snow modeling

[malimog]

hi
i am trying to simulate the effects of snow on total moisture content of roof by WUFI PRO.
and i want to know that is there any possibility to change surface temperature and relative humidity of roof(i want to put 0 degree Celsius and 100% rel.) to simulate snow on the roof.i mean i want to keep them constant during the time we have snow on the roof.

i tried another way but it didn't give me logical result.i ran a roof with normal climate then i exported JUST surface temperature and relative humidity and used those to create a climate file then i changed temperature to 0 and relative humidity to 100% for that period we have snow and ran it again with these climate file.
in my result there is not any drying period even for summer and it makes me really suspicious about my results.(i think it was happened because i just export temperature and rel.humidity and neglect the other properties like solar radiation )
so i would be very appreciated if you can help me to solve this problem.
thanks

[Christian Bludau]

Hi malimog,

the second way is a good possibility. What kind of climate data file did you generate? In this case a kli-file with only temperature and relative humidity on the surface will work well, because you do not have to consider about radiation, orientation etc. in this case. You should not use a wac-file for that.
IMPORTANT doing this is to set the heat transfer resistance to ZERO, because you use values directly measured on the surface. Then it should work.

Best regards,
Christian

[malimog]

i used WAC file .
when we want to create kli file we should input monthly average of temperature and rel.humidity?and how about air pressure?
regarding heat transfer resistance ,you mean i have to put 0 for heat resistance for both side(interior and exterior)?

[Christian Bludau]

Did you use the createclimatefile.xls? There is a sheet for kli as well.
Use hourly values for temperature and relative humidity. For the air pressure us a yearly mean or a typical value, maybe 1024 or 930hpa. It is not important, but it may not be zero.
Leave the columns you don´t need empty. In your case you only need three columns: time, out temp and out rh.
The heat transfer resistance is zero for measured or calculated surface data, because there is no resistance to the surface if measured on that. In your case the exterior resistance should be enough to set to zero. For the interior side use the climate you used for your first calculation and the heat transfer resistance of 0.125.

Good success,
Christian

[malimog]

first of all thanks for your quick response.
when we just create a climate file just with temperature and rel.humidity it means that we neglect radiation and rain and etc or by putting 0 for heat resistance we consider those elements?

[Christian Bludau]

But if you use calculated data from the surface, in your first calculation the radiation is included. If I understand you right you wanted to export these data and use it for new calculations.
The heat resistance of zero means that the first element of the construction gets the same temperature as the boundary condition.
Rain is a problem indeed. If you like to calculate with rain, you can put the value in the kli file as well (rain on surface, there is no more information of orientation or inclination). But in the case of a flat roof you usually do not have to consider the rain because of the roofing felt. I most time implement the roofing felt as sd-value in the boundary condition and switch off the rain.
Christian

[malimog]

thanks for your help.
last question ,what is different between different climate formats?wac,kli,wet and etc

[Christian Bludau]

Please refer to the Wufi Help for that question. Search for "Topic 30".
Best regards,
Christian