The typical active design approach when considering A/C buildings is the most compact and massive type, with minimum opening and sealed to avoid excessive convective gains. The typical passive design approach when considering houses in tropical regions is a building with many openings on the North and South walls for natural ventilation, lightweight and completely shaded to avoid solar heat gains. This houses designed for full cross ventilation was quite successful in achieving relative comfort as long as the residential densities were low. With the growth of suburban densities, the air velocity is reduced to such an extent that it no longer produces the desired relief. Furthermore, this type of construction does not seem to cope with noise problems, privacy necessities and thermal comfort for different activities.

From traditional knowledge, low mass materials such as wood construction are considered appropriate for free running operation in hot humid climates as their indoor temperature drops rapidly in the evening, when the winds usually subside. High-mass buildings cool down more slowly during the night, which causes discomfort during sleep.

The dual mode project has demonstrated that ventilated high mass buildings can have lower indoor maximum temperature than low-mass buildings. High mass buildings on a 24- hour period can have more discomfort in cumulative degree hours of discomfort but on a daytime basis only have far more advantages. And also, if at night time there is ventilation (natural or ceiling fans), the indoor night temperature in high mass buildings is very close to those in low mass buildings. The conclusion is that for free running operation, if there is assisted ventilation at night, high mass buildings can be more comfortable during most of the time than low mass ones.

For a conditioned operation, a high mass building can be more energy efficient during a 24 hour period. If insulated, a low mass building can also have high performance. During daytime as well, high mass is far more efficient. However, for nighttime use only, the accumulated heat of the high mass structure almost triples the energy requirements for high mass buildings. This could be reduced by an "economy-cycle” — (night air flush) operation of the A/C system.

In summary, compared to the base case, an optimized all free running house will improve up to 19% the levels of thermal comfort. However, it will be unsuitable for air conditioning operation. An optimized fully conditioned house will improve up to 35%, but will have high levels of thermal discomfort if a free running operation is used. All the dual mode cases (1­

5) had superior performance for both conditioned and free running operation modes. If a dual mode operation (5 use patterns) is being used, the following savings are possible, compared to the base case:

1) TOC o "1-5" h z 51% improvement in thermal comfort and 87% reduction in cooling loads

2) 17% improvement thermal comfort and 78% reduction in cooling loads

3) 38% improvement in thermal comfort and 66% reduction in cooling loads

4) 31% improvement in thermal comfort and 98% reduction in cooling loads

5) 40% improvement in thermal comfort and 89% reduction in cooling loads

The validation primarily includes the model of the building as well as some special plant components. The internationally accepted testing procedure BESTEST is applied to the building model. Fig 3 shows results from the room-temperature calculation of a freely oscil­lating room built first using both light materials and then using a solid style of construction. Results from Lacasa (bold red line) are comparable to the results from well-known soft­ware-tools like TRNSYS, DOE2 or TAS. Models for all components were validated by measurement data from test stations as well as data from real constructions.

■— BLAST = — DOE21D = —SUNCODE = —SERI-RES = — ESP = — BLAST = —DOE2.1D = —SUNCODE = —SERI-RES = —ESP =

—S3PAS = —TRNSYS = —TASE = —LACASA = — S3PAS = — TRNSYS = — TASE = —LACASA =

Lacasa has up to now been successfully used as a supportive planning tool in 9 projects for the renovation and improvement in energy use in public buildings. Two of the most complex projects included the Humbold-University of Berlin with 10 buildings and an area of 135.000 m2, plus an educational institute in Schwelm with a heated area of 135.000 m2.

Lacasa was used to determine the reduction of operational costs and to evaluate different renovation concepts.

6 Summary

Lacasa has introduced a new standard for the practical and intuition-based simulation of building systems and components. The system meets both practical planning engineering demands as well as scientific requirements. Ennox®-Systemoptimierung GmbH (www. ennox. com) has been

established as a result of this project, whose Managing Director was the Project Leader at the Solar Institute in Julich. With the establishment of the company, the know-how, conti­nuity and further development of the software in conjunction with the Solar Institute in Julich is assured.

Christiane Egger, O. O. Energiesparverband Christine Ohlinger, O. O. Energiesparverband LandstraRe 45, 4020 Linz T: +43-732-7720-14380, F: -14383 E: office@esv. or. at. I: www. esv. or. at

Based on the regional energy strategy and implemented by O. O. Energiesparverband, the regional energy agency of Upper Austria, a commercial buildings programme was launched. The new programme is based on the successful previous buildings programmes which led to a 30% energy reduction in 95% of all new one-family houses since 1993.

The commercial building programme features especially low energy and passive house commercial buildings and includes a number of support activities ranging from energy and auditing services, information and awareness raising activities and a regional third party financing programme to special supports for industry & companies and a regional R&D programme.

Introduction

The basis of all programmes is the Upper Austrian energy strategy and action plan. It started in 1994, when the first Energy Plan was passed which defined concrete goals to reduce fossil fuel consumption by increasing both energy efficiency (EE) and the use of renewable energy sources (RES) by the year 2000. A comprehensive energy action plan was developed and implemented, which led to the significant market development of RES:

• increase of RES from 25% in 1993 to more than 30% in the year 2002

• reduction of energy consumption in new single-family buildings by more than 30% since 1993

• in total, renewable energy sources provide or secure employment for 15,000 people.

In the year 2000, the Upper Austrian Government passed the "Energy 21" strategy, continuing the strategy of the successful first energy plan (1994-2000) into the 21st century. Concrete goals were defined to be reached by 2010, including for example:

• doubling biomass and solar thermal installations

• increasing energy efficiency by 1 % annually

Again the new energy strategy combines a clear political commitment and targets with the implementation of a detailed action plan. O. O. Energiesparverband is responsible for the implementation of most of the measures included in the action plan. One central activity within the energy strategy and action plan is the new commercial buildings programme.

Usually a storage tank with 250 litre covers the hot water demand of at least one day. So it is necessary to heat it up only once a day. This is the basic assumption of the control strategy: The heat source with a better relation of thermal energy gain to electric consumption is the first choice, in this case the solar collector. Fortunately, there is some knowledge on the availability of solar energy. The expectation of solar gains is high in the morning, lower in the afternoon an zero at night. So it would be good to heat up the storage with the heat-pump in the late afternoon. The hot water consumption in the evening and in the morning will cool down the lower part of the storage and allow a maximum of solar gains.

But as an other complication also the heat-pump has a relatively low power and needs several hours to heat up the storage. It is necessary to have more knowledge of the temperature profile in the storage.

The control strategy was developed in computer simulations with MATLAB Carnot [1]. In the simulations, it has been shown that three temperature sensors are sufficient for the knowledge of the temperature profile. The strategy defines a time at which the storage has to be at set point temperature (e. g. 5 p. m.). The 1.5 kW heat-pump may rise the temperature in the storage with a rate of approx. 5 K/h. A temperature ramp is calculated
and compared to the average of the 3 storage temperature sensors (see figure 2). On a day with no solar gains the average temperature will cross the ramp early and the heat — pump will start to heat the storage. With high solar gains the average temperature will always be above the ramp.

When the temperature at the top sensor drops below the set-pint the heat-pump and eventually the electric heating are switched on immediately.

In the computer simulations the control strategy has a solar fraction between 40 and 50 %, depending on the hot water demand (5 m2 flat plate collector, weather data Wuerzburg, 200 litre per day at 45 °C).

Results

The strategy was tested on the test rig under different conditions. The first tests were carried out with a prototype of the compact unit. The control program was running under MATLAB on a normal PC and the compact unit was controlled with an IO-card.

The hot water demand was varied from 100 to 300 litres per day. The control strategy works well with a hot water consumption up to 200 litres. At higher values the losses and thermal conduction in the storage may force the heat-pump to heat the storage more than once a day and the solar gains are reduced. The control strategy is not very sensitive to variations of the taping profile unless the daily consumption is not more than 200 to 220 litres.

In summer 2002 the first compact unit was installed in a passive house. The house has a surface of 180 m2 and a heating demand of 14.1 kWh/(m2y) (PHPP result [2]). A 3 m2 vacuum tube collector (type Vitosol 200) is installed. The consumption is relatively low with less than 100 litres per day. The solar fraction in 2003 was about 53 %.

Figure 3 shows the temperatures in the storage during a day with moderate solar gain.

Conclusions

The test rig results and the first data from field tests show a good behaviour of the system. For the compact unit with a small heat-pump it is a very convenient solution since heat — pump and solar collector have a better performance if they are allowed to work on the lower cold part of the storage tank.

The control strategy may be a solution for a simple solar system with a relatively small storage tank if a solar fraction of about 50 % is accepted.

The strategy may also be applied in standard systems with a bivalent storage tank (two separated heat exchangers). In this case the strategy may help to reduce the charging of the storage with the backup heating in the morning when the expectation of solar gains is still high. For a backup heat source with a higher power the knowledge of the temperature profile in the storage is less important. The two sensors which usually installed are sufficient.

[1]

The indoor thermal climate conditions are primarily depended on the internal heating load from people, equipment, artificial light and the sun. The indoor thermal climate is regulated by ventilation and night cooling of the building by using the internal mass of the library, e. g. concrete floor and books.

For reducing the internal heat load as much as possible and thus reducing the numbers of hours the fans needs to assist the natural ventilation, integrated blinds are used in the facade windows and the artificial lighting is subdued/shut off after the level of daylight.

The indoor thermal climate has been simulated with the thermal simulation program BSim2002 (BuildingSimulation 2002), which is a computer based calculation program for simulation and analysis of the indoor climate and energy consumption in buildings. By constructing a
detailed mathematical model of the structure, it is possible to simulate a large number of indoor climate and energy parameters. This is done taking into consideration the dynamic interaction between the outdoor climate and miscellaneous design of structures, installations and running situations.

4.1 The model

Based upon the construction details derived from among others the daylight simulations and the natural ventilation system the following building model was made in BSim2002 that corresponds close to the actual conditions.

The library is divided into 4 sections, children’s section (south), north section, east section and a west section that is closed and has its own mechanical ventilation system with cooling. The west section is the administrative area for the library, while the rest of the library is public.

The most important elements in this simulation are the ventilation system, the internal mass from all the books and the internal heating load from the artificial lighting system due to high demand of lighting level on the bookshelves and wishes for the artificial light by the architects.

4.2 Natural Ventilation system

The ventilation system is a natural ventilation system with fan assistance. The minimum temperature of the intake air is 18 °C and the amount of fresh air is regulated by the CO2 level during the heating season and by the indoor temperature outside the heating season. There is no cooling coil in the ventilation system. The air change is set to a maximum of 1 h-1 during the heating season and 5 h"1 outside heating season. The high rate of air change, 5 h, during the summer is kept by the assisting fans. The low rate of air change during the heating season and the fact that it is controlled by the level of CO2 decreases the energy demand for space heating and ventilation. During summertime, when needed, night cooling is initiated and with fan assistance if needed. The internal mass from all the books acts as a good buffer and has been taken into account in the simulations.

In the case of natural ventilation the flow rate is determined by the heat field, the duct geometry, the fluid dynamic head losses and the wind velocity and direction. If the effects due to the wind are neglected the mean air velocity W0 at the ventilated duct inlet section can be expressed by the following relation [8, 10]:

with <T> and <1/T> mean temperature values calculated along the wall full length and Tou=T (x=L).

In Eq. (2) by f the friction factor of the duct, by Xin and Xou the friction factors of the head losses located on the inlet and outlet sections and by g the acceleration due to gravity are indicated. In the Eq. (2) the factor a, defined as the ratio between the mean value of the velocity square and the square of the velocity mean value, has been considered for the calculation of the kinetic energy of the air flowing into the duct [10]. In the case of laminar flow and parabolic velocity profile it results that a=6/5.

For the friction factor f the relation f=96/Re [12] has been used. The friction factors Xin and Xoj are characterized by the following minimum values: Xin=0.5 (sudden air inlet from the atmosphere) and Xou=1 (sudden air outlet into the atmosphere); the presence of narrowings, obstructions, various shapings, protection grills, dirt accumulation, determines a considerable increase in these values.

In the field of glazed collectors, one of the main issues is the aesthetical problem due to the transparency of the glazing: black appearance of the absorber, visible pipes and imperfections of the absorber surface that gleam through the glass. Moreover, the transparent glass just acts as a showcase for these elements, drawing attention to the problematic parts.

The second research project, developed at the Laboratory of Solar Energy (LESO) with the collaboration of the University of Basel (Prof. Oelhafen’s group), aims at solving this problem by modifying the transparency of the glazing used in front of the absorber, without sacrificing the efficiency of the whole collector.

The current work aims at designing special filters tailored to this purpose, using thin film interference layers deposited on glass.

Fig. 6 New filter principle.

These newly developed thin film filters reflect only a small part of the sun’s spectrum in the visible range, letting most of the energy pass through, to be collected by the standard absorber placed behind. By selecting carefully the spectral position and weight of the peak reflection, one can freely choose the colour and intensity of the light reflected back by the collector’s glass (Fig 6).

As in the case of unglazed collectors, these new properties open new possibilities to the architectural integration work. Here are a few tracks that these new glazing elements will allow to investigate further:

• Curtain wall facades (Fig. 7)

The new physical characteristics of this glazing combined with the due attention to the detail’s design can bring solar collectors into curtain facades. For instance, using the transparency quality of the treated glass in the windows openings and its reflective properties to hide the collectors behind in the plain surfaces will make the design of homogeneous active solar facades possible. With made to measure elements, this approach will really become formally interesting.

• Double skin facades (Fig. 8 a and b)

Using the new glazing in double skin facades will bring the question of the transparency level to be selected. A more transparent coating might be used to let perceive the fagade as a double skin while being reflecting enough to make the absorber colour and surface imperfections acceptable. Technical problems related to the thermal collectors use in these facades will have to be addressed as part of the global study.

• Frosted glass look (Fig. 8 b & c)

Another interesting approach is to combine the coloured effect of the thin film interference filters deposited on the internal side of the glass with special treatments on the other side. One promising option is the frosted glass. The combination of the selective coating in the inner side with the frosted treatment in the outer side will create a non-specular, semi-transparent coloured material.

This will offer a real option for the fagade covering, corresponding to both energy and aesthetical trends.

Fig. 8 a) Herzog & de Meuron, Hospital Pharmacy, Basel. b) Peter Zumthor, Kunsthaus, Bregenz. c) Diener & Diener Architekten, Power Tower, Baden.

• Collector glass fixing (9)

One main point in developing new collector concepts for fagade use is the radical change from the "glazed shoebox" of standard collectors. Together with other technical details modifications, the design of the glass fixing will be an essential issue in order to offer an aesthetically attractive alternative to the frame jointing proposed by the traditional glazed solar collectors.

Conclusion

Starting from the "colour" problem, seen at first as the major obstacle to the integration of solar collectors into facades, several developments are bringing both new colours and new questions: how to use this new freedom in the facades? How to make the thermal collector an architectural element?

The answers will be coming out from the cooperation between engineers and architects, keeping in mind construction market trends, and the role renovation is playing and will play in the future.

To validate the simulation results, we built up a testing site for wall samples of the size 50 cm x 50 cm (Fig. 5). The wall sample is pressed between two copper plates, which can be heated and cooled independently.

This allows various temperature profiles as input on the surface of the wall samples. By measuring the resulting heat flux and the temperatures in several layers of the sample you can determine the thermal performance of the walls (see Fig. 5). One method is to put a constant heat flux on both sides of the sample and measure the resulting temperature in the middle of the sample. Here you can see the linear temperature increase below (and above) the melting range and how the rise of the temperature is slowed down near the melting point. In this case, the comfort temperature (below 27°C) could be hold 6 hours longer than with the reference material (dotted line).

This measurement can be used to determine the shape of the enthalpy function of the used material as a function of temperature, which is an important input for the simula­tion. This results are also useful in optimising the structure of multilayer constructions with PCMs.

The reusing building is part of the Marzotto’s University Site situated inside the town medieval surrounding walls, still to-day, the historic centre of the city of Pisa [7].

This site is one of the few industrial archeology examples existing on the territory of Pisa; ex textile workshop, belonging to the company “Marzotto”, worked for about thirty years (1939­1968) marking the city industrial development. The site has now become a didactic pole of the scientific area as a result of a long recovery intervention, started more than ten years ago by now, on the various pavilions of the factory.

The pavilion “D”, behind the medieval walls from which it is about a metre far (Fig. 1), is the only one of the five buildings composing the old textile factory which has not yet undergone
a real recovery intervention, but just partial adaptations (i. e. Student Secretariate and four lecture halls).

The pavilion “D” is expected to undergo a recovery intervention resulting in its reuse as university library; in particular, the transfer there of the Library of Mathematics, Informatics and Phisics having, at the moment, their seats inside the pavilion “B” is supposed to take place. The library current site results to be quite critical both from an accessibility point of view, i. e. the structure is situated on the first floor of the building, and direction one, i. e. the co-presence within the same building of activities with different requirements, such as departments, lecture halls, offices, library, gives rise to coordination problems and limits, in the case of the library, the potentialities of the services offered to the users. The transfer into the pavilion “D” has to be, therefore, seen as the attempt of giving to the library an autonomous seat and making it more accessible and “visible” to the users.

The current state analysis recognizes within the building three different bodies (Fig. 2): a central one, characterized by four rectangular modules having the same dimensions (the lecture halls) and two trapeziform side wings (the Secretariate). The two side wings show a simple flat roof interrupted by small skylights, while the central body is characterized by four barrel vaults interrupted on the top by interesting lanterns, elements peculiar to the industrial architecture of the beginning of the twentieth century.

The four lanterns, with a very lengthy rectangular plan, show vertical large glass windows along the whole perimeter and an opaque slightly curved roof (Fig. 3). Since they are disposed in the east-west direction, the light penetrates through the lanterns only from the glass window facing south; as a consequence, the side facing north, inside, will turn out to be always the most lighted one, while the side facing south will result to be in the shade.

The recovery project (Fig. 4) provides for the removal of the central body from the medieval walls: in particular the two central bays shrink lengthwise creating, between the building and the walls (from which they are now about 7.50 m far), an open space enjoyable by the library users. Such an open space could become, in summer months, an extension, on the outside, of the reading room, situated inside the central body — the most significant from an architectonic point of view. The reading, studying and consultation room (including also a wide zone provided with open shelves) are organized into two floors as a result of the introduction of a mezzanine floor with a steel structure, placed side by side flanked on the existing skeleton and lying behind with the eastern and western facades, so that the originary architectural module could result to be always legible and the light coming from the lantern could filter out up to the lower level. A large glass facade at full length replaces the old opaque building envelope closing the building towards the medieval walls: in such a way the "town monument” becomes a valuable scenographic side-scene of the new reading room. In the side wings the library service rooms (i. e. library historical fund, warehouse, offices, services for the users) and two conference rooms are placed.

The measurement difficulties for obtaining the values of parameters of Table I and the low weight of the decor layout in the view-though index formula has suggested a new experimental approach.

Establishing the quality of vision is not an easy work. Vision is a very complex exercise even if it seems effortless. The first step of vision considers the formation of an optical image upon the retinal mosaic receptors, then the optical image passed through several sampling process and reach the brain where perception and cognition acts start.

The vision of a scene trough glasses with geometrical obstructions is affected by the interference of geometrical pattern at both levels of the vision process. The geometrical obstructions generate well localised diffusion effects that can play a relevant role, depending on the geometrical pattern of the obstructions, in the vision process.

First of all the geometric obstructions affect the image formation in the eye, then image cognition in brain. For these reasons it is better to analyse the problem under two different aspects: the influence of the glass pattern on the contrast sensitivity (image formation) and on the scene perception.

The influences on image formation can be easily investigated considering the principles of the Fourier optics. Fourier analysis is usually applied to optical imaging systems where a very simple method to analyse their performances is to consider the spatial modulation transfer function (MTF), i. e. the frequency response of the system to spatial variation in
luminance, of the object framed. This target has usually sine wave or square wave luminance variation.

This kind of analysis was extend to the human visual system in the latter part of the XX century and actually is well established in literature [5, 6].

A sine wave or square wave luminance variation target are used to test the contrast sensitivity at different luminance contrast levels and for different spatial frequency (of luminance variation) in cycles per degree.

If a dispersive medium is interpose, i. e. a glass with geometrical obstruction, a degradation of the MTF of the eye occurs. This degradation is directly related to the modulation transfer function of the whole system, i. e. eye plus dispersive medium (glass). The dispersive medium acts like a two-dimensional filter, which attenuate amplitude and introduce phase shift in the image. Because the MTF function of the system is related to the Fourier Transform (FT) of the image, to investigate the degradation it is necessary to calculate the FT of the image

At this stage of the analysis we are only interested in the evaluation of the interferences of the dispersive medium and the FT is studied using a CCD camera. Two simple target of know luminance variation (sine wave and square wave variation) are acquired with a scientific CCD camera peltier cooled, with the glass, with geometrical pattern, interpose on the optical path. An example of CCD acquisition a test target is shown in figure 6.

A square wave variation can be easily obtained using a source framed by a rectangular diaphragm obtaining a line function. The luminance contrast of this kind of target is also easily variable. While about the sine wave variation it is know that the variation measured along the optical axis is:

1 = Im + 10 Sin(2wTA )

where Im is the mean intensity and nl is the spatial frequency of the target.

The MTF function of the glass is obtained as ratio between the MTF of the target with and without the glass. In this kind of analysis the noise of the image plays a relevant role affecting the final results. To minimise the noise the source lighting the target is a current stabilised incandescent lamp and the CCD camera used to acquired the image is peltier cooled to minimise electronic noise, with a 14 bit AD controller. These features can assure the minimum noise for the analysis.

This approach does not required complex measurement and expensive instrumentation and can give a good evaluation of the glass performance if the geometrical measurement conditions are correctly selected, considering the actual condition of vision and perception. For these reason, after the mathematical study of the influences of obstructed glass on the vision system (image formation) it is necessary to analyse the second level of vision: the image cognition.

The image cognition and perception is a very complex field of study well established in literature [7]. In the image cognition and perception analysis, the image transmitted to the brain is filtered several time and some phenomenon of image finishing, that allows the correct interpretation of the scene, arrives.

In the case of vision trough geometrical obstructions mechanisms of attentive vision are involved. Attention enables visual processing in a wide variety of ways, one that is interesting for us is that enables binding.

The visual cognition system, using the geometrical properties of binding contours and closure of the scene, is able to connect the contours using an organizing process based on the continuity perception (Gestalt school).

In the vision trough obstructed glass the attention is lasting and sustained, a top down elaboration process scene arrives.

To understand how obstructed glass affect the vision quality at this stage it is obvious that some perceptive experiments must be carried out using selected observers.

A simple test can be performed using standard visual acuity target: Landolt rings. The observer can be exposed to the target with and without the glass interposed at different adaptation levels. In this way it will be possible to check the influences on visual acuity. Otherwise to test the influences on complex scene, more complex visual task must be used. A parameter can be the time necessary to recover a specific detail in a complex scene, or perform repeated search on two similar images, seeing one trough the glass, to find the differences.

The subjective experiments should be planned considering not only the geometrical pattern of the glass obstructions but also the behaviour in which the glass panes will be installed, taking care of the effective visual tasks of users viewing through the glass. Actually some preliminary experiments to identify the main parameters are in the development phase.

Conclusions

New advance transparent systems are on the market or in a well developed research phase. Such products aim at merging the glazing functionality with more aesthetics concepts. Printed or laminated glass pane with many different decors can have several applications, but it is important the evaluation of how the quality of vision is affected. Photometric measurements stressed that the behaviour of such systems does not differ very much from conventional glazings and the amount of the transmitted energy strongly depend on the ration of obstructed area to the total one. For the three selected sample good light transmittance was measured, at off normal incidence as well. Goniophotometric measurements confirmed the visual inspection of the sample, which means mainly regular transmission of the samples, no redirecting component and very low scattering behaviour. The view through index also stressed that decors do not strongly affect the quality of vision. As tested by the pictures survey, colours and shapes are not strongly modified by the obstructions of the glass panes.

To analyse in depth the phenomenon of the quality of vision, a new approach is introduced. It is based on the analysis of image by CCD camera. The development of a complete methodology will need lot of investigations in terms of optical measurements and subjective responses of users under fixed experimental conditions. This part will be the next phase of the research on obstructed glass panes for building and daylighting applications.