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Condensation question

Stephen Biddle
Hi All


We have a product, which is sensitive to moisture, so it's in an IP66/67 enclosure, so far so good, that keeps out the water.  The potential problem is that it does not keep out the water vapour so if the temperature drops we can get condensation on the surfaces.  To combat this we have an anti condensation heater set to come on when the air temp drops to 30 C.  The problem we have is that it's in a very humid climate with an ambient of 40 C in the day that drops to around 0 C at night.  My question is, can the condensation form on the surfaces as the humid air drops from 40 C to 30 C, which is the lower limit.  I suspect it can.  Any ideas?


Stephen
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    You could use a table like this one
    http://www.tis-gdv.de/tis_e/misc/klima.htm


    Which shows that the Relative humidity (RH) must be greater than 60% when the external air temperature reaches 40 DegC in the middle of the day, for the dew point to be reached with a drop in external air temperature of 10 DegC. The RH will be a minimum during the hot daytime and a maximum during the cooler nighttime.


    Here are some 24 hour time series for a humid place Hong Kong, which shows how the RH varied a couple of days ago.
    http://www.hko.gov.hk/wxinfo/ts/display_element_tt_e.htm

    I expect you could find similar data for your site.


    Heating the product as you are doing should stop condensation occurring in the morning due to the thermal inertia of the device.


    In the evening the thermal inertia of the device should make the the above dew point calculation a worst case one since the internal air temp inside your device will be higher than the outside ambient air temp as it begins its fall to the 30 DegC thermostat switch temp set for the heater.


    James


     


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  • 0


    You could use a table like this one
    http://www.tis-gdv.de/tis_e/misc/klima.htm


    Which shows that the Relative humidity (RH) must be greater than 60% when the external air temperature reaches 40 DegC in the middle of the day, for the dew point to be reached with a drop in external air temperature of 10 DegC. The RH will be a minimum during the hot daytime and a maximum during the cooler nighttime.


    Here are some 24 hour time series for a humid place Hong Kong, which shows how the RH varied a couple of days ago.
    http://www.hko.gov.hk/wxinfo/ts/display_element_tt_e.htm

    I expect you could find similar data for your site.


    Heating the product as you are doing should stop condensation occurring in the morning due to the thermal inertia of the device.


    In the evening the thermal inertia of the device should make the the above dew point calculation a worst case one since the internal air temp inside your device will be higher than the outside ambient air temp as it begins its fall to the 30 DegC thermostat switch temp set for the heater.


    James


     


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