[Bldg-sim] TRANSFER FUNCTION FOR HEAVY AND THICK WALLS
Joe Huang
yjhuang at whiteboxtechnologies.com
Fri May 16 15:28:10 PDT 2014
Correction to typo below.
Joe
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
http://weather.whiteboxtechnologies.com for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
On 5/16/2014 3:16 PM, Joe Huang wrote:
> Luis,
>
> I'm not sure if I have an answer for your problem, but I want to point out some
> technical details that may be being overlooked.
>
> 1. DOE-2 does not use CTFs, it uses Response Factors, which shares the same approach as
> CTFs but uses a different formulation.
>
> 2. When DOE-2 says it cannot simulate a layer because it's too thick, that's not because
> the RF methodology fails but because DOE-2 has a maximum of 100 time-steps, i.e., 100
> hours, for the three response factors (X,Y,Z) to converge to constant COMMON RATIOs that
> are used to compute the residual responses from that point on.
>
> 3. There are two situations that could cause such convergence problems - (a) the layer
> is simply too massive. I know from trial and error that the thickest single-layer of
> dirt allowed in DOE-2 is 5.25 ft (1.6 meters), (b) this thickness will be greatly
> reduced if there are multiple layers with contrasting thermal properties; again, from
> trial-and-error, if there is a layer of insulation below the dirt, the maximum allowable
> thickness of the dirt layer will be reduced by half or more. You've mentioned that
> someone has mentioned creating multiple thin layers. This will do help with (a), but
> could help with (b), provided that the
should be "This would not help with (a), but would
help with (b), provided that the ..."
> thin layers are graduated in their thermal properties; I've never tried this so I can't
> tell how much benefit would there be, but my guess is not very much.
>
> 3. I don't know EnergyPlus well enough to say whether it has a similar hard limit on
> convergence and if so, what is it. If not, you might be able to model the same layer in
> EnergyPlus and not encounter any difficulties.
>
> 4. If all else fails, as others have already mentioned, you can do an explicit solution
> using the Finite Difference Method in EnergyPlus, but expect that to slow down your
> simulations considerably.
>
> Joe
> Joe Huang
> White Box Technologies, Inc.
> 346 Rheem Blvd., Suite 108D
> Moraga CA 94556
> yjhuang at whiteboxtechnologies.com
> http://weather.whiteboxtechnologies.com for simulation-ready weather data
> (o) (925)388-0265
> (c) (510)928-2683
> "building energy simulations at your fingertips"
>
> On 5/16/2014 6:37 AM, Luis Miguel Blanes Restoy wrote:
>> Luis
>>
>> You may explore E+ different ways of dealing with CTF (state space method mainly). CTF
>> calculations become unstable for short time steps and massive constructions (it is at
>> the end a computational problem). E-Quest may decide on your arrangement to be unstable
>> before running the simulation (not sure of this). There are solutions to solve this
>> problem (Seem 1987), and I guess these have been incorporated into CTF calculation
>> within E+. It is a matter of giving E+ a go and try out if your example may work there.
>>
>> E+ also handles Finite Differences Methods for CTF calculations, but I am not versed in
>> this field.
>>
>> You can find more information in the E+ Engineering Reference Manual.
>>
>> Regards
>> Abrazos desde Hibernia
>> Luis
>>
>>
>>
>>
>> 2014-05-16 14:06 GMT+01:00 Luis Peréz-Lombard <lpl at us.es <mailto:lpl at us.es>>:
>>
>> Dear colleagues,
>>
>> As you probably know, Conduction Transfer Function (CTF) method does not handle
>> thick and massive walls, because the accuracy of the CTF coefficients is degraded.
>> In particular, in DOE-2, you get the following message:
>>
>> /“Cannot simulate LAYERS …….. as given. The wall is too thick or too dense”/
>>
>> I have heard of a possible solution to solve this problem by dividing the wall into
>> thin layers. I have made an attempt in e-quest, but the problem remains, and I do
>> not know how to proceed.
>>
>> Any insight on this issue would be appreciated.
>>
>> Sincerely,
>>
>> LPL
>>
>> -------------------------------------------------------------
>> Luis Pérez-Lombard
>> Dr. Ingeniero Industrial
>> Profesor Contratado Doctor
>> Departamento de Ingeniería Energética
>> Escuela Superior de Ingenieros
>> Universidad de Sevilla
>> Camino de los Descubrimientos s/n
>> 41092 SEVILLA
>> Tfno.: 95.448.72.56
>> Fax: 95.446.31.53
>> e-mail: lpl at us.es <mailto:lpl at us.es>
>> -------------------------------------------------------------
>>
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>>
>>
>> --
>> LUIS M BLANES RESTOY
>> *IRUSE
>> *INFORMATICS RESEARCH UNIT FOR SUSTAINABLE ENGINEERING
>> www.iruse.ie <http://www.iruse.ie>
>> mobile Ireland: +353 83 1346875
>> mobile Spain: +34 609097818
>> skype: lmblanes
>> email: lmblanes at gmail.com <mailto:lmblanes at gmail.com>
>>
>>
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