Message Board Thread - "Measuring the rate of heat loss through glass/tint film"

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Measuring the rate of heat loss through glass/tint film Tabasco 5/6/2008
Hello I am new to thermography and I have a T400.

I could use some help measuring heat convection and retention through double pane glass with and with out window tinting film.

1) Is there a formula out there that shows heat transfer through glass (single or double pane)?

2) Would employing "black tape" to both exterior and interior windows with/without tinting film on the same window give me the retention and heat loss analysis I am looking for?

Your ideas and insights would be greatly accepted.
Thank you,
David from Central Oregon
 
Re:Measuring the rate of heat loss through glass/tint film Doctir bob 5/6/2008
The standard technique is to measure the steady state heat flow through the "air film" at the interior window surface. One needs to know the interior window surface emissivity, window interior surface temperature, interior air temperature and interior reflected apparent temperature. Heat transfer by radiation (about 2/3 the total for vertical surface high emissivity materials) and convection (about 1/3 the total for interior vertical surface air films) comprise the heat flow through the air film. In steady state all the heat that flows through the air film, flows through the window. The R-Value can also be readily calculated, knowing the exterior air temperature.

A major caveat is the requirement for steady state heat flow conditions. This is a biggie as rarely is a window or wall in such a state in the real world.

The black tape could be used to measure emissivity of the window surface. For the heat flow calculation above, only the interior emissvity is needed. Low e glass has the coating on the inside of the window panes between the glazings. One would not 'see' it directly with the IR camera. Materials applied to the interior window surface on the living space side would be a different matter. One would not want to use the black tape surface for heat flow calculations as it's emissivity could be very different from the real surface and the heat flow could then be very different, especially for IR radiation.

I plan on presenting a paper on such types of calculations at our InfraMation conference in November, 2008. See our website http://www.inframation.org/ for details of the conference.
 
Re:Measuring the rate of heat loss through glass/tint film Tabasco 5/7/2008
Thank you Bob for your response.

One more question - how does the window casing material (wood, aluminum, or plastic) effect the convection or retention process or is that already considered in part of determining the steady state heat transfer?

Thank you,
David - Central Oregon
 
Re:Measuring the rate of heat loss through glass/tint film Apprentice 5/19/2008
If i were you i would try to get hold of a lens for that specific flir type camera that makes glass apear transparrent at a certain amount of microns,dont know if there is lenses like that for T-400...If im not mistaken in the region of 3.4 To 3.9 Microns ?
 
Re:Measuring the rate of heat loss through glass/tint film Apprentice 5/19/2008
Apprentice wrote:
re you i would try to get hold of a lens for that specific flir type camera that makes glass apear transparrent at a certain amount of microns,dont know if there is lenses like that for T-400...If im not mistaken in the region of 3.4 To 3.9 Microns ?
on the other hand,those lenses might cost a second bond on a house,there are mentioned alternatives.on the other hand.How highly proffesional will your work and study's be?
 
Re:Measuring the rate of heat loss through glass/tint film glassman 7/1/2008
Tabasco wrote:
am new to thermography and I have a T400.

I could use some help measuring heat convection and retention through double pane glass with and with out window tinting film.

1) Is there a formula out there that shows heat transfer through glass (single or double pane)?

2) Would employing "black tape" to both exterior and interior windows with/without tinting film on the same window give me the retention and heat loss analysis I am looking for?

Your ideas and insights would be greatly accepted.
Thank you,
David from Central Oregon
Hi David
I can answer this for you and so will all the large double glazing manufacturers it is called the 'U' value. First you need to know glass thickness, then the type of tint as some have metalic particales as part of their structure. you then need to look at the film as it is highly likly you could get heat gain from the double glazed unit itself. After all that you are then ready to go and be ready for a few surprises. If you do not wish to go through the hoop so to speak all film manufacturers will have their ratings on record and can give you them if pressed hard enough. This is how it is decided what type to use in what location and on what elevaion. You ask about black tape well you are going to need a few rolls so I would give it a miss and pick a dull day with minimal moisture content on the building to prevent miss readings.
Another oint to watch out for is double glazed units with gas in the cavity this can give a different reading across the panel.
Stay Well
The verifier.
 


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