Re: [EnergyPlus_Support] Thermal Conductance

[Chris Jones <cj@xxxxxxxxx>]

Any algorithm is only as good as its inputs.  The assumption EnergyPlus is 
making is that it has good data re wind speed on the outside, solar direct 
and diffuse on the exterior wall for Surface Ext Convection.  For Surface 
Int Convection assumptions re radiant effects of lighting, and air flows 
due to the HVAC system need to be made.  Does EnergyPlus account for the 
time varying effect of shading devices such as overhangs, building soffits, 
trees etc?  Is the wind speed assumed constant over each hour or 
varying?  For the interior, is the position of lights and diffusers, air 
flows, etc. taken into account when calculating the Surface Int 
Convection?  If the answer to any of these question is No, then a single 
value for outise and inside film coefficent is just as accurate.

At 13:57 02/01/2003 -0600, Michael J. Witte wrote:
>EnergyPlus does account for inside and outside film coefficients, but
>not in the way that this has traditionally been handled in many
>simulation programs. When a film coefficient is used in other
>programs, it is often a fixed value and does not vary. In
>EnergyPlus, not only does this value vary with the conditions of the
>surface and the surroundings, it can also split the radiation and
>convection terms into separate terms. This should result in a more
>accurate solution. The report value in the construction output only
>takes the user-defined portion of the wall construction into
>account. Note that it is possible to obtain the convection
>coefficients as output, if the user is interested in seeing its value
>or how it varies:
>
>Surface Int Convection Coeff[W/m2-K]
>Surface Ext Convection Coeff[W/m2-K]
>
>
>On 2 Jan 2003, at 16:51, Alexander Beisteiner wrote:
>
> > Dear E+ User
> > Looking at the construction output file, I found that the thermal
> > resistance (W/m²-K) of a construction is the sum of the resistances of
> > all layers- of course. But what about the thermal resistance of inside
> > and outside air surface film? Does not E+ account for these values? I
> > am looking forward to your comment. Regards Alexander
> >
> > __________________________________
> > DI (FH) Alexander Beisteiner
> > Forschungs- und Technologietransfer
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> > alexander.beisteiner@xxxxxxxxxxxxxxxxxx
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> > Tel.: 0043/3357/45370-1324
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Chris Jones, P. Eng.
14 Oneida Avenue
Toronto, ON M5J 2E3
Tel. 416 203-7465
Fax. 416 203-8249




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