15
4.6.
Recirculation
of
clean
air
into
room
If
the
clean
air
is
to
be
fed
back
into
the
working
area,
the
Ordinance
on
Hazardous
Substances
and
its
technical
rules
must
be
observed.
We
recommend
that
you
feed
the
clean
air
back
into
the
work
room
via
a
return
air
duct
with
integrated
shutters
to
ensure
draft
‐
free
air
distribution.
The
exhaust
air
and
return
air
flows
can
be
distributed
by
means
of
a
switch
in
the
exhaust
line.
4.7.
Humidification
of
air
Formation
of
condensate
The
exhaust
air
will
probably
require
humidification
depending
on
the
tem
‐
perature
and
relative
humidity
of
the
exhaust
air.
You
should
assume
hu
‐
midification
of
the
exhaust
air
of
around
90%
in
the
device.
The
air
volume
of
the
work
room
should
be
at
least
¼
of
the
air
quantity
re
‐
circulated
by
the
device
per
hour
so
that
when
the
device
is
working
at
full
return
air
level,
excessive
humidification
of
the
ambient
air
along
with
the
formation
of
condensation
does
not
occur.
This
prevents
a
relative
humidity
of
75%
being
exceeded.
Example
Device
air
power
of
2354
ft³/min
=
minimum
room
volume
of
35315
ft³
