Investigations into the effectiveness of measures to reduce the energy requirements of domestic dwellings in Cyprus

Abstract

In recent years there has been an increasing trend in the provision of central heating and split vapour compression air conditioning systems to domestic dwellings in Cyprus. To minimise their economic and environmental impact, this study examines the feasibility and economic viability of energy conservation measures and the feasibility of the application of solar driven LiBr-water absorption system for space conditioning. Initially, the study compares through simulation, the heating and cooling requirements of domestic dwellings constructed in Cyprus during the last century. The simulations required values for the thermal conductivity of local building materials, like the hollow brick and mud and straw block. These were not available, and measurements were performed on a machine specifically purchased for the project to establish these values for the first time. These material properties will be of value to building services engineers in Cyprus and the Middle East for the more precise determination of building heating and cooling loads. Evaluation of the internal conditions resulting from the various types of constructions indicated that the traditional and insulated modem houses, could maintain indoor temperature in winter between 16°C and 20°C, but in the summer temperatures exceeded 36°C. The use of natural and mechanical ventilation could reduce slightly the maximum indoor summertime temperatures, but not to a level that could provide thermal comfort. Window gains are an important factor in domestic building energy requirements, and significant savings can result when extra measures are taken. The savings in cooling energy demand for a well-insulated house may be as high as 24% when low-emissivity double glazed windows are used compared to clear double glazed windows giving a pay-back period of 3.8 years. Other factors investigated are the effect of overhangs, shape and orientation of buildings and thermal mass. The results show that the roof is the most important structural element of domestic dwellings in the Cypriot environment. For good thermal performance, the roof must offer a discharge time of 6 hours or more and have a thermal conductivity of less than 0.48 W/m-K. Life cycle cost analysis has shown that measures that increase the roof insulation pay back in a short period of time, between 3.5 to 5 years. However, measures taken to increase wall insulation pay back in a longer period of time, approximately 10 years. The only natural energy resource abundantly available in Cyprus is solar energy, which could be used to power a low energy active cooling system based on the absorption cycle. To facilitate investigation of the feasibility of the application of solar driven absorption systems for domestic cooling, a 1 kW LiBr-water absorption-cooling unit was designed and constructed. The unit was used to determine experimentally the heat and mass transfer coefficients in the heat exchangers of absorption systems. In certain cases these were found to differ considerably from values obtained from heat and mass transfer correlations published by other investigators. The 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. 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. This drawback can be balanced by a lower total equivalent warming impact being 2.7 times smaller compared to conventional cooling systems.