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  1. #1
    Join Date
    Jul 2007
    Posts
    5

    Return Air Sizing...too loud!

    I'm a general contractor and have been using the same HVAC sub for the last 5 years, up until last week that is. It's not so much that he is not very good, just not there when i need him and installs seem to take way too long, not to mention poor follow up on any problems. Anyway, that's a different story.

    My main problem right now is a new home I built last year. Inside, he installed 16 SEER Carrier Infinity units both up and down. The outside compressors are Carrier Performance Series, a 5 ton down for about 2,300 square feet of living area and a 2 ton on the second floor for about 800 sq. feet of living. 1st floor unit works great...quiet and cools very efficiently.

    The problem is with the second floor unit. The home is located in the deep south with typical summer temps of 93 to 98 degrees on a daily basis. The attic usually does not get above 95 degrees. The home is well insulated with R30 in the ceilings and R13 in the wall cavities.

    At night the unit cools well, but during the day, when temps rise, with the thermostat set on 70, the temp will not drop below 79 to 75. The system is about one year old and I just had my new HVAC contractor check it. Puron level was about a pound low due to a leaky connection, but he fixed that. It now cools better, but not as good as it should during the day.

    The Totaline Digital thermostat is set so that the 1st stage of the compressor never kicks in. I also have it adjusted +10 degrees. The air flow being sucked into the return seems unusually loud. You can hear the sucking noise from downstairs. Could the air return be too small? It's 20"x20" for the 2 ton unit cooling approx. 800 sq. feet, which seems like it should be plenty big enough for the square footage. The owners tried one of those pleated air filters and the unit was so loud they had to go to the cheapie type filter. Also, radiant heat from windows on the second level is not an issue.

    We're going to further insulate the attic space with a radiant heat barrier. Not because of the unit in particular, but because it makes such a huge difference in overall comfort of the home in areas where it gets this hot.

    Any ideas on what I can do to increase the efficiency of this unit?

    Thanks!
    Last edited by TABCON; 07-15-2007 at 10:49 AM.

  2. #2
    Join Date
    Jan 2007
    Location
    in my lumpy chair
    Posts
    1,952
    did you go low bid?
    I dont warranty Tinkeritus

  3. #3
    Join Date
    Jun 2007
    Location
    Central, FL
    Posts
    871

    Thumbs up Carrrier 16seer

    Well at that eff. I'm sure we are dealing with a R-410a unit or puron system. I always recommend that a subcooling be performed on the unit. Charging a unit by pressures is not the correct way of making sure a unit is charged properly.You may want call the tech that came out and ask if he performed a subcooling to the unit. If he tries to talk you out of it, or has no idea what you are talking about just call someone who does. About your return box its 20x20 but is there a flex connected to the box? If so whats the size of it? Also you may want to check the supply,a small supply or obstructed supply(vents shut closed)will cause just as much noise as a small return. Good luck there!
    WARNING:IF YOU DON'T KNOW THEN DON'T DO, SO THOSE WHO KNOW WHAT YOU DIDN'T KNOW DON'T END UP UNDOING WHAT YOU DID SO IT COULD GET DONE RIGHT!

  4. #4
    Join Date
    Jul 2007
    Posts
    5
    Low bid? LOL, no, never. I would have used window units for that...lol.
    Seriously, we only build high end custom homes with square footage costs of $200+ per sq.foot living. I don't like to be called back on problems, so we only use the best of everything.

    The actual size of the rigid return air plenum box is larger than 20x20, that is just the filter size. But the rush of air going into the 20x20 hole in the wall sounds very loud. Also, no flex, all rigid wood frame with insulation panels.

    I will also have my new contractor check on the charging method you mentioned.

    Thanks guys.

  5. #5
    Join Date
    Jun 2007
    Location
    Central, FL
    Posts
    871

    Hmmmmm

    You may have a control issue, maybe the dead band on the thermostat is not set right, or the t-stat is not calling the proper stage of cooling. Any how you should right down on paper your compliant and have a tech come out again. If they still can't figure it out they will call a Factory tech which knows the product by heart. GOOD LUCK
    WARNING:IF YOU DON'T KNOW THEN DON'T DO, SO THOSE WHO KNOW WHAT YOU DIDN'T KNOW DON'T END UP UNDOING WHAT YOU DID SO IT COULD GET DONE RIGHT!

  6. #6
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,841
    Quote Originally Posted by TABCON View Post
    Low bid? LOL, no, never. I would have used window units for that...lol.
    Seriously, we only build high end custom homes with square footage costs of $200+ per sq.foot living. I don't like to be called back on problems, so we only use the best of everything.

    The actual size of the rigid return air plenum box is larger than 20x20, that is just the filter size. But the rush of air going into the 20x20 hole in the wall sounds very loud. Also, no flex, all rigid wood frame with insulation panels.

    I will also have my new contractor check on the charging method you mentioned.

    Thanks guys.
    I think you're actually mixing two different issues here, which could at some point intersect but right now I'd treat them as separate issues.

    #1 Issue: The system is not cooling to the clients satisfaction
    #2 Issue: The return air is noisy.

    Understanding that you do not wish to have these issues at all upon system commissioning and also that you do high end homes, which you indicate and your equimpent selection indicate hour are not taking the 'lowest bid' for the sake of cutting corners. That all SHOULD work in your favor but sometimes the company or companies you hire, may not be up to your standards, except to supply the equipment. What I'm saying is that if the company you were using in the past or are now considering using in the future does not start work from an achitects plan and do a Manual 'J' load calculation, Manual 'D' duct design and Manual 'S' equipment selection, you're not getting what you think you're paying form.

    When a proper load analysis is done, if the equipment is then not performing up to design specifications (outdoor temp/indoor temp/indoor humidity) then it should be a relatively easy task to go through the entire system, step by step and determine what parameter is outside specifications, what it will take to bring it into spec. and then do that repair/mod.

    When a duct design by Manual 'D' is done, the system should not be noisy. Airflow ratings are determined by the size of the duct the air is flowing through, the total volume of air flowing through that duct and the actual speed of the air moving through the duct. As an example, when our company installs a duct system with a variable speed blower motor, experience has taught us that the face velocity throught a return air grille can set up a harmonic that will cause some 'singing' of the louvers in the grille. So as a matter of company policy, we increase the size of the grille by 25%. You say you have a 2-ton system there and normally that would be approximately 800 CFM. We'd increase that airflow to 1,000 CFM and select a return air grille that would would handle at least 1,000 CFM. I think you indicated your client is using a filter grille so I looked at a Hart & Cooley #659 filter grille and at 20 x 20 size, 700 FPM face velocity, it is rated at 1,342 CFM, more than enough to satisfy the example system. As you can see from that simple research, the finger would point to some other location in the system for the noise besides the return air filter grille.

    So if your original installer did not do the load analysis and duct design, I'd hire a new company to do that. The results may not be what you want to hear but it's money well invested to both resolve the current issue and maybe to prevent future issues. Usually you'll find that companies who start properly, end properly, fully support their installations and employe the best people. Naturally, they're NEVER the lowest bid and may be higher than you've been accustomed to paying but they're worth every penny in the long run. Hope this helps.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  7. #7
    Join Date
    Mar 2002
    Posts
    327
    I think all the replies have missed a major problem.

    As I read the origional post, Tabcon says that average summer temperature is 95 to 98 degrees and the attic temperature stays at 95 degrees? Ninety five???? 5 degrees less that 100? 3 degrees less than the outdoor temperature?

    Maybe he turned the boots the wrong way and is blowing air into the attic!
    (sarcasm intended)

    Can you say leaky ductwork?

  8. #8
    Join Date
    Apr 2004
    Location
    Charlotte, NC
    Posts
    648
    Restriction in the return?
    "Fighting Ignorance since 1973 (It’s taking longer than we thought)." The Straight Dope.

  9. #9
    Join Date
    May 2007
    Location
    Wildomar Ca
    Posts
    221
    Why is the first stage wired so it never kicks in.??

  10. #10
    Join Date
    Jun 2007
    Location
    Galveston
    Posts
    85
    the return air is 20"x20" whats the grill size? The grill could b too small or the path rest. in another way

  11. #11
    Join Date
    Jul 2007
    Posts
    5
    Quote Originally Posted by skippedover View Post
    I think you're actually mixing two different issues here, which could at some point intersect but right now I'd treat them as separate issues.

    #1 Issue: The system is not cooling to the clients satisfaction
    #2 Issue: The return air is noisy.

    Understanding that you do not wish to have these issues at all upon system commissioning and also that you do high end homes, which you indicate and your equimpent selection indicate hour are not taking the 'lowest bid' for the sake of cutting corners. That all SHOULD work in your favor but sometimes the company or companies you hire, may not be up to your standards, except to supply the equipment. What I'm saying is that if the company you were using in the past or are now considering using in the future does not start work from an achitects plan and do a Manual 'J' load calculation, Manual 'D' duct design and Manual 'S' equipment selection, you're not getting what you think you're paying form.

    When a proper load analysis is done, if the equipment is then not performing up to design specifications (outdoor temp/indoor temp/indoor humidity) then it should be a relatively easy task to go through the entire system, step by step and determine what parameter is outside specifications, what it will take to bring it into spec. and then do that repair/mod.

    When a duct design by Manual 'D' is done, the system should not be noisy. Airflow ratings are determined by the size of the duct the air is flowing through, the total volume of air flowing through that duct and the actual speed of the air moving through the duct. As an example, when our company installs a duct system with a variable speed blower motor, experience has taught us that the face velocity throught a return air grille can set up a harmonic that will cause some 'singing' of the louvers in the grille. So as a matter of company policy, we increase the size of the grille by 25%. You say you have a 2-ton system there and normally that would be approximately 800 CFM. We'd increase that airflow to 1,000 CFM and select a return air grille that would would handle at least 1,000 CFM. I think you indicated your client is using a filter grille so I looked at a Hart & Cooley #659 filter grille and at 20 x 20 size, 700 FPM face velocity, it is rated at 1,342 CFM, more than enough to satisfy the example system. As you can see from that simple research, the finger would point to some other location in the system for the noise besides the return air filter grille.

    So if your original installer did not do the load analysis and duct design, I'd hire a new company to do that. The results may not be what you want to hear but it's money well invested to both resolve the current issue and maybe to prevent future issues. Usually you'll find that companies who start properly, end properly, fully support their installations and employe the best people. Naturally, they're NEVER the lowest bid and may be higher than you've been accustomed to paying but they're worth every penny in the long run. Hope this helps.

    First of all, thanks for the time you took to really address my problem. I wish you were located around here. I'd hire your company in a NY minute. You see, since hurricane Katrina, a great deal of the expert help in this area moved on and many of the best subcontractors are booked up a year or more in advance.

    A great deal of the work I do is designed and specked by architects and engineers, especially homes on the waterfront. Some of the spec books are the size of a book like War and Peace. Also, most call for rigid duct work and loads of different zones. To date, I've never had a problem with my HVAC sub. I'm still not sure what's going on now. It really bothers me that I had to go out and find a new sub, and that his service has fallen down to zip. All I can speculate is that he's tired and wants to either go on welfare or retire.

    Based on what you say, the return air plenum and opening are more than large enough. So, we will look elsewhere. As a matter of course, I'm going to have all the coils and evap's cleaned. Construction and grading can cause a great deal of dust and regardless of what steps you take, some sub always cranks the ac down to 55 with the doors open.

    Yea, maybe I was wrong on the attic temps. The last time I checked it was around 95, but it was a cloudy day. But the duct work is sealed properly and no leaks were found.

    Also, no restrictions noted in the return. I was advised that in this heat, having the first stage kick in is useless. The thermostat is not "wired" that way, just adjusted per the menu that way. It's a Totaline digital that gives you that option.

  12. #12
    Join Date
    Jul 2007
    Posts
    5
    Quote Originally Posted by James Tramel View Post
    the return air is 20"x20" whats the grill size? The grill could b too small or the path rest. in another way
    That is the size of the filter. The actual framed in plenum is much larger, maybe 24" x 32"?

  13. #13
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,841
    Quote Originally Posted by TABCON View Post
    First of all, thanks for the time you took to really address my problem. I wish you were located around here. I'd hire your company in a NY minute. You see, since hurricane Katrina, a great deal of the expert help in this area moved on and many of the best subcontractors are booked up a year or more in advance.

    A great deal of the work I do is designed and specked by architects and engineers, especially homes on the waterfront. Some of the spec books are the size of a book like War and Peace. Also, most call for rigid duct work and loads of different zones. To date, I've never had a problem with my HVAC sub. I'm still not sure what's going on now. It really bothers me that I had to go out and find a new sub, and that his service has fallen down to zip. All I can speculate is that he's tired and wants to either go on welfare or retire.

    Based on what you say, the return air plenum and opening are more than large enough. So, we will look elsewhere. As a matter of course, I'm going to have all the coils and evap's cleaned. Construction and grading can cause a great deal of dust and regardless of what steps you take, some sub always cranks the ac down to 55 with the doors open.

    Yea, maybe I was wrong on the attic temps. The last time I checked it was around 95, but it was a cloudy day. But the duct work is sealed properly and no leaks were found.

    Also, no restrictions noted in the return. I was advised that in this heat, having the first stage kick in is useless. The thermostat is not "wired" that way, just adjusted per the menu that way. It's a Totaline digital that gives you that option.
    You're welcome and I too am sorry we're not in your service area. But we're all still here to help.

    Okay so you say you have a mechanical engineer or architect spec out the system size. That should be good news but for me it's not necessarily so. I've corrected any number of mechanical engineers for undersized systems. So we always do an in house Manual 'J' just to be sure because we don't want to be a participant in the finger pointing if things don't go right. For that matter, we always have our geo-thermal loads double checked by the engineers at the equipment suppliers for the same reason.

    So assuming the calculations are correct for the moment, it then becomes a matter of going down a checklist for troubleshooting purposes. That checklist should include such things as gauge readings hi & lo, super heat & subcooling numbers, OAT & outdoor wb at the time of reading, static pressures as taken in the supply & return plenums, temperature rise across the condenser, temperature drop across the evaporator, wb & db temps indoors, motor amp ratings & actual amp readings. From these readings a good tech can tell you if the equipment is operating up to specs or if there's some reading that is NOT up to specs, indicating a problem. If the equipment all shows it's up to specs, then the Manual 'J' calc is thrown under a cloud of suspicion. I'd also recommend that you take an actual temperature reading in the attic because if it's coole than very hot up there, then there's something cooling it down.

    I'm really quite suspicious of that return air noise. A temp drop across the evap would tell a lot in that regard.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

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