Georgios Kokogiannakis

Comparison of the simplified methods of the ISO 13790 standard and detailed modelling programs in a regulatory context

The CEN standards that support the European Energy Performance of Buildings Directive requirement for calculation of the energy consumption of buildings allow various methods to be used for the same calculation. The impact of using the different methods within the updated ISO 13790 standard for space heating and cooling energy calculations was examined with a parametric analysis of a common building specification. The impact was assessed by considering the energy band, which would be assigned for the building based on the calculation results. The standard describes three different methods that can be used for the calculations: a monthly quasi-steady state method, a simplified hourly method and detailed simulation. For most cases studied, differences in the building rating given by the various methods were a maximum of one band. More significant differences were noticed in some cases. Parameter values in the monthly method were determined, which would lead to improved matching.

Effectiveness of an intensive green roof in a sub-tropical region

The overall assessment of an intensive green roof located in a sub-tropical region has been undertaken. The results showed a fairly good agreement between the published and measured solar radiation data and also confirmed July and January as the hottest and coldest periods, respectively, for the region. The soil was established as a silt type with good planting medium properties for green roofs. The overall thermal performance showed that the green roof provided an average temperature reduction of 3.3℃ (i.e. 50% temperature reduction) through the roof in July. Equally, its performance was remarkable during the coldest period of January. A maximum differential temperature of 15.5℃ was achieved with the soil contributing to 24% of the temperature difference through the roof. Further studies are, however, needed to cover a wider area of influence such as effects of different types of construction materials, plants, locations and soil. In view of the limitation of the theoretical model, it would also be useful to consider some of the factors which were either neglected or assumed to be constant in any future comparative studies.

Numerical and experimental analysis into the thermal performance of a novel phase change material gypsum board

Thermal evaluation of non-deform laminated composite phase change material (PCM) gypsum board has been carried out. The theoretical studies covered the analysis of different thicknesses of PCM layers and their corresponding heat transfer rates during energy storage and discharge processes. For the purpose of experimental validation, a laminated gypsum board consisting of a 4 mm PCM layer was evaluated and achieved a maximum heat flux and energy storage capacity of 15.6 W/m 2 and 363.7 kJ/m 2 respectively. A model room built with the laminated PCM gypsum board was also evaluated and obtained a maximum temperature reduction of 5 °C as compared with 1.8 °C for the model room with ordinary gypsum board. Even though about 25% of the energy stored could not be released within the targeted period, the overall thermal performance of the PCM gypsum board was found to be quite remarkable.

Numerical modeling and simulation of an integrated TEG/PCM system for the enhancement of PV power output

A high Photovoltaic (PV) cell temperature has an adverse effect on the conversion efficiency. A thermoelectric generator (TEG) can convert waste heat into electricity whereas phase change materials (PCMs) are able to utilise latent heat to store a large amount of energy at a relative stable temperature. An integrated TEG/PCM system for the enhancement of PV power output is thus proposed and evaluated. Results show that PCM layer during the phase change period shows a clear process to curb the increase of the PV temperature, but the PV temperature at thermal equilibrium is hardly lowered. Given a high surface resistance in natural convection, thicknesses of PCM layer and conductivities of PCM show limited effects on the system temperature profiling. TEG output is found to be negligible but the integrated system improves PV efficiency from 10.35% to 11% averaged in 1 hour.

Evaluation of Energy Saving Potential of Green Roofs in Sub-tropical Regions

The overall thermal performance assessment of an intensive green roof located in a sub-tropical region has been conducted. The results showed good agreement between the theoretical and the practical data and also confirmed July and January as the hottest and coldest periods respectively for the region. The soil was established as a silt type with good planting medium properties for green roofs. The overall thermal performance showed that the green roof provided an average temperature reduction of 3.3 o C and 50% heat transfer reduction during the hottest period of the year. Equally, its performance was remarkable during the coldest period of January. A maximum differential temperature of -15.5 o C was achieved with the soil contributing to 24% reduction of cold energy transfer through the roof. Further studies are however encouraged to cover a wider area of influence such as different locations at other latitudes, different types of construction materials, plants and soil.

Evaluation of an Earth-tube (E-tube) ventilation system

1 The concept of an earth-tube ventilation system as an energy saving technology has been practically evaluated and compared with theoretical results. The results have shown that the system can help to considerably reduce energy consumptions in buildings. For instance for the autumn and winter periods investigated reduction of 81% in cooling and 50% reduction in heating loads were achieved in comparison with non-earth tube ventilation system. Humidity levels were also improved considerably to average values of 66% and 49% for the two periods respectively. However there are certain factors such as thermophysical properties of heat transfer in wet, freezing or dry soils which could affect the thermal response of the system. Further monitoring and investigation into the impact of these properties of the surrounding soil is therefore being urged.