Control principles

Principles for controlling airflow

CAV, VAV, DCV and aDCV - what they stand for

In many building types, the various rooms are used to different extents at different times of the day. In schools, the staffroom is practically empty while teaching is in progress, but subject to heavy load at midday. The opposite is the case with classrooms, where the load is high when teaching is underway and low when the pupils are at break or in a laboratory or workshop. 

In office buildings a proportion of the staff will often be away, either at meetings, on courses or off sick. Or there may be meeting rooms which are not used all the time, leading to highly variable ventilation requirements.

Experience and research from schools and office buildings shows that the average airflow required is normally only about 50–60% of the dimensioned airflow.

A typical room is only used about 60% of the time, and when it is in use, the load is only around 75%.

This clearly highlights the need for ventilation control to minimise wasted energy.

Control principles

On-demand control is a way to reduce the energy consumption of ventilation units.

By reducing airflow when there is no-one in a room or building, or by regulating airflow to the required load, energy is saved (less outdoor air to warm up) and at the same time, the electrical consumption of the fans is reduced.

Four different control principles are used in a ventilation system,either individually or in combination:

What does the abbreviation stand for?
Link to more information
CAV Constant Air Volume Read more about CAV here
VAV Variable Air Volume Read more about VAV here
DCV Demand Controlled air Volume   Read more about DCV here
aDCV Adaptive Demand Controlled air Volume   Read more about aDCV here

NB: Currently, VEX4000 and VEX5000 can be controlled with aDCV

Comparison of control principles

The following graph shows the energy consumption for each control principle 

Yearly energy consumption in %
Yearly energy consumption in %


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