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Re: [EnergyPlus_Support] Thermal Conductance

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Thermal Conductance
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Thu, 2 Jan 2003 16:58:35 -0600
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Yes, EnergyPlus does account for the time varying shading effect of 
shading devices.  

No, EnergyPlus does not currently use anything other than the wind 
speed on the weather file, and no modification is made for the effect 
that trees, other buildings, etc. might have on a local wind speed at 
a particular surface.  

No, the exact position of the lights and diffusers is not taken into 
account when calculating interior convection.  It does account for 
the fact that radiant energy from people, lights, and equipment will 
be incident on surfaces and can thus impact natural convection at the 
interior surfaces.  

Some HVAC system effects can be modeled by selecting the 
"CeilingDiffuser" interior convection model.  This can be done 
globally using the INSIDE CONVECTION ALGORITHM object, or it can be 
specified for a particular zone using the Zone Inside Convection 
Algorithm field in the ZONE object.

There are also two models for both inside and outside convection.  
For more details on these, see INSIDE CONVECTION ALGORITHM (Input 
Output Reference, p. 10) and OUTSIDE CONVECTION ALGORITHM (p. 11).



On 2 Jan 2003, at 15:32, Chris Jones wrote:

> 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
> > > Pinkafeld GmbH
> > > Steinamangerstrasse 21
> > > 7423 Pinkafeld
> > >
> > > alexander.beisteiner@xxxxxxxxxxxxxxxxxx
> > >  <http://www.fh-pinkafeld.ac.at/> http://www.fh-pinkafeld.ac.at
> > > Tel.: 0043/3357/45370-1324
> > > Fax: 0043/3357/45370/1010
> > >
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> > >
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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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Follow-Ups:
- [EnergyPlus_Support] Performance curve
  - From: HSIEH Chun-Ming

References:
- Re: [EnergyPlus_Support] Thermal Conductance
  - From: Michael J. Witte
- Re: [EnergyPlus_Support] Thermal Conductance
  - From: Chris Jones

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