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  1. #1
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    New Home AC System - unable to reach set point - builder quality HVAC install?

    So we built a new 3300sf home in Houston TX, read tons on Energy Vanguard and HVAC-Talk and tried to do things right: Put the AC equipment in a mechanical room in, put all the ducts in conditioned space and hired a third party HVAC designer to do the Manual J+S+D. He came up with 2 tons AC (105 % per Manual S - with 59TP6040) downstairs and 1.5 tons HP upstairs (125% per Manual S - with FV4C24), using the Houston TX design of 96 outdoor and 75 indoor.

    We have ecobee thermostats and have them programmed for 78 away and 75 home.

    The issues since we moved in 4 days ago (outdoor temps have been at design or even 1-2 degrees higher):
    - When we come home at around 4:30 and the ecobee set point changes from 78 to 75 both upstairs and downstairs are unable to lower the temp for a while. Upstairs will reach the set point by about 8pm whereas downstairs makes it to 77 within an hour but then takes until 9pm to get to 76 and even until midnight to reach 75. This is almost without any internal gains, only two people, all lights off, no cooking, etc.

    - Measured with a laser thermometer, the supply register temperature downstairs closest to the AHU is around 58 degrees but then a bit further away in the same room goes to 65 degrees and the master bedroom which is furthest away is even 70 degrees. There is a slight change in room temperature in those further away rooms but surprisingly not a lot (maybe 1-1.5 degrees max) since we have all the doors open. The humidity is between 48 % and 55 % throughout the day everywhere. In comparison, upstairs the air out of all supply registers is between 58 (closest) and 64 (furthest).

    - I noticed that there is strong air blowing out of the condensate drain pipes (they have an open standpipe T) for the downstairs unit. The upstairs unit has the same but there is very little air that comes out of the FV4C air handler.

    - The front of the coil door of the downstairs AHU is leaking quite a bit of cold air as well.

    - The HVAC installers didn't modify the dip switches on the 59TP6 VS furnace per the designer's instructions. The unit was incredibly loud when I first moved in which made me check the switches. I turned the unit off and set the right switches myself (per the Manual this reduced the airflow from 1065 cfm at 0.5 WIC to 800 cfm at 0.5 WIC.

    The builder sent somebody from the HVAC company out (two young guys, didn't leave a savvy impression ...) and they checked the pressure out at the compressor and said it was fine. Then they measured the temperature right at the AHU and said the return was 77 and supply was 56 which was perfect and that the system was running at it's best. I was shocked that they just rammed the probe straight into the flex duct instead of having an opening in the plenum. They didn't even tape over it afterwards. Doesn't that leave a duct leak?? I asked them about the static pressure between return and supply since per the Manual D this was supposed to be 0.5 and that if it was different the air might flow faster or slower than the 800cfm design but they said they don't measure static pressure!?! They told me to talk to their boss if I really wanted the extra measurements or items addressed.

    Sorry for this long background, my main questions are what I can expect an HVAC installer to do without being unreasonable?

    1) Should I not expect a system to recover from a set back during design conditions? (meaning I should not go from 78 to 75 at 4:30 in the hottest days of the summer)?

    2) Is the 70F air coming out of the "further away" supplies downstairs a duct system issue or is this normal for longer duct runs and nothing to worry about since the temperature downstairs with all doors open balances out rather well?

    3) Should I insist on a static pressure measurement to confirm it is WIC 0.5 per the Manual D design?

    4) Should I insist that they seal around the coil to prevent the air leaks?

    5) Is the strong airflow out of the open standpipe normal?

  2. #2
    Join Date
    Nov 2004
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    ALL THE DUCTS IN CONDITIONED SPACE and
    having the poor performance at further away rooms
    point toward duct installation as Very Poor air distribution And/Or LEAKY.

    1. NO.!
    … Normal: somewhere in the range of _ 1'F / hour after the O.A. temperature is < 90'F.
    …
    2. Reply Above
    3. Yes as part of a COMPLETE AIR BALANCE.
    4. .. IS THE DOOR FIT-UP Extremely Poor?
    5. SEEMS LIKE static pressure is out-of-control.

    What did the HVAC Designer state during his final inspection?
    Designer Dan
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  3. #3
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    Jan 2004
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    Recovery during the hottest part of the day takes a long long time. Mine took over 5 hours last night to drop the temp 4 degrees. My system will maintain 72 on a 98 degree day.

    IR thermometers aren't real accurate for checking the actual air temp out of a register.

    What to expect out of a contractor, varies with the contractor. Most don't know how to check static properly.
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    How many times must one fix something before it is fixed?

  4. #4
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    Feb 2013
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    Thread Starter
    Quote Originally Posted by dan sw fl View Post
    ALL THE DUCTS IN CONDITIONED SPACE and
    having the poor performance at further away rooms
    point toward duct installation as Very Poor air distribution And/Or LEAKY.

    1. NO.!
    … Normal: somewhere in the range of _ 1'F / hour after the O.A. temperature is < 90'F.
    …
    2. Reply Above
    3. Yes as part of a COMPLETE AIR BALANCE.
    4. .. IS THE DOOR FIT-UP Extremely Poor?
    5. SEEMS LIKE static pressure is out-of-control.

    What did the HVAC Designer state during his final inspection?
    Thanks Dan!

    The builder ran a duct blaster test during the rough in stage and they came back at 129cfm25 downstairs and 66cfm25 upstairs and the target cfm was 132 for the whole house so they were out of code. He told me that he made the AC contractor come back to do more duct sealing but I just now found out a few days ago that he never performed a duct blaster test again. I was not as concerned about it since I figured the air is all within conditioned space so it's not being "wasted" but it looks like I figured wrong and this is an issue.

    The designer did not do any inspections either. We hired him through the builder and followed the builder's procedure and he said the designer usually does not come out for routine inspections, he only comes out if there are issues ... (so I guess it's time to get him out).

    When you say complete air balance, does that mean flow hoods under each register and verifying the cfm matches the Manual D?

  5. #5
    Join Date
    Aug 2003
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    Fort Worth, TX
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    With all ducts in conditioned space yet warmer supply air temps at outlets further away from air handler, if I was on site at your place, and if having ruled out duct leakage as a significant factor, I would next look at refrigerant charge level and airflow across cooling coils. I've seen air in motion within a duct actually thermally stratify. Blew me away first time I measured it. In your case the cooling coil may not be uniformly cooling the air passing through it, and further if this is the case AND the air leaving the coil is not adequately mixing, it will fly down the duct stratified, with one outlet getting the cooler air and another getting warmer air. An undercharged system will allow pockets of warmer air to leave the coil without adequate cooling.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  6. #6
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    Feb 2013
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    Thread Starter
    I decided to do a little more investigation myself tonight since the guys that came to "check the system" didn't do much. First thing I did was open the Honeywell F100 filter box and saw that the airflow arrow was pointing in the wrong direction! I may have found my static pressure issue?

    I didn't flip it around since it was already dusty on one side and I didn't want to blow that into the furnace. But tomorrow I will go get a new filter from home depot. One question: they only carry their own HD model numbers. My filter currently is the FC100A1029 - MERV 11 16x25x4.

    Main question: are the HD honeywell filters identical to their regular models, mainly are the static pressure curves the same? This info cannot be found for the HD models ... and I don't want to add more static pressure

    e.g. this looks like FC100A1029
    https://www.homedepot.com/p/Honeywel...25-E/202564481

    and this looks like FC200E1029
    https://www.homedepot.com/p/Honeywel...1625/203781261

    I still took some pictures of the duct installation in the mechanical room (see in next post). I think some of the take offs from the plenum probably have poor airflow because they are kinked?

    Should I ask them to use metal elbows coming out of the plenum?

  7. #7
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    Thread Starter
    Here the pictures. The curved ones on the bottom are 12" returns and a 6" fresh air intake with Honeywell controller and damper.

    The 4 take offs are from the plenum (one on each side)

    The two ducts running fully horizontally on the ceiling are part of a different AHU.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

  8. #8
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    Aug 2003
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    There's a shipload of wrong with that duct system. And to think I was under the impression that ductopusses only lived in attics. No, apparently they also like comfy, roomy mechanical rooms!
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  9. #9
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    At least its not a Goodman!

  10. #10
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    Thread Starter
    Quote Originally Posted by Shophound View Post
    There's a shipload of wrong with that duct system.
    The HVAC contractor, HVAC designer and builder will come to meet with me on Tuesday morning. I'm not sure if the designer is mainly a WrightSoft computer person or if he will also be able to tell us "hands-on" what is wrong with the installation. Therefore, anything you can let me know specifically, I can request to be changed. I'm hoping the static pressure can be improved enough by only modifying this mechanical room so that we don't have to open any drywall ceilings.

    Quote Originally Posted by Shophound View Post
    And to think I was under the impression that ductopusses only lived in attics. No, apparently they also like comfy, roomy mechanical rooms!
    Everybody was shaking their head about the mechanical room in the first place. All the builders we interviewed asked me why I don't want it in the attic "where it belongs". I selected the only builder that hires a third party HVAC designer since I thought this was a "quality sign". I found out months later, mid way through the build, that the reason he hires the designer is because his HVAC contractor would not know how to run a Manual J and wouldn't know how to size equipment ...


    By the way: putting in a brand new air filter with the airflow this time in the correct direction, unfortunately did not help much. There is still cold air blowing out of the condensation lines and from the coil door and the temperature at the furthest registers is still around 68-70 degrees.

    I would really appreciate any tips/help so that I know what to ask for on Tuesday. I'm also linking the Manual J+S+D from the designer in case that helps. The only deviation that happend in the field is the placement within the mechanical room. The downstairs furance got moved to where the upstairs unit is on the plan and the upstairs unit got moved to where the hot water heater is to shorten the distances.

    Manual J+S: https://drive.google.com/open?id=1H-..._NRFsWVk4pGg0Y
    Manual D: https://drive.google.com/open?id=1zk...SF_98vMRCjATpG
    Duct Design Plan https://drive.google.com/open?id=1R6...BoTgwxuP12RRQK

  11. #11
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    Nov 2006
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    That is SO UGLY!
    Why isn’t there any trunk? All those turns on the flex absolutely kill air flow.
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  12. #12
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    rhawke

    Ask the installing contractor for a full startup and commissioning report.

  13. #13
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    Jun 2006
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    Wow, wonder what you can't see. Installers must have been into bondage.

    Flex shouldn't be bent like that. the "horse shoe" return is probably 1/2 kinked off. All of the bends of flex should be taken off, metal elbows and metal duct installed to get rid of the bondage. Also, eventually that flex will sag at all those corners and cut off flow even more.
    I wish I had a $1.00 for every response I deleted.....

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