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Re: [EnergyPlus_Support] Rooftop outdoor air temperatures



Sorry, no research I know of. 

But experience of rooftop ducting adding 2 K to the overburdened office supply air temperature  in summer is known of in my office and a factory project we had here in Berlin has similar issues.

Rooftop surface temperatures ranges definately go to 56 C (also measured by myself as licenced IR Thermographer) and seen in e+ simulations. 

Microclimate at the rooftop air intakes, i.e. air temperatures, I have not measured, but I can well imagine them being 2 K higher than weather air temps...similar to a parking lot heat island. It would be significantly wind dependant, I would think and only very near the surface (.5 m).

I have also never included this effect. I hope the number of hours that the effect is non-negligable is not many.  

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

i. A.
Jean Marais
b.i.g. bechtold
Tel.   +49 30 6706662-23

On 19.07.2014, at 19:37, "Jim Dirkes jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

 

Dear Forum,

I have had clients in the past who refused to place HVAC equipment on the roof in Dallas, Texas because they knew the near-roof temperatures were much warmer than the temperature farther away.  The situations have been for large, black roofs which get very warm in the summer.

I have not thought about that much for energy models other than defining high SRI roofing materials.  Yesterday, however, I was talking to an infrared thermal imaging professional who says that he has measured roof temperatures that were 100F / 56C higher(!) than the nominal outdoor temperature.  If that is true, then all of my energy calculations for rooftop equipment are WRONG ? not a happy thought for someone who wants results that aree realistic.

The resulting questions to the most knowledgeable modeling community in the world (as far as I can tell) are:

·         Are you aware of research which has measured or characterized near-roof temperatures?

·         Do you have a modeling practice that accounts for the near-roof impact on outdoor air intakes or roof-mounted chillers, condensing units or cooling towers?

 

Thanks in advance for your insights!

 

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]
Sent: Friday, July 18, 2014 3:37 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Curve Fit Tool

 

 

Thank you very much for you help

 

Kind Regards,

 

Felipe Durán

Posted by: Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
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