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HUMIDIFICATION & DEHUMIDIFICATION


Why managing moisture is critical in the pursuit of healthier, low-carbon homes


Nicola Rivers, climate division head at Zehnder Group UK explains why humidity control is a critical factor in building performance and indoor environmental quality (IEQ)


T


he UK has a humidity problem – and climate change is making it worse. In the winter, it is wet and cold causing


condensation and mould in our homes, and in the summer, temperatures are intensifying, bringing hot and highly humid conditions. There is no escaping it. In addition to the weather extremes, the way we


live our lives has changed too. Our homes used to be somewhere to simply live, but they have now taken on the role of office, gym and even entertainment centre. Cooking, bathing, working out and having more people in rooms all day have led to increased levels of water vapour being released into the air. With these increased levels of humidity in our


lives, you must ask yourself: where does all the water go? Historically, older buildings were naturally


leakier, allowing moisture-laden air to escape through gaps in the building fabric. As modern buildings become increasingly airtight to improve energy efficiency, that moisture is now more likely to become trapped indoors, leading to higher humidity levels and an increased risk of damp. While the building industry focuses heavily on


reducing energy use, carbon emissions, insulation levels and airtightness, moisture management frequently receives far less attention – but that is a dangerous game to play. Humidity is often the “hidden factor” in building decarbonisation. By ignoring it, many low-carbon buildings can inadvertently create indoor environmental problems if ventilation and humidity control are not considered alongside energy efficiency measures.


The role of humidity in buildings


Maintaining the right level of humidity is essential for comfort and health. Too little moisture in the air can leave us feeling dry and irritated, while too much can make us feel clammy and uncomfortable. Humidity is measured as relative humidity (RH) – the amount of moisture the air can hold at a given temperature. Because warm air can hold more moisture than


cool air, indoor spaces often feel more humid as temperatures rise. CIBSE recommends maintaining


Left: Nicola Rivers, climate division head at Zehnder Group UK


vulnerable people and those with existing health conditions. Effective, on-demand ventilation is therefore essential for maintaining healthy humidity levels and creating fresher, healthier indoor environments.


Ventilation for positive humidity management


indoor RH between 40–60% for optimal comfort and wellbeing. Without effective ventilation and moisture control, humidity can quickly move outside this range, affecting both occupant health as well as the fabric of the building itself. During winter, moisture generated through


everyday activities can build up indoors. Without adequate ventilation, this moisture condenses on colder surfaces, creating the conditions for damp and mould growth, which can have serious health consequences. In summer, warmer air holds more moisture,


causing humidity levels to rise and making indoor spaces feel hotter and more uncomfortable than the temperature alone suggests. This leaves occupants feeling sticky, lethargic and uncomfortable. While unpleasant for everyone, these conditions can pose higher risks for


Until now, if a mechanical ventilation strategy was considered, a heat recovery unit would be the obvious choice, helping to retain heat in the winter and reducing AC load in the summer. But in this new, varying UK climate, we now need a different type of ventilation, and the industry should be looking more at Enthalpy Recovery Ventilation (ERV). This system transfers BOTH heat and moisture between airstreams to improve comfort and efficiency and promotes better overall indoor environment quality (IEQ) through improved indoor air quality and thermal comfort. Unlike simple, passive ventilation, ERV systems use an enthalpy exchanger to recover both heat and moisture from outgoing air. This pre- cools and dehumidifies incoming air in summer, while pre-heating and humidifying it in winter, reducing energy demand and improving comfort. By recovering up to 8.6 litres of moisture per day during colder months and using intelligent, demand-led controls, ERV systems help maintain healthy humidity levels and comfortable indoor environments with minimal energy consumption. The permeable enthalpy membrane allows


excess water vapour to pass through while blocking odours, pollutants and contaminants. Zehnder’s patented antimicrobial technology further protects against mould, bacteria and spores, helping to maintain system hygiene and performance. The result is balanced heat and moisture recovery that supports healthier, more comfortable indoor environments. Simply put, ERV systems will deliver balanced


ventilation while recovering up to 96% of heat and 70% of humidity, supporting both decarbonisation goals and healthy indoor environments for years to come.


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