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[EnergyPlus_Support] Re: Zone Temperature Peaks too Early
Jeremiah,
Yeah, that's the project. I'm mainly looking at the PCM side. It's difficult to use the other side as a true "control" because of vastly different energy use habits and somewhat different solar exposure.
The model peak offsets are present with and without the PCM, so I'm thinking it's due to something else. I tried updating the shadowing calculation daily and it made very little difference, but I might try the TimestepFrequency just for fun. I'm thinking it has something to do with the way diffuse radiation is modeled, so investigating solar distribution seems like a good next step.
Also, thanks for the Shrestha paper and attached resources. That's helpful.
Jeff
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Jeremiah Crossett <jcrossett@...> wrote:
>
> Jeffrey,
> Agreed about the need to rule out the slab first and then to use
> FullInteriorAndExterior solar calculations. You might also experiment with
> the new TimestepFrequency solar shadowing calculation. Further I suggest
> you use a room air model with a ZoneDryBulbTemperature gradient and that
> you use a full Air flow network with your window sensor results for
> scheduled controls.
>
> This is for the Trek house that is testing of bioPCM by the green
> building research lab that you work at correct?
> https://www.dropbox.com/s/bhefli5om94t9se/PSU-PASSAVE-HOUSE-BioPCM_Poster.pdf
>
> I suppose you are first validating your control case then your PCM case.
> The PCM case should likely be a bit off because of the lack of ability to
> model hysteresis the lack of a defined method to model the effects of PCM
> on convection.
>
> You might read: MODELING PCM-ENHANCED INSULATION SYSTEM AND BENCHMARKING
> ENERGYPLUS AGAINST CONTROLLED FIELD DATA Som Shrestha Page 804
> https://www.dropbox.com/s/8g3q68cs4kx6tum/SOM-PCM-VALA.pdf
> "Among the various algorithms available in E+ for surface convection at the
> inside and outside face of the heat transfer surfaces, "SimpleCombined"
> model showed the best match between measured and E+ predicted outside
> surface temperature and "CeilingDiffuser" model showed the best match for
> inside surface temperature."
>
> And the three attached docs on testing of PCM's and how PCM transition
> effects convection, and how convection effects model results. .
>
> If I where you I might setup a parametric study with jE+ alternating
> through the many convection algorithms to see what shows the closest
> agreement with the experimental data curves.
>
> Looking forward to your results.
>
>
>
> *
> *
> *
> *
> *Jeremiah D. Crossett | Senior Analyst | Phase Change Energy Solutions*
> *
> 120 E. Pritchard St. | Asheboro, NC 27203 | Mobile 503-688-8951
> www.phasechange.com
> *
>
> *
> *
> *
> *
>
>
>
> On Thu, May 9, 2013 at 5:35 AM, Jean marais <jeannieboef@...> wrote:
>
> > **
> >
> >
> > Was the space occupied for your measuring time? i.e. were occupants
> > opening and closing windows? I assume no, but it is a fundimental for how
> > you model "natural ventilation" (which I try to keep mentally seperate from
> > "natural infiltration").
> >
> > For a passive house the effects of infiltration, especially in summer, are
> > probably not the issue here. Infiltration is also less (usually) when
> > mechanical fans are on. I aggree thermal break modelling of either walls or
> > slab as well as the thermal mass effects thereof is probably not the root
> > of the shift.
> >
> > Brent's suggestion of the air node capacity was worth a try as it is
> > thermally a more direct coupling, but as you point out, the main problem
> > here is shift, not amplitude of spike. More accuracy for the slab modelling
> > of a naturally ventilated building has been known to have a large effect in
> > warmer climes and in your case I would do this even if it is also probably
> > not the root of the shift.
> >
> > Solar distribution model is a question. The basic model ("FullExterior")
> > throws all the solar on the floor surface and redistributes the reflected
> > amount area weighted to the rest of the surfaces thereafter. If you are
> > using say an adaptive convection algorithm (several to choose from here),
> > you may find surfaces like walls may not be recieving the energy of the
> > solar in, in the same proportions as they would in reality. The vertical
> > surfaces however normally have a much higher convection coefficient
> > attributed to them (either by the algorithm or user defined) and could
> > possibly play a larger role in speeding up heat transfer from surface to
> > air node. If by accident more energy than in reality is on the floor and
> > ceiling surface with smaller convections coeff.s, it may explain a retarded
> > heat transfer to the air node.
> >
> > So I find the combination of solar radiation distribution model and
> > convection coefficient assignment modelling, may play a role here.
> >
> > Facinating thread, also what Ned said about how SLAB reacted to his
> > measured data. PS keep in mind you may have to itterate a couple of times
> > with SLAB, but don't overkill it, as it is probably not the root issue.
> >
> > Keep us posted,
> >
> > Jean
> >
> >
> >
>
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