EDSL UK Weather Data Guide

UK Weather data sets guide

There are so many different weather files available these days and with a large number of assessments, each specifying weather data files to use it can be hard to keep track of which weather files are required for which assessments. We’ve put together a guide outlining most of the applicable weather files for assessments that are commonly undertaken using our software to help keep track of when to use each weather set. Here are some of the commonly used weather data sets:

CIBSE TRY (Test Reference year) – This is designed to be a typical year of weather data, it is composed of 12 separate months of data which are not necessarily from the same year, each month chosen to be the most average month from the collected data. The 2006 TRY files are based on weather data from 1984-2004, the 2016 TRY files are based on weather data from 1984-2013.


CIBSE DSY (Design Summer Year) – This represents a warmer than typical year. For the 2006 DSY files the year with the third hottest summer from 1984-2004 was selected. For the 2016 DSY weather files the methodology was updated and three files for each location were produced from the weather data recorded from 1984-2013:

DSY1 – A moderately warm summer.

DSY2 – A summer with a short intense spell.

DSY3 – A summer with a longer less intense warm spell.

CIBSE future weather files – These are predicted future weather files based on the UKCP09 projections and are available for a number of years with different emissions scenarios and percentiles. The percentiles represent that likelihood that the mean air temperature will be less than predicted. The CIBSE TRYs and DSYs are available for the following scenarios:
2020s – High emissions scenario – 10th, 50th, 90th percentile
2050s – Medium – 10th, 50th, 90th percentile
2050s – High – 10th, 50th, 90th percentile
2080s – Low – 10th, 50th, 90th percentile
2080s – Medium – 10th, 50th, 90th percentile
2080s – High – 10th, 50th, 90th percentile
PROMETHEUS Exeter University future weather files – These are also future weather files created using UKCP09 and were created as a set of future weather data for free distribution and use by industry and academics. The files are available from University of Exeter’s website and are available for the following emissions scenarios for a number of locations:
2030s medium (A1B)
2030s high (A1FI)
2050s medium (A1B)
2050s high (A1FI)
2080s medium (A1B)
2080s high (A1FI)

Assessments and the current guidance on weather data files given in them


L2 & EPC (2013): The (November 2017 update to the) NCM modelling guide states that the 2006 CIBSE TRY must be used. Please note that CIBSE are seeking endorsement for use of the new weather sets in compliance calculations so this may change to the 2016 TRY files in the future. CIBSE have produced a weather locations look-up EXCEL sheet which states which weather file should be used depending on the postcode of the building, this can be downloaded here.


TM52 (2013): it is suggested that an appropriate DSY weather file is used in the simulation. We would suggest checking which location weather file would be most appropriate for the building and initially running with a DSY1 weather file.

TM59 (2017): Developments should refer to the latest CIBSE DSY weather files and it is required to pass the assessment with the DSY1 file most appropriate to the site location, for the 2020s, high emissions 50th percentile scenario. Other files including the more extreme DSY2 and DSY3 files, as well as future files (i.e. 2050s or 2080s) should be used to further test designs of particular concern, but a pass is not mandatory for the purposes of the simpler test presented in this document.

BB101 (August 2018): The CIBSE DSY1 50th percentile range 2020s weather file most appropriate to the location of the school building should be used for the thermal comfort assessment.


BREEAM HEA04 thermal comfort – Adaptability for a projected climate change credit: PROMETHEUS project at Exeter University projected climate change weather files. For free running buildings the 2050s medium (A1B) emissions scenario DSY should be used. For mechanically ventilated or mixed mode buildings the 2030s medium (A1B) emissions scenario DSY should be used.

*BREEAM HEA04 Update – The latest version of BREEAM HEA04 now states that for the projected climate change assessment, the CIBSE 2050s medium emissions DSY2 and DSY3 future weather files should be used for naturally ventilated buildings and the CIBSE 2020s high emissions DSY2 and DSY3 future weather files should be used for mechanically ventilated or mixed mode buildings. It’s important to check what the BREEAM document you’re working towards states.

GN32 – Prediction of operational energy consumption: The current 2016 CIBSE TRY weather file may represent “typical” weather. For extreme weather DSY weather files should be used. The current DSY1 weather file is recommended to represent weather outside of London, whilst DSY data sets reflecting urban, semi-urban and rural locations are recommended for locations in greater London – guidance on this is given in TM49.


Heating & Cooling Loads: If not using cyclic or steady state design days for loads assessments, then a dynamic assessment could be used. If so then the modeller is free to make the most appropriate choice, taking into account the location of the building and if they want to allow for future changes in the weather. Often TRY files are used but DSY files could be used for cooling loads to account for warmer summers and worst case values.

Energy Models: There isn’t specific guidance on which weather file should be used, again the modeller should make the most appropriate choice for the building. A 2016 TRY file appropriate to the building location may give the best all round results but the modeller can use DSYs and future weather files to check the impact of warmer summers and future climate changes on the building performance.