Craig,
Thanks for circulating this report, which goes a long ways in answering the question of how much do the air temperatures above a roof change when the roof reflectance changes (answer seems to be very little, around 0.3 C). Has anyone also looked into the impact of the increased solar gain on the AHU due to more reflected solar from the roof ? This reminds me of the conversation I had with a colleague at an ASHRAE conference two years ago, who thought that increasing the albedo of streets and pavement might actually increase rather than decrease thermal discomfort of pedestrians due to the increased reflected solar, as well as visual discomfort.
Joe
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 108D Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx http://weather.whiteboxtechnologies.com for simulation-ready weather data (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"
On 7/19/2014 11:39 AM, Craig Wray CPWray@xxxxxxx [EnergyPlus_Support] wrote:
There is indeed some related research on the effects of roof reflectance on air temperatures near rooftop condensing units. See:
Regards, Craig Wray
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Saturday, July 19, 2014 10:38
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Rooftop outdoor air temperatures
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
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Posted by: Joe Huang <yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx>
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