After the dimensions of the skylights and the constructive solar shading were found with Relux, a building model for the whole library was made in Relux, including all skylights with fins and all inventories in the library. In figure 5, the model is seen from northeast with the Children’s section facing south.

Figure 5\mpdel of the library made in Relux fir$fessional/Vision seen from northeast with skylights including all fins working as constructive solar shading.

The model was simulated with an overcast CIE sky. The long simulation time (6 days) due to all the fins in the skylights, limited the mesh that was set to 0.5 meters. After ended simulation it is possible to have a walk through the library and get a feeling of the daylight conditions. Thereby it is possible to optimize the indoor daylight conditions and place the permanent working spaces and inventory so the daylight is used where it is needed the most and avoid glare problems.

Figure 6, shows the simulated daylight conditions in lux for the whole library on an overcast CIE sky in a plane 0.85m above the floor. The lux level is 0 — 600 lux.

From figure 6, it can be seen that the daylight level is at a sufficient level, exceeding 200 lux (daylight factor = 2), in most of the library. Especially the public section of the library has a daylight level above 200 lux. It is also interesting to note, that the daylight level is higher between the skylights than right underneath them. The bookshelves are situated right between the skylights thus taking advantage of the high level of daylight there. The higher level of daylight between the skylights can also been seen in figure 7, where the actual daylight distribution on a sunny day is shown.

Figure 8 shows the simulated daylight distribution in the library seen from the west end of the library with the children’s section on the right on an overcast CIE sky expressed from 10 cd/m2 to 50 cd/m2.

In figure 9 and 10, the actual daylight conditions on a sunny day are shown for the almost finished library.

The traces of sun on the floor and facade from the skylights and due to the constructive solar shading, gives a finishing touch on the daylight distribution. The traces of sun also moves relative fast so the traces have moved from one side of each skylight to the other during a couple of hours. Furthermore, the number of hours the sun traces are appearing each day is highest during summer and goes to zero during wintertime.

1.2 Conclusion

From detailed simulations carried out for the library, constructive solar shading in the skylights has been developed. The constructive solar shading has a depth of 200 mm and is placed every 500 mm in each side of each skylight. The constructive solar shading contributes to an optimized daylight distribution inside the library and at the same time decreases the level of solar radiation into the library thus increasing the level of thermal and visual comfort.

Furthermore, the level of daylight and daylight distribution has been optimized with simulations. After construction the level and distribution of daylight met our expectations. Glare problems has been avoided by the constructive solar shading in the skylights, a solar curtain in the children’s section and by using the daylight simulations to optimize the inventory plan.

The ventilated walls are composed of two slabs delimiting a duct into which air flows; the air flow is generally due to chimney effect and the ventilation is natural. The duct is usually 10­15 cm in thickness and the air flow is turbulent with Reynolds numbers about 10000.

The use of ASW for buildings with outdoor external insulation has recently become widespread in building practice: it is walls in which the outer slab, that is to say, the so-called "advanced screen”, instead of adhering to the insulating layer, is outdistanced from this so as to form a narrow ventilated duct. In these cases the duct is normally 4-5 cm in thickness and the air flow is laminar [9-10]. The ASW reduce thermal stresses, allow the possible condensation water to be drained and the inner slab to be covered using various materials in order to satisfy all the formal and aesthetic requirements peculiar to the site and the surrondings.

The outer slab can be realized with "traditional” materials (e. g. brick, stone, ceramics) or "innovative” materials: metals (e. g. aluminium, stainless steel, copper, titanium), plastics (e. g. high-pressure plastic laminated, thermosetting synthetic resins) and concretes (e. g. Portland mixed with tenso-stabilizers, pasted with glass fibers, fibrous concretes).

The fixing of the outer slab to the structure lying behind is very often carried out by using the techniques peculiar to the "dry-walled” stratified buildings, with various kinds of mechanical fastenings, without having resort to the traditional cement mortars ("moist-wall installation”).

Caption:

1 — Outer slab

2 — Ventilation duct

3 — Thermal insulation

4 — Cement mortar

5 — Inner brick wall

6 — Lime mortar plaster

Figure 1 — Ventilated facade of the Banca Popolare di Lodi by R. Piano (Lodi-I, 1999): outer slab made of terracotta tiles, detail near the duct air outlet.

Figure 2 — Schematization of the advanced screen wall (ASW).

The main building of the Banca Popolare di Lodi by R. Piano, in which the outer slab is made of panels composed of four terracotta tiles, grooved on the outer face and about 4.0 cm in thickness, is an example of brick ASW. The panels, preassembled by fixing the tiles to an apt counter-framework, are anchored to the building structure with a suspension system, consisting of stainless steel components. In Figure 1 a facade detail, lying near the duct air outlet is shown. Notice the original eaves element made of stratified and tempered glass.

It is a widespread tendency to use, for the outer slab, metallic materials in plates of peculiar shapes and dimensions (e. g. the Jewish Museum by D. Libeskind, Berlin-D, 1988; the Guggenheim Musem by F. O. Ghery, Bilbao-E, 1997).

In this paper two examples of ASW are going to be investigated, the first one with a brick outer slab (BW) and the second one with a copper outer slab (CW).

Thermophysical and geometrical properties of the layers composing the ASW are shown in Table 1.

The examined ASW show the same overall thermal resistance (Rtnv=1.87 m2KW-1) and then the same energy behaviour when the air duct is closed; thermal resistance distribution among the layers composing the walls is, on the contrary, very different (see Tab. 1).

Maria Cristina Munari Probst, Christian Roecker, Andreas Schuler, Jean Louis Scartezzini Laboratoire d’Energie Solaire et Physique du Batiment — LESO-PB, Swiss Federal Institute of Technology-Lausanne,.

Integration of solar thermal collectors into facades has always been problematic for architects because of the lack of freedom in the choice of panels’ details, and consequently the hardly controllable visual impact these elements have.

The irremediably black colour, the visible piping, the absorber’s imperfections gleaming through the glass in the glazed collectors, together with the dimensions and the fixing details of the existing single panels may be acceptable for roof plants, but need to be redesigned for the use of the collectors in facades.

A recent study conducted in Austria by AEE INTEC shows that the large majority of architects are not satisfied with the black colour of the absorber and would prefer a choice of different colours even if that means a reduction in the yield of the collector.

The study also shows the importance of the dimensioning of the single panel in order to make the architectural integration with the other elements of the facade possible. This also explains the consequent inclination of the planners in using the collectors in new buildings rather than in the refurbishment of old buildings where boundary conditions are imposed.

Two recent developments in surface coating are leading to possible major innovations in the integration of these collectors into building facades.

The first consists in corrosion resistant, selective coloured coatings for steel absorbers developed within the European project SOLABS.

The second presents a promising option for the glazed collectors market with newly developed thin film interference filters deposited on glass. As they are reflecting only a small part of the sun’s spectrum, in the visible range, they are letting most of the energy pass through, allowing the use of a standard black collector hidden behind.

P Schossig, H.-M. Henning, T. Haussmann
Fraunhofer-institute for Solar Energy Systems ISE
Heidenhofstr. 2, 79110 Freiburg
Tel: 0049 761 /4588 5130, Fax: 0049 761 /4588 9000
email: schossig@ise. fhg. de

Abstract

The idea to enhance the thermal comfort of lightweight buildings by integrating Phase — Change-Materials (PCM) into the building structure was targeted in several research projects over decades. Most of these attempts handled macro-capsules or direct im­mersion processes, both techniques with several drawbacks. Due to these problems, none of this PCM-products was successful a wider market. The new possibility to mi­croencapsulate PCMs, a key-technology which overcomes lots of these problems, may open the building industry for PCM-Products.

This paper describes the work at Fraunhofer ISE done in a german government founded project over the last 5 years, from building simulations to first measurements of real size rooms equipped with PCM. First products are now available on the market.

1. Introduction

Since the 1970’s several researchers have tried to use PCMs in buildings to enhance the thermal comfort of lightweight constructions, especially to overcome the overheating prob­lems in summer. They have used techniques like immersion processes ([1],[2]) or macro­capsules (e. g.[3]) to integrate the PCM. Both types have different drawbacks. Unencapsu­lated PCMs may interact with the building structure and change the other properties of the matrix materials or leakage may be a problem over the life time of many years. Macrocap­sules have the disadvantage that they have to be protected against destruction while the building is used (no drilling or nailing in the walls/ceiling). Next the macrocapsules often need much more work at the building site to be integrated into the building structure, mak­ing these systems expensive. Another problem with macrocapsules is the decreasing heat transfer during the solidification process when using PCMs with bad heat transfer coeffi­cients in the solid state like paraffins. This may lead to limitations to discharge the system over the night. Due to these limitations, none of the PCM-products had a big market im­pact.

Recent advances in the technology of microencapsulation may change this situation. The possibility of formaldehyde-free microencapsulation of paraffins allows the straightforward integration of PCMs into conventional construction materials. These only a few microm­eter big capsules can be integrated in special optimised building materials, independent from the phase of the PCM. This solves the above mentioned problems: the capsule shell prevents the interaction between the PCM and the matrix material, there is no extra work

at the building-site to integrate the PCM-products and the capsules are small enough that there is no need to protect them from destruction. The distribution of the small PCM cap­sules in the wall offers a much bigger heat exchange surface, so the heat transfer to charge and discharge the storage is enhanced significantly Fig. 1 shows a schematic drawing of this idea to integrate PCM-microcapules in plaster and fig. 2 a SEM (Scanning electron mi­croscope) picture of these capsules in gypsum plaster.

The Fraunhofer ISE researches in a cooperative project, supported by the german ministry for science and work (BMWA), the opportunities resulting out of the new key-technology of microencapsulation. The industrial partners involved are the Companies BASF, Caparol, maxit and Sto. The work at ISE started with building simulations to identify reasonable ap­plications and useful material parameters. In parallel we did material testing from DSC — measurements over 50 cm x 50 cm wall samples to real size office rooms.

The comparison of the cosine response of the two different types of photometers used in this study shows large discrepancies (cf. Figure 10). The BEHA luxmeter, employed in the test room, contributes to the underestimation of illuminances (lower response to internal reflected component at grazing angles), while the LMT luxmeter used in the scale model, has tends to overestimate illuminances (larger response to internal reflected component at grazing angle). The average relative divergence between both sensors reaches up to 20 % point difference.

a. b.

Figure 10 : Comparison of cosine response of the photometric sensors a. LMT luxmeter used in the scale model, b. BEHA luxmeter used in the test module.

According to this result, most of the remaining overestimation of daylight factors and illuminances observed in the scale model compared to the test module can be explained by the different features of the photometers use in this case (cosine-response).

CONCLUSION

This study is an attempt to identify the main sources of experimental errors occurring in the assessment of building daylighting perfoarmance by the way of scale models. Beside the impact of the mocking-up of the geometrical dimension of the test module (a 1 : 1 simple office room), indoor surfaces reflectance of the scale model, as well as the photometers cosine-response, remained the principal sources of experimental errors, leading to an overestimation of daylight factors and illuminance in scale models compared to the test module.

Large relative divergence were found when comparing the impact of slight differences in surface reflectance in the model, a 6% point difference of surface reflectance leading up to 84% divergence of daylight factors in the deeper part of the test module. Scale model location in this case appears to be non significant, the divergence remaining constant for two different locations close to the test module. The different cosine-response of the photometers used in the scale model and the test module are responsible for a 20% relative divergence between the monitored daylighting performance. Other experimental factors, such as photometers placement and levelling, can explain the remaining discrepancies, which appear difficult to reduce underneath 20 to 30% relative divergence.

Care should be brought, as a consequence, to the construction of scale models used to predict the daylighting performances of buildings, if a reasonable accuracy on daylight factors and work plane illuminance is expected to be reached. Photometers should be carefully calibrated and placed within the model. All these measures should contribute to reduce the overestimation tendency of the scale models in daylighting performance assessment.

Further studies are required however to investigate the other sources of experimental errors, still occurring today even with the new generations of sky simulator.

ACKNOWLEDGMENTS

The author would like to acknowledge the financial support of the Federal Commission for scholarship for foreign Students (FCS) of the Swiss Confederation. P. Loesch assisted in the scale model construction and A. Machacek in the model material selection.

One of the functions required to the transparent systems is to make the user able to receive a series of information from the outdoor environment. Conventional clear glazings are very good to ensure this function. Glazing systems with obstruction, which might be inhomogeneous internal or external shading devices or obstruction embedded into the materials, as the case in exam, cannot properly guarantee such function. As an example, the outdoor vision is partially affected by the obstruction texture of the samples 12 and 13, see figure 5.

Sometimes, in contrast, hiding to sight a particular room or office is needed in order to ensure privacy or to reach an aesthetic purpose. In both cases it would be useful to give a parameter (or index) that is directly linked to the visual quality of the external enviroment.

No recognised standards exist at international levels, even if some research was carried out in the recent past. Next sub paragraph analyses the quality of vision issue, on the basis of the results obtained by the European project REVIS. Next an alternative approach, based on digital image analyses by cCd, is attempted. The results obtained with the two methods will be compared when the geometrical parameters for measurement in the second method will be defined using subjective tests.

The test runs were carried out under controlled conditions to assure a detailed characterisation of the complete system including storage module and heat sources under steady state and dynamic operation conditions. The objectives were to run specific test cycles and gain operation experience of the storage. The data were analysed and evaluated regarding energy flows, storage capacity and temperature level achieved. A major objective was to find suitable operation modes, control strategies and recommendations for a redesign of the system for a broader use. The gained experience will now be used as a feedback for the development of the second generation prototype.

The development of an optimised control cycle which will be able to operate the storage in a reliable and automatic way is an important goal of the new project. For this reason, a control program was written. The pressure in the various components was used as one of the main control parameters. The following cycle operation was implemented:

• Measurement of the pressure in the condensate storage module

• Measurement of the pressure in the adsorption reactor

• The measured pressures are compared and the valves for charging or discharging of the storage are opened according to the predefined program

• A fourth step is reserved for the relaxation of the system

First tests showed that long-term heat storage using solid sorption processes with water vapour as working fluid is technically feasible.

With the previous investigations, this question can be answered. Since the room temperature responds to the heat / loss-coefficient and the time constant of the building, this discrepancy at first view is discussed on the basis of the energy balance model according to Eqs. (1) and (2). An investigation concerning the user behaviour concluded that in 2003 the windows were open more often: Fig. 4 shows exemplarily the ambient air temperature in 2002 and 2003 at the Fraunhofer ISE building. While in summer 2002 the daily mean outdoor air temperature sometimes falls below 20 °C, this occurs very seldom in 2003. Taking a typical user behaviour into account, the windows were closed more often in 2002 than in 2003 due to these low ambient air temperatures. This user behaviour have been shown in each of these buildings, cf. [12], [13] and [14].

As the windows are opened more often

in 2003, the heat loss factor H is higher in 2003. The mean indoor temperature Ti>m is calculated according to Eq. (2) from the mean ambient air temperature Ta, m and the gain-to — loss ratio y=Gm/H. In 2003, the heat gains Gm were (almost) identical to the heat gains in 2002 but more windows were open, which suggests that the heat loss factor H was larger in 2003. Thus, the excess temperature у is smaller in 2003 than in 2002.

Fig. 4: Outdoor and mean indoor air temperature during the summer period (June 1 — August 31) in the Fraunhofer ISE building in the summers of 2002 and 2003.

Why do the room temperatures exceed the comfort criteria more often 2003?

The temperature amplitude ДТ is calculated according to Eq. (2) from the temperature amplitude ДТ, the quotient of the heat gain amplitude and the heat loss factor AG/H and the time constant t=C/H. The heat gain amplitude AG was (almost) identical in 2002 and 2003. The daily temperature amplitudes are similar in both years, too: ATa,2002=3.8K, ATa,2003=3.9K, AT,2002=1.3K and ATi,2003=1.2K. The conversion of Eq. (2) to C shows that C is proportional to H and, hence, increases with H, if all other input parameters are held constant. With the monitored data from 2002 and 2003, the conclusion can be drawn that the daily heat storage capacity is (almost) identical in both years.

Thus, the more frequent occurrence of high room air temperatures corresponds with the long-term behaviour of the building: Due to the continuous thermal exposure in 2003, the long-term heat storage of the building is heated and cannot compensate for temperature changes which continue for several days.

This hypothesis is verified with Fig. 5 in connection with the simulation study according to Fig. 2. The building structure could not thermally regenerate due to long warm periods. This is the reason, why the slope in the regression line in Fig. 3 is steeper and, hence, the room temperature exceeded more often the comfort criteria, cf. Fig. 1, in 2003 than in 2002.

Conclusions

An analysis of monitored data from summer 2002 (typical summer weather) and 2003 (summer weather with long and extremely warm periods) reveals that office buildings in central European climate do not need to be air-conditioned, if they are accurately designed and rationally operated. However, none of the buildings utilised the passive cooling potential completely.

Starting from the statements si — 4, the influence of the chronology of climate situations has been discussed, and the increased failure to meet the comfort standard in 2003 can be actually explained by using smaller time constants than in 2002. The precise calculation of the heat storage capacity is essential for the accurate calculation of the thermal building performance in summer and, especially, for the design of passive cooling concepts, which make use of the heat modulation due to the building’s thermal inertia.

As these conclusions have been drawn from a simplified cross-section analysis, a parametric model, which focuses on the essential building parameters, can be used successfully for data analysis and enhances the reliability concerning the design and
operation of passive cooling systems: The very complex interactions, which influence the thermal building behaviour, can be accurately modelled with a few concise parameters.

Acknowledgement

The research has been funded by the German Ministry of Economics and Labour within the framework of the German research programme SolarBau:Monitor under the reference O335007C.

The author wishes to thank Katrin Schlegel (Zentrum fur Umweltbewusstes Bauen, Kassel) and Peter Seeberger (University of Applied Science, Department of Building Physics) for the provision of data from the long-term monitoring campaign and the good co-operation in the projects and during the short-term measurements.

The simulation model has been used to evaluate how the building performs compared to a reference building close to the regional common practice and under identical operational and environmental conditions.

The reference building considered is identical to the real building except for the following passive techniques: shading devices are removed, double glazed windows are replaced for single glazed windows, the ceiling polystyrene vault is removed, walls insulation are reduced 1cm. The reference building accomplishes the obligated normative, Spanish Standard for Thermal Conditions in Buildings, 1979. The design is close to the

26 24

22 20 18 16

72 172 272 372 472 572

Time (hours)

Figure 11: Simulated indoor air temperature for the reference ad the real building.

common construction practice on the region.

The predicted indoor air temperature for the reference and the real building is showed in Figure 11. The mean day maximum temperature is for the reference building 22.5 °C while for the real building this is 20.8 °C.

2

1,5 1

0,5 0

72 172 272 372 472 572

Time (hour)

Figure 12: Values of the difference between the indoor air temperature simulated for the real building and the indoor air temperature simulated for the reference building.

The difference mean is 1.05 °C and its standard deviation is 0.45 °C. It present a clear 24 h periodicity, differences are higher during the day and lower during nights. In addition differences are lower during the colder days than during warmer ones. It indicates that the implemented techniques have stronger influence during warm periods. This is reasonably as the implemented techniques were conceived for and arid Mediterranean climate, with extreme summer conditions and longer summer periods than the winter ones.

Conclusions

The thermal performance of an energy-efficient building in South Spain has been analysed by means of measurements and simulation, during three weeks of Spring.

Experimental results show that the indoor air temperature standard deviation is reduced from the outdoor 5.1 °C to the indoor 1.6 °C, while the mean air temperature augments 1°C the 18.8 °C outdoor air temperature. The air relative humidity standard deviation is reduced from the outdoor 21.3 % to the indoor 6.3 % The spectrum analysis of the available data shows that the system is mainly excited over the frequency range [0,1/10 h" 1] and that the building acts as a low pass filter.

The model has been created using the TRNSYS simulation code and the whether data recorded. Usual modelling hypothesis have been adopted. Differences between the measured and simulated indoor air temperature (residuals) mean is 0.37 °C and standard deviation is 0.45 °C. Residuals are not stationary and present trends which follows outside temperature trends, residuals are lower during the colder days. Besides residual spectrum analysis shows that main disagreements between measurements and simulations are observed at the frequencies in which the system is mainly excited.

The simulated thermal behaviour of the reference building in comparison to that one of the real building shows that the techniques under analysis present stronger influence during the day than during the night. The day maximum temperature mean is for the reference building 22.5 °C while for the real building this is 20.8 °C. As well they present stronger influence during warm days than during cold days, this is reasonable since the strategies were conceived for a sub arid Mediterranean climate.

This preliminary results will be used in further analysis on the building energy performance.

J. M. ROBIN1, B. FLAMENT2, C. VASILE3,

1Robin Sun SARL, BP 90216 — F.67005 Strasbourg, T/F: +49 (0) 7853.17347,

robinsun@web. de

2,3 HVAC Department, National Institute of Applied Sciences (INSA)

24, Bd de la Victoire, F — 67084 Strasbourg Cedex, flament@mail. insa-strasbourg. fr

1) Introduction.

The facades are often presented like a very significant potential market for solar thermal systems.

One of the barriers to the solar installations development is related to the difficulty of architectural integration of the collectors. In the field of photovoltaic, solutions of integration are currently available in double-glazing with inserted photovoltaic cells. The aim of the article is to present a new product, the glass collector, which is designed to be in the solar thermal field the equivalent of photovoltaic double glazing systems.

The motivations which led to the development of the glass collector were to obtain a whole component integrated in the facades. The glass collector has to:

• combine at the same time an active and passive role in the collecting of solar energy,

• easy assembly, like double glazed windows, instead of walls,

• offer free dimensions for the architects,

• use an already existing process to reduce the costs.

The glass collector is currently in the pre-industrialization phase.