[Bldg-sim] Bldg-sim Digest, Vol 60, Issue 1

[Tianzhen Hong]

You can also look at a state-space model, I developed almost 20 years ago,
that can directly output what you need. The model is now used in a tool
DeST developed by Tsinghua University, China.

Tianzhen

On Thu, Nov 1, 2012 at 1:00 PM, <bldg-sim-request at lists.onebuilding.org>wrote:

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>    1. Re: Estimating system matrix A from simulation engine
>       (Bryan Eisenhower)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 31 Oct 2012 17:24:40 -0700
> From: Bryan Eisenhower <bryane at engr.ucsb.edu>
> To: bldg-sim at lists.onebuilding.org
> Cc: ??? <deukwookim at skku.edu>
> Subject: Re: [Bldg-sim] Estimating system matrix A from simulation
>         engine
> Message-ID: <5091C148.6090501 at engr.ucsb.edu>
> Content-Type: text/plain; charset="utf-8"; Format="flowed"
>
> Deuk-Woo,
>
> I have thought of this a lot before and will outline my experience
> below, in summary, if you are looking for accurate dynamical systems
> matrices from a building energy model (other than a hand-built RC
> network model), you will probably want to learn *Modelica*. Folks in the
> Modelica community have been using this method to study dynamics and
> controls for over a decade in the automotive, aerospace, and other
> industries.
>
> As for other simulation environments, its really up to the one you
> pick.  Remember that the equations in an energy model are an
> approximation to reality.  The numerical solution of these equations are
> yet another approximation to the dynamics in the equations.  So, if you
> are going to do system identification on the model, you are going to get
> artifacts of both approximations.  In my experience, the numerical
> solvers in programs like E+ and TRNSYS are not developed for accuracy in
> dynamics that you would need for this approach.  They are developed more
> for long term analysis and numerical stability - both of which they do a
> great job on.
>
> I have been involved with a project to try and obtain ABCD matrices from
> *TRNSYS*.  In this project, we went into the fortran code and wrote
> extra code to perturb state variables to observe how they relax and
> obtain matrices from this.  We were successful in implementing this but
> did not trust the results because we felt the solver was overwriting the
> short term dynamics in the equations.
>
> I also worked on ABCD matrices using *EnergyPlus*, this time using a
> different approach.  In this approach, I wrote an analytical model that
> can 'talk' to the EnergyPlus input file and .sql database files.  In the
> sql file, there is most of the information about materials (e.g.
> capacitance), as well as all the bookkeeping on view factors and which
> constructions pertain to which zones.  I wrote some scripts that read
> this file and automatically generate a linearized model.  The linearized
> model does not take any time trace information (it does take some
> operating point information).  It was a lot of work and although I trust
> the results, I wouldn't pass on the code to anyone else because it was a
> bit of a mess in the end. I have published this work this year and if
> you would like the papers, please write me personally.
>
> A fourth data point: *IDA-ICE* is another modeling tool that has a nice
> solver should capture short term dynamics.  I asked Per Sahlin at IBPSA
> London this September if there was a way to produce ABCD matrices from
> the model and he said his customers were not interested (my paraphrasing
> - hopefully correct) - which is completely fair.  My understanding is
> that the historical intersection of control analysis and building energy
> models has been on longer time scales (e.g. setback / setpoint analysis)
> or just time trace analysis - very little stability, frequency domain,
> or other advanced traditional techniques.
>
> Good luck!  Since I have thought of this for some time, I'd be
> interested to discuss further with you, especially if you obtain any
> good results.
>
> Bryan
>
>
>
> On 10/30/2012 6:32 PM, ??? wrote:
> >
> > Thank you for your reply.
> >
> > Unfortunately, I?m not familiar with Modelica simulation environments.
> >
> > If you don?t mind, could you please let me know any other ways?
> >
> > Best Regards,
> > Deuk-Woo Kim
> >
> > *From:*Michael Wetter [mailto:mwetter at lbl.gov]
> > *Sent:* Wednesday, October 31, 2012 1:49 AM
> > *To:* ???
> > *Cc:* bldg-sim at lists.onebuilding.org
> > *Subject:* Re: [Bldg-sim] Estimating system matrix A from simulation
> > engine
> >
> > Most Modelica simulation environments allow you to linearize a model
> > at the current state and save the A,B,C and D matrix that are its
> > state-space representation at the point of linearization. See
> >
> > Michael Wetter.
> >
> > Modelica-based Modeling and Simulation to Support Research and
> > Development in Building Energy and Control Systems.
> > <http://dx.doi.org/10.1080/19401490902818259>
> >
> > /Journal of Building Performance Simulation/, 2(2):143-161, 2009.
> >
> > Also available as LBNL Technical Report LBNL-2740E.pdf
> > <http://simulationresearch.lbl.gov/wetter/download/LBNL-2740E.pdf>.
> >
> > where this is demonstrated for a nonlinear heat exchanger model. The
> > Modelica Buildings library
> > (http://simulationresearch.lbl.gov/modelica/) contains a room model
> > which you should be able to use for the same process to get the A,B,C
> > and D matrices for a building model.
> >
> > Best,
> >
> > Michael
> >
> > On Sun, Oct 28, 2012 at 6:54 AM, ???<deukwookim at skku.edu
> > <mailto:deukwookim at skku.edu>> wrote:
> >
> > Dear all,
> >
> > Is there a method to estimate system matrix *A* (of zone or building)
> > from simulation engines such as E+, ESP-r??
> >
> > (The*A* is commonly found in state-space equation, e.g. x? = *A*x + Bu.)
> >
> > As far as I know, only system identification method can be applied in
> > this situation.
> >
> > (but, I not sure that it is reliable)
> >
> > If there is more advanced way or efficient way to estimate *A, *please
> > let me know.
> >
> > Any comments would be appreciated.
> >
> > Thanks in advance.
> >
> > Best Regards,
> > Deuk-Woo Kim
> >
> >
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