The design reference year – a new approach to testing a building in more extreme weather using UKCP09 projections

Current practice in building design is to assess a building’s performance using average or typical weather, a test reference year (TRY), and then to see how it performs when ‘stressed’, using a design summer year (DSY). The DSY is an actual year of hourly data which has the third warmest summer in 20 years’ summers. One of the problems with the DSY method is that it does not explicitly take into account solar radiation, or humidity, nor when more extreme weather occurs – it is selected solely on the mean six monthly temperature from April to September. A DSY may actually be cloudier than the average weather of a TRY. This article proposes an alternative approach using a new type of design reference year (DRY) consisting of a year formed from individual more extreme weather months. The DRY is used in simulating the performance of a building and to identify a single critical month for over-heating, or maximum cooling load. This article compares the characteristics of the DSY and proposed DRY using future projected weather data from UKCIP.

Practical applications: Building designers are increasingly required by their clients to demonstrate how a proposed building will perform under a future rather than historical climate. This article describes a method of processing the latest future climate projections (UK Climate Impacts Programme’s (UKCIP’s) CP09 data released in June 2009) and generating a design reference year (DRY) for use in building simulation programmes. The DRY is proposed as a replacement for the design summer year (DSY), which has a number of limitations.