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Re: [EnergyPlus_Support] Re: space cooling load calculation for each contributor?
"Opaque Surface Inside Face Conduction" is the most misunderstood report
variable in EnergyPlus. Opaque Surface Inside Face Conduction is intended for
detailed examination of the heat balance on a particular inside surface,
primarly to support comparisons with measured data. It is not meaningful as a
component of the current heating or cooling load. Surfaces interact with the
zone air heat balance by convection. So, the value of most interest is
(SurfaceInsideTemperature - ZoneAir Temperature) * SurfaceArea *
SurfaceInsideConvectionCoefficient The best way to calculate the contribution
from the envelope is to take the total load and subtract off the gains from
windows, internal loads, infiltration, and ventilation. The remainder will be
the impact of the envelope.
You also need to distinguish between heat gains (such as the current solar
transmitted through a window) and space conditioning loads. Depending on the
current surface temperatures, solar entering now may not become a cooling load
until later in the day or it may never become a cooling load if part of it is
conducted outside. Are you trying to split up gains or loads?
On 30 Aug 2004, at 11:39, drajmarsh wrote:
> Hi Michael,
> Having just read your reply - I'm gutted :)
> I've been writing a graphical viewer for ESO files and need a
> standard report which breaks space loads into separate FABIC, DIRECT
> SOLAR, VENTILATION and INTERNAL components (ideally I'd like to
> isolate sol-air and inter-zonal gains as well, but that's for
> later). This viewer also reads the output from a few other thermal
> analysis tools and this kind of report is great for passive analysis
> as it shows the relative percentage contribution of each to overall
> loads on each space.
> I've been having trouble interpreting the different variables and had
> a support forum post almost ready to go - however reading your
> comment suggests that it's not practical to do in EnergyPlus.
> My draft post is as follows, it might be that I've mis-understood
> what you were saying...
> I figured I could start with:
> Fabric Gains = 'Zone Opaque Surface Inside Face Conduction Gain'
> - 'Zone Opaque Surface Inside Face Conduction Loss'
> + 'Zone Window Heat Gain'
> - 'Zone Window Heat Loss'
> Solar Gains = 'Zone Transmitted Solar'
> Ventilation Gains = 'Infiltration-Sensible Heat Gain'
> - 'Infiltration-Sensible Heat Loss'
> Internal Gains = 'Lights-Total Heat Gain'
> + 'Electric Eq-Total Heat Gain'
> + 'People-Total Heat Gain'
> Looking at the ESO file, 'Zone Window Heat Gain' is always greater
> than 'Zone Transmitted Solar', so it seems obvious that you subtract
> the solar gains from the transmitted to get a conducted/radiant
> value. However, the 'Zone Opaque Surface Inside Face Conduction
> Gain/Loss' values also appear to contain a solar element. You would
> expect some sol-air effects, but for 'Zone Opaque Surface Inside Face
> Conduction Loss' as well...
> The solar element in both 'Zone Opaque Surface Inside Face Conduction
> Gain/Loss' is far greater than I would expect with the different
> materials I have experimented with (lightweight/heavyweight,
> light/dark coloured, insulated/non-insulated), and shows virtually no
> time-lag effects. If anyone is interested (or thinks I'm a nut :), I
> have a bunch of graphs and stuff showing all this on both very simple
> 1-zone and complex multi-zone models.
> Can anyone help with the following questions:
> 1. Am I double counting some solar effect - such as the window frame
> conduction (possible included in both the Opaque and Window heat
> gains) ?
> 2. Is this solar effect in the 'Zone Opaque Surface Inside Face
> Conduction Gain' solely a sol-air gain and the apparent solar effect
> in 'Zone Opaque Surface Inside Face Conduction Loss' due to
> conduction losses back out of windows ? If so, am I double-counting
> some losses by using 'Zone Window Heat Loss' as well ?
> 3. Have I missed a more obvious or better way of isolating these
> various elements ?
> Any help on this one would be hugely appreciated as I'm kinda stuck
> at the moment...
> Kind regards,
> // Dr. Andrew Marsh
> // -- -- -- -- -- -- -- -- -- -- -- --
> // Architectural Science Research Unit
> // Welsh School of Architecture (ARCHI)
> // Bute Building, King Edward VII Ave
> // Cardiff, CF10 3NB, United Kingdom
> // Tel: +44 (0) 29 2087 6207
> // Fax: +44 (0) 29 2087 4926
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
> <mjwitte@g...> wrote:
> > EnergyPlus does not report component loads, because the heat
> balance is done as
> > a combined solution and the presence of one load can affect the
> impact of
> > another load. The best way to determine this breakdown is to run
> > simulations, first with just the envelope, then a run adding
> infiltration, then
> > add ventilation, and so on until all components are present in the
> run. If you
> > change the order in which you add components, you may get slightly
> > answers for the incremental component loads.
> > Mike
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Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
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