To analyse the performance of facades addressed to produce space heating, the top part of the tank in the facade is considered linked to a heat exchanger (a thermal radiator). Water from tank is pumped through the heat exchanger delivering heat to the annex room, and then it returns to the facade entering at bottom.

The following assumptions have been considered:

-Indoor room temperature is considered constant and equal to 20°C.

-Global heat transfer coefficient of heat exchanger has been considered constant UA = 100 W/°C. Return temperature to the facade is calculated according to:

QLOAD = UAIT — Tg) = mcp(OTL — Tinlet) (1)

where:

T = 0.5 (OTL + Tinlet) (2)

Tg is the indoor ambient temperature, OTL is the outlet water temperature from the facade, is the water flow rate [kg/s], QLOAD stands for the energy delivered from the heat ex­changer and Tinlet is the return temperature.

-The facade delivers heat from 17 to 24 hours each day of the heating months.

In the past, a number of different glare indices have been developed. All of them were basically aimed for artificial lighting and considered only small sized glare sources. Only one of them, the Daylight Glare Index (DGI) has been adapted to large glare sources and daylight conditions. Velds (2000) and Gall et al. (2000) found in their tests little or no correlation between the glare formula and the user assessments. This has been proven

by our own studies in 2003, when 27 subjects in test offices at the Fraunhofer ISE were tested under different lighting conditions. As can be seen in the following graph, there exists almost no correlation between DGI and user reaction.

The main reason for the big discrepancy is that, for the initial study, less than 10 people were used to develop the DGI formula. Another problem was that the studies were originally carried out under artificial and not real daylight conditions, nor under real office conditions.

Chauvel et al. (1982) argued that the weak correlation between the DGI and the observed glare from windows is compounded by other visual and aesthetic factors such as the quality of the view, the appearance of the window as well as the visual and aesthetic interior qualities of the room.

There was a greater tolerance of mild degrees of glare from the sky seen through the window than from a comparable artificial lighting situation with the same value of glare index, but that this tolerance did not extend to severe degrees of glare (Boubekri and Boyer, 1992; Chauvel et al., 1982). Chauvel et al. (1982) also observed that the discomfort glare resulting from the direct view through windows has been found to vary greatly from observer to observer and also to vary with factors associated with the appearance of the window, the view outside and the surroundings.

Iwata et al. (1990/91) showed that the subjects judged the light to be less uncomfortable even after only 30 seconds, suggesting that the most serious glare problems occur during the transition i. e. the time immediately after exposure to the glare source. Also, Osterhaus (1996) observed that the research subjects (32) in his experiment commented on becoming more sensitive to glare as the experiment progressed (2-2.5 hours) and that this impression was confirmed by experimental data. Osterhaus and Bailey (1992) also pointed out that no data is currently available on perceived comfort or discomfort and the relations between comfort and task performance under conditions in which the glare source borders or surrounds a work task. All existing discomfort glare indices were developed by assessments of subjects directly viewing the glare source rather than focusing on a work task.

Osterhaus (1996) also suggested carrying out glare experiments with subjects exposed to the daylighting situation for at least the eight hours of a regular workday. Decreasing work performance would be expected due to fatigue and distraction induced by glare discomfort. Sivak and Flannagan (1991) found that task difficulty affected discomfort glare. In their study, smaller gapsizes in a gap-detection task resulted in more discomfort glare responses concerning a simultaneous presented light source. They concluded that the assessment of discomfort glare requires the inclusion of the relevant visual task the observer is involved in during the presentation of the glare stimulus.

Data plots:

A typical testing day is characterized for a certain number of heliostats focused over the receiver. This number is increased in case of mist that makes the solar direct radiation lower, but otherwise it is fixed. On the other hand, in one test day, the mass flow rate is decreased several times until the temperatures approach certain limits in each section. In a clear day, with an approximately constant solar radiation, the temperatures increase when the air flow rate decreases. From all the data recorded for the DAS, a plot is drawn for the most relevant parameters (see fig.2): direct solar radiation (in W/m2), overall mass flow rate (in kg/s, over the secondary axis in the chart) and air outlet temperatures (in °С) from the cups of interest (all of them adjacent and located at the central part of the receiver). Moreover, the average temperature of the 36 absorber cups is represented to have an idea of the temperature level in the whole receiver.

Selection of steady states:

To present the response of the volumetric solar absorbers under certain known parameters, it would advisable that the system was in a steady state. However, this is nearly impossible, since solar radiation is always slowly increasing until noon and decreasing from then. In addition, the clouds in the sky may cause transitories in the incoming radiation. The solution is to find quasy-steady states where the main input parameters of the receiver do not change very much. But also the response of the receiver has to be considered. Thus, the input and output parameters values must keep inside a certain range during a large period of time related to the response time. This time is calculated as the time that takes the receiver to react and to reach the 65% of the final value of the output variable after a quick change in one input variable, while the other input parameters remain constant. For this receiver, the response time is in the order of some minutes, between 3 and 5 depending on the temperature selected as output variable.

To identify the quasy-steady states, several criteria have been used, but in all of them the incoming radiation and mass flow rate, as input parameters, and receiver average temperature, as output parameters, must not change more than 4% or 5% in a previous period corresponding to 4 or 5 times the response time of the receiver. In other words, to consider that a measurement value is inside a steady period it is compared to the values taken in the last minutes (between 12 and 20, depending on the selected criterion). In addition, the change gradients of these parameter must be less than 1% (or 1.25%) in every former response time step.

As an example, all the experimental points for the 3 parameters of interest that comply with the all the requirements at the same time for the one of the strictest criteria are marked in the fig.2. This criterion compared every value of direct solar radiation and overall mass flow rate with their values during the last twenty minutes and they must not vary more than a 4% (and no more than 1% every 5 minute step). Meanwhile, the average absorbers temperature must not change more than a 5% (no more than 1.25 in every step).

After calculating the quasy-steady periods of a test, the mean value and the standard deviation of each variable are calculated from its values from the beginning to the end of the steady period. Thus, the number of experimental points is reduced from several thousands to some dozens in the best days, or just a few or even any steady data when direct radiation was unstable.

L. C.S. Mesquita, D. Thomey, S. J. Harrison.

Department of Mechanical and Materials Engineering, McLaughlin Hall, Queen’s University, Kingston, ON. Canada, K7L 3N6. Email :mesquita@me. queensu. ca

INTRODUCTION

In the last few years there has been renewed interest in solar driven air-conditioning

[1] . Some of the work have been focused in desiccant cooling systems. Such systems have the advantage of improved humidity control, particularly in applications with high ventilation rates [2]. Most of the systems already developed employ solid desiccants, with relatively high regeneration temperatures. One alternative is the use of liquid-desiccant systems. In these systems, lower regeneration temperatures can be employed, allowing for a more efficient use of heat from low temperature sources, e. g., flat plate solar collectors [3]. Another advantage of liquid-desiccant systems is the potential of using the desiccant solution for energy storage.

The main components in a liquid-desiccant air-conditioning system are the dehumidifier and the regenerator. Many different technologies have been developed for these two components. For the dehumidifier, the most common technology employed today is the packed bed. However, packed beds must work with high

desiccant flow rates, in order to achieve good dehumidification levels without internal cooling. Higher desiccant flow rates imply on small changes in the concentration of the desiccant solution during the process. This, and the higher level of heat dumping from the regenerated solution that follows higher flow rates, reduce the coefficient of performance of the liquid-desiccant cycle. One option that allows lower flow rates is the use of internally cooled dehumidifiers [4,5]. Figure 1 presents the schematics for one channel of a internally cooled dehumidifier, wich is composed of several of these channels stacked together.

In the present work, mathematical and numerical models were developed for internally cooled dehumidifiers, using three different approaches. The first approach uses heat and mass transfer correlations. The second one numerically solves the differential equations for energy and species for a constant thickness film, using the finite-difference method. The third approach introduces a variable film thickness. All approaches assume fully developed laminar flow for the liquid and air streams.

First a test prototype of the chiller with a cooling capacity of about 10 kW was built and tested under laboratory conditions. For the second prototype some improvements were done and the cooling capacity was raised to 15 kW.

The cooling capacity and the coefficient of performance (COP) of the second prototype for different cold water temperatures are shown in Figure 3 and Figure 4.

The figures show a distinct dependency on the cold water temperature. The higher the cold water temperature the higher is the cooling capacity and the coefficient of perform­ance of the chiller. In this capacity range the chiller will mostly be used for cooling only but not for air-dehumidification. By considering the cold water temperature when designing the room cooling system a high COP and cooling capacity can be achieved.

Figure 4: Coefficient of performance for different cold water temperatures

Field test

After prototype testing under laboratory conditions a field test was carried out in the sum­mer of 2003. At three test sites the new absorption chiller was installed. The locations of the test sites and the different peripheral equipment that was used is specified in Table 2.

The field test showed good results. The absorption chiller worked with a high reliability and operational safety. It is able to work over a wide range of external conditions. The test in Italy showed that the chiller even works with flat plate collectors (lower heating tempera­tures achievable than with vacuum tube collectors) and a dry cooler for re-cooling (rela­tively high cooling water temperatures during daytime).

At the test site in Kothen the room cooling system (gravity cooling units without ventilation) was already installed. It is designed for lower cold water temperatures and could not be changed for this field test. Therefore the absorption chiller had to work with cold water temperatures of 10…12 °C. Also the hot and cold water flow rates were below design con­ditions. Because of these conditions the absorption chiller reached a lower COP as shown before.

Results of the chiller operation in Kothen for one summer day are shown in Figure 5 and Figure 6. On this day some variations of the solution flow rate and the desorber heating temperature were carried out.

The tests also showed that a precise adjustment of the two solution flow rates is very im­portant for achieving a high COP. If one solution pump is pumping more solution than the other one solution reservoir will frequently be empty. This results in a short stop (some seconds) of the operation of the pump. During this stop the solution heat exchanger is without effect which affects the whole cycle of the absorption chiller. The chiller needs minutes to recover and to reach the former values of operation (COP and cooling perform­ance).

The experiences of the field test lead to some further improvements of the chiller design to increase the COP and the flexibility. The electrical power consumption of the peripheral equipment (pumps) could be reduced.

The chiller that is shown in Figure 7 was presented at the IKK fair in Hannover in October 2003. Additional field testing and the composition of "standard” solar thermal cooling con­figurations using the small capacity absorption chiller are planned for the next cooling sea­son.

Another focal point will be the coupling of the absorption chiller with other heat sources for example waste heat of thermal biomass usage or cogeneration units.

SHAPE * MERGEFORMAT

The main entry lobby to the museum is used as a gallery for the display of oil paintings and metal sculptures. In 1996, Philip Johnson made changes to the museum’s east fagade by replacing the glass to a dark tinted one with visible transmittance (Tvis) of less than 5% and UV protection. Even with those modifications and the arched portico, direct sunlight strikes the lobby every morning throughout the year except few days around summer solstice. The fish-eye photo from Figure 8 indicates that the painting receives direct sun year-round for about 55% of the morning hours. The horizontal ceiling of the portico protects the paintings from the sun for about an hour everyday of the year. Figure 9 shows the amount of sunlight penetrating this gallery on March 5 at 9:00 AM. Illuminance levels measured over the paintings at this time reached values of 2,400 lux, which is about 12 times higher than the recommended IES standards for moderately light susceptible display materials. Every night each of the oil paintings of this gallery are covered with boards to protect them from the morning sun and UV radiation. Every morning, the boards are removed from the painting few minutes before the museum open its doors for visitors (10:00 AM).

South-facing gallery (2nd floor):

This gallery is the only one on the second floor that receives natural light directly from a side light window. The gallery is located right over the South entrance to the museum.

The gallery displays mainly oil paintings and metal sculptures (Figure 10). The 210-ft2- window area (19.5 m2) has a five-feet (1.5 m) external horizontal overhang, and the visible transmittance (Tvis) of the glass is 12%. The window wall ratio (wwr) of the gallery is 58%, and the window floor ratio (wfr) is 28%.

Direct sunlight inundates the gallery all day throughout the year. Fish eye views taken from the painting’s viewpoint show that it receives direct sunlight between 2:00 and 4:00 PM from November to January (Figures 11 and 12). Illuminance measurements taken over the painting under direct sun reached up to 2,200 lux, which is 11 times higher than the IES recommended standards for oil paintings. The total illuminance-hours during these two hours of sunlight over the painting is around 404,800 lux-hours, when added the illuminance-hours over the painting during the rest of daylight hours 700,000 lux-hours, the total over exceeds the maximum annual exposure to light recommended by IES for oil paintings. Figure 12 also shows that the horizontal overhang blocks sunlight few hours around wintertime, but does not shade enough the window to protect the painting. Paintings in this gallery are exposed to daylight at all times without any device that could help to reduce the illuminance levels over light susceptible artwork.

Figures 13 and 14 show the illuminance levels simulated with the Desktop RADIANCE lighting program in the south gallery on November 28, at 3:40 PM. Simulated illuminance levels were calibrated with the measured illuminance levels during site visits. Lighting simulations were done at different times during the day to evaluate the sunlight patterns in the gallery. Results from these simulations showed that the display areas over the walls

receive direct sun in the morning (west wall) and afternoon (east wall) for about two hours around winter solstice.

Figure 14: Radiance model of Amon Carter Museum’s south gallery on November 28 at 3:40 PM; false color image with illuminance levels (bottom).

The house has been simulated with the DEROB LTH (Dynamic Energy Response Of Buildings) version 00.04, developed by the Swedish Department of Building Science belonging to the Lund Institute of Technology. Natural ventilation has been considered

during the whole year.

The results indicate that the volume A will re and 2812 kWh/y for cooling (30 kWh/m2y). This is a lower demand compared to the heating demand of a typical Italian residential building.

4.2 The heating systems (solar and biomass)

Since the energy consumption for heating is low, a great part of it could be covered by a solar heating system. Therefore two solar heating systems have been designed: a water solar system with solar collectors to cover a great part of the heating demand and the DHW needs (Costruzioni Solari s. r.l.[16]) and an air solar system (Solarwall[17]) to preheat the inlet air during the winter sunny days. The

solar system will heat the house through a radiant pavement system at low temperature. The whole solar system is integrated with a wood stove to cover the complete heating demand during the coldest period.

The water solar system

Six solar thermal collectors of 1,9 sq meters each and one boiler of 700 litres for the space heating system are located in the south wall as reported in figure 9. The solar system scheme is reported in figure 10. This system should cover from 64% to 100% of the heating demand. In order to increase this percentage, a solar air system has been designed.

Daniela Enz and Robert Hastings Architecture, Energy & Environment AEU GmbH Kirchstrasse 1, CH-8304 Wallisellen Tel. +41 -1 883 17 16 /17 daniela. enz@aeu. ch, robert. hastings@aeu. ch

To help architects plan very low energy housing for the first time, reference values can be useful for making critical decisions affecting performance. The authors have analyzed documentation from 20 Swiss projects built to extreme low energy standards, such as the Passivhaus and Minergie-P Standard. The results illustrate how Swiss house-builders have adapted German and Austrian Passivhaus concepts to local housing markets. The number of such high performance houses in Switzerland is still small but interest by home owners and subsequently by architects is growing. An initial sampling of the key values for the envelope and technical solutions are presented here. It is noteworthy, that for some key design parameters, a few projects lie quite outside the average, yet still achieve excellent energy performance by compensating in other parameters. This demonstrates that there is indeed considerable design freedom for engineering high performance housing.

A. J. Vazquez, C. Sierra,

CENIM-CSIC, Av. Gregorio del Amo, 8, 28040-Madrid. Spain (UE)
avazquez@cenim. csic. es

Introduction

One field of big interest inside the frame of Solar Energy applications is that of application to materials. A lot of work was done in different groups joined to biog installations. Odeillo, Denver, Tashkent, etc. In most of the cases the work done was on high temperature ceramic materials. In the Denver Institute of DOE more work was done on metallic materials and also in China an UK, several papers on heat treatment of metallic materials, welding, etc. were performed.

Our group start their work on this topic in the ‘90 with large installations such as those of PSA, Almeria (Spain-UE), later with CNRS, Odeillo (France-UE) and IFS, Tashkent (Uzbekistan).

Several works were made also with a simulator consisting in a 7 kW Xenon lamp and more recently we install a Fresnel lens equipment to get surface modification of Metallic Materials (1-3).

The most recent application consist in the combination of Concentrated Solar Energy with this Fresnel equipment with the Self High Temperature Synthesis to produce coatings of intermetallics. In this paper we will describe the basic Fresnel equipment and the application to the SHS to produce coatings [7-9].

The main aspect of the Fresnel CSE equipment is that of price, size a power density. Price is lower, ca. 15.000 €, size is small and power density, in Madrid installation, is enough good, ca. 250 W sq. cm., i. e. 2500 kW sq. m.

All this characteristics makes this equipment suitable to be used in any research institute or university Department of materials because it falls inside the budget of any research group. The advantages of this equipment are clear:

1. — It is an installation that increases the direct power density ca. 4.000 to 5.000 times

2. — The power density achieved is enough high to produce a lot of metallurgical processes

a. — all typical heat treatments used in metallurgy: quenching, tempering, stress relieving, thermal fatigue, etc.

b. — gas-metal reactions, e. g., nitriding of Ti alloys

c. — melting processes such as coating alloying and cladding, welding, etc.

d. — recently SHS is combined to obtain coatings

e. — any other metallurgical process.

3. — It is strong and very easy to control and can be used as a teaching tool to students in the Materials career and as a research tool as we are doing.

4. — It is the best equipment to transmit to all future professionals working in materials the idea that CSE can be used only for heating sanitary water at home, desalinate brackish or sea water, or to produce electricity, etc. but it can be used in very high temperature applications with small installations.

All the work we did in the past is devoted to transmit this idea: SCE can be used in as many metallurgical operations as we can imagine. We have the tool and it is only a matter of imagination to apply it to real applications. But to start is a need that young students know this real and near possibility to their lives, because most of them don’t know large installations exists.

2. — OBJECTIVE

The standard DEC systems currently used for air-conditioning are mostly based on solid sorbent, and show a process path similar to the one shown in Figure 1. These systems present thermodynamic limits, which affect the process performance. In particular:

— Limited dehumidification efficiency: the dehumidification process is nearly adiabatic. The heat of condensation and the heat of bonding released during the sorption process causes an increase in temperature of the air and the sorption material; the latter results in a lower sorption potential.

— Cooling potential not completely exploited: the return stream is saturated before entering the heat exchanger wheel (7) but it leaves with a state far distant from saturation. If it could be humidified during the heat exchange process, the potential uptake of heat and thus the potential cooling would be far higher.

— Low efficient processes sequence: during the standard DEC process the supply air is heated, i. e., during the dehumidification (1)-(2) and then cooled by means of the heat recovery wheel (2)-(3). The sequence is not efficient since one of the aims of the process is the air temperature reduction. Moreover the sequence of the two processes (i. e., dehumidification and heat transfer) sets thermodynamic limits of the cycle and restricts the applicability of the cycle in severe conditions, i. e., conditions at high ambient air temperature and humidity.

Furthermore conventional DEC technology, following the scheme of Figure 2, is not used for small size systems (typically below 3000 m3/h). The main reason is that they result economically not convenient in comparison to other technologies. Furthermore on small capacity plants technical problems such as leakages between return and supply air are more difficult to tackle with success [2].