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Adiabatic in EnergyPlus and Convective heat gain rate

asked 2017-04-06 03:07:20 -0600

lee gravatar image

updated 2017-04-10 08:35:41 -0600

I am studying the effect of altering the insulation performance(u-value) of walls and windows that are directly exposed to ambient air in buildings with high internal temperatures. I use Energy Plus together with design builders.

So other walls (inner wall, ceiling, floor) except the outer wall are setting adiabatic . Because it is only to see change of outer wall.

And I select the output in E+ Surface average face conduction heat transfer rate.

I think, other walls have to have a value of zero except for the outer wall, but it's not. They all have value. Why?

In addition, when the U-value of the outer wall is enhanced, ( I mean that the wall's u-value 0.5 -> 0.2) Outer wall's "Surface inside face convection heat gain rate" value decreased, and other walls values are increased. Why?

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answered 2017-04-06 18:41:20 -0600

From the EnergyPlus Engineering Reference:

"Adiabatic boundary conditions are applied to two surface types in EnergyPlus:

1) Surfaces with adiabatic outside boundary conditions

2) Internal Mass objects

For both surface types, EnergyPlus will apply the same boundary conditions to each side of the construction so that there is no temperature difference across the surface. In this case, all heat transfer into the surface is a result of the dynamic response of the construction to varying inside boundary conditions. The surface will store and release heat only at the inside face of the surface (it is assumed that the outside face is not within the zone). If both faces are within the zone, this situation can be modeled either by creating another adiabatic or internal mass surface with the reverse construction, or, for symmetric constructions, simply doubling the area of the surface."

So the surface is still storing and releasing heat - it is just no passing that on to the outdoors or another zone.

More on the face conduction heat transfer rate.

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Asked: 2017-04-06 03:07:20 -0600

Seen: 413 times

Last updated: Apr 10 '17