AIR CONDITIONING & AIR QUALITY
Fixing poor air quality without an AHU: a decentralised approach
T
Ian Thomas, product manager at TROX UK explains the benefits of decentralised ventilation in commercial buildings
he recent heatwaves have raised awareness of the importance of room temperature and air quality in spaces which require high cognitive performance, such as schools and workplaces. The link between ventilation and our ability to concentrate has been understood for many years, and the Indoor Air Quality report of 2022 provided clear evidence of the strong correlation between high CO2 levels and reduced cognitive performance and attention levels. Sadly, the spaces often at the greatest risk of poor air quality may also have the most urgent need for effective ventilation. Care homes, schools, offices and gyms, for example, may have an urgent demand for good air quality, but often these sites are not ideally suited (or able to afford) the kind of systems present in the country’s office blocks and high-rise buildings. Measures taken by individuals to overcome high temperatures and poor ventilation, such as the introduction of standalone fans, are counterproductive as well as limited in terms of impact. These ad hoc attempts to improve occupant comfort can destroy any attempt to manage energy usage. For building services engineers, estates managers and facilities managers this can result in a complete loss of control over the carbon and financial impacts of buildings for which they are responsible and held accountable. Many buildings already have methods of achieving the optimum conditions with AHUs (Air Handling Units) and VAV (Variable Air Ventilation) systems, complete with filters specifically designed to combat airborne contaminants. However, there are still many spaces for which these systems aren’t feasible. To exacerbate the problem, in today’s more air tight buildings, the air quality problems are likely to be worse rather than better in spaces that cannot be ventilated using traditional air conditioning, due to the reduced levels of fresh air escaping into the building from outside. Furthermore, many buildings in use today are modular, and are best suited to plug and play HVAC systems rather than site-wide centralised systems. Lastly, when upgrading air quality in heritage and listed buildings, the alterations to the fabric of the building that would be needed to accommodate traditional air conditioning systems may simply not be acceptable or allowable. There’s no reason to give up on these problem spaces though. Decentralised ventilation offers options for tricky spaces, and provides relief for room occupants.
Benefits of decentralised ventilation
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 TROX decentralised units, for
example, 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. 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.
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. In contrast to recuperative heat exchangers (where the airflows are separate and pass along numerous plates), rotary heat exchangers (such as those used in some of the TROX units) 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. As an example, the nominal airflow of the TROX units is from 400 to 800 m3/h, with a boost function (600 to 1100 m3/h) offering additional reserves which can be activated for temporary flushing of rooms during breaks. The improved comfort levels and quiet operation of the units (with the help of patented sound attenuators) aid concentration, for higher performance of room occupants.
Practicalities and installation
The wide number of options for location of decentralised ventilation units simplifies planning and minimises loss of space, to offer greater
14 BUILDING SERVICES & ENVIRONMENTAL ENGINEER AUGUST 2026
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. And even though the units are perfectly capable of operating independently, they can also be connected to the central building management system. These practical benefits even make them suitable for small spaces requiring improvements in air quality, such as classrooms. Just two TROX units with a rated performance of 400 m3/h, for example, provide a standard classroom with the required fresh air in order to achieve and ensure an average CO2 concentration of less than 1000 ppm.
The benefits of high air quality are always worth looking into. No matter how complicated the space, the likelihood is that there’s a more comfortable and energy-efficient solution that will avoid room occupants resorting to their own measures, such as standalone fans.
Read the latest at:
www.bsee.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38
