Welcome to the official discussion thread for the webinar Infrared Standards for Building Applications- June 18, 2008 at 11:00 a.m. EDT.   I encourage you to join us for a post-webinar discussion here on this thread where participants can:

• Ask the presenter additional questions.
• Network with other thermographers who attended this session.

Webinar Overview:  Conducting infrared analysis of buildings without an in-depth understanding of existing national and international standards is similar to getting behind the wheel of a 18-wheel truck and believing all the same rules apply as to driving a golf cart. This presentation will provide an overview of the current published standard practices for thermographic inspections of buildings. Focus will be on presenting the key concepts and recommended practices of conducting a variety of thermographic building inspections with associated thermal images. ASTM C1060, ASTM E1186 and applicable ISO standards will be discussed and compared.

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Matt Schwoegler
The Snell Group

Our Knowledge. Your Advantage.

Question for Rob:

 Air exfiltration / infiltration out of / into a building is plausible due to the pressurizing / depressurizing the interior by way of a blower door or similar.

You mentioned "air wash through insulation" in your presentation, i.e. air movement through the insulation without entering the interior of the building. What is the driving force for air entering the insulation from the outside and again exiting to the outside with no pressure difference? Or, what creates a potential pressure difference in this case?

Dieter 

 

Dieter,

Pressure diffences are relatively easy to understand from inside to out and from top to bottom. However pressure differences are very complex and variable. If you hold up a piece of ply wood to the wind there will be pressure differences across the plywood from windward to leeward and from top to middle and middle to top due to an infinate number of varible such as wind speed, wind direction, the size of the plywood and the orientation of the plywood to the wind. It is these variable that can cause wind to enter through cracks in the bottom of a wall cavity from the outside and move rather unobstructed through fiberglass insulation and then exit through cracks in the top of the wall cavity back to the outside. I have witnessed this a number of times as the thermal image I showed during the webinar demonstrated.

 When wall cavities are not sealed well there will always be some air movement through the interstitial, the amount and direction of flow will be related to the temperature and pressure diffences both from inside to out but also within the wall cavity.

 Hope this helps.

Rob

Rob Spring, P.E.

 

 

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Rob Spring, P.E.
ASNT NDT LIII #65375
The Snell Group
rspring@thesnellgroup.com
800-636-9820

The "pressure path" often also causes outside air to move into the wall where it moves indirectly into the conditioned space. The attached shows a sheetrock corner where there was not DIRECT air leakage into the room but the cold air was clearly present inside the wall at the point of entry. From here it can move through the wall until if finds a point of entry into the conditioned space.

These patterns often "ripen" nicely when you use a blower door in a building. Depressurizing the building to enhance to flow across the envelope can help to show how the point of entry into the wall connects with the exit point into the room. 

Regardless of the air flow pathway the insulation loses much of the specified value which is based upon very limited internal convection, i.e. "dead air space." Fiber batt insulation, as Rob suggest, is "unforgiving" and, thus, the most susceptible to this phenomenon.To think that we can "seal" walls against this sort of action is simply not practical in the real world. Far better to use an insulation that does a better job of reducing air flow, such as blow-in cellulose or spray foam.

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Thermally Yours,

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

Rob,

thanks, yes this answers the question. However at the same time it poses another one. It is my understanding that thermography is done best when it is calm, so as to the wind not blowing away thermal evidence on the outside of a building shell.

With wind we can establish whether or not there is air wash through the insulation. The wind on the other side may make it impossible to detect thermal irregularities on the outside.

Without wind  we will find thermal irregularities on the outside but have no information re. air wash.

 Now what, do you go back twice under different wind conditions? Where do you compromise?

Dieter 

 

Dieter,

 Your question is a good one and one that many building inspectors stuggle with. An infrared building inspection is in reality at least two separate inspections; an inspection to evaluate the presence and condition of the insulation system and then an inspection to detect air movement through the buildings thermal envelope. The way this is usually done is to first do the insulation inspection when is relatively calm and then induce a pressure differential,using a blower door, fans or the HVAC system, and do the air inspection second. The reason to do the air inspection second is because if you do it first and there is significant interstitial infiltration the wall, floor and ceiling cavities may not come back to thermal equilibrium for many hours thus delaying or preventing an inspection of the insulation. I have seen fully insulated wall and floor sections turn completely black in the thermal image within minutes of inducing a pressure differential due to air flow through the fiberglass insulation.

A blower door is the method of choice for inducing pressure differentials in small buildings, but we have used box fans in windows as well as turned on all the exhaust fans in small to moderate size and relatively tight homes. If the building is really leaky it is tough to get a significant differential with out some serious air movement. This is the advantage of the blower door, which also provides quantifiable air flow and documentation capabilities.

 Rob

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Rob Spring, P.E.
ASNT NDT LIII #65375
The Snell Group
rspring@thesnellgroup.com
800-636-9820

John, 

these cold corners where walls and ceiling meet are quite familiar to me. Corners for structural resons have additional 2x6 studs or other elements which leave little if any space for insulation. Therefore I always thought this cold pattern was caused by a lack of insulation due to space constraints. What makes you believe that in your case it is air infiltration as opposed to just inadequate insulation?

Dieter 

It is, of course, not always possible to be 100% certain but uniform signatures tend to be associated with framing conduction issues and non-uniform signatures are more often related to air leakage. Also, if you can depressurize the building, any changes tend to be related to air leakage.

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Thermally Yours,

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