Limitations of the CIBSE design summer year approach for delivering representative near-extreme summer weather conditions

Abstract

Representative, site-specific weather data is a key requirement for building performance simulation. In the UK, such data is available in two formats, Test Reference Years for analysing building services loads under 'typical' year conditions and Design Summer Years for estimating summer discomfort of naturally ventilated and free-running buildings. Currently, Design Summer Years are determined as a complete year based on the rank of the average dry bulb temperature from April to September. The simplicity of this approach does not take into account extreme temperature values in individual months or the incident solar radiation, both of which are however of great significance for the summer overheating performance of a building. This paper analyses the implications of this simplified approach for the resulting data. It is shown that there is no consistent relation between the Design Summer Years and the corresponding Test Reference Years and that, for some sites, building performance simulations using Design Summer Year files deliver unreliable results. Practical application: This paper demonstrates that the current approach for deriving Design Summer Years (DSYs) can lead to data series that are not representative for near-extreme summer conditions at a given location. It highlights that a new approach for deriving near-extreme summer years for building performance simulation is needed in order to overcome the inherent shortfalls of the current DSY data.

An update of the UK’s test reference year: The implications of a revised climate on building design

“…Further work 9 showed that the methodology could produce weather files which generated the average energy use from the thousands of weather years from the UKCP09 weather generator. Similarly Jentsch et al 10 found that the TRY mean monthly temperature sits within the centre of the long-term data as would be expected.…”

“…The method for selecting candidate months for the TRY has long been established and as described above the method has been found to be robust [8][9][10] . Although the method is detailed formally elsewhere 1,6 , for completeness the method will be briefly described.…”

Probabilistic adaptive thermal comfort for resilient design

“…The DSY is the year that falls in the middle of the upper-quartile of the base years' dataset, ranked according to summertime (April to September) average dry bulb temperature; this is generally the third warmest summer for a base dataset of 20 years. The DSY does not take into account extreme temperatures in individual months or incident solar radiation, both of which are of great significance for assessing the overheating performance of buildings [17]. This means that periods of high temperature (such as heat waves) in relatively cool summers are not considered.…”

“…Furthermore, as it is known that different weather parameters have a differing influence on the relative risk of overheating for different building types [23], three design reference years were selected in [26] based on the daily mean temperature, relative humidity and solar radiation respectively. In addition, different sampling methods [26,27] and statistical adjustment methods [28] have been used to develop new DSYs but none of them have been found to overcome all the shortcomings in the simple DSY selection discussed in [29].…”

Future probabilistic hot summer years for overheating risk assessments

“…For instance, among the 21 years, years with significant amounts of missing data were discarded so that the number of complete years available for each site varied from 6 (Southampton and Swindon) to 21 (Edinburgh and Glasgow). Thus DSYs exist for sites with a small number of complete years which hence might not be particularly warm compared to the long-term mean [12]. CIBSE also provides Test Reference Years (TRY), which are used for predicting the energy consumption of buildings.…”