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Re: [EnergyPlus_Support] DOE-2 and EnergyPlus calculated different cooling loads for the same building
You say in your response to Edwin that you used Purchased Air, but that is not
the case in the uploaded EnergyPlus input files. These have full-blown VAV
systems. So, it is not clear what is being compared here. Based on a quick
review of the inputs files, there are two obvious factors. One, the EnergyPlus
runs are cooling to 25.56C, while the DOE-2 runs are cooling to 25.1 to 25.3C.
EnergyPlus has no throttling range on the thermostat, while DOE-2 does. Set
the DOE-2 throttling range as small as possible to achieve closer zone
temperatures.
The most likely influence which could produce a near-constant offset in cooling
loads is the foundation. In the EnergyPlus simulation, the concrete floors are
exposed to a constant 18C outside surface temperatures. This is not realistic.
If I remember correctly, in DOE-2, the ground temperatures come from the
weather files, so it's not clear from these files what temperatures are driving
the floors in the DOE-2 model. Looking at the EnergyPlus temperature graphs,
all of the zones are being pulled down to the heating setpoint of 21.1C for one
or more hours at night. The floors are doing this. I suspect the DOE-2 floors
have warmer boundary conditions, so that is why the zones do not cool down as
quickly at night. (Also - note that the floor construction in the DOE-2 file
is wrong for Space2-1.)
I would also recommend using custom weighting factors in the DOE-2 model to
avoid the need to guess at floor weights.
Mike
On 7 Dec 2007 at 16:59, Simge Andolsun wrote:
> Please find the attached EnergyPlus(1) and DOE-2(2) files. These two files are
> supposed to be the DOE-2 and EnergyPlus simulations of the same building. Thus,
> they are supposed to exhibit the same cooling energy consumptions. The cooling
> energy consumptions, however, differ. Please find the attached line graph (3)
> that shows the cooling energy consumption of the building with respect to
> EnergyPlus and DOE-2 simulations on the peak cooling day (3rd of July). The
> DOE-2 output exhibited twice of EneryPlus results. Please also find the attached
> line graphs (4) that show the temperature fluctuations in the interior zones of
> DOE-2 and EnergyPlus spaces. When compared to EnergyPlus simulation, there was a
> time-lag in the temperature fluctuations of the DOE-2 interior space. This made
> us consider FLOOR-WEIGHT factor in DOE-2 as a probable reason. We tried
> different floor-weight values. This however did not help much. Moreover, the
> cooling energy graphs (3) showed a very similar
> behavior although the values were very different. This suggested that there
> might be a single definite reason for the difference in cooling loads
> calculated by the two programs. With your experience on EnergyPlus, which input
> would you recommend us to check as the probable reason for the difference in
> results?
>
> Thanks in advance for your reply,
> ps: If I should upload the attached files, please let me know.
>
> Simge Andolsun
> Graduate Research Assistant
> Texas A&M University
> Energy Systems Laboratory
>
>
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx
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