Overview
SIST EN ISO 14438:2004 is a European Standard developed by CEN that specifies a calculation method for determining the energy balance value of glazing used in building windows. This standard applies to transparent materials such as glass and glass combinations installed as window glazing in buildings. The method evaluates the balance between heat loss through the glazing and useful solar heat gain over a specified period, expressed as an average rate called the energy balance value, measured in W/(m²·K).
This calculation method is intended to assist manufacturers and designers in comparing the thermal performance of glazing products, focusing on their overall energy balance rather than precise heating or energy use calculations. It provides a standardized approach for assessing glazing performance related to solar radiation and thermal transmittance.
Key Topics
- Energy Balance Value (E): Represents the net effect of heat loss due to thermal transmittance minus solar heat gain from solar radiation through the glazing. It is calculated via a specific formula considering U-value, solar transmittance, solar radiation, utility factor, and maintenance factors.
- U Value (Thermal Transmittance): Measured per EN 673, 674, or 675, this value quantifies the rate of heat transfer through glazing per unit area and temperature difference.
- Solar Energy Transmittance (g-value): Defined by EN 410, this factor reflects the portion of solar radiation transmitted through glass, including direct transmission and absorbed/ re-radiated heat.
- Utility Factor (η): A parameter representing the effective use of solar heat gain in displacing heating loads within a building, generally ranging from 0.4 to 0.8. For comparative purposes, a standard value of 0.6 is used.
- Glazing Maintenance and Shadow Factor (f): Accounts for dirt accumulation and shading effects on glazing performance. A default value of 0.8 is applied for vertical or near-vertical surfaces.
- Solar Radiation Incident (Hₚ): The unobstructed solar radiation impacting a vertical glazing surface during the evaluation period, expressed in kWh/m².
- Degree Days (Dₚ): A temperature index representing heating demand over the period based on temperature difference from a specified base temperature (18°C used by default).
Applications
- Product Performance Comparison: Enables glazing manufacturers to benchmark the thermal performance and energy balance of different glazing products under standardized conditions.
- Building Design: Facilitates informed decision-making in selecting glazing systems that optimize the balance between heat retention and solar heat gain, enhancing building energy efficiency.
- Energy Assessment: Supports architects and engineers in evaluating glazing options to balance thermal comfort with energy savings during heating seasons.
- Climate Region Adaptation: The method incorporates climatic data (solar radiation and degree days) for different locations to tailor glazing evaluations regionally.
- Regulatory and Quality Standards Compliance: Assists in meeting CEN and ISO requirements for glazing energy performance ratings.
Related Standards
- EN 410: Glass in Building - Determination of luminous and solar characteristics of glazing, essential for determining the solar transmittance (g-value).
- EN 673: Glass in Building - Determination of thermal transmittance (U-value) - Calculation method, used to calculate the heat transfer rate through glazing.
- EN 674 and EN 675: Methods for measuring the thermal transmittance of glazing using guarded hot plate and heat flow meter methods, respectively.
- EN 832: Thermal performance of buildings - Calculation of energy use for heating - Residential buildings, relevant for determining the utility factor η based on heating needs.
SIST EN ISO 14438:2004 provides a practical and consistent framework for evaluating glazing products' energy performance with a focus on balancing thermal losses and solar gains. This standard is essential for glazing producers, building designers, and energy assessors aiming to enhance building envelope performance and contribute to energy-efficient construction.