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Set People and Lights for Internal Mass

asked 2015-07-23 21:39:11 -0500

Eva gravatar image

Hi when the matched surfaces like floor and roof ceiling are translated into Internal Mass in EnergyPlus, how to deal with the internal load?

I mean for light, equipment and people etc, ususally we set x watts per Zone Floor Area. But you know in this case, Internal Mass is not floor area anymore.


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answered 2015-07-23 22:57:35 -0500

Although I would not recommend using the InternalMass object to model changes in thermal mass for floors (and ceilings for multi-floor buildings), I guess you could model certain aspects of building materials using this method.

From the Input Output Reference document:

InternalMass is used to specify the construction/material parameters and
area of items within the space that are important to heat transfer
calculations but not necessarily important geometrically. (For example,
furniture within the space - particularly for large spaces). Internal mass
can also be used for internal walls that are not needed (when
FullInteriorAndExterior Solar Distribution is in effect) for solar 
distribution or to represent many, if not all, interior walls when solar
is distributed to the floors only.

In this case, the use of Lighting Level or Equipment Level can be used to model internal gains. Since, for a given building model, the floor area is fixed, changing the internal loads input from W per floor area to W is not an impediment to the model.

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yes we can do that, thanks rraustad!

In addition you mentioned that internalMass for floors is not recommended , could you please tell me why? This would be very important for me, because I intended to use internalmass to simplify my model.

Thanks again =)

Eva gravatar imageEva ( 2015-07-24 00:42:18 -0500 )edit

Differences in ground heat transfer (and steady state ground temperature) and solar radiation to the floor through windows are probably the most dominant.

rraustad gravatar imagerraustad ( 2015-07-24 10:00:43 -0500 )edit

If you user a floor as internal mass instead of modeling it as a zone floor you will also misrepresent your building area and also any internal loads based on area such as occupancy.

David Goldwasser gravatar imageDavid Goldwasser ( 2015-07-24 10:21:53 -0500 )edit

thanks very much=)

Eva gravatar imageEva ( 2015-07-26 21:10:15 -0500 )edit

answered 2015-07-23 23:00:53 -0500

updated 2015-07-23 23:04:12 -0500

If you are using OpenStudio and have multiple spaces in a single thermal zone, an internal mass object will be made for each pair of surfaces that are matched by spaces within the zone. The internal mass object has an area and a construction. It doesn't matter for this what the floor area or number of people are.

Beyond internal mass made by matched surfaces within a zone you can also add internal mass using the internal load tab of OpenStudio. In addition to just defining an area, you can also define an internal mass area per floor area, or per person.
image description

Lastly if you use interior partitions in your model you can check a box to have them export as internal mass objects.

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thanks David :)

Eva gravatar imageEva ( 2015-07-24 00:54:46 -0500 )edit

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Asked: 2015-07-23 21:39:11 -0500

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Last updated: Jul 23 '15