Low Energy Cooling for Sustainable Buildings

Book info: Low Energy Cooling for Sustainable Buildings (Hardcover, 280 pages) – Wiley, 2009. Language: English.

This long-awaited reference guide provides a complete overview of low energy cooling systems for buildings, covering a wide range of existing and emerging sustainable energy technologies in one comprehensive volume. An excellent data source on cooling performance, such as building loads or solar thermal chiller efficiencies, it is essential reading for building services and renewable energy engineers and researchers covering sustainable design.

The book is unique in including a large set of experimental results from years of monitoring actual building and energy plants, as well as detailed laboratory and simulation analyses.   These demonstrate which systems really work in buildings, what the real costs are and how operation can be optimized – crucial information for planners, builders and architects to gain confidence in applying new technologies in the building sector.

Inside you will find valuable insights into:

• the energy demand of residential and office buildings;
• facades and summer performance of buildings;
• passive cooling strategies;
• geothermal cooling;
• active thermal cooling technologies, including absorption cooling, desiccant cooling and new developments in low power chillers;
• sustainable building operation using simulation.

Supporting case study material makes this a useful text for senior undergraduate students on renewable and sustainable energy courses. Practical and informative, it is the best up-to-date volume on the important and rapidly growing area of cooling.

About the Author

Ursula Eicker is a physicist who carries out international research projects on solar cooling, heating, electricity production and building energy efficiency at the University of Applied Sciences in Stuttgart. She obtained her PhD in amorphous silicon thin-film solar cells from Heriot-Watt University in Edinburgh and then worked on the process development of large-scale amorphous silicon modules in France. She continued her research in photovoltaic system technology at the Centre for Solar Energy and Hydrogen Research in Stuttgart. She set up the Solar Energy and Building Physics Research Group in Stuttgart in 1993. Her current research emphasis is on the development and implementation of active solar thermal cooling technologies, low-energy buildings and sustainable communities, control strategies and simulation technology, heat transfer in façades, etc. Since 2002 she has been the scientific director of the research centre on sustainable energy technologies (zafh.net) in BadenWürttemberg. She also heads the Institute of Applied Research of the University of Applied Sciences in Stuttgart, where building physicists, geoinformation scientists, mathematicians, civil engineers and architects cooperate. During the last 10 years Professor Eicker has coordinated numerous research projects on sustainable communities with renewable energy systems and highly efficient buildings. The largest projects include the European Integrated POLYCITY Project, a demonstration project on sustainable buildings and systems in Germany, Italy and Spain, and the European PhD school CITYNET on information system design for sustainable communities.

Excerpt. © Reprinted by permission. All rights reserved. Low Energy Cooling for Sustainable BuildingsBy Ursula EickerJohn Wiley & SonsCopyright © 2009 John Wiley & Sons, Ltd
All right reserved.
ISBN: 978-0-470-69744-3

Chapter OneEnergy Demand of Buildings

Buildings today account for 40% of the world's primary energy consumption and are responsible for about one-third of global CO2 emissions (24% according to IEA, 2008; 33% according to Price et al., 2006). The energy-saving potential is large, with 20% savings expected until 2020 in the European Union alone. The cost efficiency of building-related energy savings is high, as shown in a recent study for the Intergovernmental Panel on Climate Change ( Urge-Vorsatz and Novikova, 2008). In the industrialized countries, between 12 and 25% of building-related C[O.sub.2] emissions can be reduced at net negative costs, mainly through heat-related measures. In the developing countries, electricity savings through more efficient appliances and lighting are more important with 13 to 52% of the measures being economically feasible until 2020. As published in the Green Paper on energy efficiency by the European Commission, end energy-consumption in 2005 reached 12 x [10.sup.9] MWh per year, 40% of which can be attributed to buildings (see Figure 1.1). In the USA, 36% of the total energy consumption occur in buildings. Especially in urban areas, building energy consumption is typically twice as high than transport energy, for example by a factor of 2.2 in London (Steemers, 2003).

Under the Kyoto Protocol, the European Union has committed itself to reducing the emission of greenhouse gases by 8% in 2012 compared with the 1990 level and buildings have to play a major role in achieving this goal. If building energy efficiency is improved by 22%, 45 million tonnes of C[O.sub.2] can be saved, nearly 14% of the agreed total savings of 330 million tonnes.

The European Directive for Energy Performance of Buildings, signed by the European Parliament and Council in 2002, was created to unify the diverse national regulations and calculation methods, to define minimum common standards on building energy performance and to provide certification and inspection rules for a building and its heating and cooling plants. Although the performance directive only defines a common methodology for energy certification, most European countries have now increased their requirements to limit new buildings' energy demand. On average, allowed building transmission losses are now 25% lower. The heat transfer coefficient (U-value) is defined as the reciprocal sum of heat transfer resistances between room and ambient air and is today on average between 0.3 and 0.4 W [m.sup.-2] [K.sup.-1] for a building.

The reduction of energy consumption in buildings is of high socioeconomic relevance, with the construction sector as Europe's largest industrial employer representing an annual investment of 910 x [10.sup.9] euros (2003), corresponding to 10% of gross domestic product. Almost 2 million companies, 97% of them small and medium enterprises, directly employ 11.8 million people.

The total primary energy consumption in Germany is about 4 x [10.sup.9] MWh, corresponding to 13 878 PJ (2007 data), and is estimated to decrease by 15% until 2030 (EWI/Prognos, 2005). The main efficiency gains are expected through the reduction of transformation losses, which today are responsible for 3984 PJ and are due to decrease by 37% until 2030. In the building sector, on the contrary, the final energy consumption of 2599 PJ (2000) is only estimated to decline by 4% until 2030, which is due to the slow rate of rehabilitation.

In moderate European climates such as Germany's, about 80% of the total energy consumption is used for space heating, 12% for warm water production and the rest for electrical appliances, communication and lighting. The dominance of heat consumption, almost 80% of the primary energy consumption of households, is caused by low thermal insulation standards in existing buildings. They dominate the residential building stock with 90% of all buildings. Even in 2050, 60% of residential space will be located in existing buildings (Ministry for Transport and Buildings, Germany, 2000). Since the 1970s' oil crises the heating energy demand, particularly of new buildings, has been continuously reduced by gradually intensified energy legislation. With high heat insulation standards and the ventilation concept of passive houses, a low limit of heat consumption has meanwhile been achieved, which is around 20 times lower than today's average values. A crucial factor for the low consumption of passive buildings was the development of new glazing and window technologies, which enable windows to be passive solar elements and at the same time cause only low transmission heat losses.

In new buildings with low heating requirements, other energy consumption in the form of electricity for lighting, power and air-conditioning, as well as warm water in residential buildings, is becoming more and more dominant. Electricity consumption in the European Union is estimated to rise by 50% by 2020. Renewable sources of energy can make an important contribution to the supply of electricity and heat. Cooling and refrigeration account for about 15% of total electricity consumption worldwide, and as much as 30% in highly developed countries with a warm climate such as Hong Kong (Government Information Centre, Hong Kong, 2004). Peak electricity loads in many countries now occur in summer rather than in winter. In South Australia, for example, cooling and refrigeration were reported to account for 46% of total electricity consumption on a hot summer's day.

Urban energy management systems should include demand predictions, databases of consumption as well as strategies for operational control and optimization. Consumption data is rarely available on an urban scale, which makes projections of energy requirements difficult. Often there is no strategic energy management plan and demand and supply are not properly matched. Surveys on energy consumption patterns in communities are therefore often based on calculated demand, for example using the appliances used in residential buildings and estimated hours of operation (Zia and Devadas, 2007). A similar demand simulation approach was chosen to analyse the energy efficiency and C[O.sub.2] reduction potential in the commercial sector in Japan until 2050 (Yamaguchi et al., 2007). Assuming relatively low increases in insulation thickness (from zero in the year 2000 to 60 mm in 2050), the main efficiency gains were expected through improvements in appliance electrical efficiency. This led to the surprising fact that heat demand even rises, as internal loads due to equipment were supposed to drop. A case study in the UK town of Leicester obtained energy savings of 20% by more efficient lighting in residential buildings, based on measured electricity load curves from the energy supplier (Brownsword et al., 2005).

The chapter aims to contribute information on how much energy is consumed in its different forms in the building sector and which reductions are possible in best case examples. Embedded energy in the building materials and construction process is not included in the analysis, although several studies indicate a rather high importance of material and resource use during building construction and maintenance: for example, Pulselli and colleagues calculated that 49% of all energy is needed for the building manufacturing process, 35% for maintenance and only 15% for use (Pulselli et al., 2007).

1.1 Residential Buildings

1.1.1 Heating Energy

Due to the wide geographical extent of the European Union covering nearly 35 of geographical latitude (from 36 in Greece to 70 in northern Scandinavia), a wide range of climatic boundary conditions are covered. In Helsinki (60.3 N), average exterior air temperatures reach -6 C in January, when southern cities such as Athens at 40 N latitude still have averages of +10 C. Consequently, building construction practice varies widely: whereas average heat transfer coefficients (U-values) for detached houses are about 1 W [m.sup.-2] [K.sup.-1]in Italy, they are 0.4 W [m.sup.-2] [K.sup.-1] in Finland (see Table 1.1). The heating energy demand calculated from monthly energy balances (according to European Standard EN 832) is comparable in both cases at about 50 kWh [m.sup.-2] [a.sup.-1].

If existing building standards are improved to the so-called passive building standard, heating energy consumption can be lowered to less than 20 kWh [m.sup.-2] [a.sup.-1]. Studies in Switzerland showed that additional investment costs for passive residential buildings are about 14% (Minergie P label). For buildings with a low energy standard (reaching the Swiss Minergie label) investment costs were about 6 to 9% higher (Binz, 2006). Depending on the assumptions made for energy price increases, the additional investment costs can be compensated by lower energy costs during operation. In Germany with its high number of passive building projects, additional investment costs for the high standard are only 3 to 5%.

Since the implementation of the European Building Performance Directive in 2003, nearly all European countries have significantly increased the requirements to reduce transmission heat losses. The European Performance Directive asks for the establishment of a calculation methodology for energy demand and an energy certification process, whereas limits on energy demand are regulated by national laws.

Average U-values for new buildings are about 25% lower than in 2003. The required U-values to achieve passive building standards are listed in Table 1.1 for some cities from different European climates. For these insulation standards, heating energy consumption is between 15 and 20 kWh [m.sup.-2] [a.sup.-1]. By comparison, today's residential buildings in Germany with low energy standards have annual heating energy consumption values of around 70 kWh [m.sup.-2] [a.sup.-1]. Several hundred houses in rows constructed after the year 2000 in the town of Ostfildern were measured within the European POLYCITY demonstration project (see Figure 1.2). The consumption varies strongly even for the same building type and standard deviations are about 35% of the mean value (Figure 1.3). The distributions for two years of measurement are shown in Figure 1.4.

Although 20% of all buildings in Germany were constructed after 1980, they only consume 5% of the total heating energy. Depending on building age and type, older buildings' heating energy consumption varies between 100 and 400 kWh [m.sup.-2] [a.sup.-1]. The main challenge of the next decades will therefore be the reduction of heating energy consumption for existing buildings.

Within the POLYCITY project the existing building stock of the town of Cerdanyola near Barcelona in Spain was analysed with over 6000 buildings: 44% of them are single storey buildings, 28% have two floors. More than 90% of the buildings were constructed after 1960 and 65% of the apartments are between 60 and 90 [m.sup.2]. The average heating energy consumption is between 90 and 100 kWh [m.sup.-2] [a.sup.-1] and has increased slightly during the last decade due to increased use of central heating systems with integrated warm water production (see Figure 1.7). In comparison, in the urban area of Barcelona with multi-family apartment blocks, heating energy consumption is only 34 kWh [m.sup.-2] [a.sup.-1] on average (Reol, 2005).

1.1.2 Domestic Hot Water

Independent of the level of insulation, water heating is always necessary in residential buildings. The energy consumption is between about 220 (low requirement) and 1750 kWh per person and year (high requirement), depending on the pattern of consumption. For the middle requirement range of 30-60 litres per person and day, with a warm water temperature of 45 C, the consumption is 440-880 kWh per person or 1760-3520 kWh for an average four-person household. Related to a square metre of heated residential space, a rather low average value of 12.5 kWh [m.sup.-2] [a.sup.-1] is for example used in German legislation. In Switzerland, a fixed value of 14 kWh [m.sup.-2] [a.sup.-1] is used. To increase the share of renewable energy for water heating, some local or regional governments have introduced legislation to cover typically 60% of the warm water demand by solar thermal energy. In Catalunya in Spain, about 75% of the local communities have so-called local ordinances to oblige building constructors to implement solar thermal energy. In Mediterranean climates, the energy need for warm water heating is of the same order of magnitude as heating energy consumption, even for the given building stock. An investigation for urban housing in Barcelona in Spain showed that from a total end energy consumption of 8310 kWh [a.sup.-1] for residential housing of 90 [m.sup.2] average size, 29% or 26 kWh [m.sup.-2] [a.sup.-1] was used for warm water production and 38% for heating. Cooling energy need on the other hand is less than 10 kWh [m.sup.-2] [a.sup.-1] (Reol, 2005).

1.1.3 Electricity Consumption

The average electricity consumption of private households is around 3600 kWh per household and year in Germany. Related to a square metre of heated residential space, an average value of 31 kWh [m.sup.-2] [a.sup.-1] is obtained. An electricity-saving household needs only around 2000 kWh [a.sup.-1]. Measured electricity consumption for several hundred newly built houses in Ostfildern showed average annual consumption values between 30 and 50 kWh [m.sup.-2] [a.sup.-1] (see Figure 1.5). The highest number of buildings was in the class between 40 and 50 kWh [m.sup.-2] [a.sup.-1] (see Figure 1.6). In a passive building project in Darmstadt (Germany), consumptions of between 1400 and 2200 kWh per household per year were measured, which corresponds to an average value of 12 kWh [m.sup.-2] [a.sup.-1].

Within the urban housing study in Barcelona, the average electricity consumption was 2160 kWh per household, which corresponds to 24 kWh [m.sup.-2] [a.sup.-1]. In the nearby town of Cerdanyola, the measured electricity consumption for mainly single or two-storey buildings was 70 kWh [m.sup.-2] [a.sup.-1], with decreasing consumption during the last decade due to the replacement of electric water heaters (Figure 1.7). The high average consumption can be mainly attributed to a housing stock which is partially heated and cooled with electricity. Apartments without electrical heating systems have electricity consumption values between 40 and 50 kWh [m.sup.-2] [a.sup.-1]. Measurements of electricity consumption were also taken in a social housing district with 2500 inhabitants in Turin, Italy, within the POLYCITY project: 622 apartments within 30 building blocks were analysed. Here the average electricity consumption per household is low, about 1750 kWh per year, which corresponds to a specific consumption between 14 and 20 kWh [m.sup.-2] [a.sup.-1].

1.2 Office Buildings

1.2.1 Heating Energy

Existing office and administrative buildings have approximately the same consumption of heat as residential buildings and most have a higher electricity consumption. According to a survey of the energy consumption of public buildings in the state of Baden-Wrttemberg in Germany, the average consumption of heat is 217 kWh [m.sup.-2] [a.sup.-1]. The specific energy consumption of naturally ventilated office buildings in the UK is in a similar range of 200-220 kWh [m.sup.-2] [a.sup.-1] (Zimmermann and Andersson, 1998). From the commercial sector in Japan, values of 59 kWh [m.sup.-2] [a.sup.-1] have been reported (Yamaguchi et al., 2007). Measured heating energy data from a variety of the author's projects (Lamparter office in Weilheim, Germany, Town Hall Ostfildern, Germany, Isbank Tower, Istanbul) and case studies literature has been gathered by the author and is shown in Figure 1.8. Heat consumption in administrative buildings can be reduced without difficulty, by improved thermal insulation, to under 100 kWh [m.sup.-2] [a.sup.-1], and even to a few kilowatt hour per square metre and year in a passive building.

1.2.2 Electricity Consumption

Total Electricity Consumption

Both heat and electricity consumption depend strongly on the building's use. In terms of the specific costs, electricity almost always dominates. A survey carried out in public buildings of the German state of Baden-Wrttemberg found an average electricity consumption of 54 kWh [m.sup.-2] [a.sup.-1], in the UK values between 48 and 85 kWh [m.sup.-2] [a.sup.-1] were measured (see Figure 1.9).

When comparing the energy costs of commercial buildings with the remaining current monthly operating costs, the relevance of a cost-saving energy concept is apparent: more than half of the running costs are accounted for by energy and technical services. A large part of the energy costs is due to ventilation and air-conditioning.

Electricity consumption dominates total energy consumption where the building shell is energy optimized and can be reduced by 50% at most. Even in an optimized passive energy office building in southern Germany, electricity consumption remained at about 35 kWh [m.sup.-2] [a.sup.-1], mainly due to the consumption by office equipment such as computers (see Figure 1.10).

(Continues...)

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