IEC 62194-2005 pdf – Method of evaluating the thermal performance of enclosures.
1 Scope This International Standard provides a method of thermal performance evaluation for empty indoor enclosures according to IEC 60917 and IEC 60297, and, for outdoor enclosures according to IEC 61969. This standard contains criteria to determine the thermal absorption factors relating to – principles of enclosure design; – internal heat load; – sun radiation. The enclosure absorption factor is intended to provide a common value for comparing and selecting enclosures built in accordance with this standard. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60297 (all parts), Dimensions of mechanical structures of the 482,6 mm (19 in) series IEC 60721-2-4, Classification of environmental conditions – Part 2-4: Environmental condi- tions appearing in nature Solar radiation and temperature IEC 60917 (all parts), Modular order for the development of mechanical structures for electronic equipment practices IEC 61969 (all parts), Mechanical structures for electronic equipment – Outdoor enclosures
3 Terms, definitions, symbols and abbreviations 3.1 Definition of enclosure design principles The enclosure design influences heat flow. The following enclosure types are defined and illustrated in Figure 1. A Single-wall B Double-wall (with insulation/without insulation/with or without airflow) C Single-wall and sun-shield D Double-wall and sun-shield (with insulation/without insulation/with or without airflow)
6 Environmental conditions 6.1 Outdoor applications 6.1.1 Ambient temperature limits Understanding the ambient temperature limits is necessary for the following calculations: t a,max maximum ambient temperature in degrees Celsius (°C); t i,max maximum allowed temperature inside the enclosure in degrees Celsius (°C). 6.1.2 Solar radiation The solar total radiation s q is indicated in W/m 2 . It is dependent on the enclosure installation site, the time of the day, the time of the year and on the turbidity coefficient of the atmosphere. The Angstrom turbidity coefficient expresses the scattering and absorption of the aerosol particles in the atmosphere. For further details, refer to IEC 60721-2-4. The total solar radiation is composed of direct and diffused radiation. The following describes different methods to determine the solar radiation for an enclosure by a) measuring the solar total radiation when falling perpendicularly to one of the individual surfaces of the enclosure; b) measuring the global radiation at the installation site. The resulting quantity shall be converted to the individual surfaces of the enclosure. This can be accomplished by using the geometric relations as presented in Annex B using formula (B.2); c) using meteorological tables. The radiation that falls perpendicularly on the enclosure surfaces shall be determined. The method by which the solar radiation was determined shall be established. 6.1.3 Wind The wind speed and ambient air temperature present have an influence on the heat transfer to the surfaces of the enclosure. If no general formula is used to determine the convection heat transfer coefficients for outside ka and inside ki of the enclosure, the values indicated in Table 1 can be used. These values are dependent on the wind speed.
6.2 Indoor applications Ambient temperature limits for indoor application: t a,max maximum ambient temperature in degrees Celsius (°C); t i,max maximum allowed temperature inside the enclosure in degrees Celsius (°C). 7 Determination of the enclosure absorption factor 7.1 Measurement set-up The test set-up shown in Figure 3 shall measure the enclosure absorption factor which is acquired by measuring the largest wall. This wall has to face the South in the Northern hemisphere and the North in the Southern hemisphere. The temperature sensor a) shall be placed in the centre of the measured wall. A heat source shall be installed inside the enclosure to simulate heat load. The heat load is chosen corresponding to i q of 250 W/m 2 .