[EnergyPlus_Support] Re: Ground heat transfer from an uninsulated floor of an unconditioned sunspace

["ooikoonbeng" <ooi_kb3@xxxxxxxxxxx>]

i believe the ultimate objective of the SLAB or BASEMENT programs is to get a more accurate estimate of the energy used to condition the indoors. 

The SLAB and BASEMENT preprocessors calculate the 3-D heat transfers and will give the outside face temperature when the indoor air is maintained at a certain temperature. The computer runs with a constant indoor temperature until the outside face temperature converges. This may take several years.  

The outside face temperatures are then used in the monthly fields of the Site:GroundTemperature:BuildingSurface object. If one knows how often the thermal diffusivity changes (in practice this could be changes in the soil moisture, which is a main variable affecting the thermal diffusivity) throughout the year, then one can run this the preprocessor with different soil thermal diffusivity to get more accurate monthly outside temperatures.     

The Auxiliary Programs documentation also shows the minimal, less than 1C change in the outside face temperature when the indoor air temperature varies sinusoidally with an amplitude of +/- 2C.

Just my small contribution to this discussion. Best regards, ooi

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Joe Huang <YJHuang@...> wrote:
>
> Ed,
> 
> I think you're right. SLAB is a stand-alone 3-D conduction program for the foundation and 
> subsoil, using the room air temperature as the indoor boundary condition.  If your 
> building has lots of solar gain, did you ever experiment with inputting the "sol-air" 
> temperature of the slab surface in place of the room air temperature?  That might be more 
> defensible than manually adjusting the slab temperature values.  Of course, the best 
> solution would be to actually
> couple a slab model with the zone model, so there's proper feedback between the two. 
> Various people have looked into this, going as far back as the early 1980's (Zulfi Cumali, 
> Moncef Krarti, etc.).  Someone who's looked into this lately with EnergyPlus is Neal Kruis 
> of Big Ladder Software, but I understand Neal is out of the office this week.  Hopefully, 
> Neal might be enticed to share his thoughts on this topic :-)
> 
> Joe
> 
> Joe Huang
> White Box Technologies, Inc.
> 346 Rheem Blvd., Suite 108D
> Moraga CA 94556
> yjhuang@...
> www.whiteboxtechnologies.com
> (o) (925)388-0265
> (c) (510)928-2683
> "building energy simulations at your fingertips"
> 
> 
> On 6/4/2013 10:24 AM, Edward G. Lyon wrote:
> >
> > My most recent analysis was an unconditioned building with lots of solar gain.  I tried 
> > iterating slab with calculated space temperatures, but it would not match my measured 
> > conditions during the summer. I could only match measured summer conditions by manually 
> > inputting under slab temperature values.  I think a hint about the issue is that slab 
> > works with the space temperature but does not concern itself with solar gain.  Slab 
> > probably works fine for a dark basement.
> >
> > *Ned Lyon, P.E. (MA, WV)**
> > *Staff Consultant
> >
> > *SIMPSON GUMPERTZ & HEGER***
> > 781.907.9000 main
> > 781.907.9350 direct
> > 781.907.9009 fax
> > www.sgh.com
> >
> > *From:*EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] 
> > *On Behalf Of *FrancescoP
> > *Sent:* Tuesday, June 04, 2013 12:49 PM
> > *To:* EnergyPlus_Support@xxxxxxxxxxxxxxx
> > *Subject:* [EnergyPlus_Support] Re: Ground heat transfer from an uninsulated floor of an 
> > unconditioned sunspace
> >
> > I add that I'm considering F. Droulia et al (2009) "Ground temperature estimations using 
> > simplified analytical and semi-empirical approaches" and other methods in order to 
> > estimate the ground temperature to use in the object Site:GroundTemperature:BuildingSurface
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx <mailto:EnergyPlus_Support%40yahoogroups.com>, 
> > "FrancescoP" <fpasserini.tn@ <mailto:fpasserini.tn@>> wrote:
> > >
> > > I'm modelling an unconditioned sunspace. The floor is not insulated: it is made by 10 
> > cm concrete and then there is the ground. The adjacent building is unconditioned too. It 
> > is situated in an Alpine region in Northern Italy. I have to validate the model through 
> > a comparison between the output data of the simulation and the monitored data.
> > > I wondering whether using the "slab pre-processor" would be the best solution. In 
> > fact, in the model of the "slab pre-processor" the internal temperature has a sinusoidal 
> > hourly variation while in my case the internal temperature changes quickly and 
> > irregularly and because of the solar radiation the temperature inside the sunspace is 
> > often very different than the outdoor air.
> > > I think that an alternative solution could be modelling the floor considering not only 
> > the concrete, but also a depth of the ground. I have calculated the thermal trasmittance 
> > through the ground between sunspace and external environment with a FEM software, then I 
> > have createe a construction with 10cm concrete + ground (50cm ?) + "virtual layer" in 
> > order to match the calculated U-value. On the bottom side of the construction, in the 
> > field "Outside Boundary Condition" of the object BuildingSurface:Detailed relative to 
> > the floor, I'm trying using both using "Outside" and using "Ground" but I see only a 
> > small difference, probably because of the great thickness of the ground layer.
> > > Any suggestion, please? Should I use the "slab pre-processor"?
> > > Moreover, I think the problems that I have with the validation concern also the 
> > distribution of solar radiation, but for this message I think I have written enough :-)
> > > Regards
> > > Francesco Passerini
> > >
> >
> >
>



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