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Thread: Question on upcoming HVAC installation .

  1. #1
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    Question on upcoming HVAC installation .

    Hello,

    I'm glad to have found this forum. Although it seems I found it a tad bit late as my new HVAC installation is scheduled for this weekend (my first!)

    Following is the necessary background:
    1) Single story primary residence located in Phoenix area, AZ. 1998 built, 2050 sq ft, high ceilings, glass windows, french doors. Most windows have sun shade.

    2) Currently installed HVAC equip - 1997 5 ton R-22 Carrier AC + Gas furnace (80%??). Split system (furnace and evaporative coil in the attic)

    3) New upcoming installation -
    Trane16 SEER 5-ton XR16 split gas system.
    Model#
    4TTR6061C1000
    S8X1C100M5PSA
    4TXCC009DS3

    4) Decision between 14 seer and 16 seer was just based on the fact with Fed and utility credits, they were coming out to be almost similarly priced.

    5) All the contractors I spoke with insisted on 5ton for my area/built size. I was told Manual J will be required anyway to qualify for utility rebates. But I'm not sure when it will be performed.

    Current issues:
    One of the main problems with the current setup is that there’s uneven distribution of cold air throughout the house. The fact that Sun hits every room differently doesn’t help either.
    The main reason for the uneven distribution, I am being told, is the way “output” (supply?) ducts are sized. The biggest one dumps most of the air in bedroom (air taking the path of least resistance) leaving smaller proportion for other rooms.
    I discussed this with my installer and he suggested:
    A) Adding balancing dampers with the new plenums.
    B) Installing an additional air return (currently there's just one in the ceiling. I use two 20x20x1 filters ).

    I wanted to discuss the last part in more detail. I skimmed through the forum last night and at least got the importance of right duct sizing. From what I got a 5 ton AC means 400*5=2000CFM.

    Q1) Does this mean that both the supply and return path should be able to sustain this flow rate separately (2000 CFM on both the paths)?
    Q2) How can ensure that my existing ducts are capable of handling this ? ( As mentioned above, the current system is also 5 ton, but that doesn’t necessarily mean much). I don't think, I can get a Manual D calc done in two days. Are there any "rough" estimations I can do ?
    Q2) I started looking at the chart shared below. This is a handy chart that shows the “expected” return and supply air CFM and Grille size (see pic below). I understand the latter - Grille sizing..but for supply and return column, should their summation be at least equal to the HVAC's CFM?
    Q3) Anything else that you would suggest me, I can do in the next 2 days before the installation beings ?

    Thanks a lot for reading this.
    Appreciate any guidance on this.
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  2. #2
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    Thread Starter
    Bumping up, in case any one wants to share their thoughts. Thanks!

  3. #3
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    In AZ, where humidity isn't a factor, 5 tons means 450 x 5 so, 2250CFM to cover sensible loads.
    That is a LOT of air to move in a 2050sqft residence...
    The TRUE highest cost system is the system not installed properly...

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  5. #4
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    I would insist on the manual J and a manual D printout before allowing work to begin.
    The TRUE highest cost system is the system not installed properly...

    Find a HVAC-Talk Contractor by clicking here

    Click below to BECOME a pro member
    https://hvac-talk.com/vbb/forumdispl...ip-Information

    Do you go to a boat repairman with a sinking boat, and tell him to put in a bigger motor when he tells you to fix the holes?

    I am yourmrfixit

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  7. #5
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    Quote Originally Posted by vstech View Post
    I would insist on the manual J and a manual D printout before allowing work to begin.
    X2 After the installation is too late.
    *********
    https://www.hvac20.com/ High efficiency equipment alone does not provide home comfort and efficiency. HVAC2.0 is a process for finding the real needs of the house and the occupants. Offer the customer a menu of work to address their problems and give them a probability of success.

    Find contractors with specialized training in combustion analysis, residential system performance, air flow, and duct optimization https://www.myhomecomfort.org/


    Site member map HERE!

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  9. #6
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    Quote Originally Posted by Froodo View Post
    Hello,

    I'm glad to have found this forum. Although it seems I found it a tad bit late as my new HVAC installation is scheduled for this weekend (my first!)

    Following is the necessary background:


    1) Single story primary residence located in Phoenix area, AZ.

    1998 built,
    2050 sq ft,

    high ceilings,
    glass windows,
    french doors.

    Most windows have sun shade.

    2) Currently installed HVAC equip - 1997 5 ton R-22 Carrier AC + Gas furnace (80%??). Split system (furnace and evaporative coil in the attic)

    3) New upcoming installation -
    Trane16 SEER 5-ton XR16 split gas system.
    Model#
    4TTR6061C1000
    S8X1C100M5PSA
    4TXCC009DS3

    4) Decision between 14 seer and 16 seer was just based on the fact with Fed and utility credits, they were coming out to be almost similarly priced.

    5) All the contractors I spoke with insisted on 5ton for my area/built size. I was told Manual J will be required anyway to qualify for utility rebates. But I'm not sure when it will be performed.

    Q3) Anything else that you would suggest me, I can do in the next 2 days before the installation beings ?

    Thanks a lot for reading this.
    Appreciate any guidance on this.
    Get the equipment out of the attic.

    Attic is ~ 140' + F in Mid-Afternoon

    PENALTY: about 30% increase in heat gains.

    Reduce the equipment to 3.5 or 4.0 tons
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

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  11. #7
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    Thank you all for your valuable comments.
    I regret to report that the installation is already done now. How I wish I had learned about these things a few months back

    Now that being said, I wanted to know what can be done next ? I know not much, but specifically with respect to:

    1. Some of the rooms still are getting disproportionately higher percentage of cool air (better than before..but still not I want). For example my bathroom vents seems to be getting the most air.
    I was told by the installer that they can come after a week to adjust the flow rate (I suppose by adjusting the balancing dampers). But I'm sure they will try to tell me that they have done their best when I still complain (I already heard him say "this is a short duct ..so it will receive the max flow).
    As I understand the dampers may only affect the main supply duct from the plenum (I think I have three of those). But what if I want to control the flow from a distributary/secondary supply duct coming out from one of the main duct. What's the process to achieve that ?

    2. Since humidity is not a major concern in AZ, I guess the other issue with over-sized HVAC now will be wear of the system due to short-cycling. Two questions here:
    a) How short a runtime can be as termed short cycling ?
    I guess the answer would depend on the the temp difference between outside and thermostat... but i wanted to get a general idea. Is 15 minutes too short ? 20 minutes ?
    b) I read about anti-short cycle timer in the Trane spec sheet. Is that something that can be useful ?

    3. Does any other idea like blowing extra cold air to garage, seem feasible ? Note, I still need to fix my hot-cold issue.


    Although I feel duped (only I am to be blamed), I would still like to continue learning.
    Thanks to all again !

  12. #8
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    Quote Originally Posted by Froodo View Post
    Thank you all for your valuable comments.
    I regret to report that the installation is already done now. How I wish I had learned about these things a few months back

    Now that being said, I wanted to know what can be done next ? I know not much, but specifically with respect to:

    1. Some of the rooms still are getting disproportionately higher percentage of cool air (better than before..but still not I want). For example my bathroom vents seems to be getting the most air.
    I was told by the installer that they can come after a week to adjust the flow rate (I suppose by adjusting the balancing dampers). But I'm sure they will try to tell me that they have done their best when I still complain (I already heard him say "this is a short duct ..so it will receive the max flow).
    As I understand the dampers may only affect the main supply duct from the plenum (I think I have three of those). But what if I want to control the flow from a distributary/secondary supply duct coming out from one of the main duct. What's the process to achieve that ?

    2. Since humidity is not a major concern in AZ, I guess the other issue with over-sized HVAC now will be wear of the system due to short-cycling. Two questions here:
    a) How short a runtime can be as termed short cycling ?
    I guess the answer would depend on the the temp difference between outside and thermostat... but i wanted to get a general idea. Is 15 minutes too short ? 20 minutes ?
    b) I read about anti-short cycle timer in the Trane spec sheet. Is that something that can be useful ?

    3. Does any other idea like blowing extra cold air to garage, seem feasible ? Note, I still need to fix my hot-cold issue.


    Although I feel duped (only I am to be blamed), I would still like to continue learning.
    Thanks to all again !
    It seems I need to post these questions in the general forum via a new thread, to help me get clarification on these basic HVAC concepts.
    Thanks for your replies. I think, this thread can be considered close now.

  13. #9
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    I the equipment is too big you can open windows so the load will match the equipment. It's not an ideal solution, though.
    *********
    https://www.hvac20.com/ High efficiency equipment alone does not provide home comfort and efficiency. HVAC2.0 is a process for finding the real needs of the house and the occupants. Offer the customer a menu of work to address their problems and give them a probability of success.

    Find contractors with specialized training in combustion analysis, residential system performance, air flow, and duct optimization https://www.myhomecomfort.org/


    Site member map HERE!

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  15. #10
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    The only true test for short cycling is at design conditions it runs constant and maintains temp your golden. If it runs less than 75% of the time you are way over sized, if you loose a degree then makes it up again as the sun goes down your just a bit under.

    To balance the air flow you would need a damper in each duct so each can be tweaked to what is needed. You could use the damper in the register but that tends to lead to air noise from the register. Or you can have a room by room load done, have the duct sized by the needs of each room and upgrade the duct system. Another option would be to add a zone package with the dampers daisychained for each area of the house. This can get messy and cause problems if not done right and may need all new duct work. The thing about a zone system is you can put the different thermal zones on the house on the same thermostat. So if you have rooms that get hot in the morning but are fine the rest of the day they can go on one zone, ro0oms that get hot in the PM can go on another. Kitchen dinning may go on another based on time used as may living and sleeping areas.

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  17. #11
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    It is better for equipment to be a little undersized than a little oversized. Design temperature is 1% of the year. Your concern should be about how much it is oversized the rest of year. Smaller is better for other 99% of the time.
    *********
    https://www.hvac20.com/ High efficiency equipment alone does not provide home comfort and efficiency. HVAC2.0 is a process for finding the real needs of the house and the occupants. Offer the customer a menu of work to address their problems and give them a probability of success.

    Find contractors with specialized training in combustion analysis, residential system performance, air flow, and duct optimization https://www.myhomecomfort.org/


    Site member map HERE!

  18. #12
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    One of the issues of getting any system sized right these days is, a 3-ton condenser comes with a 2-ton compressor, not literally, but you get the idea. For a 3-ton system, you would be better off installing a 3.5 ton condenser. JMO.
    __________________________________________________ _______________________
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  20. #13
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    .
    Did you say you had 1- 20 x 20 return or are there 2...?
    ..
    Do not attempt vast projects with
    half vast experience and ideas.
    ...

  21. #14
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    Quote Originally Posted by kdean1 View Post
    I the equipment is too big you can open windows so the load will match the equipment. It's not an ideal solution, though.
    That's an interesting suggestion. Thanks !
    Although, the current thermostat placement (in the hallway, away from external doors/windows) will make this less effective.

    I have a Nest E thermostat. So, if I have to go down this path, perhaps I can add a sensor (works with gen "e") and place it in a "hotter" location.

  22. #15
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    Quote Originally Posted by Sleuth View Post
    .
    Did you say you had 1- 20 x 20 return or are there 2...?
    ..
    Yes I had to use 2, 20"x20"X"1 filters side by side before. So I'm assuming the total return size was 2x20x20.

    Now, they have another 20"x20" on a separate location (still in the same area)

  23. #16
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    Quote Originally Posted by kdean1 View Post
    It is better for equipment to be a little undersized than a little oversized. Design temperature is 1% of the year. Your concern should be about how much it is oversized the rest of year. Smaller is better for other 99% of the time.
    Can you please elaborate your statement Design temperature is 1% of the year.
    Do you mean, 1% plus/minus the average temp over an year, of the place of installation?

  24. #17
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    Quote Originally Posted by Froodo View Post
    Yes I had to use 2, 20"x20"X"1 filters side by side before. So I'm assuming the total return size was 2x20x20.

    Now, they have another 20"x20" on a separate location (still in the same area)
    Youir rerturn size is now a total of 60x20 not as I understand your post. You had 2 side by side which would be 40x20 plus the new 20x20.

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  26. #18
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    Quote Originally Posted by Froodo View Post
    Can you please elaborate your statement Design temperature is 1% of the year.
    Do you mean, 1% plus/minus the average temp over an year, of the place of installation?
    From an authoritative reply on the Green Building Advisor site-
    "
    1% cooling, means 1% of the time it has been hotter historically (over something like the last 25-50 years). There are 8760 hours in a year, so for 87 hours it will typically exceed the cooling design temperature each year."

    It is the temperature used for calculating loads. It is the hottest expected temperature based on a historical average. That is the most load your system will experience, an only for a very limited time. My point is, don't obsess about the 1%. Be more concerned about the majority of the cooling season and what the system will do when it is NOT running continuously.

    *********
    https://www.hvac20.com/ High efficiency equipment alone does not provide home comfort and efficiency. HVAC2.0 is a process for finding the real needs of the house and the occupants. Offer the customer a menu of work to address their problems and give them a probability of success.

    Find contractors with specialized training in combustion analysis, residential system performance, air flow, and duct optimization https://www.myhomecomfort.org/


    Site member map HERE!

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  28. #19
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    Quote Originally Posted by Froodo View Post
    Can you please elaborate your statement Design temperature is 1% of the year.
    Do you mean, 1% plus/minus the average temp over an year, of the place of installation?
    Basically, they take 30 years of data and come up with peak averages.

    My design temp is 100* and I think 22*....Most years we will have a couple days below 22* and higher than 100*. But if you design a system that runs at 1 speed to cool for a 110* day you will be grossly oversized on any day under about 100*

    Your design temps should be part of the load calc....

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  30. #20
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    Quote Originally Posted by Froodo View Post
    Thank you all for your valuable comments.
    I regret to report that the installation is already done now. How I wish I had learned about these things a few months back

    Now that being said, I wanted to know what can be done next ? I know not much, but specifically with respect to:

    1. Some of the rooms still are getting disproportionately higher percentage of cool air (better than before..but still not I want). For example my bathroom vents seems to be getting the most air.
    I was told by the installer that they can come after a week to adjust the flow rate (I suppose by adjusting the balancing dampers). But I'm sure they will try to tell me that they have done their best when I still complain (I already heard him say "this is a short duct ..so it will receive the max flow).
    As I understand the dampers may only affect the main supply duct from the plenum (I think I have three of those). But what if I want to control the flow from a distributary/secondary supply duct coming out from one of the main duct. What's the process to achieve that ?

    2. Since humidity is not a major concern in AZ, I guess the other issue with over-sized HVAC now will be wear of the system due to short-cycling. Two questions here:
    a) How short a runtime can be as termed short cycling ?
    I guess the answer would depend on the the temp difference between outside and thermostat... but i wanted to get a general idea. Is 15 minutes too short ? 20 minutes ?
    b) I read about anti-short cycle timer in the Trane spec sheet. Is that something that can be useful ?

    3. Does any other idea like blowing extra cold air to garage, seem feasible ? Note, I still need to fix my hot-cold issue.


    Although I feel duped (only I am to be blamed), I would still like to continue learning.
    Thanks to all again !
    An AC doesn't even make it to its rated SEER rating until about 15 of run time. So its very poor energy efficiencies to start with and it builds as it runs. 15 minutes later you'll be close to the rating, in your case 16 SEER....

    Yes you are correct. If the mechanical dampers are on the supply plenum and you have 3 supply ducts coming off of that, each damper will simply control airflow down stream. If it branches to 3 rooms all will be affected. In order to do what your asking you would need to install dampers at each wye/take off going to each room. Then go up and adjust them as you like. Fun Stuff....

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