ISO 15927-6:2007

Overview

ISO 15927-6:2007, “Hygrothermal performance of buildings - Calculation and presentation of climatic data - Part 6: Accumulated temperature differences (degree‑days)”, defines how to compute and present accumulated temperature differences (commonly called heating degree‑hours or heating degree‑days) used to assess energy used for space heating. The standard specifies definitions, units (degree‑hours, degree‑days), exact and approximate computational methods, and guidance for presentation and accuracy of data. It is part of the ISO 15927 series on climatic data for building hygrothermal performance.

Key topics and requirements

• Definition and units: clear terminology for hourly/daily temperature differences, accumulated totals and base temperature concepts.
• Base temperature: recommended standard base temperature is 12 °C; other integer bases (preferably multiples of 2 °C) may be used.
• Computation methods:
  • Exact calculation from hourly temperature data (hourly temperature differences summed as degree‑hours or converted to degree‑days).
  • Approximate estimation from daily mean or from daily maximum/minimum temperatures when hourly data are unavailable.
  • Methods to estimate monthly totals for any base temperature using climatological statistics.
• Data sources & measurement: temperatures must be measured according to WMO/meteorological methods (WMO Guide No. 8).
• Presentation & accuracy: guidance on reference altitude, lapse rate considerations, statistical parameters (monthly means, standard deviations) and recommended formats for monthly, seasonal and annual totals.
• Limitations: the standard does not cover national methods that use threshold temperatures different from the base temperature.

Practical applications and users

ISO 15927-6 is practical for:

• Building designers and HVAC engineers - quick indices for heating demand estimation in early design or retrofit options.
• Energy managers and facility operators - monitoring heating plant performance and normalizing energy consumption to weather (degree‑day correction).
• Energy modelers and researchers - benchmarking and comparing climate severity across locations and periods.
• Policymakers and analysts - evaluating economic impacts of insulation or efficiency measures across building stocks using standardized degree‑day data.
• Utilities - load forecasting and billing normalization.

Degree‑day data from ISO 15927-6 are best suited to small or simple heating systems and steady‑state analyses; more complex building simulations may require richer climatological inputs (e.g., test reference years).

Related standards

• ISO 15927 (other parts): Part 1 (monthly means), Part 2 (hourly data for cooling), Part 4 (hourly data for annual energy use), Part 5 (design heat load).
• ISO 6243 (symbols for climatic data) and WMO Guide to Meteorological Instruments and Methods of Observation (No. 8) for measurement practice.

Keywords: ISO 15927-6, degree‑days, heating degree‑days, accumulated temperature differences, base temperature, climatic data, hygrothermal performance, energy use for space heating.