SIST EN ISO 15927-1:2004

Hygrothermal performance of buildings - Calculation and presentation of climatic data - Part 1: Monthly means of single meteorological elements (ISO 15927-1:2003)

This European Standard specifies procedures for calculating and presenting the monthly means of those parameters of climatic data needed to assess some aspects of the thermal and moisture performance of buildings.  Numerical values for any locations should be obtained from the meteorological service in the relevant country.
This European Standard covers the following single climate variables:
   air temperature;
   atmospheric humidity;
   wind speed;
   precipitation;
   solar radiation;
   longwave radiation.
Meteorological instrumentation and methods of observation are not covered; these are specified by the World Meteorological Organisation (WMO).

Wärme- und feuchteschutztechnisches Verhalten von Gebäuden - Berechnung und Darstellung von Klimadaten - Teil 1: Monats- und Jahresmittelwerte einzelner meteorologischer Elemente (ISO 15927-1:2002)

Diese Norm legt Verfahren zur Berechnung und Darstellung von monatlichen Klimadaten fest, die für die Bewertung unterschiedlicher Aspekte des wärme- und feuchteschutztechnischen Verhaltens von Gebäuden notwendig sind. Die Zahlenwerte für bestimmte Orte sind vom meteorologischen Dienst des betreffenden Landes zu erhalten.
Gegenstand dieser Norm sind die folgenden einzelnen Klimaelemente:
   Lufttemperatur;
   Luftfeuchte;
   Windgeschwindigkeit;
   Niederschlag;
   Sonnenstrahlung;
   Langwellige Strahlung.
Meteorologische Geräte und Beobachtungsverfahren werden nicht behandelt; sie werden von der World Meteorological Organisation (WMO) festgelegt.

Performance hygrothermique des bâtiments - Calcul et présentation des données climatiques - Partie 1: Moyennes mensuelles et annuelles des éléments météorologiques simples (ISO 15927-1:2002)

La présente Norme européenne spécifie les méthodes de calcul et de présentation des moyennes mensuelles des parametres de données climatiques nécessaires a l'évaluation de certains aspects des performances thermiques et hygroscopiques des bâtiments. Il convient que les valeurs numériques soient obtenues aupres du service météorologique du pays correspondant.
La présente Norme européenne couvre les variables climatiques simples suivantes :
- température de l'air ;
- humidité atmosphérique ;
- vitesse du vent ;
- précipitations ;
- rayonnement solaire ;
- rayonnement de grandes longueurs d'onde.
Les instruments météorologiques et les méthodes d'observation ne sont pas traités ; ils sont spécifiés par l'Organisation météorologique mondiale (WMO).

Higrotermalne značilnosti stavb - Izračun in predstavitev podnebnih podatkov - 1. del: Mesečno in letno povprečje posameznih vremenskih elementov (ISO 15927-1:2003)

General Information

• Status: Published
• Publication Date: 31-Aug-2004
• ICS: 07.060 - Geology. Meteorology. Hydrology
• ICS: 91.120.10 - Thermal insulation of buildings
• Technical Committee: TOP - Thermal insulation
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Sep-2004
• Due Date: 01-Sep-2004
• Completion Date: 01-Sep-2004
• Directive: 89/106/EEC - Construction products
• Directive: TRRTP129 - Tehnična smernica TSG-12640-001:2008 Zdravstveni objekti
• Ref Project: EN ISO 15927-1:2003 - Hygrothermal performance of buildings - Calculation and presentation of climatic data - Part 1: Monthly means of single meteorological elements (ISO 15927-1:2003)

Relations

• Child: SIST EN ISO 15927-5:2005 - Hygrothermal performance of buildings - Calculation and presentation of climatic data - Part 5: Data for design heat load for space heating (ISO 15927-5:2004)
• Effective Date: 22-Dec-2008
• Child: SIST EN ISO 15927-4:2005 - Hygrothermal performance of buildings - Calculation and presentation of climatic data - Part 4: Hourly data for assessing the annual energy use for heating and cooling (ISO 15927-4:2005)
• Effective Date: 22-Dec-2008

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 15927-1:2004
01-september-2004
Higrotermalne značilnosti stavb - Izračun in predstavitev podnebnih podatkov - 1.
del: Mesečno in letno povprečje posameznih vremenskih elementov (ISO 15927-
1:2003)
Hygrothermal performance of buildings - Calculation and presentation of climatic data -
Part 1: Monthly means of single meteorological elements (ISO 15927-1:2003)
Wärme- und feuchteschutztechnisches Verhalten von Gebäuden - Berechnung und
Darstellung von Klimadaten - Teil 1: Monats- und Jahresmittelwerte einzelner
meteorologischer Elemente (ISO 15927-1:2002)
Performance hygrothermique des bâtiments - Calcul et présentation des données
climatiques - Partie 1: Moyennes mensuelles et annuelles des éléments
météorologiques simples (ISO 15927-1:2002)
Ta slovenski standard je istoveten z: EN ISO 15927-1:2003
ICS:
07.060 Geologija. Meteorologija. Geology. Meteorology.
Hidrologija Hydrology
91.120.10 Toplotna izolacija stavb Thermal insulation of
buildings
SIST EN ISO 15927-1:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 15927-1:2004

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SIST EN ISO 15927-1:2004
EUROPEAN STANDARD
EN ISO 15927-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2003
ICS 91.120.10; 91.120.30
English version
Hygrothermal performance of buildings - Calculation and
presentation of climatic data - Part 1: Monthly means of single
meteorological elements (ISO 15927-1:2003)
Performance hygrothermique des bâtiments - Calcul et Wärme- und feuchteschutztechnisches Verhalten von
présentation des données climatiques - Partie 1: Moyennes Gebäuden - Berechnung und Darstellung von Klimadaten -
mensuelles et annuelles des éléments météorologiques Teil 1: Monats- und Jahresmittelwerte einzelner
simples (ISO 15927-1:2002) meteorologischer Elemente (ISO 15927-1:2002)
This European Standard was approved by CEN on 10 April 2003.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2003 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15927-1:2003 E
worldwide for CEN national Members.

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Contents
Page
Foreword.3
1 Scope .4
2 Normative references .4
3 Terms, definitions, symbols and units .4
3.1 Terms and definitions.4
3.2 Symbols and units .6
4 Periods over which parameters are calculated .7
5 Air temperature .8
5.1 Sources of data .8
5.2 Calculation of the monthly mean .8
5.3 Calculation of the standard deviation of daily means about the monthly mean.9
5.4 Calculation of the annual mean and standard deviation.10
5.5 Expression of results .10
6 Atmospheric humidity.11
6.1 Sources of data .11
6.2 Relationships between temperature and humidity parameters.11
6.3 Calculation of monthly mean.13
6.4 Expression of results .14
7 Wind speed and direction .16
7.1 Methods of measurement .16
7.2 Environmental influence on mean wind speed.16
7.3 Statistical elements .20
7.4 Expression of results .21
8 Precipitation .22
8.1 Sources of data .22
8.2 Calculation of monthly total.22
8.3 Expression of results .22
9 Solar radiation.22
9.1 Sources of data .22
9.2 Calculation of monthly total solar irradiation .23
9.3 Expression of results .24
9.4 Estimating irradiances that are not measured.24
10 Longwave radiation .24
10.1 General.24
10.2 Sources of data .24
10.3 Calculation of monthly total longwave irradiation from the atmosphere (sky).24
10.4 Expression of results .25
Annex A (informative) Methods for splitting global solar irradiance into the direct and diffuse parts.26
Annex B (informative) Methods for estimating the longwave atmospheric irradiances (longwave sky
irradiances)and the sky temperature.27
Bibliography .29
2

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Foreword
This document (EN ISO 15927-1:2003) has been prepared by Technical Committee CEN/TC 89, “Thermal
performance of buildings and building components”, the secretariat of which is held by SIS, in collaboration with
Technical Committee ISO/TC 163, “Thermal performance and energy use in the built environment”,
Subcommittee SC 2 "Calculation methods".
This European Standard shall be given the status of a national standard, either by publication of an identical text
or by endorsement, at the latest by May 2004, and conflicting national standards shall be withdrawn at the latest
by May 2004.
This standard is one of a series of standards on calculation methods for the design and evaluation of the thermal
and moisture performance of buildings. EN ISO 15927, Hygrothermal performance of buildings – Calculation and
presentation of climatic data, consists of six parts:
Part 1: Monthly means of single meteorological elements;
Part 2: Data for design cooling loads and risk of overheating;
Part 3: Calculation of a driving rain index for vertical surfaces from hourly wind and rain data;
Part 4: Data for assessing the annual energy for heating and cooling;
Part 5: Winter external design air temperatures and related wind data;
Part 6: Accumulated temperature differences for assessing energy use in space heating.
Annexes A and B are informative.
This document includes a Bibliography.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,
Slovakia, Spain, Sweden, Switzerland and the United Kingdom.
3

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
1 Scope
This European Standard specifies procedures for calculating and presenting the monthly means of those
parameters of climatic data needed to assess some aspects of the thermal and moisture performance of
buildings. Numerical values should be obtained from the meteorological service in the relevant country.
This European Standard covers the following single climate variables:
� air temperature;
� atmospheric humidity;
� wind speed;
� precipitation;
� solar radiation;
� longwave radiation.
Meteorological instrumentation and methods of observation are not covered; these are specified by the World
Meteorological Organisation (WMO).
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies (including amendments).
World Meteorological Organisation: Guide to meteorological instruments and methods of observation. 6th Edition
WMO - No.8 1996.
3 Terms, definitions, symbols and units
3.1 Terms and definitions
For the purposes of this European Standard, the following terms and definitions apply.
3.1.1
mixing ratio
ratio of the mass of water vapour to the mass of dry air with which the water vapour is associated
3.1.2
water vapour pressure
part of the total atmospheric pressure exerted by water vapour
3.1.3
saturated vapour pressure over water
vapour pressure of moist air in equilibrium with a plane liquid water surface
3.1.4
relative humidity
ratio of the vapour pressure of moist air to the vapour pressure it would have if it were saturated
3.1.5
reference wind speed
wind speed measured at a height of 10 m above ground level in open country without nearby obstacles
3.1.6
gust speed
greatest instantaneous wind speed observed during the period over which the mean is calculated
4

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
3.1.7
solar irradiance
radiation power per area generated by the reception of solar radiation on a plane of any tilt and orientation
The following special quantities can be distinguished according to the conditions of reception:
3.1.7.1
global solar irradiance
irradiance generated by reception of solar radiation from the full hemisphere
NOTE According to the following definitions it is equal to the reception of direct solar and diffuse solar radiation on a
horizontal plane. In the case of tilted planes a portion of the ground reflected global solar radiation is also received.
3.1.7.2
direct solar irradiance
irradiance generated by the reception of solar radiation from a conical angle which surrounds concentrically the
apparent solar disk
NOTE 1 Also referred to as "beam solar radiation".
NOTE 2 The horizontal component of the direct solar irradiance is a part of the global solar irradiance.
NOTE 3 Any component of the direct solar irradiance is generated nearly exclusively from unscattered solar radiation.
NOTE 4 The diameter of the apparent solar disk corresponds to about 0,5 degrees; for technical reasons the available
radiometers receive the direct solar irradiance from solid angles around the solar disk which correspond mostly to field-of-view
angles between 3� and 6�.
3.1.7.3
diffuse solar irradiance
irradiance generated by the reception of scattered solar radiation from the full sky hemisphere , with the exception
of that solid angle which is used to measure the direct solar irradiance
NOTE 1 Practical measurement requires a sun following disk, which permanently shades the receiver of the radiometer
with a ‘field of shade’ angle which equals the field of view angle used for measuring direct solar irradiance. This allows the
global irradiance to be calculated as the sum of diffuse solar and the horizontal component of the direct solar irradiance.
NOTE 2 The use of a ring to shade the sun along its daily path instead of a disk requires an equation to correct for the
corresponding losses of diffuse solar irradiance.
3.1.7.4
reflected solar irradiance
irradiance generated by reception of the rising reflected global radiation on a downward looking plane
NOTE 1 The ratio of reflected solar and global solar irradiance is called albedo.
NOTE 2 Part of the reflected global solar radiation is received on any tilted plane.
3.1.8
solar irradiation
radiant energy per area received from the sun on a plane of defined inclination and orientation during a given
period of time
NOTE The same components as indicated in 3.1.7 for irradiance can be distinguished.
3.1.9
longwave (terrestrial) radiation
radiation with wavelength greater than 3 �m from surfaces at the ground and from the atmosphere
NOTE The exchange of longwave radiation occurs permanently between buildings, the ground and the atmosphere at
temperatures between 240 K and 340 K.
5

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
3.1.10
thermometer screen
white painted, wooden, plastic, or aluminium louvered enclosure, which allows a free flow of air over
thermometers while shielding them from solar radiation, longwave radiation and precipitation
3.2 Symbols and units
Symbol Quantity Unit
C roughness coefficient -
R
C topography coefficient -
T
D
wind direction from North �
d
number of days in a month -
m
d number of days in a year -
y
2
G longwave irradiancefrom the atmosphere on a horizontal plane
l,a �W/m
2
G solar irradiance W/m
s
2
G direct (beam) solar irradiance W/m
s,b
2
G diffuse solar irradiance W/m
s,d
2
G global solar irradiance W/m
s,g
2
G reflected global solar irradiance
W�m
s,r
H
effective height of topographic feature m
2
H solar irradiation MJ/m
s
h
number of hours in a month -
m
K terrain factor -
R
L actual length of downwind slope m
d
L effective length of upwind slope m
e
L actual length of upwind slope m
u
R rainfall total (or equivalent amount of melted solid precipitation) mm
P total atmospheric pressure hPa
p
water vapour pressure hPa
p (�) hPa
saturated vapour pressure over water at temperature �
sat
s scale factor for topography coefficient -
T
temperature K
v wind speed m/s
vˆ gust wind speed m/s
6

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Symbol Quantity Unit
v reference mean wind speed m/s
r
v mean wind speed at a site m/s
s
x mixing ratio g/kg
g/kg
x (�) saturated mixing ratio with respect to liquid water at temperature �
sat
y
horizontal distance of site from crest of topographic feature m
z height above ground m
z
minimum height m
min
z roughness height m
0
� ratio of gas constant of dry air to gas constant of water vapour -
(� = 0,62198)
air temperature
� �C
� upwind slope of topographic feature -
relative humidity -
�
3.2.1 Subscripts
Subscript Meaning
a atmosphere
dm
mean over a day
dx maximum over a day
dn minimum over a day
h values representative of an hour (either instantaneous measurements or the
mean of many readings in the hour)
ic inclination of a surface
mm mean over a month
N values representative of a number of hours N (e.g. 3 h, 6 h or 12 h but less
than 24 h) (either instantaneous measurements or the mean of many
readings in the period)
l longwave
pq value exceeded for q % of the time
s solar
sd standard deviation
4 Periods over which parameters are calculated
The methods specified in clauses 5 to 9 can be used to calculate monthly means or totals from either individual
months (e.g. a January from a specified year) or from all the corresponding months from many years (e.g. all the
Januarys from a 30 year data set).
Calculations of the standard deviation of daily means or totals about the monthly or annual means or totals
(see 5.3 and 5.4) shall refer to a specified month or year.
7

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
The specified year or the multi-year period over which all parameters are calculated shall be quoted with the
values of the parameters.
5 Air temperature
5.1 Sources of data
The dry-bulb air temperature data used to calculate monthly means shall come from observations from a
thermometer screen fitted with louvers to allow a free flow of air.
5.2 Calculation of the monthly mean
5.2.1 From hourly data
The hourly temperature may be either: a) the mean of continuous measurements recorded during that hour or b)
measurements recorded at a particular moment within the hour (e.g. on the hour).
The monthly means shall be calculated as:
h
m
�
� h
h�1
� � (1)
mm
h
m
where
� is the hourly temperature, in �C;
h
h is the number of hours in the month under consideration.
m
5.2.2 From data measured at intervals of 3 h or 6 h
If dry-bulb outdoor air temperature data are available at intervals of 3 h or 6 h (each value may be either the mean
of continuous measurements during the interval or an instantaneous measurement taken on the interval), the
monthly mean is calculated from:
n
m
�
N
�
N�1
� � (2)
mm
n
m
where
n = 8 d for data at three-hour intervals;
m m
= 4 d for data at six-hour intervals;
m
d is the number of days in the month under consideration.
m
5.2.3 From daily maximum and minimum data
If the only dry-bulb outdoor air temperatures available are the daily maximum and minimum for each day of the
month, the daily mean for each day is calculated as:
� ��
dn dx
� � (3)
dm
2
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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
and the monthly means obtained as:
d
m
�
d m
�
d�1
� � (4)
mm
d
m
where
d is the number of days in the month under consideration.
m
NOTE Daily means calculated from the daily maximum and minimum temperature will, in general, be different from those
calculated from hourly values. Most (95 %) of the differences lie between � 1,0 �C but they can range up to � 2,0 �C. Monthly
means calculated from daily maximum and minimum values will also differ from those calculated from hourly values, but in this
case 95 % of the differences lie between � 0,2 �C and the maximum difference lies between � 0,25 �C.
5.2.4 From instantaneous data at 07:30, 14:30 and 21:30 or at other similar times
If dry-bulb outdoor air temperature data are available only at 07:30, 14:30 and 21:30, or at other similar times, the
daily mean for each day is calculated using Equation (5), or the equivalent equation for the appropriate times.
� �� � 2�
07:30 14:30 21:30
� � (5)
d m
4
and the monthly mean obtained from Equation (4).
5.3 Calculation of the standard deviation of daily means about the monthly mean
If not defined in 5.2.2, 5.2.3 or 5.2.4, the daily mean temperatures for each day in the month are calculated from
data measured at one, three or six hourly intervals using:
n
d
�
� N
N�1
� � (6)
d m
n
d
where
n = 24 for data at one-hour intervals;
d
= 8 for data at three-hour intervals;
= 4 for data at six-hour intervals;
or from daily maximum and minimum data using Equation (3) or at 07:30, 14:30 and 21:30 or similar times using
Equation (5).
Then the standard deviation of the daily means from the monthly mean is given by:
2
d d
m � m �
2 � �
d � � �
m� � d m
d m
� �
d�1 d�1
� �
� � (7)
sdm
d (d � 1)
m m
9

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
5.4 Calculation of the annual mean and standard deviation
The annual mean temperature shall be calculated from the daily means using:
d
y
�
� d m
d�1
� � (8)
ym
d
y
The standard deviation of the daily means from the annual mean shall be calculated by:
2
d
dy
� y �
2
� �
d � � �
y� � d m
d m
� �
� �
d�1 d�1
� �
� � (9)
sd y
d (d � 1)
y y
5.5 Expression of results
Monthly mean values of the dry-bulb outdoor temperature shall be expressed to the nearest 0,1 �C and the type of
data (i.e. hourly, daily, etc.) used for the monthly mean calculation shall be specified.
The following parameters shall be reported for each month:
a) the measurement dates from which the parameters are calculated;
b) the monthly means of the dry-bulb outdoor temperature;
c) the standard deviation of the daily mean dry-bulb temperature about the monthly mean;
and, when available:
d) the maximum value of the hourly dry-bulb outdoor temperatures;
e) the minimum value of the hourly dry bulb outdoor temperatures;
f) the values of the hourly dry-bulb outdoor temperature at the 1 %, 5 %, 10 %, 90 %, 95 % and 99 %
percentiles.
NOTE If four or more values of the dry-bulb outdoor temperature per day are available, provided that these values are
reasonably spread through the day, it is possible to estimate hourly values by linear or other interpolation of the raw data and
then calculate the statistical values specified in f).
These parameters summarised in b) to f) shall be presented in tabular form similar to the example shown in
Table 1.
10

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Table 1 — Sample table of monthly and annual mean temperatures
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR
� 5,7 5,4 6,2 8,1 10,4 13,1 14,1 14,7 13,0 10,9 8,1 6,2 9,7
mm
� 3,0 3,0 2,7 2,8 2,6 2,3 2,0 2,3 1,7 2,3 2,2 2,9 4,2
Sdm
-4,0 -1,7 -3,5 1,7 5,5 7,8 9,0 9,3 6,6 4,2 1,1 -0,8 -4,0
�
min
-2,4 -1,1 -1,4 2,0 6,0 8,8 9,5 10,2 7,9 5,8 2,2 -0,6 -0,1
�
p1
0,6 -0,1 2,0 3,5 7,0 9,8 10,6 11,6 10,5 7,2 3,9 0,4 2,5
�
p5
1,4 0,5 3,4 4,2 7,6 10,2 11,5 12,3 11,0 8,2 5,0 1,9 4,3
�
p10
9,4 9,0 9,2 11,3 13,7 16,1 16,7 17,1 15,3 13,9 10,6 9,5 15,0
�
p90
10,1 9,4 11,0 12,4 15,9 17,2 17,3 19,3 15,9 14,9 11,1 10,2 16,0
�
p95
10,9 9,9 15,8 15,0 18,7 20,3 18,7 23,4 16,7 16,3 12,2 11,5 18,4
�
p99
11,1 10,3 18,9 16,5 23,0 21,6 19,7 25,6 17,5 16,8 13,9 11,8 25,6
�
max
6 Atmospheric humidity
6.1 Sources of data
All humidity data used to calculate monthly means shall come from either
a) observations with mechanically ventilated wet and dry bulb thermometers; or
b) a chilled mirror dewpoint meter; or
c) a capacitance hygrometer; or
d) hair hygrometer.
Data derived from wet and dry bulb temperatures measured in a thermometer screen without mechanical
ventilation, as is the practice in many climatological stations, or from hair or similar hygrometers, are too imprecise
to be usable when calculating monthly means.
6.2 Relationships between temperature and humidity parameters
6.2.1 Saturated vapour pressure and temperature
The saturated vapour pressure is given as a function of temperature in Table 2.
11

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Table 2 — Saturated vapour pressure in hPa as a function of temperature �� + ��T
��T
�C
��
+0 +1 +2 +3 +4 +5 +6 +7 +8 +9
�C
-20 1,03 1,13 1,24 1,37 1,50 1,65 1,81 1,98 2,17 2,37
-10 2,59 2,83 3,09 3,38 3,68 4,01 4,37 4,75 5,17 5,62
0 6,11 6,56 7,05 7,57 8,13 8,72 9,35 10,01 10,72 11,47
10 12,27 13,12 14,02 14,97 15,98 17,04 18,17 19,37 20,63 21,96
20 23,37 24,86 26,42 28,08 29,82 31,66 33,59 35,63 37,78 40,03
30 42,41 44,90 47,52 50,27 53,16 56,19 59,37 62,71 66,21 69,87
Intermediate values may be found by linear interpolation.
NOTE Saturated vapour pressure can also be calculated using the empirical equations:
� 17,269� �
��
p � � 6,105 exp� � for � � 0 (10)

sat
237,3��
� �
� 21,875� �
��
p � � 6,105 exp� � for � < 0 (11)
sat
265,5 ��
� �
6.2.2 Mixing ratio and vapour pressure
Vapour pressure is calculated from mixing ratio using
xP
p � (12)
� � x
where P is the total atmospheric pressure measured at the site, in hPa.
6.2.3 Relative humidity
Relative humidity is calculated from dry-bulb temperature and vapour pressure using
p
� � (13)
��
p �
sat
where the saturated vapour pressure is derived from temperature as specified in 6.2.1.
NOTE 1 Relative humidity is commonly expressed as a percentage.
NOTE 2 Relative humidity can also be measured directly.
12

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
6.3 Calculation of monthly mean
6.3.1 From hourly data
If hourly values (either as hourly means or values measured at a set time during the hour) of temperature and
vapour pressure (or mixing ratio) are available, the monthly mean temperature shall be calculated as specified in
5.2.1, and the monthly mean vapour pressure shall be calculated from:
h
m
p
h
�
h�1
p � (14)
mm
h
m
and the mean mixing ratio from:
h
m
x
� h
h�1
x � (15)
mm
h
m
where h is the number of hours in the month under consideration.
m
The hourly saturated vapour pressure shall be obtained from Table 2 or calculated from the hourly temperatures
using Equation (10) or (11) as appropriate.
The monthly mean relative humidity shall then be calculated from the monthly mean vapour pressure and
saturated vapour pressure using Equation (13). Equation (12) may be used to convert from the monthly mean
mixing ratio to the monthly mean vapour pressure, if necessary.
If hourly values of temperature and relative humidity are available, the hourly vapour pressure shall be calculated
from
p � p (� )� (16)
h sat h
and then used to calculate the monthly means as specified above.
Due to the non-linear relationship between saturated vapour pressure and temperature, calculating the monthly
mean vapour pressure from the mean relative humidity and temperature will lead to significant errors, especially in
warm climates. Monthly mean vapour pressures should be calculated from the highest frequency vapour
pressure data available.
6.3.2 Data measured at intervals of three, four or six hours
If temperature and vapour pressure data are available at intervals of three, four or six hours, these shall be
averaged over the month and the mean relative humidity calculated as in 6.3.1.
6.3.3 From instantaneous data measured at 7:30, 14:30 and 21:30 or at other similar times
If the relative humidity is available only at 7:30, 14:30 and 21:30, or at other similar times, the daily mean for each
day is calculated using Equation (17) or the equivalent equation for the appropriate times.
� �� � 2�
07:30 14:30 21:30
� � (17)
d m
4
and the monthly means are obtained using Equation (18):
13

---------------------- Page: 15 -------
...

SLOVENSKI STANDARD
SIST EN ISO 15927-1:2004
01-september-2004
+LJURWHUPDOQHNDUDNWHULVWLNHVWDYE±5DþXQDQMHLQSUHGVWDYLWHYNOLPDWVNLK
SRGDWNRY±GHO0HVHþQRLQOHWQRSRYSUHþMHSRVDPH]QLKYUHPHQVNLKHOHPHQWRY
,62
Hygrothermal performance of buildings - Calculation and presentation of climatic data -
Part 1: Monthly means of single meteorological elements (ISO 15927-1:2003)
Wärme- und feuchteschutztechnisches Verhalten von Gebäuden - Berechnung und
Darstellung von Klimadaten - Teil 1: Monats- und Jahresmittelwerte einzelner
meteorologischer Elemente (ISO 15927-1:2002)
Performance hygrothermique des bâtiments - Calcul et présentation des données
climatiques - Partie 1: Moyennes mensuelles et annuelles des éléments météorologiques
simples (ISO 15927-1:2002)
Ta slovenski standard je istoveten z: EN ISO 15927-1:2003
ICS:
07.060 Geologija. Meteorologija. Geology. Meteorology.
Hidrologija Hydrology
91.120.10 Toplotna izolacija stavb Thermal insulation
SIST EN ISO 15927-1:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 15927-1:2004

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SIST EN ISO 15927-1:2004
EUROPEAN STANDARD
EN ISO 15927-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2003
ICS 91.120.10; 91.120.30
English version
Hygrothermal performance of buildings - Calculation and
presentation of climatic data - Part 1: Monthly means of single
meteorological elements (ISO 15927-1:2003)
Performance hygrothermique des bâtiments - Calcul et Wärme- und feuchteschutztechnisches Verhalten von
présentation des données climatiques - Partie 1: Moyennes Gebäuden - Berechnung und Darstellung von Klimadaten -
mensuelles et annuelles des éléments météorologiques Teil 1: Monats- und Jahresmittelwerte einzelner
simples (ISO 15927-1:2002) meteorologischer Elemente (ISO 15927-1:2002)
This European Standard was approved by CEN on 10 April 2003.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2003 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15927-1:2003 E
worldwide for CEN national Members.

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Contents
Page
Foreword.3
1 Scope .4
2 Normative references .4
3 Terms, definitions, symbols and units .4
3.1 Terms and definitions.4
3.2 Symbols and units .6
4 Periods over which parameters are calculated .7
5 Air temperature .8
5.1 Sources of data .8
5.2 Calculation of the monthly mean .8
5.3 Calculation of the standard deviation of daily means about the monthly mean.9
5.4 Calculation of the annual mean and standard deviation.10
5.5 Expression of results .10
6 Atmospheric humidity.11
6.1 Sources of data .11
6.2 Relationships between temperature and humidity parameters.11
6.3 Calculation of monthly mean.13
6.4 Expression of results .14
7 Wind speed and direction .16
7.1 Methods of measurement .16
7.2 Environmental influence on mean wind speed.16
7.3 Statistical elements .20
7.4 Expression of results .21
8 Precipitation .22
8.1 Sources of data .22
8.2 Calculation of monthly total.22
8.3 Expression of results .22
9 Solar radiation.22
9.1 Sources of data .22
9.2 Calculation of monthly total solar irradiation .23
9.3 Expression of results .24
9.4 Estimating irradiances that are not measured.24
10 Longwave radiation .24
10.1 General.24
10.2 Sources of data .24
10.3 Calculation of monthly total longwave irradiation from the atmosphere (sky).24
10.4 Expression of results .25
Annex A (informative) Methods for splitting global solar irradiance into the direct and diffuse parts.26
Annex B (informative) Methods for estimating the longwave atmospheric irradiances (longwave sky
irradiances)and the sky temperature.27
Bibliography .29
2

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Foreword
This document (EN ISO 15927-1:2003) has been prepared by Technical Committee CEN/TC 89, “Thermal
performance of buildings and building components”, the secretariat of which is held by SIS, in collaboration with
Technical Committee ISO/TC 163, “Thermal performance and energy use in the built environment”,
Subcommittee SC 2 "Calculation methods".
This European Standard shall be given the status of a national standard, either by publication of an identical text
or by endorsement, at the latest by May 2004, and conflicting national standards shall be withdrawn at the latest
by May 2004.
This standard is one of a series of standards on calculation methods for the design and evaluation of the thermal
and moisture performance of buildings. EN ISO 15927, Hygrothermal performance of buildings – Calculation and
presentation of climatic data, consists of six parts:
Part 1: Monthly means of single meteorological elements;
Part 2: Data for design cooling loads and risk of overheating;
Part 3: Calculation of a driving rain index for vertical surfaces from hourly wind and rain data;
Part 4: Data for assessing the annual energy for heating and cooling;
Part 5: Winter external design air temperatures and related wind data;
Part 6: Accumulated temperature differences for assessing energy use in space heating.
Annexes A and B are informative.
This document includes a Bibliography.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,
Slovakia, Spain, Sweden, Switzerland and the United Kingdom.
3

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
1 Scope
This European Standard specifies procedures for calculating and presenting the monthly means of those
parameters of climatic data needed to assess some aspects of the thermal and moisture performance of
buildings. Numerical values should be obtained from the meteorological service in the relevant country.
This European Standard covers the following single climate variables:
air temperature;
atmospheric humidity;
wind speed;
precipitation;
solar radiation;
longwave radiation.
Meteorological instrumentation and methods of observation are not covered; these are specified by the World
Meteorological Organisation (WMO).
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies (including amendments).
World Meteorological Organisation: Guide to meteorological instruments and methods of observation. 6th Edition
WMO - No.8 1996.
3 Terms, definitions, symbols and units
3.1 Terms and definitions
For the purposes of this European Standard, the following terms and definitions apply.
3.1.1
mixing ratio
ratio of the mass of water vapour to the mass of dry air with which the water vapour is associated
3.1.2
water vapour pressure
part of the total atmospheric pressure exerted by water vapour
3.1.3
saturated vapour pressure over water
vapour pressure of moist air in equilibrium with a plane liquid water surface
3.1.4
relative humidity
ratio of the vapour pressure of moist air to the vapour pressure it would have if it were saturated
3.1.5
reference wind speed
wind speed measured at a height of 10 m above ground level in open country without nearby obstacles
3.1.6
gust speed
greatest instantaneous wind speed observed during the period over which the mean is calculated
4

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
3.1.7
solar irradiance
radiation power per area generated by the reception of solar radiation on a plane of any tilt and orientation
The following special quantities can be distinguished according to the conditions of reception:
3.1.7.1
global solar irradiance
irradiance generated by reception of solar radiation from the full hemisphere
NOTE According to the following definitions it is equal to the reception of direct solar and diffuse solar radiation on a
horizontal plane. In the case of tilted planes a portion of the ground reflected global solar radiation is also received.
3.1.7.2
direct solar irradiance
irradiance generated by the reception of solar radiation from a conical angle which surrounds concentrically the
apparent solar disk
NOTE 1 Also referred to as "beam solar radiation".
NOTE 2 The horizontal component of the direct solar irradiance is a part of the global solar irradiance.
NOTE 3 Any component of the direct solar irradiance is generated nearly exclusively from unscattered solar radiation.
NOTE 4 The diameter of the apparent solar disk corresponds to about 0,5 degrees; for technical reasons the available
radiometers receive the direct solar irradiance from solid angles around the solar disk which correspond mostly to field-of-view
angles between 3 and 6.
3.1.7.3
diffuse solar irradiance
irradiance generated by the reception of scattered solar radiation from the full sky hemisphere , with the exception
of that solid angle which is used to measure the direct solar irradiance
NOTE 1 Practical measurement requires a sun following disk, which permanently shades the receiver of the radiometer
with a ‘field of shade’ angle which equals the field of view angle used for measuring direct solar irradiance. This allows the
global irradiance to be calculated as the sum of diffuse solar and the horizontal component of the direct solar irradiance.
NOTE 2 The use of a ring to shade the sun along its daily path instead of a disk requires an equation to correct for the
corresponding losses of diffuse solar irradiance.
3.1.7.4
reflected solar irradiance
irradiance generated by reception of the rising reflected global radiation on a downward looking plane
NOTE 1 The ratio of reflected solar and global solar irradiance is called albedo.
NOTE 2 Part of the reflected global solar radiation is received on any tilted plane.
3.1.8
solar irradiation
radiant energy per area received from the sun on a plane of defined inclination and orientation during a given
period of time
NOTE The same components as indicated in 3.1.7 for irradiance can be distinguished.
3.1.9
longwave (terrestrial) radiation
radiation with wavelength greater than 3 m from surfaces at the ground and from the atmosphere
NOTE The exchange of longwave radiation occurs permanently between buildings, the ground and the atmosphere at
temperatures between 240 K and 340 K.
5

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
3.1.10
thermometer screen
white painted, wooden, plastic, or aluminium louvered enclosure, which allows a free flow of air over
thermometers while shielding them from solar radiation, longwave radiation and precipitation
3.2 Symbols and units
Symbol Quantity Unit
C roughness coefficient -
R
C topography coefficient -
T
D
wind direction from North
d
number of days in a month -
m
d number of days in a year -
y
2
G longwave irradiancefrom the atmosphere on a horizontal plane
l,aW/m
2
G solar irradiance W/m
s
2
G direct (beam) solar irradiance W/m
s,b
2
G diffuse solar irradiance W/m
s,d
2
G global solar irradiance W/m
s,g
2
G reflected global solar irradiance
Wm
s,r
H
effective height of topographic feature m
2
H solar irradiation MJ/m
s
h
number of hours in a month -
m
K terrain factor -
R
L actual length of downwind slope m
d
L effective length of upwind slope m
e
L actual length of upwind slope m
u
R rainfall total (or equivalent amount of melted solid precipitation) mm
P total atmospheric pressure hPa
p
water vapour pressure hPa
p () hPa
saturated vapour pressure over water at temperature sat
s scale factor for topography coefficient -
T
temperature K
v wind speed m/s
vˆ gust wind speed m/s
6

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Symbol Quantity Unit
v reference mean wind speed m/s
r
v mean wind speed at a site m/s
s
x mixing ratio g/kg
g/kg
x () saturated mixing ratio with respect to liquid water at temperature sat
y
horizontal distance of site from crest of topographic feature m
z height above ground m
z
minimum height m
min
z roughness height m
0
ratio of gas constant of dry air to gas constant of water vapour -
( = 0,62198)
air temperatureC
upwind slope of topographic feature -
relative humidity -
3.2.1 Subscripts
Subscript Meaning
a atmosphere
dm
mean over a day
dx maximum over a day
dn minimum over a day
h values representative of an hour (either instantaneous measurements or the
mean of many readings in the hour)
ic inclination of a surface
mm mean over a month
N values representative of a number of hours N (e.g. 3 h, 6 h or 12 h but less
than 24 h) (either instantaneous measurements or the mean of many
readings in the period)
l longwave
pq value exceeded for q % of the time
s solar
sd standard deviation
4 Periods over which parameters are calculated
The methods specified in clauses 5 to 9 can be used to calculate monthly means or totals from either individual
months (e.g. a January from a specified year) or from all the corresponding months from many years (e.g. all the
Januarys from a 30 year data set).
Calculations of the standard deviation of daily means or totals about the monthly or annual means or totals
(see 5.3 and 5.4) shall refer to a specified month or year.
7

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
The specified year or the multi-year period over which all parameters are calculated shall be quoted with the
values of the parameters.
5 Air temperature
5.1 Sources of data
The dry-bulb air temperature data used to calculate monthly means shall come from observations from a
thermometer screen fitted with louvers to allow a free flow of air.
5.2 Calculation of the monthly mean
5.2.1 From hourly data
The hourly temperature may be either: a) the mean of continuous measurements recorded during that hour or b)
measurements recorded at a particular moment within the hour (e.g. on the hour).
The monthly means shall be calculated as:
h
m

h
h1
(1)
mm
h
m
where
is the hourly temperature, in C;
h
h is the number of hours in the month under consideration.
m
5.2.2 From data measured at intervals of 3 h or 6 h
If dry-bulb outdoor air temperature data are available at intervals of 3 h or 6 h (each value may be either the mean
of continuous measurements during the interval or an instantaneous measurement taken on the interval), the
monthly mean is calculated from:
n
m
N
N1
(2)
mm
n
m
where
n = 8 d for data at three-hour intervals;
m m
= 4 d for data at six-hour intervals;
m
d is the number of days in the month under consideration.
m
5.2.3 From daily maximum and minimum data
If the only dry-bulb outdoor air temperatures available are the daily maximum and minimum for each day of the
month, the daily mean for each day is calculated as:
dn dx
(3)
dm
2
8

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
and the monthly means obtained as:
d
m
d m
d1
(4)
mm
d
m
where
d is the number of days in the month under consideration.
m
NOTE Daily means calculated from the daily maximum and minimum temperature will, in general, be different from those
calculated from hourly values. Most (95 %) of the differences lie between 1,0 C but they can range up to 2,0 C. Monthly
means calculated from daily maximum and minimum values will also differ from those calculated from hourly values, but in this
case 95 % of the differences lie between 0,2 C and the maximum difference lies between 0,25 C.
5.2.4 From instantaneous data at 07:30, 14:30 and 21:30 or at other similar times
If dry-bulb outdoor air temperature data are available only at 07:30, 14:30 and 21:30, or at other similar times, the
daily mean for each day is calculated using Equation (5), or the equivalent equation for the appropriate times.
207:30 14:30 21:30
(5)
d m
4
and the monthly mean obtained from Equation (4).
5.3 Calculation of the standard deviation of daily means about the monthly mean
If not defined in 5.2.2, 5.2.3 or 5.2.4, the daily mean temperatures for each day in the month are calculated from
data measured at one, three or six hourly intervals using:
n
d

N
N1
(6)
d m
n
d
where
n = 24 for data at one-hour intervals;
d
= 8 for data at three-hour intervals;
= 4 for data at six-hour intervals;
or from daily maximum and minimum data using Equation (3) or at 07:30, 14:30 and 21:30 or similar times using
Equation (5).
Then the standard deviation of the daily means from the monthly mean is given by:
2
d d
mm
2
d
md m
d m
d1 d1
(7)
sdm
d (d1)
m m
9

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
5.4 Calculation of the annual mean and standard deviation
The annual mean temperature shall be calculated from the daily means using:
d
y

d m
d1
(8)
ym
d
y
The standard deviation of the daily means from the annual mean shall be calculated by:
2
d
dyy
2

d
yd m
d m

d1 d1

(9)
sd y
d (d1)
y y
5.5 Expression of results
Monthly mean values of the dry-bulb outdoor temperature shall be expressed to the nearest 0,1 C and the type of
data (i.e. hourly, daily, etc.) used for the monthly mean calculation shall be specified.
The following parameters shall be reported for each month:
a) the measurement dates from which the parameters are calculated;
b) the monthly means of the dry-bulb outdoor temperature;
c) the standard deviation of the daily mean dry-bulb temperature about the monthly mean;
and, when available:
d) the maximum value of the hourly dry-bulb outdoor temperatures;
e) the minimum value of the hourly dry bulb outdoor temperatures;
f) the values of the hourly dry-bulb outdoor temperature at the 1 %, 5 %, 10 %, 90 %, 95 % and 99 %
percentiles.
NOTE If four or more values of the dry-bulb outdoor temperature per day are available, provided that these values are
reasonably spread through the day, it is possible to estimate hourly values by linear or other interpolation of the raw data and
then calculate the statistical values specified in f).
These parameters summarised in b) to f) shall be presented in tabular form similar to the example shown in
Table 1.
10

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Table 1 — Sample table of monthly and annual mean temperatures
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR
5,7 5,4 6,2 8,1 10,4 13,1 14,1 14,7 13,0 10,9 8,1 6,2 9,7
mm
3,0 3,0 2,7 2,8 2,6 2,3 2,0 2,3 1,7 2,3 2,2 2,9 4,2
Sdm
-4,0 -1,7 -3,5 1,7 5,5 7,8 9,0 9,3 6,6 4,2 1,1 -0,8 -4,0min
-2,4 -1,1 -1,4 2,0 6,0 8,8 9,5 10,2 7,9 5,8 2,2 -0,6 -0,1p1
0,6 -0,1 2,0 3,5 7,0 9,8 10,6 11,6 10,5 7,2 3,9 0,4 2,5p5
1,4 0,5 3,4 4,2 7,6 10,2 11,5 12,3 11,0 8,2 5,0 1,9 4,3p10
9,4 9,0 9,2 11,3 13,7 16,1 16,7 17,1 15,3 13,9 10,6 9,5 15,0p90
10,1 9,4 11,0 12,4 15,9 17,2 17,3 19,3 15,9 14,9 11,1 10,2 16,0p95
10,9 9,9 15,8 15,0 18,7 20,3 18,7 23,4 16,7 16,3 12,2 11,5 18,4p99
11,1 10,3 18,9 16,5 23,0 21,6 19,7 25,6 17,5 16,8 13,9 11,8 25,6max
6 Atmospheric humidity
6.1 Sources of data
All humidity data used to calculate monthly means shall come from either
a) observations with mechanically ventilated wet and dry bulb thermometers; or
b) a chilled mirror dewpoint meter; or
c) a capacitance hygrometer; or
d) hair hygrometer.
Data derived from wet and dry bulb temperatures measured in a thermometer screen without mechanical
ventilation, as is the practice in many climatological stations, or from hair or similar hygrometers, are too imprecise
to be usable when calculating monthly means.
6.2 Relationships between temperature and humidity parameters
6.2.1 Saturated vapour pressure and temperature
The saturated vapour pressure is given as a function of temperature in Table 2.
11

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
Table 2 — Saturated vapour pressure in hPa as a function of temperature + T
T
C

+0 +1 +2 +3 +4 +5 +6 +7 +8 +9
C
-20 1,03 1,13 1,24 1,37 1,50 1,65 1,81 1,98 2,17 2,37
-10 2,59 2,83 3,09 3,38 3,68 4,01 4,37 4,75 5,17 5,62
0 6,11 6,56 7,05 7,57 8,13 8,72 9,35 10,01 10,72 11,47
10 12,27 13,12 14,02 14,97 15,98 17,04 18,17 19,37 20,63 21,96
20 23,37 24,86 26,42 28,08 29,82 31,66 33,59 35,63 37,78 40,03
30 42,41 44,90 47,52 50,27 53,16 56,19 59,37 62,71 66,21 69,87
Intermediate values may be found by linear interpolation.
NOTE Saturated vapour pressure can also be calculated using the empirical equations:
17,269
p6,105expfor  0 (10)
sat
237,3
21,875
p6,105expfor < 0 (11)
sat
265,5
6.2.2 Mixing ratio and vapour pressure
Vapour pressure is calculated from mixing ratio using
xP
p(12)
x
where P is the total atmospheric pressure measured at the site, in hPa.
6.2.3 Relative humidity
Relative humidity is calculated from dry-bulb temperature and vapour pressure using
p
(13)
p
sat
where the saturated vapour pressure is derived from temperature as specified in 6.2.1.
NOTE 1 Relative humidity is commonly expressed as a percentage.
NOTE 2 Relative humidity can also be measured directly.
12

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
6.3 Calculation of monthly mean
6.3.1 From hourly data
If hourly values (either as hourly means or values measured at a set time during the hour) of temperature and
vapour pressure (or mixing ratio) are available, the monthly mean temperature shall be calculated as specified in
5.2.1, and the monthly mean vapour pressure shall be calculated from:
h
m
p
h
h1
p(14)
mm
h
m
and the mean mixing ratio from:
h
m
x
h
h1
x(15)
mm
h
m
where h is the number of hours in the month under consideration.
m
The hourly saturated vapour pressure shall be obtained from Table 2 or calculated from the hourly temperatures
using Equation (10) or (11) as appropriate.
The monthly mean relative humidity shall then be calculated from the monthly mean vapour pressure and
saturated vapour pressure using Equation (13). Equation (12) may be used to convert from the monthly mean
mixing ratio to the monthly mean vapour pressure, if necessary.
If hourly values of temperature and relative humidity are available, the hourly vapour pressure shall be calculated
from
pp( )(16)
h sat h
and then used to calculate the monthly means as specified above.
Due to the non-linear relationship between saturated vapour pressure and temperature, calculating the monthly
mean vapour pressure from the mean relative humidity and temperature will lead to significant errors, especially in
warm climates. Monthly mean vapour pressures should be calculated from the highest frequency vapour
pressure data available.
6.3.2 Data measured at intervals of three, four or six hours
If temperature and vapour pressure data are available at intervals of three, four or six hours, these shall be
averaged over the month and the mean relative humidity calculated as in 6.3.1.
6.3.3 From instantaneous data measured at 7:30, 14:30 and 21:30 or at other similar times
If the relative humidity is available only at 7:30, 14:30 and 21:30, or at other similar times, the daily mean for each
day is calculated using Equation (17) or the equivalent equation for the appropriate times.
2
07:30 14:30 21:30
(17)
d m
4
and the monthly means are obtained using Equation (18):
13

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SIST EN ISO 15927-1:2004
EN ISO 15927-1:2003 (E)
d
m

d m
N1
(18)
mm
d
m
6.3.4 Calculation of the annual means
The annual mean temperature shall be calculated using Equation (7) and the annual mean water vapour pressure
calculated from:
d
y
p
d m
d1
p(19)
ym
d
y
and the mean mixi
...