The Modern Art Museum of Fort Worth was designed by Japanese architect Tadao Ando in 2000-2001. This two-story museum opened its new building at the end of 2002. The museum’s permanent collection consists of more than 2,600 works, including paintings, sculpture, site-specific installations, drawings, prints, photographs, and video and digital imagery. The building is set on eleven acres, including a large reflecting pool and areas of outdoor sculptures. The building has 53,000 square feet of gallery space (Reference 1).

The Modern Art Museum introduces natural light into the galleries through different fenestration systems that include skylights, clerestories with interior and exterior louvers, and side light windows with and without interior screens (Figure 2).

Patricia Ferro

Via Portoferraio, 22 — 00182 Roma — criferro@tiscali. it

1. Introduction

Yearly energy consumption (heating, hot water and electricity) for Italian residential buildings averages from 150 in south and central Italy to 200 kWh/m2 in north Italy1. This paper describes a house designed with the whole building approach whose estimated energy consumption (heating, hot water and electricity) is estimated less than 70 kWh/m2 year.

The house will be built in central Italy (Casaprota, Rieti Province, 450 meters a. s.l., 42° 24’ N — 12° 52’ E ), a typical Italian Mediterranean hilly landscape.

The paper focuses on some of the design results, in particular those regarding daylighting, space heating and electricity demand, whose production will be 100% from renewable energy (solar and biomass).

To achieve these results, special attention has been given during the design to the siting, the house lay out, the local renewable energy resources available, the local architecture and the construction traditions.

Lazio Regional Government awarded the design of this house within the "Zero Emission residential buildings" competition. The award includes a funding support for the house construction.

The most obvious improvement is the comfort level for those working and visiting the building. In a region which has 50 frosts and below freezing temperatures in winter, over 40 degree C heat in summer, and a diurnal range in spring and autumn of 20 degrees C plus, the benefit of a pleasant work environment goes without saying.

Previously the staff were cold in winter, often supplying their own small electric blow heaters at each desk, whilst in summer only a few offices had individual air conditioning units, and most of the staff sweltered in the heat. A comparison of power consumption over similar periods between the new completed building and the previous two buildings combined, indicates that although floor area has increased, the energy use per m2 is only marginally greater, and at times slightly less — refer Graph 1. Thus, despite the addition of full heating and cooling to the larger building, it has not significantly increased its impact on the environment, producing an average of 109.5 kg CO2/m2 (gross area) annually.

NOTE: Vacation of the main building to enable construction commenced in April, 1999, and the completed building was not fully back in operation until April 2000; Whilst consumption records for the new building have been provided monthly, the old building

Graph 1 —

Series 1 — Old Buildings, May 1998 to Jan 1999 Series 2 — New Building, May 2000 to Jan 2001 Series 3 — New Building, May 2003 to Jan 2004

Further, using the SEDA benchmark for office buildings with full HVAC systems3, rated for NSW at 135 kWh/m2/pa or 486 Mj/m2/pa, this building potentially performs extremely well. Although the figures above are based on gross floor area, it is expected that when a thorough AGBR rating (Australia Building Greenhouse Rating) is carried out, the building will still score extremely well, most likely above industry best practice.

Taking into account the increase in both floor area and services, the increased energy use and therefore emissions generation is in effect less than that generated by the old buildings — refer Table 3. And this is in a climate of extremes and heavy heating and cooling loadings.

Marcelino Sanchez, Maria J. Marcos, Manuel Romero, CIEMAT, High Solar Concentration Systems, Avenida Complutense 22, 28040 Madrid, Spain

Claudio Estrada, CIE-UNAM, Aptdo. Postal 34, CP 62580 Temixco, Morelos, Mexico

The application of monolithic volumetric receivers to solar processes is increasing due to their optimal optical-thermal properties. At high temperature, the volumetric absorber design means that the effective area for solar absorption is many times larger than the receiver aperture area, this effect leads to a minimization of radiation losses. For thermal and photochemical applications monolithic catalysts have significant advantages in lowering pressure drop and improving both chemical and photon contact surfaces. For those and other applications the precise calculation of photons penetrability as a function of monolithic parameters such as pitch length, wall thickness, and material reflectance, has to be performed in order to choose the optimal configuration. Photon trap efficiency and thermal performance is not at all trivial for this 3D structures where contradictory effects may appear regarding “volumetricity”. The authors analyze the influence and the relationship between that parameters. A sensitivity analysis of photons penetrability is performed by means of ray tracing techniques and discussed in connection to three-dimensional CFD simulation of heat transfer efficiency and thermal losses for a single channel. The results obtained suggest that many experimental experiences with volumetric receivers reported until now are noticeable away from a theoretical highly volumetric structure and that operational limits still remain unexplored offering enough room for design improvements.

Introduction

Porous volumetric absorbers have a large potential for use in receivers of solar thermal power plants, high-temperature catalysis or hot air supply in industrial process heat. Early solar prototypes of several-hundred kW were developed by Sanders in the USA in late seventies [1] and Sulzer in Europe in middle eighties [2]. Since then, the more extensive operational experience in the field has been collected at the Plataforma Solar de Almeria where more than 20 different absorbers and receivers have been tested within the range between 200 to 3,000 kW [3]. The list of materials and porous structures tested includes high-temperature metallic alloys and high thermal conductivity ceramics composing wire mesh absorbers, fibres, foams, fins and monolithic channels [4].

In general the volumetric concept offers experimental absorber efficiencies higher than 80%. In spite of the high temperature at the working fluid, above 700°C, the high efficiency is due to the photon trap effect of the porous medium. Theoretically, the porous material of the absorbing surface and the gradual absorption through the porous matrix acts as a black body and leads to much lower temperature gradients between the wall temperature (solid) and the thermal fluid. Solar flux is high at the cold air inlet (front surface) and it is low at the hot air outlet. This means that both air and wall temperatures are higher at the inner portion of the absorber, leading to lower IR radiation losses.

One of the options offering substantial benefits as volumetric absorbers are monolithic matrixes made of prismatic channels. Indeed monolithic structures are commonly used in photo-catalytic applications because of their outstanding properties as photon/heat exchangers [5]. Monolithic solar absorbers made of metallic foils or ceramic honeycomb

have significant advantages in lowering pressure drop and improving both chemical and photon contact surfaces. These makes them especially useful for receiver designs with large flowrates and treatment capacities, and subsequently for scaling-up the volumetric receiver technology. In addition, prismatic channels allow to compartmentalize air flow patterns in individual ducts so that high degrees of “volumetricity” can be achieved but controlling fluid-dynamics by means of appropriate modular designs [6].

A good design of a monolithic volumetric absorber must necessarily be associated to a balance between photon penetrability, absorber porosity, radiation losses and profile of the heat transfer to the fluid. Even though experimental results have demonstrated the feasibility of producing hot air at temperatures above 700°C with absorber thermal efficiencies higher than 80%, it is also evident that current designs can be significantly improved in terms of solar radiation penetration, heat transfer efficiency a nd minimization of radiation losses. Then, the real operational limits of volumetric receivers still remain unexplored in practice. The present work analyzes the effect of several, sometimes contradictory, parameters like channel dimensions, solar concentrator/receiver aperture view angle, material reflectivity and specularity, on photons penetrability and the corresponding effect in terms of thermal behaviour.

The 4th order Runge-Kutta method allowed the numerical solution of the system of equations governing the collector loop. The development of a program for computing the thermodynamic properties of the working fluids was necessary for the theoretical analysis of the cooling cycle.

• Results and discussion

It is obvious that the global performances of the studied system depend on the levels of temperature of the heat sources and sinks (Coefficient of Performance of the endoreversible cooling system) and the efficiency of the solar collector.

The theoretical parametric study of the three heat reservoir cooling system showed the influence:

— of the site (Algiers (north algeria), Hassi-Messaoud, Tamanrasset (south algeria))

— of the geometrical parameters of the collector (thickness of the absorber, spacing between tubes, diameter of tubes) and of the characteristics of material of the absorber.

— of the nature of the working fluid (R134-a and R123).

As shown in Figures 5, 7, 8, 9, the performances obtained with the refrigerant R123 are sharply better than those obtained with the R134-a but the coefficient of performance COPF, Q remains relatively low for both fluids compared to conventional cooling systems. For an ambient temperature of 40°C and a cold reservoir temperature of 0°C, the coefficient of performance COP varies from 0.1 to 0.6 in average.

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• Conclusion

The main objective of this paper is to present the results of theoretical performances of a solar powered ejector cooling system using R123 or R134a as the working fluid. We have developed a program that allows calculation of the cooling power. It is maily composed of four subroutines computing the solar radiation, the thermodynamic properties of working fluids, the vapour driving massflowrate and the cooling power respectively.

The parametric study, based on the cycle analysis, shows the influence of the working fluid, the site, the day, the ejector geometry, the solar collector type, the system configuration, etc…

In the comparative study of the cooling performances for the two working fluids, it comes out to be the R123 which leads to better results. The cooling power is about 4 kW in average. However, due to the low massflowrate at the collector exit, the coefficient of performance is relatively low for both fluids compared to conventional cooling systems. That makes this cycle more suitable for air conditioning applications than refrigeration but one can for example, use it with hybrid cycles to improve the efficiency of conventional [4] and non conventional refrigeration systems.

K. Sumathy

Department of Mechanical Engineering, University of Hong Kong, Hong Kong

Introduction

Refrigeration is an attractive application of solar energy, because, the supply of sunshine and the need for refrigeration reach maximum levels in the same season. One of the very effective form of solar refrigeration is the production of ice, because ice accumulates much latent heat in it, so that the volume of ice maker can be small. In 1981, Pons and Grenier [1] worked on a solid adsorption pair of zeolite and water, to produce the refrigerating effect and the coefficient of performance was about 0.1. Lately, they had successfully experimented with the adsorption pair of activated carbon and methanol. Sakoda[2], had presented the advantages and limitations of the simultaneous transport of heat and adsorbate in closed type adsorption cooling system, utilizing solar heat. This paper focus on a solar-powered ice-maker with solid adsorption pair of activated carbon + methanol. A simple flat-plate collector having an exposed area of 0.92 m2 is employed to produce ice of about 4-5 kg/day.

System Description

The system consists of a flat-plate collector, a fin-type condenser/heat exchanger and an evaporator which acts as a refrigerator, as shown in Fig. 1. The collector is supplied with activated carbon which is adsorbed with methanol. During the daytime, when solar energy is available on the collector, methanol gets heated up and evaporates from the activated carbon. The vapour is then condensed through the heat exchanger(condenser), and the liquid methanol is stored in the evaporator, which is said to be the regenerating course of the activated carbon. During the nighttime, the collector temperature begins to decrease
due to the heavy heat loss to the atmosphere. In this period, methanol begins to evaporate by absorbing heat from the liquid (water) and gets adsorbed by the activated carbon inside the collector. Since adsorption is a process of releasing heat, the collector must be cooled efficiently at night. As mentioned above, the ice maker operates in an intermittent way to produce the refrigerating effect.

The principle of the solid-adsorption ice-maker is explained using a P-T-X diagram as shown in Fig.2. To begin with, the adsorption bed along with the refrigerant gets heated up, and when it reaches the required desorption temperature(Td1), the methanol gets desorbed. In the evening, the flat-plate collector (adsorption bed) looses its heat to the surroundings and hence the temperature of the adsorbent bed is reduced rapidly (Td2 ? Tai), and the pressure in the adsorber drops to a value below evaporation pressure (Pe). During this period, evaporation could happen, and ice will be made in the refrigeration box.

As explained above, the system works in an intermittent way. This system can be made to operate continuously to produce ice, by incorporating two absorbers such that while one works in desorption mode, the other would be set in for absorption.

Line A-B : Represents the heating of AC along with methanol.

Qa-B = (C pa + CpmWA )(TB — TA) (3)

Line B-D : Shows that, the collector is connected with the condenser and progressive heating of the adsorbent from B to D causes some adsorbate to be desorbed and its vapour to be condensed.

Line D-F : The collector is closed and cooled. The decrease in temperature from D to F induces the decrease in pressure from PC to PE.

Line F-A : The collector is connected with the evaporator during when the adsorption as well as evaporation occur while the adsorbent is cooled from F to A.

The total energy input (QT) to the system is given by,

TOC o "1-5" h z Qt = Qa-b + Qb-d (3)

The cooling effect (for ice production) is given by,

Qc =(Wa — Wd )[l — Cpm (Ta — TE )J (4)

Therefore, the system efficiency is given by,

COPTH = (5)

TH Qt ( )

The luminance value at the window is about 5500 cd /m2. The luminance values for the various variants are given in figure 2. The dark line gives the measurements for the empty window, thus the reference values. With a luminance value of 40 cd/m2 on the wall, this amounts to a luminance ratio of 5500 / 40 = 140, which is much too high. From the light grey lines in figure 2 one can conclude that absorption is not a good way to reduce the contrast ratio between the window and the wall. Luckily, however, from the dark grey lines in figure 2 it can be concluded that reflection and the combination of reflection and absorption is a way to increase the amount of light on the wall next to the window opening, thus decreasing the luminance ratio between the window and the wall to a minimum luminance ratio of 40 for the translucent foil 1 cm in front of the window.

The Solar Window is evaluated for its properties as a building component. From this perspective, it can be regarded as a normal window with added features, such as solar shading and internal insulation by the reflector screens. The window consists of

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of daylight from the reflectors needs to be observed and reduced to a minimum. A two-dimensional ray-tracing analysis, made by hand in a CAD program (see figure 5), shows that most of the radiation reflected will be distributed upwards to the next element above and then spread again. For solar angles at 20° and lower, there is a small risk of glare from the concentrated daylight. This problem is likely solved by reducing the rotation angle from 95° (which was set for minimizing the horizontal obstruction of view) to 90°.

A key question is how the value of m affects the prediction of plant power. As a reference condition use the case where V = Vmax/(n+1)1/n and pt/pp = n/(n+1), and denote it with an asterisk (*). When pt/pp = n/(n+1) in the power law model, then from Eqs. (1), (2) and (3):

к

= (n + 1)V. n-m (19)

-L

Substitute Eq. (19) into Eq. (6) to get the volume flow at MFP condition:

Vmfp = (m + 1)V. n-m )

= (m + 1)1/(n-m)V. (20)

By substituting Eqs. (20) and (21) into (4), the fluid power at the MFP condition follows:

Pmfp = [1-m)(1 + m)(1+m)/(n-m)P* (22)

In the table below, volume flow, pressure potential and power, all at MFP condition, are listed as a fraction of the respective reference value over a range of collector transfer efficiencies at n = 2. At a collector transfer efficiency of 70 % (m = -0.70) we can see that the MFP volume flow may be as low as 64 %, the MFP turbine pressure drop may be as high as 185 % and the power production may be 118 % compared to the reference value. Even at moderate collector floor-to-exit efficiencies of around 50 % the optimal turbine pressure drop may be seriously underestimated by using the 2/3 rule.

Schlaich (1995) gives typical values of ncoll around 0.55 and a around 0.80, leading to ncfe = 0.69. Applying the above model we get m = -0.69 and from Eq. 8 and assuming n = 2 the optimal ratio is pt/pp = (n-m)/(n+1) = 2.69/3 = 0.90. This value is much higher than the value of 2/3, and also higher than the value of 0.82 derived from values in a table of data given by Schlaich (1995). On the other hand, a value of pt/pp = 0.82 corresponds to ncfe = 0.46, and if a = 0.8, to ncoll = 0.8×0.46 = 0.37, which is very low. The value of 0.9 agrees with the value recommended by Bernardes (2003). In his analysis he found optimum values of as high as 0.97, resulting in m = -0.91. This would, in combination with his value of collector floor absorption coefficient, a = 0.9, imply a collector transfer efficiency of 0.91/0.9, which exceeds 100 %. If the value of 0.8 for a given by Schlaich is replaced by 0.9 in his data set, then ncfe = 0.61, with optimal ratio of pt/pp = 0.87.

As the tabulated data in Schlaich (1995) were not obtained with a pt/pp ratio of 2/3, we cannot apply Eqs. (20-22) directly to come up with the values for volume flow, turbine pressure drop and power at MFP condition. We first have to find the equivalent * condition, by using Eqs. (1) and (2) to get values for Kp and KL. Assuming these coefficients as well as the exponents m and n to remain constant over a restricted range of flow rate and using the * condition together with Eqs. (1) and (2) from Eq. (19) V* is:

1

m-n

(23)

The value of m follows from ^cfe, and n is taken as 2. We can then find V* and evaluate pp*, pt*, pL*, and P*, and find values for the same variables at the MFP condition with Eqs. (20-22).

Since n is numerically about three times as large as m, V* is rather insensitive to the exact value of m. Taking m = -0.66 and working with the 100 MW plant data we find that PMFP is 3.7 % higher than PSchlaich (for the 30 MW plant it is 3.5 % and for the 5 MW it is 3.0 %). Changing m by 20 % to -0.79 leads to a PMFP that is 8.4 % higher than PSchlaich, a change of only 4.5 %.

Per Henrik Pedersen, Seren Poulsen & Ivan Katic

Danish Technological Institute

P. O.Box 141

2630 Taastrup

Denmark

Introduction

A solar powered refrigerator (SolarChill) has been developed in an international project involving Greenpeace International, GTZ, UNICEF, UNEP, WHO, industrial partners and Danish Technological Institute. The refrigerator is able to operate directly on solar PV panels, without battery or additional electronics, and is therefore suitable for locations where little maintenance and reliable operation is mandatory. The main objective of the SolarChill Project is to help deliver vaccines and refrigeration to the rural poor. To achieve this objective, the SolarChill Project developed — and plans to make freely available a versatile refrigeration technology that is environmentally sound, technologically reliable, and affordable. SolarChill does not use any fluorocarbons in its cooling system or in the insulation.

For domestic and small business applications, another type of solar refrigerator is under development. This is an upright type, suitable for cool storage of food and beverages in areas where grid power is non-existent or unstable. The market potential for this type is thus present in industrialised countries as well as in countries under development.

The unique feature of SolarChill is that energy is stored in ice instead of in batteries. An ice compartment keeps the cabinet at desired temperatures during the night. SolarChill is made from mass produced standard components, which results in a favourable cost compared with other vaccine solar refrigerators.

The SolarChill has undergone intensive laboratory tests in Denmark, proving that it fulfils the objectives set for the project. In addition, a field test programme in three different developing countries is ongoing with the aim to gather practical experience from health clinics.

The paper describes the product development, possible SolarChill applications and experience with the two types of solar refrigerators, as well as results from the laboratory and field test.

Background

A developing project funded by the Danish Energy Agency and conducted by the Danish Technological Institute started in 1999 in co-operation with Danfoss Compressors, Vestfrost and other Danish companies. The aim was to develop a photovoltaic powered vaccine cooler without battery back-up. Instead energy storage of ice should keep the temperature stable during nights and periods without sunshine.

In parallel to that discussions were held at various times (starting in 1998-99) between UNEP, WHO, Greenpeace and GTZ with the objective to promote environmentally sound refrigerators. The idea to bring all these interested parties together arose at a refrigeration summit in Chicago in November 2000, which then led to a common meeting at GTZ headquarters in 2001. This resulted in an international project with the aim to develop, test, and use environmental sound, affordable and reliable photovoltaic powered vaccine cooler.

The Solar Chill project is a unique partnership among key international agencies, research

and industry bodies. The Project Partners and their main respective roles are:

□ Greenpeace International provides project coordination and fundraising;

□ GTZ Proklima provides technology advice and assessment and fund raising;

□ United Nations Children’s Fund provides need analysis and technology advice and assessment;

□ United Nations Environment Programme provides overall technology assessment and policy advice;

□ World Health Organization provides equipment specifications and technology advice and assessment

□ Program for Appropriate Technology in Health provides technology advice and conducts field test

□ Industry partners: Vestfrost, Vibocold, Danfoss, Gaia Solar provide hardware

□ Danish Technological Institute coordinates the technology development;