ISO 15927-2:2009

Overview - ISO 15927-2:2009 (Hourly data for design cooling load)

ISO 15927-2:2009 is part of the ISO 15927 series on the hygrothermal performance of buildings and specifies how to calculate and present monthly external design climate based on hourly data for use in determining the design cooling load of buildings and sizing air‑conditioning systems. The standard defines procedures to identify representative “design days” from long-term meteorological records and to extract hourly peak values (dry‑bulb and dewpoint temperatures and solar irradiation) needed for HVAC design.

Key topics and technical requirements

• Data sources and quality
  • Use hourly meteorological files covering at least 10 years; data must be measured in accordance with the WMO Guide No. 8.
  • Preferred radiation metric: global solar irradiation (better building performance index) or, where unavailable, sunshine hours.
• Design-day identification
  • Calculate daily mean values (dry‑bulb temperature, global solar irradiation/sunshine hours) for each day.
  • Determine values exceeded on 5%, 2% and 1% of days per calendar month (risk levels).
  • Define initial intervals (e.g., daily mean dry‑bulb ±0.5 °C, solar irradiation ±0.05 kWh/m2·d) and iteratively narrow or widen intervals to isolate a single design day per month and risk level.
• Parameters
  • Mandatory: dry‑bulb temperature and global solar irradiation / sunshine hours.
  • Optional (as relevant to building type): dewpoint temperature, daily temperature swing, wind speed, and other site-specific parameters.
• Air conditioning design data
  • From hourly records compute dry‑bulb temperatures exceeded on 1%, 2% and 5% of hours and corresponding dewpoint temperatures within narrow temperature bands for use in equipment sizing.
• Reporting requirements
  • Report station location, data period, for each month and risk level the date of the design day and hourly (or 3‑hourly) parameter values; report the computed exceedance values used in AC design.

Practical applications and typical users

• Applications:
  • Sizing HVAC systems and selecting equipment capacities
  • Creating representative design days for building energy simulation and cooling load calculations
  • Peak load and resilience planning for buildings in hot climates
• Typical users:
  • HVAC and building services engineers
  • Energy modelers and building performance analysts
  • Meteorological data providers, standards bodies, and consultants involved in building design

Related standards

• ISO 15927-1: Monthly means of single meteorological elements (normative reference)
• Other parts of ISO 15927 series: Part 3 (driving rain index), Part 4 (hourly data for annual heating/cooling energy), Part 5 (design heat load), Part 6 (degree‑days)
• WMO Guide No. 8 (meteorological instruments and observation methods)

Keywords: ISO 15927-2, hygrothermal performance, design cooling load, hourly climatic data, design day, global solar irradiation, dry‑bulb temperature, dewpoint, HVAC design.