Regular Guest
I know that it is standard 400 CFM per ton for residential AC / Heat... What is standard CFM for heat pumps? I have been told by my instructor that 450 is a rule if thumb but I can not find any hard evidence in that. Need some help please!
Professional Member*
MurDoc4, You must be studying at _ School of Ancient History _.
Heat Loss and Heat Gain are expressed in units of BTU/HR.
Heat Loss might be in the range of 0.238 to 0.382 BTU/HR per degree F / Square Feet of floor area.
_____________ ... ___________ ... _____________________
House might be in Alaska, Cayman Islands or in between
Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities
Professional Member*
2,000 SQ FT
Average
BTU/HR ___ O.A. Temperature
24,800 ___ 30'F
31,000 ___ 20
37,200 ___ 10
43,400 ___ 0
Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities
Professional Member*
The simple answer is 400 cfm per ton... But it really depends on the Sensible Heat Ratio (SHR). The SHR is the ratio between the sensible load (heat gain) and latent load (moisture). Lets say I live in Florida, I might have a high latent load (really humid), I might need my cfm as low as 350. My coil will be colder and will remove more moisture. But lets say I live in Colorado, (really dry) very small latent load, my cfm might be 450. I will have a warmer coil, I don't need the latent capacity. All this can be found in the ACCA Manual S. An A/C dude really needs to understand this. On the heat side I need enough cfm to condense my vapor, 450 cfm might be a little drafty. The right grille selection would fix that... Grille selection can be found in ACCA Manual T. An A/C dude really needs to understand grille selection too, It can make or break the most wonderful of systems.Originally Posted by MurDoc04
Thank you,
Rick Boggs
Professional Member*
the airflow for heat pumps is the same as the air conditioner , a few units have some airflows that are differnt for heat then cool like the new trane hyperions
Professional Member*
There is no general rule of thumb when one is addressing
use of Inverter technology and Outside Air temperature variations.
Single-speed units ought to go the way of R-22 in the next decade or two.
Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities
Regular Guest
I'm being to think my teach is a little out of touch on heat pumps and that irritates me because I'm paying for this school. Thank you fellows for the info.
Regular Guest
Beginning I meant
Professional Member*
Generally it's the same. However for comfort, a lot of mfgs will allow 350-375CFM/ton for heating and cooling for better humidity removal. Carrier seems ot design all of their equipment for about 375CFM/ton nominal. Infinity controls will run down to about 300CFM per ton in high humidity conditions depending on outside air temperature (system capacity). In heating mode, in lower outside temps they will also lower CFM for higher temp rise.
450CFM will give you more capacity and usually more effciency especially in warmer weather. But will impact comfort. You temp rise in colder weather might dorp down to 10F, which makes the system seem drafty unless the ehat strips are on.
As mentioned above, inverters are all over the place depending on the comfort profile selected and indoor and outdoor tmepratures. The bottom end is usually around 300CFM/ton. Belwo that unless its' really cold out or inside you can have high pressure issues.
Professional Member*
Huh?
I think he asked about airflow per ton, not heat loss per suqre foot. The "Rule of Thumb" fooled you.
Professional Member*
I had the same problem with instructors at trade school
the older teacher was the more progressive,
the younger teacher was stuck on rule of thumb sizing, and
that heat pumps were crap.
sure was glad I had the older teacher.
20+ years ago heat pumps didn't work as well as they do
now. some teachers/techs/hvac company owners are still
convinced that heat pumps don't work. their loss...but
you'll learn differently.
best of luck.
The cure of the part should not be attempted without the cure of the whole. ~Plato
Professional Member*
Extruded curved blade registers and terminal velocity make heat pumps a wonderful thing.
Professional Member*
http://sanjuanupdate.com/2011/03/ken...egrine-falcon/
http://wn.com/terminal_velocity?orde...ime=this_month
Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities
God Speed, Jim. We'll miss you - 2-26-23
A few years back there was a thread or 2 about this in the Pro forums. I believe it was Normchris that posted that heat pumps are more efficient at 450 CFM per ton.
Professional Member*
Systems are designed for nominal 400 cfm per ton. The air handler doesn't differentiate between heat and cool modes, and a heat pump is an air conditioner first.
Yes there are some exceptions - carrier built equipment is designed at 350, and one day every system will have a variable speed air handler and an inverter drive compressor, Skynet will become self-aware, and we will all be checking superheat in the matrix. Until then, 400 cfm per ton.
God Speed, Jim. We'll miss you - 2-26-23
Many systems are also commonly sized using .1" FR. Doesn't mean its right, its just commonly done.
Regular Guest
Just from this thread I understand more about heat pumps now. I'm still new to this field and I'm slowly learning but I'm getting there.
Professional Member*
I would order Manual S and H from ACCA's website and do a little reading. I just spent the week with the author of these two books ( along with Manual J and D) and believe me he's not into rule of thumbs!
And 400cfm per ton on A/C is also BS.
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Professional Member*
RIGHT, 400 CFM/ ton +/-10% is a good observation
_ and B asic S cience.
Q = 1.08 * CFM * dT
Q ton = 12,000
SHR avg 0.75
Q sensible 9,000 ______ 9,000 ____ 9,000
dt = ____ 21 ______ 18 ________ 23
_______ 1.08 ______ 1.08 ______ 1.08
_ CFM 397 ____ 463 ____ 362
Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities
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