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Does OpenStudio or Energy plus actually output loads calculated for sizing purposes?

asked 2018-11-13 17:18:41 -0600

jmbattis gravatar image

I am trying to run my energy model as a load model (rather than construct a new one in another software) and am wondering where I can find the results of the system sizing portion of the simulation. Seems like it should be pretty straightforward, but I'm having difficulty getting this information. I'm running with Ideal Air Loads enabled and simply want to know peak heating and cooling load. Originally I simply took this from peak heating/cooling demand from the annual simulation, but realized that this inaccurate as it allows for internal gains, solar gains, and thermal mass to play into the equation...things that are not desirable when sizing. I also tried summing each of the individual design loads and ventilation load, but realized that these peaks don't necessarily coincide - resulting in an overestimate in load.

Where is the system level sizing information stored and/or how can I calculate from the results?

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answered 2018-11-15 13:09:07 -0600

  1. All EnergyPlus sizing calculations will include internal gains, solar gains, thermal mass, etc. unless the user inputs remove them. For example, all of the SizingPeriod:DesignDay objects for heating which are in the ddy files bundled with the weather files have zero sun and constant outdoor temperature for the WinterDesignDay. Also, internal gain schedules should be zero for day type "WinterDesignDay". These inputs effectively remove all of the above from the heating sizing calculations. For cooling sizing, you want all of these items to be included.

  2. With ideal loads, run the design days only, and take the peak loads from there. See SimulationControl "Run Simulation for Sizing Periods". The system "coil" loads are reported as output variable "Ideal Loads Supply Air * ".

  3. If you want EnergyPlus to do system-level sizing, then you'll need to add a full HVAC system with appropriate Sizing:System inputs.

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To follow up:

  1. Yup! And it seems that OpenStudio is smart enough to do this automatically. The default lighting, occupancy, and equipment schedules are zeroed for the winter design day and maxed for summer. The only reason my "sizing" results were not reflecting this is because I was trying to pull peak load from the annual simulation.

  2. So, in OpenStudio's "Simulation Control," I see "Run Simulation For Sizing Periods." I've toggled this to "Yes" and I assume "Run Simulation For Weather File Run Periods" should be "No" (?).

jmbattis gravatar imagejmbattis ( 2018-11-21 10:12:00 -0600 )edit
  1. ^^

  2. ^^

  3. Vocabulary issue on my end, I think. I simply wanted the total (space+ventilation) load seen by the system.

jmbattis gravatar imagejmbattis ( 2018-11-21 10:13:06 -0600 )edit
  1. You can set both "Run Sizing Periods" and "Run Weather File Run Periods" to yes in the same simulation if you want. The time series output will have data for the sizing periods followed by the weather files periods. But many users do as you suggest, run either the sizing periods or the weather file periods.
MJWitte gravatar imageMJWitte ( 2018-11-23 09:44:33 -0600 )edit

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Asked: 2018-11-13 17:18:41 -0600

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Last updated: Nov 15