[bldg-sim] EnergyPlus - DOE

[Shaun Martin]

Brent, my 2 cents.  If all you want is building-scale energy results, a
model employing simplified zoning (eg 5 zones per floor) is fine and you'll
get reasonable runtimes. If you want to use EnergyPlus for design (eg
10-20-30 unique zones per floor), expect much longer runtimes.  If you have
errors-warnings-cautions coming out of your model, 4 minutes can easily
become 4 hours. Mahabir, this sounds like what may have happened to you. E+
just doesn't stop after a sensible number of errors has been generated, and
there are several different types of problems in a model that can cause a
simulation to run on interminably.  It's only when you're model is reaching
completion that the runtimes improve.

Renato, have you looked through the gettingstarted.pdf and
engineeringdoc.pdf? These describe a lot of the differences.

Shaun Martin



 -----Original Message-----
From: bldg-sim at gard.com [mailto:bldg-sim at gard.com]On Behalf Of Griffith,
Brent
Sent: January 19, 2006 10:56 AM
To: bldg-sim at gard.com
Subject: [bldg-sim] EnergyPlus - DOE


  Here is some more information on EnergyPlus simulation run times.

  I recently did a study with 5,374 EnergyPlus baseline models covering
virtually every kind and size of commercial building out there (as reflected
in 1999 CBECS public use data).  These are all full-blown, annual building
models with 5-zone-per-floor thermal zoning, 15-minute timesteps, PSZ and
VAV HVAC systems, etc, etc.

  Here is a summary of the run times I encountered:

  Average:  4.53 minutes
  Standard Deviation: 3.15 minutes
  Minimum: 0.92 minutes
  Maximum: 16.6 minutes

  These were run on 3GHz, 64 bit AMD processors running Linux with a
64-bit-compile of Version 1.2.3.

  I have learned the hard way that it is entirely possible (and quite
tempting) to create overly-complicated EnergyPlus models that will lead to
excessive run times.  To speed things up, use Zone multipliers wherever
practical and keep the number of windows and surfaces low.   I also set
Minimum System Timestep to 5 minutes, and Maximum HVAC Iterations to 5.

  Brent Griffith, NREL



   -----Original Message-----
  From: bldg-sim at gard.com [mailto:bldg-sim at gard.com]On Behalf Of Mahabir
Bhandari
  Sent: Wednesday, January 18, 2006 11:41 AM
  To: bldg-sim at gard.com
  Subject: [bldg-sim] EnergyPlus - DOE


    Brian,



    I think one additional difference from uses’ point of view, which is not
reported in this report, is simulation run time. It seems EnergyPlus takes
5-10 times longer to complete a whole year simulations than DOE2. I was
running a simple 5 story building with VAV system and it took me more than
40 minutes for annual hourly simulations (1 hr time step) in EnergyPlus
while eQuest could run the same building in less than 5 minutes. I am
interested in hearing from others on the run time issue.



    Mahabir Bhandari






----------------------------------------------------------------------------

    From: Brian Fountain [mailto:bfountain at greensim.com]
    Sent: Wednesday, January 18, 2006 12:12 PM
    To: bldg-sim at gard.com
    Subject: [bldg-sim] EnergyPlus - DOE



    That is a big question.



    For a comparison of current energy simulation software, you could look
at Dru Crawley’s paper comparing 20 tools:

    http://www.energytoolsdirectory.gov/pdfs/contrasting_the_capabilities_of
_building_energy_performance_simulation_programs_v1.0.pdf



    Main differences between DOE and EnergyPlus:

    1)      DOE calculates the space loads for each hour then calculates the
system and plant response for each hour.  EnergyPlus simultaneously solves
the loads the system/plant response for each timestep.

    2)      DOE has a fixed 1 hour timestep, EnergyPlus has a variable
timestep (down to 1 minute?).

    3)      There are also key issues with the weighting factor assumptions,
the wall convective coefficients.



    I haven’t used EnergyPlus much yet.  What did I miss guys?



    Brian Fountain



    -----Original Message-----
    From: bldg-sim at gard.com [mailto:bldg-sim at gard.com] On Behalf Of Renato
Sousa
    Sent: January 18, 2006 10:56 AM
    To: bldg-sim at gard.com
    Subject: [bldg-sim] EnergyPlus - DOE



    Hello everybody.



    I would like to know if anybody has experience on using both EnergyPlus
and DOE.

    Currently I'm using an interface for EnergyPlus. From the software
description I couldn't find out the main differences between EnergyPlus and
DOE. Does anyone know the main differences or where can I find them?



    From the description it is said that EnergyPlus was based on DOE and
BLAST so I suppose EnergyPlus has some extra features but I'm not sure if
that is right.



    Best regards,

    Renato Sousa

    Tel: +351 919 316 221 | E-mail: renato.sousa at fluidinova.pt



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