Improving air quality in problem spaces
Ian Thomas, Product Manager at TROX UK, discusses whether decentralised ventilation can deliver without the need for an air handling unit.
A number of factors have coincided in 2026, placing air quality in buildings under the spotlight. New government guidance on ventilation in education and childcare settings was published in February this year, recommending that teachers and school leadership teams take responsibility for monitoring CO2 levels and maintaining air quality.
The guidance recommends the use of environmental monitors across school sites to measure levels of CO2, and provides recommended levels, measured in parts per million (ppm), that are appropriate for pupils and staff. This announcement was followed by heatwaves in the UK, which made it impossible to ignore the problems of spaces without air conditioning, or those buildings with existing (but inadequate) ventilation.
Whilst traditional air conditioning systems are suitable for most buildings, a major problem facing the HVAC industry is how to address ventilation in those buildings that, for a variety of reasons, cannot accommodate air handling units (AHUs). Often, spaces with an urgent need for good air quality, such as care homes, schools, offices and gyms, are not ideally suited (or able to afford) the kind of systems present in the country’s office blocks and high-rise buildings.
Decentralised ventilation
There is an effective solution for these problems though. Decentralised ventilation has been embraced by system designers in other parts of Europe, and is starting to take off here in the UK. A major benefit of this approach is that it does not require the use of a central AHU, or connection to a building-wide ventilation system. The decentralised units deliver fresh air, heating, cooling and heat recovery directly within the room – eliminating the need for long duct runs or central air handling plant. Unlike localised ventilation driven from a central point, decentralised ventilation units are completely self-contained. Fresh air is delivered into the space by the unit, from the perimeter or fascia of the building, or from the ceiling void, and the units incorporate high-efficiency EC fans to move air effectively.
Another important benefit is that decentralised ventilation units have integrated cross-flow or rotary heat exchangers which prevent the heat from the room air being conducted outside without being used. Heat is recovered via the heat exchangers as the air passes through the units, providing free heating of the air in winter or free cooling in summer. Best-in-class units are those incorporating rotary heat exchangers. In contrast to recuperative heat exchangers (where the airflows are separate and pass along numerous plates), rotary heat exchangers operate regeneratively. The thermal energy is temporarily stored in the storage mass, a solid, slowly rotating wheel, and then, as the wheel comes into contact with the other airflow, is transferred to this other airflow. This process results in much higher efficiency levels.
Automatic control of air quality is another advantage. Technology for measurement of air quality is already integrated into each ventilation unit, to ensure that fresh air supply adapts automatically to demands, as levels of occupancy and types of usage of the room change during the day. An integrated air quality sensor in the TROX units, for example, calculates and adjusts to demand.
Design freedom
Lastly, the wide number of options for location of decentralised ventilation units simplifies planning and minimises loss of space, to offer greater flexibility and design freedom. All components for filtration, heat recovery, thermal treatment of the air and control are already integrated in the units for ease of installation. Even though the units are perfectly capable of operating independently, the TROX range for example, can also be connected to the central building management system due to the integrated FSL Control III control, for management and monitoring. These practical benefits even make them suitable for small spaces requiring improvements in air quality, such as classrooms.
When selecting decentralised ventilation units for a building it is advisable to look for a product range which includes units suitable for installation in a wide range of physical locations, to make best possible use of the available sources of fresh air.
Figure 1 illustrates the different locations in which units might be situated.
To conclude, with the availability of decentralised ventilation units, good air quality can now be achieved in problem spaces by using energy efficient alternatives to traditional air conditioning.
