Based on the simple case with one window, an obstruction opposite to the window is con­sidered here, as represented in Figure 6. It is assumed that the obstruction shows horizon­tal symmetry with respect to the window centre. Then three additional factors apply: the horizontal and vertical obstruction angles a and ф, respectively, and the average obstruc­tion reflectivity p. These factors replace pW, pD and d of the original case. The floor reflec­tion is now much more important than the reflections of walls and ceiling because due to the obstruction zenith light is the main daylight source. The results are shown in Figure 7.

The daylight quantity is reduced by appr. 30% as compared to the un-obstructed case. The vertical obstruction size and the lintel height show strong negative effects. The single factor effects show a greater uniformity.

Figure 7: Factors, definition bounds and resulting main effects on D for the case of the room daylit by one window with an obstruction opposite

In modern architecture, highly transparent facades and increasing daylight utilisation are very common. A high energy efficiency as well as thermal and visual comfort are strong requirements that can be fulfilled only with a sophisticated use of the solar irradiation. Microstructured light-guiding systems have the ability to guide or reflect the light incident under certain angles and are therefore a way to improve daylighting and solar control. Interference lithography1 offers the possibility to generate these microstructures in large scale. Another approach for solar control glazing are switchchable glazings like

gaschromic4 or thermotropic windows. It is possible to combine both concepts. The Fraunhofer ISE is focusing on two general types of microstructures for light guiding and sun shading systems2 The first concept, shown in figure 1, is a prismatic array where prisms and coplanar areas are alternating. In between two critical angles of incidence, most of the light entering the structure will be reflected due to total internal reflection at the lower face and the backside of the structure. The structure uses the effect of self shadowing of the coplanar areas for increasing incidence angles. This allows an outside view for coplanar sections and solar-control function of the prism elements. The critical angles are depending on some parameters such as the geometry of the prisms, the aspect ratio of the prism-section and the coplanar section and the index of refraction. These parameters can be chosen in a way that one can achieve a minimum of transmittance for directions that are corresponding to the incidence angles of the summer sun on a vertical south facade. There are several sets of parameters suitable for this requirements. Samples and prototype glazings have been manufactured for two different types of microsprism arrays for the use as sunshading devices in glazings.

The second concept is based on an array of one dimensional Compound Parabolic Concentrators (CPCs)3. CPCs focus radiation incident between certain aperture angles onto the lower exit of the structure. If this aperture is covered by a reflector, the element reflects all radiation incident between the aperture angles. Incident radiation at angles larger than the critical aperture angles is mostly transmitted. Because the rejection angles of CPCs are in the vicinity of the surface normal of the structured sheet, they are best suitable for tilted/tiltable applications like roof windows or venetian blinds. Figure 2 shows a replication of a CPC array of period approx. 9 pm with the tips (exit aperture) area- selectively coated with a metallic film.

The experimental set up consisted in a test structure of 2m long, 1m high that holds 3 small scale test cells of 0.6m x 0.6m x 0.6m and three air conditioning apparatus to each cell are coupled. Each cell has 4 insulated surfaces (3 walls and the floor), the test window is placed in the frontal wall and on the top surface (ceiling) a test roof is placed. On the back wall there were two rounded holes of 0.1016 m of diameter to connect the air conditioning system. Figure 1 shows a schematic diagram of the experimental set up of the small scale test cells and the air conditioning apparatus.

Figure 2 shows a small scale test cell and its elements. The surface walls and floor were 0.6m x 0.6m built as pine wood-3cm polystyrene-pine wood with a traverse area of 10.8cm2 surrounded by stripes of pine wood of 0.635m of thickness. The interior of each surface wall was painted with opaque black paint and the exterior was insulated with wool glass fiber of 5.08 of thickness.

Figure 2. Schematic diagram of one of the small scale test cell.

The glazings were 6mm thicknes and consisted of clear glass, filter glass and reflective glass. Each roof of the three modules has a concrete slab of 2.54 cm of thickness. Table 1 presents the thermal properties of each component of the small scale test cells and Table 2 presents the measured optical properties of the glazings.

Model 1. It is intrinsic to the initial period of the superinsulation investigation. The superinsulation is considered as a system of parallel layers with surfaces reflecting thermal radiation according to the Stephen-Boltzman law. In addition, the thermal shunting of the layer is absent in the model. This model implied a small degree of surface blackness. The superinsulation according to Model 1 is considered as a system of poor or "defected” reflectors [13]. The following superinsulation damage sources have been proposed: adsorption of water vapours, working liquid and volatile components of the padding material [14] as well as tunnel-radiation phenomena in the area of contact between the padding material and the reflecting surface [15].

Model 2. It describes the superinsulation as a system of screen-reflectors with a small value of the emissivity factor and heat shunted by means of conductive-conduction pads located between them [16-18]. In accordance with this model, the pad’s parameters, the fibre diameter, the total thickness of pad, the number of bonds in the padding should be of major importance. In addition, the fibre diameter and the pad’s thickness is determined by the number of contact areas in the heat flow direction and the amount of the bundle, which is normally concentrated in the contact area, is determined by the heat resistance of this contacts.

Model 3. It describes the superinsulation as a system of effective screens of radiant energy shunted by pads, which entire heat resistance is concentrated in the area of their
contact with the screens. According to this model, the pad thickness is of secondary value [19-21].

Model 4. It describes the superinsulation as a system of screens with a small degree of surface blackness shunted by the interlayer gas being in the free molecular mode (the Knudsen criterion >1). According to this model, the pad thickness is insignificant, the main importance belongs to the number of sections, into which the gas space is divided and the residual gas pressure in this space. The pad parameters are important only insofar as they influence on the residual gas pressure [22-28].

Model 5 (belonging to the author of this review). It describes the superinsulation as a system of screens with a small degree of surface blackness shunted by the interlayer gas being in the free molecular mode. According to this model, the pad thickness is insignificant, the most important are the number of sections, into which the gas space is divided, the screen material, the composition and pressure of residual gases in this space as well as the effusion magnitude and composition. The pad parameters are important only in connection with the fact that they influence on the residual gas pressure [6,7].

Model 6 (G. G. Zhun’s model). It describes the superinsulation as a peculiar pump [29].

Model 7 (belonging to the author of this review). It describes the superinsulation as a “quasicapacitor”, in which the charge generator on the superinsulation screens is the evaporating cryoliquid [30].

Model 8 (belonging to the author of this review). It describes the superinsulation as a system being unstable in warm layers and having the number of adsorption centres, which varied depending upon the ambient conditions.

The triangular site comprises 7.5ha of farmland located in the metropolitan green belt. The boundary of the site is formed, to the south, by the M25 orbital motorway; to the west, by the mainline London to Glasgow railway; and, to the north-east, by a private road. The egg farm is set out on an axis, which, if extended northwards, aligns with the Ovaltine factory — the destination of all the eggs laid on the old farm. The layout of the various elements comprising the development is shown on the site plan. Its location adjacent to one of Europe’s busiest motorways brings sustainability in action closer to the millions of people using the road

The Energy Strategy

It is intended that all energy used at the Renewable Energy Centre be provided by renewable sources located on the site. The project demonstrates the integration of passive solar techniques with a range of inter-related renewable energy systems. The energy provision derives from:

• Optimising the use of natural ventilation, daylight, high insulation, low air infiltration, solar control, materials that derive from the minimum use of energy in their manufacture and transport (low embodied energy materials), recycled materials, the minimisation of resource depletion, low use of water, car sharing and the encouragement of the use of public transport.

• A hybrid photovoltaic/thermal (PVT) array providing both electricity and hot water installed as the roof to a biomass crop store, the heat of which is passed to:

• A seasonal heat store, comprising a 1100m2 body of water concealed beneath the ground, used to assist heating of the buildings in winter.

• A biomass crop (miscanthus or ‘elephant grass’) cultivated on the surrounding land, harvested annually, dried and stored in the earth-sheltered space beneath the PVT array.

• Future biomass plant which shreds the miscanthus and burns it to provide heating for the building (and, possibly, in a forthcoming adaptation, combined heat and power (CHP)).

• Ground water cooling pumped from an 80m deep bore hole to cool the buildings in summer (and then passed out of the building to irrigate the biomass crop).

• A 225kW wind turbine supplying, with the PVT installation, all the electrical power required by the building and a significant surplus fed into the National Grid.

SHAPE * MERGEFORMAT

AIR

PVT/ Heat Store / Space Heating

Adriana Angelotti, Dipartimento di Energetica, Politecnico di Milano, Italy Lorenzo Pagliano, Dipartimento di Energetica, Politecnico di Milano, Italy Giulio Solaini, Dipartimento BEST, Politecnico di Milano, Italy

Introduction

During the last years in Italy and in southern European countries the demand for summer comfort has been rapidly growing. The increasing popularity of air­conditioning is producing a significant rise of the electricity consumption, causing serious security of supply and environmental concerns.

In this context there is a great interest in the techniques that can be applied to provide thermal comfort with a low energy consumption. Among them indirect ground cooling represents a promising option. A few meters under the surface the earth temperature is stable all over the year and significantly lower than the ambient air temperature in summer. By using proper earth-to-fluid heat exchangers indirect coupling between the building and the ground is achieved and the building thermal loads can be transferred to the ground.

Most experimental and theoretical studies on ground cooling systems focus on air as the thermovector fluid [1-6]. Anyhow the use of air can lead to some sanitary problems due to the presence of stagnant water, either caused by humidity condensation or by infiltration from the surrounding medium. On the other side earth-to-water heat exchangers are commonly used in conjunction with ground source heat pumps, resulting in more complex and energy intensive systems. A test ground cooling system built in Milano, connecting earth-to-water heat exchangers to radiant panels in the building without making use of a heat pump, has been proposed and studied by the authors [7-9]. In this paper the results of a monitoring campaign carried out using the experimental set up are reported and discussed. A dynamic simulation model, developed within the TRNSYS environment, is used to simulate the system and the building. Two performance indicators, one for comfort conditions and one for energy efficiency, are introduced. Through dynamic simulations the influence of the main parameters on the system performance is investigated, obtaining some operating and design guidelines.

Photovoltaic modules have been placed on the southern fagade, sloped at 60 degrees to the ground. Behind the PV wall, there is an inner atrium and a passage, which acts as a huge solar arcade. It is a bold example of integration of PV modules with energy saving measures according to the rules of the passive solar architecture. It comprises buffer zones combined with a massive floor, constructional walls and slabs as a thermal mass. These elements are aimed at

efficient passive solar energy utilization. It is also connected with thermal comfort of the

inner environment. The massive elements moderate effects of sudden fluctuations of temperature (fig.5).

The solar arcade is lit by means of glass modules integrated with PV surface, grouped horizontally on three levels according to the floors in the office zone. The photovoltaic modules are not transparent, so visual contact with the surrounding is interrupted. There is also highly contrasting game of light and shadow inside the arcade fig® a view from the inside during sunny periods (fig.6). towards PVfacade