1.1. Configurations Studied

In this study, three configurations of BIPV multi-glazing systems are considered, as shown in Fig. 1. Configurations A and B consist of double-glazed and triple-glazed assemblies where a PV laminate is used as the outer pane. Configuration C is also triple-glazed, but the PV laminate replaces the middle pane and the outer air cavity is naturally vented during daytime to avoid overheating of the cells. The PV laminate in all three configurations is of high PV cells density and the thickness of the different layers are assumed to be 5mm, 2mm and 6mm for the outer pane, combined PV and EVA layer and inner pane, respectively.

1.2. Model Description and Assumptions

The model developed to predict the PV electricity production and the temperatures within the BIPV system consists of a series of energy balance equations performed in the middle of each layer of the assembly. It accounts for thermal capacity, but is one-dimensional. Thus, each layer, including the PV+EVA layer, is assumed to be at a uniform temperature, except in configuration C, where a temperature gradient along the window height is considered in the outer air cavity since it is naturally ventilated. In addition, the following assumptions were made:

• No solar radiation is transmitted to the layers behind the PV because of the high PV density

• The convective heat transfer coefficient at the outer and inner surfaces of an air cavity are the same

• The PV cells work at maximum power point

• The inlet temperature of the air entering the vented air cavity is at ambient temperature

The composition of the developed PV-window is based on state-of-the art technology. The PV — pane is built up as a 3-layer construction with gas filling and a TPS spacer profile.

The composition of the PV-pane and hence a simplified production method are the key elements in reducing the price of the PV-window with up till 20 % or more compared to similar products.

As an additional choice the buyer can buy the PV-window with screen printing, which is used to hide the view from the inside of the building to the unpleasant looking backside of the PV-cell, cf. figure 2.

The screen printing is available in many colors in the RAL color system and the pattern can graphically also fill a part of the spaces between the cells giving possibilities for extended design expressions than just the pattern of the PV-cells.

The degree of freedom in carving and placement of the PV-cells in the pane mentioned in paragraph 2.3 makes it possible for architects to use/place the PV-window anywhere in the building design according to the need of daylight in the rooms. Figure 3 illustrates a typical design of the PV-window — notice the carving in the PV-cells (holes) and screen printing (green).

The external wires are hidden inside the wooden frame of the window. The window comes with a plus and a minus plug (hidden in either side of window frame) and enough cable to span a standard joint (hidden in the edge of the frame). Therefore the installation becomes extremely easy and really “plug and play”-like. For broader joints extension cables can be fitted. By-pass diodes are integrated in the frames too and couples out the individual windows if shadowed so that the system still functions brilliantly even when parts are shadowed. The diodes are placed in a box in the frame and can easily be replaced if broken.

The results from building simulations, of window shading profiles in summer, indicate that if shutters remain open on the north and west orientated fenestration, the increase of solar gains and consequently the rise of indoor temperature is insignificant. This causes no deviation from comfort levels (0.1 to 0.2 degrees, Tables 2, 1.4, 1.3, 1.2 and 1.1). This is mainly attributed to:

i) Area — The window area on North and West sides is limited.

ii) Orientation — There is no direct solar incidence on these facades.

In case half of South facing glazing is left unshaded, in summer, the solar gains increase rising indoor temperature by 0.1 to 0.6 degrees centigrade and reaching 1.2 degrees increase as the unshaded window area extends to all South fenestration area. However, the temperature increase causes no deviation of indoor temperature from comfort levels (Table 2, 1.2, 1.3, 1.4). This is attributed to two main reasons:

i) Orientation — South orientated windows have no direct solar insolation in the summer.

ii) Design — The optimized design of overhangs and extended vertical walls for south glazing. The above results indicate the effectiveness of the optimization of permanent shading devices.

3.1 Analysis of the base-case design

As stated in section 1, the first criterion to fulfil the regulation RCCTE is that the envelope obeys to certain minimum requirements. Table 4 shows the results of the evaluation of the base-case retrofit design against the requirements of RCCTE. The results show that several envelope elements do not fulfil the minimum requirements of the regulation.

Four out of the six analysed apartments do not comply the requirement for the U-value, because no insulation was foreseen in the design. Another four apartments do not comply with the requirement for the maximum solar factor of the windows. This is mostly because they foresee a thick layer of low-weight gypsum at the internal face of the walls and ceilings, which cuts the effects of the thermal inertia from the walls and slabs, resulting in low thermal inertia. The maximum solar factor allowed for buildings with low thermal inertia is only 0.15, so the windows with internal curtains do not fulfil the requirement. The solution may either be to increase the thermal inertia to medium, or to adopt external shading which leads to solar factors below 0.15 (the first solution seems more advisable here).

Planar thermal bridges are also subjected to quality requirements but none was identified in the apartments analysed, because the structure essentially relied upon the massive granite walls, so no concrete beams were identified.

In this research project the three main approaches from the Delft Design Approach have been the point of departure for the analysis of the PV design cases. From each sub-approach a number of essential design guidelines can be derived. It is hypothesised that thStructue more systematic these guidelines have been applied, the more successful the PV-product design will be and the more efficient and transparent the design process. First, we will describe here the three sub-models.

This experience is developed in the framework of the “Programme of Habitat and Productive Conditions Improvement for Disperse Rural Inhabitants and Small Communities from Chubut”. It aims to: “show the interdisciplinary and inter-sectorial experience developed on sustainable rural housing”, and its objectives are: a) to achieve bioclimatic suitability of the rural popular domestic habitat; b) to adopt appropriate and appropriable architectural technologies and dispositions; c) to promote actions for local development. Within this framework, from 2004, the Housing Provincial Institute-IPV and DU- from Chubut and the Nacional University of Tucuman — UNT-, have had an agreement between the Technological Connection Unit and the Project “Strategies and

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Technologies for a Sustained and Healthy Habitat” of the FAU-SeCyT-, UNT — CONICET) based on pre-existing bonds.

M. Krause*, C. Lauterbach, J. Kaiser, D. Schmidt

1 Fraunhofer Institute for Building Physics, Gottschalkstr. 28a, 34127 Kassel, Germany
* Corresponding Author, michael. krause@ibp. fraunhofer. de

Abstract

The present paper deals with the potentials of using solar thermal driven systems for air conditioning of office buildings and central server rooms. For this, a system model consisting of a building according to passive house standard, a server room and a solar air conditioning system using absorption chillers was developed for TRNSYS and evaluated regarding its thermal behaviour. Hereby, the energy demand of the building as well as the server room was determined. The investigations showed that for such a building, an active cooling system can increase the comfort in the office rooms significantly, even for mild climates. It has been proven that using solar air conditioning systems in combination with free cooling for server cooling is a promising concept and can lead to significant reductions of primary energy consumptions. However, special measures have to be addressed to increase the solar fraction of the system up to suitable levels.

Keywords: solar air conditioning, buildings, server cooling, simulations

1. Introduction

Within the European Union, the building sector is responsible for more than 40 % of the overal energy consumption. In order to reduce greenhouse gas emissions of 50% by 2050 [1], a distinctive reduction of the energy consumption in the building sector is essential. A promising and already established approach is the passive house concept. Here, a high insulation standard is combined with large south facing transparent areas and ventilation systems with high efficient heat recovery to increase solar gains and reduce the heating demand. However, high solar and internal gains are sometimes even in mild climates responsible for uncomfortable indoor temperatures [2]. As a result, the market for air conditioning systems and thus the energy consumption has been increasing within the last decades [3].

In addition, independent on the location of the building, computer centres and server rooms show a rapidly increasing cooling demand. According to [4], the electricity consumption of server rooms can be responsible for up to 60% of the overall electricity consumption within such buildings, half of which is caused by the cooling and ventilation demand and the resulting use of conventional vapour compression chillers.

Regarding this, the present paper is dealing with the use of alternative cooling technologies for buildings and server rooms. One promising option for this is the integration of thermal driven cooling technologies like absorption or adsorption chillers in combination with solar thermal systems. On overview of existing technologies for solar air conditioning can be found in [5].

Within the present investigations, a model of a passive office building and its server room was implemented in the simulation program TRNSYS. With this, the heating and cooling energy demand was evaluated for the defined reference case as well as for different variations regarding insulation standard, shading strategy, infiltration rate and cooling strategy. In addition, a thermally driven cooling system for the building and the server room was integrated in model. With these

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models, possibilities to cool passive houses and server rooms with solar thermal cooling systems have been investigated and compared to conventional cooling systems and strategies.

1.1.

Selected buildings for the study

The residential buildings selected — Navitejo, Pertejo, Alcantara-Rro in Lisbon — were built after the implementation of the first Thermal Regulation, which impose minimum quality levels to the constructive solutions to be adopted in the opaque and non-opaque envelope (thermal insulation and double glasses introduction) to guarantee a better thermal and energetic performance of the buildings.

Murielle Martin1, Francois Garde1, Mathieu David1, Laetitia Adelard1, Michael Donn2

1LPBS. -Laboratoire de Physique du Batiment et des Systemes Universite de La Reunion. 40 avenue Soweto

97410 Saint-Pierre

2Centre for Building Performance Research Victoria University of Wellington, New Zealand

murielle. martin@univ-reunion. fr

Abstract

In the building sector in tropical climates, the quality of solar shading of windows is often preferred to a good natural lighting. Few design guides exist in the field of natural lighting/solar shading in tropical climates and

This paper deals with the taking into account of efficient solar protections coupled with an efficient natural lighting. We focused on overhang type solar shadings. First the lighting index of windows is determined for different size of overhangs then compared to the design values of PERENE -Building design guide for Reunion Island. Second, the daylight autonomy and the luminance level are calculated for different size of overhangs. The paper concludes that the PERENE design rules are too demanding in terms of solar factor to meet and that it is impossible to have an efficient solar shading of windows and an acceptable mean luminance level. It is thus proposed to reduce the luminance level to 250 lux and to set a minimum daylight autonomy percentage.

KEYWORDS : Daylighting, solar shading, tropical climate.

1. Introduction

The design of low energy buildings in tropical climate and in warm climate first concerns generally the quality of solar shading. Solar shading is a prevailing parameter to avoid the overheating inside the building and thus decrease the cooling capacity of air conditioning. The operating time of air conditioning systems can be reduced or avoided if solar shading is combined with an adequate architectural design such as cross natural ventilation.

As the reduction of the consumption in the building sector constitutes now a priority objective to achieve, the consideration of the natural lighting in study is essential as well. Few projects take into account the design of natural lighting. The solar impact of the protections on natural lighting is not much studied. In certain cases, it is even possible to use artificial lighting because of too efficient solar protections. This makes an overconsumption while one thought that the best had already been done with the solar protections to reduce air-conditioning. A compromise must also be found between effective solar protections and a suitable natural lighting. The combination of both objectives in terms of reducing the overall building consumption is not obvious.

This paper presents a preliminary works of the simultaneous taking into account of solar shading and natural lighting in a typical room. The studied room is a cross ventilated classroom with a porosity of 20 %. The solar protection studied is a overhang-type one. After a brief thinking about the index used in mainland France such as Daylight Factor, the first values of the glazing ligting index vs the overhang size will be presented.

Then, the classroom daylight autonomy according to the overhang size will be presented for two different azimuths.

The main features and technologies used in the construction of the bioclimatic building are listed below. The building is projected to have two floors with approximately 400 m2 each, and a 300 m2 cellar. Laboratories and office rooms will be oriented to the south, whereas rooms of general use (like bathrooms, meeting rooms, conference room…) will face North. The building shape is rectangular and its main facade will be oriented to the South.

Figures 1 and 2 show some views of the building as it will definitively look.

The concrete technologies involved are the following:

• Construction according to the local climate parameters of Badajoz.

• Monitoring of energy fluxes and of wind, as well as installation of human presence detectors, in order to achieve an automatic operation to control such fluxes.

• Application of the specific concepts concerning passive solar heating. Use of Trombe walls. Ventilation of South facade by installing photovoltaic panels. Avoid direct solar radiation into the building during the summer (and vice versa during the winter).

• Efficient thermal insulation, avoiding thermal bridging.

• Window and cover shadowing.

• Natural lighting, combined with high efficiency artificial support lighting.

• Mixed solar-biomass acclimatisation. Installation of approximately 70 m2 high efficiency solar surface collectors using a biomass boiler (pellets), which will serve as energy supply to a cooling absorption engine.

• Full monitoring of the building.

• Real time data transfer to the internet.

2. Techniques

The most innovative techniques will be applied in order to ensure the bioclimatic behaviour of the building, the installation of efficient insulation and the use of renewable energy sources. The specific actions concerning each of the technical aspects are described in next subsections: