Category Archives: BACKGROUND

Figure 8 : Comparison of illuminances monitored in the test module and in scale model 2 a. 2.2 m., b. 4.2 m., c. 6.2 m. from window side c. . Photometric Sensors

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.

Degree

t— BEHA luxmeter

Degree — cos

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.

Evaluation of the visual quality of the selected samples

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.

Figure 5 Landscape observed through a window equipped with S12 and S13

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.

Experimental Results of the Test Runs

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.

Why is the excess temperature in 2003 smaller than in 2002

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?

1.6 8.6 15.6 22.6 29.6 6.7 13.7 20.7 27.7 3.8 10.8 17.8 24.8 31.8

10 I…… I…… I…… I…… I…. I….. I…….. I…… I…. I….. I…….. I…… I…… I

1.6 8.6 15.6 22.6 29.6 6.7 13.7 20.7 27.7 3.8 10.8 17.8 24.8 31.8

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.


Performance of the building compared to a reference building

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.

A new solution for the architectural integration

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.

The room daylit by one window with an opposite obstruction

Based on the simple case with one window, an obstruction opposite to the window is con­sidered here, as represented in Figure 6. It is assumed that the obstruction shows horizon­tal symmetry with respect to the window centre. Then three additional factors apply: the horizontal and vertical obstruction angles a and ф, respectively, and the average obstruc­tion reflectivity p. These factors replace pW, pD and d of the original case. The floor reflec­tion is now much more important than the reflections of walls and ceiling because due to the obstruction zenith light is the main daylight source. The results are shown in Figure 7.

Figure 6: Geometry of the room daylit by one window with an obstruction opposite

The daylight quantity is reduced by appr. 30% as compared to the un-obstructed case. The vertical obstruction size and the lintel height show strong negative effects. The single factor effects show a greater uniformity.

Factor

Range of Def.

Mean

2.12%

2-10 12 3

Min.

Max.

1

1

WWR

0.20

0.60

0.25

2

T

1.50

3.00

-0.23

3

s

0.00

0.25

-0.35

4

B

1.50

3.00

0.19

5

a

30.00

60.00

-0.21

6

Ф

30.00

60.00

-0.38

7

Pv

0.40

0.60

0.11

8

Pb

0.20

0.40

0.02

9

Hf

0.60

0.75

-0.11

Teff

0.00

1.00

relative effect

Figure 7: Factors, definition bounds and resulting main effects on D for the case of the room daylit by one window with an obstruction opposite

Realized micro structured sun shading systems

Fig. 1: SEM-image of a prism array in photoresist build by interference lithography, structure size 17 gm. The arrows are representing the retroreflecting effect for high incidence angles. Light of lower incident angles is largely transmitted.

Fig. 2: replication of CPC s generated by interference lithography in PMMA. The „exit aperture“ is coated with a metallic mirror. The period is 9.3 gm. Function: light with near normal incidence is reflected while light with lower incidence angle is transmitted

In modern architecture, highly transparent facades and increasing daylight utilisation are very common. A high energy efficiency as well as thermal and visual comfort are strong requirements that can be fulfilled only with a sophisticated use of the solar irradiation. Microstructured light-guiding systems have the ability to guide or reflect the light incident under certain angles and are therefore a way to improve daylighting and solar control. Interference lithography1 offers the possibility to generate these microstructures in large scale. Another approach for solar control glazing are switchchable glazings like

gaschromic4 or thermotropic windows. It is possible to combine both concepts. The Fraunhofer ISE is focusing on two general types of microstructures for light guiding and sun shading systems2 The first concept, shown in figure 1, is a prismatic array where prisms and coplanar areas are alternating. In between two critical angles of incidence, most of the light entering the structure will be reflected due to total internal reflection at the lower face and the backside of the structure. The structure uses the effect of self shadowing of the coplanar areas for increasing incidence angles. This allows an outside view for coplanar sections and solar-control function of the prism elements. The critical angles are depending on some parameters such as the geometry of the prisms, the aspect ratio of the prism-section and the coplanar section and the index of refraction. These parameters can be chosen in a way that one can achieve a minimum of transmittance for directions that are corresponding to the incidence angles of the summer sun on a vertical south facade. There are several sets of parameters suitable for this requirements. Samples and prototype glazings have been manufactured for two different types of microsprism arrays for the use as sunshading devices in glazings.

The second concept is based on an array of one dimensional Compound Parabolic Concentrators (CPCs)3. CPCs focus radiation incident between certain aperture angles onto the lower exit of the structure. If this aperture is covered by a reflector, the element reflects all radiation incident between the aperture angles. Incident radiation at angles larger than the critical aperture angles is mostly transmitted. Because the rejection angles of CPCs are in the vicinity of the surface normal of the structured sheet, they are best suitable for tilted/tiltable applications like roof windows or venetian blinds. Figure 2 shows a replication of a CPC array of period approx. 9 pm with the tips (exit aperture) area- selectively coated with a metallic film.

DESCRIPTION OF THE SMALL SCALE TEST CELLS

Figure 1. Schematic diagram of the experimental set up of the three test cells and the air conditioning apparatus.

The experimental set up consisted in a test structure of 2m long, 1m high that holds 3 small scale test cells of 0.6m x 0.6m x 0.6m and three air conditioning apparatus to each cell are coupled. Each cell has 4 insulated surfaces (3 walls and the floor), the test window is placed in the frontal wall and on the top surface (ceiling) a test roof is placed. On the back wall there were two rounded holes of 0.1016 m of diameter to connect the air conditioning system. Figure 1 shows a schematic diagram of the experimental set up of the small scale test cells and the air conditioning apparatus.

Figure 2 shows a small scale test cell and its elements. The surface walls and floor were 0.6m x 0.6m built as pine wood-3cm polystyrene-pine wood with a traverse area of 10.8cm2 surrounded by stripes of pine wood of 0.635m of thickness. The interior of each surface wall was painted with opaque black paint and the exterior was insulated with wool glass fiber of 5.08 of thickness.

Figure 2. Schematic diagram of one of the small scale test cell.

The glazings were 6mm thicknes and consisted of clear glass, filter glass and reflective glass. Each roof of the three modules has a concrete slab of 2.54 cm of thickness. Table 1 presents the thermal properties of each component of the small scale test cells and Table 2 presents the measured optical properties of the glazings.

Table 1. Thermophysical properties of small scale test cells.

ELEMEN

T

MATERIAL

V

M3

K

W/M°

C

P

KG/M

3

M

KG

CP

KJ/KG°

C

CONCR

ETE

SLAB

mCp

J/°C

Roof

Concrete slab

0.0085

0.76

1900

16.15

0.88

14212.00

Window

Glass

0.0015

0.78

2700

4.05

0.84

3402.00

Frame

Wood

0.0018

0.12

545

0.98

1.25

1191.92

Cell

Plywood

0.0243

0.12

545

13.24

1.21

16090.24

Aislant

Glass fiber

0.0804

0.039

24

1.93

0.66

1273.54

Polystyrene

0.0312

0.027

55

1.72

1.21

2076.36

Air

0.1586

0.026

1.16

0.18

1.01

185.49

TO!

fAL

38431.55

Table 2. Optical properties of clear glass, filter glass and reflective glass for concrete

roof slab.

TYPE OF GLASS

VISIBLE LIGHT

SOLAR HEAT

P

T

a

P

T

Clear glass

0.08

0.90

0.06

0.08

0.86

Filter glass

0.08

0.45

0.48

0.05

0.47

Reflective glass

0.38

0.08

0.59

0.32

0.09

SYSTEMATISATION OF HEAT TRANSFER MECHANISM MODELS IN SUPERINSULATION SYSTEMS

Model 1. It is intrinsic to the initial period of the superinsulation investigation. The superinsulation is considered as a system of parallel layers with surfaces reflecting thermal radiation according to the Stephen-Boltzman law. In addition, the thermal shunting of the layer is absent in the model. This model implied a small degree of surface blackness. The superinsulation according to Model 1 is considered as a system of poor or "defected” reflectors [13]. The following superinsulation damage sources have been proposed: adsorption of water vapours, working liquid and volatile components of the padding material [14] as well as tunnel-radiation phenomena in the area of contact between the padding material and the reflecting surface [15].

Model 2. It describes the superinsulation as a system of screen-reflectors with a small value of the emissivity factor and heat shunted by means of conductive-conduction pads located between them [16-18]. In accordance with this model, the pad’s parameters, the fibre diameter, the total thickness of pad, the number of bonds in the padding should be of major importance. In addition, the fibre diameter and the pad’s thickness is determined by the number of contact areas in the heat flow direction and the amount of the bundle, which is normally concentrated in the contact area, is determined by the heat resistance of this contacts.

Model 3. It describes the superinsulation as a system of effective screens of radiant energy shunted by pads, which entire heat resistance is concentrated in the area of their
contact with the screens. According to this model, the pad thickness is of secondary value [19-21].

Model 4. It describes the superinsulation as a system of screens with a small degree of surface blackness shunted by the interlayer gas being in the free molecular mode (the Knudsen criterion >1). According to this model, the pad thickness is insignificant, the main importance belongs to the number of sections, into which the gas space is divided and the residual gas pressure in this space. The pad parameters are important only insofar as they influence on the residual gas pressure [22-28].

Model 5 (belonging to the author of this review). It describes the superinsulation as a system of screens with a small degree of surface blackness shunted by the interlayer gas being in the free molecular mode. According to this model, the pad thickness is insignificant, the most important are the number of sections, into which the gas space is divided, the screen material, the composition and pressure of residual gases in this space as well as the effusion magnitude and composition. The pad parameters are important only in connection with the fact that they influence on the residual gas pressure [6,7].

Model 6 (G. G. Zhun’s model). It describes the superinsulation as a peculiar pump [29].

Model 7 (belonging to the author of this review). It describes the superinsulation as a “quasicapacitor”, in which the charge generator on the superinsulation screens is the evaporating cryoliquid [30].

Model 8 (belonging to the author of this review). It describes the superinsulation as a system being unstable in warm layers and having the number of adsorption centres, which varied depending upon the ambient conditions.