[BLDG-SIM] "Cool Roofing"

Tom Anderson hvac at cx-assoc.com
Mon Oct 7 13:31:39 PDT 2002

Oh Contrair.

 I ran load calcs for a 100,000 square foot single story big box store
in the Burlington, VT area last year to determine what if any benefits
would result from changing the flat membrane roof color from dark to
light. Occupancy was typical urban sprawl well-known national retailers.

Peak air conditioning roof  heat gain was reduced by 50%.

Roof was insulated to about R-22, plenum return, packaged DX rooftops.
Ran the numbers using Carrier HAP.  Annual AC energy savings came in at
about 3%.  Software did show a *slight* heating season penalty, but that
was because the software did not account for the usual snow cover on a
Vermont roof in winter. There was a worthwhile installed tonnage
reduction also.

     Thomas E. Anderson
     Cx Associates, Ltd.
     Building Commissioning Specialists
     933 Road 101
     Jeffersonville, Vermont 05464 USA
     hvac at cx-assoc.com
     Tel: 802-644-5616 Fax: 802-644-6797

Marcus Sheffer wrote:

>  Whenever we have modeled this in the Northeast we also have seen
> negligible savings using PowerDOE and others.
> We have come to the conclusion that the savings depend upon the amount
> of roof insulation and type of building.  If we enter minimal
> insulation the effect of a white roof is larger especially in a
> cooling dominated building, high internal loads, etc.
> If you are installing even moderate amounts of insulation (R15 or
> more) then the effect of a white roof in the Northeast is virtually
> nil for most any building type.
> Now when it comes to the urban heat island effect it can have a
> tremendously positive impact . . . but that is another issue.
> At 01:55 PM 10/07/2002 -0400, you wrote:
>> Has anyone had any success modeling cool roofing options (i.e.
>> reflective or light colored surfaces) in PowerDOE?  So far, I have
>> seen negligible results from the adjustment of roof construction
>> absorptance values (emissivity is also known to play a role, but
>> there is no input for this in PowerDOE).  I have seen data showing
>> cooling energy savings from 0.06 to 0.54 kWh/sqft/yr, depending on
>> building type.  I am getting only a very small fraction of this.
>> Data collected in the study was from facilities in the southern and
>> western US, and I work primarily on buildings in the Northeast.
>> My questions:
>> How well can I expect PowerDOE to simulate this?  Is there a better
>> way to simulate cool roofing?  Is the sun simply too low in the sky
>> in New England to yield substantial savings?
>> Your thoughts are appreciated.
>> Wade McLaughlin
>> DMI
> Marcus B. Sheffer                          energy & environmental
> consulting
> Energy Opportunities                     717-292-2636
> 1200 E Camping Area Road            Fax: 717-292-0585
> Wellsville, PA USA 17365-9783        sheffer at sevengroup.com
> a Seven Group member company   www.sevengroup.com

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