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Thread: Getting The Correct ESP From A Furnace With A PSC Motor Compared To One With A ECM?

  1. #1
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    Getting The Correct ESP From A Furnace With A PSC Motor Compared To One With A ECM?

    Hello Im trying to see if Im on the right path when it comes to getting the maximum operating (ESP) External Static Pressure on the new ECM Furnaces compared to the old PSC motors.

    When it comes to the PSC Furnaces the furnace has already been lab tested for the maximum (ESP) and they would put it on the Data Plate while with the new ECM Furnaces requires us to go by the Manufacturers Fan Performance Chart? Im studying using Manual D and I just want to know if this is correct?

    Thanks!

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    Hello Cook42 - I believe that all air handlers, all devices with inside Blowers, will have the maximum external static pressure listed on the unit.
    But you could always go look at the fan perf chart and you will see where the Static Pressure maxes out which will be where the flow numbers stop.
    Does that help?

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    Quote Originally Posted by Tom Thermo View Post
    Hello Cook42 - I believe that all air handlers, all devices with inside Blowers, will have the maximum external static pressure listed on the unit.
    But you could always go look at the fan perf chart and you will see where the Static Pressure maxes out which will be where the flow numbers stop.
    Does that help?
    Hello and thanks I was just trying to make sure! Thanks!

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    Lots of newer installs will exceed the data plate. It's not unusual to bump .8 +with some coils I'm told (Carrier)
    Don't pay too much attention to ESP. The fans are rated under lab conditions with no inlet restrictions.
    Why do you want to max out the fan? Is the CFM not what your looking for?
    ESP is OK for troubleshooting but there are better ways to measure performance.
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    I would say it is better not to max out the fan so it has room for when things get dirty or added so it can move the needed air without struggle.

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    Quote Originally Posted by hvacker View Post
    Lots of newer installs will exceed the data plate. It's not unusual to bump .8 +with some coils I'm told (Carrier)
    Don't pay too much attention to ESP. The fans are rated under lab conditions with no inlet restrictions.
    Why do you want to max out the fan? Is the CFM not what your looking for?
    ESP is OK for troubleshooting but there are better ways to measure performance.
    I was learning about how to get the friction rate and how to calculate in order to do ductwork design. I know that you need the Manual J to actually get the information I need to begin to design the system I just noticed on this one particular Concord unit I didnt see the info on it and I was just wondering since its a ECM motor do you have to get the info out of the manual? And I total agree about not setting the static pressure to the Max I was thinking more like .5 IWC.

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    Quote Originally Posted by BNME8EZ View Post
    I would say it is better not to max out the fan so it has room for when things get dirty or added so it can move the needed air without struggle.
    I totally agree and thanks I would think we would try to set it in the middle.

  8. #8
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    Quote Originally Posted by Tom Thermo View Post
    Hello Cook42 - I believe that all air handlers, all devices with inside Blowers, will have the maximum external static pressure listed on the unit.
    But you could always go look at the fan perf chart and you will see where the Static Pressure maxes out which will be where the flow numbers stop.
    Does that help?
    Yes it does thank you so much!

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    Unless otherwise stated on equipment or in manual, I always go with TESP 0.5”wc.
    With that said, that doesn’t mean you set the ductulator to 0.5”, more like .05-0.1”. The biggest restrictions are going to be fittings, boxes, diffusers, etc. fitting design make A LOT of difference.
    Don’t make manual D more complicated than what it is. It’s not some crazy difficult thing that takes years to learn. Some guys act like you need some expensive program in order to calculate ducting, or manual S equipment size. Far from the truth, especially in residential.

    Now fitting design/fab does take some time to learn. I always laugh when some oblivious customers look at a two-way offset transition in order to bend around some obstruction, while still maintaining proper cross sectional area, and they say, oh that’s all you had to do? Most companies around here will throw a flex line on it, all kinked an squished.
    Last edited by mgenius33; 02-28-2021 at 09:45 AM.
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    Quote Originally Posted by mgenius33 View Post
    Unless otherwise stated on equipment or in manual, I always go with TESP 0.5wc.
    With that said, that doesnt mean you set the ductulator to 0.5, more like .05-0.1. The biggest restrictions are going to be fittings, boxes, diffusers, etc. fitting design make A LOT of difference.
    Dont make manual D more complicated than what it is. Its not some crazy difficult thing that takes years to learn. Some guys act like you need some expensive program in order to calculate ducting, or manual S equipment size. Far from the truth, especially in residential.

    Now fitting design/fab does take some time to learn. I always laugh when some oblivious customers look at a two-way offset transition in order to bend around some obstruction, while still maintaining proper cross sectional area, and they say, oh thats all you had to do? Most companies around here will throw a flex line on it, all kinked an squished.
    So basically 0.5 will be the benchmark and until you add up all the component pressure drops and subtract that from the 0.5 to get the available static pressure then we will use that number to set my static pressure? And I will use that available static pressure number put it in a formula to get the friction rate for the hold duct system?

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