BS EN ISO 14438:2002 – Glass in building — Determination of energy balance value — Calculation method
1 Scope
This European Standard specifies a calculation method to determine the energy balance value of glazing. This European Standard applies to transparent materials such as glass and combinations of glass used to glaze windows in buildings.
This method is intended to evaluate the balance of heat loss and useful heat gain by solar radiation entering the building through the glazing for a given period by means of an average rate of loss (or gain) of heat called the energy balance value.
The method enables producers to compare the performance of their glazing products. The energy balance value should not be used for energy use or heating capacity calculations in buildings.
2 Normative references
This European Standard incorporates by dated or undated references, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).
EN 410 Glass in building – Determination of luminous and solar characteristics of glazing
EN 673 Glass in building – Determination of thermal transmittance (U value) – Calculation method
EN 674 Glass in building – Determination of thermal transmittance (U value) – Guarded hot plate method
EN 675 Glass in building – Determination of thermal transmittance (U value) – Heat flow meter method
EN 832 Thermal performance of buildings – Calculation of energy use for heating – Residential buildings
3 Symbols
D degree days K·24 h
utility factor
H unobstructed incident solar radiation kWh/m2
g total solar energy transmittance (solar factor)
U thermal transmittance (U value) W/(m2·K)
f factor due to glazing maintenance and shadow effects
S function of H and D characterising a given region W/(m2·K)
E energy balance value W/(m2·K)
Subscripts
p period of application
4 Basic formula
The energy balance value, E, for a given period is calculated according to the following equation:
where:
U is the U value of the glazing;
is the utility factor;
f is the factor due to glazing maintenance and shadow effects;
g is the glazing total solar energy transmittance (solar factor);
Hp is the unobstructed incident solar radiation during the given period;
Dp is the degree day total for the given period.
NOTE An example of calculation is given in annex B.
5 Basic material properties
5.1 U Value (thermal transmittance)
The U value of the glazing is determined by calculation, in accordance with EN 673 or measurement in accordance with EN 674 or EN 675.
5.2 Utility factor,
The utility factor for a building or space in a building is the ratio of the useful heat gains, which displace the functional heating over a defined period, to the total heat gains during the period.
The utility factor is essentially a property of the building design.
BS EN ISO 14438:2002 – Glass in building — Determination of energy balance value — Calculation method