Bsi bs en 00832 2000 (2001)

BRITISH STANDARD

Thermal performance of
buildings Ð Calculation
of energy use for
heating Ð Residential
buildings

The European Standard EN 832:1998 has the status of a
British Standard

ICS 91.140.10

NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW

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BS EN 832:2000

National foreword
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 Committee
B/540, Energy performance of materials, components and buildings, to
Subcommittee B/540/1, European Standards for thermal insulation, which has the
responsibility to:
Ð aid enquirers to understand the text;
Ð present to the responsible European committee any enquiries on the
interpretation, or proposals for change, and keep the UK interests informed;
Ð monitor related international and European developments and promulgate
them 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 error
has 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
element Vx9 when it should have contained the element VÇ9x. This error has been
corrected in the text.
Cross-references
The British Standards which implement international or European publications
referred to in this document may be found in the BSI Standards Catalogue under the
section entitled ªInternational Standards Correspondence Indexº, or by using the
ªFindº facility of the BSI Standards Electronic Catalogue.
A British Standard does not purport to include all the necessary provisions of a
contract. 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.

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

July 2001

Indicated by a sideline

corrigendum No.1

EN 832

EUROPEAN STANDARD
NORME EUROPÊENNE
EUROPẰISCHE NORM

September 1998

ICS 91.140.10

Incorporating corrigendum May 2000

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 Ð
Berechnung 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.

CEN
European Committee for Standardization
Comite EuropeÂen de Normalisation
EuropaÈisches 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 national
Members.
Ref. No. EN 832:1998 E


Page 2
EN 832:1998

Foreword
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.

Contents
Foreword
Introduction
1 Scope
2 Normative references
3 Definitions, symbols and units
4 Outline of the calculation procedure
and required data
5 Heat losses at constant internal
temperature
6 Heat gains

7 Heat use
8 Annual heat use of the building
9 Heating energy use
10 Report
Annex A (normative) Application to existing
buildings
Annex B (normative) Calculation method
for multi-zone buildings
Annex C (normative) Additional losses for
special envelope elements
Annex D (normative) Solar gains of special
elements
Annex E (informative) Envelope elements
with heating devices
Annex F (informative) Data for estimation
of natural ventilation and infiltration
Annex G (informative) Data for solar gains
Annex H (informative) Calculation of
effective thermal capacity
Annex J (informative) Heat losses with
intermittent heating or set-back
Annex K (informative) Accuracy of the
method
Annex L (informative) Calculation example
Annex M (informative) Bibliography
Annex ZB (informative) A-deviations

Page
2
3

3
3
3
5
7
9
10
10
11
12
13
13
14
16
19
19
20
21
22
26
26
31
32

 BSI 07-2001


Page 3
EN 832:1998

Introduction

2 Normative references

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.

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 the publications
apply to this European Standard only when
incorporated in it or by amendment or revision. For
undated references, the latest edition of the publication
referred 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)

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.

 BSI 07-2001

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 mean
radiant temperature at room centre (internal dry
resultant temperature)
3.1.3
set-point temperature
design internal temperature
3.1.4
intermittent heating
heating pattern where, during the course of time, the
temperature is allowed to fall below the design
temperature


Page 4
EN 832:1998

3.1.5
heated space
rooms or enclosures heated to one or more given
set-point temperatures
3.1.6
unheated space
room or enclosure which is not part of the heated
space
3.1.7

thermal zone
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

3.2 Symbols and units
For the purposes of this standard, the following terms
and symbols apply.
Table 1 Ð Symbols and units
Symbol

A
a
b
C
c
e
F
f
g

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

H

3.1.10
heat loss coefficient
heat transfer coefficient from the heated space to the
external environment

l
n
Q
R
T
t
U
V
VÇ
a

NOTE The heat loss coefficient can be defined only for a single
zone building.

3.1.11
heat gain

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

h
I

b
g
d

e
h
u
k
r
s

Name of quantity

area
numerical parameter in
utilization factor
correction factor for unheated
zones
effective heat capacity of a zone
specific heat capacity
wind shielding coefficient
factor
coefficient related to wind
exposure
total solar energy transmittance
of a building element
heat transfer coefficient, heat
loss coefficient
surface coefficient of heat
transfer
quantity of heat or energy per
unit area
length
air change rate

quantity of heat or energy
thermal resistance
thermodynamic temperature
time, period of time
thermal transmittance
volume of air in a heated zone
air flow rate
absorption coefficient of a
surface for solar radiation
fraction of the time period with
fans on
gain/loss ratio
ratio of the accumulated
internal-external temperature
difference when the ventilation
is on to its value over the
calculation period
emissivity of a surface for
thermal radiation
efficiency, utilization factor for
the gains
Celsius temperature
factor related to heat losses of
ventilated solar walls
density
Stefan-Boltzmann constant
(s = 5,67 3 1028)

Unit

m2
Ð
Ð
J/K
J/(kg´K)
Ð
Ð
Ð
Ð
W/K
W/(m2´K)
J/m2
M
s21 or h21
J
m2´K/W
K
s
W/(m2´K)
m3
m3/s
Ð
Ð
Ð

Ð
Ð
Ð
8C
Ð

kg/m3
W/(m2´K4)

 BSI 07-2001

|


Page 5
EN 832:1998

Table 1 Ð Symbols and units (continued)
Symbol

t
F
x
C
v

Name of quantity

Unit

time constant
heat flow rate
point thermal transmittance
linear thermal transmittance
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

s
W
W/K
W/(m´K)

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.

|

C
D
F
G
P
S
T
W
V
a
c
d

e

curtain
direct
frame
ground
related to power
shading
transmission
wall
ventilation
air; actual
capacity
daily; distribution
external; emission

ex
f
g
gc
ge
h
i
j, k,
l
o
p
ps

4 Outline of the calculation procedure

and required data
4.1 Energy balance
The energy balance is defined as including the
following (only sensible heat is considered):
Ð transmission and ventilation losses from the
internal to the external environment;
Ð transmission and ventilation heat losses or heat
gains with adjacent zones;
Ð the useful internal heat gains, that is the used
heat output from the internal heat sources;
Ð the used solar gains;
Ð the generation, distribution, emission and control
losses of the heating system;
Ð the energy input to the heating system.
The terms of the energy balance are illustrated in
Figure 1.

Table 2 Ð Subscripts
exhaust
fan
gains
control
generation
heating; heated
internal
m, n dummy integers
loss; layer
output
partition wall
permanent shading

pp
r
s
sup
t
u
v
w
x
y, z
⊥
0
50

peak power
radiative; recovered
solar, sunspace
supply
total; technical
unheated
ventilation
windows; water
extra; additional
zone number
perpendicular
base; reference
at 50 Pa pressure difference

Figure 1 Ð Annual energy balance of a building

 BSI 07-2001


Page 6
EN 832:1998

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 the
gain/loss ratios differ by less than 0,4 (e.g. between
south and north zones); or
b) doors between zones are likely to be open; or
c) one zone is small and it can be expected that the
total energy use of the building will not change by
more than 5 % by merging it to the adjacent larger
zone.
In such cases, even if the set-point temperature is not
uniform, the single zone calculation applies. Then the
internal temperature to be used is:

∑

ui =

Hzuiz

z

∑

(1)

Hz

z

where
uiz
Hz

is the set-point temperature of zone z;
is the heat loss coefficient of zone z, according
to clause 5.

In other cases, in particular for buildings that include
more than one type of premises under the same roof,
the building is divided into several zones, and the
calculation 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 from
national standards or other suitable documents, and
these should be used where available. The informative
annexes to this standard give values or methods to
obtain values when the required information is
otherwise not available.
For optimization of a planned building or retrofitting
an existing building, the best available estimate for that
particular building shall be used (see annex A).
However, if no better estimates are available,
conventional values can be used as first
approximations.
For predicting the energy needs or judging compliance
with standards, conventional values shall be used, in
order to make the results comparable between

different buildings.
The physical dimensions of the building construction
shall be consistent throughout the calculation. Internal,
external or overall internal dimensions can be used,
but the same type shall be kept for the whole
calculation and the type of dimensions used shall be
clearly indicated in the report.
NOTE Some linear thermal transmittances of thermal bridges
depend on the type of dimensions used.

 BSI 07-2001


Page 7
EN 832:1998

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
C
t
hh

internal volume of the heated space;
internal heat capacity of the heated space,
according to 7.2; or
time constant of the heated space;

heating system efficiency.

Additional data should be collected for envelope
elements containing heating devices and components
collecting solar radiation, such as transparent
insulation, ventilated solar walls, sunspaces, etc., as
well as for calculation of the effect of intermittent
heating. The required data are listed in the
corresponding annexes.
4.4.5 Climatic data
ue
Is, j

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
n50

VÇ f
hv

design air change rate;
air change rate at 50 Pa pressure difference;
design air flow rate through ventilation fans;
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
FF
FC
Fs
g

area of opening in the building envelope for
each window or door;
frame factor, i.e. transparent fraction of the
area A, not occupied by a frame;
curtain factor, i.e. fraction of the solar
radiation transmitted by permanent curtains;

shading correction factor, i.e. average shaded
fraction of area A;
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.
 BSI 07-2001

monthly or seasonal average of external
temperatures;
monthly or seasonal total solar radiation per
unit area for each orientation, in J/m2.

4.4.6 Occupancy data
ui

set-point temperature.

Additional data should be collected when the effect of
intermittent heating should be considered. These are
listed in annex J.

5 Heat losses at constant internal

temperature
5.1 Principle
The total heat loss, Ql, of a single zone building at
uniform internal temperature during a given period of
time is:
(2)
Ql = H(ui 2 ue)t
where
ui
ue
t
H

is the set-point temperature;
is the average external temperature during the
calculation period;
is the duration of the calculation period;
is the heat loss coefficient of the building:

H = HT + HV
where

(3)

HT is the transmission heat loss coefficient,
calculated according to EN 13789 (for
envelope elements incorporating ventilating
devices, see annex C);
HV is the ventilation heat loss coefficient
(see 5.2).

NOTE (ui 2 ue)t is related to degree days defined in different
ways in various countries.

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


Page 8
EN 832:1998

5.2 Ventilation heat loss coefficient
5.2.1 Principle
The ventilation heat loss coefficient, HV, is calculated
by:
HV = VÇ raca
(4)
where
VÇ
raca

is the air flow rate through the building;
including air flow through unheated spaces;
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 m3/h, raca = 0,34 W´h/(m3´K).

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

estimate of the air change rate, n, by:
VÇ = Vn
where
V

(5)

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:
nmin. = 0,5 h21

hence

VÇ min. = 0,5V m3/h

For balanced ventilation systems, VÇ f is equal to
the greater of the supply air flow rate, VÇ sup, and
exhaust air flow rate, VÇ ex.
NOTE When no national information exists, the estimation of the
additional air flow rate, VÇ x, can be calculated from:

V ´ n50 ´ e
VÇ x =
(9)
2
f  VÇ sup 2 VÇ ex
1+
e  V ´ n50 
where
n50

is the air change rate resulting from a pressure
difference of 50 Pa between inside and outside,
including the effects of air inlets;

e and f

are shielding coefficients which can be found in
annex F.

If there is mechanical ventilation switched on for a
part of the time, the air flow rate is calculated by:
VÇ = (VÇ0 + VÇ9x)(1 2 b) + (VÇf + VÇx)b
(10)
where:
VÇf
VÇx
VÇ0
VÇ9x

b

(6)

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 VÇ min. and the
design ventilation rate VÇ d:
VÇ = max. [VÇ min; VÇ d]
(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, VÇ f
and an additional air flow rate, VÇ x, induced by wind
and stack effect on an untight envelope:
VÇ = VÇ f + VÇ x
(8)

is the design air flow rate due to mechanical
ventilation;
is the additional infiltration air flow rate with
fans on, due to wind and stack effect;
is the air flow rate with natural ventilation,
with fans off, including flows through ducts of

the mechanical system;
is the additional infiltration air flow rate with
fans off, due to wind and stack effect;
VÇ9x = Vn50e;
is the fraction of the time period with fans on.

For mechanical systems with variable design air flow
rate, VÇ f is the average air flow rate through the fans
during their running time.
5.2.5 Mechanical systems with heat exchangers
For buildings with heat recovery from exhaust air to
inlet air, the heat losses by the mechanical ventilation
are reduced by the factor (1 2 hv) where hv is the
efficiency factor of the air to air heat recovery system.
Thus, the effective air flow rate for the heat loss
calculation is determined from:
(11)
VÇ = VÇ f(1 2 hv) + VÇ x
For systems with heat recovery from the exhaust air to
the hot water or space heating system via a heat pump,
the ventilation rate is calculated without reduction. The
reduction in energy use due to heat recovery shall be
allowed 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 to
lowering of the average internal temperature. Heat
losses with intermittent heating may be calculated
from equation (2), the set-point temperature being
replaced by the average internal temperature. The

reduction in heat losses can also be calculated directly.

 BSI 07-2001

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Page 9
EN 832:1998

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:
Qg = Qi + Qs
(12)
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:
Qi = [Fih + (1 2 b)Fiu]´t = Fit
(13)
where
Fih
Fiu
Fi
b

is the average power of the internal gains in
heated spaces;
is the average power of the internal gains in
unheated spaces;
is the average power of the internal gains; and
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
calculated as follows:
Qs = ∑ Isj ∑ Asnj
(14)
j

n

where the first sum is over all orientations, j, and the
second over all the surfaces, n, collecting the solar
radiation, and:
Isj
Asnj

is the total energy of the global solar radiation
on a surface unity having orientation j during
the calculation period;
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 Isj can be replaced by an orientation factor multiplying
the total solar radiation per unit area for a single orientation
(e.g. vertical south).
 BSI 07-2001

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 heated
space (see annex D).
6.3.2 Effective collecting area
The effective collecting area, As, of a glazed envelope
element such as a window is given by:
As = AFSFCFFg
(15)
where
A
FS
FC
FF

g

is the area of the opening of the collecting
surface (e.g. window area);
is the shading correction factor;
is the curtain factor;
is the frame factor, equal to the ratio of the
transparent area to the total area of the glazed
unit;
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 of
energy passing through the unshaded element to that
incident upon it. For windows or other glazed
envelope elements, EN 410 provides a method to
obtain the solar energy transmittance for radiation
perpendicular to the glazing. This figure, g⊥ , is
somewhat higher than the time-averaged transmittance,
and a correction factor, Fw, shall be used:
g = Fwg⊥
(16)
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 the
range 0 to 1, represents any reduction in incident solar
radiation due to permanent shading of the surface
concerned 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 outer
surface of the external wall.

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EN 832:1998

The shading correction factor is defined by:
Is,ps
FS =
Is
where

(17)

and a time constant, t, characterizing the internal
thermal inertia of the heated space:
C
g=
(20)
H
where

Is,ps is the total solar radiation received on the
collecting plane with the permanent shading
during the heating season;
is the total solar radiation which would have
Is
been received on the collecting surface
without shading.
NOTE Annex G provides some information on shading correction
factors.

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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:
(18)
Qh = Ql 2 hQg
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:
Qg
g=
(19)
Q1

C

is the effective internal thermal capacity, that
is, the heat stored in the structure of the
building if the internal temperature varies
sinusoidally with a period of 24 h and an
amplitude 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:
1 2 ga
1 2 ga + 1
a
h=
a+1
h=

if g Þ 1

(21)

if g = 1

(22)

where
a

is a numerical parameter depending on the time
constant, t, defined in equation (23):

t
t0
The values of a0 and t0 are provided in Table 3.
a = a0 +

(23)

Table 3 Ð Numerical values of the parameter

a0 and the reference time constant t0
a0

t0
(h)

Monthly calculation method

1

16

Seasonal calculation method

0,8

28

Figure 2 gives utilization factors for monthly
calculation 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. The
annual heat use is the sum over all months for which
the average external temperature is lower than the
set-point temperature:
Qh =

∑

Qhn

(24)

n

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Page 11
EN 832:1998

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,
that is when:
h0Qgd
ued # uid 2
(25)
Htd
where
ued
uid
h0
Qgd
H
td

is the daily average external temperature;
is the daily average internal temperature;
is the conventional utilization factor calculated
with g = 1;
are the daily average internal and solar gains;
is the heat loss coefficient of the building;
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.

 BSI 07-2001

9 Heating energy use
9.1 Energy input
Efficiencies and heat losses due to the heating system
given below are related to heat flows, and used to
obtain the energy required for heating. Heating systems
generally use auxiliary equipment (pumps, fans, control
electronics, etc.), which use mostly electrical energy. A
part of this energy is recovered for heating. This
auxiliary equipment depends on the kind of heating
system and is not taken into account in this
calculation. It should nevertheless be considered, if
relevant, in a complete energy balance.
As long as no European Standard exists, the heat
losses due to the heating system and efficiencies are
defined and calculated according to national
information.
Over a given period, the energy input to the heating
system, Q, is given by the equation:
(26)
Q + Qr = Qh + Qw + Qt
where
Q
Qr

Qh
Qw
Qt

is the building energy use for heating;
is the heat recovered from auxiliary
equipment, heating systems and the
environment;
is the heat use for space heating;
is the heat required for hot water;
is the total of the heat losses due to the
heating system.


Page 12
EN 832:1998

9.2 Heat for hot water preparation
The heat required for hot water preparation is:
Qw = rcVw(uw 2 u0)
where
r
c
Vw
uw
u0

(27)

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

is the specific heat of water, c = 4 180 J/(kg´K);
is the volume of hot water required during the
calculation period;
is the temperature of the delivered hot water;
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:
(28)
Qt = Qe + Qc + Qd + Qge + Qgc
where the different individual heat losses are defined
below:
Qe

Qc

Qd

Qge
Qgc

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;
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;
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;
is the heat generator losses occurring during
operation and during standby;
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:
Q + Qw
Q + Qr = h

(29)
hh

where the efficiency of the heating system is defined
as:
Qh + Qw
hh =
(30)
Qh + Qt + Qw
NOTE hh can 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 heating
energy use of a building obtained in accordance with
this standard shall include at least the following
information.
10.1 Input data
All input data shall be listed and justified, e.g. by
reference to international and national standards, or
reference to the appropriate annexes to this standard
or to other documents. An estimate of the accuracy of
input data shall also be given. Conventional data are
assumed to have perfect accuracy.
In addition, the report shall include:
a) reference to this standard;
b) the purpose of the calculation (e.g. for judging
compliance with regulations, optimizing energy
performance, assessing the effects of possible energy
conservation measures, predicting energy resource

needs on a given scale, etc.);
c) a description of the building, its construction and
its 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 used
are internal or external;
f) a note indicating which method (monthly based or
seasonal) was used;
g) the relevant information if intermittence was
taken 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. Energy
consumption from different sources (electricity, oil,
gas, coal, etc.) shall be listed separately, together
with the total.
When input data other than conventional values are
used, an estimate of the uncertainty resulting from
inaccuracy 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.

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EN 832:1998

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.

 BSI 07-2001

A.4 Energy declaration
For purpose 1 (energy declaration), the input set is
modified using conventional occupancy conditions and
the energy consumption of the building is determined
again.
A.5 Planning retrofit measures
For purpose 2 (planning retrofit measures), actual data
are used for calculation. However, if it appears that the
building is misused (e.g. by under- or overheating,
under or over ventilation), reasonable data shall be
used instead of the measured ones for planning retrofit
measures. The base energy consumption of the
building as it is, is calculated using these reasonable
data. Then, the input set is modified according to the
planned retrofit measure and the calculation performed
again 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,
is as follows.
1) The heated space is defined, according to 4.3.1.
2) It is divided into heated zones according to 4.3.2.
For each zone, z, the input data according to 4.4 are
collected.

3) In addition to building data gathered according
to 4.4, inter-zone data are collected. These are:
HT,zy
Uj,zy

Aj,zy
Ck,zy
lk,zy
xn,zy
VÇ zy and VÇ yz

transmission heat loss coefficient
between zones z and y; or
thermal transmittance of each
building element j, separating these
zones;
area of building element j;
linear thermal transmittance of
two-dimensional thermal bridge k;
length of two-dimensional thermal
bridge;
point thermal transmittance of the
three-dimensional thermal bridge n;
air flow rates between zones y
and z.

4) The heat loss coefficient of each zone, Hz, is
calculated separately, according to clause 5, using
the entering air flow rate for ventilation heat loss.

Page 14
EN 832:1998

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5) The heat transfer coefficients between zones z
and y, Hzy , 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:
(B.1)
Hzy = HT,zy + racaVÇ zy
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:
Ql,zy = Hzy(uz 2 uy)t

and

Ql,z = ∑ Ql,zy + Hz(ui 2 ue)t

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

(B.2)

y

When Ql,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 Qg,z are calculated
according to 6.2 and 6.3.
9) The utilization factor hz is determined according
to 7.2.
10) The net heat use is obtained from the difference
between the loss and the used gains:
Qh,z = Ql,z 2 hzQg,z
(B.3)
The total building heat use for each month is the
sum of all the uses of each zone:
Qh = ∑ Qh,z
(B.4)
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.

C.1.1 Required data
A
As
Ri
Re
Rl
VÇ
hc and hr

Is

area of the ventilated solar wall;
effective collecting area of the
ventilated solar wall (see 6.3.2);
internal thermal resistance of the wall,
between the air layer and the interior;
external thermal resistance of the wall,
between the air layer and the exterior;
thermal resistance of the air layer;
set value of the air flow rate through
the ventilated layer;

respectively the convective and
radiative surface transfer coefficients in
the air layer;
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 and
external temperatures. Solar gains are calculated
according to D.3. The additional heat loss coefficient
of such a wall is calculated by:
2
U 
DH = racaVÇ  e dk
(C.1)
 Ui 
where
ra and ca
Ui and Ue

d

are as defined in 5.2;
are the internal and external thermal
transmittances:
1
1
and Ue =
Ui =
(C.2)

Rl
R
Ri +
Re + l
2
2
is the ratio of the accumulated
internal-external temperature difference
when the ventilation is on, to its value
over the whole calculation period. It is
given in Figure C.2.

 BSI 07-2001


Page 15
EN 832:1998

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
period, as a function of gal
This ratio can be calculated by:
g
d = 0,3gal + 0,03(0,000 3 al 2 1)
where
gal

(C.3)

Shielding class

is the ratio of the solar gains, Qg, to the heat
loss of the air layer, Ql,al, during the
calculation period, given by:
Qg = IsAs
Ql,al = UeA(ui 2 ue)t

k is a factor calculated by:
AZ  


k =  1 2 exp 2
 racaVÇ  

where Z is a parameter defined by:
1
hr
1
=
+
Z hc(hc + 2hr) Ui + Ue

Table C.1 Ð Ventilation requirements for
the application of the method
No shielding
Moderate
Heavy shielding

Requirement

Mechanical exhaust and supply
Mechanical exhaust or supply
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.

(C.4)

(C.5)

C.2 Ventilated envelope elements
C.2.1 Domain of application
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
(see Figure C.3);
Ð the thickness of the air layer is between 15 mm
and 100 mm;
Ð the air tightness of the remaining parts of the
envelope is high;
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.
 BSI 07-2001

Figure C.3 Ð Air path in the wall


Page 16
EN 832:1998

C.2.2 Procedure
The efficiency factor of the equivalent air-to-air heat
exchanger is given by:
hv =

U20
UiUe

k

(C.6)

where
Ui and Ue

U0

k

are, respectively, the thermal
transmittances of the internal and
external parts of the envelope element
containing the air space (see C 1.2);
is the thermal transmittance of this
envelope element, assuming the air
space is not ventilated;
is the factor defined in equation (C.4).

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
FF
FS
g
Aw
Ae

In addition, the data below should be assessed:
Aj

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.

curtain factor;
frame factor;
shading correction factor;
total solar energy transmittance of glazing;
area of windows in partition wall;
area of sunspace envelope.

aSj
Ii
Up
Upe

area of each surface, j, absorbing the solar
radiation in the sunspace (floor, opaque walls;
opaque part of the partition wall has
subscript p);
average solar absorption factor of absorbing
surface j in the sunspace;
quantity of solar radiation on surface i during

each calculation period;
thermal transmittance of the opaque part in
partition wall;
thermal transmittance between the absorbing
surface 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:
QSs = QSd + QSi
(D.1)
It is assumed, in a first approximation, that the
absorbing surfaces are all shaded in the same
proportion by external obstacles and by the outer
envelope of the sunspace.
The direct solar gains QSd are the sum of the gains
through the transparent (subscript w) and opaque
(subscript p) parts of the partition wall, that is:
U
QSd = IpFSFCeFFege FCwFFwgwAw + aSpAp p  (D.2)

Upe
The indirect gains are calculated by summing the solar
gains of each absorbing area, j, in the sunspace, but
deducting the direct gains through the opaque part of
the partition wall:
Up 


QSi = (1 2 b)FSFCeFFege ∑ ISjaSjAj 2 IpaSpAp U 
pe 
 j

Figure D.1 Ð Attached sunspace with gains
and heat loss coefficients, and electrical
equivalent network

(D.3)

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.

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Page 17
EN 832:1998

D.2 Opaque elements with transparent
insulation
D.2.1 Required data
A
U
Ue
FF
FS

gTI
a

total area of the element;
thermal transmittance of the element;
external thermal transmittance of the element,
outside the surface absorbing the solar
radiation;
frame factor;
shading correction factor;
total solar energy transmittance of the
transparent insulation;
absorption coefficient of the surface absorbing
the solar radiation.

D.3.2 Procedure
Additional losses for ventilated solar walls are
calculated according to C.2. Solar gains are calculated
according to 6.3 using as the effective collecting area:
a) if the ventilated layer is covered by an opaque
external layer:
U
VÇ
U 

As = AaFSFF 0  1 + 02 raca kv
(D.5)
A
Ui
he 


where
Ui and k
v

D.2.2 Procedure
Heat losses are calculated according to clause 5, as for
usual envelope elements. The solar gain of an opaque
element with transparent insulation, having the
orientation j, is calculated according to 6.3 using as the
effective collecting area:
U
As = AFSFF agTI
(D.4)
Ue
These gains are added to the other solar gains.
NOTE This simplified method may underestimate the solar gains
from elements with transparent insulation. More accurate methods
require additional information on the components of the element.

D.3 Ventilated solar walls (Trombe walls)
The following applies to ventilated solar walls as
defined in C.2.
D.3.1 Required data
In addition to the data listed in C.1.1, the following
input data are necessary:
FF
FS
a
gw

frame factor;
shading correction factor;
absorption coefficient of the surface receiving
the solar radiation;
total solar energy transmittance of the glazing
covering the air layer.

are calculated according to C.1.2;
is the 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; v is given in Figure D.2. It can
be calculated by:
v = 1 2 e22,2?gal

(D.6)

where
gal is the ratio of the solar gains to
the heat losses of the air layer
during the calculation period
defined in C.1.2;
1
Ri + Rl + Re
is the thermal transmittance of the wall;
b) if the air layer is covered with a glazing:
U0

=

(D.7)



U2R
Ç
As = AaFSFFgw U0Re + 0 i raca V kv
(D.8)
A
UiUe


D.4 Ventilated envelope elements
If the supply air for ventilation is taken through
envelope elements, it can be heated on one hand by
the transmission heat loss through the element
(see C.3) and on the other hand by solar radiation
absorbed either by the external opaque pane or by the
internal surface of the air layer if this layer is covered
with a glazing.





Figure D.2 Ð Ratio v of the total solar radiation falling on the element when the air layer
is open to the total solar radiation during the calculation period, as a function of gal

 BSI 07-2001

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EN 832:1998

D.4.1 Required data
In addition to the data listed in C.2.2, the following
input data are necessary:
A
FF
FS
a
Ri

Re
Rl
VÇ
he
gw
hc
hr

area of the element;
frame factor;
shading correction factor;
absorption coefficient of the surface receiving
the solar radiation;

internal thermal resistance of the wall,
between the air layer and the internal
environment;
external thermal resistance, between the air
layer and the external environment;
thermal resistance of the air layer;
air flow rate through the ventilated layer;
surface transfer coefficient at the external
surface;
total solar energy transmittance of the glazing
covering the air layer;
convective surface heat transfer coefficients in
the air space;
radiative surface heat transfer coefficients in
the air space.

D.4.2 Procedure
The efficiency of the equivalent heat exchanger is
calculated according to C.2. Solar gains are calculated
according to 6.3 with the following effective collecting
areas:
a) if the ventilated layer is covered by an opaque
external layer:
U
VÇ 
U 
As = AaFSFF 0  1 + 02 raca k
(D.9)
A 
Ui

he 
b) if the air layer is covered with a glazing:

U2R
As = AaFSFFgw U0Re + 0 i raca
UiUe




VÇ 
k
A 



(D.10)

D.5 Solar gains of opaque envelope elements
D.5.1 Domain of application
The annual net solar gains of opaque elements without
transparent insulation are a small portion of the total
solar gains and are partially compensated by radiation
losses from the building to the clear sky. They can
therefore be neglected. Solar gains of opaque elements
with transparent insulation are considered in D.2.
If, however, solar gains through opaque elements are
expected to be important, e.g. for dark, highly insulated
surfaces, or if radiation losses of any envelope element
are expected to be important, e.g. large areas facing the

sky, the gains and losses of all envelope elements
(opaque and transparent) shall take account of the
radiation balance between short wave and long wave
radiation.

D.5.2 Required data
U
A
As
Re
a
Isj
Ff

hr
Duer
t

thermal transmittance of the element;
total area of the element;
equivalent collecting area of a transparent
element;
external surface resistance of the element;
absorption coefficient for solar radiation of the
element;
global solar radiation on the orientation j;
form factor between the element and the sky
(1 for unshaded horizontal roof, 0,5 for
unshaded vertical wall);
external radiative coefficient;

average difference between the outdoor air
temperature and the apparent sky temperature;
time duration of the calculation period.

D.5.3 Procedure
The net radiative gain of an element having the
orientation j, is calculated as follows:
a) opaque element without transparent covering:
Qs = UARe(aIsj 2 FfhrDuert)
(D.11)
b) transparent element:
Qs = (AsjIsj 2 UAReFfhrDuert)
(D.12)
The external radiative coefficient hr is given by:
hr = 4es(uss + 273)3
(D.13)
where
e
s
uss

is the emissivity for thermal radiation of the
outside surface;
is the Stefan-Boltzmann constant:
= 5,67 3 1028 W/(m2´K4);
is the arithmetic average of the surface
temperature and the sky temperature.

In a first approximation, hr can be taken as
5e W/(m2´K), which corresponds to an average

temperature of 10 8C.
When the sky temperature is not found in climatic
data, the difference Duer between the outside air
temperature and the sky temperature should be taken
as 9 K in northern Europe, 11 K in the Mediterranean
areas and 10 K in intermediate zones.
For opaque elements without transparent insulation,
the net gain is subtracted from the loss, the utilization
factor being equal to one.

 BSI 07-2001