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Thread: Heat Pumps?

  1. #1
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    Heat Pumps?

    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!

  2. #2
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    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". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
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    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". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  4. #4
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    Quote Originally Posted by MurDoc04 View Post
    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!
    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.

    Thank you,
    Rick Boggs

  5. #5
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    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
    We really need change now

  6. #6
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    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". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
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    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.

  8. #8
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    Beginning I meant

  9. #9
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    Quote Originally Posted by MurDoc04 View Post
    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!
    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.

  10. #10
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    Quote Originally Posted by dan sw fl View Post
    2,000 SQ FT

    Average
    BTU/HR ___ O.A. Temperature
    24,800 ___ 30'F
    31,000 ___ 20
    37,200 ___ 10
    43,400 ___ 0
    Huh?

    I think he asked about airflow per ton, not heat loss per suqre foot. The "Rule of Thumb" fooled you.

  11. #11
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    south louisiana
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    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

  12. #12
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    Quote Originally Posted by energy_rater_La View Post
    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.
    Extruded curved blade registers and terminal velocity make heat pumps a wonderful thing.

  13. #13
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    Quote Originally Posted by rickboggs View Post
    Extruded curved blade registers and terminal velocity make heat pumps a wonderful thing.
    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". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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