One-dimensional models for the two double fagade concepts described above have been developed by Charron and Athienitis [4]. Here, a simplified version of these models is employed for the case of Figure 2 in order to study the impact of major parameters such as convective heat transfer coefficient. Considering the fagade with PV as exterior layer we may represent it with the thermal network model shown in Figure 5.

PV

The mean air temperature Tma is determined from a differential analysis which finds the air temperature as a function of vertical distance x. It is assumed that the air speed is constant, that is, air it is drawn into the window by a fan in the HVAC system fresh air intake. The actual air temperature T(x) is then used to determine the Tma. This is then employed to find the correct values of Tpv and Tb which are utilized to fine tune the calculations. Considering an element dx in the vertical direction, we have:

M-c-p-dT= W•dx-h-(Tpv — T) + W-dx-h-(Tb — t) (!)

where M = flow rate = V * A (V is average velocity and A is cross-sectional area) and W is width of fagade. Note that the convective coefficient h is an average for both cavity surfaces (in reality it will generally be higher on the hotter surface).

Note that in this simple model we assume equal convective heat transfer coefficient h for both cavity surfaces. The following ordinary differential equation is obtained:

a-—T + 2T= Tb + Tpv dx P

M-c-p

a :=

with Wh

An exponential variation is obtained for the air temperature as follows:

The PV and back panel temperatures are obtained as:

where U represents conductance between the various nodes (Uo= A ho, Ur= A hr,

Ua= Ub= A h, and U3 is negligible).

The average surface temperatures predicted with this model for various values of the convective heat transfer coefficient are compared in Table 1. Note that there is significant uncertainty about the value of this coefficient and this team is currently performing CFD studies on this topic. Nevertheless, simple models such as the one presented above are instrumental in studying the fundamentals of the problem. A value of 14 W/m2K was employed for the exterior film coefficient ho (other measurements also confirm this value) and 4.0 for the radiation heat transfer coefficient hr.

As can be seen from Table 1, a value of about 8 W/m2K for h gives reasonably accurate temperature predictions for the air and for the two surfaces. Note that the accuracy of the average velocity measurement is about 5%. The value of the convective heat transfer

coefficient is relatively high because of the short height of the PV panel (about 1m) and as expected h is high near the leading edge of the boundary layer forming on the PV panel.

Conclusion

The results of an experimental study and a simple analytical model for a double skin fagade with integrated photovoltaic panels are presented and analyzed. Air enters from the bottom part of the fagade through an intake, gets heated as it flows upwards driven by buoyancy and a fan, and finally enters the HVAC system. During the winter, fresh air increases the efficiency of the photovoltaic panels as it flows around them while at the same time it is preheated. Experimental results show that combined thermal-electric efficiency of the system could easily exceed 70% with airflow on both sides of the PV panel.

A major result of the study is estimation of the impact of the convective heat transfer coefficient. For velocities of about 0.6 m/s, an average coefficient of 8 W/m2K (over a height of 1 m) was found to give good agreement with experimental measurements for air temperature rise and for the average temperature of the panels.

Acknowledgements

The financial and in-kind support of this project from NSERC, ATS, Dept of Natural Resources of Quebec, and CETC-Varennes is gratefully acknowledged.

References

1. IEA 1999, Workshop on PV/Thermal Solar Systems, Amersfoot, Netherlands, 17-18 Sep.

2. Lloret et al. (1995) The Mataro public library: a 53 KWp grid connected building with integrated PV — thermal multifunctional modules. 13th European PV Solar Energy Conference, Nice, France, pp. 490 — 493.

3. D. Infield, L. Mei, U. Eicker, "Thermal performance estimation for ventilated PV fagades”, Solar Energy, Vol. 76, pp. 93-98

4. Charron R. and Athienitis A. K., 2003, Optimization of the Performance of PV-Integrated Double-Fagades, Proc. of International Solar Energy Society World Congress, Goteborg, June.

At high hydrogen concentrations in the residual medium, the (EIHIS, EIHCIS, MADHM) effects play a positive role of a peculiar safety device against the excessive heat flow during hot time of the day.

These effects perfectly match the present-day concepts in the field of quantum chemistry [42] and classical thermodynamics [43-47]. In accordance with the classification of classical thermodynamics, a chemically active open complicated thermodynamic system has been considered in this review [45]. The set of dissipative processes being considered vividly demonstrates the non-equilibrium ability to serve as a source of ordering through fluctuations. The (EIHIS, EIHCIS, MADHM) effects are the manifestation of self-arrangement in non-equilibrium systems. The discovery of these effects [6,7] shows the non-suitability of the description formalism of similar thermodynamic systems with superinsulation in the field of instability based on the Boltzman principle. During the experiments on reduction of the hydrogen concentration in the vacuum cavity of the filled cryogenic reservoir, the consecutive oscillatory and bifurcation processes of the residual hydrogen pressure variation have been noted.

So some instabilities, secondary bifurcations of time-periodic cycles observed have been noted. These bifurcations in case of a three-molecular models can be obtained analytically.

The investigation conducted has shown that a gradual decreasing of the amplitude of superinsulation heat conduction oscillations occurs at reduction of the residual hydrogen concentration.

Monthly values of thermal and electrical measurements in the system described above and the results of a simulation for the period from September 2003 to February 2004 are presented in Table 1. From November 2003, thermal energy for space heating is obtained from a gas heater. But thermal energy for domestic hot water preparation is only partly covered with the gas heater. Diagram in Figure 5 shows monthly values of the fractions in thermal energy supply. It is obvious that the excess of thermal energy produced in solar collectors in September covers the shortage of thermal energy in October. In this case the additional heating from the gas heater is not required. Figure 6 shows the comparison between the simulation and measurements in the pilot project "Solar roof Spansko — Zagreb”.

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I 150 100 50 0

Wolfgang Streicher

Institute of Thermal Engineering, Graz University of Technology
Inffeldgasse 25/B, A-8010 Graz
Tel: +43-316-873-7306, Fax: +43-316-873-7305,

E-Mail: streicher@iwt. tugraz. at, heimrath@iwt. tugraz. at

Additional authors

Thomas Mach, Richard Heimrath, Karin Schweyer, Robert Kouba,
Institute of Thermal Engineering, Graz University of Technology, Austria
Alexander Thur, Dagmar Jahnig, Irene Bergmann,
Arbeitsgemeinschaft ERNEUERBARE ENERGIE, AEE INTEC, Austria
Jurgen Suschek-Berger, Harald Rohracher,

Interuniversitares Forschungszentrum fur Technik, Arbeit und Kultur, IFZ, Austria,
Helmut Krapmeier, Energieinstitut Vorarlberg, Austria

Introduction

The energy demand of new buildings has been decreased significantly during the last 25 years. This is due to the development of new building materials and building technology. Whereas 10 years ago common windows had a U-value of 3 W/(m2K) today’s U-values are half of this at the same price. Similar developments have been achieved for other building materials which results in a specific energy demand of only one sixth (50 kWh/mPa) of today’s buildings compared to buildings 30 years ago without additional costs. With little higher investment cost the energy demand can be decreased even further.

Low energy buildings (or passivehouses) have different demands for the heating systems than conventional buildings. This paper deals with these demands and an analysis of various heating systems with respect to end-use and primary energy demand, greenhouse relevant emissions, heat delivery costs (including capital costs) and qualitative criteria.

The passivehouse is defined by

Max. 15 kWh/mFa space heat demand (with ventilation system with air heat recovery)

Max. 42 kWh/mPa total end use energy demand including electricity for HVAC and others Max. 120 kWh/mPa total primary energy demand

The main goal was the development of a comprehensive evaluation method for heating systems for buildings insulated according to passivehouse criteria.

This project was financed in the frame of the Austrian Research Initiative „Building of the Future" of the Federal Austrian Ministry of Transportation, Innovation and Technology (BMVIT).

The test chamber (Fig. 1) was built on the roof of the Faculty of Civil Engineering, UL, Ljubljana (46.0° latitude, 300 m altitude). The test chamber has dimensions 1 m x 1 m x 1 m and is designed especially for control design purposes. The cell is shifted off the ground and the roof is ventilated in order to avoid the influence of overheating caused by direct radiation on the roof. Walls, floor and ceiling are built of lightweight brick blocks. Material properties are shown in Table 1.

Table 1 Material properties of the test chamber envelope

The south wall is completely glazed with double-glazing composed of two layers of standard clear glass and air fill, and the thickness of the wooden frame is 5 cm. The alternating geometry of the window is made with the moveable roller blind, the position of which can be automatically controlled.

With the measuring equipment the following values for outdoor and indoor conditions are measured:

• direct and reflected solar radiation with pyranomether CM-B (Kipp&Zonnen Delft BV),

• outdoor and indoor air temperature with thermocouples type T, and

• indoor illumination with luxmeter LUX cells.

The transparent area surface size of the envelope depends on the temporary roller blind position, and is expressed as the percentage of the shaded area related to the whole glazing area. The displacement sensor measures the exact roll position.

The regulation equipment enables the controlled optical response of the test chamber to the outside conditions. This equipment contains a programmable logic controller PLC, PC and operator panel. PLC sends the signals for proper functioning of the actuator — roller blind using electric engine. The illumination control algorithm was developed in the IDR BLOCK [7] environment and it is loaded on the PLC. Remote PC and control panel are used for the process supervision and they are also used for the visualization of experiments. The measured values and process variables are collected and stored in the PC, with an application in Factory Link environment developed for this purpose. For the realization of the introduced control system the following program tools were used:

• MAC Programmer is a software package for operator panel, which satisfies the demands for human-machine (PLC -Mitsubishi controller) communications.

• Melsec Meldoc Plus program for sequential control of the Mitsubishi programmable logic controller PLC.

•

A system software package IDR BLOK for designing the control algorithm, which enables the PLC to perform the direct digital control DDC operations on the test chamber.

• Fuzzy logic controllers FLC implemented by Fuzzy blocks in an IDR BLOK program.

• The developed application in the Factory Link program environment used for the visualization of the experiments, data acquisition of the measurements and for preparing temperature and illumination set point values for experiments.

In 54 houses and apartment buildings across Europe (A, CH, FIN, D, I, NL, S) as well as countries of other continents (AU, CAN, J) the building design features, energy demand and energy supply have been investigated. Different housing types have been evaluated: 19 detached, 8 semi-detached, 18 row and 9 apartment houses. Five buildings are located in a cold climatic region, 4 in a warm climatic region while the majority are located in a moderate climatic area such as middle Europe.

Building design

Massive construction, light building elements and mixed constructions (such as massive side wall, ceiling and floors and light facade construction) are found in the housing examples. The useable space per occupant averages 43 m2 net heated area (maximum 86 m2 per person and minimum 21 m2 per person). Most of the buildings are very compact, with a form factor (envelope area to enclosed volume) averaging 0.63 m-1 (between 0.4 to

1.1 m-1). A low value simplifies achieving a very low heat demand. The efficiency of the volume, the relation of the net heated volume to the gross volume, averages 71 %, though here also big ranges can be observed due to the thickness of wall and roof insulation. Values range between 51 % and 91 %. Figure 2 shows the relation between the volume efficiency and form factor. The apartment buildings have a small form factor with an average volume efficiency of about 70 %. These apartment houses are all "passive- houses”. The values for the row houses are comparable but as expected slightly higher than those of the apartment buildings. As follows, the heating demand is also greater. Buildings achieving the “passive-house”-standard all have similar values, while detached and semidetached houses show a much greater scatter. This is explained by the fact that the buildings in our selection in these categories are not all built to this standard.

♦

40 ,——- ,——— ,——— ,——— ,——— ,——— ,——— ,——— ,——— ,

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

form factor [pro m]

Figure 2 Relation between volume efficiency and form factor for the demonstration buildings, according to building type

All buildings have a high insulation standard. The average of the U-value is 0.27 W/m2K (between 0.13 to 0.73 W/m2K), but 48 % (26 houses) have an average U-value under 0.25 W/m2K and 42 % (23 buildings) have an U-value between 0.25 and 0.50 W/m2 K (related to the building envelope area). All buildings have excellent windows with an U- Value averaging about 1.1 W/m2K, in many buildings the window U-values are as low as 0.7 to 0.8 W/m2K. The transmission losses over the total building envelope is impressively small, with a mean value of about 0.62 W/tFK.

Figure 3 reviews the relationship between U-Values and the transmission losses in all the demonstration buildings. Most of the efficient row houses and part of the detached and apartment houses have very low U-Values, under 0.2 W/tFK and very low transmission losses under 0.6 W/tFK. These buildings are passive-houses.

specific

transmission losses
[W/m2K]

1.6 ————

1.4 ————

♦

0 I————- 1———- 1———— 1———- 1———— 1———— 1————- 1———— 1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

U-Value [W/m2K]

Figure 3 Relation between the middle U-value and the specific transmission losses of the total house envelope ( related to the facade area)

The gross window area averages about 24 % of the total facade (maximum 54%). The window aperture (ratio between the glass area and the wall opening) has a mean value of
about 70 %. In other terms: the frame area averages 30 % of the window. A frame area as small as possible is beneficial to the frame heat losses through the frame and maximize passive solar gains and daylighting through glass.

Following an initial experimental study (Thanachareonkit, 2003), which confirmed the larger work plane illuminances and daylight factors observed in a 1:10 scale model in comparison to the corresponding figures in the test module, the main sources of discrepancies were analysed by considering more carefully three different sets of physical parameters : 1) the indoor surfaces reflectance, 2) the scale model outdoor location and 3) the photometers features.

To avoid any bias due to an inadequate mocking-up of the test room, the physical parameters of the 1:10 scale model, comprising geometrical and photometrical features, were reproduced in a very accurate way through an iterative model construction procedure. Table 1 gives the corresponding figures for the test module and the scale model, placed under identical outdoor lighting conditions.

Surface reflectance and workplane illuminance were measured in the test module and in the scale model at the same corresponding height (resp 0.74 m and 74 mm above the floor). An illuminance profile, perpendicular to the single window side, was measured by the way of 6 BEHA photometers placed at 1 m distance each in the test module. An LMT photometer moved by hand in the scale model at the six corresponding positions was used to monitor work plane illuminance in the same way every 15 minutes. Figure 1 shows indoor and outdoor views of the test module and the scale model.

Figure 1: Study process to outline the effect of inaccuracies of the scale model reflectances (a) and location (b).

Michele Zinzi, ENEA Ente Nazionale Energia e Ambiente Giuseppe Rossi, IEN Istituto Tecnico Nazionale Galileo Ferraris Paola Iacomussi, IEN Istituto Tecnico Nazionale Galileo Ferraris Giacomo Zangiacomi, Stazione Sperimentale del Vetro

The glass industry is oriented towards the production of always new materials, sometimes to improve the performances of transparent systems, sometimes to improve their aesthetics and building envelopes. Obstructed glazings can be used for both functions, in fact reducing the amount of solar radiation transmitted by the transparent system, they can avoidoverheating and glare for users, as well as lower cooling loads for the air conditioning. At the same time, they can be used by architects for innovative fagade solutions in buildings.

Even if the light and energy performance must be evaluated according to the relevant European and international standards, some more information should be submitted to the public for a more comprehensive evaluation of the product. One important issue is the obstruction of the view through the transparent system cause by the obstructions, which can be printed on the glass or put down on a plastic layer successively laminated between two glass sheets.

In this paper a complete light and visual characterization of some of such innovative products is presented. In particular the angular hemispherical and the bi-directional transmittance are measured with two experimental facilities. The view-through index, as defined in the REVIS project, is calculated. An innovative method, whose methodology is still at a preliminary stage, to evaluate the quality of vision is then presented. Such method is based on the analysis of images collected by CCD detector and successive mathematical evaluation. If after subjective tests this correlation will be enough accurate an alternative and comparable measurement procedure might be proposed.

The commercial buildings programme is carried out by O. O. Energiesparverband. O. O. Energiesparverband is the regional energy agency of Upper Austria and was established in 1991 by the regional government. Aim of the agency is the promotion of energy efficiency, RES and innovative energy technologies. O. O. Energiesparverband is a central institution for energy information and one of Europe’s largest energy advice and information providers. Services to different target groups, from private households to SME’s and public bodies are offered.

The main services of O. O. Energiesparverband include:

• energy information and awareness raising activities

• energy advice for private households and industry: 15,000 energy advice sessions annually

• international co-operation & European projects: vice-precidency of FEDARENE, member of EUFORES, co-ordinator of the OPET-RES-e network

• management of a sustainable buildings programme which includes energy certification for buildings and the calculation of an energy index for every new single family house (> 30,000 calculations carried out)

• a great number of different training activities (for energy advisors, for installers etc.)

• organisation of conferences, workshops, seminars, competitions

• management of the OEC, the network of green energy businesses.

Conclusions

The example of O. O. Energiesparverband and Upper Austria clearly demonstrates that a lot can be done at a regional level, provided the necessary political backing is given and a comprehensive action plan including information and promotion programmes is carried out.

These experiments are evaluated by using a thermodynamic model and the comfort criteria according to DIN 1946 [5]. Based on this evaluation, differences between the summer 2002 and the very hot summer 2003 can be evaluated for every building in order to characterise the building physics and weak points in the specific building concept.

The thermodynamic model is based on the specification in EN 832 [6] and focuses on the essential building parameters according to Keller’s approach [7]. The underlying theory can be taken from Baehr’s textbook [8]. The indoor room temperature Ti oscillates periodic around its mean value T, m with the amplitude ATi. Mean temperature and amplitude can be derived from the heat loss coefficient H, the specific heat gain Gm and its amplitude AG and the time constant т or the heat storage C of the room, respectively.

T(t) = Tm +AT’sin(®-1) with ® = 2n/t0 with t0 = cycle period

with Tm = Tam + — and AT = to -[at, +— | with C/H

l, m am H 1 2-n-z I a H )

Applications

The authors [9] have shown that this simplified model corresponds to a sophisticated building simulation and have applied this method successfully to experiments (with well — known boundary conditions) and field measurements which are associated with uncertainties.

As the thermal performance of a specific building can be discerned accurately by this method, the data model can be practically used

— for data analysis of field measurements (here: passively cooled buildings).

— for quality assurance of the building simulation during the design phase since the complex interactions calculated by the building simulation can be verified with a few concise parameters.

— for measurements during the implementation phase or during the operation to determine the building parameters for advanced control strategies, i. e. predictive controllers.

with an acceptable time effort.

The Summer of 2003

In Germany, the three summer months June, July and August 2003 were significantly too warm. The daily mean temperature was 19.6 °C, 3.4 K above the reference temperature. This extreme summer weather can be predicted by the numerical climate models; summer conditions like those experienced in 2003 should occur statistically every 1,000 years [10], even if the anthropogenic global warming is taken into account. In particular regions (e. g. Freiburg), the mean ambient air temperature was 5 K higher than the reference year.

If the summer 2003 was used as design weather for passive cooling concepts, (almost) every building would need air-conditioning to meet the comfort criteria. Though the summer 2003 is not suitable for design studies, its impact on the design of mechanical and passive cooling systems is discussed intensely.