Overview
ISO 14438:2002 - "Glass in building - Determination of energy balance value - Calculation method" defines a standardized calculation method to evaluate the energy balance value of glazing. The method quantifies the average rate of heat loss (or gain) through transparent materials (glass and glazing combinations) by balancing thermal transmittance against useful solar heat gains over a chosen period (typically the heating season). It is intended for product comparison and labelling, not for whole-building energy use or heating-capacity sizing.
Key topics and requirements
- Basic formula: The energy balance value E is calculated from the glazing U‑value and the useful solar gains. In principle:
- E = U − (η · g · f · Hp) / Dp
- where U is thermal transmittance (W/m²·K), η is the utility factor, g is total solar energy transmittance (solar factor), f is the maintenance/shading factor, Hp is unobstructed incident solar radiation for the period, and Dp is degree‑day total for the period.
- Units and presentation: E is expressed in W/(m²·K) rounded to one decimal place and accompanied by the assumptions used (location, orientation, degree‑day source, etc.).
- Prescribed default values for comparisons:
- Utility factor η = 0.6 (for product comparisons)
- Maintenance/shadow factor f = 0.8 (vertical or near‑vertical glazing)
- Base temperature for degree‑day calculations = 18 °C
- Period: the heating season (site‑specific degree‑days and incident solar radiation)
- Material properties and measurement:
- U‑value determined by EN 673 (calculation) or EN 674 / EN 675 (measurement)
- Solar factor g determined by EN 410
- Alternative form: A simplified form E = U − g·S, where S = (η·f·Hp)/Dp, allows use of "deemed to satisfy" S‑values for regions or orientations.
Practical applications
- Enables glazing manufacturers to present an objective, comparable indicator of net thermal performance (losses minus useful solar gains) across product lines.
- Useful to product certifiers, façade specifiers, architects, and facility planners when comparing glazing options for a given orientation and climate.
- Supports marketing data and technical datasheets by providing a standardized energy‑balance metric.
- Not intended for-nor to be used in-detailed building energy simulations, sizing of heating systems, or regulatory compliance of whole‑building energy use.
- Glazing and IGU manufacturers
- Test laboratories and certification bodies
- Architectural and façade consultants
- Product data managers and technical sales teams
Related standards and references
- EN 410 - Determination of luminous and solar characteristics of glazing (solar factor g)
- EN 673 / EN 674 / EN 675 - Determination of U‑value (calculation and test methods)
- EN 832 - Calculation of energy use for heating (utility factor determination)
- European Solar Radiation Atlas (referenced for climate data)
Keywords: ISO 14438, energy balance value, glazing, glass in building, solar transmittance, U‑value, utility factor, degree days, heating season, calculation method.