Creating true indoor comfort
Stuart Smith, Commercial Director at Zehnder Group UK, explains how you can create the perfect indoor conditions with heat and moisture recovery.
The way we live our lives has changed. Over the past few years, the functionality of
our buildings has evolved and adapted dramatically and where an apartment, student halls or assisted living community used to be somewhere to simply live, they have now taken on the role of office, gym and even entertainment centre. The rise of convenience culture has also firmly established itself into modern culture, meaning that often we don’t need to leave for anything.
As a result, statistics show that we now spend over 90% of our time indoors, but this modern way of living presents challenges when the workings of our buildings aren’t set up right for these increased pressures on their systems.
Humidity is one of these challenges and is becoming more of a problem as our mixed UK climate changes. In addition to the weather extremes, cooking, bathing, working out and having more people in rooms all day lead to increased levels of water vapour being released into the air. In fact, four people in a space together at one time can easily create 24 pints of it a day, but once produced, where does it go?
In previous times, our leaky buildings would cope better with this challenge as natural ventilation points in the building’s fabric would exist to allow air to flow naturally. If mechanical ventilation was installed, a heat recovery unit would be the obvious choice, helping to retain heat in the winter and reducing AC load in the summer. Our modern buildings however are now being more tightly insulated for energy efficiency and, as a result, moisture is becoming trapped inside with no room to escape, making them more humid and damper.
The excess humidity build-up in a building, combined with a lack of adequate airflow to ventilate that moisture effectively, causes condensation to form on cold surfaces, turning water vapour into liquid. Without means to remove it, droplets become too heavy to
stay in the air and settle on cold spots – often windows or sills. These damp conditions provide the perfect environment for mould and mildew to develop, which can have a serious impact on the building’s structural integrity and indoor air quality (IAQ) that affects the health of those inside.
In these modern times, 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 IAQ and thermal comfort.
Why humidity matters
As human beings, we need a relative level of moisture in the air to feel comfortable and healthy – too little and we feel too dry, too much and we feel clammy and uncomfortable. How moisture levels in a room feel is linked to relative humidity, which is how much moisture the air can hold based on the room’s temperature.
Warm air can hold more moisture than cool air, meaning indoor spaces feel more humid when it’s hot. The Chartered Institute of Building Services Engineers (CIBSE) recommends indoor relative humidity levels (RH) stay between 40-60% for comfort and health, but without effective ventilation, heat and moisture control, indoor environments can easily fall out this range, making them not only uncomfortable but also potentially damaging to our health and the fabric of the building.
In the winter months, when it’s cold outside but warm inside, the water vapour we produce becomes too dense and heavy and can’t be held in the air. Without adequate ventilation, that excess moisture falls out of the air and lands on our skin, making us feel clammy. It also finds the coldest spots in the room and lands as condensation, which if left untreated, leads to mould outbreaks, which can be seriously detrimental to our health.
In summer, it’s the opposite issue. As warm air holds more moisture and heat is trapped inside, humidity levels rise beyond comfortable levels, making our skin feel clammy and our surfaces feel damp. In commercial buildings populated by vulnerable people, like care homes or assisted living facilities, these conditions can have serious health implications, from respiratory issues to heart failure. The World Heath Organisation found that heat-related mortality for people over 65 had risen by 85% between 2000–2004 and 2017–2021.
Non-ventilated, overheated rooms in summer are uncomfortable and clammy, but even worse, they contain stale air and pollutants which are trapped in. The stale air has high relative humidity meaning the moisture drops onto your skin, leaving you feeling like you are almost suffocating. These conditions are not ideal for anyone, but they are particularly bad for vulnerable people with existing health conditions. Therefore, mechanical, on-demand ventilation to remove this moisture is critical in maintaining that relative humidity balance – keeping indoor spaces healthy and us feeling fresh and happy. Control the humidity and you control the climate inside – and also use less energy in the process.
Ventilation for positive humidity management
When consultants evaluate commercial buildings, they complete psychrometric charts, measuring different variables within the indoor space, including dry-bulb temperature, wet-bulb temperature, relative humidity and dew point temperature. Due to the complexity of ventilating properties designed to trap in heat, different systems need to be mapped depending on the specific needs of the building, whether it be student accommodation, assisted living facilities, care homes, or even offices.
Choosing a strategy that best fits these spaces means finding a way to effectively ventilate and balance temperature and humidity to create healthy, comfortable indoor environments. This is where ERV systems shine, providing optimised, balanced ventilation with heat recovery up to 96% as well as recovery of up to 70% humidity.
Unlike simple passive ventilation that allows heat to freely flow out of the building, ERV systems have been innovated to pass the extracted air over an enthalpy recovery exchanger, which transfers both heat and moisture between airstreams. In summer this helps to pre-cool and dehumidify the supply air and in the winter pre-heats the incoming air and humidifies it to replace the moisture lost through central heating. This adds huge efficiencies in terms of how much energy it takes to heat a room.
An enthalpy recovery exchanger is permeable, meaning water vapour that isn’t required can pass through the filter and be pushed out into the atmosphere. They are selective, meaning harmful particulates in the air are blocked whilst water vapour can pass through. They also are anti-microbial, preventing mould from gathering on the surface of the system. These features combine to contribute to a system that not only recovers heat but also maintains a balanced and comfortable moisture level.
When it is cold, ERV systems create comfortable indoor conditions by balancing moisture levels to avoid the drying effect of heating. These systems recover between 4.3 and 8.6 litres of water a day that would otherwise be wasted, providing additional moisture where required to bring humidity levels within a comfortable range.
They have a low power consumption due to their active cooling system, which responds to outdoor temperatures, pulling in cool air from outside where possible, and using optimised fan speeds that reduce wasted energy use.
These systems provide a perfect solution to create indoor spaces with balanced, comfortable levels of heat and moisture. Without these systems in place, occupants risk
an uncomfortable and potentially dangerous living environment.
ERV represents the next step in creating sustainable, people-centric environments. By balancing both heat and humidity, we can address one of the most overlooked yet critical aspects of modern living – a truly comfortable indoor climate.
