1、BRITISH STANDARD BS 7527-2.4: 1991 IEC 721-2-4: 1987 (Incorporating Amendment No. 1) Classification of environmental conditions Part 2: Environmental conditions appearing in nature Section 2.4 Solar radiation and temperature (Implementation of CENELEC HD 478.2.4 S1)BS7527-2.4:1991 This British Stand
2、ard, having been prepared under the direction of the General Electrotechnical Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 29 November 1991 BSI 07-1999 The following BSI references relate to the work on this standard: Committee referen
3、ce GEL/15 Special announcement in BSINews July 1991 ISBN 0 580 20168 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the General Electrotechnical Standards Policy Committee (GEL/-) to Technical Committee GEL/15, upon which the following bo
4、dies were represented: Directorate of Telecommunications EEA (the Association of Electronics, Telecommunications and Business Equipment Industries) Electronic Components Industry Federation Ministry of Defence National Supervising Inspectorate Society of Environmental Engineers Society of Motor Manu
5、facturers and Traders Limited Amendments issued since publication Amd. No. Date CommentsBS7527-2.4:1991 BSI 07-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Object 1 3 General 1 4 Solar radiation physics 1 5 Levels of global radiation 2 6 Minimum lev
6、els of atmospheric radiation at night 2 Appendix A World distribution of daily global irradiation 6 Figure 1 Atmospheric radiation from a clear night sky 4 Figure 2 Spectra of electromagnetic radiation from the sun and the surface of the Earth 5 Figure A.1 Mean relative global irradiation for the mo
7、nth of June (in percent) 7 Figure A.2 Mean relative global irradiation for the month of December (in percent) 8 Figure A.3 Mean relative global irradiation for the year (in percent) 9 Table I Typical peak values of global irradiance (in watts per square metre from a cloudless sky) 2 Table A.1 Mean d
8、aily extraterrestrial global irradiation 6 Publication(s) referred to Inside back coverBS7527-2.4:1991 ii BSI 07-1999 National foreword This Section ofBS7527 has been prepared under the direction of the General Electrotechnical Standards Policy Committee. It is identical with IECPublication721-2-4:1
9、987 “Classification of environmental conditions Part2:Environmental conditions appearing in nature. Solar radiation and temperature” as amended by Amendment No. 1 (1988), published by the International Electrotechnical Commission (IEC). The changes added by Amendment No. 1 (1988) are indicated by a
10、single vertical line in the margin. This Section ofBS7527 implements CENELEC Harmonization Document (HD)478.2.4 S1. For the purposes of this British Standard, any references to IECpage numbers in the text should be ignored. Other Parts of this British Standard are as follows. Part 1: Environmental p
11、arameters and their severities; Part 2: Environmental conditions appearing in nature; Section 2.1: Temperature and humidity; Section 2.2: Precipitation and wind; Section 2.3: Air pressure; Section 2.5: Dust, sand, salt mist; Section 2.6: Earthquake vibration and shock; Section 2.7: Fauna and flora;
12、Part 3: Classification of groups of environmental parameters and their severities; Section 3.0: Introduction; Section 3.1: Storage; Section 3.2: Transportation; Section 3.3: Stationary use at weatherprotected locations; Section 3.4: Stationary use at non-weatherprotected locations; Section 3.5: Grou
13、nd vehicle installations; Section 3.6: Ship environment; Section 3.7: Portable and non-stationary use. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standa
14、rd does not of itself confer immunity from legal obligations. Cross-references International standard Corresponding British Standard IEC 721-1:1990 BS 7527 Classification of environmental conditions Part 1:1991 Environmental parameters and their severities (Identical) IEC 721-2-1:1982 Section 2.1:19
15、91 Temperature and humidity (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indi
16、cated in the amendment table on theinside front cover.IEC721-2-4:1987 BSI 07-1999 1 1 Scope This part of the standard presents a broad division into types of solar radiation areas. It is intended to be used as part of the background material when selecting appropriate severities of solar radiation f
17、or product applications. All types of geographical areas are covered, except areas with altitudes above5000m. When selecting severities of solar radiation for product applications, the values which are given in IEC Publication 721-1: Classification of Environmental Conditions, Part 1: Classification
18、 of Environmental Parameters and Their Severities, should be applied. 2 Object To define limiting severities of solar radiation to which products are liable to be exposed during transportation, storage and use. 3 General Solar radiation can affect products primarily by heating of material and their
19、environment or by photochemical degradation of material. The ultraviolet content of solar radiation causes photochemical degradation of most organic materials. Elasticity and plasticity of certain rubber compounds and plastic materials are affected. Optical glass may become opaque. Solar radiation b
20、leaches out colours in paints, textiles, paper, etc. This can be of importance, for example for the colour coding of components. The heating of material is the most important effect of exposure to solar radiation. The presentation of severities of solar radiation is therefore related to the power de
21、nsity radiated towards a surface, or irradiance, expressed in watts per square metre. An object subjected to solar radiation will attain a temperature depending primarily on the surrounding air temperature, the energy radiated from the sun, and the incidence angle of the radiation on the object. Oth
22、er factors, for example wind and heat conduction to mountings, can be of importance. In addition, the absorptance sof the surface for the solar spectrum is of importance. An artificial air temperature t smay be defined, which, under steady-state conditions, results in the same surface temperature of
23、 an object as the combination of the actual air temperature t uand the solar radiation of the irradiance E. An approximate value can be obtained from the following equation: The coefficient h yis the heat transfer coefficient for the surface, in watts per square metre and degree Celsius, and include
24、s thermal radiation to the surroundings, heat conduction and convection due to wind. The absorptance sdepends on the thermal colour, the reflectance and the transmittance of the surface. Typical clear sky values are: s= 0.7 h y= 20 W/(m 2 . C) E = 900 W/m 2 resulting in an “overtemperature” due to s
25、olar radiation of about30 C. It can then be seen that an error of10 % in the estimation of the intensity of the solar radiation will influence the temperature involved by less than5 C. Therefore, there is no need in this classification for extremely accurate severities of solar radiation and minor f
26、actors affecting the heat radiated have therefore been disregarded here. The heating effect is caused mainly by short-term radiation of high intensity, i.e. the solar radiation around noon on cloudless days. Such values are presented in Table I. It may also be of interest to identify the lowest poss
27、ible values of atmospheric radiation during clear nights in order to determine the “undertemperature” of products exposed to the night sky. Such values are given in Figure 1, page 4. 4 Solar radiation physics The electromagnetic radiation from the sun to the Earth covers a rather broad spectrum from
28、 the ultraviolet to the near infra-red. Most of the energy reaching the surface of the earth is in the wavelength range of0.34m to44m with a maximum in the visible range around0.54m. Typical spectra are shown in Figure 2, page 5. The amount of radiant energy from the sun which falls upon unit area o
29、f a plane normal to the suns rays just outside the atmosphere at the mean distance from Earth to sun is called the solar constant. Its value is approximately1.37kW/m 2 . The distance from Earth to sun varies during the year, and consequently the radiation varies from approximately1.41kW/m 2in Januar
30、y to approximately1.32kW/m 2in July.IEC721-2-4:1987 2 BSI 07-1999 Approximately 99 % of the energy of the sun is emitted at wavelengths below44m. Most of the energy below0.34m is absorbed by the atmosphere and does not reach the surface of the Earth. Further absorption and scattering of the radiatio
31、n takes place, due to particles and gases, during passage through the atmosphere. The scattering of the direct solar radiation in the atmosphere results in diffuse radiation from the sky. Thus the energy received at a certain place on the earth is the sum of the direct solar radiation and the diffus
32、e solar radiation, which is referred to as the “global radiation”. From the point of view of heating effects, this sum is of interest and the levels given in this standard are therefore related to global radiation. 5 Levels of global radiation 5.1 Maximum levels The maximum level of global radiation
33、 on a clear day occurs at noon. The highest value of the power achieved on a cloudless day at noon at a surface perpendicular to the direction of the sun depends on the content of aerosol particles, ozone and water vapour in the air. It varies considerably with geographical latitude and type of clim
34、ate. The global radiation on a surface perpendicular tothe direction of the sun may reach a value of1120W/m 2at noon on a cloudless day with approximately1cm water vapour content,2mm ozone and aerosols of =0.05, where is thengstrm turbidity coefficient. The value1120W/m 2is typical for flat land far
35、 away from industrial areas and from large cities at solar elevations exceeding 60 . NOTEThe water vapour content of a vertical column of the atmosphere is measured as the height, in centimetres, of the corresponding precipitated water. Analogously, the ozone content of a vertical column of the atmo
36、sphere is measured as the height of the corresponding ozone column at normal temperature and pressure. The scattering and absorption by aerosol particles is expressed by the ngstrm turbidity coefficient, which is the optical depth of the atmosphere with respect to extinction of monochromatic radiati
37、on of wavelength = 1 4m. The direct solar radiation decreases with increasing turbidity. Turbidity is high in subtropical climates and in deserts where the concentration of particles in the air is high. It is also high in large cities and low in mountainous areas. The levels in Table I are recommend
38、ed for application as peak values of global irradiance at noon, experienced by a surface perpendicular to the direction of the sun in a cloudless sky. The level varies only a few percent within the hours nearest to noon and can therefore be assumed to be representative for a few hours at a time. Tab
39、le I Typical peak values of global irradiance (in watts per square metre from a cloudless sky) 5.2 Mean monthly and annual global solar radiation Whilst the maximum heating effect of solar radiation on a surface is normally dependent on short-term irradiance around noon, the photochemical effects ar
40、e related to radiation, integrated over time, i.e. irradiation. For the purpose of comparison, daily global irradiation is the most convenient and commonly used value. In December, the monthly mean average of daily irradiation reaches approximately10.8kWh/m 2close to the South Pole, because of the d
41、uration of daylight. Outside the Antarctic area daily levels reach approximately8.4kWh/m 2 . The highest annual mean averages of daily global irradiation, up to6.6kWh/m 2 , are found mainly in desert areas. 5.3 Simultaneous values of maximum air temperatures and solar radiation The lowest values of
42、the turbidity coefficient are found in cold air masses. Therefore, the levels in Table I do not occur at the highest values of air temperature. It may be assumed that global irradiance does not reach more than 80 % of the values given in Table I at the maximum air temperatures given in IECPublicatio
43、n 721-2-1: Classification of Environmental Conditions, Part 2: Environmental Conditions Appearing in Nature. Temperature and Humidity. 5.4 World distribution of daily global irradiation For the distribution of daily global irradiation, seeAppendix A. 6 Minimum levels of atmospheric radiation at nigh
44、t In cloudless nights when the atmospheric radiation is very low, objects exposed to the night sky will attain surface temperatures below the surrounding air temperature. Area Large cities Flat land Mountainous areas Subtropical climates and deserts 700 750 1 180 Other areas 1 050 1 120 1 180IEC721-
45、2-4:1987 BSI 07-1999 3 The theoretical temperature T 0 , in kelvins, of an object in equilibrium with the atmospheric radiation is given by Boltzmanns law: where: In practice, temperatures will be higher due to heat conduction, convection and water condensation. As an example it has been found that
46、the surface of a horizontal disk thermally isolated from the ground and exposed to the night sky during a clear night can attain a temperature of 14 C when the air temperature is 0 C and the relative humidity is close to 100 %. Figure 1 shows the atmospheric radiation from the night sky in clear air
47、 as a function of air temperature at a height of2m above the ground level. The relative humidity is normally very high on clear nights. is Stefan-Boltzmanns constant, 5.67.10 8W/(m 2 K 4 ) A is atmospheric radiation in W/m 2(see Figure 1, page 4).IEC721-2-4:1987 4 BSI 07-1999 Figure 1 Atmospheric ra
48、diation from a clear night skyIEC721-2-4:1987 BSI 07-1999 5 A = Radiation outside the atmosphere from the sun represented as a black body of temperature6000K (1.60 kW/m 2 ) B = Solar radiation outside the atmosphere (1.37kW/m 2 ) C = Direct solar radiation at the surface of the Earth perpendicular t
49、o the direction of radiation (e.g. 0.9kW/m 2 ) D = Diffuse solar radiation at the surface of the Earth (e.g.0.10kW/m 2 ) E = Absorption bands of water vapour and carbon dioxide F = Absorption by oxygen and ozone G = Radiation of a black body at300K (0.47kW/m 2 ) H = Thermal radiation from the Earth (e.g.0.07kW/m 2 ) Figure 2 Spectra of electromagnetic radiation from the sun and the surface of the EarthIEC721-2-4:1987 6 BSI 07-1999 Appendix A World distribution of daily global irradi
