Author: John Lloyd, Associate, Performance
The argument for demand-controlled ventilation.
For the past 15 or so years, energy consumption has been a major consideration when designing buildings. Almost every project we work on now has specific energy consumption targets (if not, we would encourage setting some). These targets usually focus on reducing CO2 emissions, improving an EPC rating, or achieving more BREEAM points.
In recent times, as a society we’ve become increasingly aware of health & wellbeing… and, with that, air pollution levels.
Google Trends report that interest in ‘wellbeing’ has increased three-fold since 2013.
The relationship between health & wellbeing and air quality is an area that falls firmly within the influence of building services engineers. It is vital for us to step up and develop solutions.
The air quality conundrum.
We know that increasing the amount of filtered fresh air will give us better air quality, and natural ventilation has received a lot of positive promotion over the years. It can do a great job on warm days, but opening windows on cold days to improve air quality only creates problems elsewhere. This means we often have to look at mechanical or hybrid ventilation systems – the problem being that these use a lot of energy.
We can’t ignore energy consumption simply because health & wellbeing may now be deemed more important – Part L is not going anywhere.
As with most engineering solutions, a compromise is therefore needed between increasing ventilation rates and reducing energy consumption.
Demand controlled ventilation.
One answer will be demand controlled ventilation. This is a system where the amount of fresh air is continually adjusted by a control system in response to the temperature, humidity and air quality conditions both inside and outside the building. By doing this, the control system ensures that all spaces receive the ventilation rates they need to maintain comfortable and healthy conditions.
But is demand-controlled ventilation energy efficient?
Here in the Performance team, we recently looked at how a demand controlled ventilation system within a laboratory building has been operating over its first 12 months of use. Designed by our firm, the system continually adjusts the ventilation to each room by monitoring air quality and boosting ventilation rates to specific rooms when needed – all while maintaining the buildings strict pressure regime.
The system has proven to perform extremely well, delivering great air quality in addition to big energy savings over a traditional fixed speed system.
Our analysis showed that, while the system results in a 47% reduction in energy consumption and cost, its full potential was still not being reached.
With a few simple control changes applied through the BMS, we discovered further savings could be made that would reduce the energy consumption to just 30% of a traditional system. So it seems, when it comes to higher standards of air quality and energy consumption, it really is possible to tick both boxes.
One question remains unanswered:
How much more energy does demand-controlled ventilation use over the natural ventilation alternative? As a Performance team, we are looking to provide an answer… but this may become a moot point if natural ventilation can’t provide sufficient air quality standards.