History of 400 CFM standard

repj2y

Interesting posts from everyone ! Without making a science project out of 400 CFM
per ton; I've heard every arguement for 38 yrs!
I have yet to find anything of legitimate value based on ASHRAE standards !
I have heard from Bohn, Carrier, and Trane Engineers, that; a compromise was made
in the late 60's that maximum heat transfer and noise abatement was obtained utilizing 400 CFM for residential cooling ! Every American manufacturer utilizes
that standard on Air Handlers for residential cooling. I'll accept that !
The only thing I disagree with would be manufacturers using 4 ton Air Handlers
(TXV) with 3 ton condensers to improve the SEER ! The fan delay with an ECM
motor shooting carry-over from the coil back into the conditioned space is a joke.
Visualize this: The reason why a floral walk-in has a huge elongated evaporator
is to drop the temperature quickly and not de-humidify and ruin the flowers !
Why would any designer recirc moisture back into a conditioned space and put up
with mold etc.! Once that compressor stops and the fan is still running "You ain't
removing any BTU's !" You're feeling residual cooling, but; it's not 60*!
So; how can you justify the SEER going up !

beenthere

There is residual cooling, or you wouldn't have cooler air coming out of the register then what went into the return. And that is all that was needed to increase the SEER.

Remember, SEER is a time dependent rating also.

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hvaclover

I love this Guy!
I have not heard that piece of arcana in I don't know how long.
But it's true! I have Rses material that gos back to the fifties that showed CFM tables for certain apps. The table went from 300 to 485 cfm per ton.
Some specialty apps took only 285 cfm but the coils for the tonnage were monstrous and had very low Delta T. The moved huge volumes of air at low speed. No noise no sudden blast of cold air...those were good systems.

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repj2y

I remember the EER changing to SEER in 1978. The reasoning of the COP with
heat pumps running in both heating mode and cooling. Referring back to the recirc air
(moisture laden) back into the conditioned space: That's a big time problem in Florida. Compound that with outside air make-up in light commercial apps, you; have
a bigger problem. I'm sure most of us agree on how to calculate SEER and EER
ratings. Head pressure and amp draw dictate any SEER calculation. If wattage is
out of whack for whatever reason; your SEER & EER is shot full of holes ! That's
why I mentioned: when the compressor stops; you ain't pumping no BTU's !
The only wattage is the fan ! When the system cycles again; you have to work
the compressor to remove the moisture you sent back into the conditioned space
from the fan delay ! I have had regular customers leave the fan on continuous all
the time no matter what season! Big time mildew build-up! I'll clean every grille
for a fee! Thank you very much! Then they wonder why they have condensate
drain line problems. Well you know! 90% of the condensate drains on the off-cycle !
Enough of my rambling. Bud light and football got me going ! Later ! (my bottle is empty)

beenthere

EER BTUs per watt consumed while running.

SEER is BTUs averaged over time, and then adjusted for a season. And that blower off delay adds just enough BTUs to reach min requirements.

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jakereynolds

I'm pretty sure Willis Carrier stated that 400 CFM/ton was ideal, and it has stuck with the industry since, for better or worse.

Love2HVAC420

Thanks for this topic!
Great info here.

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spinfisher

lol!

francisfundal

hi to all...

any one can help me bout my problem how can we get CFM and what is the standard CFM/tons?

beenthere

Might want to start your own thread. So you get more people to see it, and answer.

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