Indoor relative humidity reaches 100% when windows are closed
I'm assessing indoor thermal comfort (Fanger model) with natural ventilation (ZoneVentilation:WindandStackOpenArea) through doors and windows using EnergyPlus. The model is a single thermal zone (3 m x 3m x 3m), windows placed on north and west facade, and door on south facade. Surface area of the door is 2 m2 and window is 1 m2. A total of 8 people are arranged in the thermal zone with light activity level as120 W/person, work efficiency as 0.5 and clothing as 0.6. The simulation is made run for summer weather conditions (May month) in India. Now the problem is whenever I closed the doors or windows (Schedule:Compact) mostly during night time, the indoor relative humidity in the zone reaches 100%. Also, this only happens when I've applied InternalGains:People for thermal comfort assessment. I am not getting what is wrong, please guide me.
I usually input 120W /Person not 120W/m2
I did the same way. 120 W/person, my mistake actually in typing. It is 120 W/person only.
This seems like a very high people load for such a small space. If these people are still present when you close the doors and windows and there is no means of introducing dry air to, and exhausting humid air from, the space during those periods, then I suppose I would not be too surprised if the relative humidity reached close to 100%. You could probably write a little SciLab or Python script that tracks the humidity in the space over time, just to get a "second opinion".
Hi Matt! I did different iterations with increasing zone floor area (increased to 22 m2) and keeping the number of occupants same (8), keeping original zone floor area (9 m2) and reducing the number of occupants (from 8 to 1). The trend in relative humidity was same (RH = 100% when windows were closed) in both the cases, except when there was only 1 occupant in the zone. For both the cases, indoor RH nearly followed the pattern of Outdoor RH when there was only 1 occupant in the zone.
I'm not getting why on increasing the floor size the indoor RH reaches 100%. I think 22 m2 floor area is sufficient to occupy 8 occupants in the zone. Also, even if I keep windows ON for 24 Hr then it won't cater my purpose to evaluate the indoor thermal performance of different kind of building materials. Because, the indoor air temperature will get equivalent to the outdoor air temperature. .
I did a back of an envelope estimate using humid air/psychrometry, though have not had time to really double check. It does seem, though, like a single human represents enough latent load to saturate a volume of 22 m2 x 3 m when non-ventilated for 24 hours. When increased to 220 m2 x 3 m, saturation within 24 h is avoided.
I got some improvement in indoor air RH when i applied Air Change per Hour (ZoneVentilation:DesignFlowRate). I applied ACH of 0.5 when windows and door were closed. So, during that time duration indoor RH was in range of outdoor RH.