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  1. #1
    Join Date
    Mar 2012
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    39

    NEW CONSTRUCTION: Acceptable cooling temps in Texas

    Hello. Throughout our build process this forum has been a great help. We are at the final stage of our construction in deep South Texas and I have a question regarding acceptable standards. We have a 5000 sq foot (living) single story home with very very high ceilings throughout. The construction is 2 inch concrete block covered by stucco and open cell foam spray throughout for insulation. Windows are relatively large though few and small only on the south facing side of the home. The home has three units consisting of a 5 ton and two 3 ton units.

    What is the acceptable temperature low for a home in this environment (average 100 degree day)? In other words, should the home be able to cool to 72 degrees, 76 degrees, etc?

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,292
    Can you actually cool that large house to 72 degrees on a 100 degree day? I mean, have you actually tried it? And...do you need it to be that cool to be comfortable? In my experience, asking a system to keep a house that cold is often symptomatic of subpar system design. If everything was sized and installed correctly, you should be comfortable at 75 or 76 degrees. The key is humidity control, which is the first thing that suffers if the system design is not right.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    Mar 2012
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    39
    Quote Originally Posted by Shophound View Post
    Can you actually cool that large house to 72 degrees on a 100 degree day? I mean, have you actually tried it? And...do you need it to be that cool to be comfortable? In my experience, asking a system to keep a house that cold is often symptomatic of subpar system design. If everything was sized and installed correctly, you should be comfortable at 75 or 76 degrees. The key is humidity control, which is the first thing that suffers if the system design is not right.

    Humidity has been steady in mid/upper 40s to mid 50s max. Peak heat outside today was 98 degrees and the central area of the home (large family room, kitchen, dining, theater room) would not reach below 78 degrees until now (7pm) where it finally hit 77. The system has been running continuously for hours. The two other sides of the home have reached down to 75-76. We are comfortable at 77 in this heat but we are very concerned that the unit in the main area of the home is inadequate. Temperatures are guaranteed to rise an additional 5-7 degrees over the next few months.

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,292
    When you say you have very, very high ceilings, just how high is that? And where are the supply registers located in the large room with very high ceilings that won't drop below 77 degrees?

    Also, did you go with a sealed attic insulated at the roof deck, or is it a standard vented attic with a dark shingled roof with insulation on the attic floor? Are there many penetrations in the ceiling such as recessed lights? Do you have pulldown stairs to the attic inside the house? How well shaded are your windows during the day?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #5
    Join Date
    Mar 2012
    Posts
    39
    Quote Originally Posted by Shophound View Post
    When you say you have very, very high ceilings, just how high is that? And where are the supply registers located in the large room with very high ceilings that won't drop below 77 degrees?

    Also, did you go with a sealed attic insulated at the roof deck, or is it a standard vented attic with a dark shingled roof with insulation on the attic floor? Are there many penetrations in the ceiling such as recessed lights? Do you have pulldown stairs to the attic inside the house? How well shaded are your windows during the day?
    The central area is a family room/kitchen with suspended beams. The peak hits 26 ft. Windows are facing north. There is no attic space above and the space between roof and ceiling was filled with open cell. Shingles are clay. The remainder of the home has attic space insulated throughout at the roof deck and also blown in above the garage. Supply registers are located at approximately 16 ft up (2 above kitchen) and 11 ft up (3 in family room). The design, unfortunately, did not allow for higher registers. The builder has built this home once prior and the owner is not having the same issues though I am not informed of the systems design.

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,243
    Quote Originally Posted by BAVE View Post
    Hello.. The construction is 2 inch concrete block covered by stucco and open cell foam spray throughout for insulation.

    What is the acceptable temperature low for a home in this environment (average 100 degree day)? In other words, should the home be able to cool to 72 degrees, 76 degrees, etc?
    Do you really have to worry about Any Temperature?

    2" concrete block may not be able to withstand a 40 MPH wind.
    Regular block is 8 x 8 x 16" Minimum.

    http://www.marshallconcreteproducts....ShapesandSizes
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,243
    Quote Originally Posted by BAVE View Post
    Supply registers are located at approximately 16 ft up (2 above kitchen) and 11 ft up (3 in family room).
    5 supply registers for 11 tons is Not adequate for 5,000 Square foot house with 26 foot high walls built with 2" blocks.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  8. #8
    Join Date
    Mar 2012
    Posts
    39
    Another HVAC tech had commented that the issue may be the return. Our main room is an open 22x37 room with the return located around the corner approximately one foot into the connecting hallway in a closet housing the unit (complete air flow into unit via louvered door).

  9. #9
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    I'm assuming that when you say 2" concrete block covered by stucco, that the walls are also framed, and have insulation in the stud spaces?

    If the house was truly insulated as you say, and is sealed somewhat tighter than a pole barn, 11 tons of cooling is way more than that house should ever need if the equipment and house are actually performing properly.

    Unfortunately, the usual scenario is that neither the HVAC equipment or house perform as they should because of design and installation problems.
    If more government is the answer, then it's a really stupid question.

  10. #10
    Join Date
    Mar 2012
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    39
    Quote Originally Posted by dan sw fl View Post
    5 supply registers for 11 tons is Not adequate for 5,000 Square foot house with 26 foot high walls built with 2" blocks.
    5 registers is for one room with the 3.5 ton unit. There are dozens of registers in the home. The 2" solid Contec block is in place of brick (stucco home) and in addition to framing, barrier, etc.

  11. #11
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,986
    Quote Originally Posted by BAVE View Post
    Hello. Throughout our build process this forum has been a great help. We are at the final stage of our construction in deep South Texas and I have a question regarding acceptable standards. We have a 5000 sq foot (living) single story home with very very high ceilings throughout. The construction is 2 inch concrete block covered by stucco and open cell foam spray throughout for insulation. Windows are relatively large though few and small only on the south facing side of the home. The home has three units consisting of a 5 ton and two 3 ton units.

    What is the acceptable temperature low for a home in this environment (average 100 degree day)? In other words, should the home be able to cool to 72 degrees, 76 degrees, etc?
    First thing is how many days has the air conditioning been running? Are you leaving the home closed up 24/7 and running the a/c? How long had the systems been running when you became concerned about the lowest temperatures you were seeing?

    Main reason I'm asking is that your a/c systems will put a lot of their capacity into dehumidifying a structure (especially a brand new one) when first turned on. With the size of yours and depending on the moisture that could be contained within the home's structure and items in it, this moisture removal "time" could be potentially days. Not saying this is your issue, but if we assume that the systems have been installed and "adjusted" to peak operating efficiency and they were sized correctly this would be some of the first things I'd check.

    A way to see if there is excessive moisture in the home is to turn all the a/c off for an hour and monitor how quickly the humidity level rises. Not a scientific way by any means, but it can give an idea.

    The other thing you can do is check how much condensate/water is coming from the drains for each unit. Again not a measure of anything other than it gives an idea how much moisture the system(s) are working to remove.

    Being a new home it comes down to asking questions of the contractor that put the systems in. They are the only ones that know what went in and how it's working..... or they should.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  12. #12
    Join Date
    Mar 2012
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    39
    Quote Originally Posted by mark beiser View Post
    I'm assuming that when you say 2" concrete block covered by stucco, that the walls are also framed, and have insulation in the stud spaces?

    If the house was truly insulated as you say, and is sealed somewhat tighter than a pole barn, 11 tons of cooling is way more than that house should ever need if the equipment and house are actually performing properly.

    Unfortunately, the usual scenario is that neither the HVAC equipment or house perform as they should because of design and installation problems.

    This is what we've been concerned about all along. There is no shortage of shoddy contractors out here. We assumed because our builder usually builds multi million dollar homes our smaller home would be an "easy build". The cubic footage of this home is probably far from customary for a 5000 sq ft home. Some bedrooms reach 16 ft high in addition to attic space above. Most hallways are 10-12 ft high and formal areas reach 18-26 ft.

  13. #13
    Join Date
    Mar 2012
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    Quote Originally Posted by firecontrol View Post
    First thing is how many days has the air conditioning been running? Are you leaving the home closed up 24/7 and running the a/c? How long had the systems been running when you became concerned about the lowest temperatures you were seeing?

    Main reason I'm asking is that your a/c systems will put a lot of their capacity into dehumidifying a structure (especially a brand new one) when first turned on. With the size of yours and depending on the moisture that could be contained within the home's structure and items in it, this moisture removal "time" could be potentially days. Not saying this is your issue, but if we assume that the systems have been installed and "adjusted" to peak operating efficiency and they were sized correctly this would be some of the first things I'd check.

    A way to see if there is excessive moisture in the home is to turn all the a/c off for an hour and monitor how quickly the humidity level rises. Not a scientific way by any means, but it can give an idea.

    The other thing you can do is check how much condensate/water is coming from the drains for each unit. Again not a measure of anything other than it gives an idea how much moisture the system(s) are working to remove.

    Being a new home it comes down to asking questions of the contractor that put the systems in. They are the only ones that know what went in and how it's working..... or they should.

    The systems have been on and running for approximately 6 weeks. We are living in the home but the home is not 100% complete. The HVAC sub has been back and forth increasing supply registers, balancing, and has even changed out two of the air handlers (upgraded to more efficient units). The rest of the homes system seems to be functioning well. They repeatedly site the Manual J report but have yet to produce it when requested.

    Also, all of the units are removing quite a bit of moisture. Its pretty apparent when observing the air handlers.

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