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  1. #1
    Join Date
    May 2010
    Posts
    12

    Carrier Infinity Airflow Question

    I have a Carrier Infinity system with a 24ANA160 5 Ton AC unit and a 58MVC-120-20 furnace. In the rooms with the longest duct runs we have heating/cooling variances of between 5-8 degrees from the thermostat. I believe we have poor airflow. The contractor disagrees with me but does not offer much in the way of solutions on the temperature variance and says it is withing "industry standards"

    Here is a picture of what I am getting currently.

    Name:  thermostat.jpg
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    Is the static pressure good enough when in high heat mode?

    The air delivery Chart says high heat mode should be 1900 cfm from static pressures between .1 and .5. After .5 the cfm drops off. Would higher static pressures give me more airflow or higher velocity of the current airflow to adequately heat the rooms I have issues with?

  2. #2
    Join Date
    May 2010
    Posts
    12
    I'm not sure if the picture will show up. It is showing 0.03 inches at 1922 cfm

  3. #3
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    You must have very good work and an air filter with very low resistance. It's impressively low for 1922 CFM. Is the air filter even installed? It's almost unusually low. Usually you don't see values that low until you're on low speed. It might be near the bottom speed limit on low stage 400RPM). I really woudl think the coil alone should create at least a 0.1" pressure drop.

    Higher static won't help. The VS motor on the blower will deliver constant airflow unless it's at minimum or maximum RPM. I don't have a shart in front of me, but I'm guessing your at around 1000 RPM?

    IS this a very large house with a LOT of ductwork and a big... really big plenum or something? Maybe this just shows what a really good retrun and supply plenum can do.

  4. #4
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,644
    I don't think the stat is reading correctly. But, that said, your ductwork (supply and return) must be nicely sized.

    The airflow problem may be fixed by "dampering" down the supplies to the rooms closest to the furnace (and small room,i.e., bathrooms or unused rooms) to make the airflow stronger to the far away (and/or larger) rooms.

    Sounds like, if the basement is unfinished, that the Carrier Infinity zone system may have been in order if this has been a problem in the past.

    But let me guess, the HVAC guy told you the variable-speed blower would do the trick.

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    SOrry, got fixated by the picture and didn't notice hte reference to the balance issue. Yes, best solution as mentioned is to add manual dampers to each branch or at least the branches with the most airflow.

    Look at it this way. The farthest roosm are not nessesarily getting too little airflow, as mcuh as the room closest are getting too much. Reduce the airflwo to the overconditioned rooms and it will improve the others, un;ess the ducts are collapsed, disconnected or badly leaking. That's another problem.


    Another thing is equipment sizing. A 120k furnace is too commonly installed on a medium sized home. I have a 3200sqft home and if on a single zoned system, I woudl only have a 80k BTU furnace with a 0F design temp. A 120k BTU furnace could easily heat a 5000sqft home with a well installed zone system. IF you actually "need" 120k BTU's, your natural gas bills should be around $600-800 in Jan. Oversized equipment that short cycles wll make a temeprature imbalance much, much worse. A bigger blower and furance will not "push" air farther.

    For esample My 60k BTU furnace is a little oversized but it's the smallest you can get in an Infinity furance.... sadly. It's at I think about 150 hours in low stage and 20 hours in high stage... last i checked or about 70 therms since the start of the heating season. I'd say that a properly sized unit (45k, smallest furnace currently made) would be at about 30 hours on high and 200 hours on low. My previous 80k BTU furance on the other hand would have only ran about 90 hours in comparison. SO going from 80k BTU single stage to a 60k BTU 2 stage doubled my run time (it's a LOT more comfortable) going to a 45k or a modulating furnace would increase it by another 50%.

  6. #6
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    I think the problem is they forgot to connect your furnace to the duct work.

    Definitely need a LOT more pictures. Your duct, your return drops, and your media filters are huge to have so little pressure. There may be a huge hole or disconnect in your system.

    Duct work is like a garden sprinkler. There is a broad range at which every hole gets even flow out of it, ideally you want between .5 and .1 on high output.

    More pressure doesn't change things, just burns energy. More pressure doesn't fix crappy flow, though many think that's the cure.

    At some point less pressure changes things. If the whole system doesn't see pressure, some holes flow and some don't.

    At .03 I don't think your duct work is pressurized. 1900 cfm is a LOT of air, I wonder where it's going...
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  7. #7
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,784
    I agree with tedkidd, .03 is unusually low sp. it's like there is no pressure. I think your sensor is not working correctly.

  8. #8
    Join Date
    May 2010
    Posts
    12
    I have a supply diagram and a return diagram that I drew up on what is existing as well as a manual j and manual d and a new duct diagram that will supposedly fix my issues that I commissioned from an internet designer.

    Supply Diagram:
    https://www.dropbox.com/s/y9w90liqma...%20Diagram.pdf

    Return Diagram:
    https://www.dropbox.com/s/hlprzdk106...%20Diagram.pdf

    Manual J
    Lloyd man J reports.pdf

    Manual D
    Lloyd man D report.pdf

    New Duct diagram
    Lloyd schematics.pdf

  9. #9
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,784
    Yep, that should solve it. Gonna cost a pretty penny to install all that, might as well throw in the infinity zone system while you're at it for an additional penny.

  10. #10
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    I'm baffled by the static pressure issue. 1900 cfm with virtually no static indicates huge flow with no restriction. Not sure where to go without that sorted.


    What's the house, 2500 sf/floor x2? How old? Energy Star?
    Do you have your blower door cfm50 number? Are you playing thermostat games, or managing for comfort within a narrow range?

    That's really big equipment. That looks like a really nice house. Seems like somebody used a sledge in place of a mallet unless build quality is crappy. Blower door number would tell.

    Unfortunate because if the equipment was smaller (assuming tight, well insulated enclosure) communicating zoning would be the treat. You only need 3 dampers. But that monster might not like being leashed. Although THAT static number indicates otherwise.

    Does the equipment cycle off?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  11. #11
    Join Date
    May 2010
    Posts
    12
    I'm baffled by the static pressure issue. 1900 cfm with virtually no static indicates huge flow with no restriction. Not sure where to go without that sorted.


    What's the house, 2500 sf/floor x2? roughly 5600 sq

    How old? 3 years old

    Energy Star? Not energy star rated, but it has spray foam in the walls, low-e double pane windows and R44 in the ceiling.

    Do you have your blower door cfm50 number? a blower door test has not been done.

    Are you playing thermostat games, or managing for comfort within a narrow range? I leave the thermostat set at 69 and my master bedroom is usually around 62-64 when heating. I blocked off returns and kicked the thermostat into high heat mode and the bedroom would finally get to temperature. The basement is always cold.


    That's really big equipment. That looks like a really nice house. Seems like somebody used a sledge in place of a mallet unless build quality is crappy. Blower door number would tell.

    Unfortunate because if the equipment was smaller (assuming tight, well insulated enclosure) communicating zoning would be the treat. You only need 3 dampers. But that monster might not like being leashed. Although THAT static number indicates otherwise.

    How would you damper with 3 zones. I am getting a quote for zoning, but they want to zone each main trunk and put a thermostat in the master bedroom, the main hall, and the basement. The problem I forsee is the thermostats in the master bedroom and the main hall would fight against each other because most of the supplys in the trunk going to the master bedroom feed the main open areas in the house.

    Does the equipment cycle off? I'm not sure what you mean by cycle off. The system does turn on and off, and I think the AC short cycles.

  12. #12
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,644
    Something does not add up. From reviewing your return air diagram, you are short on return air side.

    Your static reading should be out of sight depending on how long the 10" flex is.

    You said this home is a 2 story? Is the HVAC system in the basement?

    I need to turn my screen on it's side to read the supply diagram and I don't have the patience to do so.

  13. #13
    Join Date
    Nov 2012
    Location
    New Jersey
    Posts
    3
    The newer variable speed blower motors have limiters built into them so that even if its being told to push more air, the motor takes over and protects itself. When this happens you'll see extremely odd readings on the thermostat.

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