LMA calculation

[mahesh-t]

Hi, What is the formula used by the software for LMA calculation? Regards, Mahesh

[Jon.Wilde]

As far as I know, it is an industry standard. If you Google 'local mean age' you should find a ton of articles on it, like this.

[mahesh-t]

Hi Jon, Thank you for the link given. Please help me to relate LMA with Air change per hour(ACH). How to calculate ACH from LMA. Please give some reference if available. Regards, Mahesh

[Amal.C]

Hi @mahesh-t,

Please take a look at the article How to calculate the number of air changes in a room and let us know if you have questions or further concerns.

Thanks,

Amal

[Amal.C]

Hi @mahesh-t,

I wanted to check if the article I shared with you helped answer your question.

Please let us know if you still need help!

Thanks,

Amal

[mahesh-t]

Sorry for late reply Thank you for giving the article. Please help for the following also 1. As per my knowledge LMA is the time needed for air to travel from air inlet area to the specific location. How residence time differs from this. 2. How to calculate Air change per hour (ACH) from residence time. 3. I calculated the residence time from traces by selecting points, and I compared the LMA at that point with residence time. The observations were a. At some points LMA was greater than residence time. b. At some points residence time was greater than LMA. c. Some points both were almost same. So how can I relate LMA with residence time. 4. When I selected traces at some points it was not showing from inlet to outlet. Please help Regards, Mahesh

[marco.mueller]

You are right with the LMA defintion.

I dont think that there is an easy concept to get ACH out of LMA. By the way ACH is a very rough / old concept that gives you just a global idea. LMA is much better suited for local predictions of the flow exchange.

Maybe translating LMA to ACH is a bit as if you were asking for the chemical elements representation in the old classical element idea (earth, water, air, fire)... it just doesnt work well.

If you want to know how long a fluid particle travels from a certain location to the outlet, you can utilize the residence time of massed particles (which are solely calculated forwards). The mass density /particle size should be as low as possible.

Marco

[Jon.Wilde]

Awesome analogy, I wish there was a 'double kudos' button 😄