Category Archives: EuroSun2008-4

Optical and thermal properties of functional coatings for future high performance windows

A. M. Nilsson1* and A. Roos1

1 Uppsala University, Department of Engineering Sciences, The Angstrom Laboratory, Uppsala, Sweden
* Corresponding Author, Annica. Nilsson@Angstrom. uu. se

Abstract

With modern society facing the task of reducing energy consumption in all areas of life, modern windows provide an enormous potential to reduce energy consumption for the heating, cooling and lighting of buildings. For future buildings and for the retrofitting of older buildings the window is more and more becoming an integral part of the building’s energy system. In this paper we present the optical properties for a selection of different window coatings and discuss their impact on the performance of the window. Special emphasis is put on switchable glazing. Optimum performance for switchable glazing is often a trade off between minimum energy consumption for cooling heating and lighting. This can sometimes be in conflict with occupancy preferences. As an example we show how different control strategies for electrochromic windows can influence the energy balance of the window, and that small variations in the control algorithm can lead to improvements. The results were obtained by using the WinSel window simulation tool.

Keywords: Switchable glazing, control strategies, energy balance calculations

1. Introduction

As a reaction to climate change and depletion of energy resources the EU has declared energy efficiency as one of the top priority issues of the political agenda. In the “Action plan for energy efficiency” the European Commission has recognised that the largest cost effective savings potential lies in the residential and commercial building sectors. Thus, the demanding goal recently set by the member states is to save 20% (compared to the level of 2005) of the overall energy consumption in the building sector by the year 2020. Today buildings account for about 40% of the European energy consumption and in 2002 the European Commission published an EU Directive on the energy performance of buildings. Moreover, all member states must introduce an energy performance certification system for buildings, which should be implemented already by the end of 2008. The directive emphasizes the importance of energy efficiency in buildings and requires that new production and major refurbishments meet minimum standard for energy performance. It is important that the standard includes renovations of the current building stock in addition to new construction. The majority of buildings will still predate the standards, but substituting old building components with more energy efficient ones can still provide significant energy savings.

The window is perhaps the single building component with the highest impact on the energy performance, and window technology has undergone major improvements over the past 20 years, transferring the window from an energy-drain to a possible resource in the energy supply system. The development can mainly be attributed to the improvements in large area glass coating technology, making it possible to design low emissivity (low-e) glazing with different solar transmittance. Low emissivity is necessary for obtaining a low thermal transmittance (U-value), i. e. a low heat transfer through the window. This is, together with a high solar transmittance, especially

important in heating dominated climates. To avoid overheating and reduce the energy needed for air conditioning on the other hand, the solar transmittance should be minimized for cooling dominated climates. [1]

The most recent advancement in window coating technology is electrochromic coatings [2,3]. These switch between a bleached, highly transparent, state and a dark, absorbing, state, when a low electric voltage is applied across the switchable coating. Previous simulation studies have shown that, compared to static low-e coatings, significant energy savings can be obtained with variable transmittance glazing [4-6]. When designing the electrochromic control strategy it is important that both energy and daylighting issues are considered in order to avoid glare and reduce electric lighting use, while energy consumption for both heating and cooling is minimized.

In this study, we have used the WinSel window energy balance simulation tool to estimate possible energy saving potentials when an electrochromic window is controlled with four different strategies for energy-efficiency and daylighting [7,8]. The simulations were performed for three locations, Stockholm, Brussels, and Rome, with two static solar control coatings as references. The objective has not been to develop the “best” control strategy, but to illustrate the complexity of the problem and to give some insight into what possibilities these coatings offer. The objective was also to show that useful results can be obtained using a simple window energy balance simulation tool without having to perform detailed building simulations.

2. Background

Designing and Rating a Tritherm Solar Ejector System for. Residential Cooling. An Energetic and Exergetic Evaluation

A. Hemidi*, J. M. Seynhaeve, Y. Bartosiewicz

Universite catholique de Louvain UCL, Ecole Polytechnique de Louvain, Mechanical Engineering

Department, TERM Division,

Place du Levant 2, B-1348, Louvain-la-Neuve, Belgium.

* Email: amel. hemidi@uclouvain. be, Tel: +32 10 47 22 01, Fax: +32 10 45 26 92

Abstract

The PROFESSI project aims at optimizing an Ejector Air-Conditioning System (EACS). This paper presents a detailed rating modeling of this system. This model can predict the EACS performances when this system is submitted to climatic conditions changes. The effect of a subcooler integration is studied as well. It was concluded that the subcooler must be bypassed when the external temperature goes beyond a critical temperature. Before this threshold, the subcooler improves the COP and cooling capacity. Moreover, a solution is proposed in order to keep the operation of the system even at off-design condition through the use of a regulator heat- exchanger. An exergetic analysis allowed valorising the use of low grade energy for the EACS by comparing performances with a conventional vapor compression system.

Keywords: ejector air conditioning system, sizing, rating, exergy analysis.

1. Introduction

High electricity consumption and use of fluids with high Global Warming and Ozone Depletion Potentials are imputed to the air-conditioning, based on vapor compression systems. For energy saving and environmental protection issues, the solar ejector air-conditioning system (EACS) is mainly investigated in the research field to overcome these drawbacks. An EACS is composed of six main devices (fig. 1): the generator, the evaporator, the condenser, the pump, the throttling valve and the ejector. The generator is fed with the solar energy. The primary flow at high pressure Pg (generator) entrains the secondary flow at low pressure Pe (evaporator) within the ejector. Both

streams are mixed and compressed downstream out of the ejector to a backpressure Pc imposed by the condenser. The primary flow rate returns to the generator with the pump and the secondary expands through the throttling valve and goes back to the evaporator, where the cooling effect is achieved. In the foreseen bench, fraction a of mw is extracted from the generator to perform a

superheat. This system could be integrated into a combined domestic hot water/heating system, to use the extra power supplied by the solar collectors during summer. Several researchers carried out a rating study of the EACS, to determine performances according to given external and saturated temperatures [1,2]. An exergy analysis of the EACS was carried out by [3] to establish a distribution of losses due to the irreversibilities in the cycle.

A sizing program was developed to design the overall EACS and to choice the most appropriate refrigerant [4]. This paper is focused on the rating model, which consists in evaluating and predicting the performances of the chosen cycle under different climatic conditions. All the thermodynamic conditions at the refrigerant side are computed thanks to a detailed mathematical procedure for the heat exchangers and the ejector. Those sizing and rating program modules are

written in FORTRAN and coupled with the REFPROP/NIST routines. An exergetic analysis is proposed to compare performances of the EACS with a conventional vapor compression system in order to valorise the use of low grade energy. For this study, the refrigerant is the propane.

image201

Fig. 1: An Ejector Air Conditioning System. Subscripts: w: water, r: refrigerant, e: evaporator, g: generator,

c: condenser, ej: ejector, sup: superheater, i: inlet.

Operational Experience

Due to delays during the construction of the building, partly caused by the cold winter in 2005, the commissioning of the building had to be done under operating conditions. Immediately after the commissioning the extreme complexity of the requirements for the building controls were observed. Caused by the desired interrelations of the energy fluxes — the waste heat of the chillers for example can be used to heat the building — many conditions have to be accounted for the control strategy. Thereby it was barely possible for the manufacturer of the measurement and control system to use standard components for programming the controllers. A great part of the control strategy had to be programmed without a template. Since there was no time for extensive testing, especially under changing conditions in spring and autumn, the malfunctions have to be corrected during normal operation.

Very soon it became obvious, that the installed cooling power, which was provided only by the absorption chiller, was not sufficient. In the technical plans an additional compression chiller was considered which was not assembled in the beginning because of the stringency of the energy

concept. Furthermore, the absorption chiller did not achieve its designated performance. The inspection of the flow rates showed a lack of flow in the re-cooling unit of the chiller.

In spring 2006 a compression chiller with a capacity of 50 kW for peak load and backup was installed. The cooling tower had been already designed for this additional load. Hence no retrofitting was necessary for the re-cooling. Also the pumps in the re-cooling circuit of the absorption chiller were reinforced. The required flow rate was now reached in this part of the system too.

Integration of Photovoltaic Panels in Portuguese High Schools: Feasibility Study

G. Carrilho da Graca1,2*, A. Augusto1, M. Lerer2

University of Lisbon, DEGGE. 2NaturalWorks, Lisbon.
Corresponding Author: gcg@natural-works. com

Abstract

The Portuguese education ministry is in the process of modernizing the country’s high schools. The first phase of this operation comprises 172 buildings that will be rehabilitated and expanded. This initiative aims to improve indoor comfort in the schools (lighting, acoustics, ventilation and thermal comfort) as well as the environmental/energetic performance of the buildings [1]. This large rehabilitation effort coincides with the recent transposition (04/2006) of the 2002/91/CE directive on the energy performance of buildings. This study evaluates the possibility of integrating photovoltaic solar panels (PV) on the school roofs, creating a distributed renewable electrical energy production system. The expected PV generated electricity and the resultant reduction in CO2 equivalent emissions are estimated. Electrical production and avoided emissions will range between 20 and 31GWh/year, and 7 to 11 MtonCO2 /year, depending on the area of the system. The reduction in the net electrical energy consumption of the schools can exceed 60%.

Keywords: photovoltaic, integration, emissions

1. Introduction

Most of the electricity consumed in Portugal is produced in large power stations (thermal, hydro) usually located far from the demand, resulting in relevant power losses in the grid (around 10%). The existing energy infrastructure must be improved to meet increased demand with reduced emissions. In this scenario distributed renewable electrical energy production systems are attractive, reducing power losses in the grid and decreasing dependance on fossil fuel. As expected, most of the portuguese high schools are integrated in populated areas and have large roof to floor area ratios (0.2-0.3), making them suitable to PV integration in the roofs. Integration of renewable energy systems in schools is also important from an educational perspective as the systems become part of the daily life of the students.

This large school rehabilitation effort coincides with the recent transposition (04/2006) [2][3][4] of the 2002/91/CE [5] directive on the energy performance of buildings. This new legislation imposes limits on primary energy consumption as well as thermal comfort standards. As in most working environments, improved thermal conditions should also improve the performance of students and teachers. Still, as most schools currently have limited or no climate control systems and poor ventilation, the introduction of ventilation and air conditioning systems will result in increased energy costs. In this context the PV system may have the additional advantage of reducing the energy bills that schools will be faced with after the renewal process.

In order to evaluate the feasibility of this system we will answer the following questions:

• What is the area available for solar energy collection (roof area)

• What is the cost and payback of the PV systems

• What is the the impact in the electrical energy demand of the schools

• What is the reduction in overall Portuguese CO2 emissions.

Selective And Switching Window Coatings For Cooling And Daylighting In Tropical Climate

C. U. Okujagu 1* and C. E. Okeke 2

department of Physics University of Port Harcourt, P. M.B 5323 Port Harcourt Nigeria.
department of Physics and Astronomy University of Nigeria Nsukka.

* Corresponding Author: info@okuiagu. com

Abstract

Overheating of the interior of building with highly glazed faqade can cause discomfort to persons living and working in such buildings in tropical climate. Solar and thermal control in buildings can be achieved either by conventional air conditioning or by non-conventional architectural and ventilation methods or by innovative switchable or selective glazing systems. Switchable and selective single layer thin films can offer a technically one-step option for the reduction of indoor temperature and maintenance of an acceptable luminous (daylighting) level within the building thereby creating both thermal and visual comfort within the building. Photo-optical and selectivity properties of Iron (Fe), Tin (Sn) and Manganese (Mn) Halide films show that these films are highly reflecting in the Near infrared (NIR), transmuting in the visible (VIS) while absorbing in the near ultraviolet (NUV). Hence the films act as optical shutters to both UV and IR radiations which could raise the indoor temperature of the buildings, while it is highly transmutting in the visible region and therefore can maintain acceptable level of daylight (luminosity) within the building. This will create comfortable indoor environment and could serve as Natural Air — Condition coating for buildings and cars.

Introduction

Solar radiation that is transmitted into buildings with highly glazed facade can lead to overheating of buildings interiors causing great discomfort to persons living and working in such buildings, especially in tropical (hot and humid) climate and an increase in energy demand for heating/cooling of such buildings [1-2]. Under such condition, the issues of Solar — thermal control for indoor thermal/visual comfort and energy efficiency for the building becomes very crucial [3-5]. Many researchers have suggested and developed various methods for creating comfort and /or reducing energy cost in such environment.

These solutions include the use of;

Conventional air conditioning and water cooling methods to reduce indoor thermal level. This method has a disadvantage of increasing energy consumption and hence cost.

Non-conventional approaches which incorporate heat reduction techniques into the architectural design and orientation of buildings (Solar Buildings), thus allowing the glazing to admit far less solar heat and glare into the building [5-10]. This may lead to complicated and sophisticated architectural/constructional technicalities and increased cost as well.

Various shading and ventilation devices such as blinds and louvers which may be fixed or motorized, natural or mechanical and passive or active/dynamic; all aimed at improving indoor thermal and visual comfort and contributing to the energy saving schemes[5-12]. Such

technologies will definitely lead to increased cost. In addition, the system may suffer from wear due to extreme metrological conditions and can also lead to overheating when they are poorly installed.

Double skinned facades supply air windows and solar chimneys of various designs to circulate air or to create an insulating air layer that is aimed at improving ventilation, solar shading and daylighting levels in buildings [12-30]. This will automatically raise the cost of achieving thermal comfort in the buildings.

Hybrid systems which combine a number of architectural designs and shading devices to create conducive indoor environment [17-31]. This approach is very cumbersome and may be complicated and expensive.

Although these methods have recorded various degrees of successes in reducing indoor temperature to appreciable limits, some of them actually cause reduction in daylighting levels in the buildings there by introducing another dimension into the problem of visual comfort. To redress this, effort has to be made to improve the daylighting level, thus leading to complicated architectural designs, sophisticated daylighting technologies and hybridization schemes that will definitely increase cost in most cases [32-41]. This means that conventional high performance glazing cannot fulfill the entire requirement concerning energy saving and improved indoor comfort. Therefore innovative solutions for glazing systems and transparent facades have to be developed in order to achieve the objective of thermal/visual comfort as well as energy efficiency and cost reduction. Up till the present, the main approaches that have been suggested, developed and manufactured in commercial quantities are: [7, 43-47].

Sun Protection Glasses (SPG’s).

Single and Multilayer Inorganic/Metellic Coatings.

Organically coated glasses and Plastics.

These glazing system and coatings act as either solar thermal control devices with static/fixed properties which are incapable of adjusting their properties according to the variable demands on heating, cooling and lighting load in a building apartment. For example, a low emittance (thermal control) coating is adequate during winter in reducing thermal losses, but will cause overheating in summer. On the other hand, solar control coating may be adequate for offering cooling comfort in summer, but may cause excessive heat loss in winter. In addition to this delimitation, some of these system may cut of vital wavelength for better visual comfort, hence effort has to be made to incorporate day lighting equipment (light guides) into the building which will increase the cost for the building [40-42].

Another highly innovative glazing approach is the use of chromic/tropic coatings with dynamic properties to achieve switchable/adjustable characteristics within a single glazing system [48-58]. These glazing systems are the so called “smart windows” which have gained popularity within the last few decades but which have not really hit the market stand in large commercial quantities [7]. Nevertheless, these innovative glasses seem to hold the future for transparent facades because they are not produced as external attachments to the glazing and facades systems but are integrated with the glazing itself as external coating on the glass, to achieve variable transmittance without the use of any control devices. Thus the glazing change their characteristic color (chromic) or transmission/reflection/scattering (tropic) properties in response to a critical temperature or luminosity transition values.

The different types of switchable coatings are:

Chromogenic glasses; [49-54, 56-58]. These change their color (from light to dark or vise versa) at predetermined critical transition temperature (thermochromic) or luminosity (photochromic) or electronic/ionic transition (electrochromic).

Tropogenic Glasses; [48, 58] These change their optical

(transmission/reflection)(scattering) properties (from highly transmutting to highly reflecting or from highly absorbing to highly transmutting) at certain predetermined critical transition temperature (thermotropic) or luminousity (phototropic) or electron transition (electrotropic). The production of smart windows with appropriate chromic (color) and tropic (transmission) characteristic require some sophisticated deposition or coating techniques which are expensive. Hence the product in the market so far has not reached optimum performance due to soaring production coast [7, 43]. As the search for these and other products for glazing and facade applications intensify, it is also pertinent to look at other products (coatings) which can be used to achieve reduction of indoor temperature and create comfortable daylighting level as well a cost reduction on heating/cooling and which can be produced with simple (complicated) technology.

This work is therefore a contribution to the search for such coatings and glazing systems and materials.

Thermal characteristics

3.1 Thermal insulation

Both layers of the double facade have specific parameters of thermal insulation. The value of the thermal coefficient (U) of the double facade as a whole cannot be precisely determined, because it is not a constant. Schuco, one of the producers of glass double facades, commissioned a study on how the impact of sun radiation affects the facade’s heat permeability [5]. This research was carried out in winter, when the value of this coefficient is important for the building’s demand for heating energy. It follows from the study that during periods of intensive radiation of the sun this coefficient can even double. When there is no intensive sun operation, the improvement in this coefficient is slight. Facades facing north lead to no noticeable thermal gains. The facade’s thermal effectiveness is therefore greatly dependent on climatic conditions, orientation with respect to the sun and possible shading from the surrounding buildings. Thermal gains from sun radiation can only be achieved from facades exposed to the sun — southern and to less extent south-eastern and south-western.

The estimated average data for sun radiation falling on double facade was used to calculate the mean value of its thermal coefficient. For the wall in question, with open ventilation ducts, this value was 20% lower than for the internal double-pane wall. Temperature readings from the inter­facade area showed that it was about 10°C higher that the external temperature under intensive sun radiation and some 2°C higher under slight sun operation. The closing of ventilation flaps reduces the U (k) coefficient by 30%.

A study of the double facade in the office building of Stadttor in Dusseldorf (designed by Petzinka and Partners) points to an even more advantageous influence of an additional layer of glass for the thermal coefficient for the whole building [7]. This coefficient for the external layer is rated at 1,5W/m2K. When ventilation flaps are closed in the external wall, the value of U coefficient falls to 1,0W/m2K, which leads to favourable temperatures of the internal wall when compared to room temperatures on cold days [7].

Measures to reach the target of 75% energy reduction

Starting from the middle bar in figure 1, the question is how to further reduce the primary energy consumption of a dwelling, in particular the (net) electricity consumption. Following the Kyoto pyramid, the three steps to reduce energy consumption are (in this order): 1) reducing energy demand, 2) application of renewable energy and 3) efficient use of fossil energy. Let’s explore how far we can
go in each step. In relation to the renovation concepts, building related measures are of particular interest.

Solarch.-Vision

Solarch.-Vision is a perspective, plan or etc. diagram which shows the situation of the building skin under the kind/unkind faces of the sun. It brings a brand new vision to the architects, urban designers and landscape architects to discover the advantage/disadvantage of decisions about kind/unkind faces of the sun in each location through the design process.

By selecting a city from the list or entering the available data of a location such as latitude, elevation, turbidity, monthly average of min. and max. temperatures, the architect could define the building site. As the codes of Solarch.-Vision(by author #1) has been developed on MAXScript(the built-in scripting language for 3ds Max and Autodesk VIZ.), it is easy for the architect to use 3dsMax or any other CAD software to model everything needed. Next the architect would set up the date and time definition of analysis, and by selecting the cameras it is possible to observe an extraordinary solar diagram.

image170

Fig. 7. Yearly Solarch.-Vision of building complex in Tabas(left), Shiraz(middle) and Hamedan(right)

image171

Fig. 8. The situation palette from red(in undesirable shade/shine) to blue (in desirable shade/shine)

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Fig. 9. Solarch.-Vision in summer(left) and winter(right)

10th October, Lisbon — Portugal *

Подпись: Delete | Подпись: Hide Diagonal Edges

North Direction: 0.0 t

Подпись: + solarch Vision

Sky Radius (km):

1150000000.0

Sky Origin:

Fig. 10. Solarch.-Vision rollouts in Autodesk 3ds Max

1. Conclusion

The method and software described in this article will help architects, urban designers and landscape architects of the world to design better with the sun in the early next years; but still there are many problems that a proper architecture must solve.

References

[1] Samimi Mojtaba, “Thesis: From the Sun to the Architect”, Library of the Faculty of Architecture and Urban Planning, Shahid Beheshti University, Tehran, 2007.

[2] Samimi Mojtaba, Parvizsedghy Laya, Adib Morteza, “A New Approach for Solar Analysis of Buildings”, SERP, WORLDCOMP’08, Nevada, 2008.

[3] Remund J, Kunz S., “METEONORM”, Bern METEOTEST, Fabrikstrasse, 2003.

[4] Tahbaz Mansore, “The Sun and Building Orientation”, Library of the School of Architecture, Shahid Beheshti University, Tehran, 1983.

[5] Olgyay Victor, Olgyay Aledar, “Solar Control & Shading Devices”, Princeton University Press,

image176Princeton N. Y., 1976.

Suitability Tests

Commercially available single-component and composite microstructured films are supplied for testing by industry partners. Single component films are manufactured by compression molding of thermoplastic polymers (acrylic, polycarbonate, etc.) in a thickness down to 0.4 mm and are commonly used for the fabrication of large format optical components. Composite films, which consist of a UV-cured acrylic resin coated on a polyester substrate, are much thinner (0.1-0.25 mm) and mainly used as brightness enhancement films for liquid crystal displays. Unstructured films made of the same materials and with similar thickness are tested as well, to separately evaluate the effects of microstructuring on the results.

Our investigations focus on the optical properties of the products, which are responsible for the energy performance of the glazing, and on their suitability for the application as middle layer suspended inside an insulating glass unit.

Topics and Methodology

In coporation with the Institute of Thermal Engineering at the Graz University of Technology arsenal research applied expert tools in order to support the ENERGYbase planning team by providing scientific expertise. Herewith the energy performance of ENERGYbase office building has been considered and analysed in an early phase of the planning procedure and additionally some important advises and analysis in order to optimise the energy system performance were

developed and conducted. The scientific support actvities were based on using simulation expert tools and were mainly focused on following emphasis:

• Scientific support of an integrative planning procedure:

Challenging is both the complexity of planning and the integration of non-standard technologies and systems in such a building project. Therefore an integrative planning approach has been applied in order to achieve the ambitious ENERGYbase project targets by involving scientific energy experts in the communication process from the beginning on. arsenal research as a centre of excellence for sustainable buildings and energy systems has scientifically supported the planning team and did essential contribution and advice in time, especially related to the HVAC concept and renewable energy systems. The scientific support was mainly based on operating expert tools — like transient building an system simulation and computational fluid dynamics CFD (2)- and herewith generated results and their comprehensive analysis and intepretation have been presented and discussed on project planning meetings.

• Assessment of the energy and thermal building performance:

The overall ENERGYbase concept meaning both the architectural and energy system design aims to achieve high values of energy efficiency, to use of renewable energy sources and to provide an strongly improved user indoor comfort. In order to assess the thermal building performance of the office building arsenal research applied the simulation environment TRNSYS (3) and developed a comprehensive and flexible building modell. Due to this approach the impact on the ENERGYbase building performance by changing energy and/or comfort relevant parameter could be quantified based on the current status of planning. Consequently a continious assessment of the energy building performance improved the quality of planning, especially with regard on pre-defined energy and comfort targets.

• Detailed analysis on selected energy systems

The indoor temperature of ENERGYbase offices is controlled by thermal mass activated construction elements. Due to the fact that the heat transfer of the thermal mass activation is limited arsenal research modelled and simulated this low temperature distribution system in order to confirm whether the internal and external loads of ENERGYbase offices can be rejected or additional equipment has to be integrated. Furthermore by using transient system simulation arsenal research gave advice which control strategy of the thermal mass activated construction elements results into a low energy demand and a sufficient indoor comfort.

The indoor humdity of ENERGYbase offices is controlled by an air-conditioning system which uses a solar thermally driven desiccant evaporative cooling technology (DEC). This solar-assisted air-conditioning system is an non-standard system which uses solar heat to regenerate the dehumidification unit. Because the DEC system technology is characterised by thermodynamic limits arsenal research modelled and simulated the system performance and assessed the overall system design and concept.

• Detailled comfort analysis of south oriented offices

The architectual ENERGYbase design and the concept of the south faced facade allows a high ratio of daylight use in the entire office building which enables a significant reduction of electricity demand for artifical lighting. Additionally special internal jalousies guide daylight into the deepness of the south offices which improves daylight comfort. arsenal research did scientific studies on the thermal comfort for an future ENERGYbase users which would be placed near to the

south faced facade. Different types of internal jalousie were modelled and investigated regarding their impact on thermal comfort.