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can we get the temperature of the air around the outside of a roof surface?

asked 2015-08-22 11:15:27 -0500

oat gravatar image

updated 2017-05-04 09:15:39 -0500

May I ask if EnergyPlus can output the temperature of the air around the outside of surface?

Is it the same as the outside surface temperature?

Or does EP assume that the temperature of the air around the entire building envelope is uniform and equals to the air temperature as specified in the epw weather file for a given hour?

I ask this is because I'm trying to model a PV panel as a shading surface put above the roof surface in close distance. I want to know if the temperature of the air between the PV panel and the roof surface is hot enough to affect the output efficiency of the PV panel, assuming a certain desired temperature range for optimal PV output.

Thanks!

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answered 2015-08-22 15:51:44 -0500

updated 2015-08-22 19:18:58 -0500

If you search in this page on simple PV you will find a section on Integrated Exterior Vented Cavity, which is one of 5 methods available to calculate module operating temperatures. This is will let you do building integrated PV with a naturally vented air cavity. I believe there is an example file installed with E+ as well.

If the user specifies “Integrated Exterior Vented Cavity” for this parameter, then the temperature result for the exterior cavity is used for the cell temperature. Also the energy exported from the baffle surface as electricity is deprecated using a source term in the baffle’s temperature modeling.

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Hi Which Example file you are referring to? I am having trouble to go through this approach.

s_pourm gravatar images_pourm ( 2015-10-19 14:01:29 -0500 )edit

GeneratorswithPV.idf uses SURFACEPROPERTY:EXTERIORNATURALVENTEDCAVITY
ShopWithSimplePVT.idf uses SOLARCOLLECTORPERFORMANCE:PHOTOVOLTAICTHERMAL:SIMPLE

At first glance, didn't see an example that used both of these

David Goldwasser gravatar imageDavid Goldwasser ( 2015-10-19 14:39:09 -0500 )edit

Thanks David In my model, I have a fan working with BIPV/T system, But I don't know how can I add that. are all the models based on natural ventilation?

s_pourm gravatar images_pourm ( 2015-10-19 15:36:20 -0500 )edit

Thank you very much, David, for your advice.

oat gravatar imageoat ( 2018-04-05 03:12:41 -0500 )edit
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answered 2015-08-24 10:42:38 -0500

The local outdoor atmospheric properties (temperature and wind speed) are calculated independently for each surface, zone, and outdoor air node. The calculations of these properties are described in the Engineering Reference here. These calculations can be controlled with coefficients of a Site:HeightVariation object.

The calculated properties can be output from the model by requesting the output variables described here.

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Thank you very much, Eric, for your detailed advice. Will take a look of the references you suggested.

oat gravatar imageoat ( 2018-04-05 03:13:12 -0500 )edit
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answered 2015-08-24 10:20:02 -0500

NickC gravatar image

updated 2015-08-24 10:21:36 -0500

Hello Oat; I'm also interested in the answer to your question "...does E+ assume that the temperature of the air around the entire building envelope is uniform and equals to the air temperature as specified in the epw weather file for a given hour?"

My assumption was that E+ did not perform complex exterior air calcs (like finite element or finite volume solutions)...perhaps I am mistaken!

I was searching around in the E+ engineering reference and came across the following exterior surface object SurfaceProperty:ExteriorNaturalVentedCavity and felt it might be of use.

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Asked: 2015-08-22 11:15:27 -0500

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Last updated: Aug 24 '15