CEN/TR 16798-8:2017

Energy performance of buildings - Ventilation for buildings - Part 8: Interpretation of the requirements in EN 16798-7 - Calculation methods for the determination of air flow rates in buildings including infiltration - (Module M5-5)

This Technical Report refers to the standard EN 16798-7.
It contains information to support the correct understanding and use of this standard.

Energieeffizienz von Gebäuden - Lüftung von Gebäuden - Teil 8: Interpretation der Anforderungen der EN 16798-7 - Berechnungsmethoden zur Bestimmung der Luftvolumenströme in Gebäuden einschließlich Infiltration (Modul M5-5)

Performance énergétique des bâtiments - Ventilation des bâtiments - Partie 8 : Interprétation des exigences de l’EN 16798-7 - Méthodes de calcul pour la détermination des débits d'air dans les bâtiments y compris les infiltrations (Module M5-5)

Energijske lastnosti stavb - Prezračevanje stavb - 8. del: Razlaga in utemeljitev EN 16798-7 - Metode za izračun in določanje količine zraka v stavbah, vključno z infiltracijo - Modul M5-5

To tehnično poročilo se nanaša na standard EN 16798-7.
Vsebuje informacije za pomoč pri pravilnem razumevanju in uporabi tega standarda.

General Information

• Status: Published
• Publication Date: 13-Jun-2017
• ICS: 91.120.10 - Thermal insulation of buildings
• ICS: 91.140.30 - Ventilation and air-conditioning systems
• Technical Committee: CEN/TC 156 - Ventilation for buildings
• Drafting Committee: CEN/TC 156/WG 21 - Revision of calculation standards EN15241, 15242 and 15243
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 14-Jun-2017
• Due Date: 15-Nov-2015
• Completion Date: 14-Jun-2017
• Directive: 2010/31/EU - Directive 2010/31/eu of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings (recast)
• Mandate: M/480 - Mandate to CEN, CENELEC and ETSI for the elaboration and adoption of standards for a methodology calculating the integrated energy performance of buildings and promoting the energy efficiency of buildings, in accordance with the terms set in the recast of the Directive on the energy performance buildings (2010/31/EU)
• Ref Project: SIST-TP CEN/TR 16798-8:2018 - Energy performance of buildings - Ventilation for buildings - Part 8: Interpretation of the requirements in EN 16798-7 - Calculation methods for the determination of air flow rates in buildings including infiltration - (Module M5-5)

Standards Content (Sample)

SLOVENSKI STANDARD
01-julij-2018
(QHUJLMVNHODVWQRVWLVWDYE3UH]UDþHYDQMHVWDYEGHO5D]ODJDLQXWHPHOMLWHY(1
0HWRGH]DL]UDþXQLQGRORþDQMHNROLþLQH]UDNDYVWDYEDKYNOMXþQR]
LQILOWUDFLMR0RGXO0
Energy performance of buildings - Ventilation for buildings - Part 8: Interpretation of the
requirements in EN 16798-7 - Calculation methods for the determination of air flow rates
in buildings including infiltration - (Module M5-5)
Energieeffizienz von Gebäuden - Lüftung von Gebäuden - Teil 8: Interpretation der
Anforderungen der EN 16798-7 - Berechnungsmethoden zur Bestimmung der
Luftvolumenströme in Gebäuden einschließlich Infiltration (Modul M5-5)
Performance énergétique des bâtiments - Ventilation des bâtiments - Partie 8 :
Interprétation des exigences de l’EN 16798-7 - Méthodes de calcul pour la détermination
des débits d'air dans les bâtiments y compris les infiltrations (Module M5-5)
Ta slovenski standard je istoveten z: CEN/TR 16798-8:2017
ICS:
91.140.30 3UH]UDþHYDOQLLQNOLPDWVNL Ventilation and air-
VLVWHPL conditioning systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN/TR 16798-8
TECHNICAL REPORT
RAPPORT TECHNIQUE
June 2017
TECHNISCHER BERICHT
ICS 91.120.10; 91.140.30
English Version
Energy performance of buildings - Ventilation for buildings
- Part 8: Interpretation of the requirements in EN 16798-7
- Calculation methods for the determination of air flow
rates in buildings including infiltration - (Module M5-5)
Performance énergétique des bâtiments - Ventilation Energieeffizienz von Gebäuden - Lüftung von
des bâtiments - Partie 8 : Interprétation des exigences Gebäuden - Teil 8: Interpretation der Anforderungen
de l'EN 16798-7 - Méthodes de calcul pour la der EN 16798-7 - Berechnungsmethoden zur
détermination des débits d'air dans les bâtiments y Bestimmung der Luftvolumenströme in Gebäuden
compris les infiltrations (Module M5-5) einschließlich Infiltration (Modul M5-5)

This Technical Report was approved by CEN on 27 February 2017. It has been drawn up by the Technical Committee CEN/TC
156.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16798-8:2017 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 7
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 9
4 Symbols, subscripts and abbreviations. 9
4.1 Symbols . 9
4.2 Subscripts . 10
4.3 Abbreviations . 11
5 Brief description of the methods . 11
5.1 Output of the method . 11
5.1.1 General . 11
5.1.2 Energy use outputs . 11
5.1.3 Indoor air quality outputs . 11
5.1.4 Summer comfort using ventilative cooling . 11
5.2 General description of the methods . 12
5.2.1 Multiple ventilation zones . 12
5.2.2 Airflows within a ventilation zone . 12
5.2.3 Separation of the ventilation zones into elementary spaces. 12
5.3 Selection criteria between the methods . 13
6 Calculation method, method 1 — Determination of air flow rates based on detailed
building characteristics . 14
6.1 Output data . 14
6.2 Calculation intervals . 14
6.3 Input data . 14
6.4 Calculation procedure, method 1 . 14
6.4.1 Applicable time intervals and states of operation . 14
6.4.2 Operating conditions calculation . 15
6.4.3 Calculation of air flow rates. 17
7 Method 2 – Determination of air flow rates based on statistical approach . 21
8 Quality control . 21
9 Compliance check. 21
10 Worked out examples, method 1 — Example 1. 22
10.1 Description . 22
10.2 Calculation details . 22
10.3 Observations . 22
Annex A (informative) Input and method selection data sheet — Template . 23
A.1 General . 23
A.2 References . 23
A.3 Input data method 1 . 23
A.4 Input data method 2 . 23
Annex B (informative) Input and method selection data sheet — Default choices . 24
B.1 General . 24
B.2 References . 24
B.3 Input data method 1 . 24
B.4 Input data method 2 . 24
Annex C (informative) Extract and supply air volume flow rate from a ventilation zone
(q , q ) — Calculation flowchart . 25
V;ETA;dis V;SUP;dis
Annex D (informative) Calculation examples — Example 1 . 26
Bibliography . 41

European foreword
This document (CEN/TR 16798-8:2017) has been prepared by Technical Committee CEN/TC 156
“Ventilation for buildings”, the secretariat of which is held by BSI.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
This document has been produced to meet the requirements of Directive 2010/31/EU 19 May 2010 on
the energy performance of buildings (recast), referred to as “recast EPDB”.
For the convenience of Standards users CEN/TC 156, together with responsible Working Group
Convenors, have prepared a simple table below relating, where appropriate, the relationship between
the ‘EPBD’ and ‘recast EPBD’ standard numbers prepared by Technical Committee CEN/TC 156
“Ventilation for buildings”.
EPBD EN Recast EPBD EN
Title
Number Number
Energy performance of buildings – Ventilation for buildings –
Part 1: Indoor environmental input parameters for design
EN 15251 EN 16798-1 and assessment of energy performance of buildings
addressing indoor air quality, thermal environment, lighting
and acoustics (Module M1-6)
Energy performance of buildings – Ventilation for buildings –
Part 2: Interpretation of the requirements in EN 16798-1 –
Indoor environmental input parameters for design and
N/A CEN/TR 16798-2
assessment of energy performance of buildings addressing
indoor air quality, thermal environment, lighting and
acoustics (Module M1-6)
Energy performance of buildings – Ventilation for buildings –
Part 3: For non-residential buildings – Performance
EN 16798-3
requirements for ventilation and room-conditioning systems
EN 13779
(Modules M5-1, M5-4)
Energy performance of buildings – Ventilation for buildings –
Part 4: Interpretation of the requirements in EN 16798- 3 –
N/A CEN/TR 16798-4 For non-residential buildings – Performance requirements
for ventilation and room-conditioning systems (Modules M5-
1, M5-4)
Energy performance of buildings – Ventilation for buildings –
Part 5-1: Calculation methods for energy requirements of
ventilation and air conditioning systems (Modules M5-6, M5-
EN 15241 EN 16798-5-1
8, M6-5, M6-8, M7-5, M7-8) – Method 1: Distribution and
generation
Energy performance of buildings – Ventilation for buildings –
Part 5-2: Calculation methods for energy requirements of
ventilation systems (Modules M5-6.2, M5-8.2) – Method 2:
EN 15241 EN 16798-5-2
Distribution and generation
Energy performance of buildings – Ventilation for buildings –
Part 6: Interpretation of the requirements in EN 16798-5–1
N/A CEN/TR 16798-6 and EN 16798-5-2 – Calculation methods for energy
requirements of ventilation and air conditioning systems
(Modules M5-6, M5-8, M 6-5, M6-8 , M7-5, M7-8)
Energy performance of buildings – Ventilation for buildings –
Part 7: Calculation methods for the determination of air flow
EN 15242 EN 16798-7
rates in buildings including infiltration (Module M5-5)

Energy performance of buildings – Ventilation for buildings –
Part 8: Interpretation of the requirements in EN 16798-7 –
N/A CEN/TR 16798-8
Calculation methods for the determination of air flow rates in
buildings including infiltration – (Module M5-5)
Energy performance of buildings – Ventilation for buildings –
EN 15243 EN 16798-9 Part 9: Calculation methods for energy requirements of
cooling systems (Modules M4-1, M4-4, M4-9) – General
Energy performance of buildings – Ventilation for buildings –
Part 10: Interpretation of the requirements in EN 16798-9 –
Calculation methods for energy requirements of cooling
N/A CEN/TR 16798-10
systems (Module M4-1,M4-4, M4-9) – General

Energy performance of buildings – Ventilation for buildings –
EN 15243 EN 16798-13 Part 13: Calculation of cooling systems (Module M4-8) –
Generation
Energy performance of buildings – Ventilation for buildings –
EN 15243 CEN/TR 16798-14 Part 14: Interpretation of the requirements in EN 16798-13 –
Calculation of cooling systems (Module M4-8) – Generation
Energy performance of buildings – Ventilation for buildings –
N/A EN 16798-15 Part 15: Calculation of cooling systems (Module M4-7) –
Storage
Energy performance of buildings – Ventilation for buildings –
N/A CEN/TR 16798-16 Part 16: Interpretation of the requirements in EN 16798-15 –
Calculation of cooling systems (Module M4-7) – Storage
Energy performance of buildings – Ventilation for buildings –
EN 15239 and
EN 16798-17 Part 17: Guidelines for inspection of ventilation and air-
EN 15240
conditioning systems (Module M4-11, M5-11, M6-11, M7-11)
Energy performance of buildings – Ventilation for buildings –
Part 18: Interpretation of the requirements in EN 16798-17 –
N/A CEN/TR 16798-18
Guidelines for inspection of ventilation and air-conditioning
systems (Module M4-11, M5-11, M6-11, M7-11)

Introduction
The set of EPB standards, Technical Reports and supporting tools
In order to facilitate the necessary overall consistency and coherence, in terminology, approach,
input/output relations and formats, for the whole set of EPB-standards, the following documents and
tools are available:
a) a document with basic principles to be followed in drafting EPB-standards: CEN/TS 16628, Energy
Performance of Buildings — Basic Principles for the set of EPB standards [1];
b) a document with detailed technical rules to be followed in drafting EPB-standards; CEN/TS 16629,
Energy Performance of Buildings — Detailed Technical Rules for the set of EPB-standards [2]; and
c) the detailed technical rules are the basis for the following tools:
1) a common template for each EPB standard, including specific drafting instructions for the
relevant clauses,
2) a common template for each Technical Report that accompanies an EPB standard or a cluster of
EPB standards, including specific drafting instructions for the relevant clauses, and
3) a common template for the spreadsheet that accompanies each EPB standard, to demonstrate
the correctness of the EPB calculation procedures.
Each EPB standard follows the basic principles and the detailed technical rules and relates to the
overarching EPB-standard, EN ISO 52000-1 [3].
One of the main purposes of the revision of the EPB-standards is to enable that laws and regulations
directly refer to the EPB-standards and make compliance with them compulsory. This requires that the
set of EPB-standards consists of a systematic, clear, comprehensive and unambiguous set of energy
performance procedures. The number of options provided is kept as low as possible, taking into
account national and regional differences in climate, culture and building tradition, policy and legal
frameworks (subsidiarity principle). For each option, an informative default option is provided
(Annex B).
Rationale behind the EPB technical reports
There is a risk that the purpose and limitations of the EPB standards will be misunderstood, unless the
background and context to their contents – and the thinking behind them – is explained in some detail
to readers of the standards. Consequently, various types of informative contents are recorded and made
available for users to properly understand, apply and nationally or regionally implement the EPB
standards.
If this explanation would have been attempted in the standards themselves, the result is likely to be
confusing and cumbersome, especially if the standards are implemented or referenced in national or
regional building codes.
Therefore, each EPB standard is accompanied by an informative Technical Report, like this one, where
all informative content is collected, to ensure a clear separation between normative and informative
contents (see CEN/TS 16629 [2]):
— to avoid flooding and confusing the actual normative part with informative content;
— to reduce the page count of the actual standard; and
— to facilitate understanding of the set of EPB standards.
This was also one of the main recommendations from the European CENSE project [5] that laid the
foundation for the preparation of the set of EPB standards.
This Technical Report
This Technical Report accompanies the suite of EPB standards on thermal transmission properties of
building elements. It relates to the international standard EN 16798-7, which forms part of a set of
standards related to the evaluation of the energy performance of buildings (EPB).
The role and the positioning of the accompanied standard in the set of EPB standards is defined in the
Introduction to the standard.
Accompanying spreadsheet(s)
Concerning the accompanied standard EN 16798-7, the following spreadsheets were produced:
— on EN 16798-7.
In this Technical Report, examples of each of these calculation sheets are included.
1 Scope
This Technical Report refers to the standard EN 16798-7.
It contains information to support the correct understanding and use of this standard.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
NOTE More information on the use of EPB module numbers for normative references between EPB standards
is given in CEN ISO/TR 52000-2.
EN 16798-5-1, Energy performance of buildings — Ventilation for buildings — Part 5-1: Calculation
methods for energy requirements of ventilation and air conditioning systems (Modules M5-6, M5-8, M6-5,
M6-8, M7-5, M7-8) — Method 1: Distribution and generation
EN 16798-5-2, Energy performance of buildings — Ventilation for buildings — Part 5-2: Calculation
methods for energy requirements of ventilation and air conditioning systems (Modules M5-6, M5-8, M6-5,
M6-8, M7-5, M7-8) — Method 2: Distribution and generation
EN 16798-7:2017, Energy performance of buildings — Ventilation for buildings — Part 7: Calculation
methods for the determination of air flow rates in buildings including infiltration (Module M5-5)
EN ISO 15927-1:2003, Hygrothermal performance of buildings — Calculation and presentation of
climatic data — Part 1: Monthly means of single meteorological elements (ISO 15927-1:2003)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 16798-7 apply.
NOTE More information on some key EPB terms and definitions is given in CEN ISO/TR 52000-2.
4 Symbols, subscripts and abbreviations
4.1 Symbols
For the purposes of this document, the symbols given in the accompanied EPB standard, EN 16798-7,
apply.
More information on key EPB symbols is given in CEN ISO/TR 52000-2.
Additional symbols are given in Table 1.
Table 1 — Symbols and units
Symbol Quantity Unit
b width of the building m
B
b width of the nearest obstacle m
obst
C wind pressure coefficient of the last flow —
p;end;l
element of the loop l
C —
wind pressure coefficient of the first flow
p;start;l
element of the loop l
C roughness coefficient —
rgh
d distance between the nearest obstacle and m
obst
the building
h height of the building m
B
h height of loop node m
loop_n,i
h height of the nearest obstacle (upstream) m
obst
K terrain factor —
R
N number of flow elements in loop l —
loop_e;l
N number of nodes in loop l —
loop_n;l
u wind speed at the reference regional m/s
ref
location
z height at which wind velocity is estimated m
z roughness height m
z minimum height m
min
Δp pressure drop through a flow element of the Pa
loop_e
loop
ρ air density between pressure node i and kg/m
a;
i,i+1
pressure note i+1
4.2 Subscripts
For the purposes of this document, the subscripts given in the accompanied EPB standard, EN 16798-7,
apply.
More information on key EPB subscripts is given in CEN ISO/TR 52000-2.
Additional subscripts are given in Table 2.
Table 2 —Subscripts
Subscript Term Subscript Term Subscript Term
B Building loop_n node of a loop Pint At intermediate load
loop_e element of a loop obst obstacle

4.3 Abbreviations
For the purposes of this document, the abbreviations given in the accompanied EPB standards,
EN 16798-5-1 and EN 16798-5-2, apply.
More information on key EPB abbreviations is given in CEN ISO/TR 52000-2.
5 Brief description of the methods
5.1 Output of the method
5.1.1 General
The outputs can be used as the basis for calculations related to the following issues:
— energy use;
— indoor air quality; and
— summer comfort using ventilative cooling.
5.1.2 Energy use outputs
Regarding energy use, EN 16798-7:2017, Table 4 gives the intended destination of the outputs in an
overall building energy calculation.
5.1.3 Indoor air quality outputs
Regarding indoor air quality, the calculation method can be adapted depending on the parameters of
interest for the user, which may depend on national context. These parameters may include one of the
following items:
— overall air change for a given zone;
— fresh air for habitable rooms;
— exhaust air for service rooms;
— transfer air for circulation; and
— threshold limit for pollutant(s) (in this case, the source(s) should be specified).
5.1.4 Summer comfort using ventilative cooling
The ventilation can be used for cooling purposes by increasing the fresh flow rates (compared to
hygienic values) when outdoor temperature is lower than indoor temperature.
This can be done using the different kind of ventilation and airing systems.
For mechanical systems, it is important to also consider the fan energy as the results can be inefficient,
especially for low indoor outdoor temperatures differences. Risks of overcooling should be also taken
into account.
For manually operated windows, it will rely on the occupant behaviour for which some assumptions
shall be made at national level. For night ventilation in residential building, outdoor noise should be
taken into account.
For windows opening at night, hazards, e.g. security, rain, etc. should be considered.
5.2 General description of the methods
5.2.1 Multiple ventilation zones
The formulae given in EN 16798-7 can be used to calculate the air flow rates pertaining to several
ventilation zones in an overall simulation programme. The limitation of EN 16798-7 is, however, that
these are ventilation zones, i.e. the leakages between two adjacent zones are sufficiently low to be
neglected, and there is no possibility of air transfer between two zones.
5.2.2 Airflows within a ventilation zone
EN 16798-7 does not give formulae that can be readily used to describe airflows within a ventilation
zone. It assumes that the internal pressure is homogeneous within the zone.
The relevance of this assumption depends on the characteristics of the spaces identified with the overall
partitioning of the building, in particular the significance of internal resistances compared to the
resistance to the flow through the zone boundary.
5.2.3 Separation of the ventilation zones into elementary spaces
5.2.3.1 General
If one wishes to divide ventilation zone(s) into elementary spaces, assumptions shall be made regarding
the flow pattern between those elementary spaces.
5.2.3.2 N+1 approach
The so-called n+1 approach assumes that each elementary space is connected to a common hall space
(in general it will be actual hallways of the building) and no other internal space (Figure 1).
Key
1 plan view
Figure 1 — General scheme for air flow pattern description. Building with 3 ventilation zones,
each divided into elementary spaces connected by a hall space. Section and plan view
Once a hall space is defined, the calculation procedure is as follows:
— calculate the internal pressure for the ventilation zone assuming no partitions;
— for all elementary spaces, calculate the air flow rates entering and leaving each elementary space
separately (therefore, mass balance is not necessarily true when summing all the mass air flow
rates pertaining to a single elementary space); and
— for the hall space, assign the air flow rate ensuring mass balance for each elementary space to the
hall space.
This approach is convenient for thermal simulation models because it does not require the time-
consuming calculation of the internal reference pressure for each elementary space.
5.2.3.3 Elaborated network airflow models
More elaborated airflow patterns can be modelled including e.g. use of physical characteristics of the
elementary spaces or the air flow rates between elementary spaces. For this, the reader is referred to
computer programmes such as CONTAM [6] or COMIS [7].
5.3 Selection criteria between the methods
Method 1 should provide better accuracy than Method 2 with correct input values. Method 1 allows the
user to describe the building with some flexibility in the details, including the possibility to use default
values for several inputs. Leakage and vent distributions can have a significant impact on the resulting
airflow rates in method 1. Using default values for these distributions is an effective way to reduce data
collection time and variations in the results.
On the other hand, Method 2 requires less time and expertise. The quantity of inputs can be
substantially limited compared to Method 1. Method 2 can be useful in particular for existing buildings.
The geographical scope of such statistical correlations is limited at best to a national coverage.
Differences in climate and building type can lead to several correlations for a given state.
6 Calculation method, method 1 — Determination of air flow rates based on
detailed building characteristics
6.1 Output data
No additional information beyond EN 16798-7.
6.2 Calculation intervals
No additional information beyond EN 16798-7.
6.3 Input data
No additional information beyond EN 16798-7.
6.4 Calculation procedure, method 1
6.4.1 Applicable time intervals and states of operation
In monthly calculations, the following input parameters can be used to determine the states of
operation for a given month:
— The wind speed: it can be divided into 20 % occurrence bins based on climate data, giving 5 wind
speeds corresponding to these occurrence bins;
— Supply an extract mechanical air flow rate: they can be divided in occupied and unoccupied periods
with corresponding fan electric power demand;
— The window opening state: it can be defined with 2 states (open/closed); and
— The air flow rate due to combustion appliances: it can be divided into 3 states (without combustion
air flow rate, with combustion air flow rate due to heating, combustion air flow rate due to
domestic hot water).
In this case, as much as 60 states of operation can be defined (5 × 2 × 2 × 3). Additionally, for each of
these states, various indoor temperatures can be considered.
For each state of operation, the following can be calculated:
— probability of occurrence;
— air flow rates (based on EN 16798-7); and
— fan energy use (based on EN 16798-5).
For a given indoor air temperature, the time-weighted average values of airflow rates and fan energy
use can be used as outputs for the energy calculation.
6.4.2 Operating conditions calculation
6.4.2.1 Air density calculation
No additional information beyond EN 16798-7.
6.4.2.2 Reference wind speed at site
The wind speed at site depends on the reference regional wind speed and the terrain class. The default
roughness and topography factors of EN 16798-7 were calculated using the following formulae
(see EN ISO 15927-1):
u =uC⋅ ⋅ C
(1)
site ref rgh;site top;site
with
u reference regional wind;
ref
u
u = (2)
ref
C ⋅ C
rgh;met top;met
 
z
CK⋅ln  for z≥ z (3)
rgh R min
 
z
 0
 
z
min
CK⋅ln  for z< z (4)
rgh R min
 
z
 
Note that the logarithm law profile is a rough approximation.
Table 3 gives parameters according terrain categories.
Table 3 — Terrain categories and related parameters
Terrain category KR z0 z
min
I Rough open sea; lake shore with 0,17 0,01 2
at least 5 km fetch up wind and
smooth flat country without
obstacles
II Farm land with boundary 0,19 0,05 4
hedges, occasional small farm
structures, houses or trees
III Suburban or industrial areas 0,22 0,3 8
and permanent forests
V Urban areas in which at least 0,24 1 16
15 % of the surface is covered with
buildings of average height
exceeding 15 m
When meteorological stations are located in farm land (terrain category II), Formula (3) and Table 3
give C ≈1 at 10 m. Moreover if there is no hill close from the meteorological station C = 1
rgh;met top;met
see EN ISO 15927-1:2003, 7.2.3, in this case u approximately uref.
=
=
6.4.2.3 Pressure coefficients associated to an air flow path
EN 16798-7 assumes that the facades can be split into 3 parts where average pressure coefficients can
be determined independently from the other parts:
— lower part (altitude 0 m to 15 m);
— medium part (altitude 15 m to 50 m); and
— high part (altitude ≥ 50 m).
The pressure coefficients depend on exposure to wind characterized with the identifier SHIELD_CLASS
(see EN 16798-7:2017, Annex B).
If the building and its environment can be represented schematically as in Figure 2, the following hints
can be used to determine whether the building can be considered as not shielded, partially shielded or
shielded from the wind.
a) An obstacle is defined as any building structure or object for which b /b > 0,5.
obst B
b) Building height versus height of nearest obstacle:
1) if h ≥ 0,5 (min (h ;15)) the lower part of the facade can be shielded,
obst B
2) if h −15 ≥ 0,5 (min(35; (h −15))) the lower part and the medium part of the facade can be
obst B
shielded, or
3) the high part is always considered as not shielded.
c) For a given wind direction, the shielding class depends on the ratio d / h
obst obst.
Table 4 — Shielding classes depending on the obstacle height and relative distance
Shielding class Relative distance
d /h
obst obst
Open > 4
Normal 1,5 – 4
Shielded < 1,5
Key
1 high part 5 width bobst
2 wind 6 low part (0 m to 15 m)
3 medium part (15 m to 50 m) 7 distance d
obst
4 height hobst 8 width build bB
Figure 2 — Obstacle and building
6.4.2.4 Pressure difference at an air flow path
No additional information beyond EN 16798-7.
6.4.2.5 Required supply temperature for mechanical ventilation air condition calculations
No additional information beyond EN 16798-7.
6.4.3 Calculation of air flow rates
6.4.3.1 General
No additional information beyond EN 16798-7.
6.4.3.2 Mechanical airflow calculations
No additional information beyond EN 16798-7.
6.4.3.3 Passive and hybrid duct ventilation
6.4.3.3.1 General
A ducted natural ventilation system is composed of:
— air inlets;
— cowl;
— duct; and
— air outlets.
The aim of the calculation is to calculate the air flow in the system taking into account outdoor and
indoor conditions.
Hybrid ventilation switches from natural mode to mechanical mode depending on its control. The
control strategy is part of the design phase and can be described at national level.
For existing buildings, if detailed information cannot be obtained in a reasonable time, national default
values can be used to characterize the system.
6.4.3.3.2 Pressure loss at internal air terminal devices
No additional information beyond EN 16798-7.
6.4.3.3.3 Pressure losses in the ductwork
No additional information beyond EN 16798-7.
6.4.3.3.4 Cowl characteristics and corrections according to roof angle and position and height of
the cowl
No additional information beyond EN 16798-7.
6.4.3.3.5 Overall calculation
EN 16798-7:2017, Formula (32) assumes that Δppdu does not include the effect of the height difference
on the pressure drop as it is included in the second term of the formula.
EN 16798-7:2017, Formula (32) is based on the “loop pressure compatibility approach”.
6.4.3.3.6 Switching to mechanical ventilation with hybrid systems
No additional information beyond EN 16798-7.
6.4.3.4 Combustion air flows
No additional information beyond EN 16798-7.
6.4.3.5 Airflow due to windows opening
6.4.3.5.1 General
No additional information beyond EN 16798-7.
6.4.3.5.2 Window opening free area
The windows considered as possibly opened, as well as the time schedule for that can be defined at
national level. R can depend on external temperature, wind speed, outdoor noise to account for the
w;arg
impact of draught risks and comfort issues on windows opening behaviour.
If outdoor noise issues can be neglected, when a window is opened (R ≠0), R can be estimated
w;arg w;arg
with the following formula:
R CC⋅ (5)
w;arg w;kind e
where
C coefficient depending on the kind of window
w;kind
C coefficient depending on external conditions (temperature and wind)
e
Table 5 gives default values for C
w;kind
Table 5 — Default values for C
w;kind
Kind of window C
w;kind
Casement window 1
Sliding window (horizontal or vertical slinding 0,5
windows)
Hinged windows with an opening angle α[°] (see See Formula (6)
NOTES 1 and 2) (for example bottom-hung, top-
hung and roof windows)
Other 0,3
−7 3 −42 −2
(6)
C = 2,6⋅ 10⋅−αα1,,19⋅ 10 + 1 86⋅ 10⋅α
w;kind
NOTE 1 For hinged windows, the value given for Cw;kind applies to window sizes used for residential
buildings, not to windows with height close to full room height, and for height to width geometries of the titled
window section of approx. 1:1 to 2:1.
NOTE 2 For hinged windows α is between 0 and 90°.
 
 

TT−
e0
 
 
C min 1;max 0; 1− 0,1⋅ u⋅+ 0,2 (7)
( )
e 10;site
  
 

 
 
6.4.3.5.3 Simplified calculation
When the indoor air quality only relies on windows opening, it is taken into account that the user
behaviour leads to air flow rates higher than the required ones. The f coefficient takes this point into
arg
account.
The coefficient f should take into account the occupant opening efficiency regarding windows opening
arg
(but assuming the required air flow rates are fulfilled) but also the occupancy pattern of the room.
6.4.3.5.4 Calculation of ventilation through windows using wind velocity and temperature
difference as inputs
For single-sided ventilation, the projections on the horizontal plane of the normal vectors of the
windows are within a 90° angle or less.
=
=
6.4.3.5.5 Calculation of ventilation through windows using internal pressure as input
The division of a window into several parts is useful in particular when multi-directional air flows can
occur through the window of interest. This can be observed with large temperature differences
between inside and outside combined with tall windows.
6.4.3.6 Airflow through vents and envelope leakage
6.4.3.6.1 General
No additional information beyond EN 16798-7.
6.4.3.6.2 Distribution of vents
One way sometimes used to account for little air transfer between the levels of a zone is to attribute a
lower height for the vent paths in that case, e.g.:
— Path height 1 = 0,25 min(h ; 3)
z
— Path height 2 = 0,75 min(h ; 3)
z
This distribution shall be done at elementary space level if airflows between elementary spaces of the
ventilation zone are considered.
6.4.3.6.3 Envelope leakage distribution
As the positions of air leakages are unknown, a conventional splitting of them between windward and
leeward facades should be assumed. The air leakage is defined as C value for the whole zone,
lea
assuming a flow exponent n .
lea
One way sometimes used to account for little air transfer between the levels of a zone is to attribute a
lower height for the leakage paths in that case, e.g.:
— Path height 1 = 0,25 min(h ; 3)
z
— Path height 2 = 0,75 min(h ; 3)
z
— Path height 3 = min(h ; 3)
z
This distribution shall be done at elementary space level if airflows between elementary spaces of the
ventilation zone are considered.
6.4.3.6.4 Airflow through vents (openings in the external envelope intended for ventilation
(other than windows))
No additional information beyond EN 16798-7.
6.4.3.6.5 Air flow through leaks
No additional information beyond EN 16798-7.
6.4.3.7 Other air flow paths through the ventilation zone
No additional information beyond EN 16798-7.
6.4.3.8 Conversion to mass air flow rates
No additional information beyond EN 16798-7.
6.4.3.9 Implicit mass balance formula for determining internal reference pressure
With multiple zones, it can be useful to use the “loop compatibility approach” similarly to what is done
for to calculate the air flow rate through passive and hybrid duct ventilation.
This approach is commonly used to design piping networks, but can also be used to size ventilation
system components and design natural ventilation systems. It is based on the definition of close loops,
usually starting and ending outdoors and with intermediate nodes. Going through any loop, the sum of
the pressure differences between the nodes when closing the loop is equal to zero. The mass air flow
rates between the nodes are adjusted until the sum of pressures over each loop reaches zero.
To apply this approach to a set of ventilation zones, the set of zones shall be split into independent
loops. In practice:
— each loop starts and ends outside (atmospheric pressure); and
— each loop includes at least one flow element which is used in no other loop.
The formula that applies to each loop l is:
iN iN −1
loop_e,l loop_n,l
ρ
a;e
∆ρp ⋅⋅g h− h+ u⋅ C− C (8)
( ) ( )
∑∑
loop_e;i a;,ii++1 loop_n;i loop_n;i 1 site p;start;l p;end;l
ii11
6.4.3.10 Total air flow rate entering and leaving the ventilation zone
No additional information beyond EN 16798-7.
7 Method 2 – Determination of air flow rates based on statistical approach
No additional information beyond EN 16798-7.
8 Quality control
In method 1, to estimate the convergence of the mass balance, the following criteria can be used:
— square of residuals of Formula (66) smaller than 0,000 1;
— square of the residuals of Formula (29) smaller than 0,000 1.
9 Compliance check
The following items could be checked additionally if relevant:
— location and characteristics of windows (A , R , α , β );
w;max w;arg w w
— height of ventilation zone (h );
z
— envelope airtightness index of ventilation zone (q ); and
V;ΔPlea;ref
— control type (SUP_AIR_TEMP_CTRL, SUP _AIR_FLW_CTRL).
==
=
= =
10 Worked out examples, method 1 — Example 1
10.1 Description
The calculation example in Annex D represents the case of a 11/2-storey single-family houses (floor
area: 100 m ) with four windows open. It highlights the major impact of windows opening on airflow
rates. It also calculates the impact of every system described in the standard (leakage, vents,
combustion appliance, passive duct and windows airing). Where possible, default values were used. The
description of vents, leakage and mechanical ventilation system corresponds to a typical single-family
house.
10.2 Calculation details
Main characteristics of the single-family house are:
— balanced ventilation with no heating or cooling needs to be covered by ventilation;
3 3
— mechanical ventilation volume air flowrates of 210 m /h including 3 m /h due to leakages in
ductworks;
— four open windows distributed leeward and windward (total windows area: 5 m );
— four vents of 100 cm each distributed on leeward an windward façade;
3 2
— an airtightness of q = 1,2 m /h/
...