Modeling soffit conditions, crawlspaces, etc

Michael Hurd · Post by **Michael Hurd** » Thu Aug 04, 2011 9:49 am -1100

Many of our buildings have floor slabs that extend past the face of the building below creating a soffit condition that requires insulation of the floor slab, in addition we frequently have crawlspaces that occur below the lowest level of a building - these spaces would be ventilated per our bldg codes - my question is whether or not there is way in WUFI to model either of these conditions?

Daniel · Post by **Daniel** » Sun Aug 07, 2011 8:56 pm -1100

Dear Michael,

you can try to simulate your building component including for example 1 m of earth to consider the thermal inertia of the soil - on the bottom you can use for example measured soil temperatures (we have some in the Holzkirchen climate file but they are of course only representative for Germany).

For the crawl spacae you can use an additional ventilated air space between floor slab assembly and soil to approach reality.

At the technical university in Munich and MFPA Leipzig some measurements were performed to check the conditions in crawl spaces. Here the exterior air temperature (ten days average values) varied beween 3 °C and 23°C while in the crawl space only 8 to 20 °C occurred. The RH conditions differ: without a foil on the soil the RH in summer rises most time to values between 90 and 100 % - with a foil the RH is close to the outdoor climate.

So maybe a simple approach with a sine curve during the year - a little bit colder in summer and warmer in winter time would be the easiest way for both - without ventilation the conditions should even be closer to the indoor climate.

Hope this helps a little bit...

best regards
Daniel

Michael Hurd · Post by **Michael Hurd** » Wed Aug 17, 2011 11:28 am -1100

Daniel, the particular crawlspace that I am trying to model has a vapor retarder on the earth and the crawlspace is ventilated to the outdoors - I am expecting that the temperature and humidity of the space will be very similar to the outdoor conditions - however, I don't think that WUFI will allow me to place an outdoor condition on the underside of the elevated structural slab, won't it place the outdoor condition on top, thinking its a roof I'm modeling?

Daniel · Post by **Daniel** » Wed Aug 17, 2011 8:18 pm -1100

Dear Michael,

on the left side you can use the outdoor climate either as a sine curve or with the outdoor temperature and RH to be on the safe side.

On the left side is the outdoor climate on the right the indoor climate - you only have to consicer the correct order of the layers - the difference between roof and crawlspace you can take into account by switching off rain and radiation absorption and emission and maybe by adapting the surface transfer coefficient...

best regards
Daniel