


Thermal performance of buildings 




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, ECO, SIA380/1, SIA380/4, SIA2044, EN 13790, DLGs 311, SIA384.201, RT2005, RT2012, DGNG, BREEAM)

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 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 setpoint temperatures or heat gains exist, a multizone 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.
1 
Definition of the heated space boundaries (all the building elements separating the considered heated space from external environment or zones). When significant differences in setpoint temperatures or heat gains exist, a multizone calculation should be carried out; otherwise a single zone calculation applies. 
2 
Definition of the periods having different heating and ventilation patterns, in case of intermittent heating or ventilation. 
3 
Heat losses calculation 
Single zone

qi , setpoint temperature
qe , average external temperature during the calculation period
t, duration of the calculation period
H, heat loss coefficient of the building 
Multizone

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 


4 
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 


5 
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 


6 
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)
References:
EN ISO 13790 Thermal performance of buildings  Calculation of energy use for space heating




