ISO 21927-4:2019 Smoke and heat control systems – Part 4: Natural smoke and heat exhaust ventilators一Design, requirements and installation. This document applies to the design and installation of natural smoke and heat exhaust ventilators (NSHEVs) for spaces from which smoke is extracted vertically by thermal buoyancy via the roof in the case of single-storey buildings and via the uppermost storey in the case of multi-storey buildings. It also applies to spaces in which NSHEVs are installed in external walls. This document includes tables and calculation methods for the design of clear layers in order to comply with the requirements of various protection objectives. This document includes information and provisions to be taken into account when applying the design rules set out herein and when installing NSHEVs. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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. Iso 13943, Fire safety — Vocabulary ISO 2 1927-1, Smoke and heat control systems — Part 1: Specification for smoke barriers ISO 21927-2, Smoke and heat control systems — Part 2: Specification for natural smoke and heat exhaust yen tila tors 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 13943 and the following apply. ISO and IEC maintain term inological databases for use in standardization at the following addresses: — IEC Electropedia: available at https://www1electropedia.org/ — ISO Online browsing platform: available at httpsJ/www.iso.org/ub 3.1 aerodynamic free area measure of smoke and heat exhaust area of the ventilator Note 1 to entry: It is the geometric area multiplied by the coefficient of discharge. 3.2 automatic activation initiation of operation without direct human intervention 3.3 coefficient of discharge aerodynamic efficiency cv ratio of actual flow rate, measured under specified conditions, to the theoretical flow rate through the ventilator Note 1 to entry: The coefficient takes into account any obstructions in the ventilator, such as controls, louvres and vanes, and the effect of external side winds. 3.4 exhaust ventilator device for the movement of gases out of the construction works 3.5 initiation device device that activates the operating mechanism of the component, e.g. of a damper or a ventilator, on receipt of information from a fire detection system...
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