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Advice on reading thermal images

 
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Well & Truly Off The Grid
Last Post by colinc 3 months ago
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Mars
 Mars
(@editor)
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Topic starter 23/02/2022 2:33 pm  

We have borrowed a thermal imaging camera (FLIR One) for a few days to identify heat leaks from house. Working from inside the house was relatively easy. Rooms were warm, with some cool spots in the corners of windows – nothing major. Easy to spot and fix.

We then took some thermal images from outside – the ambient temperature was 9-10C. The house was heated to 21-22C. Am I reading the thermal imaging correctly and that we're not really leaking signifiant heat?

 

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 George
(@george)
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23/02/2022 2:42 pm  

I think its better to get closer and do the exterior in much smaller sections to try to find cold spots or leaky areas.


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 Derek M
(@derek-m)
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23/02/2022 2:49 pm  
Posted by: @editor

We have borrowed a thermal imaging camera (FLIR One) for a few days to identify heat leaks from house. Working from inside the house was relatively easy. Rooms were warm, with some cool spots in the corners of windows – nothing major. Easy to spot and fix.

We then took some thermal images from outside – the ambient temperature was 9-10C. The house was heated to 21-22C. Am I reading the thermal imaging correctly and that we're not really leaking signifiant heat?

Hi Mars,

The brighter the area the higher the temperature, so for images taken from outside, bright is bad, dark is good. Obviously the reverse applies when the images are taken indoors.

To ensure that it is not solar gain that you are measuring rather than heat loss due to poor insulation, I would suggest that you take the same images again as late as possible after the Sun has gone down.

Numerous test that I have performed would indicate that the fabric of a building can absorb quite a high degree of solar energy, even at this time of year. The energy from direct sunlight can be as high as 700W/m2.



   
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Mars
 Mars
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Topic starter 23/02/2022 2:50 pm  

@George, that's what we did inside. We did a lot of close ups. We'll do the same from outside.


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Mars
 Mars
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Topic starter 23/02/2022 2:52 pm  

@derek-m, I had that same thought process. I did the exercise in the late afternoon which probably wasn't sensible. I think I'll do it again in the evening when the ambient temperature has dropped to 2-3C.


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 Derek M
(@derek-m)
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23/02/2022 3:05 pm  
Posted by: @editor

@derek-m, I had that same thought process. I did the exercise in the late afternoon which probably wasn't sensible. I think I'll do it again in the evening when the ambient temperature has dropped to 2-3C.

I would suggest leaving the task as late as possible, since the fabric of the building can retain the heat energy for hours. An alternative would be early in the morning, just before or just after sunrise.



   
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Mars
 Mars
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Topic starter 23/02/2022 3:07 pm  

@derek-m, before sunrise is not going to happen 🤣

I'll go out tonight at around 23:00 and see what we can capture.


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 Peterr
(@peterr)
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24/02/2022 8:43 am  

I found that when taking images outside it was better to go closer so that there was no sky in the frame.  The sky shows as a lot colder than the house, so the camera is having to colour a wide temperature difference.  If you can exclude the sky the range to be coloured is a lot smaller so any leaky hot spots should be easier to spot.



   
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Mars
 Mars
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Topic starter 24/02/2022 9:24 am  

@peterr, that's a very good tip. I think I need to get closer and cut out the sky because it's definitely "tainting" the colour spectrum.

@derek-m, I got up at 5 and took some shots – the house temperature was around 3C-4C, so 'better' than the 10C. Inside temperature at 21C.

In the two images I've posted, it speaks to your point @Peterr.

From a distance, I get "yellows" around the windows when the sky is captured – when close up, it's purples and blues. If you ignore the colours, and just read the C figures, you can still see leaks, but to be honest, I think the house is a lot better than I thought it was from an insulation perspective.

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Majordennisbloodnok
 Majordennisbloodnok
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24/02/2022 9:46 am  

@editor, when you took these images, did you also take one or two baseline shots? I've generally found it useful to have an idea of the temperature of something like a tree trunk at the same time so your 3-4degC reading can be seen in context of how much warmer the house is than its surroundings.

Certainly when I measured my house, I wasn't much interested in actual temperatures as much as temperature differences. My walls were getting to within 1-2 degrees of outside temperature and my double glazing was perhaps only a degree above wall temperature. The front door, however, was consistently about 5-6 degrees above outside temperature, so was an obvious candidate for replacement.


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Mars
 Mars
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Topic starter 24/02/2022 10:25 am  

@majordennisbloodnok, good points. To my mind, after the first couple of goes, I realised that while the colours are helpful they are not necessarily indicative of "heat losses" – what I did as part of my last session was to walk the length of the house and I took a reading of the brick work temperatures – they were typically in the range of 3-3.5C. 

I then worked my way back the other way looking at windows and doors. The windows were all at 4.2-4.7C which to my mind isn't a massive differential. 

This, to me, would indicate that we're not losing too much heat via the windows. 

When inside the house, the colours were far more indicative of the temperature variations, and the corners of windows where you can sometimes feel air "movement" the temperatures were 1-2.5C lower than the room temperature. These gaps will all be sealed in the next few days. We have also received a groovy insulation cream that we will apply to the brickwork outside under the windows where we get some leaks. 

All in all, I think that this has been a helpful exercise so far. I will continue to experiment and get more proficient with the thermal camera.


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 Derek M
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24/02/2022 12:02 pm  

@editor 

Hi Mars,

It would be interesting to see the variation in the temperature of the building fabric between area in sunlight against those in shade.



   
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