14 Performing the measurement
83
It can be assumed that, with effective fume hood systems, at least 400 m
3
/h of
air are extracted (with exhaust air driers the quantity of air is not significantly
below this, very powerful fume hood systems extract over 1000 m
3
/h of air).
With very high air extraction performances, an underpressure measurement is
frequently not expedient in apartments or comparable usage units.
As a rule, the solution here can simply be an opening to the outside, so for
example a tilted window with a window tilt switch. In a case of this kind, the
measurement only makes sense if the owner/operator of the firing installation is
absolutely intent on having the proof of the underpressure being too high.
The area of application of underpressure measurement in equipment rooms is
therefore primarily where the power of the indoor air extraction systems is
estimated to be low or there are particular physical conditions which suggest
that the underpressure does not exceed the permissible value (4 or 8 Pa) when
the firing installation(s) and indoor air extraction system(s) are operated
together.
The check that no dangerous underpressure can arise should be carried out
using pressure measuring instruments that have undergone qualification testing
for the "measurement of underpressures in rooms where firing installations are
set up".
The measurement is carried out according to the following process outline:
1. Close all the usage unit's windows and doors. If there are blinds present on
the windows and external doors, these should also be closed. Switch
differential pressure measuring instrument on and wait for the zero point to
be determined, connect capillary hoses to the measuring instrument
(reference = (-) connection, equipment room = (+) connection), open
windows, and if applicable blinds, and lay external capillary hose (for
reference pressure), check zero point on the reading display, start pressure
progression recording, wait approx. 30 seconds with open window or
external door to register zero line.
2. Start up firing installation(s) and set to maximum power. For manually loaded
firing installations for solid fuels, full load operation must be achieved. All
available air extraction equipment should be started up. The process must
involve the measurement recording the most unfavourable condition, that is
the evaluation should be carried out with the air extraction system(s) at the
highest level of power. In cases where the ventilation equipment is not
located in the same room as the firing installation, all doors and openings
between the room where the firing installation is set up and the ventilation
equipment are to be kept open. The zero point should not change after
starting up the firing installation and air extraction equipment with the
window or external door of the equipment room open.
3. Close door/window, wait approx. 30 seconds, check underpressure, check
clean extraction of the flue gases. If a blind is present on the
window/external door of the equipment room, this should be closed and
opened at the same time in each case.
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