I recently conducted a building envelope inspection.  This was a two story heart hospital in south Texas.  Ambient temps ranged from 80 degrees to 105 degrees, morning to afternoon.  I was able to show areas of air leakage using normal pressure versus positive pressure conditions. 

 The question I have is what is recommended for background temperature?  I scanned the low level background and observed vehicles over 120 F.  The sky obviously varied from cold to about 78 F for clouds.  I took many images of the entire two stories.  As a consequence, I used 78 degrees consistently in my survey.

Any recommendations?

Bill

 

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Bill Galbraith

When correcting for emissivity and, thus, background reflected temperature, we are typically correcting for a single spot at a time. So the real question is what spot(s) on your image do you want to correct for? At that point imagine that the spot is a visual mirror. What precisely are you seeing in that mirror from your vantage point and what is the temperature of that area being reflected.

 For example, if you are viewing a window on the second floor, part of the window could be reflecting the clear sky and part a cloud and another part a taller building or tree nearby. Three separate corrections would be required if you wanted to measure the window temperature in those three specific locations. The attached image shows how complex this can be as we are also dealing with reflections of warmer and cooler building facades!

 The idea that we can make a "global" correction for either emissivity or background is not a common occurrence!

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Thermally Yours,

John
ASNT NDT Level III #48166
The Snell Group
www.thesnellgroup.com
www.thermalsolutions.org
800-636-9820

John,

 I understand your response.  In this instance I was looking for first and second floor temperature differentials.  After conducting my initial visit, I learned the walls had no insulation other than one to two inches of styrofoam on the outside covered by metal cladding.  I decided to show the customer how normal pressures versus positive pressure was affecting heat transfer.  He knew insulation was the factor but wanted to rule out window leakage, which did not appear to be a factor. 

 These images show the cooling effect before and after pressurization of the building.  This was my objective.  The exterior walls on the South and West cooled 3-4 degrees after inducing positive pressure in the building.  You could walk around the building and feel cool air exiting from cladding and door seams.  I told the customer he is cooling South Texas. 

Thanks,

Bill

 

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Bill Galbraith

Very nice work, Bill! I also wonder what it might have looked like from inside with depressurization? Regarding background temperature correction, given the fairly forgiving angle from which you are viewing the low-rise building, I suspect the background will be very close to ambient air temperature. Since the surfaces you are viewing are fairly high-emissivity (the window being the lowest at 0.80), and the fact that you are looking at the same areas in each of the two images, your measurements should be very accurate regardless. Hopefully your client will opt for some major air sealing work as a result of these compelling thermal images!

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Thermally Yours,

John
ASNT NDT Level III #48166
The Snell Group
www.thesnellgroup.com
www.thermalsolutions.org
800-636-9820

Thanks, John.

I recorded some images inside the lobby of East windows in the afternoon with all exhaust fans operating.  The frame temperatures ranged from 90 F at the top to 80 F at the bottom.  I did not observe any infiltration patterns.  Inside ambient was 75 F.  This is a Heart Hospital so access to most rooms is difficult without an escort and permission.

The Engineering Director plans to send my report to Corporate HQ for evaluation.  A subsequent inside survey may help to identify certain areas they should work on first.  Overall, the building has serious insulation problems.

This Director is over four hospitals in the area.  He was my very first customer when I started my business in 1994.  I conduct electrical inspections every December at all four facilities. 

Last December he was telling me about water infiltration during Hurricane Dolly last July.  I was fortunate to be there for another customer at the time.  My first hurricane experience.  I am used to tornadoes here in Oklahoma!!!

He said the water entering the West wall windows was so excessive they could not keep up.  Water was cascading down the stairwells and elevator shafts.  His insurance company recommended replacing the windows at a cost of $4 million.  I scanned the West walls and some on the East and showed him some areas that need attention.  He said this is what he wanted to show corporate, that he has a seal problem, not a window problem.  He is now getting bids for repair and expects to pay $1 million.  Guess I helped him save about $3 million.

I also found areas of probable water below windows inside the exterior surface.  Image attached.

 

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Bill Galbraith