Re: [EnergyPlus_Support] Re: double skin + internal blinds + daylighting dimming: possible and reliable?

Dear Pedro,

Thanks for the tip about reporting the inside temperature of the outer skin to get the shading temperature!

Regarding the wind data, my usual approach is to not iuse wind data to size a naturally ventilated space and first rely on stack effect to determine opening size requirement. I do that because then I size based on the minimum available pressure difference which ensures that the space will have this or greater pressure difference if there is wind provided that opening are sized and located so that wind cannot be a counter pressure. The second reason is what you pointed pout about wind data. Personnally I don't really have a reliable database about it and it is quite costly to get it either from a dedicated database or a CFD specific application. That has been so far my design approach but I am opened to critic!

Now about your comment on the blind slat width that will impact the separation parameter if one wants to keep a constant number of slats, what you say is right but in my case, since I wanted to try the combined effect of the slat as a solar shading AND as a light shelve, I put it horizontal. If it is horizontal, how does the program handle the number of slat as a function of their separation? I believe it matters not because a horizontal slat has no projection on the glazing area therefore it occupies the same space and only the separation is involved in the calculation...What do you think?

As for the daylighting, I still have to dig. I am currently comparing dynamic results from Eplus with a daylight software to evaluate my approach...

Thanks!
Aymeric

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Pedro Peixeiro <ppeixeiro@...> wrote:
>
> Aymeric,
>
> If you mount a shading device in your DSF and you dont ventilate it, it
> will heat up considerably. this is a problem that can occur even during
> the winter if the climate is predominantly hot. I would point out
> initially for a ventilated façade, even if its just to prevent it from
> heating up too much and cause an adittional heating load into the main
> zone. Run some tests and check surface temperatures (note: if you report
> the surface inside temperature for the outer pane of the DSF, you'll get
> the shading temperature) and overall heating loads. It will all depend
> mostly on climate, and make sure you use reliable data on wind speed and
> direction, it will influence a lot DSF natural ventilation (i'm assuming
> you'll use Airflow Network).
>
> As for the blind simulation: if you want to check the difference with
> slat width, don't forget to change the slat separation accordingly. if
> you don't, E+ will proportionaly increase the number of slats according
> to the change you make in the slat width, in order to occupy the entire
> glazing area.
>
> As for light shelves is concerned: unfortunately i'm not a daylight
> expert, can't give you any special advice on how to model them other
> than to follow instructions on the I/O reference. but i would guess
> that, depending on the blinds, you could benefit from the shelves since
> daylighting would normally be reduced when the shading is on. I would
> also suggest using DElight objects, they seem to be able to handle
> inter-reflections better (Eng. Reference, pag 183).
>
> Pedro
>
>
>
>
> On 02-03-2011 3:36, aymericnovel wrote:
> >
> > Hi Pedro,
> >
> > From what I read at p.444, E+ can handle daylight through the DSF but
> > won't manage all inter reflexions, especially those going out on the
> > other side of the zone. But that can be surely considered as a small
> > fraction.
> >
> > As for the DSF, it is a summer dominated climate so the main use if
> > ventilated cavity. However, the whole simulation study is broader and
> > aims at determining if the DSF should be tightly closed and vented in
> > summer to allow a double use and act as a buffer in winter of if we
> > should just let it not tight and therefore design it like a giant
> > external shading only used for summer protection. Given the low degree
> > days in this location I believe we are likely to go for option 2. It
> > is also of course a question of cost and fire safety considerations.
> >
> > For the blinds I was trying to understand what the model was actually
> > doing so I have been varying the slat width, separations and visible
> > reflectance. Separation and reflectance variations showed logical
> > results and sensitivity but slat width variation, as I said before,
> > when getting close to 0, should give results closer and closer to the
> > "unshaded" simulation. But it is not, and far from that. So I assume
> > the whole blind model for daylight works only in a typical range of
> > blind geometrical properties because I don't observe continuity of
> > results.
> >
> > I don't think it is very useful to be used as a light shelve anyway
> > because it is so glazed, but lighting requirements are high too and
> > take a major part of the bill so it deserves a triple check to know if
> > I can or cannot bring more light deeper in the space.
> >
> > but if you have another idea to model a light shelve in the DSF cavity
> > and correctly determine its solar shading and light shelve combined
> > effect, I'll take any advise because this is typically a case where it
> > is difficult to know where the program is reliable or not...
> >
> > Regards,
> > Aymeric
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, Pedro Peixeiro
> > <ppeixeiro@> wrote:
> > >
> > > Hi Aymeric.
> > >
> > > The calculation method for daylight takes into consideration the
> > > presence of a DSF when one exists (I/O reference, pag. 444). As for the
> > > construction being fully glazed, its an interesting case scenario.
> > Can't
> > > provide you with an answer, but i'm also curious as to know if E+ can
> > > handle all the transmissions/reflections that occurs in such a zone.
> > >
> > > Some questions: do you have some kind of ventilation on your DSF or is
> > > it acting like a buffer? And what parameter or parameters of the blind
> > > are you actually using to reduse its size?
> > >
> > > Pedro.
> > >
> > >
> > > On 01-03-2011 9:56, aymericnovel wrote:
> > > >
> > > > Dear all,
> > > >
> > > > I am facing a quite challenging design right now and I a m not
> > sure if
> > > > the current Eplus can do it. the software isn't bugging but I am
> > > > worrying about the validity of the model.
> > > >
> > > > Rough description is:
> > > > Fully glazed double skin open space for sport activity
> > > > 10m floor to height ceiling and 64m side lenght (it's a square)
> > > > Double skin design (double pane for internal skin and simple pane for
> > > > external skin)
> > > >
> > > > So far I have not even tempted to read results obtained from the real
> > > > architecture that includes some details that makes it not exactly a
> > > > square geometry. I want to validate the simple square model.
> > > >
> > > > I am not sure of:
> > > > 1) Is the geometry not compatible with energy plus daylighting
> > > > calculation capabilities (flux split method is said to be limited to
> > > > cases where room depth is less than 3 times floor to height ceiling):
> > > > Here it is not the case but the space is fully glazed.
> > > >
> > > > 2) Is the daylighting model capable of properly handling the daylight
> > > > distribution in the sport area with a double skin zone between it and
> > > > outside?
> > > >
> > > > 3) If 2) is possible, what happens if I put a blind in the double
> > skin
> > > > zone? I have tried many simulations and I believe this is not working
> > > > well. When one tries to reduce the blind dimensions to almost nothing
> > > > to get close to the case where there is no blind, results don't
> > get close.
> > > >
> > > > It is a very tricky design and the architect counts on these
> > > > simulations to be sure of his facade design. Of course it is a hot
> > and
> > > > sunny climate so the guy came and said "hey, can you help me doing an
> > > > energy efficient glass cube under the sun?".
> > > >
> > > > Any help on the above questions and/or about a proper methodology to
> > > > assess such a case would be immensely appreciated!
> > > >
> > > > Thanks a lot!
> > > > Aymeric
> > > >
> > > >
> > >
> >
> >
>