Re: [EnergyPlus_Support] EER Calculations

Dear forum,

Not too long ago, there was a thread of conversation regarding a simple way to calculate the COP needed for a DX coil so that a desired EER would result in EnergyPlus output. For example, if you want your DX system to have an EER of 11.0 so as to meet minimum ASHRAE 90.1 efficiency, what coil COP should be used?

I posted something on this topic a week or two ago, but canâ??t find it, so Iâ??m posting a new message after some very helpful discussions with Bereket Nigusse of the Help Desk and updating the spreadsheet I use for these calculations.

I hope that it is helpful to many of you!

In short:

Â· Make a successful auto-sizing run and determine â??nominalâ?? coil capacity and airflow
(when manually defining a coil, the procedure varies slightly and is described in the attached spreadsheet)

Â· Enter the nominal capacity, airflow and desired system EER in the spreadsheet to have it calculate the â??Reqâ??d COPe+â??

Â· Use the â??Reqâ??d COPe+â?? as the DX coil COP in your IDF.

Â· Expect perfect EER calculation without trial and error!

James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Sungmo Seo
Sent: Wednesday, September 04, 2013 3:08 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Warning explanation needed

I can't understand well about bean shape roof. is it mean circle?

I recommend you that check a BuildingSurface:Detailed in IDF file.

That's a list of surfaces and surface's detail.

And that consist with Vertices coordination. These mean points of each surface.

for example, rectangle made by for point.

Than if you make circle shape surface, that consist with a lot of point.

Then it will make some warning or error.

If you want a making of bean-shape roof(if it means half circle roof) you should change to triangle shape or polygon shape.

I want a it will be help for you work.

2013/9/4 jeannieboef@xxxxxxxxx <jeannieboef@xxxxxxxxx>

Thanks. Would a bean-shaped roof without skylight also have this warning?

It is hard to mentally picture the "shadow clipping". I believe the warning is saying that non-convex receiving surfaces may result in inaccurate shading, but as shadow clipping is not the same as ray tracing, it is hard to visualize. Does the .shd file post a geometry of the shadow which I can then import with OpenStudio to better visualize where the program is placing shadows? That would be an interesting implementation.

Mit freundlichen GrÃ¼Ã?en- Sent from my iPhone (excuse the brevity)

i. A.

Jean Marais

b.i.g. bechtold

Tel. +49 30 6706662-23

On 04.09.2013, at 08:07, Sungmo Seo <ddims123@xxxxxxxxx> wrote:

I think this warning made by modeling of skylight.

because of skylight, your roof has a hole.

If you want remove this warning, you must cut roof as rectangles

Same like

____________________
l l roof l l
l l_____________l l
l r l l r l
l o l Skylight l o l
l o l____________ l o l
l f l roof l f l
l___l_____________l___l

2013/9/3 Linda Lawrie <linda@xxxxxxxxxxxxxx>

Well, it is a warning, not a severe.

Your roof is a receiving surface but it is non-convex. If you have shading surfaces shading it, it is warning you that the shadowing values could be inaccurate (but may not be)

At 01:42 AM 9/3/2013, jeannieboef@xxxxxxxxx wrote:

** Warning ** DetermineShadowingCombinations: Surface="118434_ROOF_0_0_0" is a receiving surface and is non-convex.
** ~~~ ** ...Shadowing values may be inaccurate.

The surface is plannar. The zone is non-convex. Surely this only has an effect if a skylight (roof window) had to have light fall downwards, it would also fall "around the corner" and in that way be inaccurate. But this model uses FullExterior, i.e. this warning is moot, right?