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

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.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.Higher Technical Institute Research Committe

Rheological characterization of a thixotropic semisolid slurry by means of numerical simulations of squeeze flow experiments

We propose a methodology for the rheological characterization of a semisolid metal slurry using experimental squeeze flow data. The slurry is modeled as a structural thixotropic viscoplastic material, obeying the regularized Herschel-Bulkley constitutive equation. All rheological parameters are assumed to vary with the structure parameter that is governed by a first-order kinetics accounting for the material structure breakdown and build-up. The squeeze flow is simulated using finite elements in a Lagrangian framework. The evolution of the sample height has been studied for wide ranges of the Bingham and Reynolds numbers, the power-law exponent as well as the kinetics parameters of the structure parameter. Systematic comparisons have been carried out with available experimental data on a semisolid aluminium alloy (A356), where the sample is compressed from its topside under a specified strain of 80% at a temperature of 582 oC while the bottom side remains fixed. Excellent agreement with the experimental data could be achieved provided that at the initial instances (up to 0.01s) of the experiment the applied load is much higher than the nominal experimental load and that the yield stress and the power-law exponent vary linearly with the structure parameter. The first assumption implies that a different model, such as an elastoviscoplastic one, needs to be employed during the initial stages of the experiment. As for the second one, the evolution of the sample height can be reproduced allowing the yield stress to vary from 0 (no structure) to a maximum nominal value (full structure) and the power-law exponent from 0.2 to 1.4, i.e., from the shear-thinning to the shear-thickening regime. These variations are consistent with the internal microstructure variation pattern known to be exhibited by semisolid slurries.Comment: 33 pages, 21 figures, 42 reference

Investigation and determination of the geothermal parameters of the ground in Cyprus for the exploitation of geothermal energy and the impact of the results in the design of the geothermal systems

The Energy Service of the Ministry of Commerce, Industry and Tourism has the overall responsibility for Energy matters in Cyprus and specifically for preparing and implementing programmes for energy conservation, the promotion of renewable energy sources (RES) and the development of technologies for the utilization of RES. The Government of Cyprus being aware of the benefits of geothermal energy and in order to increase the share of energy from renewable sources consumed in heating and cooling in 2020, promotes the geothermal energy systems through a Scheme that provides financial incentives for the utilization of RES for heating and cooling. However, the lack of valid data for the ground thermal properties in Cyprus was one of the main obstacles for the design of efficient geothermal systems, the implementation of the Schemes in the field of geothermal energy and the calculation of the share of energy from renewable sources for heating and cooling according to the methodology defined by the E.U in the directive 2009/28/EC. In an effort to identify suitable energy efficient systems for heating and cooling of buildings and the correct calculations of their contribution to the national targets, the Energy Service participated in a project founded by the Research Promotion Foundation of Cyprus to investigate and determine the geothermal parameters of the ground of Cyprus at six representative sites in Cyprus, for use in the design of ground heat exchanger applications and ground thermal storage. The paper presents the importance of the Isothermal map that helps consultants to design efficiently geothermal energy systems, calculate effectively heat losses of buildings to the ground and design the thermal energy storage equipment. The importance’s of the results are analyzed by national authorities’ experts’ point of view for evaluating geothermal applications bridging in this way the gap between technical output and commercial reality

Experimental investigation of the thermosiphonic phenomenon in domestic solar water heaters

The deeper understanding of the ‘thermosiphonic phenomenon’ and the identification of the key parameters affecting it, is the main aim of a research project currently in process in Cyprus. In this work a review of the existing standards and scientific knowledge concerning domestic solar water heaters is presented. The first preliminary results of the experimental investigation of the ‘thermosiphonic phenomenon’ in domestic solar water heaters are also presented. For this purpose a special test rig was set up and equipped with all sensors necessary to measure all parameters that are most likely to affect the ‘thermosiphonic phenomenon’. All tests were conducted according to ISO 9459- 2:1995(E). At first, the solar collector was tested according to EN12975-2:2006 in order to determine the thermal performance characteristics at a flow and operation conditions specified by the standard. Consequently, the efficiency of the collector operating thermosiphonically was calculated based on quasi-dynamic approach. Finally, a series of correlations were attempted using the data acquired when the collector is operating themosiphonically which are the following: (i) the temperature difference of the water at the outlet and the inlet of the collector (ΔΤ) with the solar global radiation, (ii) the water mass flow with the solar global radiation, (iii) the water mass flow with the temperature difference of the water at the outlet and the inlet of the collector (ΔΤ). The results of the data analysis showed that these parameters are very well correlated between them since the coefficient of determination (R2) is over 0.91 in all cases

Investigation of the parameters affecting the thermosiphonic phenomenon in solar water heaters

Cyprus is currently the leading country in the world with respect to the application of solar water heaters for domestic applications, with more than 93% of the houses equipped with such a system. The great majority of these solar water heaters are of the thermosiphonic type. Thermosiphonic is a natural phenomenon where the flow of the solar heated water from the collector to the storage tank occurs from a small flow created due to the difference in density between hot and cold water. The main advantage of such systems is that they do not require a pump for circulating the water and circulation exists as long as there is sunshine. This reduces the maintenance requirements and the system is foolproof. In spite of the fact that extensive analyses of the performance of solar water heaters has been carried out by numerous researchers, almost all of them concerned forced circulation systems which use a circulating pump. Currently, the knowledge on the parameters affecting the ‘thermosiphonic phenomenon’ is rather poor while on an international level (ISO and CEN committees) there isn’t any standard to test thermosiphon solar collectors. The deeper understanding of the ‘thermosiphonic phenomenon’ and the identification of the key parameters affecting it, is the main aim of a research project currently in process in Cyprus. In this work the first preliminary results of the experimental procedure are presented. More specifically, a special test rig was set up and equipped with all sensors necessary to measure all parameters that are most likely to affect the ‘thermosiphonic phenomenon’. All tests were conducted according to ISO 9459- 2:1995(E). The system was able to operate in various weather and operating conditions and could accommodate the change of inclination of the collector. Initially, the solar collector was tested according to EN12975-2:2006 in order to determine the thermal performance at a flow and operation conditions specified by the standard. Subsequently, the efficiency of the collector operating thermosiphonically was calculated based on quasi-dynamic approach. Finally, a series of correlations were attempted using the data acquired when the collector is operating themosiphonically which are the following: (i) the temperature difference of the water at the outlet and the inlet of the collector (ΔΤ) with the solar global radiation, (ii) the water mass flow with the solar global radiation, (iii) the water mass flow with the temperature difference of the water at the outlet and the inlet of the collector (ΔΤ). The results of the data analysis showed that these parameters are very well correlated between them since the coefficient of determination (R2) is over 0.91 in all cases

Cyprus building energy performance methodology: A comparison of the calculated and measured energy consumption results

In order to fulfil article 4 of the 2002/91/EC Directive (EPBD) a national methodology for the energy performance of buildings was drafted and approved by the Government of Cyprus in 2009. This methodology is in line with the European standards prepared to facilitate EPBD implementation and follows the asset rating approach that is, it represents the intrinsic annual energy use of a building under standardised conditions. CEN standards leave an option, quite suitable for existing and complex buildings, for operational rating, which is an energy rating based on measured amounts of delivered and exported energy. The calculated and measured rating exhibit advantages and disadvantages and as expected the results of the two approaches vary, since the measured rating approach takes into account the effect of user behaviour, the actual weather conditions and the realized (actual) thermal comfort conditions inside the building. This paper presents the Cyprus legal framework for adopting the EPBD and exhibits the Cyprus methodology for the energy performance of buildings. Moreover the advantages and disadvantages of the asset and operational rating approaches are discussed and a comparison of the results of these two approaches for a selected number of dwellings is presented. One of these cases is also examined with respect to the climatic conditions, by changing the climatic zone in which the building is erected. The latter reveals the effect of climate on the calculated energy requirements of the building for both heating and cooling

Characterisation of ground thermal and thermo-mechanical behaviour for shallow geothermal energy applications

Increasing use of the ground as a thermal reservoir is expected in the near future. Shallow geothermal energy (SGE) systems have proved to be sustainable alternative solutions for buildings and infrastructure conditioning in many areas across the globe in the past decades. Recently novel solutions, including energy geostructures, where SGE systems are coupled with foundation heat exchangers, have also been developed. The performance of these systems is dependent on a series of factors, among which the thermal properties of the soil play one of major roles. The purpose of this paper is to present, in an integrated manner, the main methods and procedures to assess ground thermal properties for SGE systems and to carry out a critical review of the methods. In particular, laboratory testing through either steady-state or transient methods are discussed and a new synthesis comparing results for different techniques is presented. In-situ testing including all variations of the thermal response test is presented in detail, including a first comparison between new and traditional approaches. The issue of different scales between laboratory and in-situ measurements is then analysed in detail. Finally, thermo-hydro-mechanical behaviour of soil is introduced and discussed. These coupled processes are important for confirming the structural integrity of energy geostructures, but routine methods for parameter determination are still lacking

Solar space heating and cooling systems

This chapter examines solar space heating and cooling systems. Initially, the basic system configurations are presented which include active solar systems in which direct circulation systems, indirect water-heating systems, and air water-heating systems are presented, space heating and service hot water systems which include air and water systems, issues concerning the location of auxiliary and heat pump systems, and solar cooling, which includes adsorption units, absorption units, lithium--water absorption systems, ammonia--water absorption systems, and solar cooling with absorption refrigeration. Subsequently, heat storage systems are examined which include air and liquid systems thermal storage. Finally, details of various aspects of system design are presented which include module and array design, heat exchangers, and differential temperature controllers

Solar space heating and cooling systems

This chapter examines solar space heating and cooling systems. Initially, the basic system configurations are presented which include active solar systems in which direct circulation systems, indirect water-heating systems, and air water-heating systems are presented, space heating and service hot water systems which include air and water systems, issues concerning the location of auxiliary and heat pump systems, and solar cooling, which includes adsorption units, absorption units, lithium--water absorption systems, ammonia--water absorption systems, and solar cooling with absorption refrigeration. Subsequently, heat storage systems are examined which include air and liquid systems thermal storage. Finally, details of various aspects of system design are presented which include module and array design, heat exchangers, and differential temperature controllers