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1-11. Intaking Fresh Air of Semi-Concealed Type and Concealed-Duct Type
•
Precautions Regarding External Air Intake
(1) Ventilation Load
Ensure that the design of the air-conditioner takes air-conditioning loads into consideration when external air
intake is involved.
(2) Restrictions on External Air Intake
Ensure that the design conforms to the restrictions on air intake volume stipulated in accordance with the model
of the indoor unit and the intake method. Consideration must also be taken to mixed air content listed in (3)
below without fail.
* If the air intake volume does not satisfy the required ventilation volume, air must be fed into the room
separately with the use of a total heat exchanger or a fresh air processing air-conditioner, etc.
(3) Mixed Air
The amount of external air intake must be set within the scope of the unit's usage conditions when external air and
internal air is mixed together. This is especially important in the following cases, in which it is necessary to either
feed external air into the room after it has been processed or reduce the amount of external air that is fed in.
When the external dew-point temperature is greater than the dry-bulb temperature of the air sucked into the unit.
Ensure that processing is performed so that the external dew-point temperature is lower than the temperature of
the air sucked into the unit to prevent the risk of condensation building up.
In the case of low external temperatures.
There are cases in which the temperature of mixed air is lower than the operating range of the unit if excessive
amounts of external air intake are used when the external temperature is low. This problem is to be solved by
either feeding external air into the room after it has been processed or reducing the amount of external air that is
fed in.
When used in combination with humidifi ers
External air must always be processed when the external air temperature reaches freezing point to prevent the
risk of the humidifi er freezing.
(4) Arranging Ducts and Filters in the Field
External air intake ducting must be arranged in the fi eld. External air fi lters must also be installed without fail in
order to prevent the intake of dust and grit.
(5) Thermal Insulation for Ducts
Ensure that all external air intake ducting is heat-insulated without fail. Failure to observe this may result in the
build-up of condensation.
(6) External Air Intake Coupling
Ensure that the design for external air intake is coupled with
the fan blower operations of the indoor unit. There are cases
in which the dust that accumulates in the fi lter is blown into the
room if the external air is fed from the fi lter. There are also cases
in which the noise of external air being fed into the room can
be heard from the indoor unit if external air is forcibly fed when
the booster fan or other components on the indoor unit are not
operating.
(7) Booster Fan Selection
Select the booster fan in accordance with the resistance of
the external air intake duct (diagram on the pressure loss
characteristics of the air fl ow volume for fl exible cylindrical ducts)
and the resistance prevalent inside the unit (volume of external
air fed and the resistance within the unit).
(8) Attaching the External Air Intake Flange
Flexible Cylindrical Duct
o100
30
20
10
6
4
2
1
0.8
0.6
0.4
0.2
0.1
Air Flow Volume for Flexible Cylindrical
Duct-Pressure Loss
1-319
30
50
100
200 300
400
500
3
Airfl ow (m
/h)
1
o125
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