[Bldg-sim] Insulate the roof in summer without HVAC system yes or no? COOL ROOFS

[Graham Carter & Megan Lyall]

Depending on your climate, you may find a CoolRoof may add more value than insulation.  There are some products that claim very high solar reflectance (90%+) combined with high long wave emissivity (.92+) which can keep the roof itself cool thus reducing the sub-roof temperature and under some conditions creating a negative heat pump effect due to sky cooling that occurs in the daytime.  There are a number of products out there that use a ceramic nanospehere particle additive to the roof paint that lifts solar reflectance by 15-20%.  So when applied to a TiO2 white you can get into the 90%'s.

If your climate is cooling dominated you may find this a useful strategy.  If you have a cold climate then this can work against you but it sounds like cooling is the problem.

Melbourne Airport has successfully used such a product so I don't believe there are any concerns with the high diffusing reflectance around airports.

Most software packages will model a truly cool roof properly including IES-VE and the DOE-2.2 / E+ engines.  The problem is they don't represent more conventional and absorptive roofs which create a roof micro-climate that is biased upwards from ambient.  I am digressing, but thought I would promote this issue a bit as I would love our industry software to recognise this microclimate effect so that we drive better roof designs.  And where we have cooling equipment and outdoor air intakes at roof level, that we have the mechanisms to account for the higher condensing temperatures and higher ventilation air temperatures.  The issues are particular to large roofs like shopping centres, airports, manufacturing facilities etc.  I wrote a paper on this (attached) to try and give this issue some visibility.  Please keep asking your software vendors for these issues to be represented in your software fully ...

Also with your hangar do you have the space stratified?  While you can stratify in IES-VE and get an indication of annual bulk conditions, it would be best tested in CFD using IES-VE to get your boundary conditions if you are interested in more than just every, i.e. comfort.

Regards,
Graham

On 20/04/2013, at 12:23 AM, Jeremiah Crossett wrote:

> Insulation does trap heat and this is a real issue that happens in the real world and not justin models.  There was a thread on this form last year about it and papers posted.  I would suggest you look into phase change materials rather then insulation- they will absorb the energy and cool the space down to enhance comfort during the day and release that heat into the space at night to keep it warm. There is a video of a metal building install at this link---> http://www.phasechange.com/index.php/en/install-portfolio/videos
> 
> In addition to PCM's I suggest you look into high emissivity / reflectivity paints or coatings. 
> 
> 
> Jeremiah D. Crossett  | Senior Analyst  |  Phase Change Energy Solutions
> 120 E. Pritchard St.  | Asheboro, NC 27203  | Mobile 503-688-8951
> www.phasechange.com 
>   
> 
> 
> 
> 
> 
> On Fri, Apr 19, 2013 at 5:22 AM, David GARCIA-SANCHEZ <dgarciasanchez at greenaffair.com> wrote:
> Hi,
> 
>  
> 
> Thanks for your answer. Yes we have strong internal gains in this hangar (we suppose a high rate of lighting gain and a heavy occupant metabolism). But, for me is still very strange the fact that we supposed to have natural ventilation who it supposed to help control this strong gain.
> 
>  
> 
> Even if air temperature is high, the roof temperature is also higher with insulation that without insulation.
> 
>  
> 
> Maybe modeling results are “correct” but one might expect that the temperature of wall should get reduced by using a very thin film of insulation. Despite the fact of the strong internal gains which are the same in both examples,
> 
>  
> 
> This is a difficult case, where you wonder if the “dynamic model” is in a different sense of “reality”
> 
>  
> 
> Bes regards and thanks again,
> 
>  
> 
> David GARCIA-SANCHEZ
> 
>  
> 
>  
> 
>  
> 
> <image001.png>
> 
> David GARCIA-SANCHEZ
> 
> greenaffair
> 
> Tel. +33 (0)1 46 03 08 02
> 
> Mobile +33 (0)6 78 15 08 09
> 
> 102 avenue Edouard Vaillant – 92100 Boulogne-Billancourt
> 
> www.greenaffair.com
> 
>  
> 
>  
> 
> De : Álvaro Lapa [mailto:ajlapa at gmail.com] 
> Envoyé : Friday, April 19, 2013 11:46 AM
> À : David GARCIA-SANCHEZ
> Objet : Re: [Bldg-sim] Insulate the roof in summer without HVAC system yes or no?
> 
>  
> 
> The increase in temperature (when isolated) could be caused by the internal gains. Try to confirm that.
> 
>  
> 
> 2013/4/19 David GARCIA-SANCHEZ <dgarciasanchez at greenaffair.com>
> 
> Hi all
> 
>  
> 
> I have a project where I need to model a maintenance hangar,
> 
>  
> 
> In this project we are evaluating the relevance of insulate the roof to improve the comfort level in summer. The hangar has no air conditioned system but we use natural ventilation which seems to work well in our model (we use IES VE).
> 
>  
> 
> The problem came when we try to put some insulating material to the actual roof (which is composed of only metal sheet of 2 cms). Unlike one might expect the temperature in the hangar increases, as the roof temperature.
> 
>  
> 
> This is to some extent logic, and I know it depends of the insulate type and thickness. But we agree (I think) that at least one insulation with les of 2cm to the actual roof should give an improvement in at least roof or air temperature. I know that insulation can serve as a “trap” of interior thermal conditions, so it’s improve HVAC systems performance. But also it serves to avoid the external conditions gets-in.
> 
>  
> 
> I have tried several configurations without success, internal, external insulation.
> 
>  
> 
> And maybe some of you have already some experience in model this kind of configuration. We agree (I think) that I can’t recommend to my architect that he shouldn’t insulate its roof, but also I want to explain the pertinence of this with a dynamic thermal modeling.
> 
>  
> 
> Thanks in advance for any advice on this,
> 
>  
> 
> David Garcia
> 
>  
> 
> 
> David GARCIA-SANCHEZ
> 
> greenaffair
> 
> Tel. +33 (0)1 46 03 08 02
> 
> Mobile +33 (0)6 78 15 08 09
> 
> 102 avenue Edouard Vaillant – 92100 Boulogne-Billancourt
> 
> www.greenaffair.com
> 
>  
> 
>  
> 
> 
> _______________________________________________
> Bldg-sim mailing list
> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG
> 
>  
> 
> 
> _______________________________________________
> Bldg-sim mailing list
> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG
> 
> 
> _______________________________________________
> Bldg-sim mailing list
> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130420/f1fbada4/attachment-0004.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2012_06_01[1].pdf
Type: application/pdf
Size: 1840103 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130420/f1fbada4/attachment-0002.pdf>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130420/f1fbada4/attachment-0005.htm>