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Quantitative building thermography
03-21-2019, 03:09 PM
Post: #1
Quantitative building thermography
I read some papers on quantitative thermography of building envelope. They measured wall surface temperature using thermal image and used it for the calculation of heat transfer through the wall. They mentioned some important things for an accurate measurement of surface temperature for example set the correct emissivity and reflective temperature in thermal camera. In my work I am doing the quantitative thermography for a group of buildings using drone but the measured temperature does not seem to be accurate or even close to the real temperature because when I compare two different photos of the same wall which are from different views they show different temperatures. How can I take good thermal photos for my work? This idea of an accurate measurement of building surface temperature using a drone at the height of 60 m is doable or not? I found some works that did qualitative thermography with drone but they did not use the drone for quantitative thermography. Two photos of a buildings are also attached. [Image: view?usp=sharing][Image: view?usp=sharing]


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03-21-2019, 05:53 PM
Post: #2
RE: Quantitative building thermography
Hello,

I might be able to help you with some things, but I would like to know your application and the drone/payload combo that you usually utilize for these kinds of jobs.
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03-21-2019, 06:27 PM (This post was last modified: 03-21-2019 06:28 PM by alikatal.)
Post: #3
RE: Quantitative building thermography
My application is to measure the surface temperature of a group of buildings by a thermal camera installed on the drone and use the temperature for calculation of building U-value. I am using a DJI drone but I don't remember the exact model.

(03-21-2019 05:53 PM)bdayyani Wrote:  Hello,

I might be able to help you with some things, but I would like to know your application and the drone/payload combo that you usually utilize for these kinds of jobs.


My application is to measure the surface temperature of a group of buildings by a thermal camera installed on the drone and use the temperature for calculation of building U-value. I am using a DJI drone but I don't remember the exact model.
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03-22-2019, 09:51 AM
Post: #4
RE: Quantitative building thermography
Well, I might be able to help you with measuring the temperature of a spot on an image, but measuring the whole building is a whole different story. Are you utilizing any third-party software packages? I have some experience with the DJI drones but knowing the exact model can help.
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03-22-2019, 12:40 PM
Post: #5
RE: Quantitative building thermography
(03-22-2019 09:51 AM)bdayyani Wrote:  Well, I might be able to help you with measuring the temperature of a spot on an image, but measuring the whole building is a whole different story. Are you utilizing any third-party software packages? I have some experience with the DJI drones but knowing the exact model can help.


I just need to read the temperature of one or two points on the building surface. I am using the FLIR tool to read the temperature but my problem is that I am not sure it shows the correct temperature because in thermography it's important to set the correct emissivity and reflective temperature to measure the correct temperature. for a group of buildings, I don't know the emissivity and reflective temperature of each building.
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03-22-2019, 04:37 PM
Post: #6
RE: Quantitative building thermography
Well, have you passed Level 1 Thermography course? Because the questions that you are asking can be somewhat answered in Level 1 training. On the other hand, for an accurate true-temperature measurement, you would need to enter the distance, atmospheric temperature and relative humidity as well.
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03-24-2019, 02:27 PM
Post: #7
RE: Quantitative building thermography
(03-22-2019 04:37 PM)bdayyani Wrote:  Well, have you passed Level 1 Thermography course? Because the questions that you are asking can be somewhat answered in Level 1 training. On the other hand, for an accurate true-temperature measurement, you would need to enter the distance, atmospheric temperature and relative humidity as well.


No, I did not pass the level 1 course. I entered the correct values of distance, RH, and atmospheric temperatures but for the emissivity and reflective temperature, I don't know the correct values. I know that these two parameters can be found by using black tape and aluminum foil on building surface but in my application that I am doing thermography by drone for a group of buildings I can't estimate them for all buildings.
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03-25-2019, 09:03 AM
Post: #8
RE: Quantitative building thermography
Do you have a digital image of a section of one of your buildings so we can see what you're dealing with?
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04-03-2019, 05:04 AM
Post: #9
RE: Quantitative building thermography
What you are trying to do is extremely difficult even with training. It is not just a matter of using standardised values for emissiivity and reflected temp. You need to understand how and why these give you errors, this takes quite a bit of training and experience.

What you are experiencing is that thermography is not as easy as you thought, and this if anything is highlighting the need for training.

My advice is not to try to measure U values from a drone based camera at a distance of 60m without any training. Stick to qualitative thermography, if you need to measure accurate U values, then you will need additional instrumentation, and strong knowledge of building physics, it will not be possible to do it accurately just with a drone.
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04-03-2019, 11:56 AM (This post was last modified: 04-03-2019 11:59 AM by alikatal.)
Post: #10
RE: Quantitative building thermography
Yes, I agree with you. As I said, other researchers did quantitative thermography only for one building and from a close distance so they could measure the correct temperature because they estimated the emissivity and reflective temperature using black tape and a piece of foil on the wall surface. They also mentioned the angle us important in thermography but in my case, I cannot meet all these conditions for an accurate measurement. I know that it's almost impossible to do accurate quantitative thermography using a drone for a group of buildings but my supervisor does not believe me and says that there should be a solution for it.

(04-03-2019 05:04 AM)Bobberry Wrote:  What you are trying to do is extremely difficult even with training. It is not just a matter of using standardised values for emissiivity and reflected temp. You need to understand how and why these give you errors, this takes quite a bit of training and experience.

What you are experiencing is that thermography is not as easy as you thought, and this if anything is highlighting the need for training.

My advice is not to try to measure U values from a drone based camera at a distance of 60m without any training. Stick to qualitative thermography, if you need to measure accurate U values, then you will need additional instrumentation, and strong knowledge of building physics, it will not be possible to do it accurately just with a drone.

attached is an image of one of the buildings.

(03-25-2019 09:03 AM)jvoitl Wrote:  Do you have a digital image of a section of one of your buildings so we can see what you're dealing with?


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