# Commission Delegated Regulation (EU) 2017/654 of 19 December 2016 supplementing Regulation (EU) 2016/1628 of the European Parliament and of the Council with regard to technical and general requirements relating to emission limits and type-approval for internal combustion engines for non-road mobile machinery, Division 3.3.2.1: Vapour pressure of water

Extent: E+W+S+N.I.

The vapour pressure of water p H2O [kPa] for a given saturation temperature condition, T sat [K], shall be calculated by means of equations (7-77) or (7-78):
(a) For humidity measurements made at ambient temperatures from 0 to 100 °C or for humidity measurements made over super-cooled water at ambient temperatures from – 50 to 0 °C:
log 10 p H2O = 10,79574 × 1 − 273,16 T sat − 5,02800 × log 10 T sat 273,16 + 1,50475 × 10 − 4 × 1 − 10 − 8,2969 × T sat 273,16 − 1 + 0,42873 × 10 − 3 × 10 4,76955 × 1 − 273,16 T sat − 1 − 0,2138602
(7-77)
Where:
p H2O vapour pressure of water at saturation temperature condition [kPa]
T sat saturation temperature of water at measured condition [K]
(b) For humidity measurements made over ice at ambient temperatures from (– 100 to 0) °C:
log 10 p H2O = − 9,096853 × 273,16 T sat − 1 − 3,566506 × log 10 273,16 T sat + 0,876812 × 1 − T sat 273,16 − 0,2138602
(7-78)
Where:
T sat saturation temperature of water at measured condition [K]

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Source: https://www.legislation.gov.uk/eur/2017/654/annex/VII/division/3/division/3.3/division/3.3.2/division/3.3.2.1 (the official version)
Page: https://openlegislation.uk/eu-regulation-2017-654/annex-VII/division-3/division-3.3/division-3.3.2/division-3.3.2.1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.