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Lc_shi
28-12-2004, 04:18 AM
we have failures in some application engineering in DOAS application. The system is consisted of metal cooling panel(manufactured by our own) and DOAS unit. The cooling panel occur condensate in the hottest days in summer. our boss said the DOAS unit is without enough dehumidifying capacity. i think there maybe the possibility as follows:
# cooling panel actual capacity is low than designed value
# the hottest days beyond the design consideration
# system match is not good
# control method cannot prevent the condensate happen

i'm new in this field ,pls advice.
thx

shogun7
28-12-2004, 07:30 AM
we have failures in some application engineering in DOAS application. The system is consisted of metal cooling panel(manufactured by our own) and DOAS unit. The cooling panel occur condensate in the hottest days in summer. our boss said the DOAS unit is without enough dehumidifying capacity. i think there maybe the possibility as follows:
# cooling panel actual capacity is low than designed value
# the hottest days beyond the design consideration
# system match is not good
# control method cannot prevent the condensate happen

i'm new in this field ,pls advice.
thx

Condensation can only occur if you go below the dew point of atmosphere you are working with( it is the temperature below which water vapor in the air will start to condense and it is also 100%humidity point) and the hotter the air the higher the dew point will be because the hot air can hold more moisture then cold air. If you know the dry bulb and the wet bulb you can determine, with a psychrometric chart, the relitave humidity, the dew point and many other psychrometric properties of air. If you only want to remove sensible heat then you must keep the panel temperature above the dew point of the surrounding atmosphere. :)

Peter_1
28-12-2004, 07:54 AM
What is a DOAS unit?
After editing I found via Google: Dedicated Outdoor Air System.
So an air handling unit? Am I correct?

In that case, are the metal cooling panels in the ceiling, a ceiling cooling with tubes mounted on it, mounted horizontally?

Have a look here then, great paper I got on my computer and it's still working.
http://www.zent-frenger.de/download/fachaufsaetze/English/200111_ashrae_journal_ceiling_panel_cooling_systems.pdf

and also
http://www.personal.psu.edu/users/j/q/jqj102/Morris_2003_AJ.pdf

Lc_shi
29-12-2004, 01:30 AM
thanks for your help.