Bsi bs en 00832 2000 (2001)

/home/gencode/overflow/bsen832/en832 1 10325 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |[.]

This British Standard, having

been prepared under the

direction of the Sector

Committee for Building and Civil

Engineering, was published under

the authority of the Standards

Committee and comes into effect

on 15 March 2000

 BSI 07-2001

ISBN 0 580 30259 8

Amendments issued since publication

Amd No Date Comments

11044

corrigendum No.1

July 2001 Indicated by a sideline

This British Standard is the official English language version of EN 832:1998,incorporating corrigendum May 2000

The UK participation in its preparation was entrusted by Technical CommitteeB/540, Energy performance of materials, components and buildings, toSubcommittee B/540/1, European Standards for thermal insulation, which has theresponsibility to:

Ð aid enquirers to understand the text;

Ð present to the responsible European committee any enquiries on theinterpretation, or proposals for change, and keep the UK interests informed;

Ð monitor related international and European developments and promulgatethem in the UK

A list of organizations represented on this subcommittee can be obtained on request

to its secretary

Textual error

The textual error set out below was discovered when the English language version

of Corrigendum May 2000 to EN 832 was adopted as the national standard The errorhas been reported to CEN in a proposal to amend the text of the European

Standard

Corrigendum May 2000 to EN 832 called for the replacement of Equation (10) in

subclause 5.2.4 The insertion text supplied for the equation contained the

elementVx9when it should have contained the element V Ç 9x This error has beencorrected in the text

Cross-references

The British Standards which implement international or European publicationsreferred to in this document may be found in the BSI Standards Catalogue under thesection entitled ªInternational Standards Correspondence Indexº, or by using theªFindº facility of the BSI Standards Electronic Catalogue

A British Standard does not purport to include all the necessary provisions of acontract Users of British Standards are responsible for their correct application

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Summary of pages

This document comprises a front cover, an inside front cover, the EN title page,pages 2 to 32, an inside back cover and a back cover

European Committee for StandardizationComite EuropeÂen de NormalisationEuropaÈisches Komitee fuÈr Normung

Central Secretariat: rue de Stassart 36, B-1050 Brussels

 1998 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN nationalMembers

Ref No EN 832:1998 E

Descriptors: residential buildings, thermal insulation, heating, water production, computation, heat balance, heat transfer, thermodynamic

properties, B coefficient, heat loss coefficient, efficiency, climate solar energy

English version

Thermal performance of buildings Ð Calculation of energy use

for heating Ð Residential buildings

Performance thermique des baÃtiments Ð Calcul des

besoins d'eÂnergie pour le chauffage Ð BaÃtiments

reÂsidentiels

WaÈrmertchnisches Verhalten von GebaÈuden ÐBerechnung des Heizenergiebedarfs Ð

WohngebaÈude

This European Standard was approved by CEN on 1 July 1998

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 Central Secretariat 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 Central Secretariat 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, Iceland, Ireland, Italy,

Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and

United Kingdom

This European Standard has been prepared by

Technical Committee CEN/TC 89, Thermal performance

of buildings and building components, the Secretariat

of which is held by SIS

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 March 1999,

and conflicting national standards shall be withdrawn

at the latest by July 1999

This standard is one of a series of standard calculation

methods for the design and evaluation of thermal

performance of buildings and building components

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, Iceland, Ireland,

Italy, Luxembourg, Netherlands, Norway, Portugal,

Spain, Sweden, Switzerland and the United Kingdom

3 Definitions, symbols and units 3

4 Outline of the calculation procedure

5 Heat losses at constant internal

8 Annual heat use of the building 10

special envelope elements 14Annex D (normative) Solar gains of special

Annex E (informative) Envelope elements

Annex F (informative) Data for estimation

of natural ventilation and infiltration 19Annex G (informative) Data for solar gains 20Annex H (informative) Calculation of

effective thermal capacity 21Annex J (informative) Heat losses with

intermittent heating or set-back 22Annex K (informative) Accuracy of the

Annex L (informative) Calculation example 26Annex M (informative) Bibliography 31Annex ZB (informative) A-deviations 32

The calculation method presented in this standard is

based on a steady state energy balance, but taking

account of internal and external temperature variations

and, through a utilization factor, of the dynamic effect

of internal and solar gains

This method can be used for the following

applications:

1) judging compliance with regulations expressed in

terms of energy targets;

2) optimization of the energy performance of a

planned building, by applying the method to several

possible options;

3) displaying a conventional level of energy

performance of existing buildings;

4) assessing the effect of possible energy

conservation measures on an existing building, by

calculation of the energy use with and without the

energy conservation measure;

5) predicting future energy resource needs on a

national or international scale, by calculating the

energy uses of several buildings representative of the

building stock

The user may refer to other European Standards or to

national documents for input data and detailed

calculation procedures not provided by this standard

In some countries the calculation of energy use in

buildings forms part of the national regulation

Information about national deviations from this

standard due to regulations are given in annex ZB

1 Scope

This standard gives a simplified calculation method for

assessment of the heat use and energy needed for

space heating of a residential building, or a part of it,

which will be referred to as ªthe buildingº

This method includes the calculation of:

1) the heat losses of the building when heated to

constant temperature;

2) the annual heat needed to maintain the specified

set-point temperatures in the building;

3) the annual energy required by the heating system

of the building for space heating

The building may have several zones with different

set-point temperatures One zone may have intermittent

heating

The calculation period may be either the heating

season or a monthly period Monthly calculation gives

correct results on an annual basis, but the results for

individual months close to the end and the beginning

of the heating season may have large relative errors

Annex K provides more information on the accuracy of

the method

2 Normative references

This European Standard incorporates by dated orundated reference, provisions from other publications.These normative references are cited at the

appropriate places in the text and the publications arelisted hereafter For dated references, subsequentamendments to or revisions of any of the publicationsapply to this European Standard only when

incorporated in it or by amendment or revision Forundated references, the latest edition of the publicationreferred to applies

prEN 410, Glass in building Ð Determination of

luminous and solar characteristics of glazing.

EN ISO 7345, Thermal insulation Ð Physical

quantities and definitions.

(ISO 7345:1987)

prEN ISO 10077-1, Windows, doors and shutters Ð

Thermal transmittance Ð Part 1: Simplified calculation method.

EN ISO 13786, Thermal performance of building

components Ð Dynamic thermal characteristics Ð Calculation method.

(ISO 13786:1997)

EN ISO 13789, Thermal performance of buildings Ð

Transmission heat loss coefficient Ð Calculation method.

(ISO 13789:1997)

3 Definitions, symbols and units

3.1 Definitions

For the purposes of this standard, the definitions in

EN ISO 7345 and the following apply

3.1.1 external temperature

temperature of external air

3.1.2 internal temperature

arithmetic average of the air temperature and the meanradiant temperature at room centre (internal dryresultant temperature)

3.1.3 set-point temperature

design internal temperature

3.1.4 intermittent heating

heating pattern where, during the course of time, thetemperature is allowed to fall below the designtemperature

part of the heated space with a given set-point

temperature, throughout which the internal

temperature is assumed to have negligible spatial

variations

3.1.8

heat transfer coefficient

heat flow rate between two thermal zones divided by

the temperature difference between both zones

3.1.9

heat loss

heat transferred from heated space to the external

environment by transmission and by ventilation, during

a given period of time

3.1.10

heat loss coefficient

heat transfer coefficient from the heated space to the

heat generated within or entering into the heated space

from heat sources other than the heating system

3.1.12

utilization factor

factor reducing the total monthly or seasonal gains

(internal and passive solar), to obtain the part of the

useful gains

3.1.13

calculation period

time period considered for the calculation of heat

losses and gains

NOTE Most used calculation periods are the month and the

heating season.

3.1.14

heat use

heat to be delivered to the heated space to maintain

the internal set-point temperature of the heated space

3.1.15

energy use for heating

energy to be delivered to the heating system to satisfy

the heat use

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3.2 Symbols and units

For the purposes of this standard, the following termsand symbols apply

Table 1 Ð Symbols and units Symbol Name of quantity Unit

C effective heat capacity of a zone J/K

c specific heat capacity J/(kg´K)

e wind shielding coefficient Ð

n air change rate s21or h21

Q quantity of heat or energy J

R thermal resistance m2´K/W

T thermodynamic temperature K

t time, period of time s

U thermal transmittance W/(m2´K)

V volume of air in a heated zone m3

VÇ air flow rate m3/s

a absorption coefficient of a

surface for solar radiation Ð

b fraction of the time period with

d ratio of the accumulated

internal-external temperaturedifference when the ventilation

is on to its value over thecalculation period Ð

e emissivity of a surface for

thermal radiation Ð

h efficiency, utilization factor for

u Celsius temperature 8C

k factor related to heat losses of

ventilated solar walls Ð

s Stefan-Boltzmann constant

(s = 5,67 3 1028) W/(m2´K4)

Table 2 Ð Subscripts

P related to power ge generation t total; technical

V ventilation l loss; layer x extra; additional

d daily; distribution p partition wall 0 base; reference

e external; emission ps permanent shading 50 at 50 Pa pressure difference

Figure 1 Ð Annual energy balance of a building

Table 1 Ð Symbols and units (continued)

Symbol Name of quantity Unit

x point thermal transmittance W/K

C linear thermal transmittance W/(m´K)

v ratio of the total solar radiation

falling on the element when the

air layer is open to the total

solar radiation during the

calculation period Ð

NOTE Hours can be used as the unit of time instead of seconds

for all quantities involving time (i.e for time periods as well as for

air change rates), but in that case the unit of energy is

watt-hour [W´h] instead of joule.

4 Outline of the calculation procedure and required data

Ð the used solar gains;

Ð the generation, distribution, emission and controllosses of the heating system;

Ð the energy input to the heating system

The terms of the energy balance are illustrated inFigure 1

4.2 Procedure

The calculation procedure for the building under

consideration is listed below In addition, the special

approach given in annex A shall be followed when

applying this standard to existing buildings

1) Define the boundaries of the heated space and, if

needed, of different zones and unheated spaces,

according to 4.3;

2) single zone building: calculate the heat loss

coefficient of the heated space according to clause 5;

multi-zone buildings: follow the procedure in

annex B;

3) define the set-point temperature and, if any, the

intermittence pattern;

4) for seasonal calculation, define or calculate the

length and climatic data of the heating season,

according to 8.2.

Then, for each calculation period:

5) calculate the heat losses, Ql:

a) based on the assumption of constant internal

temperature, according to clause 5;

b) when relevant, based on intermittent heating

according to 5.3;

6) calculate the internal heat gains, Qi, according

to 6.2;

7) calculate the solar gains; Qs, according to 6.3;

8) calculate the utilization factor for total gains

according to 7.2;

9) calculate the heat use from equation (18)

Then, for the whole year:

10) calculate the annual space heating use, according

to clause 8;

11) calculate the heating energy use taking into

account the losses or the efficiency of the heating

system, according to clause 9.

4.3 Definition of boundaries and zones

4.3.1 Boundary of the heated space

The boundary of the heated space consists of the

walls, the lowest floor and decks or roofs separating

the considered heated space from the external

environment or from adjacent heated zones or

unheated spaces For purchased energy, the boundary

is at the delivery point to the building or heating plant

For exhaust air with heat recovery, the boundary is the

exit of the recovery unit

4.3.2 Thermal zones

The heated space can be divided into thermal zones if

necessary When the heated space is heated to the

same temperature throughout, and when internal and

solar gains are relatively small or evenly distributed

throughout the building, the single zone calculation

applies

The division in zones is not required when:

a) set-point temperatures of the zones never differ

by more than 4 K, and it is expected that thegain/loss ratios differ by less than 0,4 (e.g betweensouth and north zones); or

b) doors between zones are likely to be open; orc) one zone is small and it can be expected that thetotal energy use of the building will not change bymore than 5 % by merging it to the adjacent largerzone

In such cases, even if the set-point temperature is notuniform, the single zone calculation applies Then theinternal temperature to be used is:

uiz is the set-point temperature of zone z;

H z is the heat loss coefficient of zone z, according

to clause 5.

In other cases, in particular for buildings that includemore than one type of premises under the same roof,the building is divided into several zones, and thecalculation procedure given in annex B shall be used

4.4 Input data

4.4.1 Source and type of input data

When no European Standard is given as a reference,the necessary information may be obtained fromnational standards or other suitable documents, andthese should be used where available The informativeannexes to this standard give values or methods toobtain values when the required information isotherwise not available

For optimization of a planned building or retrofitting

an existing building, the best available estimate for thatparticular building shall be used (see annex A)

However, if no better estimates are available,conventional values can be used as firstapproximations

For predicting the energy needs or judging compliancewith standards, conventional values shall be used, inorder to make the results comparable betweendifferent buildings

The physical dimensions of the building constructionshall be consistent throughout the calculation Internal,external or overall internal dimensions can be used,but the same type shall be kept for the wholecalculation and the type of dimensions used shall beclearly indicated in the report

NOTE Some linear thermal transmittances of thermal bridges depend on the type of dimensions used.

4.4.2 Building input data

The input data required for single zone calculation are

listed below Some of these data may be different for

each calculation period (e.g shading correction factors,

airflow rates in cold months)

V internal volume of the heated space;

C internal heat capacity of the heated space,

according to 7.2; or

t time constant of the heated space;

hh heating system efficiency

NOTE Either C or t is specified, not both.

4.4.3 Input data for heat loss

HT transmission heat loss coefficient according

to EN 13789

For ventilation losses, the following data are required:

VÇ air flow rate from heated space to exterior

For determination of this air flow rate, some of the

following quantities can be used:

nd design air change rate;

n50 air change rate at 50 Pa pressure difference;

VÇf design air flow rate through ventilation fans;

hv efficiency of the heat recovery system on

exhaust air

4.4.4 Input data for heat gains

Fi average internal heat gains during the

calculation period

For glazed envelope elements, the following data shall

be collected separately for each orientation

(e.g horizontal and vertical south, north, etc.):

A area of opening in the building envelope for

each window or door;

FF frame factor, i.e transparent fraction of the

area A, not occupied by a frame;

FC curtain factor, i.e fraction of the solar

radiation transmitted by permanent curtains;

Fs shading correction factor, i.e average shaded

fraction of area A;

g total solar energy transmittance

In contrast with EN ISO 13789, 5.2, daily average values

of the thermal transmittance of windows with shutters,

determined on the basis of the values given by

EN ISO 10077-1 can be used to determine the heat loss

NOTE Collecting areas which do not provide heat directly to the

heated volume (such as thermal solar collectors connected to a

separate heat storage or photovoltaic cells) should not be taken

into account at this stage These are considered as part of the

heating system.

Additional data should be collected for envelopeelements containing heating devices and componentscollecting solar radiation, such as transparentinsulation, ventilated solar walls, sunspaces, etc., aswell as for calculation of the effect of intermittentheating The required data are listed in thecorresponding annexes

5 Heat losses at constant internal temperature

5.1 Principle

The total heat loss, Ql, of a single zone building atuniform internal temperature during a given period oftime is:

where

ui is the set-point temperature;

ue is the average external temperature during thecalculation period;

t is the duration of the calculation period;

H is the heat loss coefficient of the building:

where

HT is the transmission heat loss coefficient,calculated according to EN 13789 (forenvelope elements incorporating ventilatingdevices, see annex C);

HV is the ventilation heat loss coefficient

(see 5.2).

NOTE (ui2 ue)t is related to degree days defined in different

ways in various countries.

Equation (2) can be adapted at a national level to allowfor the use of degree days The result of the adaptedrelation shall nevertheless be the same as that ofequation (2) for any residential building

5.2 Ventilation heat loss coefficient

VÇ is the air flow rate through the building;

including air flow through unheated spaces;

raca is the heat capacity of the air per unit volume

NOTE If the air flow rate, VÇ, is in m3/s, raca= 1 200 J/(m3´K) If VÇ

is given in m 3 /h, raca= 0,34 W´h/(m 3 ´K).

The air flow rate, VÇ, can be calculated from an

estimate of the air change rate, n, by:

where

V is the volume of the heated space, calculated

on the basis of the internal dimensions

5.2.2 Minimum ventilation

For comfort and hygienic reasons a minimum

ventilation rate is needed when the building is

occupied This minimum ventilation rate should be

determined on a national basis, taking account of the

building type and the pattern of occupancy for the

building

NOTE When no national information is available, the

recommended value for dwellings is:

In buildings equipped with demand controlled ventilation, in

rooms with high ceilings and in buildings with long periods

without occupants, the required air change rate could be lower.

5.2.3 Natural ventilation

The total ventilation rate shall be determined as the

greater of the minimum ventilation rate VÇmin.and the

design ventilation rate VÇd:

VÇ = max [VÇmin; VÇd] (7)

NOTE Where no national information is available the air change

rate may be assessed from Tables F.2 or F.3.

5.2.4 Mechanical ventilation systems

The total air flow rate is determined as the sum of the

ventilation rate determined from the average air flow

rates through the system fans when in operation, VÇf

and an additional air flow rate, VÇx, induced by wind

and stack effect on an untight envelope:

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For balanced ventilation systems, VÇfis equal to

the greater of the supply air flow rate, VÇsup, and

exhaust air flow rate, VÇex

NOTE When no national information exists, the estimation of the

additional air flow rate, VÇx, can be calculated from:

n50 is the air change rate resulting from a pressure

difference of 50 Pa between inside and outside, including the effects of air inlets;

annex F.

If there is mechanical ventilation switched on for apart of the time, the air flow rate is calculated by:

VÇ = (V Ç0+ V Ç 9x)(1 2 b) + (V Çf+ V Çx)b (10)where:

V Çf is the design air flow rate due to mechanicalventilation;

V Çx is the additional infiltration air flow rate withfans on, due to wind and stack effect;

V Ç0 is the air flow rate with natural ventilation,with fans off, including flows through ducts ofthe mechanical system;

V Ç 9x is the additional infiltration air flow rate withfans off, due to wind and stack effect;

5.2.5 Mechanical systems with heat exchangers

For buildings with heat recovery from exhaust air toinlet air, the heat losses by the mechanical ventilationare reduced by the factor (1 2 hv) where hvis theefficiency factor of the air to air heat recovery system.Thus, the effective air flow rate for the heat losscalculation is determined from:

VÇ = VÇf(1 2 hv) + VÇx (11)For systems with heat recovery from the exhaust air tothe hot water or space heating system via a heat pump,the ventilation rate is calculated without reduction Thereduction in energy use due to heat recovery shall beallowed for in the calculation of the energy

consumption of the relevant system

5.3 Effect of intermittence

With intermittent heating, heat loss is reduced due tolowering of the average internal temperature Heatlosses with intermittent heating may be calculatedfrom equation (2), the set-point temperature beingreplaced by the average internal temperature Thereduction in heat losses can also be calculated directly

NOTE The heat loss with intermittent heating can be treated

using national procedures In the absence of suitable national

information, annex J provides an appropriate procedure.

6 Heat gains

6.1 Total heat gains

Internal heat gains, Qi, and solar gains, Qs, make up

the total heat gain, Qg:

6.2 Internal heat gains

Internal heat gains, Qi, include any heat generated in

the heated space by internal sources other than the

heating system, e.g.:

Ð metabolic gains from occupants;

Ð the power consumption of appliances and lighting

devices;

Ð the net gains from the water distribution and

drainage system

Average monthly or seasonal values are appropriate for

the calculation according to this standard In this case:

Fi is the average power of the internal gains; and

b is the factor defined in EN ISO 13789

NOTE There are substantial variations between households and

climates, and values should normally be determined on a national

basis If no national guidance exists, a recommended value for

internal heat gains is 5 watts per square metre of floor area of the

heated space.

6.3 Solar gains

6.3.1 Basic equation

Solar gains result from the sunshine normally available

in the locality concerned, the orientation of the

collecting areas, the permanent shading, and the solar

transmission and absorption characteristics of the

collecting areas The collecting areas to take into

consideration are the glazing, the internal walls and

floors of sunspaces, and walls behind a transparent

covering or transparent insulation For opaque areas

exposed to solar radiation, see annex D

For a given calculation period, the solar gain is

where the first sum is over all orientations, j, and the

second over all the surfaces, n, collecting the solar

radiation, and:

I sj is the total energy of the global solar radiation

on a surface unity having orientation j during

the calculation period;

A snj is the solar effective collecting area of the

surface n having orientation j, that is the area

of a black body having the same solar gain as

the surface considered

NOTE I sjcan be replaced by an orientation factor multiplying

the total solar radiation per unit area for a single orientation

(e.g vertical south).

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Solar gains in unheated spaces are multiplied by the

corresponding reduction factor, (1 2 b), defined in

EN ISO 13789, and added to solar gains of heatedspace (see annex D)

6.3.2 Effective collecting area

The effective collecting area, As, of a glazed envelopeelement such as a window is given by:

where

A is the area of the opening of the collectingsurface (e.g window area);

FS is the shading correction factor;

FC is the curtain factor;

FF is the frame factor, equal to the ratio of thetransparent area to the total area of the glazedunit;

g is the total solar energy transmittance

NOTE Only permanent shading, which is not moved in relation

to the solar gains or the internal temperature, is taken into account in the shading correction factor User-moveable or automatic solar protection is implicitly taken into account in the utilization factor.

6.3.3 Solar energy transmittance of glazing

The total solar energy transmittance g in

equation (15) should be the time-averaged ratio ofenergy passing through the unshaded element to thatincident upon it For windows or other glazedenvelope elements, EN 410 provides a method toobtain the solar energy transmittance for radiation

perpendicular to the glazing This figure, g⊥, issomewhat higher than the time-averaged transmittance,

and a correction factor, Fw, shall be used:

NOTE Guidance for the correction factor is given in annex G, together with typical solar transmission factors.

6.3.4 Shading correction factors

The shading correction factor, FS, which is in therange 0 to 1, represents any reduction in incident solarradiation due to permanent shading of the surfaceconcerned resulting from any of the following factors:

Ð shading by other buildings;

Ð shading by topography (hills, trees etc.);

Ð overhangs;

Ð shading by other elements of the same building;

Ð the position of the window relative to the outersurface of the external wall

Is,ps is the total solar radiation received on the

collecting plane with the permanent shading

during the heating season;

Is is the total solar radiation which would have

been received on the collecting surface

without shading

NOTE Annex G provides some information on shading correction

factors.

6.3.5 Curtain factors

The curtain factor differs from one only when the

curtains are permanent This factor is defined as the

ratio of the average solar energy entering the building

with the curtains to the energy that would enter the

building without curtains The solar radiation

converted into heat in curtains located inside the

building is considered to enter the building

NOTE Annex G provides some information on curtain factors.

6.3.6 Special elements

Special solar collecting elements, such as sunspaces,

attached greenhouses, transparent insulation and

ventilated envelope elements, need a special

calculation procedure to obtain their losses and solar

gains These procedures are given for some elements

in annexes C (additional loss) and D (solar gains)

7 Heat use

7.1 Heat balance

Heat losses, Ql, and heat gains, Qg, are calculated for

each calculation period The space heating use for

each calculation period is obtained from:

setting Ql= 0 and h = 0 when the average external

temperature is higher than the set-point temperature

The utilization factor, h, is a reduction factor for the

heat gain, introduced into the mean energy balance to

allow for the dynamic behaviour of the building

7.2 Utilization factor for heat gains

Assuming perfect control of the heating system, the

parameters having the greatest influence on the

utilization factor are:

the gain/loss ratio, g, which is defined as:

C is the effective internal thermal capacity, that

is, the heat stored in the structure of thebuilding if the internal temperature variessinusoidally with a period of 24 h and anamplitude of 1 K

NOTE Guidance for calculating the thermal capacity is provided in annex H The effective thermal capacity may also

be provided at a national level, based on the type of construction This figure can be approximate, and a relative accuracy ten times lower than that of the losses is sufficient Time constants for typical buildings may also be provided at a national level.

The utilization factor is then calculated by:

The values of a0and t0are provided in Table 3

Table 3 Ð Numerical values of the parameter

(h)

Monthly calculation method 1 16Seasonal calculation method 0,8 28Figure 2 gives utilization factors for monthlycalculation periods and for various time constants

NOTE The utilization factor is defined independently of the heating system characteristics, assuming perfect temperature control and infinite flexibility The effects of a slowly responsive heating system and of an imperfect control system may be important and depend upon the gain-loss ratio This should be taken into account in the heating system part of the calculation

(see 9.3).

8 Annual heat use of the building

8.1 Monthly calculation method

The length of the heating season is not specified Theannual heat use is the sum over all months for whichthe average external temperature is lower than theset-point temperature:

(24)

Qh=∑ Q hn

n

Figure 2 Ð Utilization factor for 8 hours, 1 day, 2 days, 1 week and infinite time

constants, valid for monthly calculation period

8.2 Seasonal calculation method

The first and last day of the heating season, hence its

duration and its average meteorological conditions can

be fixed at national level for a geographic zone and

typical buildings The heating season includes all days

for which the heat gain, calculated with a conventional

utilization factor, h0, does not balance the heat loss,

ued is the daily average external temperature;

uid is the daily average internal temperature;

h0 is the conventional utilization factor calculated

with g = 1;

Qgd are the daily average internal and solar gains;

H is the heat loss coefficient of the building;

td is the duration of the day

The heat gains for equation (25) may be derived from a

conventional national or regional value of the daily

global solar radiation at the limits of the heating

season The monthly average values of daily

temperatures and heat gains are attributed to the

15th day of each month Linear interpolation is used to

obtain the limiting days for which equation (25) is

verified

The heat use for the heating season is calculated

according to the procedure described in 4.2, the

calculation period being the whole season

9 Heating energy use

9.1 Energy input

Efficiencies and heat losses due to the heating systemgiven below are related to heat flows, and used toobtain the energy required for heating Heating systemsgenerally use auxiliary equipment (pumps, fans, controlelectronics, etc.), which use mostly electrical energy Apart of this energy is recovered for heating Thisauxiliary equipment depends on the kind of heatingsystem and is not taken into account in thiscalculation It should nevertheless be considered, ifrelevant, in a complete energy balance

As long as no European Standard exists, the heatlosses due to the heating system and efficiencies aredefined and calculated according to national

information

Over a given period, the energy input to the heating

system, Q, is given by the equation:

Q + Qr= Qh+ Qw + Qt (26)where

Q is the building energy use for heating;

Qr is the heat recovered from auxiliaryequipment, heating systems and theenvironment;

Qh is the heat use for space heating;

Qw is the heat required for hot water;

Qt is the total of the heat losses due to theheating system

9.2 Heat for hot water preparation

The heat required for hot water preparation is:

Qw= rcVw(uw2 u0) (27)

where

r is the density of water, r = 1 000 kg/m3;

c is the specific heat of water, c = 4 180 J/(kg´K);

Vw is the volume of hot water required during the

calculation period;

uw is the temperature of the delivered hot water;

u0 is the temperature of the water entering the

hot water system

Heat losses of the hot water system shall be included

in heat losses due to the heating system

Heat gains from the hot water network to the building

are usually close to the heat loss of the building to the

cold water network and to waste water, and can thus

be neglected in the building heat balance When these

losses and gains are taken into account, both of them

should be considered

9.3 Heat losses due to the heating system

The total heat losses can be expressed in its most

detailed form as follows:

Qt= Qe+ Qc+ Qd+ Qge+ Qgc (28)

where the different individual heat losses are defined

below:

Qe is the additional heat loss due to non-uniform

temperature distribution This loss includes,

for instance, the additional heat loss through

external walls by radiation and convection

between radiators and the surface behind;

Qc is the additional heat loss due to non-ideal

room temperature and distribution system

control This loss depends on the

characteristics of the control equipment

(accuracy of sensors, time constant,

proportional range, etc.) and on the dynamic

characteristics of the heating system;

Qd is the heat loss of the heat distribution system,

which does not contribute to the heating use

This loss depends on the layout of the piping

system, its location, its thermal insulation and

on the temperature of the heating fluid;

Qge is the heat generator losses occurring during

operation and during standby;

Qgc is the additional heat loss due to non-ideal

control of the heat generator, depending on

the intrinsic characteristics of the control

equipment and on the dynamic characteristics

of the heating system

9.4 Heating system efficiency

The building energy use can also be calculated from:

NOTE hhcan be expressed in terms of partial efficiency related

to a specific part of the heating system.

10 Report

A report giving an assessment of the annual heatingenergy use of a building obtained in accordance withthis standard shall include at least the followinginformation

10.1 Input data

All input data shall be listed and justified, e.g byreference to international and national standards, orreference to the appropriate annexes to this standard

or to other documents An estimate of the accuracy ofinput data shall also be given Conventional data areassumed to have perfect accuracy

In addition, the report shall include:

a) reference to this standard;

b) the purpose of the calculation (e.g for judgingcompliance with regulations, optimizing energyperformance, assessing the effects of possible energyconservation measures, predicting energy resourceneeds on a given scale, etc.);

c) a description of the building, its construction andits location;

d) specification of the zone division, if any, that is,the allocation of rooms to each zone;

e) a note indicating whether the dimensions usedare internal or external;

f) a note indicating which method (monthly based orseasonal) was used;

g) the relevant information if intermittence wastaken into account

10.2 Results

10.2.1 For each building zone and each calculation period

h) total heat loss at set-point temperature;

i) internal heat gains;

j) solar gains;

k) net heat use

10.2.2 For the whole building

a) annual heat use;

b) if required, annual energy use Energyconsumption from different sources (electricity, oil,gas, coal, etc.) shall be listed separately, togetherwith the total

When input data other than conventional values areused, an estimate of the uncertainty resulting frominaccuracy of the input data shall be given

NOTE 1 Guidance on the accuracy of the calculation method is given in annex K.

NOTE 2 An example of a calculation and of the corresponding report is provided in annex L.

NOTE 3 Additional information may be required at national level.

Annex A (normative)

Application to existing buildings

A.1 Possible applications

Energy assessments of existing buildings are carried

out for various purposes, such as:

Purpose 1) transparency in commercial operations

through the display of a level of energy

performance;

Purpose 2) helping in planning retrofit measures,

through prediction of energy savings

which would result from various actions

In contrast with new buildings, existing ones can

provide useful information, which can reinforce the

reliability of the results Therefore, the calculation

framework in this standard should be adapted when

possible to take account of these possibilities The

following approach shall be adopted

A.2 Data assessment

The energy consumption of the existing building shall

be assessed as accurately as possible, from recorded

data, energy bills or measurements In addition, any

information such as: actual climatic data, air

permeability of the fabric, heating system efficiencies,

actual internal conditions (occupancy, intermittent

heating, temperatures, ventilation, etc.), should be

assessed through surveys, measurements or

monitoring, as far as they are available for a

reasonable cost The confidence intervals of all data

shall be estimated

Input data that cannot be measured is taken, as for

planned buildings, from national references or

standards

NOTE Energy consumption may be correlated to climatic data

through periodic consumption and temperature recordings over a

suitable period Such methods are based on an overall modelling

of the whole system, which may differ from the model used in this

standard.

A.3 Calculations

The energy consumption of the existing building shall

be determined according to the present standard using

the collected data as input The confidence intervals of

the result shall be assessed, and compared to that of

the experimental energy consumption

If they overlap significantly, it is supposed that the

model, including estimated input data, is correct

If the confidence intervals do not overlap significantly,

further on-site investigations shall be made in order to

verify some data or to introduce new influencing

factors which may have been previously ignored, and

the calculation repeated with the new set of input data

A.4 Energy declaration

For purpose 1 (energy declaration), the input set ismodified using conventional occupancy conditions andthe energy consumption of the building is determinedagain

A.5 Planning retrofit measures

For purpose 2 (planning retrofit measures), actual dataare used for calculation However, if it appears that thebuilding is misused (e.g by under- or overheating,under or over ventilation), reasonable data shall beused instead of the measured ones for planning retrofitmeasures The base energy consumption of the

building as it is, is calculated using these reasonabledata Then, the input set is modified according to theplanned retrofit measure and the calculation performedagain in order to obtain the effect of that measure(or package of measures) on the energy consumption

Annex B (normative) Calculation method for multi-zone buildings

The procedure, based on monthly calculation periods,

3) In addition to building data gathered according

to 4.4, inter-zone data are collected These are:

H T,zy transmission heat loss coefficient

between zones z and y; or

U j,zy thermal transmittance of each

building element j, separating these

zones;

A j,zy area of building element j;

Ck,zy linear thermal transmittance of

two-dimensional thermal bridge k;

l k,zy length of two-dimensional thermal

bridge;

xn,zy point thermal transmittance of the

three-dimensional thermal bridge n;

VÇ zy and VÇ yz air flow rates between zones y

and z.

4) The heat loss coefficient of each zone, H z, is

calculated separately, according to clause 5, using

the entering air flow rate for ventilation heat loss

| 5) The heat transfer coefficients between zones z

and y, H zy, are determined in a similar way, taking

account of heat transfer between zones by

transmission (through the building elements and

through the ground) and ventilation:

H zy = H T,zy+ racaVÇ zy (B.1)

Then, for each month and for each zone

6) The heat flows including transmission and

ventilation heat transfer to and from neighbouring

zones, and between each zone and the external

environment, are calculated, based on the

assumption of constant internal temperature:

Q l,zy = H zy(uz2 uy )t and

Q l,z=∑ Q l,zy + H z(ui2 ue)t

y

(B.2)

When Q l,z < 0, zone z shall be considered as an

unheated space and calculation continued from

step 4 for the next zone

7) The effect of intermittence is determined when

required However, the simplified method given in

annex J cannot be applied when several zones have

different intermittence patterns

8) Internal and solar gains Q g,zare calculated

according to 6.2 and 6.3.

9) The utilization factor hzis determined according

to 7.2.

10) The net heat use is obtained from the difference

between the loss and the used gains:

Q h,z = Q l,z2 hz Q g,z (B.3)

The total building heat use for each month is the

sum of all the uses of each zone:

and the annual space heating use is obtained from

the sum of the uses for each month The energy use

is then calculated according to clause 9.

The division into zones shall be described in the

report

Annex C (normative)

Additional losses for special envelope

elements

C.1 Ventilated solar walls (Trombe walls)

The following applies to walls designed to collect solar

energy, according to Figure C.1, where:

Ð the air flow is automatically stopped when the air

layer is colder than the heated space; and

Ð the air flow rate is mechanically set at a constant

value, VÇ, when the air layer is warmer than the

heated space

Figure C.1 Ð Air flow path in a ventilated solar wall

C.1.1 Required data

A area of the ventilated solar wall;

As effective collecting area of the

ventilated solar wall (see 6.3.2);

Ri internal thermal resistance of the wall,

between the air layer and the interior;

Re external thermal resistance of the wall,

between the air layer and the exterior;

Rl thermal resistance of the air layer;

VÇ set value of the air flow rate through

the ventilated layer;

hcand hr respectively the convective and

radiative surface transfer coefficients inthe air layer;

Is total solar radiation on the ventilated

solar wall during the calculation period

C.1.2 Calculation method

Calculation of heat loss is based on set-point andexternal temperatures Solar gains are calculated

according to D.3 The additional heat loss coefficient

of such a wall is calculated by:

raand ca are as defined in 5.2;

Uiand Ue are the internal and external thermal

transmittances:

(C.2)

Ui= 1 and Ue=

Ri+Rl2

1

Re+Rl2

d is the ratio of the accumulated

internal-external temperature differencewhen the ventilation is on, to its valueover the whole calculation period It isgiven in Figure C.2

Figure C.2 Ð Ratio d of the accumulated internal-external temperature difference when the ventilation is on to its value over the whole calculation

This ratio can be calculated by:

d = 0,3gal+ 0,03(0,000 3gal2 1) (C.3)

where

gal is the ratio of the solar gains, Qg, to the heat

loss of the air layer, Ql,al, during the

calculation period, given by:

Circulating ventilation air within parts of the building

envelope (wall, window, roof) decreases the overall

heat losses by heat recovery, although the transmission

heat loss is increased in these building envelope

elements This effect can be expressed in terms of an

equivalent heat exchanger (see 5.2.5), the efficiency of

which being calculated with a simplified method which

is applicable under the following conditions:

Ð the air flow is parallel to the envelope surface

Ð the requirements in Table C.1 are met;

Ð the air supply, if natural, is controlled through

adjustable or self-controlled inlets located on the

internal part of the envelope

Table C.1 Ð Ventilation requirements for the application of the method Shielding class Requirement

No shielding Mechanical exhaust and supplyModerate Mechanical exhaust or supplyHeavy shielding No requirement

NOTE This method mainly applies where supply air is circulated within the building envelope elements Exhaust air may also be used, provided that suitable provisions are made to avoid any troubles due to condensation.

Figure C.3 Ð Air path in the wall

C.2.2 Procedure

The efficiency factor of the equivalent air-to-air heat

exchanger is given by:

Uiand Ue are, respectively, the thermal

transmittances of the internal andexternal parts of the envelope element

containing the air space (see C 1.2);

U0 is the thermal transmittance of this

envelope element, assuming the airspace is not ventilated;

k is the factor defined in equation (C.4)

The efficiency factor of the equivalent air-to-air heat

exchanger is always less than 0,25

Annex D (normative)

Solar gains of special elements

D.1 Sunspaces

D.1.1 Domain of application

The following applies to unheated sunspaces adjacent

to heated space, such as conservatories and attached

greenhouses where there is a partition wall between

the heated volume and the sunspace

If the sunspace is heated, or if there is a permanent

opening between the heated space and the sunspace, it

shall be considered as part of the heated space The

area to be taken into account for the losses and solar

gains is the area of the external envelope of the

sunspace, and this annex does not apply

Figure D.1 Ð Attached sunspace with gains

and heat loss coefficients, and electrical

equivalent network

D.1.2 Required data

The following data shall be collected for the

transparent part of the partition wall, (subscript w), and for the sunspace external envelope, (subscript e):

FC curtain factor;

FF frame factor;

FS shading correction factor;

g total solar energy transmittance of glazing;

Aw area of windows in partition wall;

Ae area of sunspace envelope

In addition, the data below should be assessed:

A j area of each surface, j, absorbing the solar

radiation in the sunspace (floor, opaque walls;opaque part of the partition wall has

subscript p);

aSj average solar absorption factor of absorbing

surface j in the sunspace;

I i quantity of solar radiation on surface i during

each calculation period;

Up thermal transmittance of the opaque part inpartition wall;

Upe thermal transmittance between the absorbingsurface of this wall and the sunspace

D.1.3 Procedure

The losses are calculated according to clause 5, for

unheated space The solar gain coming into the heated

space from the sunspace, QSs, is the sum of direct

gains through the partition wall, QSd, and indirect

gains, QSi, from the sunspace heated by the sun:

It is assumed, in a first approximation, that theabsorbing surfaces are all shaded in the sameproportion by external obstacles and by the outerenvelope of the sunspace

The direct solar gains QSdare the sum of the gains

through the transparent (subscript w) and opaque (subscript p) parts of the partition wall, that is:

gains of each absorbing area, j, in the sunspace, but

deducting the direct gains through the opaque part ofthe partition wall:

(D.3)

QSi= (1 2 b)FSFCeFFege



∑ I SjaSj A j 2 IpaSpApj

Up

Upe





The weighting factor (1 2 b) is the fraction of the solar

radiation absorbed in the sunspace that enters the

heated space through the partition wall The factor b is

defined in EN ISO 13789