Tackling overheating in multi-occupancy residential buildings
If one thing characterises the British, it is our seeming inability to deal with the annual fluctuations in the weather. We talk up a storm, but are not very good when it actually comes to dealing with them. A flurry of snow and the country grinds to a halt. The root cause of so many of these issues comes down to the fact that our weather, compared to many other countries, is relatively benign. When we experience exceptions to the rule problems begin.
Historically, our focus as a nation has been based on improving heat retention in the winter months, but as a result, we have been blinded to the problems of overheating, for which there also has been no regulatory consideration for design to control the problem.
Before you laugh, consider those now annual headlines of scorching Mediterranean temperatures, usually accompanied by packed UK beaches, then realise that for many that translates to extreme discomfort in the home and even premature mortality. Lomas & Poritt in their 2017 research paper on Overheating in Buildings cite the European heatwave of 2003 when more than 2,000 excess deaths were recorded in England due to the higher than normal temperatures. These were conditions experienced again this year, with temperatures exceeding those recorded during the heatwave of 1976 and they caution that this is set to be the norm by 2040, and they warn that heat-related deaths could treble by 2050.
While protection from winter cold remains a priority, the expectation is that concerns relating to summertime health, especially amongst the young or infirm will escalate to the point where the adaptations of buildings will become a necessity.
This is a critical issue because the UK’s mild climate has meant that many buildings were traditionally poorly insulated and because they did not retain heat they simply did not suffer excessive overheating. But as a direct result of the decades of effort to address and improve the energy efficiency of buildings with new standards for insulation and window systems, the heat loss the from average building stock has been reduced by 23% since 1970 (Palmer & Cooper, UK Housing Energy Fact File, 2013) but this, in turn, has made overheating a more increasingly common issue.
Modern building techniques have not helped either, the common use of thermally lightweight materials such as thin metal, wood, plastic and plaster means modern homes lack thermal mass compared to traditional brick, concrete and heavy timber construction. This is what has helped to keep older buildings cooler in the summertime. So, new or renovated buildings get hotter, which is further exacerbated by a noted reduction in ventilation which is a direct result of improved and better-fitted glazing.
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What we see is residents typically finding it harder to address summertime overheating and within our cities, the problem worsens, not only due to the increasing amount of new building but because more homes or apartments are being squeezed into smaller plots to make the most of the lettable space. This is leading to a resurgence in vertical living and with that comes further restrictions on window opening, due to tower height. Modern apartment buildings in the UK can rise to in excess of 90 storeys and now represent more than 50% of the planned new build housing stock. Currently, there are approximately 500 projects more than 15 storeys high planned for the UK in the next 10 years.
But even if people wanted to open their windows, concerns about security, air and noise pollution mean this is simply not a realistic option. Lomas & Poritt cite that on a very hot day, only 53% of people, who had the option, would keep a single window open at night because of security or noise concerns. According to a 2015 survey of more than 1,000 residents in London by WSP, 83% suffered from uncomfortably hot homes during that summer, with 31% stating that the heat left them feeling unwell.
This risk from overheating that is seen in the home is therefore increased in city centre multi-residential buildings. Here the sheer number of people, concerns over noise and pollution, the direct warming action of the sun on acres of glass and the use of centralised heating systems circulating very hot water throughout the building work to drive temperatures in rooms and internal public spaces such as corridors and landings to unexpectedly high levels.
Research by AECOM (building performance evaluation of dwellings, 2015) has also shown that these centralised modern heating networks are also highly inefficient, with a lack of coordinated control for mechanical ventilation and heating. This results in them losing as much as 50% of the total energy produced during distribution! Within the building temperatures begin to spiral upwards, getting as high as 28°C (82° F) for extended periods in corridors which is in excess of the typical maximum British summer temperature of 25°C. Despite this AECOM predict poorer still results in future for dwellings planned for London!
This is why living in a modern apartment, despite the apparent luxury surroundings and grand picture windows, is more often than not an unpleasant experience. The common problem of heat management, worsened by a lack of individual climate control quickly turns rooms into heat traps that are “like an oven” and can rapidly become unbearable for the residents.
The response to such overheating would usually be a dedicated chiller plant and a chilled water network, but this approach only addresses the symptoms, not the cause.
The answer is better building design, where the performance and selection of the distribution system and centralised plant are given much greater consideration and where architects and specifiers can regain control for the building design. To overcome these issues, the new Zeroth Energy System offers an innovative new approach when it comes to designing heating and cooling for city apartments.