ISO 15099:2003

INTERNATIONAL ISO
STANDARD 15099
First edition
2003-11-15
Thermal performance of windows, doors
and shading devices — Detailed
calculations
Performance thermique des fenêtres, portes et stores — Calculs
détaillés
Reference number
©
ISO 2003
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©  ISO 2003
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ii © ISO 2003 — All rights reserved

Contents
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Symbols . 2
3.1 General. 2
3.2 Symbols and units . 2
3.3 Subscripts. 4
4 Determination of total window and door system properties. 5
4.1 Thermal transmittance. 5
4.2 Total solar energy transmittance . 9
4.3 Visible transmittance. 10
5 Vision area properties . 10
5.1 Glazing layer optics . 10
5.2 Glazing system optics . 11
5.3 Vision area heat transfer . 13
6 Frame effects. 20
6.1 Area and lineal thermal transmittance. 20
6.2 Governing equations for calculating thermal transmittance. 20
6.3 Geometric representation and meshing. 20
6.4 Solid materials. 23
6.5 Effective conductivity — Glazing cavities. 23
6.6 Effective conductivity — Unventilated frame cavities . 23
6.7 Ventilated air cavities and grooves. 30
7 Shading devices. 31
7.1 Definitions. 31
7.2 Optical properties . 32
7.3 Slat type of shading. 34
7.4 Ventilation. 39
7.5 Total solar energy transmittance and thermal transmittance . 50
8 Boundary conditions . 50
8.1 General. 50
8.2 Reference boundary conditions . 50
8.3 Convective heat transfer . 51
8.4 Longwave radiation heat transfer . 55
8.5 Combined convective and radiative heat transfer. 58
8.6 Prescribed density of heat flow rate . 59
Annex A (informative) Solution technique for the multi-layer solar optical model . 60
Annex B (normative) Thermophysical fill gas property values . 62
Annex C (informative) Examples of calculated values for optical properties of slat type of shading
devices . 64
Bibliography . 69

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 15099 was prepared by Technical Committee ISO/TC 163, Thermal performance and energy use in the
built environment.
iv © ISO 2003 — All rights reserved

Introduction
This International Standard describes a procedure for calculating indices of merit of many window and door
products. The method provided in this International Standard allows the user to determine total window and
door product indices of merit, viz thermal transmittance, total solar energy transmittance and visible light
transmittance.
The procedures give the actual thermal performance of fenestration products for use in building energy
analysis and for the evaluation of products in specific building applications. These procedures can also be
used to produce data to compare products by using the standardized boundary conditions given either in this
International Standard or taken from the appropriate International or National Standards (e.g., ISO 12567-1,
ISO 10292, ISO 9050). This International Standard is also intended as a reference document for the
description of models used in computer programs for detailed calculation of the thermal and optical
transmission properties of window and door systems.
This International Standard gives detailed models for thermal and optical transmission in windows. These
detailed models are necessary in many types of window to get agreement between calculations and tests.
Traditionally, windows have been characterized by separately calculating the “dark” or “night-time” thermal
transmittance and the solar energy transmittance through the fenestration system. The thermal transmittance
without the effect of solar radiation is calculated using the procedures given in ISO 10292 (for the vision
portion) and the total solar energy transmittance, without taking into account the actual temperatures of the
various panes, is obtained using ISO 9050. These calculations require the use of reference conditions that are
not representative of actual conditions. In this International Standard the energy balance equations are set up
for every glazing layer taking into account the solar absorption and actual temperatures. From these energy
balance equations, the temperatures of the individual layers and gaps are determined. This is the only
standard that takes into account these complex interactions. This more detailed analysis provides results that
can then be expressed as thermal transmittance and τ -values and these values can differ from the results of
S
simpler models.
Individual indices of merit obtained using fixed reference boundary conditions are useful for comparing
products. However, the approach taken is the only way of calculating the energy performance of window
systems for other environmental conditions including those conditions that may be encountered during hot box
measurements.
Finally it must be emphasized that this International Standard is intended for use in computer programs. It was
never intended as a “simplified calculation” procedure. Simplified methods are provided in other International
Standards. It is essential that these programs produce consistent values and that they are based on a sound
standard methodology. Although more complicated than the formulae used in the simplified standards, the
formulae used in this International Standard are entirely appropriate for their intended use.

INTERNATIONAL STANDARD ISO 15099:2003(E)

Thermal performance of windows, doors and shading
devices — Detailed calculations
1 Scope
This International Standard specifies detailed calculation procedures for determining the thermal and optical
transmission properties (e.g., thermal transmittance, total solar energy transmittance) of window and door
systems based on the most up-to-date algorithms and methods, and the relevant solar and thermal properties
of all components.
Products covered by this International Standard include windows and doors incorporating:
a) single and multiple glazed fenestration products with or without solar reflective, low-emissivity coatings
and suspended plastic films;
b) glazing systems with pane spacing of any width containing gases or mixtures of gases;
c) metallic or non-metallic spacers;
d) frames of any material and design;
e) fenestration products tilted at any angle;
f) shading devices;
g) projecting products.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 7345, Thermal insulation — Physical quantities and definitions
ISO 8301, Thermal insulation — Determination of steady-state thermal resistance and related properties —
Heat flow meter apparatus
ISO 8302, Thermal insulation — Determination of steady-state thermal resistance and related properties —
Guarded hot plate apparatus
ISO 9050, Glass in building — Determination of light transmittance, solar direct transmittance, total solar
energy transmittance, ultraviolet transmittance and related glazing factors
ISO 9288, Thermal insulation — Heat transfer by radiation — Physical quantities and definitions
ISO 9845-1, Solar energy — Reference solar spectral irradiance at the ground at different rece
...