‘We all grumble about the (hot) weather but nothing is done about it’: Preparing our homes for a changing climate
By ucftc44, on 23 October 2015
19 – 25 October marks the inaugural Global Climate Change Week (#GCCW). GCCW is a new initiative designed to encourage academics in all disciplines and countries to engage with their students and communities on climate change action and solutions. UCL IEDE, UCL-Energy, UCL ISR and UCL ISH academics and students will be holding events and blogging through the week to share thoughts and ideas for the future.
Reducing the carbon footprint of the building sector through retrofit is instrumental in achieving the UK Government’s carbon emissions reduction goals. In the wake of the Government’s decision to axe the Green Deal scheme and the zero carbon homes target, it is now more important than ever to empower people and communities to improve their homes with the aim to not only reduce heat losses and carbon emissions but also create more comfortable, healthy indoor environments. Interestingly, there has been a lot of discussion lately about the potential overheating risk of newly built or retrofitted ‘eco-home’ properties that are very airtight and highly insulated.
The uptake of air conditioning is currently low in UK homes with less than 3% of households using fixed or portable air conditioning units during the summer months. However, if we experience an increased number of hot spells in the coming years, we might see a rise in the uptake of air conditioning as people may opt for a ‘quick fix’ to the problem of indoor overheating: Predicting future penetration rates of a given technology is very challenging but some researchers have suggested that air conditioning may be installed in half of all homes in England and Wales by 2050. If waste heat from air conditioning units is discharged to the outdoor environment (the urban heat canyons), it could further increase local temperatures, thus creating a vicious circle of maladaptation to a warming climate that could increase both carbon emissions and operational costs. It is crucial to note that high levels of airtightness and insulation should not cause overheating, if they are combined with appropriate means of passive cooling, such as the provision of ventilation (preferably cross ventilation) and shading (external shutters have been found to be particularly effective and offer the additional benefit of increased security). It is absolutely essential that we retrofit homes that are well prepared for both winter and summer under the current and future climate, and combine climate mitigation and adaptation strategies.
In Aesop’s Wind and Sun fable, the Wind and the Sun are disputing which is the stronger by trying to make a traveller take off her heavy winter coat: When the Wind blows, the traveller wraps the coat tighter around her; it is only when the Sun shines brighter and brighter that the traveller takes off her coat. The fable has many levels of interpretation but, at a very basic level, it shows that fighting heat can be trickier than fighting cold! Whilst adding thermal insulation layers may reduce heat losses, dissipating heat can be much more challenging. Building performance modelling and monitoring work by UCL IEDE and other research teams has indicated that although the local urban climate and microclimate are important, interventions on individual buildings can be much more effective. Before providing active cooling, a designer should first consider the 3 passive design principles:
- ‘switch off’ solar heat gains through shading or high reflectivity external surfaces,
- ‘absorb’ heat gains through the use of exposed thermal mass and
- ‘blow away’ heat through passive ventilation means.
At the citywide level, urban climate models of London have shown that only very large scale urban greening could significantly reduce the heat island. Nevertheless, the introduction of smaller scale green and water elements at the neighbourhood level would still be desirable as they could optimise the microclimate and create community spaces that encourage social interaction.
Human behaviour is also an important determinant of summer thermal discomfort. This can become rather complicated when building physics tell us that the ‘optimum’ way to behave in order to reduce overheating indoors is a set of rather counterintuitive actions, such as closing (instead of opening) the windows and switching a fan on when it is too hot outside. The way we interact with buildings and their systems is influenced not only by physical factors (such as indoor thermal conditions) but also psychological factors (acclimatisation, expectations), and social factors (social norms, habits, practices). Built environment researchers and professionals should be working closely with social scientists, psychologists and other disciplines to disentangle these complex interrelationships in order to help people prepare for a changing climate.
This requires a paradigm shift in the way we design, construct, commission and operate our buildings, and needs to be supported by policy and regulation. Whole-year flexibility, adaptability and resilience need to be embedded in our building designs from a very early stage to futureproof them for a climate of change and regulatory uncertainty.