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RE: [EnergyPlus_Support] Rooftop outdoor air temperatures



Dear Forum,

I’ve learned a few things from the various resources you sent and thank you for those.

I did not see among them a comparison of the roof temperature and an “unbiased” outdoor temperature such as would presumably be used by a TMY file.  I see that high albedo coatings cause a slight temperature reduction near the roof, but the roof could well be many degrees warmer than, say, the forest nearby or the airport where the TMY data is gathered.

Do you have any thoughts, experience or research that addresses a potential difference between the roof and what a typical weather file would use?

 

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: Monday, July 21, 2014 7:23 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Cc: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: 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 Grüßen- 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 are 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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Posted by: Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>


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