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Thermal performance of buildings

l Introduction l

l Ventilation Efficiency l

l Thermal performance of buildings l

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Calculation of energy use for space heating - EN ISO 13790

This standard is one of a series of calculation methods for

The thermal energy balance calculations software
(Minergie, SIA380/1, SIA380/4, EN 13790, DLGs 311, SIA384.201, RT2005)

Thus, it can be used for assessing compliance with energetic regulations, for displaying a conventional level of energy performance or assessing the effect of possible energy conservation measures on existing buildings, for comparing the energy performance of various design alternatives for a planned building and for predicting future energy resource needs on a national or international scale.

The thermal energy balance calculations software
(United Kingdom, Scotland,...)

The method is based on an energy balance taking account of internal and external temperature variations and, through an utilisation factor, of the dynamic effect of internal and solar gains (see Figure). The Table below describes briefly the calculation procedure.

Definition of the heated space boundaries (all the building elements separating the considered heated space from external environment or zones). When significant differences in set-point temperatures or heat gains exist, a multi-zone calculation should be carried out; otherwise a single zone calculation applies.

Definition of the periods having different heating and ventilation patterns, in case of intermittent heating or ventilation.

Heat losses calculation

Single zone

qi , set-point temperature

qe , average external temperature during the calculation period

t, duration of the calculation period

H, heat loss coefficient of the building

Multi-zone

N, n° of heating period types

N j, n° of heating periods of each type during the calculation period

q iad,j , adjusted internal temperature of the heating period j;

t j is the duration of the heating period j;

H j, heat loss coefficient of the building during period j

Heat gains (Qg) calculation

Internal heat gains

Fi,h , average power of the internal gains in heated spaces

Fi,u , average power of the internal gains in unheated spaces

Fi , average power of internal gains

b, reduction factor defined in ISO 13789

Solar gains

I sj, solar irradiance during the calculation period on a surface of area 1m 2 having orientation j

A snj, solar effective collecting area of the surface n having orientation j

Utilisation factor calculation

If g ≠1

g , gain/loss ratio (Q g/Q L)

a , numerical parameter depending on the time constant t

t = heat capacity of the building/heat loss coefficient

If g = 1

g , gain/loss ratio (Q g/Q L)

a , numerical parameter depending on the time constant t

t = heat capacity of the building/heat loss coefficient

Heat use

QL, heat losses

h , utilisation factor, it is a reduction factor for the heat gains introduced to compensate additional heat loss likely to occur when heat gains exceed the calculated heat loss

Qg, total heat gains (Q i + Q s)

All these calculations can be carried out accurately by means of advanced softwares as is the case of Lesosai (more details www.lesosai.com)

For further information contact Flavio Foradini (email: firstname.lastname@e4tech.com) from E4tech

References:

EN ISO 13790:2004 Thermal performance of buildings - Calculation of energy use for space heating

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