Preparing the built environment for intensifying heatwaves

Date Published

18th Jul 2022 @ 12:33
Richard Tibenham
MCIBSE, LCC, LCEA
Business Development Manager, UK Consultancy

The UK is experiencing a heatwave this week with temperatures anticipated to exceed 34⁰C in some parts. Temperatures at these extremes are becoming increasingly common, with experts warning that the severity and frequency of heat waves are likely to increase over the coming years as a consequence of climate change. We are already 30% more likely to experience heatwaves now than in 1750, due to higher concentrations of carbon particles in the atmosphere.

While we enjoy the sunshine across the UK this week, it is important to consider the longer-term implications for the built environment. Historically, the primary challenge in the UK has been to keep our homes affordably warm during the winter. This remains to be the case, particularly for older properties, as has been well illustrated by the ‘Cost of Living Crisis’. The situation is set to get all the worse in October, with the Ofgem price cap set to increase by a further 65%, just as the winter heating season begins.

For newer properties, however, whilst wintertime heating costs may be of lesser concern, the likelihood of summertime overheating is usually greater.

Overheating issues often lead Building Owners to install space cooling equipment to manage otherwise uncomfortable conditions. This, of course, increases demand on the energy grid. In March, Spain incurred a record demand for natural gas, after an extremely early summer heatwave incurred high air-conditioning energy demands on the electricity grid. We can anticipate similar events occurring here in the UK if space cooling energy demand outpaces renewable energy generation capacity. Obviously, this is not ideal, as the UK works towards its decarbonisation targets.

Solar PV generation is sympathetic toward space cooling energy demands, as the energy generation profile is highly correlated with the energy demand; as the sun comes out, space cooling demand increases, and so too does PV generation. However, the square meterage of PV cells required to operate air-conditioning plant is considerable, meaning that the area of PV cells required to run an A/C system may be multiples times that of a building’s footprint. If this energy cannot be sourced on-site, this means placing further demand on the energy grid.

There are often opportunities to reduce the operational energy demand of designs, particularly for new buildings and deep retrofit projects. As building designers start to grapple with the challenges of net-zero carbon, I think it’s becoming increasingly apparent that it actually takes quite a lot of PV cells to run a space heating or cooling system. In most cases, it makes a lot more sense to design out energy demands in the first instance, rather than accommodating these via renewable energy generation systems. Site orientation and architectural massing, when intelligently applied, can often deliver very high performance gains at little or no additional cost.

Recent changes to the Part L and O building regulations place greater emphasis on the balance between operational energy demand, carbon emissions, and summertime overheating risks. However, these changes will need to go further if we are to prepare the UK for a net zero-carbon scenario against a backdrop of rising summertime temperatures.

The structure of the Part L building regulations still effectively incentivises air-conditioning over less energy-intensive alternatives. Low energy strategies for space cooling, such as night-time purge ventilation, high thermal mass structures, and mechanical ventilation with heat recovery, should be encouraged to reduce summertime operational energy demand. Instead, the current regulations can appear to favour the application of higher energy intensity air-conditioning systems via the ‘notional vs. actual building’ comparison, as the notional target tends to be significantly higher for buildings with air-conditioning when compared to those with natural ventilation.

Likewise, whilst the newly introduced Part O regulations do bring some welcome attention to overheating risks, the code is constrained to residential buildings only. Whilst Part L provides some additional comments on reducing internal heat gains in commercial buildings, the requirement for an overheating assessment remains a client issue.

For those looking to deliver high levels of year-round indoor environmental quality whilst simultaneously achieving low operational energy demand, efforts over and above the building regulations remain necessary. For residential buildings, the Passivhaus code is proving to be a well-established and increasingly popular performance standard. However, for commercial buildings, advanced methods of computational modelling are required. These are generically termed ‘Enhanced Building Energy Models’, and incorporate a more accurate account of a building’s specification than would be the case for a building regulations compliance model. In particular, the modelling of heating, ventilation, and air conditioning (HVAC) systems is far more rigorous. To apply these methods, performance standards such as NABERS UK and CIBSE TM54 are becoming increasingly popular. IES Consulting now also offer a Modelling Guide, which is customiseable to individual clients needs, in the design and assessment of thermally comfortable low-energy buildings.

An accurate predictive energy model is a critical component in any low/zero carbon design. Without this level of information, design teams are working without an accurate compass, which inevitably leads to underperformance issues.

Physics-driven building modelling can be used to test sustainable measures for keeping buildings cool enough during the summer whilst providing low operational energy demands year-round. This will not only keep operating costs and emissions to a minimum but will also improve the comfort and well-being of building occupants.

On a broader scale, town and urban planning need to account for heatwaves and other weather events. Concrete and other building materials absorb heat, meaning that our cities are hotter than the countryside. This week London is set to be hotter than Jamaica and health warnings are in place due to the extreme heat. If temperatures continue to climb over the coming years, there is a danger of cities becoming unhealthy places to live.

Technology-informed urban planning tools that predict accurately how the built environment will operate under extreme weather conditions need to be integrated into every RIBA design stage to mitigate the health impacts of climate change as much as possible in urban areas.

For more information on how IES can help you assess thermal comfort of your buildings, visit www.iesve.com/services/design-analysis/thermal-comfort or send an enquiry.


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