Category Archives: BACKGROUND

Tropical House Design: Active, Passive or Both?

Rosangela Tenorio, University of Auckland

This paper demonstrates how the use of active or passive means only does not give the appropriate answers to a tropical design when considering housing. The author discusses about the idea of both modes of operation being used simultaneously or in parallel, and how this concept has been developed for one experimental prototype in tropical areas of Brazil (Northeast region). Extensive parametric simulations have been conducted using the prototype, and thermal comfort levels along with energy use were assessed and compared. The prototype design has also taken into account the appropriate use of resources through sustainable design features. The results have demonstrated that for regions such as the warm-humid tropics, the use of a mixed running strategy have optimized energy performance and provided better levels of thermal comfort in a much more effective way. It has also demonstrated the integration of energy efficiency and a PV grid connected system, while enabling those daytime electrical needs to be accomplished by the photovoltaic component.

Lacasa’s programming structure

Lacasa can be compared to a library of building blocks of buildings and technical installa­tions, ordered in "Classes" and "Subclasses", and one which allows further development and additions. Each Block models a real building block, such as walls, windows, heating units, pipes or controls. When you click on a block, a dialog window pops up, allowing the user, for example, to select the geometry of a wall or look at its construction (see Figure 1). The input parameters can be either given as numbers, or alternatively as freely defin­able variables. The latter feature is particularly interesting when using the models for an optimization procedure.

In order to account for the needs of design engineers as well as scientists, Lacasa offers the possibility to select among different applications ("ENGINEERING", "SCIENTIFIC", and various forms of data administration), just by using the mouse. For further details, an

online help can be activated from the input mask of each block, and printed out if needed (PDF file). The building-blocks structure of Lacasa propagates through all levels of the li­brary. Its intuitive and uniform operation control makes getting started easy, and vastly fa­cilitates implementing new models.

Lacasa was developed under Windows2000 using MATLAB-Simulink Version 13, but will work under Linux as well. This requires the existence of a license for MATLAB-Simulink for Linux, and recompiling all C-sources with the appropriate Linux compiler. All other files are in principle Linux-compatible. At the present stage of development, Lacasa consists of 740 files which require 40 MB of disk space. It is worthwhile pointing out that 82% of these files are aimed at user-friendliness, as for example the easy data management and the graphi­cal user interface. The computation models needed for simulations and the online-help claim only 8.2% and 8.8%, respectively, of Lacasa’s total amount of data.

Figure 1: Structure of the Lacasa library: Class-Subclass-Block input interface.

4 Database

All the data concerning the characteristics of the components and materials used in the application "ENGINEERING" are saved as text data files. The data management is such, though, that the user does not need to access the text files directly. Lacasa possesses a pre-processor for weather information, which can read any file, structured in columns,

containing raw weather data, automatically filling in the missing weather elements and generating a data set with 21 weather elements, formatted according to the requirements of Lacasa.

Building Technology and Motivation

The buildings of the Umwelt-Campus are supplied completely with renewable energies, with a various amount of converters combined with equipments for rational energy usage like photovoltaic systems, solar collectors, heat pumps, air conditioning, solar architecture, earth-heat-exchanger etc. and a biomass energy conversion plant nearby for heat and electricity. All these technical active and passive converter are integrated in the building automation. The whole system has still to be analysed and optimised. For this reason, it is advantageous to integrate these necessary work on this system in the study courses to teach students, with the possibility of students own real experiences. In a first step, project and diploma works are started, to give an overview of the single system technologies and the technical data together with the underlying physical theories. An important support for this purpose is the deeper inside and knowledge of the technical engineer Mr. Andreas Doll, who is responsible for the whole building system. His experiences and reports given to the students are very valuable. The next step would be optimisations and integration of new technologies for research and development.

One of the first works for diploma thesis is that of Jorn Herz, who analysed the earth-heat — exchanger, which is combined to a heat pump and massive absorber. The earth can be used as a solar heat storage, which can in winter as well as in summer be used for an air­preconditioning. The heat exchanger system consist of horizontal pipes under the earth surface, which guides the air from outside in the building, with a cooling effect in summer and heating in winter. The earth is therefore used as a seasonal heat storage.

Additionally, there is a heat recovery system implemented, which restores a part of the heat of the air leaving the building back to the earth. A massive absorber at the air outlet works as heat storage for a heat pump.

Aim of the diploma thesis of Mr. Herz was first to describe the installed earth heat exchange system at the Campus and the corresponding physical foundations. And second he made measurements and model calculations, to get information about the quality of this installation.

VARIATIONAL DESCRIPTION OF HEAT AND MASS EXCHANGE FOR A HETEROGENEOUS SYSTEM WITH THE ACCOUNT OF ELECTRO-SORPTION PROCESSES IN THE CONTINUUM APPROXIMATION

The variational description of heat and mass exchange processes for a heterogeneous system with the account of electro-sorption processes in the continuum approximation has been carried out with the attraction of the basics of analytical thermodynamics. Analytical thermodynamics is a new trend in the development of classical phenomenological thermodynamics. Having the investigation subject and method being common with the classical thermodynamics, analytical thermodynamics differs from it at least by two peculiarities.

In the first place, it is based on the variational principle, which consequences are basic macrosystem laws — the first and the second laws of thermodynamics, and therefore has a broader scientific basis as compared with the classical thermodynamics. In the second place, the analytical thermodynamics differs from the classical thermodynamics by the analysis method, i. e. the vector analysis. The use of vector analysis reduces a body of mathematics of the classical thermodynamics to the generally accepted one for other macrophysical theories.

The outstanding works by Onsager have laid down the beginning of the deductive theory of irreversible processes and the establishment of variational principles of non­equilibrium thermodynamics [96]. The variational formalism provides a possibility of construction of the whole phenomenological theory of thermodynamics based on the variational principle. The heat and mass exchange problems in the system in question are characterised by an unsteady nature, a considerable non-linearity, the interconnection of heat and mass transfer processes, multi-dimensionality, non-homogeneity and electrochemical activity of heat-insulating system.

To main advantages of the variational description of irreversible processes, one normally relate the following [97-104]:

— a high degree of generality of the physical content of variational principles, as they express fundamental physical laws, and differential equations of irreversible processes in macrosystems and boundary conditions of their implementation can be obtained from variational principles,

— the use of direct methods, by means of which accurate, approximate analytical and numerical solutions in the problems formulated in the variational form can be obtained,

— an opportunity to obtain rough approximation to the accurate solution of the problem, which is especially important in engineering calculations, at that most various information on the process can be used for the selection of a trial solution, including empirical data or accurate solutions of simpler problems of this class;

— the use of extreme values of variational principles functionals for obtaining of integral estimates of the approximate solution accuracy;

— a property of functionals to express important characteristics of irreversible processes such as energy dissipation or entropy production, heat taking part in the process.

The variational principle developed by my teacher V. V. Chikovani [44,45] has been called basic variational principle of the classical phenomenological thermodynamics. Such name of the variational principle is connected with the fact that the basic laws (principles) of classical thermodynamics follow from it — the first and the second laws of thermodynamics.

The main differences of the V. V. Chikovani’s variational principles from the well-known principles of thermodynamics of irreversible processes [100, 105, 106, 108, 109] as well as from the conditions of steadiness of functionals having a formal mathematical nature [101, 110-120] is that they, though being an expression of the basic variational principles of the classical phenomenological thermodynamics, have a simple and clear physical meaning expressed in terms of fundamental macrosystem properties. These principles have an integral form both by spatial variables and by time, which provides the use of not only the Kantorovich’s method but also the most effective direct method of variational calculus, i. e. the Ritz method.

As it is well-known, at the description of heat and mass exchange processes in continua, an assumption on the local equilibrium is used, in accordance with which any differential volume of the continuum is an internal equilibrium thermodynamic system [45].

Each differential continuum volume can be considered as a multi-phase system characterised not only by thermodynamic parameters of state being equilibrium over the whole differential volume but also by parameters determining irreversible processes of interphase interaction inside the differential volume being non-equilibrium within the limits of the differential volume (but being equilibrium within the limits of each phase being a part of the differential volume.

A peculiarity of the proposed superinsulation model as a continuum is the concept of any differential volume in the form of a two-phase system (V. V. Chikovani,

N. V. Dolgorukov,1991). The mass exchange occurs between the gaseous and solid phases due to sorption processes. The temperature within the limits of the differential volume is considered identical for both phases. We will describe the sorption system "adsorbent — adsorbate (solid phase)” by parameters characterising it on the whole, i. e. without account of the real structure of the adsorption phase. Such approach allows to use the gas release characteristics of the superinsulation materials being determined experimentally and obtain a mathematical model being suitable for the description of heat and mass exchange processes, both at the availability of gas adsorption in the surface layer and in the material micropores (V. V. Chikovani, N. V. Dolgorukov, 1991).

In order to obtain the variational formulation of the mathematical model of molecular heat and mass exchange processes in the superinsulation, one can use the basic principle of the classical phenomenological thermodynamics [44,45]:

bQ = 8j Pdr =8j ^Pn(xj, х2,Хз,…,xN)dxn = 0, (1)

1-2 1-2 n=l

‘where P is a vector in the N-dimensional space of macrophysical parameters of state Xn(n=1,…, N) of a thermodynamic system characterising its interaction with the environment; dr is the radius-vector differential in the same space.

The variational description of the heat and mass exchange processes for a heterogeneous system with the account of electro-sorption processes will be given in detail in the second part of the review.

Indoor Daylight Conditions

The new library is constructed with high facade windows and through-going skylights which assures a high level of daylight and a good daylight distribution in the library. The aim was to obtain the high level of daylight and good daylight distribution without glare problems and at the same time reducing the internal heat load from the sun.

For this purpose the light planning software Relux Professional/Vision was used. The calculation is based on a version of Radiance that has been revised by Relux.

1.1 Skylights

For reducing the internal heat load from the sun and overcome possible glare problems the skylights have been developed with integrated constructive solar shading, as seen in figure 3.

Figure 3. Skylight with constructive solar shading (brown) as modeled in Relux. Seen from the gable of the skylight.

The depth of the constructive solar shading (fins) is 200 mm at intervals of 500 mm has been considered carefully with Relux. The advantages of the constructive solar shading are:

— Part of the skylight construction

— Permanent solar shading

— Permanent glare shading

— No mechanical parts

— No repairs and maintenance

— Contributes to an optimized daylight distribution in the library

— Gives a special ray of solar radiation into the library, see figure 10

In figure 4, a picture of the skylight as constructed on site is shown

Figure 4. Skylight with constructive solar shading (grey) as constructed, seen from the floor and up into the skylight.

Energy performance of advanced screen walls with microventilated air duct

M. Ciampi, F. Leccese and G. Tuoni

Department of Energetica “Lorenzo Poggi” — University of Pisa

Faculty of Engineering — Via Diotisalvi, 2 — 56126 Pisa (Italy)

e-mail: m. ciampi@ing. unipi. it; f. leccese@ing. unipi. it; g. tuoni@ing. unpi. it

The energy performance of peculiar ventilated structures, such as walls with advanced screen, is investigated. In these structures the duct thickness is small and the air flow inside is laminar.

The obtained results show that an energy saving, even exceeding the 20%, can be achieved by using these structures in summer, compared to the same non — ventilated structure; in winter, the increase in heat losses, due to ventilation, can result to be remarkable and such as to make advisable closing the air duct or reducing the ventilation.

Introduction

The European Directive 2002/91/CE on the energy performance of buildings [1] devotes its attention to the necessity of more carefulness in the building design, with particular respect to its envelope, in order to reduce the energy consumption as well as the impact on the outdoor environment. The Directive also focuses its attention on the fact that the air­conditioning plants have become, in the last few years, widespread systems; this causes a remarkable electricity demand growth in summer, e. g. during the last August, in Italy, several black-outs occurred due to an excessive demand from the users. For this reason the Directive suggests adopting priority strategies which could enhance the thermal performance of buildings especially in summer. For instance, passive cooling techniques could be developed in order to improve the indoor climatic conditions as well as the microclimate around buildings. The Member States of the European Union have to bring into force the laws, regulations and administrative provisions necessary to comply with the Directive at latest on 4th January 2006.

The ventilated walls (VW) are fully included in the passive cooling techniques, explicitly provided for by the Directive. In the last few years they have been widely investigated by several authors [2-10]. In [4, 8, 10] the same authors have proposed a calculation method, suitable for design applications, in order to evaluate the reduction in summer thermal loads achievable by using VW. They have also studied, in [5], the influence of the variation of several thermal and fluid dynamic parameters on the energy performance of a VW.

In this paper, referring to several remarks synthetically reported by the same Authors in [9], the energy performance achievable, with particular reference to the summer case, by using VW characterized by small thicknesses of the air duct and by laminar flow, is investigated. These building components are generally indicated, in technical literature, as walls with advanced screen (ASW) which are frequently used in contemporary architecture. The obtained results show that an energy saving, even exceeding the 20 %, can be reached by using these structures in summer, compared to the same non — ventilated structure.

Experiments

Fig. 5. April, roller blind is fully open, luminous efficacy and inside illumination.

In order to create a well-designed illumination fuzzy controller, the first set of preliminary experiments was done. The observed variables were inside luminous efficacy and inside illumination resulting from weather conditions during the year. To find out the optical response of the test chamber the experiments were made with fully open roller blind. The figures show the inside illumination and luminous efficacy as response to the global and reflected solar radiation. The first example in Fig. 5 is measurement in April.

Inside luminous efficacy is of about 20 lm/W or less by global solar radiation with maximum by 650 W/m2. Inside illumination is extremely high (up to 12000 lx) when the sky is clear. This is because of the south orientation of the window in the small test chamber with white inside painting. Thus, it is obvious that shading is necessary during the highest solar radiation period. The experiment in Fig. 6 shows the solar radiation in September with optical response of the test chamber.

Luminous efficacy in Fig. 6 is in the range of 2-14 lm/W. On the first day of experiment it is high, up to 14 lm/W, despite of the cloudy sky conditions (solar radiation is of about 100 W/m2). By clear sky conditions solar radiation is more than 700 W/m2, and luminous efficacy is less than 13 lm/W.

Fig. 6. September, roller blind is fully open, luminous efficacy and inside illumination.

Fig. 7. December, roller blind is efficacy and inside illumination

Fig. 7 shows the luminous efficacy in wintertime conditions, when the sky is mostly overcast and the sun has the lowest elevation.

fully open, luminous

Using shading devices in dim wintertime is mostly senseless, while capturing solar radiation in the living space is desired because of energy gain for providing both inside thermal and optical effect. Inside luminous efficacy during the dim winter days is between 20 lm/W and 5 lm/W when solar radiation is between 100 and 350

W/m2. The resulting inside illumination is satisfactory — more than 400 lx. It is interesting to note that in the evenings and in the mornings the luminous efficacy is two times higher than it is at midday. High luminous efficacy on overcast days with low solar radiation derives from high grade of the diffuse component of the daylight.

The observed optical response of the test cell during the year was the basis for the design of the fuzzy controller. Fuzzy controller was progressively optimised. In Fig. 8 the examples for well-designed “winter” and “summer” fuzzy controller are shown. In wintertime regime the direct solar radiation is desired, and this fact was considered in “winter” fuzzy designing. In the summertime regime shading is necessary. Therefore, during the summer period the “summer” fuzzy controller selected higher percentage of shading on window than “winter” fuzzy controller during the winter period for equal amount of solar radiation.

blind movement was relatively moderate and continuous.

Fig. 9 shows the oscillatory movement of the roller blind on the second experiment day as response to changeable solar radiation. Luminous efficacy follows the roller blind movement during the day, it is about 10 lm/W, but in the mornings and evenings it increases extremely.

During the day the inside luminous efficacy is low, less than 8 lm/W (Fig. 10). It is because the window was shaded as response to high global solar radiation with the maximum of 900 W/m2. With the

Fig. 10. Summertime regime: controlled inside daylight illumination, roller blind positioning, luminous efficacy, glohal and reflected solar radiation. August 2004.

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Fig. 8. Examples of 3D surface as non-linear mapping between inputs and output as fuzzy controllers for wintertime and summertime illumination regulation.

The experiments with fuzzy controllers from Fig. 8 are shown in Fig. 9 and 10. The presented fuzzy controllers are well modified, which is evident from

experiments. The system was influenced by the changes of global solar radiation. In both cases, when the available solar radiation is more than 100 W/m2, the deviations of the inside illumination from the set point values are minimal, less than 50 lx. The roller

500

—SPIllum/10

—RollPosition “SolarRadtRT 1

—SolarReflRT2 ”InsideIllumn/10

ill*10/solar(rad+refl)

ILLUMINATION

FEBRUAR

K=ill*10/solar(refl+radt)

300

illumination/10

reflected solar radiation

SP

roll position

Fig. 9 Wintertime regime: controlled inside daylight illumination with roller blind positioning, luminous efficacy, glohal and reflected solar radiation. February 2004.

automatic roller blind movement the desired inside illumination level is maintained.

Fig. 11 shows the inside temperature profile when the inside illumination is controlled during the conditions represented in Fig. 10. It is evident that the inside temperatures are in the tolerable range despite the high solar radiation. Without shading the inside temperature will be at least 20 K higher than the outside air temperature. Therefore,
maintaining the inside illumination on suitable level with proper shading excludes the excessive inside temperatures.

6

Fig. 11. Summertime regime: temperatures when the illumination is controlled. August 2004.

Conclusions

The available luminous flux and illuminance in the building are closely related to the available solar radiation. We used the quantitative influence of the available solar radiation for the fuzzy design and the optimization of the

fuzzy control system, which enables optimal dynamic response of the roller blind according to the desired inside illumination and the outside conditions. To design the fuzzy system some preliminary experiments were done, where the observed variables were luminous efficacy and the inside illumination. Luminous efficacy is defined as the ratio of the luminous flux to radiant flux and tells the relationship between the optical and the thermal effect of the available solar energy. Maintaining the desired inside illumination level in the range of 500 — 1500 lx means the inside luminous efficacy between 5 lm/W (summer shaded window) and 14 lm/W (winter unshaded window). The system for the automatically adjustable window geometry is executed in the test chamber with the fuzzy control system, which makes decisions similar to human thinking process. The design of the fuzzy controller is based on setting up a set of linguistic control rules derived from the experimental optical knowledge. The controller was adjusted through experimentation. The two well-modified illumination fuzzy controllers, one for wintertime regime (direct solar radiation inside is the desired priority) and one for summertime regime (the direct solar radiation must be excluded as much as possible), are presented in the paper. The controlling performance is satisfactory and assures the inside daylight illumination with moderate continuous movement of the roller blind in the area, where the desired value oscillates up to ± 50 lx. Such illumination the fuzzy control system enables the optimal use of the available solar energy for improving the optical and thermal inside comfort, and can be applied in any building. The particularity of fuzzy control system is that it must be designed and optimized according to the site and its weather conditions in relation to the desired internal conditions, i. e. experimental designing.

Conclusions

One of the results of analyzing monitored projects in the framework of IEA SHC Task 28 "Sustainable Solar Housing” offer valuable lessons how to design housing with extremely low non-renewable energy consumption. Compact, tight and highly insulated buildings with an average envelope U-Value lower than 0.5 W/m2K facade area and a high efficient intelligent home systems are the key. At such levels, a very efficient ventilation system is also a must. Active and passive solar strategies can still contribute a valuable fraction of the remaining energy demand. All together, their are numerous combinations of strategies to achieve the same result. High performance has been demonstrated in very diverse climatic regions in Europe with much success.

The subsequent reduction in primary energy leads to both drastic reductions in the environmental impact of a house and impressive savings in the household budget of the occupants.

Many thanks all colleagues for their support, in contributing monitoring and analytical data. Also thanks to the Projekttrager PTJ Julich for the support and the German Ministry of Economics for the financial funding of the project monitoring as well as the Swiss Federal Office of Energy for funding the Operating Agent of this IEA Task.

Literature

S. R,. Hastings, Sustainable Solar Housing, Solar 2000, Gleisdorf, A

K. Voss, A. BUhring, M. Ufheil, Solarenergienutzung und Energieeinsparung im

Geschosswohnungsbau — Erfahrungen und Ergebnisse aus realisierten und geplanten Projekten, Soarthermischwes Symposium, Staffelstein 2002

C. Russ, S. R. Hastings, K. Voss, Zukunft fur Zuhause, Sonnenenergie 2, 2004, S.31 — 35

IEA Task 28 „Sustainable Solar Housing“, Internal working dokuments for building characterisation and monitoring of the demonstration projects Gemis 4. 1 Globales Emissions Model Integrierter Systeme, Februar 20O2


Scale Model Location

a. b. c.

Figure 6: Comparison of illuminancse 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, л к,*™* . . ..

14:C0 14:15 14:30 141:45 150 1515 1530 1545 1600 14:00 141:15 141:30 14:45 150 1515 1530 1545 1600 14:00 14:15 14:30 14:45 150 1515 1520 1545 Ш)

Tine Tine line

Workplane illuminances monitored within a scale model placed in two different considered locations (cf. Figure 1.b) overestimate daylighting performances of the test module. Figures 7 and 9 illustrate the observed discrepancies, which remain constant and close to 35 — 40% in relative terms for all profile positions. It shows that moving the model from one location to the other has no impact on the remaining divergence (0 — 1% percent-point reduction) : this indicates that the different sky view factors and external reflected component are apparently not responsible for the remaining discrepancy (cf. Table 3).

a. b. c.

Figure 7: Comparison of relative divergence between 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.

14:00 14:15 141:20 14:45 1500 1515 1530 1545 15C0

141:00 14:15 14130 14:45 1500 1515 1530 1545 1500

14:C0 141:15 141:30 1445 1500 1515 1520 1545 1600

a.

b.

c.

Figure 9 : Comparison of relative divergence between illuminances monitored in the test module and in scale model 2. a. 2.2 m., b. 4.2 m., . 6.2 m. from window side

Sky

condition

Maximal Discrepancies (%) First location

Maximal Discrepancies (%) Second location

Percent-point Reduction (%) between both locations

2.2m. from

window

4.2m. from

window

6.2m. from

window

2.2m. from

window

4.2m. from

window

6.2m. from window

2.2m. from

window

4.2m. from

window

6.2m. from window

Clear sky

35

36

37

34

36

37

1

0

0

Table 3 : Comparison of relative divergence for the two different scale model locations

(impact of sky view factor and external reflected component)

Exprimental part 2. Goniophotometric measurements

The parameters that quantify the redirecting or diffusing properties of a daylighting glazing system can be measured using a goniophotometer with a light beam perpendicularly incident on the sample. The luminance coefficient q, defined as the ratio between the luminance L of the sample surface and the incident illuminance on the sample as a function of the observation angle є, with 0° < e< 90°, is the main parameter. The observation angle is 0°, when the observation is normal to the sample. The goniophotometer available at Istituto Elettrotecnico Nazionale Galileo Ferraris, Torino [2, 3], was used to perform investigations on the samples 12 and 13.

If the following conditions are satisfied, an absolute (a reference standard is not required) and accurate measurement is performed:

• all the half-plane (or half-space if the sample is not isotropic) in the transmission configuration is analysed with short steps for the observation angle;

• the detector exhibits such a linearity that a sufficiently accurate ratio is obtained between the measured luminance and illuminance.

As a consequence of the rotational symmetry of the samples, they were supposed to be isotropic and measurements were performed on the horizontal half-plane (only one angular coordinate, e, is needed to establish the observation angle). The collimated light
beam was in the opposite half-plane (transmittance configuration) perpendicularly incident on the sample.

Due to the samples characteristics, the observation angle є step was varied as follows:

• between -2° a +2° to the sample normal the measurements have 0.5° as resolution step;

• between (+)2° and (+)10° the step is 1°;

• between І0° and 25° the step is 2.5°;

• between 25° and 60° the step is 5°;

• between 60° and 90° the step is 10°.

These intervals were chosen considering the low scattering properties of the selected samples. It was, hence, expected to collect the highest amount of transmitted energy, close to the normal direction, typical of materials with regular behaviour. The resolution then increase with the increase of the observation angle.

Figure 4. Angular light transmittance of the selected samples

In figure 4 the goniophtometric measurements on the samples 12 (continuous line) and 13 (dotted line) are presented. In particular the graph reports the luminance coefficient as a function of the observation angle. No experimental data are available for sample 6, since it was not available during the test campaign. As expected, no redirecting components, nor diffusing behaviour of the samples, are evident in figure 4 and the two glazings confirmed their mostly regular properties.