Why are people activity schedules all preset to 120 W/person?

asked 2020-09-09 22:39:32 -0500

mikemorris
117 ●1 ●1 ●5

updated 2020-09-10 13:30:41 -0500

Hello,

If this is baseline ignorance I apologize but I've exhausted my research options in trying to find out the answer to this question. In looking through the Input/Output file HereI got a good understanding of the sensible heat fraction that will go to dividing up the people activity into latent and sensible loads. But here are my questions.

how well does the autocalculate end up representing the ASHRAE values for people loads, for example, office being 250 Btu/h sensible and 200 Btu/h latent yet in OS the equivalent would be to set the people activity to approximately 120 W/person and then let the "autocalculate" do its magic to turn that into sensible and latent loads to the space?
When I pull library templates for all the different 90.1 - 2010 space types, the associated people activity schedules are all set to the same 120 W/person. I figured the "small hotel exercise" would want to take credit for people more vigorously moving than a lobby or private office would. Is this just up to the user to override? If that is the case then how is the "create baseline model" measure going about getting these people loads correct?

Again, I've searched a lot to try and find other attempts at answering this question and come up empty so if this is answered somewhere else I'll happily accept being pointed in that direction!

Thank you all!

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answered 2020-09-15 12:10:09 -0500

Jian Zhang
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I found the ACTIVITY_SCH to be 120 for all hours in https://www.nrel.gov/docs/fy11osti/46.... We have not studied the impacts of such assumptions during the DOE Prototype Model development. I don't think we have enough data to define the activity levels by space type. The importance of occupancy schedule inputs by space type is higher order of magnitude than activity levels and it being studied by the BEM researchers. If people need to study occupancy comfort and behaviors using the models, they may use the "autocalculate" option along with careful review or revisions of the occupancy schedules. Otherwise, for typical EEM evaluations, the current assumptions are probably sufficient.

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answered 2020-09-10 10:06:23 -0500

Aaron Boranian

13830 ●76 ●24 http://bigladdersoftware.com/

The "autocalculate" option for the Sensible Heat Fraction input field you're referring to asks EnergyPlus to calculate the sensible/latent split based on the Activity Level Schedule input field instead of being a static user input. In the Engineering Reference section describing how EnergyPlus applies the Fanger comfort model, it shows how the activity level aka metabolic rate is used in the calculations for the latent and sensible respiration loss from occupants as well as the sweat evaporation loss from occupants.
```
LatRespHeatLoss = 0.000017*ActLevel*(5867. - VapPress)
DryRespHeatLoss = 0.0014*ActLevel*(34.- AirTemp)
EvapHeatLossRegComf = 0.42*(IntHeatProd - ActLevelConv)
```
If you wanted to test that the sensible/latent gains from occupants match the 250 Btu/hr and 200 Btu/hr you expect, then you can ask OpenStudio to generate the related output variables for that (People Sensible Heating Rate and People Latent Gain Rate, respectively). Requesting output variables is done in the Outputs tab of the OpenStudio application, and you can then review these in DView or any other tool that can open the ESO file created by OpenStudio.
I've reviewed the 90.1-2013 user's manual where the building envelope trade-off schedules and loads are defined (see below). It looks like the table for sensible/latent gains from occupants is based on building area type -- not space area type within the building. So, all space types within the small hotel will have the same sensible/latent gain split. I may be interpreting that wrong, but the 250/200 Btu/hr split seems to apply to most building area types.

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@Aaron Boranian, thank you for your answer. I appreciated the in depth explanation of how the autocalculate works in the sensible heat ratio formula.

On the 2nd part of this though, i am not sure that i fully agree with the assumption, although i can see where you are coming from in saying that 250/200 applies to most it does not apply to all, and from what i'm seeing in the library files the 120 W/person does apply to all. One example is "full service restaurant" which i would say closely resembles the "dining" categories in your posted table. This is still 120W. See the image above

mikemorris ( 2020-09-10 13:29:42 -0500 )edit

@mikemorris ah, I see your point. I'm gonna rope in some NREL and OpenStudio Coalition folks to see if they can explain why all activity schedules are set to 120 W/person. @David Goldwasser @aparker @macumber