[Bldg-sim] Internal Mass Issues with Solar Distribution Model

[Joe Huang]

Jeff,

I wouldn't call it "strange stuff", but more "welcome to the real 
world".  It's always good to remember that
computer models are just that - theoretical representations that may not 
match the real world reality in all
its complexity, i.e., having all the inputs correctly defined doesn't 
necessarily give you the "right" results, especially on something as 
complex as the thermal coupling between the air and the building's 
thermal mass.

For what it's worth, my experience with another not-to-be-named 
simulation program has been that the
models tended to be much "lighter" than observed reality, i.e., one has 
to boost up the internal mass considerably beyond what's there to get 
the floating temperature profiles to match measured temperatures.
I'm not saying it would be the same for EnergyPlus, just that one 
shouldn't assume because one's got the
inputs correct (right surface area, thermal mass, etc.) that the model 
would then be right.

I'm also reminded of a paper by Joe Eto at LBNL back in the 1980's where 
he correlated measured building
energy use against variable-base degree-days and got good results, the 
only defect being that the imputed
building k-values didn't make much sense :-)

Joe


On 1/17/2015 9:21 AM, Jeff Haberl wrote:
> Hello Holly:
>
> FYI...the classic reference on the use of "empirical parameters" is the paper by Janet Manke and Doug Hittle in 1996 about their efforts to calibrate the BLAST program to a building at the Gunnison Airport in Gunnison, Colorado.  In it they show that, when you are calibrating to measured data, the "best fit" values of some of the parameters may have physically unrealistic values...such as the surface area and amount of internal mass in a building...strange stuff...
>
> Jeff
>
> Manke J, Hittle D, Hancock C. Calibrating building energy analysis models
> using short term test data. In: Proceedings of the 1996 ASME international
> solar engineering conference. San Antonio, TX; 1996. p. 369–78.
>
> 8=!  8=)  :=)  8=)  ;=)  8=)  8=(  8=)  8=()  8=)  8=|  8=)  :=')  8=) 8=?
> Jeff S. Haberl, Ph.D.,P.E.inactive,FASHRAE,FIBPSA,......jhaberl at tamu.edu
> Professor........................................................................Office Ph: 979-845-6507
> Department of Architecture............................................Lab Ph:979-845-6065
> Energy Systems Laboratory...........................................FAX: 979-862-2457
> Texas A&M University...................................................77843-3581
> College Station, Texas, USA, 77843.............................http://esl.tamu.edu
> 8=/  8=)  :=)  8=)  ;=)  8=)  8=()  8=)  :=)  8=)  8=!  8=)  8=? 8=) 8=0
>
> ________________________________________
> From: Bldg-sim [bldg-sim-bounces at lists.onebuilding.org] on behalf of Samuelson, Holly Wasilowski [hsamuelson at gsd.harvard.edu]
> Sent: Friday, January 16, 2015 4:13 PM
> To: bldg-sim at lists.onebuilding.org
> Subject: [Bldg-sim] Internal Mass Issues with Solar Distribution Model
>
> Dear Bldg Sim,
> I am trying to understand how the internal thermal mass (aka "InternalMass") is being handled in my EnergyPlus models. On page 222 of the EnergyPlus Input-Output Reference it states, "simplifying calculations using internal mass must be used with caution when the "FullInteriorAndExterior" Solar Distribution model is chosen.
>
> Could anyone kindly help me understand what that means?  Does that mean that my internal thermal mass does not "see" the solar radiation potentially hitting it (which might realistically be the case for certain interior elements if they are always in shade)?  However, would you assume that this internal mass is still exposed to the indoor air, and thus could still be absorbing or emitting heat in that way?
>
> Many thanks for any guidance.
> Best,
> Holly
>
> Holly W. Samuelson, DDes, LEED, AIA
> Assistant Professor Harvard Graduate School of Design
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