when ventilation air is used for cooling, depending on the number of air changes.

Abstract The temperature requirements of solar industrial process heat applications range from 60 °C to 260 °C. The characteristics of medium to medium-high temperature solar collectors are given and an overview of efficiency and cost of existing technologies is presented. Five collector types have been considered in this study varying from the simple stationary flat-plate to movable parabolic trough ones. Based on TRNSYS simulations, an estimation of the system efficiency of solar process heat plants operating in the Mediterranean climate are given for the different collector technologies. The annual energy gains of such systems are from 550 to 1100 kWh/m 2 a. The resulting energy costs obtained for solar heat are from 0.015 to 0.028 C£/kWh depending on the collector type applied. The viabilities of the systems depend on their initial cost and the fuel price. None of these costs however is stable but change continuously depending on international market trends and oil production rates. The costs will turn out to be more favourable when the solar collectors become cheaper and subsidisation of fuel is removed. Therefore the optimisation procedure suggested in this paper should be followed in order to select the most appropriate system in each case.

Abstract Flat plate solar collectors are of black appearance because of the color of the absorber, which is employed to maximize the absorption of solar spectrum. Generally, to avoid the monotony of the black color we can use collectors with absorbers of blue, red–brown, green or other color. These collectors are of lower thermal efficiency than that of the usual black type collectors, because of the lower collector absorptance, but they are of more interest to architects for applications on traditional or modern buildings. In this paper, applications of solar collectors with colored absorbers in a large hot water system suitable for multi-flat residential or office buildings, a house heating system, and an industrial process heat system are presented. The collectors are analyzed with respect to their performance and practical applications, aiming to give guidelines for their wider use on buildings. These systems are simulated on an annual basis at three different locations at different latitudes, Nicosia, Cyprus (35°), Athens, Greece (38°) and Madison, Wisconsin (43°). All simulations are carried out with TRNSYS. The results show that although the colored collectors present lower efficiency than the typical black type collectors, the difference in energy output depends on the absorber darkness. For a medium value of the coefficient of absorptance ( α = 0.85), the colored collectors give satisfactory results regarding the drop of the amount of collected energy for the three locations (about 7–18%), compared to collectors with black absorbers ( α = 0.95). This implies the use of proportionate larger collector aperture area to have the same energy output as that of typical black colored collectors. Additionally, the economic figures obtained for the systems investigated are very promising.

The most common sea water desalination systems available today are described. These are divided into two broad categories, namely, direct and indirect collection systems. In the former, solar energy is absorbed and used in the same piece of equipment whereas in the latter, two separate sub-systems are used, one for solar energy conversion and one for desalination. Various systems are analysed with respect to their primary energy consumption, sea water treatment requirement, cost, and suitability for solar energy utilisation. Of the various types of processes that are analysed, the multiple-effect boiling (MEB) system and, in particular, the multiple-effect stack (MES) type evaporator, is the most suitable for solar energy utilisation since it can be used under varying energy supplies without upset. In addition, this system has a low specific energy requirement, low equipment cost and also requires the simplest sea water treatment.

This paper deals with a feasibility study for the use of solar Parabolic Trough Collectors for hot water production in Cyprus. An analysis is carried out for two types of applications, domestic and hotel. The systems are optimised using the F-chart program and compared to similar systems using Flat Plate Collectors. It is shown that for large scale water production the Parabolic Trough Collectors are more efficient than the Flat Plate ones. The life cycle savings from their use as applied to a real life situation is almost 5,350 Cyprus Pounds with 60% of the available solar energy being utilised.

This paper presents a study of the characteristics of three types of PV panels: monocrystalline, polycrystalline and amorphous silicon and the effects of soiling on their performance using on-site measurements. The total system consists of the three types of panels in pairs. Initially, the characterization of the PV panels is carried out to prove the similarity of the two pairs. Another test performed is the degradation of PV's performance under extreme soiling conditions caused by the artificial deposition of dust on the panels when their surface was dry and when it was wet before the dust deposition. The results showed that especially the artificial soiling on the wet PV surface presents a serious degradation of the PV performance. Finally, the effect of natural dust deposition on the panel's surfaces for a year is investigated. During this period a total of three dust episodes were recorded. These dust episodes concern the transfer of dust from the Sahara desert and these episodes usually end with a light rain which sticks the dust on exposed surfaces including PVs. Due to the exceptionally wet weather that we had during the testing period all episodes were followed by heavy rain, but even in this case a serious degradation of the performance of about 13% of the affected PV panels was recorded. The first finding of this study is that in winter the occasional rain is adequate to keep the PV surfaces clean whereas when a dust episode occurs, the panels should be cleaned manually. This is not the case for the summer time, which for Cyprus lasts for more than 8 months. The recommended cleaning is immediately after a dust episode and every 2–3 weeks in summer time according to how much loss the owner of the PV is willing to accept and the associated cleaning cost.