General Info

1 2
The challenge.
The right measurement of air flows and the correct
determination of volume flow at ventilation outlets can be
particularly demanding from a metrological point of view.
Whereas active flow hoods usually provide more accurate
measurement results, their handling is often inconvenient for
quick spot measurements. In practice, vane anemometers
and the corresponding funnels are often used instead. And
as long as the air is flowing from the outlets straight into the
room, that is not a problem.
However, this is often not the case, because for reasons
of comfort, so-called swirl outlets are used. These are
suitable for the fast exchange of a large volume of air, in
small rooms as well as in large ones. This type of outlet is
often used in buildings in which a high level of indoor air
flow is required, e.g. in office buildings, schools, recreation
rooms, hospitals or private homes. The typical feature of
these ventilation outlets is that the input air does not flow
straight into the room. Instead, the air flow is diverted in
such a way that a continuous diffusion swirl is created. This
allows the supply air and the air already present in the room
to be mixed better. As a consequence, the mean air velocity
in the room decreases. Those present in the room generally
perceive this as more pleasant.
Testo Solution Volume flow measurement at swirl outlets
For the measurement of volume flow, however, swirl outlets
present a problem, because the swirl influences the rotation
of the vane in the measuring instrument used, in different
ways, as you can see in the illustrations 1 and 2.
In both cases, the swirl leads to a measurement error:
The volume flow is displayed as either too high (1) or too
low (2). The ventilation system is then either incorrectly
adjusted down (1.) or up (2.). As a consequence, this means
either too little fresh air in the room (1.) or a ventilation
system running under an unnecessary high load (2.).
The solution.
The patent-pending volume flow straightener testovent 417
subdues the swirling air flow coming out of the swirl outlet,
and changes it into an almost uniform flow. The influence
of the swirl on the rotation of the vane decreases, and the
volume flow can be measured quickly, easily and reliably –
for example with the vane anemometer testo 417.
Rotation direction of the swirl is opposite to that of the vane –
the measured air flow velocity is too low.
Rotation direction of the swirl is identical to that of the vane –
the measured air flow velocity is too high.
TS_PS_testovent_417_MASTER.indd 2 03.12.2013 14:01:40