Need help reconciling two statements about refrigerants

  • #1
162
25

Main Question or Discussion Point

I am a student attending a trade school, majoring in HVAC. My air-conditioning textbook says that refrigerants are heavier than air. The context for this is a chapter in my textbook about how to conduct leak testing. My textbook says something to the effect of the following: "Refrigerants are heavier than air, so one must leak check underneath a refrigerant line (as opposed to above a refrigerant line) to find a leak."

I have long known that refrigerants are heavier than air. My understanding has always been that the reason that CFCs and HCFCs have depleted the ozone layer is that the CFCs and HCFCs break up close to the ground due to chemical reactions. And then after the CFCs and HCFCs have broken up due to chemical reactions, the individual chlorine atoms float up to the stratosphere because individual chlorine atoms are lighter than air. Then when the individual chlorine atoms reach the stratosphere, then the individual chlorine atoms deplete the ozone layer. However, a sentence I read in a study guide for the EPA certification test gives me doubts about my understanding of how chlorine atoms in CFCs and HCFCs reach the stratosphere.

The study guide for the EPA certification test says the following: "CFCs and HCFCs have been found in air samples taken from the stratosphere."

The study guide for the EPA certification test does not say that individual chlorine atoms that were formerly in compounds making up CFCs and HCFCs have been found in the stratosphere. The study guide says that CFCs and HCFCs have been found in the stratosphere.

If CFC refrigerant and HCFC refrigerant is heavier than air, how can CFCs and HCFCs be in the stratosphere?
 

Answers and Replies

  • #2
19,919
4,095
The CFCs only break up when they reach the stratosphere, not close to the ground. The HCFC react with OH radicals closer to the ground, but large amounts of them also make it into the stratosphere before breaking up. The reason that the CFC and HCFC molecules are able to make it to the stratosphere is that they mix with the air and are transported upward by air currents. This happens even though they have higher molecular weight than air. So-called gravitational segregation is very little once they mix with the air.
 
  • #3
russ_watters
Mentor
19,408
5,548
In addition to being heavier than air by molecular weight, refrigerant leaking from a residential split system indoors is also likely to be cold, which would make it even more dense. It's also confined, so it doesn't get stirred-up by wind.
 
  • #4
mjc123
Science Advisor
Homework Helper
946
437
Individual chlorine atoms are also heavier than air.
 

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