Category Archives: EuroSun2008-4

Implementing A New Method For The Design. Of Bioclimatic Buildings

Joao Mariz Graga1, Joao Bento2 and Helder Gonsalves1

1 INETI — Instituto National de Engenharia, Tecnologia e Inovagao;
Estrada do Pago do Lumiar, 22, 1649-038 Lisboa
2 Instituto Superior Tecnico,

Av. Rovisco Pais, 1049-001 Lisboa

A tool for support the design of bioclimatic buildings is under development. This tool is also specialy adapted to the particular needs of buildings in the portuguese territory, since it includes the possibility of doing evaluations according to the requirements that are imposed by the new regulations of thermal performance for buildings (RCCTE). This tool will allow designers of bioclimatic architecture to easily extract reports of different energy simulation programs, such as energy Plus, Radiance and RCCTE thermal code. The system is provided with a 3D Editor that shares multiple interfaces with the different simulation programs above mencioned.

A particular method for the conception of bioclimatic architecture is assumed, however different types of evaluations can be performed with this interface program.

A particular method for the conception of bioclimatic buildings is here sugested. It begans with the evaluation of the complience with the portuguese thermal codes. Once the shape and construction for the building under design are conformant with regulations, other evaluations are sugested. The system provides the possibility of automaticaly generate a geometric definition for future energy plus simulation that maches the previous RCCTE definition, however with some simplification assumptions. This can bring closer the evaluations of the thermal code requirements with the energy Plus evaluations, and so to take advantage of a large number of energy plus features in a detailed analysis.

The program under development provides automatic generation of some particular features of Energy Plus that were found very usefull for design tasks of bioclimatic buildings, such as the generation of; adjacent zones, trombe walls zones, earth tubes, detailed window variables, etc.

Information and publication

The task is about midway in the progress, and most of the expected outcome has still to be developed.

However, some information is already available at the task web-site: www. iea-shc. org/task37

• Task 37 flyer

• The exemplary housing renovation brochures

With financial support from the Enova and the State Housing Bank in Norway, a set of films about housing renovation have been produced:

These films which are also available in Norwegian and German, are expected to be available from the task 37 web-site before the start of EuroSun 2008.

Other reports which are expected during this and next year:

• Housing segments with the greatest multiplication and energy saving potentials.

• Business Opportunities in Advanced Renovation

• Packages of technically and economically robust concepts for housing renovation which could be applied in concrete projects.

• Innovative future solutions with great potential of primary energy reduction.

• A “basics” on sustainable renovation including principles for the design and realisation of renovation projects.

Solar availability for rooms at attics

For the purpose of the presented studies, calculations of solar radiation incident on surfaces with different azimuth and inclination angles have been performed using the averaged representative hourly solar radiation data for Warsaw [3] for the anisotropic sky model, Hay — Davies — Klucher — Reindl [5]. To describe and solve problems of the dynamics of processes in the building envelope and surrounding, a mathematical model of energy transfer phenomena in opaque and transparent elements has been developed [1], [2]. Focus has been put on the influence of solar energy and because of that, special attention has been paid to energy transfer through the windows.

Window consists of three main components: centre glass area, edges of glass, frame. All these 3 components influence on each other from the point of view of the heat transfer [4]. The model of unsteady energy transfer outside and inside the window, as well as within the cavity formed by the glass sheets has been developed [1]. It includes heat conduction and heat capacity of opaque (frame) and transparent (centre glass area, edge of glass) elements. It also includes heat convection (free) with indoor and (forced) outdoor surrounding and inside window cavity; and radiation (thermal — long wave) exchange between the ground, the sky, i. e. the outdoor environment, and windows; and radiation exchange between windows and the room cavity, i. e. indoor environment; and radiation exchange between glass panes of the window.

Solar radiation incident on surfaces with different orientation and inclination is considered in details. Window constitutes three dimensional object. Solar irradiance on glazing and front surfaces of the frame is the same at given time but it differs for frame surfaces perpendicular to glazing (that have not only different orientation but inclination, too). The developed model takes into account all these phenomena and solar absorption at frame surfaces. Solar absorption, transmission and reflection of all transparent surfaces (bodies) are analysed, and the effects of orientation and inclination on them are considered.

The developed model enables to calculate energy transferred through the window into/out of the room at any time. These energy transfer takes into account not only heat transfer because of temperature difference between indoor and outdoor environment, and specific conditions at boundary surfaces (including absorption of solar energy), but also solar energy transferred directly into the room under consideration. The results of calculations of energy transferred through the some selected examples of windows throughout the averaged year are presented in Fig. 1-4. Figures 1-2 show the case of inclined (450) small (1 x 1 m2) and big (2 x 2 m2) south windows respectively and Figures 3-4 show the case of inclined (450) small (1 x 1 m2) and big (2 x 2 m2) north windows respectively. The opposite orientation (south and north) and different size of windows have been selected to show the influence of orientation and size of a window, and in consequence the influence of solar energy, on energy transferred through the window. For the south orientation the maximum hourly solar radiation that enters the room through a window is at noon in May and for the small window it is about 1,15 MJ for 1 m2 (of the window) and for the big window it is about 5,1 MJ for 4 m2 (of the window). The minimum is in December and for the small window at noon it is about 0,25 MJ for 1 m2 (of the window) and for the big window it is about 1,1 MJ for 4 m2 (of the window). For the north orientation the maximum hourly solar radiation that enters the room through a window is at noon in June and for the small window it is about 0,57 MJ for 1 m2 (of the window) and for the big window is about 2,6 MJ for 4 m2 (of the window). The minimum hourly solar radiation that enters the room through a window at noon is in December and for the small window is about 0,11 MJ for 1 m2 (of the window) and for the big window is about 0,5 MJ for 4 m2 (of the window). Generally hourly solar radiation entering the south room is about two times bigger than for the north room. It can be seen that the increase of size of the window cause the increase of energy flow through a window but not exactly proportional.

x io5 Solar heat through window, with Beta = 45, Gamma = 0 Xt = 1Yt = 1





—— Feb






— Aug

— Sep Oct

— Nov

— Dec


x io5 Solar heat through window, with Beta = 45, Gamma = 180, Xt = 1, Yt = 1


Fig. 3. Solar energy transferred into the room through the north inclined (450) small window


Подпись: Q (J)Подпись:Подпись: t (h)image388—— Jan

—— Feb

—— Mar

Apr May Jun

— Jul Aug

— Sep Oct Nov

— Dec

Thermal Performance of Residential Buildings in Lisbon. with Large Glazing Areas

M. Tavares H. Gonsalves1 and J. Bastos2

1 INETI, Department of Renewable Energies, Campus do Lumiar do INETI, 1649-038 Lisbon, Portugal
2 FA-UTL, Department Technology of Architecture, Polo Alto da Ajuda, 1349-055 Lisbon, Portugal
^Corresponding Author, marcia. tavares @ineti. pt


This work presents the results of an experimental study of residential buildings (multi-family apartments) with glazing areas greater than 75% of the total facade area, and for different solar exposures in Lisbon. These buildings were designed after the implementation of the first Portuguese Buildings Thermal Regulation and they are intrinsically related with the construction and architecture practiced in the last few years. The analysis includes the thermal behaviour of the apartments selected for the study during the summer (2007) and winter (2007-2008). During the monitoring process important data were obtained to assist in the understanding of the thermal performance of the observed units. The main thermal exchanges in a building generally take place through the transparent elements and these can be considered an element of great flexibility and adaptation to climatic variations. The mean of the interior temperature means in the different monitored compartments during the hot season was approximately 27°C (some cases close to 29°C), while in the cold season 21°C (some cases close to 18°C).

Keywords: Glazing areas, thermal behaviour, heating, cooling, thermal comfort

1. Introduction

The energetic optimization reveals how important is the building envelope, as the main element between the exterior and interior conditions. The conduction and convection transfers through glass present a similar behaviour of the opaque elements with the possibility of the air change control between the interior and exterior — opening or closing the windows. Meanwhile, radiation becomes the principal factor because its portion is transmitted directly through the glass to the interior.

The non-opaque envelope can be considered an element of great importance in the control of radiation, ventilation and natural illumination. A more dynamic element, easier to adapt and adjust to obtain the desired interior conditions, in other words, it presents a comparatively greater degree of adaptation control and flexibility to the climatic variations than the opaque envelope. In addition, glass and other transparent materials are essential elements for the successful application of the majority of the passive solar heating systems. The heat transfers occur differently depending on the types of materials and proportions being applied in a specific building (opaque and non­opaque envelope).

Solar Power Station

At the start of the project the goal was to design a PV powered bilge pump for open boats. Already in the beginning of the project it was concluded that a multifunctional product would have more market potential. This resulted in the design of the Solar Power Station as a product that can keep valuable and vulnerable products dry, and that can provide energy to a range of electric devices such a a water pump, cell phone, GPS device, and a weather station that is integrated in the product. The Solar Power Station charges it battery via the PV panel. The PV panel can be placed separate from the station, on a location where it can convert energy optimally. Also can the panel be tilted towards the sun. The devices can be connected via 12V sockets and USB sockets. The product was developed up to a prototype. The company the product was developed for announced that it is planning to produce a small series of the product.


Fig. 9. Solar Power Station prototype with tilted PV panel

Future Development

Up until now solar thermal cooling plants have been assembled on site. This requires highly trained installers and construction supervision, and is therefore both complicated and expensive. In order to reduce the construction period and the risk of mistakes, we have developed pre-fabricated units. The various components including the solar unit, cooling machine, pumps and valves, the control unit and the cold water buffer tank are all pre-assembled in a container.

The first such container was used for a project in Phoenix. These cabins are initially to be designed for projects requiring 15KW — 200KW of cooling power.

/This EnergyCabin is portable and therefore perfectly suited for contracting and leasing, even for projects abroad. The solar collectors for exclusively cooling applications are mounted close to the cabin.

Contribution of the Solar Thermal System to the Building Energy Performance — specific aspects of the Portuguese legislation

3.1. Short descriptions


The Portuguese legislation transposing the EU Directive 2002/91/CE, includes a Solar Thermal Obligation, imposing the usage of solar thermal collectors for hot water preparation if there are favourable conditions for exposure (if the roof or cover runs between SE and SW without significant obstructions) in a base of 1m2 per person. The energy necessary for the preparation of hot water constitutes one of the terms for evaluation of energy performance of the building, as well as, the heating and cooling loads of the building, according to:

This term is calculated per apartment area, Ap, and the term Qa is the heat demand for hot water preparation given by in equation (8) and it is equivalent to Qsol, use. pa is the efficiency of the conventional heating equipment used for hot water preparation (backup system). The term Eren is any other renewable energy that is used for hot water preparation or that substitutes the thermal solar system, according to the permitted cases in the legislation.

Qa =(MAQS • 4187-AT • nd )/(3600000)[kWh/yr] (8)

The mass of water to be heated is equivalent to a volume of 40 l per conventional occupant. Also the collector area to be installed is a function of the number of conventional occupants, considering 1 m2 per occupant. Conventional occupants are a function of the home typology, i. e., the number of rooms, according to Table 1.

In equation 8 the value of AT is equal to 45°C, i. e., Tload — Load temperature — 60°C and Tcold — Temperature of cold water (mains water) — 15°C.

The value nd is the number of days where hot water preparation is needed. In the case of residential buildings is equal 365.

Tablel — Number of conventional occupants in an appartment

Apartment typology

T0, T1





N. of conventional occupants






The term Esoiar is calculated using the software tool developed by INETI and called SolTerm [2], whose characteristics were shortly described in section 2.2.. This term is equivalent to QW, sol, out.

2. Results

For comparison of the two methodologies default values introduced in section 2. were used. The comparison is based on the value Qsol, out, m.

Calculations were made for one location only, Lisbon, and the monthly values of Esol, in were derived from SolTerm data base. Two flat plate collectors, one selective and one non-selective, were considered. In Table 2, the parameters of the two collectors are listed.

Table 2 — Characteristic parameters of the collectors used for comparison purposes.







[W/K m2]


[W/K2 m2]



A(selective flat plate)






B(non-selective flat-plate)






Calculations of Qsol, out were made and the yearly values were compared for different system configurations considering that the system load volume varied according to the apartment typologies given in Table 1. Results are shown in Table 3.

Table 3 — Energy delivered by the solar thermal system for hot water preparation.

Qsol out vear [KWh]





area 2


Vload Vstore


EN 15316

SolTerm 5.0


Collector A

T2 (3 m2)

2 col x 2.3 m2





T3 (4 m2)

2 col x 2.3 m2





T4 (5 m2)

3 col x 2.3 m2





T5 (6 m2)

3 col x 2.3 m2





T6 (7 m2)

4 col x 2.3 m2





Collector B

T2 (3 m2)

2 col x 1.65m2





T3 (4 m2)

3 col x 1.65m2





T4 (5 m2)

3 col x 1.65 m2





T5 (6 m2)

4 col x 1.65m2





T6 (7 m2)

5 col x 1.65 m2





The comparison between the two methods shows a strong difference as a function of the collector type, i. e., its efficiency parameters. While for a selective collector, the results obtained with the two methods have differences lower then 2%, in the case of the non-selective collector, differences can be of the order of 10%, with underestimation by the methodology of the standard EN 15316-4­


To explain this discrepancy, it is necessary to recall that the methodology of EN 15316-4-3 is based on f-chart method [6] and that this method is a result of correlations derived from several simulations using a specific configuration system and TRNSYS programme [8]. In reference [6] the range of design parameters is indicated. Two of them are dependent on collector efficiency parameters; 0.6 < (xa)n <0.9 and 2.1 < UL < 8.3 W/K m2. For flat plate collectors (xa)n =p0 and UL is the heat loss coefficient not dependent on temperature. In the case of the non-selective collector, using the efficiency curve with parameters a1 and a2 to determine a linear approximation (up to 0.07), a UL of 8.4 W/K m2 is obtained, showing that it is outside the limit of values considered in the correlations of the f-chart method.

Results considering different ratios of storage tank volume and collector area were also obtained as can be seen in Table 4 for the case of selective collector listed in Table 2.

Table 4 — Solar fraction (%) calculated for thermal solar systems with selective collectors.

Vstore = 1000 l

Vstore = 2000 l

Vstore = 3000 l

EN 15316

SolTerm 5.0

EN 15316

SolTerm 5.0

EN 15316

SolTerm 5.0

100 l/m2







75 l/m2







50 l/m2







25 l/m2







In this case, the comparison is presented by the value of yearly solar fraction. The differences using both methodologies are not dependent on the ratio between storage volume and collector area.

3. Conclusion

The European Standard EN 15316 (part 4-3) [3] includes a methodology for calculation of the energy delivered by a thermal solar system for hot water preparation based on the f-chart method

[6] . This methodology is easy to apply and can even be implemented in an Excel Sheet.

The in the work developed, a comparison of this calculation procedure with the methodology adopted in the Portuguese legislation [1] was presented, i. e., calculation using the SolTerm programme [2]. SolTerm 5.0 was the version used for comparison purposes. It is possible to see that the results obtained with both methodologies are comparable when the collectors used are of the type flat plate selective collectors.

If non selective flat plate collectors are considered the differences between the two methodologies can be of the order of 10%, where EN 15316-4-3 [3] corresponds to an underestimation of the energy delivered by the solar thermal system. The possible explanation for this difference is the fact that the methodology of EN 15316.part4-3 [3] is based on f-chart method [6], which has application limits dependent on the collector efficiency parameters.

Further investigation is necessary in the case where the collector efficiency is higher then the typical values for selective flat plate collectors, as is the case of evacuated tube collectors.

Possibility of adoption of the methodology of EN 15316 in the calculation of solar space heating systems is limited due to the fact that the standard only presents correlation coefficients for one type of space heating systems — direct floor heating system.

Подпись: A ai a2 Esol,in fst Im IAM QW,sol,out QH,sol,out QHW,sol,out Подпись:Подпись:collector aperture area according to EN 12975-2 [m2]

heat loss coefficient of solar collector related to the aperture area according to EN 12975-2 [W/Km2] temperature dependent heat loss coef. related to the aperture area according to EN 12975-2[W/K2 m2]

Incident solar energy on the plane of the collector array [kWh/m2] storage tank capacity correction factor [-]

average solar irradiance on the collector plane during the considered period [W/m2]

incidence angle modifier of the collector = К50(та), from the collector test standard EN 12975-2 [-]

Heat delivered by the thermal solar system to domestic hot water distribution [kWh]

Heat delivered by the thermal solar system to space heating distribution system [kWh]

Total heat delivered by the thermal solar system to space heating and domestic hot water distribution systems [kWh]

Auxiliary electrical energy for pumps and controllers [kWh]

recoverable auxiliary electrical energy for pumps and controllers. Part of the auxiliary electrical energy, which is recoverable for space heating [kWh]

internally recovered auxiliary electrical energy for pumps and controllers. Part of the auxiliary electrical energy, which is transferred as useful heat to the thermal solar system [kWh]

non recoverable auxiliary electrical energy for pumps and controllers. Part of the auxiliary electrical energy, which is neither recoverable for space heating nor transferred as useful heat to the thermal solar system [kWh]

Total thermal losses from the solar system [kWh]

thermal losses from the thermal solar system, which are recoverable for space heating [kWh]

Non recoverable thermal losses from the thermal solar system. Part of the total thermal losses, which are not recoverable for space heating [kWh]

monthly heat use applied to the thermal solar system, usually termed as heat demand [kWh] temperature needed for hot water preparation [°С] temperature of cold water [°С] length of the month [h]

heat loss coefficient of the collector loop (collector and pipes) [W/(m2.K)]

Uoop p overall heat loss coefficient of all pipes in the collector loop, including pipes between collectors and array

pipes between collector array and solar storage tank [W/(m2.K)]

Vload Daily volume of hot water needed for hot water preparation [l]

n0 zero-loss collector efficiency factor obtained according to EN 12975-2 and related to the aperture area [-]

nloop efficiency factor of the collector loop taking into account influence of the heat exchanger [-]

0 re/ reference temperature depending on application and storage type [°С] average outside air temperature over the considered period [°С]

e, avg

p water density [kg/liter]


[1] RCCTE, Portuguese Thermal Performance Building Code (Decreto-Lei n.° 80/2006, DR 67 SERIE I-A, 2006-04-04),

[2] SolTerm, Version: 5.0.2 — 27th April 2007, (Authors: Ricardo Aguiar and Maria Joao Carvalho), CD — ROM distribution, ISBN 978-972-676-205-8

[3] EN 15316-Part 4-3 (2007), Heating systems in buildings. Method for calculation of system energy requirements and system efficiencies. Part 4-3: Heat generation systems, thermal solar systems.

[4] EN ISO 9488 (1999), Solar Energy — Vocabulary

[5] EN 12976 (2006), Thermal solar systems and components — Factory made systems — Part 2: Test methods, European Standard.

[6] J. A. Duffie and W. A. Beckman, Solar Engineering of thermal processes, John Wiley and Sons, 3rd edition, 2006, Chapter 20 — Design of Active systems: f-chart.

[7] EN 12975 (2006), Thermal solar systems and components — Solar collectors — Part 2: Test Methods, Section 6.1. European Standard.

[8] TRNSYS: A Transient System Simulation Program (Version 15), S. A. Klein, W. A. Beckman and P. I. Cooper, Solar Energy Laboratory, Madison Wisconsin, 1998.

Passivhaus proposal to include the Mediterranean conditions

Milder winter and hotter summer climates suggested a set of modified conditions where limits to winter and summer demands are defined minimising life-cycle costs and considering local construction. Also comfort requirements needed to be met as defined by EN 15251 (2007). Lastly, country or climate specific low energy solutions proposed require to meet the energy and comfort requirements in many, if not all situations. Other solution sets, if not explicitly identified by the standard, would comply with the standard as long as the comfort and energy limits were achieved. A thorough energetic analysis under these climatic conditions demonstrated a much less necessity to promote reduced air infiltration rates or pre-heat air intake. Then the revised Passivhaus definition proposed under the Passive-On project must verify the following guidelines:

• Heating criterion: The useful energy demand for space heating does not exceed 15 kWh per m2 net habitable floor area per annum.

• Cooling criterion: The useful, sensible energy demand for space cooling does not exceed 15 kWh per m2 net habitable floor area per annum.

• Primary energy criterion: The primary energy demand for all energy services, including heating, domestic hot water, auxiliary and household electricity, does not exceed 120 kWh per m2 net habitable floor area per annum.

• Air tightness: If good indoor air quality and high thermal comfort are achieved by means of a mechanical ventilation system, the building envelope should have a pressurization test (50 Pa) result according to EN 13829 of no more than 0.6 ach-1. For locations with winter design ambient temperatures above 0 °C, a pressurization test result of 1.0 ach-1 is usually sufficient to achieve the heating criterion.

• Comfort criterion room temperature winter: The operative room temperatures can be kept above 20 °C in winter, using the above mentioned amount of energy.

• Comfort criterion room temperature summer: In warm and hot seasons, operative room temperatures remain within the comfort range defined in EN 15251. Furthermore, if an active cooling system is installed, it should be possible to keep the room temperature below 26 °C.

As the Passivhaus has a reduced amount of energy consumption for heating and cooling, it is quite often neither practical nor economical to introduce an active system, in particular for cooling. On this assumption the proposed standard adopts the adaptive comfort theory against the more constrained Fanger approach appropriate for climatised spaces. Unlike the former, method the adaptive theory claims that upon discomfort people will react in order to restore the previously comfortable condition. In practical terms an immediate energy reduction is expected as the cooling set point is set to a higher temperature and the range of comfort temperatures is wider. Several surveys showed that people’s degree of satisfaction is strongly correlated with the outside temperature and the memory of recent temperatures. The adaptive comfort method applies to non air-conditioned or naturally ventilated buildings. [4, 5]

Traditional Mediterranean architecture often makes use of its strong building inertia, coupled with night-time natural ventilation to reduce the swing and the peak of indoor temperatures. The generalised scepticism among builders around the highly airtight buildings also promotes a variation of the German standard to combine a strong inertia with naturally ventilated buildings.

2. Passive strategies

Modelling and Performance Study of a Building Integrated Photovoltaic. Facade in Northern Canadian Climate

V. Delisle

CANMET Energy Technology Centre-Varennes, Natural Resources Canada
Varennes, Quebec, Canada J3X 1S6, veronique. delisle@nrcan. gc. ca


A model was developed to predict the electrical and thermal performance of different configurations of double-glazed and triple-glazed BIPV fenestration systems. Simulations showed that using a PV laminate as the middle pane as opposed to the outer pane reduced the amount of electricity generated by more than 22%, but led to slightly warmer inner pane temperature. This last characteristic can be beneficial in artic climates since it can contribute to reduce perimeter heating requirements. The multi-glazing BIPV systems modelled were also compared with non-vision sections of a curtainwall faqade in three different Canadian cities. These substitutions had little effect on the space cooling load, but increased the space heating energy requirements by 8.9-10.6% and 4.6-5.3% for double-glazed and triple-glazed curtainwall assemblies, respectively.

Keywords: Curtainwall, Photovoltaics, BIPV

1. Introduction

Over the past years, building-integrated photovoltaics (BIPVs) have witnessed a significant increase in interest as a technology approach for incorporating PV electricity production in buildings. One of the reasons to explain this gain in popularity is that BIPV are more architecturally pleasing than rack-mounted PV systems. Furthermore, they can be considered to have lower installation cost when used to replace expensive cladding or roofing materials [1].

Recently, designs have begun integrating PV semi-transparent laminates into curtainwall constructions [2] and skylights [3]. These laminates consist of opaque PV cells encapsulated with EVA in between two layers of transparent glass sheet. The level of transparency is determined by the PV density, which is the portion of the PV laminate area covered by PV cells, and has a direct influence on the building solar heat gain, natural daylighting, and the amount of electricity generated. Research on the integration of PV into windows has mainly focused on the impact of the different fenestration parameters on buildings energy consumption. Wong et al. [4] studied numerically and experimentally the roof integration of a double-glazed semi-transparent PV window in a residential building. For a PV density of 50%, reductions in overall energy consumption in the order of 3% and 8.7% were observed compared to a standard BIPV roof for the hottest and coldest climate studied, respectively. When the PV density was increased to 80%, the cells were found to heat up more, decreasing the electrical conversion efficiency of crystalline cells. For both 50% and 80% PV density scenarios, replacing a BIPV roof by BIPV semi­transparent windows reduced the annual heating energy requirements but increased the cooling load during the summer. Fung et al. [5] developed and validated a one-dimensional transient model of a semi-transparent BIPV laminate in Hong Kong. Compared to clear glass, BIPV laminates with

cell densities of 20% and 80% were found to reduce the annual total heat gain by approximately 30% and 70%, respectively.

This paper aims at evaluating the performance of five curtainwall constructions in Canada with multi-glazed BIPV assemblies used as the non-vision sections of a building fa9ade. To achieve this objective, an analytical model was first developed to estimate the BIPV systems thermal resistance and electricity production. Then, simulations were performed to assess their impact on a building space heating and cooling loads when combined with curtainwall vision sections to form a fa9ade.

PV-cells and design

Because poly-crystalline silicon PV-cells are cheaper than mono-crystalline silicon PV-cells and still has a high efficiency these are used for the proto-types of the PV-windows. Silicon wafers are usually not transparent. Therefore the project group has worked with variations in the design of the PV-pane, e. g. the size of the silicon wafers and carving of patterns within the PV-cells, which helps to transmit more daylight through the facade, cf. figure 1. The shaping of the design adds a degree of freedom for architects to work with daylight in building design. But this degree of freedom will raise the price, reduce the total area of the PV-cells in the window and hence reduce the electricity output of the PV-window. Therefore this has to be made as an additional choice to the standard PV-pane. The design of the PV-window must reflect the desire for daylight distribution and the electricity production. Figure 1 illustrates some of the degrees of freedom in placement and carving of the PV-cells in the pane.


Figure 1. An illustration of different possibilities in placing the PV-cells in the pane.