GB.GOLDLP.170830
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We reserve the right to alter specifications without notice.
4.3 To Adjust the Pressure Balance
4.3.1 General
There should be a certain degree of negative pressure in
the extract air section so that the direction of air leakage
through the heat exchanger and the function of the purg-
ing sector will be correct. This ensures that extract air will
not be transferred to the supply air.
The pressure balance in the unit should be adjusted when
the ventilation system has been fully installed and the
airflows discharged from all the air diffusers and registers
have been adjusted, and when the supply air and extract
airflows are as they should be while the air handling unit is
operating normally.
4.3.2 To Ensure the Correct Leakage Direction
The pressure balance in the AHU is adjusted by reposition-
ing a commissioning plate mounted in the extract air inlet.
The commissioning plate is supplied separately and should
be fitted by the fitter when the extract air duct is con-
nected. See illustration.
Connect a pressure gauge to the pressure measurement
tappings of the air handling unit. The AHU has four pres-
sure measurement tappings. The two tappings closest
to the extract air duct should be used. The blue pressure
measurement tapping is used for measuring the negative
pressure in the extract air section and the white pressure
measurement tapping is used for measuring the negative
pressure in the supply air section.
The pressure measurement tappings are situated by the
junction hood.
Note that both pressure measurement tappings are used
for measuring negative pressure.
MEASURED VALUES
The negative pressure in the extract air section should be
greater or the same as the negative pressure in the supply
air section.
If the negative pressure in the extract air section is the
same or up to 20 Pa greater than the negative pressure in
the supply air section, then you have finished commission-
ing the unit.
DEVIATIONS
If the negative pressure in the extract air section is less
than that in the supply air section, then you must carry out
the following adjustment:
1. Stop the air handling unit, open the inspection door to
access the extract air filter.
Blank off an appropriate number of holes in the com-
missioning plate using the plastic plugs supplied.
3. Close the inspection door and restart the AHU.
4. Measure the pressures.
Repeat this procedure until the negative pressure in the
extract air section is just as great or up to 20 Pa greater
than the negative pressure in the supply air section
(0–20 Pa).
Pressure measurement tappings – leakage direction
(AHU shown in the right-hand version)
- (blue)
+ (white)
EXTRACT AIR
2
Commissioning plate
5. If the negative pressure in the extract air section is
greater than 20 Pa compared with the supply air sec-
tion, although the commissioning plate is dismantled,
the leakage and purging air flow will be greater than
anticipated. This means that the actual extract air flow
will deviate from the preset extract airflow. The devia-
tion increases as the difference in pressure increases.
