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Using future weather data for building design Organisations: Manchester University / University of Bath / Napier University, Northumbria University / Sheffield University / Met Office Case study focus Design and operation of buildings / Heating & cooling requirements This case study provides an overview of the coordinated research program COPSE (COincident Probabilistic climate change weather data for a Sustainable built Environment) which took place between 2008 and 2011. Building designers commonly model the thermal performance of proposed designs: first to estimate annual energy consumption and secondly to provide information on internal environmental conditions during periods of hot weather. Typically this is done using computer modelling based on a typical and exceptionally warm year of hourly weather observations. The aim of the project was to develop methodologies to assess building designs in future climates. In particular it focuses on maintaining comfort levels while minimising energy use. What was it used for? UKCP09 Weather Generator has the potential to provide high resolution data for projects but it is not produced in a form that is directly suitable for assessing climate change impacts on buildings design and operation. The project is an example of how academic researchers have harnessed UKCP09 output to develop bespoke information for use by designers, building owners engineers and decision makers. Ultimately the research findings have contributed to specific guidance, which have already been in real-world design assessments. Which UKCP09 products were used? The Weather Generator Approach and how UKCP09 was used The UKCP09 Weather Generator was used in four keys areas of COPSE: 1. The development of ‘future weather files’ for use in modelling building performance. These are based on output from the UKCP09 weather generator. 2. The weather scenarios (i.e. future weather files) were used to model the future cooling and heating requirements for four example buildings – an 1| Page office building, a primary school, a hospital and a residential care home in different geographic locations around the UK. 3. Researchers were able to test example thermal comfort standards for individual buildings and the implications these have for energy use for cooling across a range of possible future climates. 4. Assessments of future national energy requirements for space heating were made. 1. Developing future weather files Conventionally, two types of weather data are used in building design. The first is a Test Reference Year (TRY); this consists of hourly values of key weather variables (e.g. dry-bulb temperature, solar irradiance and relative humidity) which best represent average observed conditions over a year. This set is used for assessing annual energy use. The second is a Design Summer Year (DSY), which presents hourly data for the same variables that are representative of more extreme summer conditions. These data are used when modelling performance of the building during periods of hot weather to assess the likelihood of over-heating. The output from the UKCP09 Weather Generator was used as the basis for developing modified TRY and DSY ‘weather files’ for three locations: London, Manchester and Edinburgh. This was done for seven future time periods between 2020 and 2080 and for three emissions scenarios. In total, 21 TRY and DSY were developed for the 3 locations. The output from the UKCP09 Weather Generator does not include some important variables that TRY and DSY rely on. The COPSE research developed methodologies to derive wind speed, wind direction, cloud cover and barometric pressure in order to fill these gaps. 2. Modelling future heating and cooling requirements The TRY and DSY representing possible future climates were used to model the future heating and cooling requirements for four contrasting existing buildings – an office building, a primary school, a hospital and a residential care home for the elderly (see Figure 1). 2| Page Figure 1 “Thumbnails” of case study buildings Each of the buildings was simulated using ‘EnergyPlus 6’ software for time periods centred on 2030, 2050 and 2080 across three locations: London, Manchester and Edinburgh (i.e. the same building was modelled with weather data relevant for each of these locations). 3. Testing thermal comfort standards The development of the climate scenario modelling methodology allowed researchers to test different thermal comfort standards and the implications these could have for energy use for cooling across a range of possible future climates. As part of this process they developed the concept of “Adaptive Comfort Degree Days” (ACDD) – a metric of how much energy is required to cool buildings under future climate change scenarios which takes into consideration the inhabitants’ ability to adapt to high temperatures or cool themselves without necessarily resorting to air conditioning. In this instance, the research showed that ACDD was a good metric for annual cooling energy consumption, and that by extension was a good metric for the potential energy savings to be made by relying on passive cooling measures and natural ventilation instead of introducing air conditioning. 3| Page 3. Assessing national demands Research undertaken within COPSE also aimed to quantify the implications of future energy requirements for heating and cooling for the entire national stock of buildings. The basis of this was a series of graphs, which describe the relationship between “Space heating gas consumption” and outside temperature for different regions of the UK (see Figure 2). Daily mean temperatures for future time periods, under different emission scenarios, and for a location typical of each of the region, were calculated from multiple runs of the UKCP09 weather generator. This was used to calculate the national heating energy consumption for the country. Figure 2 Relationship between Space Heating Gas Consumption for the North West UK and the Effective Temperature measured at Woodford for the period 2007–2010. Results and interpretation The COPSE project had a broad scope to examine the potential impact of climate change on the design and operation of buildings over the coming decades. The core element in the project was the development of a methodology to ‘translate’ output from the UKCP09 weather generator for use in software commonly used in building design and operation. As part of the research there were a number of applied examples where this data was used to assess future energy demands of individual buildings, for example across the four shown in Figure 1. The projected annual energy 4| Page requirements for the three example locations are summarised in Figure 3. It shows a trend towards increased demand for cooling. A similar analysis was carried out for future heating requirements, where demand in winter is projected to decrease Figure 3 Annual cooling energy requirements – a) Office b) School c) Hospital d) Care home The development of the climate scenario modelling methodology allowed COPSE researchers to test thermal comfort standards and the implications these could have for energy use for cooling across a range of possible future climates. Figure 4 shows that one particular standard, European Adaptive Standard (EAS), results in more Adaptive Comfort Degree Days (ACDD) than another, ASHRAE Adaptive Standard (AAS). The graphs indicate that EAS resulted in significantly more ACDDs over the future projections and the conclusion was that the potential energy saving achieved by an EAS-compliant building would be higher. These findings reflect the higher upper limit of the thermal comfort zone in the EAS, which enables a greater number of buildings to use natural ventilation. 5| Page Figure 4 Annual number of cooling ACDDs for the AAS and the EAS for (left) High and (right) Low emissions scenarios for Edinburgh, Manchester and London for the 2020s, 2050s and 2080s. Finally, output from the UKCP09 Weather Generator was used to assess potential changes in heating energy requirements across the UK. The study showed that, depending on the emissions scenario chosen, space heating energy demand in the present UK building stock may fall by 16-18% in the 2030s with a further steady decline over the next 50 years, so that demand in the 2080s level was 27-43% lower than at present (see Figure 5). Figure 5 Annual Space Heating Gas Consumption under Low, Medium and High Emissions scenarios. Difficulties & limitations COPSE has gone a long way to bridge the apparent gap between the outputs provided by UKCP09 and the needs of professionals interested in buildings and energy. However there remains the difficult task of taking account of potential changes in weather patterns, when these can only be projected on a probabilistic 6| Page basis. The assessment of risk – e.g. the risk of overheating – given a relatively large envelope of uncertainty can be complex. A further difficulty that remains following the work of COPSE is that their estimates of future energy requirements assume no change in the building stock. But there will of course be changes in future decades, of which the most significant for heating energy use will be the introduction of energy efficiency measures in the present stock, the replacement of some of the present stock by new, more thermally efficient buildings, and the overall increase in stock expected over the next decades in response to population pressures. Estimating the impact of these changes was outside the scope of the research, but the future weather files derived through COPSE may be used in combination with consumption data revised to reflect stock changes to provide more realistic estimates of future heating energy consumption. Lessons learnt Irrespective of changes in the building stock, climate change is likely to have a significant impact on space heating and cooling energy use. With buildings accounting for a significant proportion of UK carbon emissions, and playing a key role in the health and welfare of the population, it is essential that they should be both efficient and comfortable, now and in the future. COPSE research has added to our understanding of the issues, and improved our ability to design and adapt buildings so that they will function effectively in future climates. Find out more A complete list of COPSE publications is included in the full project summary report Download the full project summary report [21 MB] Levermore, G.J., Courtney, R., Watkins, R., Cheung, H., Parkinson, J.B., Laycock, P., Natarajan, S., Nikolopoulou, M., McGilligan, C., Muneer, T., Tham, Y., Underwood, C.P., Edge, J.S., Du, H., Sharples, S., Kang, J., Barclay, M. And Sanderson, M. 2012. Deriving and using future weather data for building design from UK climate change projections – an overview of the COPSE Project. Manchester University, UK. Publication date [01/09/2014] 7| Page