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

["Jean marais" <jeannieboef@xxxxxxxxx>]

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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