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The demand for controlled ventilation
Published:  19 July, 2012

Steve Mongan, head of marketing at Xpelair Ventilation Solutions, discusses fixed vs demand controlled ventilation (DCV) and asks which system type is best.

Steve Mongan, head of marketing at Xpelair Ventilation Solutions, discusses fixed vs demand controlled ventilation (DCV) and asks which is best?

With more options available than ever before, including fixed, (MEV), (MVHR) and demand controlled ventilation (DCV), it can be a difficult process for installers to decide which system best suits the intended application.

Typically installers will choose the tried and tested systems over ones that they have little or no experience in fitting, but which is best?

Fixed ventilation is a system whereby the airflow is set to a constant ventilation rate based on the perceived maximum occupancy of a space and can be treated, heated or cooled to particular requirements.

A fixed system, however, does not take into account building occupancy, resulting in the system constantly running at a set rate. This can lead to running wastes in both energy and money, ultimately increasing carbon output.

Unlike fixed ventilation, DCV is a flexible solution that has the potential to unlock significant savings without compromising indoor air quality.

DCV uses a number of intelligent sensors that continuously measure the ambient conditions within a specific area and feed back to the zone controller in real time, adjusting the ventilation requirements as necessary. These sensors measure occupancy, temperature and CO2 levels making constant adjustments to ensure optimal indoor air quality at all times.

The constantly adapting nature of the system results in subtle continual changes to meet the needs and capacity of the environment, producing savings while ensuring optimal air quality.

This problem doesn’t occur in fixed ventilation systems where the airflow is set to a constant ventilation rate throughout the day based on the perceived maximum occupancy of a space, meaning it will never under ventilate.

However, while fixed systems are becoming more efficient, the issue remains that by running at a constant rate of ventilation, the system risks ventilating empty spaces for considerable periods of time, which in commercial and industrial environments will lead to high energy wastage and increased carbon production.

The issue lies in what installers know and feel confident using. While the efficiency gains of DCV are undeniable, fixed ventilation has been the industry standard for decades.

Installers are comfortable with the systems and are able to quickly and efficiently fit and retrofit systems, minimising disruption to clients and improving turn around times.

The same cannot be said for DCV as it has a number of additional sensors that must be calibrated and wired to the system, incurring additional costs for both the end user and installer.

While the building regulations have tried to educate installers by adapting the ISBEM tool to reflect the efficiency rates of DCV in hopes of spurring a surge in usage, the additional difficulties in fitting the system, along with the lack of demand from end users, mean that installers are consistently favouring tried and tested systems.

Ultimately, DCV is the ventilation system of the future, but slow adoption means it will take time before it becomes the primary choice for the ventilation industry in the UK.

In order to meet the demands of a carbon free world this change needs to take place sooner rather than later. But with fixed systems becoming increasingly efficient and still conforming to the building regulations, fixed ventilation still has a strong place in the market.