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C120-H007-05EN 55
4.5 Precautions Pertaining to the Installation of Air Conditioners
4.5.5 Preventing dew condensation in underfloor ventilation
In underfloor ventilation, provisions should be made to prevent dew condensation
inside and outside of devices installed in the computer room as they are exposed to
direct drafts of cold air from the air conditioner. Devices are susceptible to dew
condensation if they are at a low temperature while the room temperature is low and
also if the air inside and outside the room is at a high temperature and a high humidity.
Further, where both the temperature and humidity are regulated from the beginning,
the underfloor air could be dampened and cause dew condensation.
The air conditioning control scheme must be examined and established on the user's
own responsibility to meet their own needs. Typical air conditioning control schemes
are described below.
(1) If the room temperature is low
If the room is in low temperature, the devices installed in the computer room is also
cool. When this occurs, follow the procedure below to start the humidifiers.
1 Stop the humidifier of the air conditioner(s).
2 After reaching the target temperature only with the air conditioner in heating-drive
mode, turn on the server systems.
3 Change the drive mode of the air conditioner to cooling-drive.
4 When room temperature reaches stable circumstance, start operating the
humidifiers.
(2) If the room air is at a high temperature and a high humidity
If the room air is at a high temperature and a high humidity, the room humidity will
rise sharply when the air conditioner starts to deliver low-temperature air. When this
occurs, follow the procedure below to start operating the air conditioning.
1 Bring the room air to the target temperature and humidity points slowly while
dehumidifying the air with a high blow temperature setting and a low humidity
setting. Keep the dehumidifier stopped in the meantime.
If the room humidity does not fall below its target point before the dehumidifier is
run, the following are conceivable:
z Failing to dehumidify the air because reheater that regulates the temperature after
room air has been cooled may not operate.
z Outside air penetrating the room through gaps.
In this case, the facilities and building must be checked.