Category Archives: EuroSun2008-4

PV Park system results

Подпись: Month Fig. 5. PV park system - Monthly average of the daily energy produced, per installed peak power.
Fig. 5 presents the values of the monthly averages of the daily energy produced in the park, per installed peak power. This system produces more energy in summer periods with a maximum average daily production of 34.8 kWh at July 2006 and July 2007. The production minimum occurred at December 2007 with a daily average production of 11.1 kWh.

At Table 4 we present the yearly irradiation and energy produced by PV Park system. The yearly irradiation measured, in the 15° tilted surface, is about 1 790 kW/m2 each year and the energy production is about 1 400 kWh per kW of peak power installed. The low production in 2006 year, despite the bigger irradiation, is due to an inverter failure during two weeks in the month of May.

Table 4. Yearly energy produced by PV park system, per installed peak power

Year

Power

Irradiation

Production

(kW)

(kWh/m2)

(kWh/kW)

2006

6.00

1 799

1 366

2007

6.00

1 781

1 407

This results show that the energy production by installed peak power of the facade system is about

28.6 % lower than for the park system, this is due mainly to the lower incident irradiation on the facade surface.

Phase change materials

Systems that use Phase Change Materials (PCM) can be used to store energy. All substances store energy when their temperature changes, but when a phase change occurs in a substance, the energy stored is higher. Furthermore, heat storage and recovery occur isothermally, which makes them ideal for space heating /cooling applications.

3.8 Colour of exterior surfaces

A light colour of surfaces is an effective solution to reduce unwanted solar gains. The quantity of radiation that is absorbed by a surface depends on its colour. Light colours are effective in reducing cooling loads, whereas dark ones are more appropriate to absorb heat in thermal storage.

3. The Portuguese Passivhaus proposal

This section presents a prototype Passivhaus proposal for Portugal. Detailed results from parametric analysis as well as the other partner’s proposals for the UK, Spain, Italy and France are available in the technical guidelines produced in the project. [6]

3.1 Concept

Подпись: Fig. 1. Prototype of the Passivhaus in Portugal.

The Portuguese Passivhaus proposal is a two-bedroom house which complies with the national building thermal regulation 2006 (RCCTE, DL 80/2006). The prototype avoids imposing a specific layout allowing the architects the freedom of design. The strategies applicable to the Passivehaus proposal were adapted to the Portuguese context, in particular those regarding the cooling season. Special care was taken to adopt commonly-used building practices to avoid an increase of the overall cost and to ease the procurement and its implementation. The current proposal, with a total useful area of 110 m2, takes into account the local climate (case study for Lisbon). It relies initially on passive strategies complemented with simple active systems, if required. Three main aspects are explored in the proposed house: relation with the sun, ventilation for cooling and high thermal mass to control temperature swings.

Building Description

A typical small 3-storey office with a total floor area of 4200m2 was modelled in the Energy Efficiency Measure module of RETScreen [14] with the TMY weather data used in the TRNSYS simulations. This software is meant for pre-feasibility studies, but it was used in this case to easily compare the building space heating and cooling energy requirements of the different scenarios and avoid the complexity of multi-zone building simulation tools. The building lighting, equipment and appliances load, occupant density, natural air infiltration, ventilation rates and schedules were set to typical values for small office buildings [15]. The windows on all the non south-facing facades

were assumed to be fixed, low-e, triple-glazed and to have an overall U-value and SHGC of 1.57 W/m2oC and 0.27, respectively. The percentage of fenestration was set to 20% on the north wall and 40% on the east and west facades. The other building envelope properties for each city were selected to fulfil the minimum requirements of the Model National Energy Code for buildings (MNECB) [16] with oil selected as the principal heating source for Iqaluit and Yellowknife. The substitution of spandrel panels with multi-glazing BIPV systems was considered to have negligible effect on the lighting load.

User oriented energy assessment of classified facade systems

Подпись: Fig. 2. Comparison of three differents facades in terms of primary energy

A user of the evaluation system can find the stored energy data of any fa? ade system he is interested in by an EXCEL tool. Figure 2 shows an example with the the comparison of three different fa? ade systems in terms of primary energy for heating, cooling, ventilation, and lighting.

By the comparison of different facade systems the energetic advantages and disadvantages of morphological variations of the facades can be found easily. In order to combine the evaluation aspect of primary energy with other aspects, like e. g. embodied energy, in an overalll evaluation, the

Подпись:
transformation of energetical data into marks can be helpful. Another way of cumulation are life-cycle balances. Figure 3 shows an example for the comparison of three fa? ade systems in terms of grades / marks on a scale from 1 (low grading) and 5 (high grading). The evaluation system offers a special EXCEL tool for calculating the embodied energy, based on tables with specific values for the most common building materials.

Hourly thermal simulation

The hourly building thermal behaviour was simulated with the soft SIMEDIF for Windows, a code developed at INENCO and widely used in Argentina [3, 4]. SIMEDIF needs the building to be divided into thermal zones, that are represented by an air node with a single temperature, whose temporal evolution is determined by using the building data, materials, location, orientation, connections with other zones and climatic conditions. The zones can be connected to each other and with the outdoors by pre-defined elements, that can store and transfer heat by conduction and convection (radiation is linearized). An energy balance is performed at each node for which the temperature is to be determined. In this global balance equation, the air renewals in the room, inner

image421

heat gains, and heat transfer due to the different elements connecting the room with other zones in the building and with outdoors, are considered. More details can be found in [3].

Подпись: Fig. 3. Thermal zoning of Health and Development Sectors.

The thermal zones for Development and Health Sectors are shown in Fig. 3. The Health Sector was divided in eight thermal zones (access, South corridor, North corridor, doctors offices 1 to 3, bathrooms, doctors offices 4 and 5, laboratory and meeting room) and the Development Sector in six thermal zones (kindergarten, services, corridor, deposit, social assistant office, and classrooms). The building was simulated under a non occupancy schedule, for typical winter and summer days.

The meteorological data were obtained from Table 1 and the hourly temperature and solar irradiance was automatically calculated by SIMEDIF from mean daily values. The solar absortances were fixed in 0.3 for external wall surfaces (light colour painting) and 0.7 for external roof surfaces (dark red painting).

BALL light

The BALL light is designed as an affordable lighting solution for households in rural areas of Madagascar. The product price had to be low and the specific needs of the Malagasy users were to be taken into account. An interesting finding was that the future users indicated that the bigger the solar panel, the better the product would be for them. Other people could see better that they use PV solar energy because a it would be more visible with a big solar panel.

The BALL Light is powered via a separate PV panel. The decision to use a separate PV panel was based on the use context. A separate panel would be installed outside on the roof and proper charging of the product’s battery could be ensured. BALL Light is cheaper than other products offered for the same function. It is dimmable and can be used on the table, hanging from the ceiling, as a night-light and as an orientation light outside.

A prototype was made and as a follow up of the project, further detailing takes place in oder to take it into production.

Fig. 6. BALL light on table (left) and PV panel on roof (right)

Experience from Projects

None of the projects would be satisfying operational without detailed support and optimisation in the beginning over a period of 3 to 6 month. The supervision and adjustment of set points and flow rates has significant impact on the performance and is even for experienced people difficult to foresee.

All of the plants have proven to operate reliably. The Cooling machines achieve the COP detailed in the manufacturers’ specifications during constant operation. Low return temperatures from the cooling tower often allowed a lower flow temperature from the solar plant to be used to drive the cooling machine than that specified by the manufacturers.

The offset between maximum solar radiation and the maximum cooling requirement is approx. 2-3 hrs and can be easily covered using the buffer tank.

The efficiency of conventional flat plate collectors, as used for warm water production is noticeably reduced in this application. Flow temperatures up to 100°C on the primary side of the heat exchanger, result in a lowering of the collector efficiency curve. In large plants it is also important to balance the collector hydraulics.

In the last projects, we used a dramatically improved large area flat plate collector, which in the required temperature range collects approx. 20-30% more solar energy. The economy of the entire concept is thereby much improved. This collector has just passed certification and actually is ahead of not only flat panels, but as well significantly better performing than vacuum tubes at temperatures of 100° C. Practical experiences show we can reach solar gains of app. 750 kWh/m2 in the Arizona project on a mean temperature level for collector operation of 80 to 90°C.

The modifications to the collector include more measures towards reducing the heat loss: a Teflon sheet above the absorber plate reduces top losses, increased insulation in the rear panel and an especially airtight frame also improve performance. These new collectors also offer potential for application in district heating and process heat.

The cooling load can often be entirely covered by the solar plant when we have availability of space for solar panels — particularly on sunny days. The back up is only required on days with little solar radiation. However, the peak electricity demands on the mains supply and distribution network due to cooling requirements don’t generally occur on these days.

Absorptions chillers have proven to be really stable. Not only mishandling though local personal never affected them seriously, I actually found chillers in operation since more than 70 years that are still operating sufficiently.

Diagramm 7 shows average solar gain per day used for cooling (blue column) and
heating (red) in DOC project in Arizona.

Contribution of Solar Thermal Systems to building energy. performance — comparison of Portuguese methodology with European

Standard EN 15316 (part 4-3)

Maria Joao Carvalho ^ and Ana Neves 1

1 INETI, Department of Renewable Energies, Campus do Lumiar do INETI, 1649-038 Lisbon, Portugal
* Corresponding Author, mioao. carvalho@ineti. pt

Abstract

In the frame of European Directive for Energy Performance in Buildings, EU Directive 2002/91/CE, Portugal produced legislation transposing the EU Directive and imposing the usage of thermal solar systems for hot water preparation. The energy necessary for the preparation of hot water constitutes one of the terms for evaluation of energy performance of the building. The calculation methodology is incorporated in a software tool developed by INETI and called SolTerm. At the end of 2007, CEN also published a set of standards, EN 15316, covering “Heating systems in buildings and methodologies for calculation of system energy requirements and system efficiencies”. In this set of standards, part 4-3 is dedicated to Thermal Solar Systems and introduces a calculation methodology for determination of the energy delivered by a thermal solar system. The present work compares the results of both methodologies and shows that the difference between the two methodologies is mainly dependent on collector efficiency parameters, due to the limits of application of the methodology of EN 15316, based on f-chart method.

Keywords: thermal solar systems, hot water preparation, heat delivered, building energy performance.

1. Introduction

In the frame of European Directive for Energy Performance in Buildings (EPBD), EU Directive 2002/91/CE, Portugal produced legislation transposing the EU Directive. This legislation went in force in April 2006 and included a Solar Thermal Obligation. This obligation is present in the new Portuguese Thermal Performance Building Code (RCCTE) [1], imposing the usage of thermal solar systems for hot water preparation if there are favourable conditions of exposure (if the roof or cover runs between SE and SW without significant obstructions) in a base of 1m2 per person (that can be reduced up to 50%, in certain conditions).

In the Portuguese legislation, 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.

This term takes into account the positive contribution of the use of a thermal solar system for hot water preparation. To take this into account it was necessary to establish a calculation methodology for the energy delivered by the thermal solar system. This methodology is incorporated in a software tool developed by INETI and called SolTerm [2].

At the end of 2007, CEN also published a set of standards, EN 15316 [3], covering “Heating systems in buildings and methodologies for calculation of system energy requirements and system

efficiencies”. In this set of standards, part 4-3 is dedicated to thermal solar systems and introduces a calculation methodology for determination of the energy delivered by the solar system.

The present work compares the results of both methodologies and establishes the conditions in which it is possible to consider that they give an equivalent input to the calculation of energy needed for hot water preparation and the energy performance of the building.

In Section 2, a short description of both calculation methodologies is presented. Section 3. highlights the specific aspects of the Portuguese legislation that are relevant for the calculation of the energy contribution of the thermal solar system to the building energy performance. The results of calculations made for different situations are presented in section 4. Final conclusions are presented in section 5.

Advantages of the collector and possible applications

The described semi-transparent collector is a multifunctional architectural design element. This offers a new market potential for solar thermal energy use. At a certain distance the structure of the small openings appears as a homogeneous semi-transparent area with the silhouette of the channels. This offers interesting possibilities in design: straight vertical or horizontal channel arrangements as well as curved designs such as in a FracTherm® absorber [5] can be realized if roll-bonding or another production method with similar flexibility is used.

Подпись: Fig. 9: Semi-transparent absorber integrated into a balcony balustrade

Office buildings often feature large glazed fa? ade areas and need appropriate devices for solar control and glare protection. Moreover, cooling becomes more and more important. Provided that the collector efficiency and thus the temperatures will be high enough, it will be possible to use them to drive a solar cooling system. This could also be done floor by floor, since the collectors are nearby the room with the cooling load. The collectors can also be used in hotels, hospitals or sanatoria where both an effective solar control and a high amount of domestic hot water as well as heating water are needed. A special application is shown in Fig. 9, where the semi-transparent absorber is integrated into a balcony balustrade with the insulated flow and return pipes covered by a stainless steel handrail.

4. Outlook

The multifunctional collector is still in an early stage of research and development. The necessary work will be carried out as part of a large European research project together with industry partners.

The main challenges will be the following:

• maximization of the absorber efficiency (efficiency factor F’ and insulation of the collector, which is also necessary in order to prevent the room from overheating)

• characterization and optimization of the collector as a classical solar collector (incidence angle modifier IAM, collector efficiency curve)

• characterization and optimization of the collector as a window-like element providing solar control, glare protection, transparency and daylighting (angular-dependent g-value, U-value and transparency)

• fa? ade integration regarding dimensions, aesthetics, connection of tubes including insulation

• feasibility of absorber constructions — especially the production of the openings and coating — including economical aspects

5. Conclusion

This paper describes a multifunctional semi-transparent fa? ade collector which allows using solar energy to heat a fluid and simultaneously acts as a building element which provides solar control, glare protection, transparency and daylighting. It has been shown that the relation between the aforementioned properties can be adjusted to the specifications of an individual application by geometry and coating. The new collector is both an “active” and a “passive” architectural element which needs to be characterized and optimized with respect to its various functions. This work will be done within a European research project together with industry partners.

6. Acknowledgement

The contract for the European research project was not yet signed when this paper was written. This is the reason why the project partners are not mentioned by name. The consortium applied for the project in the call FP7-NMP-2007-LARGE-1 within the Seventh Research Framework Programme (FP7) of the European Commission.

References

[1] T. E. Kuhn, “Solar control: A general evaluation method for facades with venetian blinds or other solar control systems” Energy and Buildings, Vol 38, Issue 6, pp. 648-660, June 2006. http://dx. doi. ora/10.1016/i. enbuild.2005.10.002

[2] T. E. Kuhn, “Solar control: Comparison of two new systems with the state of the art on the basis of a new general evaluation method for facades with venetian blinds or other solar control systems”, Energy and Buildings, Vol 38, Issue 6, pp. 661-672, 2006. http://dx. doi. ora/10.1016/i. enbuild.2005.10.001

[3] I. Bergmann, W. Weifl, Fassadenintegration von thermischen Sonnenkollektoren ohne Hinterluftung, Berichte aus Energie — und Umweltforschung, 13/2002

[4]Facade-Integrated Thermal Solar Installations (2001), System and building physics fundamentals and implementation of results within the subprogram "Building of Tomorrow", Forschungsforum 3/2001, Publisher: BMVIT, http://www. nachhaltigwirtschaften. at/nw pdf/fofo/fofo3 01 en. pdf

[5]M. Hermann, FracTherm — Fractal hydraulic structures for energy efficient solar absorbers and other heat exchangers. Proceedings, EuroSun 2004, Freiburg, Germany, 20-23 June 2004, Volume 1, pp. 332-338

[6]M. Hermann, (2005). Bionische Ansatze zur Entwicklung energieeffizienter Fluidsysteme fur den Warmetransport. Dissertation, Faculty of Mechanical Engineering, Universitat Karlsruhe (TH)

[7]M. Rommel, V. Wittwer, R. Blessing (1993), The Window-Technology Collector: A new type of flat-plate collector, Proceedings of the ISES Solar World Congress in Budapest, 23-27 August, 1993.

Calculation assumptions

The reflectivity of walls, ground and ceiling are respectively 0.75, 0.45 and 0.75.

The Lighting French Association recommands an illuminance level of 300 lux in a typical office

[4] . In this study, the value of acceptable illuminance level has been set to 300 lux. To quantify the mean daylight autonomy in the room, the room has been divided into three equal strips (see Figure 3). The illuminance level is supposed to be the worst in the middle strip. For this reason, we will focus on this specific zone.

3. Results and discussion

This section presents some preliminary results of the study to determine a combination between the solar shading and daylighting in buildings.