A. Tsangrassoulis

Analysis of the green roof thermal properties and investigation of its energy performance

Abstract The advantages of the planned roofs are undoubtedly numerous from both the ecological and the social point of view. They act positively upon the climate of the city and its region, as well as upon the interior climate of the buildings beneath them. They give protection from the solar radiation, which is the main factor in passive cooling. By reducing thermal fluctuation on the outer surface of the roof and by increasing their thermal capacity, they contribute, to the cooling of the spaces below the roof during the summer and to the increase of their heat during the winter. Due to the decrease of the thermal losses, the green roofs save the energy consumption. This paper refers to the analysis of the thermal properties and energy performance study of the green roof. The investigation were implemented in two phases: during the first phase, extended surface and air temperature measurements were taken at the indoor and outdoor environment of the buildings where the green roof had installed and during the second phase of the study, the thermal properties of the green roof, as well as, the energy saving were examined, through a mathematical approach.

Modifications in energy demand in urban areas as a result of climate changes: an assessment for the southeast Mediterranean region

Abstract The impact of climate changes on the urban environment may be assessed by calculating the modifications in energy production and consumption for such daily operations as heating and cooling. In this study climate changes in the southeastern Mediterranean (the area of Greece) were simulated for the year 2030 on the basis of specially constructed climatic scenarios which describe potential reductions in the emissions of greenhouse gases, and were, thereafter, used to calculate the heating and cooling degree days for the same year. The results show that the cumulative amount of heating and cooling degree days will decrease and increase, respectively, as compared to the respective amounts for the year 1990. In terms of the cooling degree days, it was found that the areas most affected were the Attica and central Macedonia regions, the Aegean islands and Crete, whereas in terms of the heating degree days, it was found that a large part of the country will require less energy for heating.

On the energy consumption in residential buildings

Abstract A neural network approach is used in the present study for modelling and estimating the energy consumption time series for a residential building in Athens, using as inputs several climatic parameters. The hourly values of the energy consumption, for heating and cooling the building, are estimated for several years using feed forward backpropagation neural networks. Various neural network architectures are designed and trained for the output estimation, which is the building’s energy consumption. The results are tested with extensive sets of non-training measurements and it is found that they correspond well with the actual values. Furthermore, “multi-lag” output predictions of ambient air temperature and total solar radiation are used as inputs to the neural network models for modelling and predicting the future values of energy consumption with sufficient accuracy.

Theoretical and experimental analysis of daylight performance for various shading systems

Abstract The daylight coefficient approach is used for the theoretical analysis of various shading systems. Once a set of these coefficients has been calculated, it is very easy to calculate illuminance in the interior of a room under various sky luminance distributions. The present paper examines a method based on daylight coefficients to evaluate daylight in the interior of a room. The method is compared with existing radiosity and ray-tracing methods. The examined method is experimentaly validated using measurements obtained in a PASSYS test-cell equipped with shading devices.

Comparison of radiosity and ray-tracing techniques with a practical design procedure for the prediction of daylight levels in atria

Designers are often facing prescribed requirements concerning daylight in atria. For the accurate prediction of the illuminances the designers should employ either computer simulations or apply empirical equations. This study compares results obtained by a practical design procedure and simulated results using Radiance and Lightscape 3.2.

A METHOD TO INVESTIGATE THE POTENTIAL OF SOUTH-ORIENTED VERTICAL SURFACES FOR REFLECTING DAYLIGHT ONTO OPPOSITELY FACING VERTICAL SURFACES UNDER SUNNY CONDITIONS

An average monthly variable, called the Obstruction Illuminance Multiplier (OIM), defined as the ratio of the illuminance received on a vertical surface due to light received from the sky, ground and the obstruction to the illuminance on the same surface without the presence of the obstruction, is proposed as a simple tool to investigate the potential of perfectly diffuse vertical south-oriented facades to reflect daylight onto the opposing facades.

Numerical estimation of street canyon albedo consisting of vertical coated glazed facades

The method presented in this paper is a practical procedure for the derivation of a street canyon’s albedo, by taking into account the angle-dependent optical properties of a typical coated (SnO2) glazing. The development of the method is based on the flux transfer theory and can be easily implemented in a computer code permitting exploitation of a series of possibilities, such as street canyon geometry and window to wall ratios (WWRs).

A method to estimate the daylight efficiency of round skylights

The present paper presents a practical methodology to estimate the round skylight efficiency and hence the amount of daylight that reaches the interior of a room equipped with these devices. The methodology is based on flux transfer approach to model the distribution of the luminous energy inside the round skylights for various height-to-width ratios, wall reflectances and transmittances of the glazed cover under diffuse skylight and sunlight.

Development of a control algorithm to optimize airflow rates through variable size windows

The present paper aims in investigating, in a systematic way, using both experimental and theoretical tools, the potential of natural ventilation control techniques when applied to full scale buildings. Experiments have been carried out in outdoor test cell and different configurations have been tested for two window types (bottom hung and sliding) under various meteorological conditions. Based on the experimental results, specific modeling activities have been undertaken and theoretical methods for calculating airflow rates through the above-mentioned windows have been developed. The theoretical predictions are compared with the corresponding experimental data and a very satisfactory agreement has been observed. Following the data analysis an algorithm was developed for the control of the natural ventilation.

Context dependency of comfort and energy performance in mixed mode offices

This article investigates the context dependency of comfort and energy performance in mixed-mode offices in the climate of Athens, Greece. It is based on a parametric study using the simulation software EnergyPlus. Context refers to different building design priorities on the real estate market (prestige, low cost and green), occupant behaviour scenarios (ideal and worst case) and cooling strategies (fixed and adaptive set points). Results are evaluated according to energy consumption and related greenhouse gas emissions, daylight autonomy, view and percentage of working time when heating and cooling are operating. The results indicate that a holistic approach to comfort and energy performance evaluation focused on the specific context of a building and its occupants is necessary to develop appropriate optimization strategies. In early design stages, such specific information is not yet available and ideal/worst-case scenarios can indicate the magnitude of influence of occupants compared to building design.