UNI 1379000_2005

8/12/2019 UNI 1379000_2005

1/66

8/12/2019 UNI 1379000_2005

2/66

UNI Pagina IIUNI EN ISO 13790:2005

Le norme UNI sono elaborate cercando di tenere conto dei punti di vista di tutte le partiinteressate e di conciliare ogni aspetto conflittuale, per rappresentare il reale statodellarte della materia ed il necessario grado di consenso.Chiunque ritenesse, a seguito dellapplicazione di questa norma, di poter fornire sug-gerimenti per un suo miglioramento o per un suo adeguamento ad uno stato dellartein evoluzione pregato di inviare i propri contributi allUNI, Ente Nazionale Italiano diUnificazione, che li terr in considerazione per leventuale revisione della norma stessa.

Le norme UNI sono revisionate, quando necessario, con la pubblicazione di nuove edizioni odi aggiornamenti.

importante pertanto che gli utilizzatori delle stesse si accertino di essere in possessodellultima edizione e degli eventuali aggiornamenti.Si invitano inoltre gli utilizzatori a verificare lesistenza di norme UNI corrispondenti allenorme EN o ISO ove citate nei riferimenti normativi.

PREMESSA NAZIONALE

La presente norma costituisce il recepimento, in lingua inglese, del-la norma europea EN ISO 13790 (edizione giugno 2004), che assu-me cos lo status di norma nazionale italiana.

La presente norma stata elaborata sotto la competenza dellente

federato allUNI

CTI - Comitato Termotecnico Italiano

La presente norma stata ratificata dal Presidente dellUNI, condelibera dell11 marzo 2005.

L icenza d ' uso concessa a UNIVERSITA ' CENTRO A TENEO DOC.POLO M ONTE DAGO pe r l ' abbonam en to anno 2005 .

L icenza d ' uso in te rno su pos taz i one s ingo la . R ip roduz i one v ie ta ta . E ' p ro ib i t o qua l s ias i u t i l izzo in re te (LAN, in te rne t , e t c . . . )

8/12/2019 UNI 1379000_2005

3/66

EUROPEAN STANDARD

NORME EUROPENNE

EUROPISCHE NORM

EN ISO 13790

June 2004

ICS 91.140.10

English version

Thermal performance of buildings - Calculation of energy use forspace heating (ISO 13790:2004)

Performance thermique des btiments - Calcul des besoinsd'nergie pour le chauffage des locaux (ISO 13790:2004)

Wrmetechnisches Verhalten von Gebuden - Berechnungdes Heizenergiebedarfs (ISO 13790:2004)

This European Standard was approved by CEN on 8 September 2003.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards 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 translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.

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

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O MIT E U R O P E N D E N O R MA L IS A T IO N

EUROPISCHES KOMITEE FR NORMUNG

Management Centre: rue de Stassart, 36 B-1050 Brussels

2004 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.

Ref. No. EN ISO 13790:2004: E



8/12/2019 UNI 1379000_2005

4/66

EN ISO 13790:2004 (E)

2

Contents

Foreword......................................................................................................................................................................3

Introduction .................................................................................................................................................................4

1 Scope....................................................................................................................................................................4

2 Normative references..........................................................................................................................................5

3 Terms and definitions .........................................................................................................................................5

4 Symbols and abbreviations................................................................................................................................9

5 Outline of the calculation procedure and required data................................................................................11

6 Intermittent heating ...........................................................................................................................................15

7 Heat loss (single zone calculation)..................................................................................................................16

8 Heat gains...........................................................................................................................................................19

9 Heat use..............................................................................................................................................................21

10 Annual heat use of the building....................................................................................................................24

11 Energy for space heating..............................................................................................................................24

12 Report..............................................................................................................................................................25

Annex A (normative) Application to existing buildings .......................................................................................27

Annex B (normative) Multi-zone calculation method ...........................................................................................28

Annex C (normative) Intermittent heating Calculation of adjusted internal temperature..............................29

Annex D (normative) Calculation with holiday period..........................................................................................37

Annex E (normative) Heat loss of special envelope elements ............................................................................38

Annex F (normative) Solar gains of special elements..........................................................................................42

Annex G (informative) Ventilation airflow rates ....................................................................................................49

Annex H (informative) Data for solar gains............................................................................................................53

Annex I (informative) Calculation of heat use for each heating mode................................................................57

Annex J (informative) Accuracy of the method.....................................................................................................59

Annex K (informative) Conventional input data ....................................................................................................60

Annex ZA (informative) Normative references to international publications with theircorresponding European publications ...................................................................................................................62

Bibliography ..............................................................................................................................................................63



8/12/2019 UNI 1379000_2005

5/66

EN ISO 13790:2004 (E)

3

Foreword

This document EN ISO 13790:2004 has been prepared by Technical Committee CEN/TC 89 "Thermalperformance of buildings and building components, the secretariat of which is held by SIS, in collaboration withTechnical Committee ISO/TC 163, Thermal performance and energy use in the builtenvironment, sub-committee 2, Calculation methods.

This European Standard shall be given the status of a national standard, either by publication of an identical text orby endorsement, at the latest by December2004, and conflicting national standards shall be withdrawn at the latestby December2004.

Annexes A to F are normative. Annexes G to K are informative.

This document includes a Bibliography.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard : : Austria, Belgium, Cyprus, Czech Republic, Denmark,Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom



8/12/2019 UNI 1379000_2005

6/66

EN ISO 13790:2004 (E)

4

Introduction

This standard is one of a series of calculation methods for the design and evaluation of thermal performance ofbuildings and building components.

The calculation method presented in this standard is based on an energy balance taking account of internal andexternal temperature variations and, through a utilisation 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) comparing the energy performance of various design alternatives for a planned building;

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 ofseveral buildings representative of the building stock.

Reference can be made to other International Standards or to national documents for input data and detailedcalculation procedures not provided by this standard. In particular, this applies to the calculation of the efficiency orthe heat loss of the heating systems.

Unlike EN 832, whose scope is restricted to residential buildings, this standard can be applied to both residentialand non-residential buildings. The most important changes in EN ISO 13790 compared to EN 832:1998, Thermalperformance of buildings - Calculation of energy use for heating - Residential buildings, are:

1. Ventilation rates are calculated according to standards prepared by CEN/TC 156;

2. Clause 11 has been made simpler, and energy use is calculated from heat use according to existingInternational Standards or, by default, to national documents;

3. A normative method has been included to calculate the effect of intermittence.

4. New input data have been included for non-residential buildings, in particular for utilisation factors.

For all these reasons, calculation using EN ISO 13790 gives results that may slightly differ from those obtained withEN 832.

1 Scope

This standard gives a simplified calculation method for assessment of the annual energy use for space heating of aresidential or a non-residential building, or a part of it, which will be referred to as "the building".

It does not apply to buildings with air conditioning systems likely to provide space cooling during the heatingseason.

This method includes the calculation of:

1. the heat losses of the building when heated to constant internal temperature;

2. the annual heat required 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, using heating systemcharacteristics which are to be found in specific European or International Standards, or, by default, innational documents.



8/12/2019 UNI 1379000_2005

7/66

EN ISO 13790:2004 (E)

5

The building can have several zones with different set-point temperatures, and can have intermittent heating.

The calculation period is the month. For residential buildings the calculation can also be performed for the heatingseason. Monthly calculation gives correct results on an annual basis, but the results for individual months close to

the beginning and the end of the heating season can have large relative errors. Annex J provides some informationon the accuracy of the method.

2 Normative references

This European Standard incorporates by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text, and the publications are listed hereafter. Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies (including amendments).

EN ISO 7345:1995, Thermal insulation Physical quantities and definitions (ISO 7345:1987).

EN ISO 13370:1998, Thermal performance of buildings Heat transfer via the ground Calculation methods(ISO 13370:1998).

EN ISO 13789, Thermal performance of buildings Transmission heat loss coefficient Calculation method(ISO 13789:1999).

3 Terms and definitions

For the purposes of this European Standard, the terms and definitions given in EN ISO 7345:1995 and thefollowing apply.

3.1calculation period

time period for the calculation of heat losses and gains

NOTE The calculation period is the month. For residential buildings the calculation can also be performed for the heating season.

3.2external temperature

temperature of external air

NOTE For transmission heat loss calculations, the radiant temperature of the external environment is supposed equal to the external airtemperature; long-wave transmission to the sky is considered in F.5.

3.3

internal temperature

arithmetic average of the air temperature and the mean radiant temperature at the centre of the occupied zone

NOTE This is the approximate operative temperature according to ISO 7726, Ergonomics of the thermal environment - Instruments formeasuring physical quantities.

3.4set-point temperature

internal temperature, as fixed by the control system in normal heating mode

3.5

set-back temperature

minimum internal temperature to be maintained during reduced heating periods



8/12/2019 UNI 1379000_2005

8/66

8/12/2019 UNI 1379000_2005

9/66

EN ISO 13790:2004 (E)

7

3.13heated zone

part of the heated space with a given set-point temperature, throughout which the internal temperature is assumed

to have negligible spatial variations

3.14heat transfer coefficient

heat flow rate between two zones divided by the temperature difference between both zones

3.15heat loss coefficient

heat transfer coefficient from the heated space to the external environment

NOTE The heat loss coefficient of the building cannot be used when the multi-zone calculation method according to annex B is applied

3.16building heat loss

heat transferred from heated space to the external environment by transmission and by ventilation, during a givenperiod of time

3.17ventilation heat loss

heat lost with the air leaving the heated space either by exfiltration or ventilation

3.18transmission heat loss

heat loss by transmission through the building envelope and through the ground

3.19heat gains

heat generated within or entering into the heated space from heat sources other than the space and hot waterheating systems

NOTE These include internal heat gains and solar gains.

3.20internal heat gains

heat provided within the building by occupants (sensible metabolic heat) and by appliances other than the spaceand hot water heating systems (lighting, domestic appliances, office equipment, etc.)

3.21solar gains

heat provided by solar radiation entering into the building through windows or passive solar devices such assunspaces, transparent insulation and solar walls

NOTE Active solar devices such as solar collectors are considered as part of the heating system.

3.22solar irradiation

incident solar heat per area over a given period



8/12/2019 UNI 1379000_2005

10/66

EN ISO 13790:2004 (E)

8

3.23utilisation factor

factor reducing the total monthly or seasonal heat gains to obtain the resulting reduction of the heat use

3.24recovered heat

heat recovered from the environment or from heating and hot water systems (including auxiliary equipment), if notdirectly taken into account in a reduction of the heating system losses

3.25ventilation heat recovery

heat recovered from the exhaust air

3.26

heating system losses

total of the heat lost by the heating system, including recovered system heat loss



8/12/2019 UNI 1379000_2005

11/66

EN ISO 13790:2004 (E)

9

4 Symbols and abbreviations

Table 1 Symbols and unitsSymbol Quantity Unit

A area m

a numerical parameter in utilisation factor -

b correction factor for unheated zones -

C effective heat capacity of a heated space J/K

c specific heat capacity J/(kgK)

d layer thickness mF factor -

g total solar energy transmittance of a building element -

I solar irradiance J/m

H heat transfer coefficient, heat loss coefficient W/K

h surface coefficient of heat transfer W/(mK)

L length m

N number

Q quantity of heat or energy J

R thermal resistance mK/W

T thermodynamic temperature K

t time, period of time s

U thermal transmittance W/(mK)

V volume of air in a heated zone m

V airflow rate m/s

heat flow rate, heating power W

heat loss parameter for solar walls W/(mK)

absorption coefficient of a surface for solar radiation -

gain/loss ratio -

ratio of the accumulated internal-external temperature difference when theventilation is on to its value over the calculation period

-

emissivity of a surface for thermal radiation -



8/12/2019 UNI 1379000_2005

12/66

EN ISO 13790:2004 (E)

10

Symbol Quantity Unit

efficiency, utilisation factor for the gains -

factor related to heat losses of ventilated solar walls -

Celsiustemperature C

density kg/m

Stefan-Boltzmann constant ( = 5,67 10-8 ) W/(mK4)

time constant s

heat capacity per area J/(mK)

ratio of the effects of a change in heating flow rate on the internal temperatureand on the structure temperature

-

effective part of the heat capacity -

ratio of the total solar radiation falling on the element when the air layer is opento the total solar radiation during the calculation period

-

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 changerates), but in that case the unit of energy is Watt-hours [Wh] instead of Joules.



8/12/2019 UNI 1379000_2005

13/66

EN ISO 13790:2004 (E)

11

Table 2 Subscripts

C capacity, calculation,convective

f form, final r radiative, recovered,reduced

F frame g gains s solar, sunspace

G ground h heating, heated, hemispherical sb set back

L loss hol holidays se surface external

P related to power hw hot water si surface internal

S shading i internal ss surface-sky average

T transmission ih intermittent heating sw solar wall

V ventilation i,j,k,m,n dummy integers t transparent insulation

a air l layer th heating system

ad adjusted m metabolic, month u unheated

ap appliances nh no heating v ventilation

bh boost heating o overall w window

c structure p partition wall y, z zone number

d design, daily, direct pp peak power perpendicular

e exterior, envelope ps permanent shading 0 base, reference

5 Outline of the calculation procedure and required data

5.1 Energy balance

The energy balance includes the following terms (only sensible heat is considered):

5. transmission and ventilation heat loss from the heated space to the external environment;

6. transmission and ventilation heat transfer between adjacent zones;

7. internal heat gains;

8. solar gains;

9. generation, distribution, emission and control losses of the space heating system;

10. energy input to the space heating system.

It may also include recovered energy from various sources.

NOTE As heat gains may induce internal temperature to rise above the set-point, the resulting additional heat loss is taken into accountthrough a utilisation factor reducing heat gains.



8/12/2019 UNI 1379000_2005

14/66

EN ISO 13790:2004 (E)

12

The main terms of the energy balance are schematically illustrated in Figure 1.

3Q

4

Qg

Qhw

Qoa

Qm

Qi

Qg

Qs1

Qh

QVr

QT

QV

2Qr Qhs

QL

Key

Q Energy use for heating

Qoa Heat from other appliancesQr Recovered energy

Qhs Losses from the heating system

Qm Metabolic heat

Qs Passive solar gains

Qi Internal gains

Qg Total gains

Qg Useful gains

Qh Heat use

QV Ventilation heat lossQVr Ventilation heat recovery

QT Transmission heat loss

Qhw Heat for hot water preparation

QL Total heat loss

1 Boundary of the heated zone

2 Boundary of the hot water system

3 Boundary of the heating plant

4 Boundary of the building

Figure 1 Energy balance of a building

5.2 Calculation procedure

The calculation procedure is summarised below. In addition, the special approach given in annex A shall befollowed when applying this standard to existing buildings.

1) Define the boundaries of the heated space and, if appropriate, of different zones and unheated spaces,according to 5.3.

2) In case of intermittent heating or intermittent ventilation define, within the calculation period, the periods havingdifferent heating and ventilation patterns (e.g. day, night, weekend) according to clause 6.



8/12/2019 UNI 1379000_2005

15/66

EN ISO 13790:2004 (E)

13

3) For a single zone calculation, calculate the heat loss coefficientof the heated space according to clause 7; orfor a multi-zone calculation, follow the procedure in annex B.

4) For seasonal calculation, define or calculate the length and climatic data of the heating season, according

to 9.2.

Then, for each calculation period (month or heating season):

5) calculate the adjusted internal temperature for each period according to clause 6;

6) calculate the heat loss, QL, according to clause 7;

7) calculate the internal heat gains, Qi, according to 8.1;

8) calculate the solar gains, Qs, according to 8.2;

9) calculate the utilisation factor for heat gains, , according to 9.2;

10) calculate the heat use, Qh, for all calculation periods, according to clause 9;

11) calculate the annual heat use, Qh, according to clause 10;

12) calculate the energy use for heating taking into account the losses of the heating system, according toclause 11.

5.3 Definition of boundaries and zones

5.3.1 Boundary of the heated space

The boundary of the heated space consists of all the building elements separating the considered heated spacefrom external environment or from adjacent heated zones or unheated spaces.

5.3.2 Thermal zones

5.3.2.1 Single zone calculation

When the heated space is heated to the same temperature throughout, and when internal and solar gains arerelatively 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 ratiosdiffer by less than 0,4 (e.g. between south and north zones), or

b) doors between zones are likely to be frequently open.

In such cases, even if the set-point temperature is not uniform, the single zone calculation applies. Then theinternal temperature to be used is:

=

z

z

H

H

z

izz

i

(1)

where

iz is the set-point temperature of zone z;

Hz is the heat loss coefficient, according to clause 6, but calculated separately for each zone z.

In this case, a unique intermittence pattern shall be chosen.



8/12/2019 UNI 1379000_2005

16/66

EN ISO 13790:2004 (E)

14

5.3.2.2 Multi-zone calculation

In other cases with significant differences in set-point temperatures or heat gains, the building is divided intoseveral zones.

If the purpose of the calculation is to assess heat use for each zone individually, then the calculation proceduregiven in annex B shall be used.

Otherwise, each zone may be calculated independently using the single zone procedure and assuming adiabaticboundaries between zones. The energy use for the building is the sum of the energy use calculated for theindividual zones.

5.4 Input data

5.4.1 Source and type of input data

When no International 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 givevalues or methods to obtain values when the required information is otherwise not available.

For predicting the energy needs or judging compliance with regulations or specifications, conventional values shallbe used, in order to make the results comparable between different buildings.

For optimisation of a planned building or retrofitting an existing building, the best available estimate for thatparticular building shall be used (see annex A). However, if no better estimates are available, conventional valuesmay be used as first approximations.

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 andthe type of dimensions used shall be clearly indicated in the report.

NOTE 1 Some linear thermal transmittances of thermal bridges depend on the type of dimensions used.

The input data required for single zone calculation are listed below. Some of these data may be different for eachcalculation period (e.g. shading correction factors, airflow rates in cold months) and for each period of anintermittence pattern (e.g. air flow rate, thermal transmittance of windows due to closing of shutters during nightperiods). Input data for heat loss are

HT transmission heat loss coefficient according to EN ISO 13789.

NOTE 2 In contrast with EN ISO 13789, daily average values of the thermal transmittance of windows with shutters can be determined on thebasis of the values given by EN ISO 10077-1, Thermal performance of windows, doors and shutters - Calculation of thermal transmittance Part 1: Simplified method.

.V air flow rate through the building, including airflows to and from unheated spaces.

5.4.2 Input data for heat gains

i 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,pitched, and vertical south and north):

Aj area of opening in the building envelope for each window or door;

FFj frame factor, i.e. transparent fraction of the area Aj, not occupied by a frame;

Fsj shading correction factor, i.e. average shaded fraction of the area Aj;

gj total solar energy transmittance for solar radiation.



8/12/2019 UNI 1379000_2005

17/66

EN ISO 13790:2004 (E)

15

NOTE In non-residential buildings internal gains vary substantially between occupied and non-occupied periods. Gains can be firstcalculated for each occupancy period and then averaged taking into account the length of each period. This calculation is often easier on aweekly basis.

Additional data shall be collected for components that collect solar radiation, such as transparent insulation,ventilated solar walls and sunspaces, and for calculation of the effect of intermittent heating. The required data arelisted in annexes E and F. Annex H gives some information on data useful to assess the solar gains.

5.4.3 Dynamic characteristics

C heat capacity of the heated space, calculated for heat use according to 9.2;

time constant of the heated space

NOTE Either Corshould be specified, not both.

5.4.4 Input data for energy use

Qhs losses of the heating system.

5.4.5 Climatic data

The calculation method requires the following climatic data:

e monthly or seasonal average of external temperature;

Is,j monthly or seasonal total solar radiation per area for each orientationj, in J/m.

NOTE EN ISO 15927-1, Hygrothermal performance of buildings Calculation and presentation of climatic data Part 1: Monthly and annualmeans of single meteorological elements is available.

6 Intermittent heating

6.1 Intermittence patterns

When intermittent heating is applied, the calculation period(s) shall be divided into normal heating periodsalternating with reduced heating periods (e.g. nights, week-ends, and holidays).

All the normal heating periods shall have the same set-point temperature.

There may be several types of reduced heating periods with different patterns.

Within each calculation period, each type of reduced heating period is characterized by:

11. its duration;

12. the number of occurrences of that type of period in one calculation period;

13. the relevant mode of intermittence (see 3.12) ;

14. where relevant, the set-back temperature or the reduced heating power;

15. the boost mode (see 3.12.5) and the maximum heating power during the boost period.

An example is shown in Figure 2, where the calculation period includes four type A reduced heating periods (e.g.nights) and one type B reduced heating period (week-end).



8/12/2019 UNI 1379000_2005

18/66

EN ISO 13790:2004 (E)

16

t

N

tc

A

B

N N NN

A AA

Key

Set-point temperaturet Time

tc Calculation period

N Normal heating periodA Reduced heating period type A

B Reduced heating period type B

Figure 2 Example of intermittence pattern

The division into different periods is not required when:

a) set-point temperature variations between normal heating and reduced heating periods are lower than 3 K:in thiscase time average of set-point temperatures may be used;

b) the time constant of the building (see 9.2.2 ) is greater than three times the duration of the longest reducedperiod: in this case the normal set-point temperature may be used for all periods;

c) the time constant of the building is less than 0,2 times the duration of the shortest reduced heating period: in thiscase the time average of set-point temperatures may be used.

The heating system is supposed to deliver sufficient heating power to enable intermittent heating.

NOTE 1 In non residential buildings, variations of set-point temperatures and ventilation flow rates are often linked to occupancy. Splitting intodifferent periods facilitates the evaluation of the mean air flow rate in each of them.

NOTE 2 As heating patterns are usually defined on a weekly basis, their definition will be facilitated if calculations are performed for one weekper month.

6.2 Adjusted internal temperature

The adjusted internal temperature is the constant internal temperature which would result in the same heat loss asthat obtained with intermittent heating during the period.

For each reduced period, the adjusted internal temperature shall be calculated using the procedure defined inannex C for daily or weekly reductions, and annex D for holidays.

Values of adjusted internal temperature may also be provided at a national level based on the type of building,building use, heating system, etc.

7 Heat loss (single zone calculation)

7.1 Without intermittent heating

The total heat loss, QL, of a single zone building at a uniform internal temperature and for a given calculationperiod, is:



8/12/2019 UNI 1379000_2005

19/66

EN ISO 13790:2004 (E)

17

tHQ )( eiL = (2)

where

i is the set-point temperature;

e is the average external temperature during the calculation period;

t is the duration of the calculation period;

H is the heat loss coefficient of the building, calculated according to 7.3.

Equation (2) can be adapted at national level to allow for the use of degree-days. The result of the adapted relationshall nevertheless be the same as that of Equation (2) for any building.

7.2 With intermittent heating

If the division into different heating periods is not applicable, see 7.1.

If the division into different heating periods is applicable, the total heat loss, QL, of a single zone building at auniform internal temperature and for a given calculation period, is calculated from Equation (3):

=

=N

jjjjj tHNQ

1eiadL ),( (3)

where

N is the number of heating period types (e.g. 3 for normal, nights, and week-ends);

Nj is the number of heating periods of each type during the calculation period;

iad,j is the adjusted internal temperature of the heating periodj;

tj is the duration of the heating periodj;

Hj is the heat loss coefficient of the building during periodj, calculated according to 7.3.

NOTE =

N

jjj tN

1

is equal to the duration of the calculation period.

To simplify the notation the subscriptj is omitted below. Nevertheless when the division into heating periods is

applicable the calculation shall be performed for each heating period.

7.3 Heat loss coefficient

The heat loss coefficient of a single zone building at a uniform internal temperature, and for a given calculationperiod or sub-period, is defined by Equation (4):

H = HT+ HV (4)

where

HT is the transmission heat loss coefficient, calculated according to EN ISO 13789 (for envelope elementsincorporating ventilating devices, see annex E);

HV is the ventilation heat loss coefficient (see 7.5).



8/12/2019 UNI 1379000_2005

20/66

EN ISO 13790:2004 (E)

18

7.4 Buildings with significant heat loss through the ground

EN ISO 13789 states that the steady state method given in EN ISO 13370 should be used to include heat lossthrough the ground into the transmission heat loss coefficient HT. However, that could result monthly heat losses

through the ground being overestimated by 30 % to 40 % in winter and, if heat loss through the ground is animportant part of the total heat loss, detailed calculation of the ground heat loss according to B.1 of ENISO 13370:1998 shall be done. In this case, the total heat loss QLis given,

16. without division into different heating periods, by:

( )tHQ GeiL )(' += (5)

17. in case of division into different heating periods, by:

ttHNQN

jjjjj G

1eiadL ),(' +=

=

(6)

where

H' is calculated according to 7.3 but without ground heat loss;

G is the heat loss rate through the ground calculated according to EN ISO 13370.

7.5 Ventilation heat loss coefficient

7.5.1 Principle

The ventilation heat loss coefficient, HV, is calculated from:

VcH aaV = (7)

where

.V is the airflow rate through the heated space;

aca is the heat capacity of air per volume.

NOTE 1 If the air flow rate, V , is in m3/s, aca1200 J/(m3K). If V is given in m/h, aca 0,34 Wh/(m3K).

Average airflow rate over each heating period shall be used.

For residential buildings, the airflow rate, V , may be calculated either according to EN 13465, or provided atnational level based on the type of building, building use, climate, exposition, etc.

For other buildings, the airflow rate, V , may be calculated either according to an appropriate InternationalStandard, or provided at national level based on the type of building, building use, climate, exposition, etc.

NOTE 2 Unless otherwise specified, the method in annex G can be used.

7.5.2 Heat recovery

Heat recovery from exhaust air is taken into account by reducing the real airflow rate in proportion to the efficiencyof heat recovery.

This efficiency is always smaller than the effectiveness of the heat exchanger itself. It shall take account ofdifferences between supply and extract airflow rates, of leakage and infiltration through the building envelope, andrecirculation of air.



8/12/2019 UNI 1379000_2005

21/66

EN ISO 13790:2004 (E)

19

NOTE Unless otherwise specified, the method in annex G can be used.

7.6 Special elements

Special methods are needed to calculate the heat loss of some special elements such as ventilated solar walls andother ventilated envelope elements. These methods are given in annex E.

8 Heat gains

8.1 Internal heat gains

Internal heat gains, Qi,include any heat generated in the heated space by internal sources other than the spaceheating system, e.g.:

18. metabolic gains from occupants;

19. the energy consumption of appliances and lighting devices.

Average monthly or seasonal values are appropriate for the calculation according to this standard. In this case,internal heat gains are calculated from Equation (8):

Qi= [i,h+ (1-b) i,u)] t = i t (8)

where

i,h is the average power of the internal gains in heated spaces;

i,u is the average power of the internal gains in unheated spaces;

i is the average power of the internal gains;

b is the reduction factor defined in EN ISO 13789.

NOTE There are substantial variations between users and climates, and values should normally be determined on a nationalbasis. Unless otherwise specified, the conventional values given for internal gains in annex K can be used.

8.2 Solar gains

8.2.1 Basic equation

Solar gains result from the solar radiation normally available in the locality concerned, the orientation of thecollecting areas, the permanent shading, and the solar transmission and absorption characteristics of the collectingareas. 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 F.

For a given calculation period, solar gains are calculated from:

+

=

j nnjj

j nnjj AIbAIQ u,sssss )1( (9)

where the first term is for heated space and the second for unheated space. Solar gains in unheated spaces aremultiplied by(1-b),where bis the reduction factor defined in EN ISO 13789. Heat gains of sunspaces arecalculated according to annex F.

In each term, the first sum is over all orientations,j, and the second over all the surfaces,n,collecting the solarradiation, and:



8/12/2019 UNI 1379000_2005

22/66

EN ISO 13790:2004 (E)

20

Isj is the solar irradiance, e.g. the total energy of the global solar radiation during the calculation period on asurface of area 1 m having orientationj, in J/m;

Asnj is the solareffective collecting area of the surface n having orientationj, that is the area of a black body

having the same solar gain as the surface considered.

NOTE Isjcan be replaced by an orientation factor multiplied by the total solar radiation per area for a single orientation (e.g. vertical south).

8.2.2 Effective collecting area of glazed elements

The effective area of a glazed envelope element (e.g. a window) is:

As=A FSFFg (10)

where

A is the overall area of the glazed element (e.g. window area);

FS is the shading correction factor;

FF is the frame factor,ratio of the transparent area to the overall area of the glazed element;

g is the total solar energy transmittance of the glazing taking account of permanent solar protectiondevices, if any.

NOTE Only permanent shading and permanent solar protection devices are taken into account in the shading correction factor and in thetotal solar energy transmittance of the glazing.

8.2.3 Solar energy transmittance of glazing

In principle, the total solar energy transmittance g in Equation (10) is the time-averaged ratio of energy passing

through the unshaded element to that incident upon it. For windows or other glazed envelope elements, ISO 9050provides a method to obtain the solar energy transmittance for radiation perpendicular to the glazing. This value,g,is somewhat higher than the time-averaged transmittance, and a correction factor, Fw, shall be used:

g = Fwg (11)

NOTE g-values and guidance for the correction factor are given in annex H, together with typical solar transmission factors for globalradiation.

EN 13363-1 and prEN 13363-2 provide methods of determination of the total solar energy transmittance of glazingequipped with solar protection devices.

8.2.4 Shading correction factors

The shading correction factor, FS, which is in the range 0 to 1, represents the reduction in incident solar radiationdue to permanent shading of the surface concerned resulting from:

20. other buildings;

21. topography (hills, trees etc.);

22. overhangs;

23. other elements of the same building;

24. external part of the wall where the glazed element is mounted.

The shading correction factor is defined by:



8/12/2019 UNI 1379000_2005

23/66

EN ISO 13790:2004 (E)

21

s

pss,S I

IF = (12)

where

Is,ps is the total solar irradiance actually received on the collecting plane with the permanent shading duringthe heating season;

Is is the solar irradiance without shading.

NOTE Annex H provides some information on shading correctionfactors.

8.2.5 Special elements

Special methods are needed to calculate the solar gains of some passive solar collecting elements, such asunheated sunspaces, opaque elements with transparent insulation, and ventilated envelope elements. These

methods are given in annex F.

8.3 Total heat gains

Total heat gains, Qg, are:

Qg= Qi + Qs (13)

9 Heat use

9.1 General

Heat loss, QL, and heat gains, Qgare calculated for each calculation period. The heat use for space heating is

obtained for each calculation period from:

Qh= QL- Qg (14)

setting QL= 0 and = 0 when the average external temperature is higher than the set-point temperature.

The utilisation factor, , is a reduction factor for the heat gains, introduced to compensate additional heat loss likelyto occur when heat gains exceed the calculated heat loss.

9.2 Utilisation factor for heat gains

9.2.1 Gain/loss ratio

The gain/loss ratio, , is defined as:

L

g

Q

Q= (15)

9.2.2 Building time constant

This time constant,, characterises the internal thermal inertia of the heated space. It is calculated from:

HC

= (16)

whereC is the internal heat capacity of the building, calculated according to 9.2.3;



8/12/2019 UNI 1379000_2005

24/66

EN ISO 13790:2004 (E)

22

H is the heat loss coefficient of the building, calculated according to 7.3.

Conventional time constants for typical buildings may also be provided at a national level.

9.2.3 Internal heat capacity of the building

The internal heat capacity of the building, C,is calculated by summing the heat capacities of all the buildingelements in direct thermal contact with the internal air of the zone under consideration:

C = jAj = jiijcij dijAj (17)

where

j is the internal heat capacity per area of the building elementj;

Aj is the area of the elementj;

ij is the density of the material of the layeriin elementj;

cij is the specific heat capacity of the material of layeriin elementj;

dij is the thickness of the layeriin elementj.

The sum is done for all layers of each element, starting from the internal surface and stopping at the first insulatinglayer, the maximum thickness given in Table 3 or the middle of the building element; whichever comes first.

Table 3 Maximum thickness to be considered for internal heat capacity

Application Maximum thicknesscm

Determination of the utilisation factor 10

Effect of intermittence 3

The internal heat capacity of the building may also be calculated as the sum of the internal capacities of all buildingelements, each calculated according to EN ISO 13786, or provided at a national level, based on the type ofconstruction. This figure can be approximate, and a relative uncertainty ten times higher than that of the heat loss isacceptable.

9.2.4 Utilisation factor

The utilisation factor is calculated from:

if 1:11

1+

=

a

a

(18)

if = 1:1+

=a

a (19)

where ais a numerical parameter depending on the time constant, , defined by:

00

+= aa (20)

Values of a0and 0are given in Table 4. They can also be provided at a national level.



8/12/2019 UNI 1379000_2005

25/66

EN ISO 13790:2004 (E)

23

Table 4 Values of the numerical parameter a0and reference time constant 0Type of building

a0 0h

Continuously heated buildings (more than 12 h per day) such as residentialbuildings, hotels, hospitals, homes and penitentiary buildings

monthly calculation method 1 15I

seasonal calculation method 0,8 30

II Building heated during day-time only (less than 12 h per day) such aseducation, office and assembly buildings and shops

0,8 70

Figure 3 illustrates utilisation factors for monthly calculation periods and for various time constants for type I andtype II buildings.

NOTE 1 The utilisation factor is defined independently of the heating system characteristics, assuming perfect temperature control and infiniteflexibility.

NOTE 2 A slowly responding heating system and a less-than-perfect control system can significantly affect the use of gains.

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0

168

4824

8

[h]

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0

16848

24

8

[h]

Key

Utilisation factor Time constant of the building Gain/loss ratio

Figure 3 Utilisation factor for 8 h, 1 day, 2 days, 1 week and infinite time constants, valid for monthly

calculation period of continuously heated buildings (type I building, top), and for buildings heated duringthe day only (type II building, bottom)



8/12/2019 UNI 1379000_2005

26/66

EN ISO 13790:2004 (E)

24

10 Annual heat use of the building

10.1 Monthly calculation method

The annual heat use is the sum over all months with positive heat use:

Qh= n Qhn (21)

If the length of the heating season is specified at national level, the sum is taken only during that heating season.

10.2 Seasonal calculation method

This method can be applied only to type I buildings.

The first and last day of the heating season, hence its duration and its average meteorological conditions, can befixed at national level for a geographic zone and typical buildings. The heating season includes all days for whichthe heat gain, calculated with a conventional utilisation factor, 1, does not balance the heat loss, that is when:

d

gd1ided tH

Q (22)

where

ed is the daily average external temperature;

id is the daily average internal temperature;

1 is the conventional utilisation factor calculated with = 1;

Qgd are the daily average internal and solar gains;

H is the heat loss coefficient of the building;

td is the duration of the day, that is 24 h or 86 400 s.

The heat gains for Equation (22) may be derived from a conventional national or regional value of the daily globalsolar radiation at the limits of the heating season. The monthly average values of daily temperatures and heat gainsare attributed to the 15thday of each month. Linear interpolation is used to obtain the limiting days for whichEquation (22) is verified.

The annual heat use for space heating is calculated according to the procedure described in clause 9, thecalculation period being the whole heating season.

11 Energy for space heating

Over a given period, the heating energy use (thermal energy input to the heating system), Q, is:

Q = (Qh- Qr)+ Qth (23)

where

Qh is the heat use according to clause 10;

Qr is the heat recovered from auxiliary equipment, heating and hot water systems and environmentincluding renewable energy sources, where not directly taken into account as losses reduction;



8/12/2019 UNI 1379000_2005

27/66

EN ISO 13790:2004 (E)

25

Qth is the total of the heat losses due to the heating system, including recovered system heat loss. Thisalso includes the additional building heat loss due to non-uniform room temperature distribution andnon-ideal room temperature control, if they are not already taken into account in the set-pointtemperature.

In the absence of a relevant International Standard, the recovered heat and the heat losses due to the heatingsystem are defined and calculated according to national information.

12 Report

12.1 General

A report giving an assessment of the annual heating energy use of a building obtained in accordance with thisstandard shall include at least the following information.

If the calculation is performed to check compliance with regulation, conventional input data provided by theregulation are used, and no error analysis is performed.

Otherwise, an estimate of the accuracy of input data shall be given, and an error analysis shall be performed toestimate the uncertainty resulting from inaccuracy of the input data.

12.2 Input data

All input data shall be listed and justified, e.g. by reference to International or national Standards, or by reference tothe appropriate annexes to this standard or to other documents. When the input data are not conventional, anestimate of the accuracy of input data shall also be given.

In addition, the report shall include:

reference to this standard;

the purpose of the calculation (e.g. for judging compliance with regulations, optimising energy performance,assessing the effects of possible energy conservation measures, or predicting energy resource needs on agiven scale);

a description of the building, its construction and its location;

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

a note indicating whether the dimensions used are internal, or external or overall internal;

a note indicating which method (monthly or seasonal) was used and, if seasonal, the length of the heatingseason;

schedule and set-points if intermittent heating was assumed;

a note on how any thermal bridges have been taken into account.

12.3 Results

12.3.1 For each building zone and each calculation period:

a) Total heat loss;

b) Internal heat gains;

c) Solar gains;

d) Heat use.



8/12/2019 UNI 1379000_2005

28/66

EN ISO 13790:2004 (E)

26

12.3.2 For the whole building

a) Annual heat use;

b) If required, annual energy use.

NOTE 1 Guidance and comments on the accuracy of the calculation method is given in annex J.

NOTE 2 Additional information can be required at national level.



8/12/2019 UNI 1379000_2005

29/66

EN ISO 13790:2004 (E)

27

Annex A(normative)

Application to existing buildings

A.1 Possible applications

Energy assessments of existing buildings are carried out for various purposes, such as:

a) transparency in commercial operations through the display of a level of energy performance (energydeclaration);

b) helping in planning retrofit measures, through prediction of energy savings, which would result from variousactions.

In contrast to new buildings, additional information is often available for existing buildings, which can be used toenhance the reliability of the results. Therefore, the calculation framework in this standard shall be adapted whenpossible to take account of these possibilities, as described below.

A.2 Data assessment

The energy use of the existing building shall be assessed as accurately as practicable, from recorded data, energybills, or measurements. In addition, any information such as actual climatic data, air permeability of the fabric,transmission heat loss coefficients, heating system efficiencies, actual internal conditions (occupancy, intermittentheating, temperatures, ventilation, etc.), should be assessed through surveys, measurements or monitoring, as faras they are available for a reasonable cost. The confidence intervals of all data shall be estimated. Input data thatcannot be measured are taken from building technical documentation,national references or standards.

NOTE Energy use can 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 use of the existing building shall be determined according to the present standard using input datacollected according to A.2. The confidence intervals of the result shall be assessed, and compared to that of themeasured energy use.

If both confidence intervals overlap significantly, it may be assumed that the model of the building, includingestimated input data, is correct.

If the confidence intervals do not overlap significantly, further on-site investigations shall be made in order to verifythe data or to introduce new influencing factors that may have been previously ignored, and the calculation shall be

repeated with the new set of input data.

A.4 Energy declaration

For purpose a) (energy declaration), the input set is modified using conventional occupancy conditions and theenergy use of the building is determined again.

A.5 Planning retrofit measures

For purpose b) (planning retrofit measures) actual data are used for calculation. However, if it appears that thebuilding is not being used as intended in its design (e.g. by under- or overheating, under-or over ventilation),reasonable data shall be used instead of the measured ones for planning retrofit measures. As a reference, theenergy use of the building as it is, is calculated using these reasonable data.

Then, the input set is modified according to the planned retrofit measures and the calculation performed again inorder to obtain the effect of these measures on the energy use.



8/12/2019 UNI 1379000_2005

30/66

EN ISO 13790:2004 (E)

28

Annex B(normative)

Multi-zone calculation method

If the multi-zone method is used, the procedure, based on monthly calculation periods, is as follows.

1) Define the heated space, according to 5.3.1.

2) Define the heated zones according to 5.3.2. For each zone, z, the input data according to 5.4 are collected.

In addition, inter-zone data are collected. These are:

HT,zy transmission heat loss coefficient between zones z and y, or :

zyV net air flow rates between zones.

3) Calculate separately the heat loss coefficient of each zone, Hz, according to 7.3.

4) Determine the effect of intermittent heating for each zone when required.

5) Determine the heat transfer coefficients between zones zand y, Hzy, in a similar way, taking account of heattransfer between zones by transmission (through the building elements and through the ground) andventilation:

zyzyzy VcHH aa,T += (B.1)

Then, for each month and for each zone, operate steps 6) to 10):

6) Calculate the heat flow rates, including transmission and ventilation heat transferto and from adjacent zones,and between each zone and the external environment, based on the assumption of constant internaltemperature:

QL,zy= Hzy(z - y)t and QL,z= yQL,zy + Hz(i- e)t (B.2)

7) When QL,z< 0, zone zshall be considered as an unheated space and calculation continued from step 3 for theneighbouring zones.

8) Calculate internal and solar gains Qg,zaccording to 8.1 and 8.2.

9) Determine the utilisation factor zaccording to 9.2.

10) Calculate the heat use as the difference between the heat loss and the useful gains:

Qh,z= QL,z- zQg,z (B.3)

11) Calculate for each month the total building heat use as the sum of heat uses of each zone:

Qh = Qh,z (B.4)

12) Calculate the annual heat use as the sum of heat uses for each month.

13) Calculate the annual energy use according to clause 10.

The division into zones shall be described in the report.



8/12/2019 UNI 1379000_2005

31/66

EN ISO 13790:2004 (E)

29

Annex C(normative)

Intermittent heating Calculation of adjusted internal temperature

C.1 Introduction

The procedure in this annex enables the calculation of the adjusted internal temperature for one type of reducedheating period (e.g. night, week-ends, and holidays). It shall be applied to each type of reduced heating period.

The procedure is suitable for heating systems where the heat output can be varied fairly rapidly in response tochanging heat demand. This procedure will overestimate the effect of intermittent heating for heating systems thathave a large thermal inertia.

The procedure also assumes a heating system with sufficient heating capacity to ensure warm up to the internaldesign temperature when the external temperature is equal to the design external temperature. If the heatingsystem has been closely sized it should not be assumed that the heating is intermittent in the coldest months, butrather that heating is continuous.

C.2 Input data

The following information is required to calculate the effect of intermittent heating:

Cih internal heat capacity of the zone for intermittent heating, calculated using the procedure described in 9.2.3with a maximum thickness of 3 cm; C may also be provided at a national level, based on the type ofconstruction;

Aj area of each surface contributing to the heat capacity;

Rsij internal surface thermal resistance corresponding to these surfaces;

i0 set-point temperature;

2 maximum power of the heating system, i.e. the lowest of the heat emission and heat production power;

25. type of control of the heating system during reduced heating periods: cut-off, reduced heating power, or set-back;

26. type of boost strategy : fixed or optimised;

27. definition of the intermittence pattern, including for each reduced heating period:

to overall duration of the reduced heating period;

Hw transmission heat loss coefficient of lightweight elements, such as windows and doors;

HV ventilation heat loss coefficient during reduced heating period;

H2 total heat loss coefficient of the building during reduced heating period;

t3 predefined duration of the boost heating phase in fixed time boost mode (see C.6).

For set-back mode:

i2 set-back temperature

For reduced power mode:

1 reduced heating power.



8/12/2019 UNI 1379000_2005

32/66

EN ISO 13790:2004 (E)

30

C.3 Method

The method is based on the calculation of the evolution of the temperature of the building when it falls below itsnormal set-point. This evolution is calculated by using a building model with three nodes representative of the

internal and external environments and of the building structure (Figure C.1). The internal thermal inertia of thebuilding is represented by a capacitance whose temperature is the structure temperature. Heat exchanges betweenthe structure and the external environment, between the structure and the internal environment and directlybetween the internal and external environments are taken separately into account.

c HicHce

Hd

e iCih

h

Key

e External temperature

c Structure temperature

i Internal temperature

hHeating power

Cih Internalheat capacity of the zone related to intermittent heating

Hd Direct heat loss coefficient

HceHeat loss coefficient between the structure and the external environment

Hic Heat loss coefficient between the structure and the heated space

Figure C.1 Electrical equivalent representation of a zone

Structure includes all internal and external building elements in contact with the heated space. Hdis the direct heatloss coefficient by ventilation and transmission through lightweight envelopeelements.Hicis the heat loss

coefficient between the structure and the heated space. Hceis the heat loss coefficient between the structure andthe external environment, the value of which is determined to get the correct value of the overall heat losscoefficient H.

The structure temperature is the weighted average of the temperatures of the internal and external structuralelements.

The method is based on the evaluation of the length of three different phases (Figure C.2), a phase during whichthere is no heating or reduced heating power, a possible phase during which the set-back temperature ismaintained, and a phase of boost heating during which the heating system is operating with its maximum poweroutput and which ends when the internal temperature is equal to its set-point value.



8/12/2019 UNI 1379000_2005

33/66

EN ISO 13790:2004 (E)

31

i

t

t1

N NR

t

t

A

B

C

i3

h

h

'i

'i

h

i0

i2

i1

t2 t3

to

tf

i3i0

'i1

t1t3

tfto

t1to

t3 tf

i3

i0

'i1

Key

N Normal heating period

R Reduced heating period

i Internal temperature

h Heating powert Time

to Overall duration of the reduced heating period

t1 Duration of the no heating period or reducedheating power period

t2 Duration of the set-back period

t3 Duration of the boost period

tf Duration of the final period between the end of the boost and theend of the reduced heating period (close to zero with optimisedboost)

I0 Set-point temperature

i1 Equilibrium internal temperature without heating or with reducedheating power

i1 Internal temperature at the beginning of boost, without set-back

i2 Set-back temperature

i3 Equilibrium internal temperature with maximum heating power

Figure C.2 Schedule of intermittent heating, showing the considered time periods

A: set back mode; B: cut-off mode; C: reduced heating power



8/12/2019 UNI 1379000_2005

34/66

EN ISO 13790:2004 (E)

32

C.4 Building characteristics

The values of the parameters considered are those of the reduced heating periods. If some parameters are not thesame for all these periods (e.g. if the mean ventilation rate is not the same during nights and weekends), these

characteristics shall be calculated for each type of reduced heating period.

1. Calculate the heat loss coefficient of the building during the considered period, H2,according to 7.3, withinput data corresponding to reduced heating period (e.g. with reduced ventilation and closed shutters).

2. Calculate the heat transfer coefficient Hicbetween the structure and the heated space:

=j j

j

R

AH

siic (C.1)

where windows and doors are excluded from the summation, and:

Aj is the area of elementj;

Rsij is the internal surface thermal resistance of elementj.

The sum is over all elements, including internal partitions.

Hic may be provided at national level for typical buildings.

3. Calculate the direct heat loss coefficient, Hd, from internal to external environment, for lightweight structures(windows and doors) and air change, with input data corresponding to the reduced period:

Hd= Hw+HV (C.2)

where the heat loss coefficients of lightweight structures, Hw, is the sum of all heat loss coefficients ofwindows and doors, andHVis the ventilation heat loss coefficient calculated according to 7.5.

4. Calculate the heat loss coefficient between the structure and the external environment Hce;

)-(-

-(

d2ic

)d2icce HHH

HHHH = (C.3)

5. Calculate the effective fraction of the heat capacity :

ceic

ic

+ HH

H= (C.4)

6. Calculate the ratio, , between the relative variations, due to a change in heating power, on the steady-statedifferences between external temperature, on one hand, and structure and internal temperatures, on theother hand:

dic

ic

HH

H

+= (C.5)

7. Calculate the time constant of the structure temperature after a change in heating power:

2

ih

HC

P

= (C.6)

where Cihis the effective internal heat capacity, calculated as the sum of the internal capacities of all buildingelements, each calculated according to 9.2.3, with 3 cm for maximum thickness.



8/12/2019 UNI 1379000_2005

35/66

EN ISO 13790:2004 (E)

33

The effective heat capacity may also be provided at a national level, based on the type of construction. Timeconstants for typical buildings may also be provided at a national level.

8. Calculate the time constant of the structure temperature after a change in air temperaturec.

icce

ihc +

=HH

C (C.7)

C.5 Calculation of adjusted internal temperature

This calculation shall be undertaken for each calculation period and each reduced heating period (e.g. night orweekend).

The following notation is used:

i0 is the set-point temperature;

i1 is the equilibrium internal temperature with no heating or reduced heating power;

i1 is the internal temperature at the beginning of boost, without set back;

i2 is the set-back temperature;

i3 is the equilibrium internal temperature with maximum heating power;

c0 is the structure temperature at the beginning of the reduced heating period;

c1 is the structure temperature at the end of the no heating or reduced heating power phase;

c1 is the equilibrium structure temperature with no heating or reduced heating power;

c2 is the structure temperature at the end of the set-back phase;

c2 is the equilibrium structure temperature in set-back conditions;

c3 is the structure temperature at the end of the boost heating phase;

c3 is the equilibrium structure temperature with maximum heating power;

to is the overall duration of the reduced heating period;

t1 is the duration of the no heating or reduced heating power phase;

t1 is the duration of the no heating or reduced heating power phase without set back;

t2 is the duration of the set-back phase;

t3 is the actual duration of the boost heating phase in setback mode;

t3 is the duration of the optimised boost heating phase without setback;

t3 is the predefined duration of the boost heating phase in fixed time boost mode;

1 is the reduced power output of the heating system;

2

is the maximum power output of the heating system during boost mode.

9. Calculate the structure temperature, c0, at the beginning of the reduced heating period:



8/12/2019 UNI 1379000_2005

36/66

EN ISO 13790:2004 (E)

34

c0 = e + (i0-e) (C.8)

10. Calculate the structure temperature reached in steady-state when the internal temperature is maintained atthe set-back temperaturei2:

c2 = e+ (i2-e) (C.9)

11. Calculate the highest internal and structure temperatures i3 and c3which could be reached with full heatingpower:

2

2ei3

=

H

+ (C.10)

c3= e+ (i3-e) (C.11)

12. Calculate the lowest internal temperature that can be reached at equilibrium:

in cut-off mode:

i1= e (C.12)

in reduced heating power mode (e.g. with lower heating water temperature):

2

1ei1

=

H

+ (C.13)

13 Calculate the relevant equilibrium internal structure temperature:

c1= e+ (i1-e) (C.14)

14. Optimised boost:calculatethe boost heating phase duration t3without set back:

( )

( )

+

=

P

Pt

t

o1c0ci03i

1c3c3

exp

ln,0max' (C.15)

15. Optimised boost:calculate the duration of the no heating or reduced heating power phase without set-back:

t1= to- t3 (C.16)

16. Fixed time boost:calculate the duration of the no heating or reduced heating power phase without set back:

t1= to- t"3 (C.17)

t3 is input or is calculated according to C.6 if unknown.

If t3or t3 is too long (e.g. more than one or two hours), the peak power of the heating system is notsufficient. It shall be increased before going further.

17. Calculate the internal temperature, i1, reached at the beginning of the boost phase without set-back:

i1 = i1+ (c0- c1)exp

P

t

1 (C.18)

18. In set-back mode and if 2> i1, go to step 23



8/12/2019 UNI 1379000_2005

37/66

EN ISO 13790:2004 (E)

35

19. Calculate the structure temperature reached at the beginning of the boost phase without set-back:

if t1= 0 then c1= c0 (C.19)

else

1i

1i'1c

'1c

+= (C.20)

20. Since there is no set-back, the length of the set back period is 0 and the structure temperature at the end ofthe set-back phase c2is thatreached at the end of the no heating phase:

t2= 0 and c2= c1 (C.21)

21. Optimized boost:go to step 29

22. Fixed time boost: go to step 27

23. In set-back mode, calculate the time, t1,taken to reach the set-back temperature:

( )( )

=

1i2i

1c0c1 ln,0max

Pt (C.22)

24. Calculate the structure temperature at the end of that period, c1:

if t1 =0 then c1= c0 (C.23)

else

1i2i1c1c

+= (C.24)

25. Calculate the duration of theset-back phase, t2:

optimised boost ( )

( )

=

i03i

2c3c1o2 ln,0max,0max

Pttt (C.25)

fixed time boost t2= to (t1+ t3) (C.26)

where t3 can be calculated according to C.6 if it is not known.

26. Calculate the structure temperature at the end of the set-back phase, c2:

If t2 is less than or equal to 0 then t2 = 0 and c2 = c1

otherwise c2= c2 + (c1- c2) exp

P

t

2 (C.27)

27. Calculate the actual boost heating phase duration t3:

( )( )

=

i03i

2c3c3 ln,0max

Pt (C.28)

The value calculated here can be different from the value of t3

28. Fixed time boost: ift3is greater than t3then increase t3and perform the whole calculation again.

29. Calculate the structure temperature at the end of the boost heating phase c3.



8/12/2019 UNI 1379000_2005

38/66

EN ISO 13790:2004 (E)

36

If t3 = 0then c3= c2 (C.29)

otherwise

3i0i3c

'3c

+= (C.30)

30. Calculate the time remaining between the end of the boost and the end of the reduced heating period

t4= to- (t1+ t2+ t3) (C.31)

31. Calculate the adjusted internal temperature:

iad= (o

1t

(i1t1+ i2t2+i3t3+ i0t4) +P(c0 - c1+ c2 - c3)) (C.32)

C.6 Boost time

The duration of the fixed boost time t3can be estimated as follows:

1) specify the value, e0, of the external temperature for which the boost time is to be calculated;

2) apply the calculation procedure of C.5 with optimised boost and with

e=e0 (C.33)

3) an estimate of t3is obtained with Equation (C.28) with t3 = t3



8/12/2019 UNI 1379000_2005

39/66

EN ISO 13790:2004 (E)

37

Annex D(normative)

Calculation with holiday period

In some buildings, such as schools, holiday periods during the heating season lead to a reduction in heat loss, heatuse and space heating energy use.

The following method shall be applied to take account of holiday periods. Only one holiday period, of specifiedduration t (t't), is to be considered in any one month.

1) Calculate the heat use, Qhm0, for one normal month (without holiday), following the method described inclauses 5 to 9.

2) Calculate the heat use, Qh1, for the holiday period in the considered month. The method described in clauses 5to 9 is applied with the calculation period equal to the holiday period.

3) Calculate the resulting heat use,Qhm1, for the considered month:

1h0hm1hm'

QQt

ttQ +

= (D.1)

4) Calculate the yearly heat use from the sum of monthly heat use.



8/12/2019 UNI 1379000_2005

40/66

EN ISO 13790:2004 (E)

38

Annex E(normative)

Heat loss of special envelope elements

E.1 Ventilated solar walls (Trombe walls)

E.1.1 General

Figure E.1 Air flow path in a ventilated solar wall

The following applies to walls designed to collect solar energy, according to Figure E.1, where

28. the air flow is stopped automatically when the air layer is colder than the heated space, and

29. the air flow rate is set mechanically at a constant value, V , when the air layer is warmer than the heatedspace.

The heat loss coefficient of such a wall is:

H = H0+ H (E.1)

where

H0 is the heat loss coefficient of the non ventilated wall;

H is an additional heat loss coefficient to be calculated according to E.1.3.

E.1.2 Required data

A area of the ventilated solar wall;

Ri internal thermal resistance of the wall, between the air layer and the internal environment;

Re external thermal resistance of the wall, between the air layer and the external environment;

Rl thermal resistance of the air layer;

V set value of the air flow rate through the ventilated layer;

hcand hr: respectively the convective and radiative surface heat transfer coefficients in the air layer;

Qg,sw solar gains of the air layer during the calculation period: Qg,sw = Iw As,sw



8/12/2019 UNI 1379000_2005

41/66

EN ISO 13790:2004 (E)

39

QL,al heat loss of the air layer during the calculation period: QL,al = UeA(i -e) t

E.1.3 Calculation method

Calculation of heat loss is based on set-point and external temperatures. Solar gains are calculated according toF.3 in annex F. The additional heat loss coefficient of such a wall is calculated by:

2

i

UNI 1379000_2005

Documents

Transcript of UNI 1379000_2005