Category Archives: BACKGROUND

Monitoring Results

Detailed energy monitoring and data analysis allow precise values for the energy balance of the building and hence gives a more realistic picture of the resulting primary energy consumption.

DHW consumption average = 17 kWh/m2a

specific heat supply

[kWh/m2a] ■ heat recovery and ambient heat consumption

100 average = 19 kWh/2a

On average annual 25 kWh/m2 net heated floor area are used for space heating, but in one extreme case a value Qheat =2 kWh/m2 net heated floor area was measured. Ambient heat and heat recovery cover 19 kWh/mP net heated floor area of the annual space heating. 17 kWh/mP net heated floor area are need to cover the hot water demand. Thermal losses of pipes and storage in the building average 11 kWh/mF. Figure 6 shows the heat consumption of all monitored projects. Not all projects have heat recovery or preheated fresh air for heating the air supply.

Figure 6 Total heat consumption and heat losses in the evaluated projects (related to net heated floor area)

The primary energy consumption is calculate as the sum for the total heating consumption (space heating, hot water and heat recovery)including heat losses and electricity for pumps, fans and controls. In the demonstration projects the average of the annual primary energy (PE) demand reaches a value of 53 kWh/mF net heated floor area, in some projects a minimum PE = 13.7 kWh/mFa. The primary energy consumption for other household appliances, e. g. lighting, cooking and other have a mean value of about 70 kWh/mFa. Figure 7 reviews the primary energy for the heating and ventilation systems as well as for household appliances. Only 40 % of the primary energy in the houses is used to cover the heating and ventilation demand and 60 % the other household appliances.

specific primary energy

consumption [kWh/m2a] ■ household appliances average = 70 kWh/m2a

200

total HVAC average = 53 kWh/m2a

Figure 7 Primary energy consumption for HAVC and other household appliances in the analyzed buildings (related to net heated floor area)

The best results were obtained in the semi-detached house in Monte Carasso, CH. This house has a very low space heating demand and less heating losses. Heat is supplied by wood pellet combustion and solar thermal collectors to support the hot water production. An exhaust air ventilation system is installed in the building. Fresh air intake is preheated via an earth-to-air heat exchanger.

Important for a high efficient building is the energy ratio ep which consider the sum of space heating, heat recovery (Qheat) and hot water (Qdhw) relative to the primary energy consumption (PE).

ep = (Qheat+QDHW)/PE

primary energy

[kWh/m2a] detached Bsemidetached Arow ^apartment

1.45 Durbach, ultra, D

120

1.52 Durbach, NEH, D

Figure 8 Relation between measured useful energy and the calculated primary energy of the analyzed buildings. If the factor of energy expenditure (Anlagenaufwandszahl) is lower than one, the energy supply system is very efficient (related to net heated floor area).

140

The factor ep, the amount of net space heating and hot water consumption related primary energy demand, will be less than one, if renewable energy replace some of the needed auxiliary energy. The primary energy factor for renewable energies is assumed as zero for thermal solar energy and very low for biomass and pv. Figure 8 shows the relation between primary energy demand and the net energy consumption for heating and DHW in the analyzed buildings.

Most of the buildings which use solar energy or biomass as well as having ground heat exchangers and ventilation heat recovery have a factor of energy expenditure lower than one and are very efficient. These are the buildings for the future.

Photometric Sensors

The discrepancy induced by the use of different photometric sensors in the test module and the scale model was considered as main possible source of error. After an accurate calibration, LMT luxmeters showing a 10 mm diameter sensitive area and BEHA luxmeters, characterized by a 40 mm diameter sensitive area, were compared regarding their cosine response (Schiler, 1987). Illuminances, sensed by the two photometers types for varying incidence angles (0-90 degrees), were measured under a collimated light source, showing spectral features close to daylight (Scartezzini et al, 1994) were measured and compared for that purpose.

RESULTS

The preliminary results achieved within the framework of the initial experimental study, which confirmed the overestimation of daylighting performance assessment in scale models were presented in (Thanachareonkit, 2003). An extended version of this communication will be published shortly, providing a comprehensive and detailed analysis of the impact of the different sources of experimental errors. The present communication is focused on the three main causes of discrepancy between test module and scale model daylighting performance.

Exprimental part 1. Photometric measurements

Normal and angular transmittance measurements were performed at ENEA-Casaccia, Roma, by means of an integrating sphere, 1000 mm in diameter [1]. The cross-section diameter of the light beam incident on the sample was selected to be 60 mm, at normal

incidence, in order to cover a complete pattern for glass panes considered as samples in this paper. Taking into account the size of the samples, an entrance port of 250 mm in diameter was chosen in order to collect most of the transmitted radiation even at the highest angle of incidence considered in the measurements. For example at 30° of incidence the elliptical irradiated area of the sample had a minimum and maximum axes of 60 and 70 mm respectively. A complete set of angular measurements was also performed to get more information on the angular decay of the analysed products. The spectral measurements were performed between 350 and 800 nm and the resolution was 10 nm.

In figure 2, the spectral curves of the three selected samples are reported, to be noted how the coloured obstruction elements of sample 6 influence the spectral distribution of the transmitted light respect to the uncoloured glazing. The normal hemispherical transmittance xv of samples 6, 12, and 13, calculated using the Illuminant A as weight, are respectively: 0.679, 0.621 and 0.764. In figure 3, the angular light transmittance of the selected samples are plotted.

Angular Light Transmittance (Ill. A)

Figure 3. Angular light transmittance of the selected samples

Previous Projects

The Fraunhofer Institute for Solar Energy Systems (Freiburg/Breisgau, Germany) and the company UFE Solar GmbH (Berlin, Germany) started with preliminary tests and first investigations concerning seasonal heat storage based on the adsorption process in 1995. Research work was continued with financial aid of the European Commission and the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT) in the project HYDES (High Energy Density Sorption Heat Storage for Solar Space Heating). In this project, the principle technical feasibility of the sorption storage system was proved. The experience gained during this project will be of use in the frame of the new project MODESTORE which is also funded by the European Commission and on the Austrian national level by BMVIT. The work in this project started in April 2003 and will be continued for three years.

Basic Principles of an Adsorption Heat Storage System

In sensible and latent heat storage devices heat is stored together with its
corresponding amount of entropy. In these so-called direct heat storage media, heat

— i. e. energy — is transferred directly to the storage medium. The achievable energy density is limited by the entropy storage capacity of the material. Otherwise the adsorption process is a reversible physico-chemical reaction suitable to store heat in an indirect way. This kind of thermal storage allows to separate energy and entropy flow. The storage capacity is not limited to the maximum of entropy intake. The energy density can be much higher if entropy is not stored directly in the medium. Therefore a heat source and a heat sink is involved both during the charging and discharging process to withdraw or collect the necessary entropy. The storage works like a heat transformer on the principle of a chemical heat pump. During adsorption of water vapour, a phase chance takes place between vapour and liquid phase on the surface of the in this project used silica gel. The released adsorption enthalpy consists of the evaporation enthalpy of the working fluid and the binding energy of the adsorption pair.

The working principle involves several different phases illustrated in figure 1 and described below:

1. Charging process (desorption, drying of silicagel): heat from a high temperature source is fed into the device, heats the silica gel and vapour is desorbed from the porous solid. The desorbed vapour is led to the condenser and condensed at a lower temperature level. The heat of condensation has to be withdrawn to the environment.

2. Storage period: the dry adsorbent is separated from the liquid working fluid (the connecting valve is closed). As long as these components stay separate heat storage without losses is possible if the sensible heat involved is neglected.

3.

Charging

Storage

Discharging

Desorption

Adsorption

High temperature heat

Water vapour

Low temperature heat

Condensation

Water vapour

Liquid

water

Evaporation

Low temperature heat

Discharging process (adsorption, loading of silica gel with water vapour): the valve between the evaporator and the adsorber is opened. The liquid working fluid evaporates in the evaporator taking up heat at a low temperature level. The vapour is adsorbed and releases the adsorption heat at a higher temperature level. This is the useful heat.

Figure 1: The working principle of an adsorption heat storage.

There are several quantities and process parameters important when the potential energy density of a sorption pair for heat storage applications is evaluated. The main ones are:

1. Temperature lift: it depends on the current loading level of the sorbent and is a material property.

2. Adsorption enthalpy: it consists of the evaporation enthalpy of the working fluid and the binding energy of the adsorption pair. A high specific evaporation enthalpy is a must for high energy densities, therefore water is one of the primary candidates.

3. Sensible heat and process management: an intelligent system design and process management along with good insulation is essential.

4. Energy density: the energy per unit volume is the quantity of primary interest. It is the product of specific energy (energy per mass of sorbent) and the bulk density ps.

After due consideration, the process of thermo-chemical heat storage with the adsorption pair silica gel and water was selected. Silica gel is a very porous and vitreous substance. The material is made up mainly of SiO2 and is extracted from aqueous silicic acid. The equipment installed in the laboratory of AEE-INTEC in Gleisdorf/Austria is filled with commercial silica gel GRACE 127 B. This silica gel consists of spherical particles with a diameter of two to three millimetres. Its bulk density is 790 kg/m3, the interior surface is 650 m2/g. The high energy density, the quantity of primary interest, is achieved by a high evaporation enthalpy, the polarity of water and the large interior surface of silica gel. Additional components like heat exchangers reduce the energy density if the whole system is considered. The system is evacuated to enable water vapour transport without use of mechanical energy. The vapour pressure add up to 10 to 50 mbar in the system.

Design Principles

The Renewable Energy Centre is the first commercially developed building to be carbon neutral and entirely self-sufficient in energy. Indeed the various integrated renewable energy systems will, over any year, generate a surplus. This will be fed into the electricity grid for the use of the community.

The project brief was the conversion and extension of the former Ova ltine Egg Farm to provide 2,665 m2 of headquarters office accommodation for RES. This was to be carried out using, so far as economically practical, a range of renewable energy measures and employing ‘best practice’ sustainable strategies. RES was assisted in this objective by the contribution from the EC Framework 5 Programme. This funding was conditional on the adoption of a radically innovative approach to resolving sustainable issues and the involvement of a pan-European design and development team. On the basis of this innovative content, RES requested that additional facilities for visitors and parties who might wish to see and learn about the building and its energy systems.

Accordingly, the design principles upon which the development is based were to:

• Provide a fully operational head office which meets the commercial needs and conditions of the property market

• Provide exhibition, conference and facilities for the use of RES and visitors to the building

• Deliver a building that minimises energy consumption and the use of scarce resources and that contributes positively to local economic and community needs

• Deliver a building whose energy consumption is provided entirely from on-site renewable energy sources

• Integrate seamlessly the social, technical and aesthetic aspects of the project.

Performance

Figure 4 gives the PER (Primary Energy Ratio) of the sorption system as a function of the installed capacity of the sorption system (expressed as condenser/absorber power) for four

different houses and without solar system. The PER is the ratio between energy demand (heating, hot water and cooling) and primary energy used, so including electricity used for the system (especially pumps), but not the other electricity consumption in the house (lighting, etc).

We can see that the PER strongly depends on the type of house (and therefore on the space heat demand of the house). At high sorption capacity the PER is higher for houses with a higher heat demand, because the space heat demand forms a bigger part of the total demand. The sorption system is most efficient in (low temperature) space heating. At the minimum energy house the influence of the sorption system is very small.

Figure 5 gives the PER for a sorption system with solar system.

2.20

2.00

1.80 DC

1.60 D.

1.40 1.20 1.00

We can see that the PER can be far higher than without solar system (compare fig. 4). The highest PER is now reached by the minimum energy house. The influence of the sorption system is also far bigger now for the minimum energy house, because solar sorption cooling can now be active in stead of gas driven sorption cooling. For the big house the same solar system (8 m2 collector area and 300 litre of storage capacity) has not so much influence.

Figure 6: Relative contribution of the solar and sorption system (5.5 kW condenser/absorber power) as a function of the installed collector area (300 litre of storage capacity) for the average house.

Figure 7: Solar Fraction for cooling as a function of the condenser/absorber power for four different cooling demands (8 m2 of collector area and 300 litre of storage capacity).

We can see that high solar fractions are possible. A condenser/absorber power of about 4 kW is sufficient (equivalent to an evaporator power of 1.4 kW). For the higher demands the solar fraction also depends upon the installed collector area. For 16 m2 and 11 kW condenser/absorber power the solar fraction is calculated at 75 % at 2.72 GJ/year cooling demand.

THE DAYLIGHT PROJECT

The good project for daylight application should be made in an early phase of the project so to get a good level of integration [6]. It is important to know the characteristics of lighting that the room required, the activity that is supposed to be performed inside, the right position of the standing people and so on. Only when all these variables are well known it is possible to determine the sizes and the shapes of the transparent components, giving the quantity of natural light and their distribution in the wall [7].

At the end the whole lighting project should be checked by using of tables, plots abacus and codes [8].

The standard gives the formula to calculate the Daylight Factor:

DFm = Af x Ti x e x у / [( 1-pim) x Atot]

Af glass surface of the windows [m2]

Ti glass transparency

e window factor (ratio between the

window lighting and the sky radiance) у window factor reduction coefficient

(dependent on the protrusion of the wall respect the window) pim indoor surface average reflection

value

The transparency is the value of the optical transmittance for the PV component as it has been measured, depending on the optical transmittance of the transparent part and on the cell density.

In our case a project for the refurbishing of an health centre for mental disease to an university campus, with parts of the buildings available even to the inhabitants of the town.

Figure 4. A pictorial view of the intervention. The PV facades are the black zones.

In particular that building will be partially destroyed and then rebuilt, but keeping the original look by keeping the pristine outside walls, see figure 4.

In one block two PV plants will be installed in the facade acting as a sun screen by using the glass/glass technology and the spacing of the cells.

In the first case the PV modules will develop around the length of the building and should provide a good lighting on the working planes; in order to avoid the glaring and at the same

Figure 5. A rendering of the lighting project.

The second plant develops on the whole slanted surface aimed as a sun screen, the most of the lighting is provided by the side clear glassy fagade. The overheating and the glaring diseases are so reduced by using a large cell density for the photovoltaic fagade and the self shadowing of the remaining old building walls.

By using the above formula and the data shown in table 3, a daylight factor of 3.7 is obtained. This is a very good value for the use of the room as office

time to allow a good vision of the outside environment, the modules are designed on the purpose, as it can be possible to see in figure 5.

Af

Ti

Є

¥

P

cm2

PV modules

68949

30

0.5

1

windows

25380

90

0.5

1

walls

934200

0.5

ceiling

127700

0.7

floor

127700

0.3

average

1189600

0.5

DF

3.67

%

Table 3. Parameters used for the calculation of the daylight factor.

The PV modules beyond shadowing the sun they also reduce the overheating due to excess of insolation at summer. To eliminate the self shadowing of the cells the use of frames with Vasistas mechanisms for opening are considered.

CONCLUSIONS

The sun light can be efficiently used fro daylighting with many advantages; a saving on the energy bill can be gained and the increasing of the comfort from optical, thermal points of views. The diffusion of the building integrated photovoltaics in form of fagade and sun screen and the new concept for projecting the PV module according its multifunction aspect making available semitransparent or translucent module created a good potential for that application. In that case some optical characterization could prove to be important and that work presented a methodology ENEA undertook in order to investigate the optical

transmittance. That value combined with the density of the cells are parameters that are

needed for the daylight factor determination to be used in the lighting project

The paper showed as an example that replacing a traditional glass fagade with Photovoltaic

resulted on the reduction of the day light factor so giving an improvement for the comfort of

the room. By using the density of the cells the glaring effect can largely reduced if not

avoided.

Methods and Approach

The investigations are based on a combination of daylighting simulations using Radiance [RAD] with methods used for the design of experiments (DOE) [Sch97]. The simulation allows for reproducible sky conditions.

The goal is to find the qualitative and quantitative influence of elementary architectural, i. e. structural, measures on the daylight quality in interior spaces.

The DOE methodology allows multi-dimensional factor variation at minimum experimental expense. The DOE plans containing all necessary experiments show two essential charac­teristics:

• All factors are varied in discrete steps, i. e. not continuously, with the number of steps being as small as possible. Thus in the simplest case, these are two steps defining the lower and upper border of the experimental space.

• All variables are linearly transformed so that the bounds of definition range from -1 to +1. This leads to DOE matrices with orthogonal columns, DOE plans of general validity (independent of the natural variable dimensions), and to the possibility of a direct quan­titative analysis of effects.

Base case is a room lit by one un-obstructed vertical window. Two more investigations show two windows each, in two facades adjacent to and facing each other, respectively. Two variations of an obstructed single window case and two roof lighting designs complete the research work. A few restrictions apply:

• In cases with one window only, its horizontal position is central. The results do there­fore not apply for strong asymmetric placements of the window. In cases with two win­dows, the symmetry restriction holds for one of them.

• All numbers are based on a CIE overcast sky with a sun elevation of 60° above the horizon.

• All daylight openings are rectangular.

• All room geometries are rectangular except for the roof geometries in the toplit cases.

• The interior optical description is limited to the uniform average diffuse reflection coeffi­cients of floor, walls and ceiling.

Three criteria have been looked at in [Sic03]: the average daylight factor D, the daylight factor in a room depth of 4 m, D4, and the daylight factor regularity, G, which is the ratio of minimum to mean daylight factor. The most useful criterion is D. It serves as a measure for the total amount of daylight inside under overcast conditions. The regression analysis re­sults for this criterion are presented here.

Thermal Properties

In order to calculate the total solar energy transmittance (g-value) [5], the secondary heat flux Is must be calculated. The thermal simulation program HEAT2 was used to estimate the heat flow into the room caused by the absorption on the back of the reflective layer and in the glass itself. It was assumed that the glass bars were positioned 1 mm from the outer glass pane. The bars themselves had a diameter of 10 mm, and the distance from the bars to the inner glass pane was 12 mm.

g

With the secondary heat flux Isec heat, the direct and diffuse intensities (Isec dir, Isec diff) and the incident global radiation Ig given, it is possible to compute the g-value:

Fig. 7 g-value of the system (в = 90°) for days with Idir = 0 (cloudy) and Idjr > 300 W/m2

(sunny).

04

0.00

1.00

0.90

0.80

0.70

0.60

Cl)

0.50

O)

0.40

0.30

0.20

0.10

0 730 1460 2190 2920 3650 4380 5110 5840 6570 7300 8030 8760

Time [h]

Fig. 8 g-value of the tilted system (в = 30°) for days with Ib = 0 (cloudy) and Ib > 300

W/m2 (sunny).

The g-value was also estimated for the tilted system, with a slope of 30° (Fig. 8). One can see that the g-value for cloudy weather increases slightly while the one for sunny weather decreases. The latter comes from the fact that, especially in summer when radiation is strongest, we don’t get multiple reflections and so the absorptance on the darkened side remains small. This effect will be more pronounced for the secondary heat flow in this case.

As mentioned before (see Fig.4) a considerable part of the direct radiation is absorbed on the blackened side of the reflective layer. This will lead to a secondary heat flux into the room. In order to get a feeling for how much of the g-value is radiation that can be used for illumination and how much is heat radiation depending on the absorbed power, the amount of heat flowing into the room was computed with HEAT2. Figure 9 shows that even for the в = 0 case in summer the maximum heat flux into the room does not exceed 80 W/m2. For the tilted case (в = 30°) the secondary heat flow is even smaller (Fig.10).

40.0

30.0

20.0

10.0

0.0

0 730 1460 2190 2920 3650 4380 5110 5840 6570 7300 8030 8760

Time [h]

Fig. 10 Secondary heat flow into the room arising from the absorption on the blackened
side of the reflective layer, tilted case (в = 30°).

0 —

0

730 1460 2190 2920 3650 4380 5110 5840 6570 7300 8030 8760

Time [h]

Fig. 11 Contribution of the secondary heat flux (black) and the diffuse radiation (grey) to

the g-value, vertical case.

The percentile contribution of the secondary heat flux and the visible diffuse radiation to the g-value is plotted in Figure 10 for the vertical case. As one can see, the secondary heat flux Isec heat contributes only about 30 % to the total g-value, whereas the diffuse radiation transmittance makes up the greater part and should be sufficient to illuminate the room. For the tilted case Isec heat will contribute about 40% in winter and 15% in summer.

Conclusions

As has been shown, the system efficiently shuts out the direct radiation. This reduces glare. Even though the main part of the direct radiation is absorbed by the blackened side of the reflective layer, overheating should not be a problem, if the glass bars are positioned close to the outside glass pane, as the heat will be conducted that way.

Regardless of the system’s properties for direct radiation, the transmission for the diffuse radiation will be around 60% throughout the year, guaranteeing a high illumination level in the room.

Improvement could be made using photochromic layers, which would darken only on the focusing line). This would make a mechanical adjustment superfluous.

[1]

Improved case

The improved case of the SIEEB resulted from the advanced technological solutions and control strategies such as sun shading, radiant ceilings, displacement ventilation and maximizing natural and minimizing artificial lighting. In the DOE simulations, these strategies are simulated as described below:

Sun shading: the values of direct and diffuse solar radiation are reduced to 50% during summer and 80% during winter.

Radiant ceilings: the set points for thermal comfort conditions corresponding to dry bulb temperature is increased by 1°C for summer and is decreased by 2°C for winter.

Displacement ventilation: reducing the values of fresh air volume by 20%.

Lighting: high efficient lamps and control sensors (dimming)

The above hypotheses considered for simulating the advanced technological solutions and control strategies are quite reasonable and are expected to calculate the values of energy savings reasonably well.

Energy Demand — Improved Case

J FMAMJ J ASOND

Month

Figure 5 shows the monthly energy demand for cooling, heating and lighting & equipments corresponding to improved case of SIEEB preliminary design.

Figure 5. SIEEB (Improved case) — Monthly Energy Demand

The potential load reductions based on advanced technological solutions and control strategies are shown in figure 6. It has been observed that for improved case the annual energy load reductions for cooling, heating and lighting & equipments can be achieved up to 30%, 23% and 20% respectively.

2. Conclusions

A methodology for the energy efficient design of the Sino-Italy Environment & Energy Building (SIeEb) is presented. It has been shown that using various advanced technological solutions and control strategies in the SIEEB, an appreciable amount of energy savings can be achieved. Since the results, presented here, are in comparison with a reference case in which the building envelope is already optimised, therefore, compared to a baseline building, constructed as per the current practices in China, the

Energy Load Reduction

□ Reference Case □ Improved case

Figure 6. SIEEB (Improved case) — Energy Load reduction

SIEEB is expected to contribute much higher amount of energy savings. SIEEB is an ecological and energy efficient pilot building and represents a model for a new generation of sustainable buildings. SIEEB can also be seen as an ideal case for assessing the benchmark for implementing the clean development mechanism (CDM), aimed to reduce CO2 emissions according to the accounting procedures defined within Kyoto protocols (IPCC, 2000).

References

J. Chang, Dennis Y. C. Leung, C. Z. Wu, Z. H. Yuan (2003), ‘A review on the energy production, consumption, and prospect of renewable energy in China’, Renewable and Sustainable Energy Reviews, 7, 453-468.

F. Butera, S. Ferrari, N. Aste, P. Caputo, P. Oliaro, U. Beneventano and R. S. Adhikari (2003), ‘Ecological design procedures for Sino-Italian Environment and Energy Building : Results of Ist Phase on the Shape Analysis’, Proc. PLEA-2003 Conference, Santiago, Chile, November 2003.

DOE-2 Manuals (Version 2.1) (1980), US National Technical Information Service, Department of Commerce, Springfield, Virginia, USA.

J. Chen (2003) Sustainable Buildings: the Chinese Perspective, Challenges and Opportunities, Presented at the COP-9 Conference, December 1-12, 2003, Milan, Italy.

IPCC(2000), Website www. ipcc. ch.