Jäger Solar Energy Applications in Houses

Performance and Economics in Europe
1. Auflage 2013
ISBN: 978-1-4831-5530-2
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 188 Seiten

Solar Energy Applications in Houses: Performance and Economics in Europe provides information on the state of development of solar space and water heating technology and on the influence of climatic and economic factors on the attractiveness of solar systems. The book discusses the aspects of climate relevant to solar system and house designs; the impacts of the different European climates on the thermal design and heating requirements of individual houses; and the passive solar energy use in buildings. The text also describes the components of active solar energy systems; the performance of active solar energy systems; and the economics of solar space and water heating. The supporting activities for solar energy systems and other energy-saving technologies implemented by governments, companies, energy supply utilities, solar societies and the Commission of the European Communities are also considered. The book will be invaluable to potential buyers or owners of systems who need practical information on the technical and economic possibilities of domestic solar energy use in the various countries of the European Communities. The information is also important for those people in government, administration, industry and research institutions who are involved in assessing solar energy applications, in planning for the future energy supply, in developing support measures for the introduction of energy-saving methods and in marketing solar hardware.

Autoren/Hrsg.

Jäger, F.

Leseproben

CHAPTER 2

ASPECTS OF CLIMATE RELEVANT TO SOLAR SYSTEM AND HOUSE DESIGNS

Publisher Summary

This chapter discusses the aspects of climate relevant to solar system and house designs. The European community (EC) countries span a range of latitudes and longitudes, and accordingly climate characteristics vary considerably. The energy requirements and the solar system performance in a building depend predominantly on the solar irradiation and the ambient air temperature. The chapter also discusses the variation of these factors over the year and across European countries. The observed temperature distribution reflects the combined influence of the large-scale airflow patterns over Europe and the heating effects of the sun. The evaluation of solar energy applications requires radiation data for inclined surfaces and such data are given for cloudless and cloudy days. Brief mention is also made of other climatic factors, such as wind, snow and hail, which affect the (solar) house design in general. It will be seen that for an evaluation of the potential of solar energy systems, a balanced assessment of all climatic aspects must be made.

The performance of solar systems depends upon local climatic conditions. From this point of view they are very different from conventional domestic heating systems. If one wishes to understand the operation of a solar system and the differences in its performance in various places in Europe, an understanding of the variation of the major climatic factors, radiation and temperature, is required. In this chapter, therefore, the broad features of the climate in the various countries of the EC that are relevant to solar system and solar house designs are discussed. Brief mention is made of features that influence the general distribution of climate. The sunshine distributions and radiation characteristics for horizontal surfaces and slopes are discussed followed by a discussion of the temperature and wind regimes of the regions within the EC. Brief mention is also made of other climatic factors, such as snow, hail and rain, which affect solar house design more indirectly.

Climatic variations across Europe are considerable, and the effects of these variations on architectural design are not always well understood. To ensure success a solar house should be carefully designed to relate to the local climate in which it stands. In this chapter an attempt is made to present climate data on a comparative basis, though this is not always possible because of differences in methods for climatological measurements and calculations used in the EC countries.

In this chapter specific reference is made to solar house design, that is, the application of solar energy for space heating, because solar houses require that all climatic factors be taken into consideration during the design process. For other domestic solar energy systems, such as solar water heaters, climatic factors similarly determine the performance but the demand for energy is only slightly climatically influenced. In the case of solar space heating, in addition to the dependence of the solar system itself on climatic parameters, several other elements determining the heat consumption in a house are climatically sensitive. Energy losses through the building materials, for example, depend on the air temperature, wind speed and the effective temperature of the sky, which influences long-wave radiation losses. On the other hand, the heat gains of a house due to absorption of solar radiation are affected by such climatic factors as the amount of cloudiness and the atmospheric clarity. The ventilation losses are strongly affected by wind speed. For economy one needs to minimise winter energy losses and maximise winter energy gains. It is essential to ensure that the house is acceptably comfortable in summer weather through control of excessive summer heat gains by shading and other techniques. Such considerations emphasize the need to understand and to take into detailed account climatic factors in solar house design.

Climate has to be viewed on a number of different scales. Any general review of climate, as in this chapter, necessarily has to deal mainly with the large-scale characteristics. The large-scale climate, or macroclimate, of any region is modified substantially by local topography and terrain. In mountainous areas these changes are very complex. The climate of cities differs from that of the surrounding countryside. At a particular location the detailed layout of the house has to be considered in relation to adjacent landscape and buildings as these will produce further modifications of local climate, which may contribute to the success or failure of any solar house.

A consideration of only the distribution of incoming solar radiation in the EC countries might lead to the conclusion that due to the higher solar energy availability solar heating is more economically attractive in southern locations than in northern locations. The heating season in the southern areas is relatively short because of the relatively higher temperatures associated with lower cloudiness, more sunshine and less wind. However, a longer operating season of solar space heating systems can make them feasible in more northerly locations as well. Thus, the economic applicability of solar heating systems cannot be evaluated on the basis of solar energy availability alone; a balanced assessment must be made of all climatic factors.

2.1 General climate characteristics of the EC region

The majority of the land area of the EC countries is situated in the temperate latitudes where the basic airflow is frequently westerly. To the east and west of the EC region are areas that have contrasting physical characteristics; thus the day to day weather and the long-term climate in Europe strongly depend on the direction from which the air comes, that is, from the Atlantic Ocean to the west or from the massive continental land areas to the east. Additionally, on the southern side of the EC countries is the Mediterranean Sea. Here the climate in winter is generally mild, even though there may be a lot of rain and storms for a period in the autumn and winter. This is in contrast to the generally wet, windy climate of the North Atlantic coastline and the cold winter climate of Central Europe dominated by the influence of the Siberian anticyclone.

In winter the Gulf Stream exerts an important influence, and the airflows from the Atlantic are typically relatively warm and moist and therefore produce cloudy, mild, wet weather. The impact of these flows is obviously greatest in the western part of the EC area. In contrast, the airflows from the east in winter are very cold with low moisture contents. With such flows there is often less cloud and more sunshine. However, at night, in particular, there is a very substantial net flow of energy outwards from the surface by radiation, and extreme cold may be encountered. Clearly, the Siberian influence impacts most strongly on the eastern side of the EC region.

Very cold air may also move towards the EC area from the Arctic. If this air comes directly from the north it has to pass over a relatively long fetch of comparatively warm sea, and the temperature of such strong, cold winter winds is not as low as that of the high latitude air that passes over the Scandinavian land masses to the northeast. The northeasterly wind in winter tends to be a desperately cold wind in northern Europe.

In summer the same sources of airflows exist with sometimes the Atlantic circulation dominating and sometimes the continental flows dominating, but the climatic impacts on the EC region differ from those in the winter. The continental air masses coming from the east in summer tend to be warmer and their turbidity is often high due to the large dust burden. In contrast, because the ocean takes much longer to warm up than does the land surface, the airflow from the Atlantic in summer is relatively cool, moist and clean because the frequent rain washes the dust from the atmosphere.

The weather during a period in any one particular year may be dominated by one of the above-mentioned two basic flow patterns. For example, if the Atlantic circulation dominates in winter over the EC region, a relatively mild winter prevails. The mildness means that heating requirements are lower. However, this type of circulation is not necessarily advantageous for solar heating systems because of the associated cloudiness. On the other hand, if the Siberian anticyclone dominates in winter over the EC region, a cold winter prevails. Heating requirements are correspondingly higher, and the more frequent cloudless conditions are advantageous for solar heating. In the summer season, domination of the Atlantic circulation results in a cool, rainy summer, and the associated cloudiness means that solar energy systems are obviously less effective than when anticyclonic weather prevails.

The basic flows from the Atlantic, the continental area and the Mediterranean can, however, be substantially modified by the high mountain ranges within the EC region. The Alps, in particular, have a dominant influence, but other topographic features can also produce important local or regional effects.

In general, the weather in areas under the influence of the Atlantic circulation is more variable, with the frequent passage of cyclones, whereas the weather under the influence of the continental air masses is more persistent. This means that the northwest coastal area of the EC has more variable sunshine than the other areas because of its proximity to the...