In the literature review, a general background to the climate change projections was
reviewed, and in this section details of the specific data compared in this chapter are covered. Two generations of climate projections (UKCIP02 and UKCP09), and the three weather data sets that are derived from them, are included here. Two weather data sets were developed by research groups affiliated with the ARCC network - COPSE (COPSE 2011) and
PROMETHEUS (PROMETHEUS 2011). These use the UKCP09 weather generator outputs to produce simulation weather data. The third source was CIBSE future weather years (CIBSE & Met Office 2009b). Manchester was the chosen location for this study as all the required weather data were available and because it offers an alternative major urban location in the UK to London, which has been extensively analysed in recent years for climate change impacts.
This study concentrated on single-year hourly weather data sets that have been traditionally used as inputs for dynamic building simulation. Two types of weather file were used in this comparison from each source. The first were Test Reference Years (TRY), which are made up of typical months fitted together, and were used in this study for the comparison of building ventilation rates. The second weather file was the Design Summer Years (DSY), which represent near extreme years in terms of the summer temperature and was used in this study for the evaluation of overheating in Section 6.4.4. Methods for the production of these types of files are given by (Levermore & Parkinson 2006). Other proposed methods which use multiple year output from the UKCP09 weather generator, such as that proposed by (Jenkins et al. 2011), would not be as practical for this comparison due to the computational expense of running multi-zone airflow network models for large periods of simulation time. It is expected that yearlong reference sets of weather data will continue to be used to simulate
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natural ventilation, as they are a robust representation of the climate and are appropriate to the resources typically available to professionals working in the built environment.
The CIBSE future weather years have a deterministic representation of climate change due to the type of projection available from the 2002 projections (UKCIP02). With the more recent UKCP09 climate projections introduced by (Murphy et al. 2009), a probabilistic approach has been adopted to give more information about the levels of uncertainty. Part of the output from these projections has been large volumes of synthetic weather data produced by a stochastic weather generator - see (Jones et al. 2009). Methods to use this synthetic weather data for building simulation have been a central part of a number of research projects associated with the Adaption and Resilience to Climate Change (ARCC) programme - more information on the projects can be found at the programme‘s website, (ARCC 2011). Some differences in approach to the incorporation of these climate change scenarios into single-year building simulation weather data have been developed, but the importance of these differences is unclear. One use of dynamic thermal building simulation is to determine whether a natural ventilation strategy is sufficient for maintaining building comfort conditions. The avoidance of mechanical cooling whenever possible will continue to be a priority, both now and in the future. This is indicated by a recent act that aims to reduce energy consumption in the built environment, the Energy Act (DECC 2011) of October 2011. There is a need, therefore, to evaluate the differences in natural ventilation characteristics due to the type of climate change information available.
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6.1.1
UKCIP02
The CIBSE future weather years (CIBSE & Met Office 2009b) incorporate the UKCP02 climate scenarios (Hulme & Jenkins 2002) into the CIBSE TRY and DSY weather files by the morphing method described by (Belcher et al. 2005). The simplicity of this method has made it attractive for building evaluation and the consistency between weather variables, which is present in the original data, and which is likely to be preserved in the morphed version. Although there is an intention to update these CIBSE weather files by incorporating the later UKCP09 projections, the UKCP02 versions were included in the comparisons for reference. This was done through the adoption of CIBSE future weather years in the building simulation undertaken in Section 6.4 and directly by comparing wind speed change factors in Section 6.2.3. Additional details of the two sets that are derived from the UKCP09
projections are given in the next section.
The period used for the production of the latest CIBSE TRY weather data was from 1983 to 2005 i.e. close to the present. CIBSE weather files were also used as the baseline weather data in the future performance analysis of a case study building carried out with dynamic building simulation as part of the study by (Jentsch & Bahaj 2008). Their aim was to consider future proof options to avoid or reduce mechanical cooling in their case study building. To do this future weather files were produced using the weather generator tool produced by Jentsch & Bahaj. This tool incorporates the UK Climate Impacts Program (UKCIP) 2002 projections (Hulme & Jenkins 2002) by the morphing method (Belcher et al. 2005). A similar method was used to produce CIBSE‘s own future weather data (CIBSE & Met Office 2009b) and this is one of the data sets used in the comparisons presented in this chapter.
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6.1.2
UKCP09
Rather than a deterministic projection, UKCP09 adopts a probabilistic approach, which means projections are based on climate model ensembles and an indication of the weight of evidence for particular climate outcomes are given. For weather data on a daily and hourly timescale a stochastic weather generator is available, reported by (Jones et al. 2009). The two sets (PROMETHEUS and COPSE) incorporating the projections from UKCP09, are made up of TRY and DSY weather files produced from the stochastic weather generator output. From the weather generator up to 100 daily or hourly time series, each 30 years long and
representative of a single emission scenario and a future period, were available. The weather generator first produces rainfall data calibrated from the historical baseline period as the primary variable and then other variables are produced using inter-variable relationships as well as the climate change factors from UKCP09.
Both PROMETHEUS and COPSE data sets were produced from these 3000 year
(100×30years) UKCP09 weather generator outputs with reference to the methods of TRY and DSY production by (Levermore & Parkinson 2006). COPSE and PROMETHEUS were based on different runs of the weather generator, which means that although these different runs were statistically equivalent the data at each point in time would be expected to be different due to the nature of the stochastic process. Differences in method also arose due to the representation of the wind and the climate change percentile grouping of the data from which the DSYs and TRYs were produced. These differences are examined in the sections
following 6.4.1.
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