Category Archives: EuroSun2008-4

Institutional framework, aim and objectives

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

1

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

Solar Air Conditioning for Office and Server Rooms

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

1

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.

Description and Characterization of Buildings and Units Selected for the Study

1.1.

image432
image433

Selected buildings for the study

image434The 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.

Combination of daylighting and solar shading performances for buildings in tropical climates

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.

Description and technologies

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.

image509
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

Подпись: Fig.3 Position of the sun referred to the concrete location of PETER building

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:

Energy Simulation Of A Vernacular Raw Earth. Construction, In South Alentejo — A Case Study

Joao Mariz Graga1, Teresa Beirao2, Joel Vinagre2,

Pedro Macedo2, Nuno Carneiro2

1 INETI — Instituto Nacional de Engenharia, Tecnologia e Inovagao;
Estrada do Pago do Lumiar, 22, 1649-038 Lisboa

2 Universidade Lusiada de Lisboa,

Rua da Junqueira, 188 — 198, 1349-001 Lisboa

The construction of raw earth buildings is increasing in the South of Portugal. This type of construction offers a sustainable advantage. In fact, by using natural systems — which represent low embodied energy in extracting and construction process and that can also be easly reversible in the demolition process afterwords — the architecture contributes to reduce the environmental impacts of the entire life cycle assessment of the construction.

However such buildings, due to the fact of recover ancien technics, which were conceived for ancien patterns of comfort, do not always provide the same comfort levels that are actually expected. Modern life requires new levels of comfort and this affects also the energy consumption of buildings. To reduce the energy consumption of buildings Energy Building Performance Directive — 2002/91/CE, imposes rules to construction so that houses can achieve the comfort levels with less possible energy consumption. This european directive has been already transposed to the portuguese thermal codes for buildings.

With the aim of validating this type of constrution in terms of the needed requirments to comply the portuguese thermal code, an evaluation of a raw earth building, already constructed, in the portuguese South region of Alentejo, was done. Since this building was construted before the new thermal codes were published, it doesn’t conforms all of their requirments, partiularly in terms of the flat thermal bridges and energy consumptions. However, some simple construction sytems could be implemented so that the building can comply with the new codes.

Simulations with energy plus program have also been done, with the aim of compare inside comfort variable PMV of different construction solutions. A set of conclusions have been developed in terms of construction systems and natural materials that can help raw earth buildings to comply with the new thermal codes.

image403

West side of the Case Study

 

East Side of the case study

 

image404

Buffer zones

A free-running intermediate space between the interior and the exterior may reduce infiltration heat losses during winter, allow pre-heating of the supply air to the adjacent space and improve the effective U-value of the external envelope. Typical free-running spaces are entrance halls, conservatories or glazed balconies. The latter two should be located in the southern side and with advantageous window areas to allow indirect gain to adjacent spaces during winter. Shading devices prevent radiation from entering. Openings allow dissipation of heat during the hot periods.

3.3 Thermal mass

The thermal storage capacity of materials can be used to reduce the peaks of temperature in buildings. Temperature swings will also be reduced in strong inertia buildings.

During summer, thermal mass can be used to lower the upper daytime temperature, thereby reducing the need for cooling. The thermal mass is pre-cooled with night time ventilation, when outdoor temperatures are low, and allow heat dissipation the following day when indoor temperatures are high. Equally, in winter, thermal mass can absorb heat during the day for release into the space at night. This can potentially reduce heating demand. It will need a longer warming — up period, as the thermal mass has to warm up first. For this reason it is appropriate for buildings with permanent occupation and in particular with night occupancy. Offices and spaces that require a quick response to the environmental conditions may require a lower storage capacity.

Energy Balance Equations

The equations developed for each configuration are very similar. Therefore, they are presented here only for configuration C. The thermal network associated with this configuration is shown in Fig.

2.

Подпись:Подпись: Tin RadiationПодпись: Conductionimage479] Convection

The energy balance equations performed in the middle of the outer glazing layer (go), outer air cavity (ao), PV laminate outer glass layer (Lo), PV+EVA layer (Lm), PV laminate inner glass layer (Li), inner air cavity (oi) and inner glazing layer (gi) are written as follows:

4 4 dT

Подпись: (1)

image481 image482

Sgo — hcv, cmb To — Tamb ) — ™go, o (Tgo — Tsur ) — hcv, ao (Tgo — Too ) — hrd, go-Lo (Tgo — TLo ) = PgotgoCv, go

Подпись: (4)Подпись: (5)S — p, (TLo — TLm) (TLm ~ TLj) _p f C ^T^

Lm PV r r Lm Lm v, Lm dt

Rcd, Lo-Lm Rcd, Lm-Li d

(T — T ) dT

TLm — Li — hrd, Li — ATLi — Tgi) — hcv, ai(TLi — Tai) _ pjtT^—Lr

image485 image486

Rcd rm-n dt

In Equations (1) to (7), Sj represents the amount of solar radiation absorbed by layer j, ejo and j are the outdoor and indoor surface emissivity for layer j, Tamb and Tin are the ambient and indoor environment temperatures, Tj is the temperature of layer j, a is the Stefan-Boltzmann constant, Cp, ao is the specific heat at constant pressure of the air in the outer air cavity, W and H are the window width and height, Rcdj-k and hrdJ_k are the conductive thermal resistance and radiative heat transfer coefficient between layers j and k, and pj, tj and CvJ- represent the density, thickness and specific heat at constant volume of the material of layer j, respectively. hcv, in is the indoor heat transfer coefficient calculated with the relation of Curcija and Goss [6], while hcv, amb represents the outdoor heat transfer coefficient obtained with the correlation of Cole and Sturrock [7]. The outer and inner air cavities convective heat transfer coefficients, hcv, ao and hcvai,,are estimated with the relations developed by Wright [8] for non-ventilated vertical air cavities. For the naturally vented cavity, the outer and inner convective heat transfer coefficients, mass flow rate (mao) and air inlet (Taoin) and

outlet temperatures (Taoout) are determined with the correlations found in ASHRAE [9]. The surroundings temperature, Tsur, is a function of the sky temperature, Tsky, and the ground temperature, Tgnd, and is given as

Tur =F( + FgndTAgnd ) (8)

In Equation (8), Fsky and Fgnd are the view factors between the window and the sky, and the window and the ground, respectively, and correspond to 0.5 for vertical surfaces. PPV in Equation

(4) is the power produced by the PV cells at maximum power point per laminate unit area and is calculated as a function of irradiance and cells temperature with the relation found in Poissant et al. [10]. The cells were assumed to be crystalline silicon and the rated peak power of the PV assembly in the 1.44m2 laminate was set to 165W. The total irradiance striking the PV cells and the solar radiation absorbed in each layer were determined by ray-tracing technique by taking into account incidence angle effects and multiple reflections.

Calculations, tests and evaluations of the PV-window

Calculations have shown that the PV-window is thermally competitive to the nowadays low energy windows and equally fulfills the requirements within the Danish Building Regulation. Data for the developed PV-window is listed in table 1.

Table 1. Thermal data for the PV-windows illustrated in figure 1.

Dimensions (w*h)

U-value

[mm]

[W/m2K]

1230 x 1480

1.20

Furthermore the PV-window supply the building with electricity and reducers its need for primary energy. Electrical tests have shown that the PV-window is equally competitive to standard PV- panels. The only difference is the inclination of the profile and hence the electrical output.

Test at the Danish Building Research Institute has also shown, depending on the design and layout of the PV-pane, cf. figure 1, that the PV-window can supply daylight and electricity to buildings to fulfill different requirements in different areas in the building.

Students from Aarhus School of Architecture have in a workshop investigated how the developed PV-window can be used to create transparent building components which offer multiple functions apart from transparency and production of electricity. The architect found that the PV-window offers these multiple functions. Depending on the laying up, sizing and carving of the PV-cells the PV-window can offer a high production of electricity, income of daylight, solar shading and interesting reflections. The PV-pane also accentuates the changeability and dynamics within the many characters of daylight. The use of silicon wafers in building design has a cogent and technical expression and it communicate a global friendly/responsible production of electricity.

3. Conclusion

The project group is developing a low-cost PV-window with focus on optimizing the composition of the PV-pane and hence simplifying the production method. These factors can reduce the price of the PV-window with up till 20 % or more compared to similar products.

The PV-pane is built up as a 3-layer construction with gas filling and a TPS spacer profile. With a U-value of 1.2 W/m2K, the PV-window fulfills the Danish Building Regulation and is thermally competitive to the nowadays low energy windows.

As an additional choice the PV-window can be designed with screen printing, variations in the design of the PV-pane, e. g. the size of the silicon wafers and carving of patterns within the PV- cells. This will affect the price of the PV-window.

Summed up this makes the product very attractive for building owners and architects to use in building designs for both new and retrofit buildings in comparison to other renewable energy systems which often tend to deface the building from an architecturally point of view. The PV — window addresses the field of making energy right buildings, using the energy falling on the buildings to supply itself in a fully integrated an aesthetical way and not as an ad on to a building.

It helps reducing the need for primary energy, gives the building a clearly environmentally green profile and at the same time it fully fulfills the requirements within the Danish Building Regulation.

The development of this product has not been completed and will continue.

image526

Figure 5. Illustration of the developed PV-window

 

Concluding Remarks on Shading Strategy

2.3. General

The above study focuses on the analysis of fenestration shading devices and techniques which are developed previously [1], so as to reduce unwanted solar heat gains in the summer, without conflicting with beneficial ones in winter, as solar gains play opposite roles for heating and cooling in the climate of Cyprus. In the study, emphasis is given on occupancy intervention on manually operated shading devices.

For the study, characteristics of windows and shading devices are specified in terms of geometry and physical dimensions profiles, in various simulations. The intention is to describe synthetically how the quality level of the internal environment is affected in response to hypothetical occupant shutter use patterns. These accommodate possibilities of potential conflicts of the double role of solar gains and destructive interference with the effective performance of the “Zero Energy House”.

Tables 1 and 2, sum up the attempt to systematize various possible shading operations by occupants. It illustrates the correlation between solar heat gains or losses resulting from such operations, for the two seasons, and the thermal performance of the “Zero Energy House”. This is done in order to conclude optimum shading design strategies for maintaining comfort conditions in the building considering the operational aspects of shading techniques.

From the results it is evident that the occupants’ interference and misuse of the manually operated window shutters could be counter-effective and might annul the optimized fenestration design. The uncertainties associated with the shading variable and occupant behaviour can be large in occupied buildings. This occurs, where solar gains is a significant part of the design in achieving indoor comfort conditions without the need of mechanical energy, as in the case of the “Zero Energy House”.

2.4. Winter

The results explicitly indicate that the counter — effect of misused south window shutters could be of vital importance for the maintenance of internal thermal comfort level in winter.

Tables land 2 and graphs 1-4, show temperatures of ambient outdoor and indoor air. Table 1, 1.0 portrays optimised design for winter, in which all shutters are open. It illustrates that the ambient outdoor air temperature varies from 6.5 to 14.0 degrees Celsius, the swing in the inside temperature remains within the comfort zone, from 18.6 to 20.6 degrees only.

The other tables and graphs indicate a drop of indoor temperature ranging from 0.1 to 10.5 degrees Celsius, depending on the extent and orientation of window shutters left shut during the winter day. If all window shutters are left shut, the internal temperature drops below outdoor, by 0.1 to 4.0 degrees. The largest drop occurs mainly between 09.00 to 18.00 hours (table 1, 1.4). These results point out the reliance of the “Zero Energy House” on solar gains.

image368 /

T SIMULATION FOR COLD DAY

ALL FENESTRAT ON UNSHADED

D7.00-19.00

T 16

Подпись: TIME(Hours)! * Outdoor AIR T

Indoor AIR T

rig.!. Indoor and Outdoor Air temperature in >>inter. All fenestration unshaded

T S MULAT ON FOR COLD DAY

ALL FENESTRATION SHADED

D7 00-19 00

Подпись: Indoor AIR TTIME (Hours)

X I. Outdoor AIR T

rig.2. Indoor and Outdoor Air Iemperature in Winter. All fenestration shaded

Furthermore the small extent of deviation of temperature, incurring when shutters are left shut on the house elevations other than south, confirm the validity of the optimisation of fenestration distribution and orientation on the “Zero Energy House.”

2.5. Summer

Table 2, 1.4 and Fig. 4 illustrate the optimised design strategy for summer, with all shading shutters closed, when the outside temperature reaches a maximum of 35.0 degrees Celsius whilst the inside reaches only 25.5 degrees.

Examining the results of the counter-effective human intervention on the manually operated window shutter on the “all-shut” optimised shading profile for summer (Table 2, 1.4), it is noted that this poses no significant conflict on solar control. Comparing the free thermal behaviour of the building under the optimised summer strategy (Table 2, 1.4, Fig.4. “All Fenestration Shaded”), with the less than optimised (Tables 2, 1.3-1.0, Fig.3). The rise 0.4 to 1.0 degrees Celsius of internal temperature indicated for some configurations presents no serious problem. Even when all window shutters remain open during summer day the internal temperature does not deviate from the comfort zone. Over the complete period of investigation the deviation did not exceed 1.00 degree Celsius, indicating at least for the shading variable, the efficient performance of the fixed shading devices of overhangs and vertical extended walls on the southern orientations for the summer season. For both seasons, the results also emphasize the significant role of the optimisation of:

(I) Fenestration distribution and orientation

(II) Permanent shading overhangs and vertical extended walls

On the thermal performance of the “Zero Energy House”. The sun spends very little time during the summer in front of the major fenestration area which faces south; its south passage is at high altitudes, so window design optimization of shading overhangs in conjunction with extended walls, allow effective shielding from direct radiation.

3. Conclusions

The above observations show that although window shutters contribute to limiting thermal gains in the summer, by reducing indoor temperature up to 1.3 degrees Celsius (table2, 1.4 and 1.0), their negative effects of misusing them in winter defeat the optimized performance of the “Zero Energy House” to the extent of dropping indoor temperature below outdoor during winter (Table1, 1.4).

The results also indicate that the combined effect of the optimum design of fenestration orientation and permanent shading devices provide sufficient sun control without the need of the manually operated shutters and its possible counter-effects.

Even so, if design fenestration aspects such as orientation, size, distribution, and sun control devices, differ to those developed for the “Zero Energy House” the application of shutters for shading could be the only solution. For example, the fixed overhangs do not work for window facing east or west, since the sun is low in the sky in the morning and afternoon. In such cases the introduction of automatic controls is imperative in order to eliminate the negative effects of the manually operated shutters misuse presented above.

References

[1] D. k.Serghides, (1994) Zero Energy for the Cyprus House, the Architectural Association, School of Architecture, London.

[2] Centre for Experimental and Numerical Thermoflow and Department of Mechanical Engineering, University of Pretoria, (1991) “Quick-A thermal design tool and load calculation computer programme, Pretoria, Republic of South Africa.

[3] Mathews E. h., Shuttleworth A. G., and Hanna G. H., (1992) Validation of a design tool for Low Energy Architecture” Proceedings 1992 World Renewable Energy Congress. Pergamon

[4] D. k.Serghides (1988), Prototype Solar House for Cyprus, the Architectural Association, School of Architecture, London.

[5] Gunnurshaug J., Windows as Solar Collectors, SINTEF, Norwegian Institute of Technology, University of Trondheim, Norway