[esp-r] Re: FW: surface fluxes

Sun May 16 11:15:55 BST 2010

Dear luckygrass,

I have read your comments on espr-list, sorry I’m not an ESPr user, but what
is necessary to say is if you are considering that the U value has really no
sense on a transient simulation, because external temperatures are varying,
and so the ventilation inside the gap of the double skin. You could in same
way “fool the code” (I don’t know how to do it in espr because I’m not an
user) but if it is possible you could impose constant temperatures (outside
and inside) and obtain the heat flux through the façade, then divide by the
temperature difference, and you”ll get an U value.

Other way, could be, simulating some hours or a day, and postprocessing for
each instant, the heat flux through the façade, dividing by the difference
temperature for that instant. In this way, you will obtain a series of U
values, and you could obtain the mean.

But you”ll see that if you consider night and day, the results of U value
will be disappointing (because the transient conditions impose than during
night and day the results will be different and the mean has no sense) May
be you could try the same calculation, with central hours of a summer and
winter day, and obtain data relevant for you.

I have calculated some U values for double facades, with a transient code,
imposing constant conditions, with the only intention of comparing with
other U values, but I repeat this value has no sense on a transient
simulation.

I hope I could help you.

;-)

2010/5/16 Achim Geissler <achim.geissler at intergga.ch>

> Dear Daisy (?)
>
> that all the said values are zero is strange. I just checked the results of
> a double facade model and e.g. conduction(inside) is not zero for the glass
> surfaces both facing the zone and the facade gap. Which save level are you
> using? 4?
>
> Also, WIS calculates U-values for double facades both unventilated and
> ventilated (based on the approach described in ISO 15099). So, as "facade
> description", this may suffice.
>
> For the combination "building and facade", it is tricky. Any loads reported
> by ESP-r take storage effects into account, also. So it will be very
> difficult if not impossible to derive a meaningful U-value for a double
> facade (loads, gains, losses across two or more zones) from the results
> given. Additionally, all the convective heat transfer coefficients in ESP-r
> are not the same as used in standard U-value calculation by default.
>
> However, in my experience, the facade must be described by the standard
> numbers (non-transient U-value, g-value) anyway, so a contractor can deliver
> to those numbers. Which values are most beneficial to the system "building"
> must be derived from the overall model based on loads and / or comfort
> criteria results from ESP-r. Going back and forth, one could optimize the
> facade parameters to meet the building situation in this way and have a
> "contractor-ready" description of the facade parameters to hand.
>
> Best
> Achim
>
>
>
> On May 16, 2010, at 3:15 AM, 王菊花 wrote:
>
> Dear Achim,
>     I am sorry I have't expressed my minds clearly.I know there is no
> straightforward way to calculate U-value,which is exactly what I mean.So I
> want to find an easy way to do that,U=Q/⊿T.Q is the heat conduction of the
> double-skin facade.⊿T is the temperature difference of interior and
> exterior surfaces.As you say,using a simple tool like WIS can calculate U
> value.But there are many openings for the exterior glass of double-skin
> facade in my model,so there is ventilation between the air gap and
> environment.I realize this by building zones for the air gap area and flow
> connections for the openings.I try to  use* result analysis >surface
> fluxes>* *conduction(inside) or conduction(other face) *facility in
> esp-r,the output results are all zero.Maybe it is not practical to
> calculate U value in this way,I thought out another way to do this.I can use
> WINDOW5.0 to calculate U value of double-skin facade without
> ventilation,then campare loads of double-skin facade with and without
> ventilation in esp-r,divide the load difference by ⊿T.Suppose the result
> is ⊿U,then plus ⊿U with U value of double-skin facade without
> ventilation.Does the final result make sense?Anxiously expecting your kind
> answers.Many thanks.
>
>
>
>
>
> ------------------------------
> CC: esp-r at lists.strath.ac.uk
> From: achim.geissler at intergga.ch
> To: luckygrass100 at hotmail.com
> Subject: Re: [esp-r] surface fluxes
> Date: Sat, 15 May 2010 19:20:29 +0200
>
> Hi
>
> not sure what you mean. What turned out zero? All the values in the
> res-variables you name? Or your subsequent calculations? Anyway, there is no
> straightforward way to extract the U-value (if that is what you mean with
> comprehensive transfer coefficient) of a double facade construction.
>
> I would recommend using a simple tool like WIS to compare your window /
> facade constructions in regard to basic parameters (g-value, U-value). And
> look at overall loads to compare the impact on the building as a system.
>
> Regards
> Achim
>
>
> On May 15, 2010, at 1:31 PM, 王菊花 wrote:
>
> Dear Dear all，
>    I am puzzled again.I am simulating an low-carbon building with
> double-skin facade for the south facade.I need calculate out the
> comprehensive transfer coefficient h(W/m2.K),then compare it with that of
> normal single window.I was thinking maybe I can output the temperature and
> heat conduction of the interior and exterior surfaces.But when I used the
> *surface fluxes* facility,and choosed *conduction(inside) or conduction(other
> face),*it turned out all zero.Why?
>
>
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-- 
Débora Faggembauu
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