[EnergyPlus_Support] Re: Ventilated loft space - no infiltration through ceiling

["k.rosemeier" <k.rosemeier@xxxxxxxxxxxxxx>]

Thanks, Jean,

I already modelled "the hard way" with Attic as a zone, using AFN (assuming cracks in roof and ceiling).

I probably did not make my problem completely clear (was in a hurry earlier): I am after the air change rate of the rooms under the ceiling. I get results for all rooms with an exterior surface, but for a corridor (no exterior surface), I get 0. I am however assuming that there will be air exchange through the ceiling, as the ceiling has defined cracks. This is however obviously not counted as outdoor air exchange, as the ceiling has a Surface boundary condition (due to there being an Attic zone on top). 

Basically, what I would like is: outdoor air exchange rate + leakage through the ceiling for each zone. While I acknowledge that the air from the ceiling is not complete fresh, leakage from there would count towards n50, if I were to do a blower door test for the house. This is the situation I am trying to emulate.

I was toying around with SurfaceProperty:OtherSideConditionsModel and SurfaceProperty:ExteriorNaturalVentilatedCavity, but that doesn't get me there.

Is there another way?

Kara



--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jean marais" <jeannieboef@...> wrote:
>
> Very good question. I can think of two approaches...we can discuss the pros and cons of each:
> 
> 1) Model all above ceiling constructions with shading groups. Here I would suggest to set NoWind and NoSun to a) avoid false solar and b) stop the program thinking that the ceiling is fully exposed to wind...the shading group does not effect wind. The ceiling boundry condition is outdoors. This may be a good approach if there is little or no impact expected from the roof space (due to equipment heat for example). A well ventilated, uninsulated roof space. One could also consider applying othersidecoefficient to place a schedule set varying temp on the outside skin of the ceiling construction.
> 
> 2) Model the unconditioned roof space as a zone and make use of AFN or other infiltration and ventilation objects. This is far more complex. Roof overhangs must be modelled with shading groups (see tips and tricks). The only advantage is the inside roof air temperature may be predicted (but it may be questionable as to how accurately as the assumptions and set up of the natural ventilation is hard and inexact) allowing also for the heating up of the roof space somewhat more than the outside air temp (but is dependant on venting as to how much) during both summer and winter.
>




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