The discrepancy induced by the use of different photometric sensors in the test module and the scale model was considered as main possible source of error. After an accurate calibration, LMT luxmeters showing a 10 mm diameter sensitive area and BEHA luxmeters, characterized by a 40 mm diameter sensitive area, were compared regarding their cosine response (Schiler, 1987). Illuminances, sensed by the two photometers types for varying incidence angles (0-90 degrees), were measured under a collimated light source, showing spectral features close to daylight (Scartezzini et al, 1994) were measured and compared for that purpose.

RESULTS

The preliminary results achieved within the framework of the initial experimental study, which confirmed the overestimation of daylighting performance assessment in scale models were presented in (Thanachareonkit, 2003). An extended version of this communication will be published shortly, providing a comprehensive and detailed analysis of the impact of the different sources of experimental errors. The present communication is focused on the three main causes of discrepancy between test module and scale model daylighting performance.

Normal and angular transmittance measurements were performed at ENEA-Casaccia, Roma, by means of an integrating sphere, 1000 mm in diameter [1]. The cross-section diameter of the light beam incident on the sample was selected to be 60 mm, at normal

incidence, in order to cover a complete pattern for glass panes considered as samples in this paper. Taking into account the size of the samples, an entrance port of 250 mm in diameter was chosen in order to collect most of the transmitted radiation even at the highest angle of incidence considered in the measurements. For example at 30° of incidence the elliptical irradiated area of the sample had a minimum and maximum axes of 60 and 70 mm respectively. A complete set of angular measurements was also performed to get more information on the angular decay of the analysed products. The spectral measurements were performed between 350 and 800 nm and the resolution was 10 nm.

In figure 2, the spectral curves of the three selected samples are reported, to be noted how the coloured obstruction elements of sample 6 influence the spectral distribution of the transmitted light respect to the uncoloured glazing. The normal hemispherical transmittance xv of samples 6, 12, and 13, calculated using the Illuminant A as weight, are respectively: 0.679, 0.621 and 0.764. In figure 3, the angular light transmittance of the selected samples are plotted.

The Fraunhofer Institute for Solar Energy Systems (Freiburg/Breisgau, Germany) and the company UFE Solar GmbH (Berlin, Germany) started with preliminary tests and first investigations concerning seasonal heat storage based on the adsorption process in 1995. Research work was continued with financial aid of the European Commission and the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT) in the project HYDES (High Energy Density Sorption Heat Storage for Solar Space Heating). In this project, the principle technical feasibility of the sorption storage system was proved. The experience gained during this project will be of use in the frame of the new project MODESTORE which is also funded by the European Commission and on the Austrian national level by BMVIT. The work in this project started in April 2003 and will be continued for three years.

Basic Principles of an Adsorption Heat Storage System

In sensible and latent heat storage devices heat is stored together with its
corresponding amount of entropy. In these so-called direct heat storage media, heat

— i. e. energy — is transferred directly to the storage medium. The achievable energy density is limited by the entropy storage capacity of the material. Otherwise the adsorption process is a reversible physico-chemical reaction suitable to store heat in an indirect way. This kind of thermal storage allows to separate energy and entropy flow. The storage capacity is not limited to the maximum of entropy intake. The energy density can be much higher if entropy is not stored directly in the medium. Therefore a heat source and a heat sink is involved both during the charging and discharging process to withdraw or collect the necessary entropy. The storage works like a heat transformer on the principle of a chemical heat pump. During adsorption of water vapour, a phase chance takes place between vapour and liquid phase on the surface of the in this project used silica gel. The released adsorption enthalpy consists of the evaporation enthalpy of the working fluid and the binding energy of the adsorption pair.

The working principle involves several different phases illustrated in figure 1 and described below:

1. Charging process (desorption, drying of silicagel): heat from a high temperature source is fed into the device, heats the silica gel and vapour is desorbed from the porous solid. The desorbed vapour is led to the condenser and condensed at a lower temperature level. The heat of condensation has to be withdrawn to the environment.

2. Storage period: the dry adsorbent is separated from the liquid working fluid (the connecting valve is closed). As long as these components stay separate heat storage without losses is possible if the sensible heat involved is neglected.

3.

Discharging process (adsorption, loading of silica gel with water vapour): the valve between the evaporator and the adsorber is opened. The liquid working fluid evaporates in the evaporator taking up heat at a low temperature level. The vapour is adsorbed and releases the adsorption heat at a higher temperature level. This is the useful heat.

Figure 1: The working principle of an adsorption heat storage.

There are several quantities and process parameters important when the potential energy density of a sorption pair for heat storage applications is evaluated. The main ones are:

1. Temperature lift: it depends on the current loading level of the sorbent and is a material property.

2. Adsorption enthalpy: it consists of the evaporation enthalpy of the working fluid and the binding energy of the adsorption pair. A high specific evaporation enthalpy is a must for high energy densities, therefore water is one of the primary candidates.

3. Sensible heat and process management: an intelligent system design and process management along with good insulation is essential.

4. Energy density: the energy per unit volume is the quantity of primary interest. It is the product of specific energy (energy per mass of sorbent) and the bulk density ps.

After due consideration, the process of thermo-chemical heat storage with the adsorption pair silica gel and water was selected. Silica gel is a very porous and vitreous substance. The material is made up mainly of SiO2 and is extracted from aqueous silicic acid. The equipment installed in the laboratory of AEE-INTEC in Gleisdorf/Austria is filled with commercial silica gel GRACE 127 B. This silica gel consists of spherical particles with a diameter of two to three millimetres. Its bulk density is 790 kg/m3, the interior surface is 650 m2/g. The high energy density, the quantity of primary interest, is achieved by a high evaporation enthalpy, the polarity of water and the large interior surface of silica gel. Additional components like heat exchangers reduce the energy density if the whole system is considered. The system is evacuated to enable water vapour transport without use of mechanical energy. The vapour pressure add up to 10 to 50 mbar in the system.

The analysis of the temperature performance can be combined with the energy balance of the building. Table 2 shows the essential values required to evaluate the thermal building performance in summer.

The heat gains can be taken directly from measurements (i. e. internal heat gains) or have been calculated (i. e. solar heat gains) from the building geometry, material properties and meteorological data.

The heat losses are mainly caused by ventilation. Consequently, the air change rate determines the heat loss in each building. (Notice: The Lamparter building gets additionally cool supply air from an earth-to-air heat exchanger during the working hours.)

The heat storage capacity is (almost) identical in each building for the daily period. Since the building constructions are very similar, the heat storage capacity for longer cycle periods are (almost) identical, too.

Table 1: Energy balance (working days) room temperature (only working hours) for the

summer period 2002 and 2003.

On the one hand, it was found in the previous Section that all buildings responded to changes of the ambient air temperature faster in 2003 than in 2002. Obviously, the buildings’ thermal inertia could not compensate for the high ambient air temperatures because the available heat storage capacity had been already utilised completely. On the other hand, the excess temperature is smaller in 2003 than in 2002.

Simulation is a powerful tool to evaluate and optimise the system design. Accuracy of the performance of any model depends on the algorithm used and the accuracy of the data used.

The model was created using standard TRNSYS v. 15.0 components [1]. TRNSYS is an acronym for a ‘transient simulation program’. The model output is the free floating indoor air temperature. Model input variables are: the global and diffuse horizontal radiation, the outdoor air temperature and relative humidity and wind speed. The model includes the parameters describing the building which mainly concern the components geometry, materials thermophysical properties and surfaces optical properties. Thermophysical properties of the building materials and glazing optical properties are selected from [3]. Model simulation has been carried out using the measured input variables averaged and under-sampled at 1 h time step.

The floor has been treated as a wall with boundary conditions connected to the outdoor air temperature through an added insulation layer. The resistance of this added insulation was calculated as a function of the path length of the heat transfer through the soil layer using a technique recommended by [1].

Infiltration considered as air change rate has been averaged by a simple, single-zone approach based on the Lawrence Berkeley National Laboratory model (Sherman and Grimsrud 1980), indicated in [1]. This calculations are subject to high uncertainty, [1] indicates that: "The model has exhibited average errors on the order of 40% for many measurements on groups of houses and can be off by 100% in individual cases (Persily 1986)”.

An equivalent homogeneous multilayer wall is used to represent the ceiling. The soil reflectivity is supposed to be 0.2 and standard values for the convective heat transfer coefficients are adopted. The indoor air temperature is supposed to be homogeneous. When simulating a building in transient regime initial conditions must be specified. A estimation has indicated three days to reach the steady simulated thermal behaviour. Therefore the first three days has not been considered for analysis.

The time evolution of the simulated indoor air temperature is presented in Figure 8, its means is 20.1 °C and its standard deviation is 1.2 °C.

There are many sources of uncertainty when using modelling to assess the thermal performance of a proposed building. Sources of uncertainty can be categories as [10]: abstraction (concessions made to accommodate the design to the computer representation, e. g. building geometrical simplifications), database (the element to be modelled may not mach the information contained in the database and assumptions have to be made), modelled phenomena (simplification on the physical processes modelled, e. g. thermal contact with the ground), solution methods (e. g. in resorting to numerical discretisation techniques a discretisation error is introduced to the solution).

Studies have shown that the uncertainties can be quite substantial on model results. Uncertainties will be analyze in future works.

The good project for daylight application should be made in an early phase of the project so to get a good level of integration [6]. It is important to know the characteristics of lighting that the room required, the activity that is supposed to be performed inside, the right position of the standing people and so on. Only when all these variables are well known it is possible to determine the sizes and the shapes of the transparent components, giving the quantity of natural light and their distribution in the wall [7].

At the end the whole lighting project should be checked by using of tables, plots abacus and codes [8].

The standard gives the formula to calculate the Daylight Factor:

DFm = Af x Ti x e x у / [( 1-pim) x Atot]

Af glass surface of the windows [m2]

Ti glass transparency

e window factor (ratio between the

window lighting and the sky radiance) у window factor reduction coefficient

(dependent on the protrusion of the wall respect the window) pim indoor surface average reflection

value

The transparency is the value of the optical transmittance for the PV component as it has been measured, depending on the optical transmittance of the transparent part and on the cell density.

In our case a project for the refurbishing of an health centre for mental disease to an university campus, with parts of the buildings available even to the inhabitants of the town.

In particular that building will be partially destroyed and then rebuilt, but keeping the original look by keeping the pristine outside walls, see figure 4.

In one block two PV plants will be installed in the facade acting as a sun screen by using the glass/glass technology and the spacing of the cells.

In the first case the PV modules will develop around the length of the building and should provide a good lighting on the working planes; in order to avoid the glaring and at the same

time to allow a good vision of the outside environment, the modules are designed on the purpose, as it can be possible to see in figure 5.

CONCLUSIONS

The sun light can be efficiently used fro daylighting with many advantages; a saving on the energy bill can be gained and the increasing of the comfort from optical, thermal points of views. The diffusion of the building integrated photovoltaics in form of fagade and sun screen and the new concept for projecting the PV module according its multifunction aspect making available semitransparent or translucent module created a good potential for that application. In that case some optical characterization could prove to be important and that work presented a methodology ENEA undertook in order to investigate the optical

transmittance. That value combined with the density of the cells are parameters that are

needed for the daylight factor determination to be used in the lighting project

The paper showed as an example that replacing a traditional glass fagade with Photovoltaic

resulted on the reduction of the day light factor so giving an improvement for the comfort of

the room. By using the density of the cells the glaring effect can largely reduced if not

avoided.

The investigations are based on a combination of daylighting simulations using Radiance [RAD] with methods used for the design of experiments (DOE) [Sch97]. The simulation allows for reproducible sky conditions.

The goal is to find the qualitative and quantitative influence of elementary architectural, i. e. structural, measures on the daylight quality in interior spaces.

The DOE methodology allows multi-dimensional factor variation at minimum experimental expense. The DOE plans containing all necessary experiments show two essential charac­teristics:

• All factors are varied in discrete steps, i. e. not continuously, with the number of steps being as small as possible. Thus in the simplest case, these are two steps defining the lower and upper border of the experimental space.

• All variables are linearly transformed so that the bounds of definition range from -1 to +1. This leads to DOE matrices with orthogonal columns, DOE plans of general validity (independent of the natural variable dimensions), and to the possibility of a direct quan­titative analysis of effects.

Base case is a room lit by one un-obstructed vertical window. Two more investigations show two windows each, in two facades adjacent to and facing each other, respectively. Two variations of an obstructed single window case and two roof lighting designs complete the research work. A few restrictions apply:

• In cases with one window only, its horizontal position is central. The results do there­fore not apply for strong asymmetric placements of the window. In cases with two win­dows, the symmetry restriction holds for one of them.

• All numbers are based on a CIE overcast sky with a sun elevation of 60° above the horizon.

• All daylight openings are rectangular.

• All room geometries are rectangular except for the roof geometries in the toplit cases.

• The interior optical description is limited to the uniform average diffuse reflection coeffi­cients of floor, walls and ceiling.

Three criteria have been looked at in [Sic03]: the average daylight factor D, the daylight factor in a room depth of 4 m, D4, and the daylight factor regularity, G, which is the ratio of minimum to mean daylight factor. The most useful criterion is D. It serves as a measure for the total amount of daylight inside under overcast conditions. The regression analysis re­sults for this criterion are presented here.

In order to calculate the total solar energy transmittance (g-value) [5], the secondary heat flux Is must be calculated. The thermal simulation program HEAT2 was used to estimate the heat flow into the room caused by the absorption on the back of the reflective layer and in the glass itself. It was assumed that the glass bars were positioned 1 mm from the outer glass pane. The bars themselves had a diameter of 10 mm, and the distance from the bars to the inner glass pane was 12 mm.

With the secondary heat flux Isec heat, the direct and diffuse intensities (Isec dir, Isec diff) and the incident global radiation Ig given, it is possible to compute the g-value:

Fig. 7 g-value of the system (в = 90°) for days with Idir = 0 (cloudy) and Idjr > 300 W/m2

(sunny).

The g-value was also estimated for the tilted system, with a slope of 30° (Fig. 8). One can see that the g-value for cloudy weather increases slightly while the one for sunny weather decreases. The latter comes from the fact that, especially in summer when radiation is strongest, we don’t get multiple reflections and so the absorptance on the darkened side remains small. This effect will be more pronounced for the secondary heat flow in this case.

As mentioned before (see Fig.4) a considerable part of the direct radiation is absorbed on the blackened side of the reflective layer. This will lead to a secondary heat flux into the room. In order to get a feeling for how much of the g-value is radiation that can be used for illumination and how much is heat radiation depending on the absorbed power, the amount of heat flowing into the room was computed with HEAT2. Figure 9 shows that even for the в = 0 case in summer the maximum heat flux into the room does not exceed 80 W/m2. For the tilted case (в = 30°) the secondary heat flow is even smaller (Fig.10).

40.0

30.0

20.0

10.0

0.0

0 730 1460 2190 2920 3650 4380 5110 5840 6570 7300 8030 8760

Time [h]

Fig. 10 Secondary heat flow into the room arising from the absorption on the blackened
side of the reflective layer, tilted case (в = 30°).

The percentile contribution of the secondary heat flux and the visible diffuse radiation to the g-value is plotted in Figure 10 for the vertical case. As one can see, the secondary heat flux Isec heat contributes only about 30 % to the total g-value, whereas the diffuse radiation transmittance makes up the greater part and should be sufficient to illuminate the room. For the tilted case Isec heat will contribute about 40% in winter and 15% in summer.

Conclusions

As has been shown, the system efficiently shuts out the direct radiation. This reduces glare. Even though the main part of the direct radiation is absorbed by the blackened side of the reflective layer, overheating should not be a problem, if the glass bars are positioned close to the outside glass pane, as the heat will be conducted that way.

Regardless of the system’s properties for direct radiation, the transmission for the diffuse radiation will be around 60% throughout the year, guaranteeing a high illumination level in the room.

Improvement could be made using photochromic layers, which would darken only on the focusing line). This would make a mechanical adjustment superfluous.

[1]

The improved case of the SIEEB resulted from the advanced technological solutions and control strategies such as sun shading, radiant ceilings, displacement ventilation and maximizing natural and minimizing artificial lighting. In the DOE simulations, these strategies are simulated as described below:

Sun shading: the values of direct and diffuse solar radiation are reduced to 50% during summer and 80% during winter.

Radiant ceilings: the set points for thermal comfort conditions corresponding to dry bulb temperature is increased by 1°C for summer and is decreased by 2°C for winter.

Displacement ventilation: reducing the values of fresh air volume by 20%.

Lighting: high efficient lamps and control sensors (dimming)

The above hypotheses considered for simulating the advanced technological solutions and control strategies are quite reasonable and are expected to calculate the values of energy savings reasonably well.

Figure 5 shows the monthly energy demand for cooling, heating and lighting & equipments corresponding to improved case of SIEEB preliminary design.

Figure 5. SIEEB (Improved case) — Monthly Energy Demand

The potential load reductions based on advanced technological solutions and control strategies are shown in figure 6. It has been observed that for improved case the annual energy load reductions for cooling, heating and lighting & equipments can be achieved up to 30%, 23% and 20% respectively.

2. Conclusions

A methodology for the energy efficient design of the Sino-Italy Environment & Energy Building (SIeEb) is presented. It has been shown that using various advanced technological solutions and control strategies in the SIEEB, an appreciable amount of energy savings can be achieved. Since the results, presented here, are in comparison with a reference case in which the building envelope is already optimised, therefore, compared to a baseline building, constructed as per the current practices in China, the

SIEEB is expected to contribute much higher amount of energy savings. SIEEB is an ecological and energy efficient pilot building and represents a model for a new generation of sustainable buildings. SIEEB can also be seen as an ideal case for assessing the benchmark for implementing the clean development mechanism (CDM), aimed to reduce CO2 emissions according to the accounting procedures defined within Kyoto protocols (IPCC, 2000).

References

J. Chang, Dennis Y. C. Leung, C. Z. Wu, Z. H. Yuan (2003), ‘A review on the energy production, consumption, and prospect of renewable energy in China’, Renewable and Sustainable Energy Reviews, 7, 453-468.

F. Butera, S. Ferrari, N. Aste, P. Caputo, P. Oliaro, U. Beneventano and R. S. Adhikari (2003), ‘Ecological design procedures for Sino-Italian Environment and Energy Building : Results of Ist Phase on the Shape Analysis’, Proc. PLEA-2003 Conference, Santiago, Chile, November 2003.

DOE-2 Manuals (Version 2.1) (1980), US National Technical Information Service, Department of Commerce, Springfield, Virginia, USA.

J. Chen (2003) Sustainable Buildings: the Chinese Perspective, Challenges and Opportunities, Presented at the COP-9 Conference, December 1-12, 2003, Milan, Italy.

IPCC(2000), Website www. ipcc. ch.

After the superinsulation invention by P. Petersen, quite a little time has passed — only several decades. However the concept of superinsulation operation mechanism has suffered

multiple variations. In the course of time these models have allowed to develop a modern superinsulation.

P. Petersen placed screens made of aluminium foil in a vacuum volume and separated them by means of glass-fibre mats. Instead of foil, a polymer film with thin aluminium layers being applied on its both sides is most widely used now.

A number of competing concepts exists as to the heat transfer mechanism in superinsulation. These concepts were sufficiently true in order to develop a sufficiently effective superinsulation. However, in the process of operation of big cryogenic objects, researchers have noted that our ideas on thermal processes in superinsulation are not correspond to reality.

Using the latest views on superinsulation, one can make the following definition.

Screen-vacuum heat insulation (superinsulation) is a system of parallel or concentric (coaxial) gas-permeable metal films applied on a substrate being separated from other by a porous padding manufactured from a material with a high heat resistance coefficient providing a small degree of heat radiation absorption and a small degree of accommodation of the inter-screen gas molecule energy at a high and stable adsorption ability of the metal films.

At the present time, a polyethyleneterephthalate film with the thickness of 12-15 p. m with thin layers of aluminium of 0.5 p. m thick being applied thereon on both sides are widely used as screens [10, 11]. A low heat conductivity of the film and a small thickness of the aluminium layer reduce the heat transfer along the layers and increase the superinsulation effectiveness in industrial products. For the insulating pad thin-fibre (with the fibre thickness up to one micron) glass materials with low gas release are used. As the distance between the screens is sufficiently large (the packing density normally lies within 10-50 screens/cm), the screen-vacuum insulation operates most effectively at practically the same low pressure values as the pure vacuum insulation, i. e. at the pressure values below 10-2 Pa. However the effectiveness of such insulation is far higher than the vacuum and powder-vacuum insulation. The present-day industrial superinsulation provides a heat flow at the level of 0.3-0.5 W/m2. Such heat inflow values are realised at the screen number of 45-75, i. e. at the thickness values less than 0.1 m and a small insulation layer mass [11]. The best superinsulation samples within the temperature range of 10 — 350K are characterised by the effective heat conductivity coefficient equal to (2-3)*10-5 W/(m*K), i. e. significantly less that with other heat insulation types. This parameter provides for the preferable superinsulation application for the protection against heat inflows of devices operating at cryogenic temperatures. [11].

A peculiarity of superinsulation is the non-additivity of thermal resistance in respect to the number of screens and the fact that the thermal resistance of insulation practically cease increasing when a certain number of layers has been reached [12].