aDate: 2 April 2002Origin: European

Latest date for receipt of comments: 30.06.2002 Project no.: 2001/01891Responsible committee: B/540/1 European Standards For Thermal Insulation

Interested committees: B/2; B/11, CB/2

Title: Draft ENISO 15927-5 Hygrothermal performance of buildings - Calculation and presentation of climatic dataPart 5. Winter external design air temperatures and related data

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EUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORM

DRAFTprEN ISO 15927-5

February 2002

ICS

English version

Hygrothermal performance of buildings - Calculation andpresentation of climatic data - Part 5: Winter external design air

temperatures and related wind data (ISO/DIS 15927-5:2002)Wrme- und feuchteschutztechnisches Verhalten von

Gebuden - Berechnung und Darstellung von Klimadaten -Teil 5: Bemessungstemperaturen der Auenluft im Winter

und zugehrige Winddaten (ISO/DIS 15927-5:2002)

This draft European Standard is submitted to CEN members for parallel enquiry. It has been drawn up by the Technical CommitteeCEN/TC 89.

If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations whichstipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other languagemade by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the samestatus as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice andshall not be referred to as a European Standard.

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2002 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.

Ref. No. prEN ISO 15927-5:2002 E

prEN ISO 15927-5:2002 (E)

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Contents

Foreword......................................................................................................................................................................3Introduction .................................................................................................................................................................31 Scope ......................................................................................................................................................................42 Normative references............................................................................................................................................43 Definitions, symbols and units ............................................................................................................................54 Methods of calculation.........................................................................................................................................65 Coincident wind speed .........................................................................................................................................76 Dominant wind direction.......................................................................................................................................77 Reference altitude .................................................................................................................................................88 Presentation of data .............................................................................................................................................89 Data representing a geographical area, region or zone ...................................................................................9

prEN ISO 15927-5:2002 (E)

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Foreword

This document (prEN ISO 15927-5:2002) has been prepared by Technical Committee CEN/TC 89 "Thermalperformance of buildings and building components", the secretariat of which is held by SIS, in collaboration withTechnical Committee ISO/TC 163 "Thermal insulation".

This document is currently submitted to the parallel Enquiry.

This standard is one of a series of standards on calculation methods for the design and evaluation of the thermaland moisture related performance of buildings and building components.

prEN ISO 15927-5:2002 (E)

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Introduction

The choice of design load for space heating is a matter of balancing user needs against cost. On the one handusers expect a heating system to maintain the internal temperatures needed for health and comfort; on the otherhand, very high heating demand arises from time to time, when a rare meteorological extreme occurs. It is usuallyuneconomic to design heating systems for rare extremes, as this would lead to high capital (initial) cost and usuallyto lower operational efficiency of the system.

The practical solution is to choose an infrequent, but not extreme, climatological value as the basis for the designload. This means that from time to time heat demand will exceed the systems capacity, with the result that internaltemperatures will be lower than desired, or that supplementary heating will be needed (e.g. from local heaters).The methods of calculation in this standard include a standard return period or frequency, which is judged to givean acceptable balance between risk of inadequate performance and cost.

Definition of winter external design temperatures also needs to reflect the interaction between buildings and theirexternal environment. Buildings possess thermal inertia and do not respond instantly to changes in weatherconditions. The time delay (or lag) before internal conditions are significantly affected varies between differenttypes of construction and heating method. For this reason it is necessary to define more than one type of winterexternal design temperature, as follows:

a) Buildings of high thermal capacity (generally constructed of heavy materials) respond relatively slowly to heatgains and losses; for these a two-day mean air temperature is appropriate.

b) Buildings of low thermal capacity (generally constructed of lightweight materials) respond more quickly to heatgains and losses; for these an hourly mean air temperature is appropriate.

c) An hourly mean temperature is also suitable as the winter external design temperature for air handling heatingloads in air-conditioned buildings.

The influence of wind may be important in climates where infrequent, low temperatures are associated withsignificant wind speeds. This standard specifies that average coincident wind speed and range of directions shallbe determined for the conditions of the winter external design temperature. The wind speed class shall be declaredin all cases and the dominant wind direction when it is significant.

1 Scope

This standard specifies the definition, method of calculation and method of presentation of the climatic data to beused in determining the design heat load for space heating in buildings. These include:

the winter external design air temperatures;

the relevant wind speed and direction where appropriate.

Heat loss through the ground, which also contributes to the heat load for buildings, depends on longer termtemperature changes; methods for calculating ground heat loss are given in ISO 13370, Thermal performance ofbuildings - Heat transfer via the ground - Calculation methods.

2 Normative references

The following normative documents contain provisions, which through reference in this text constitute provisions ofthis standard. For dated references, subsequent amendments to, or revisions of, any of these publications do notapply. However, parties to agreements based on this standard are encouraged to investigate the possibility ofapplying the most recent editions of the normative documents indicated below. For undated references, the latestedition of the normative document referred to applies. Members of ISO and IEC maintain registers of currentlyvalid International Standards

prEN ISO 15927-5:2002 (E)

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ISO 6243

WMO - No. 8

Climatic data for building design Proposed system of symbols

Guide to meteorological instruments and methods of observation

3 Definitions, symbols and units

3.1 Definitions

For the purposes of this standard, the terms and definitions given in ISO 6243 and the following apply.

3.1.1design heat loadmaximum heat output required from the heating system of a building, in order to maintain required internaltemperatures without supplementary heating

3.1.2winter external design temperaturelow external air temperature having a defined probability of being exceeded, used to determine the design heatload of a building

3.1.3coincident wind speedaverage wind speed during a period over which temperature is averaged

3.1.4hourly temperatureaverage of instantaneous air temperatures during one hour

NOTE In the absence of continuous measurements, the air temperature observed at a particular moment (e.g. on the hour)may be substituted.

3.1.5daily maximum temperaturemaximum dry-bulb air temperature during a day (00:00 to 23:59)NOTE This can be either the highest hourly mean temperature or the recorded extreme on a maximum thermometer.

3.1.6daily minimum temperaturesminimum dry-bulb air temperature during a day (00:00 to 23:59)NOTE This can be either the lowest hourly mean temperature or the recorded extreme on a minimum thermometer.

3.1.72-day mean temperatureaverage of daily maximum temperature and daily minimum temperature on two consecutive days

3.2 Symbols, quantities and units

The letter symbols used differ in some cases from those given in ISO 6243, mainly to comply with developingpractice in other ISO Technical Committees e.g. ISO/TC 163. However, the principles of ISO 6243 have beenfollowed where possible.

prEN ISO 15927-5:2002 (E)

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Symbol Quantity Unit

dx daily maximum temperature C

dn daily minimum temperature C

hm hourly mean temperature C

2dm two day mean temperature C

*

hhourly mean design temperature C

*

2dtwo day mean design temperature C

4 Methods of calculation

4.1 Sources of data

The temperatures and wind speeds used to calculate the winter external design temperature shall have beenmeasured by the methods specified by the WMO Guide No.8.

4.2 Types of WEDT required

Two main types of winter external design temperature are required.

a two-day mean air temperature, *2d ,and

an hourly mean air temperature, *h .

4.3 Two-day mean design temperature

The two-day mean design temperature, *2d , is calculated as the two-day mean air temperature having an averagereturn period of one year (e.g. occurring 20 times in 20 years). The two-day mean air temperature on which it isbased may be calculated in one of several ways, depending on the data available:

a) Where hourly data are available, 2dm shall be calculated as the mean of 48 hourly values between 00:00 onthe first day and 23:00 on the second day:

b) Where three-hourly data are available, 2dm shall be calculated as the mean of 16 three-hourly values between00:00 on the first day and 21:00 on the second day:

c) Where temperatures observed at 07:30 (7:30), 14:30 (14:30) and 21:30 (21:30), or at other similar times, areavailable, 2dm shall be calculated using equation (1) or the equivalent equation for the appropriate times.

822 2day30:2130:1430:71day30:2130:1430:7

m2

d (1)

d) Where only daily maximum and daily minimum temperatures are available, a less accurate estimate shall beobtained using equation (2):

prEN ISO 15927-5:2002 (E)

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42daynx1daynx

m2dddd

d

(2)

The choice of calculation method has a relatively small influence on the value of *2d which should be derived fromthe most finely resolved data available for a location in order of priority from a) to d).

4.4 Hourly mean design temperature

Calculate *h as the hourly mean air temperature exceeded on average in 99 % of hours during the coldest month ofthe year. It may be either:

a) calculated from hourly temperature data, sorted into a frequency distribution, or

b) estimated from three hourly data, where hourly data are not available, using quadratic interpolation to estimatethe temperatures in intermediate hours and then treating the estimated hourly data as in a).

The coldest month is the month with the lowest average monthly mean temperature. It shall be used as the monthfrom which hourly data are drawn, even in those years (if any) when the lowest monthly mean temperature occursin a different month.

4.5 Period of records of source data

All values of winter external design temperature shall, where possible, be based on measurements recorded over acontinuous period of at least 20 years, the period being stated with the data. If any data are missing from thisperiod, meteorological advice shall be sought to ensure that the results will be representative of the distribution ofinfrequent low temperatures during the period.

5 Coincident wind speed

5.1 Determination of mean wind speed

Where continuously recorded wind speed are available, continuous average wind speeds shall be calculated asaverages over the period defined in 5.2 and 5.3. Where non-continuous data, such as 10-minute mean windspeeds, are available, continuous average wind speeds shall be estimated. All wind speeds shall be determined at,or corrected to, a height of 10 m above ground level.

Correction factors for local shelter or exposure, or for the height of buildings may be specified in national standards.

5.2 Two day mean design temperature

The coincident wind speed shall be taken as the 95-percentile wind speed from all the two-day periods with meantemperature equal to or colder than the two day mean design temperature.

5.3 Hourly mean design temperature

The coincident wind speed shall be taken as the 95-percentile wind speed from all the hours with meantemperature equal to or colder than the hourly mean design temperature.

6 Dominant wind direction

6.1 Determination of dominant wind direction

Wind directions shall be analysed by non-overlapping 30 segments. Any segment from which the wind blows for40 %, or more, of the time shall be declared a dominant wind direction. If more than one segment is dominant, the

prEN ISO 15927-5:2002 (E)

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main and secondary segments shall be reported. Dominant wind directions shall be described by the limits of theirsegment, e.g. 030 degrees - 060 degrees.

6.2 Two day mean design temperature

The dominant wind direction or directions shall be determined for the two-day period nearest in mean temperatureto the two day mean design temperature, *2d , and all the colder two-day periods in the period of records.

6.3 Hourly mean design temperature

The dominant wind direction or directions shall be determined for the hour selected as the hourly mean designtemperature, *h , and all the colder hours in the period of record.

7 Reference altitude

All winter external design temperature data shall relate to a reference altitude; this may be either:

a) the altitude of the location e.g. a meteorological station, at which the original air temperature data wererecorded;

b) a general altitude for temperature data applying to an area, region or zone; this may be mean sea level; or

c) the actual altitudes over an area of land, in the case of design temperature isopleths on maps.

Use a correction factor to estimate design temperatures at altitudes other than that at which the original airtemperature data were recorded. This factor (the lapse rate for *2d and *h ,) shall be determined from localmeteorological records. The correction factor is used to compute design temperature data for cases b) and c), andto enable the user to convert design temperature data from its reference altitude to an actual altitude, wheredifferent.

Lapse rates and other causes of local variation in low temperatures can be strongly influenced by air drainage,radiation losses and heat island effects: specialist meteorological advice should be obtained where possible.

8 Presentation of data

8.1 Data requirements

Winter external design temperature data shall be given together with coincident wind speed. Dominant winddirection shall be included when applicable.

8.2 Qualifying information to be given with all data

The following information shall be given:

a) the unit of measurement for air temperature, in C, and, where applicable for coincident wind speed, in metreper second, and direction in degrees;

b) the return period or frequency of the value, as specified for *2d in 4.2 or for *h in 4.3;

c) the period of records (number of years of measurements) from which the data were calculated;

d) except for isopleths on maps, the reference altitude in metres above mean sea level.

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8.3 Coincident wind speed

Average wind speeds shall be rounded to the nearest 0,5 m/s. Where the value is below 1 m/s, the coincident windspeed shall be described as calm (C). Where the value is 1 m/s or more, it shall be stated with the correspondingdata.

8.4 Dominant wind direction

Where the average wind speed is 2,5 m/s or more and the criteria for the dominant wind direction in clause 6 aresatisfied, the dominant wind direction(s) shall be stated with the corresponding data.

8.5 Winter external design temperature data in tables

Winter external design temperature data for specific sites (e.g. meteorological stations) shall be presented intabular form, rounded to the nearest multiple of 1 C, and stating coincident wind conditions (see 8.3).

8.6 Winter external design temperature data in maps

Winter external design temperature data for an area, region or country may be presented on maps either as zonesor isopleths (contours):

a) data applying to zones shall be rounded to the nearest multiple of 1 C and stated together with an averagecoincident wind conditions applicable to the zone.

b) data given as isopleths on maps shall be rounded to the nearest multiple of 2 C. It will not usually be possibleto show coincident wind speeds on the isopleths; these should be stated separately.

8.7 Correction for altitude

Where an altitude correction has been applied in the preparation of data, the presentation shall include thestatement Values corrected to mean sea level or Values corrected to a reference altitude of nnn m, asappropriate.When it is necessary for the user to convert data from a reference altitude to an actual altitude, the correction factorshall be stated, e.g. as a change in monthly or annual winter external design temperature values for each 100 mchange in altitude.

9 Data representing a geographical area, region or zone

Data intended to apply to an area, region or zone can be either:c) the winter external design temperatures for a single meteorological station, deemed to typify the climate of the

area, region or zone; or

d) the average of the winter external design temperatures for several representative meteorological stations, statedtogether with an appropriate altitude.

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