How a system-based approach can help tackle humidity levels and overheating
20 July 2026
Modern MVHR systems can help maintain balanced humidity levels while supporting low-energy building design and helping to address issues of over-hearting in commercial environments. Michael Page, business development manager – light commercial at Zehnder, explains how.
There’s no doubt about it – it’s hot out there! Heatwaves are coming thick and fast, and when they hit, it can feel impossible to escape. We struggle at home and work, but often overlook the impact heat has on our buildings.
As summers get hotter, we need smarter, more sustainable ways to tackle overheating in the UK’s commercial and public buildings. People still need to work and access essential services during extreme temperatures. We can’t keep grinding to an economic halt each summer because we’re unprepared for our future climate.
Feeling the heat
Unlike residential properties, which fall under the Building Regulations Approved Document Part O for overheating, there is no equivalent legislation for commercial and public buildings. To fill this gap, CIBSE’s TM52 modelling framework sets out a guide for avoiding overheating during hotter months.
CIBSE defines residential overheating according to its fixed temperature test as, ‘when the internal temperature threshold of 26°C is surpassed for over 3% of the year’. TM52 is similar, in that although it uses an adaptive rather than a fixed comfort threshold, it deems an indoor space as overheated when it exceeds that threshold for more than 3% of ‘occupied hours’.
There are other criteria, but the essential point is that exceeding this temperature threshold for extended periods impacts occupant health and wellbeing – but also their ability to work. We know that when temperatures exceed 35°C, the chance of heat stress increases, which can have severe side effects like dizziness, nausea, confusion and loss of consciousness. In the most drastic cases, it can even lead to death. People can’t be expected to work in conditions like that, except it is happening across the country.
This is not a problem that is going away anytime soon. Recently, the Climate Change Committee (CCC) published a report assessing climate risk in the UK, with a particular focus on the impact of overheating. Whilst the report didn’t go as far as recommending a maximum temperature for workplaces, it did highlight the example of Spain, where legal limits of 25°C for sedentary work and 27°C for light physical work are already in place. The report also pointed to air conditioning and other cooling solutions to tackle overheating in public buildings, like hospitals and schools.
With widespread news coverage of the report, the country took notice. But within the industry, we know solving the issue of overheating isn’t a simple case of installing an air conditioning unit and problem solved. And to the CCC’s credit, it did highlight the role other solutions will play in cooling workplaces and public spaces.
But truly solving the issue will take a systems-based approach.
Beyond air conditioning
The rush to specify and install air conditioning units within working buildings is understandable. Particularly in buildings with vulnerable occupants or workspaces where people are doing physical labour, like a hospital or care home, it is vital that temperatures are brought down to – and kept at – safer levels.
However, in addition to putting strain on the National Grid through the systems’ considerable use of energy, air conditioning units also rely on refrigerants, many of which can have a significant environmental impact if leaked into the atmosphere due to their global warming potential. On top of this, they are also expensive and often inefficient to run, adding another service on top of the standard workings within the building and sitting dormant through the winter months.
Worst of all, in seeking to protect occupants from the negative impact of overheating on health and wellbeing, installing air conditioning units may inadvertently lead to similarly adverse effects. That’s because by merely recirculating air, these systems can reintroduce potentially harmful particulates such as dust and allergens into the building, making it less safe for occupants. Just because the air is cool and provides temporary relief doesn’t mean it is necessarily safe to breathe.
No single solution
While air conditioning can quickly cool down indoor spaces, it comes with negatives, and it definitely should not be treated as a ‘fix-all’ solution to solve the overheating crisis.
Effective solutions to tackle overheating in public and commercial buildings have to go beyond just cooling the air. To ensure indoor environments are truly safe, factors like ventilation and humidity control have to be key considerations in how we tackle overheating. To balance all of these factors, a single solution will never be enough.
It is about shifting our mindset to start thinking about how we design buildings as a system, rather than relying on single solutions.
The cooling ladder is a perfect example of this. Before jumping to active cooling systems, efforts must be made to shift the microclimate. In buildings most affected by the ‘Urban Heat Island’ effect, cooling begins outdoors with trees, water and green spaces, which all help to mitigate the excess heat. Similarly, buildings that make use of light and reflective materials, rather than dark stone or asphalt, absorb less heat and in turn, make indoor spaces cooler.
And if those mitigations aren’t available, you move up the ladder to preventing heat from entering indoor spaces as much as possible. For example, external shading is highly effective for reducing solar gain.
Passive cooling
The next step is to make use of passive cooling solutions. When outdoor air becomes cooler than indoor air, heat can be naturally released from indoor spaces. Strategies like night-time ventilation, as an example, help to flush out hot air without using excess energy, but that isn’t always possible due to noise or security for example.
When these strategies have been exhausted, active cooling is necessary as a final step. But these solutions should not neglect the importance of ventilation and humidity control. Modern solutions, like mechanical ventilation with heat recovery (MVHR), cool indoor spaces whilst protecting the health and wellbeing of occupants by providing a supply of clean, fresh air. Not only are they working to filter and temper the air but also can be used all year round, so wastage is reduced and the system offers more energy efficient heat recovery – up to 96% – in winter as well as cooling in summer.
Ultimately, as temperatures continue to rise, our approaches to cooling commercial and public buildings are only effective if they enhance health and wellbeing overall. Solely relying on air-conditioning won’t achieve that. Employing a systems-led approach to the way we design, build and adapt our buildings is the best way to protect our buildings from our changing climate now, not of years gone by.
