Temperature at Supply air Grill

[jrrocks]

We usually measure SA temperature using digital thermometer's wire probe in line with the flow. I have been informed to take temperature of supply air grill surface using IR thermometer, instead of air flow . I believe, there will be difference in temperature when reading taken on SA grill (using IR) surface and reading taken on Supply airflow (wire probe). Both would not be same.

we are about to order IR thermometer for this work. I need advise, whether it would be worth buying it because I believe, wired thermometer reading will be more accurate than grill surface temp. We need air flow temperature while calculating Tonnage, not supply air grill surface temp.

 

[minanady]

most of IR thermometer measure the temperature on surface so the reading will not be accurate for example when you close the air condition and measure from IR it will give you low temperature however there is no air flow

 

[moideen]

if you want accurate reading,measure with wired meter

 

[IRstuff]

Theoretically, the grill and the air temperatures are the same, because under steady-state conditions, there is no heat transfer between the grill and the air, which means they have to be at the same temperature.

Measuring that temperature is a different matter, since the instrumentation is different. Getting a decent handle on emissivity and ensuring that sensor is only seeing the grill is non-trivial.

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[MintJulep]

I have been informed to take temperature of supply air grill surface using IR thermometer

Informed by who, and why?

IR thermometer guns look cool and are easy to use (incorrectly).

Accuracy is not one of their virtues.

You already have the proper tool for the job. Continue to use it.

 

[berkshire]

Just for kicks and grins, point that IR thermometer at 5 places on the grille. You will get 5 different readings.

You are judged not by what you know, but by what you can do.

 

[Compositepro]

Using an IR thermometer on the grille is about as good an application for the thermometer as any. A painted grille has a fairly high emissivity and the grille will be very close to air temperature. Most IR thermometers are only accurate to +/-2F, though. You can "calibrate" the IR by comparing it to readings with your other thermometers.

IR thermometers are very convenient, but few users are aware of what factors affect accuracy. The fact that they average the temperature over a field of view can be good or bad. In this case it is mostly good, as long as the grille completely fills the field of view.