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  1. #1
    Join Date
    Nov 2009
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    7

    SIPs House and Trane units not sized correct

    We have a new SIPs (Styrofoam) house (6years).
    The HVAC contractor ran the numbers and came up with 3 1/2 tons downstairs and 2 1/2 ton upstairs. (3200 ft2) 6"Styrofoam walls and 8" Styrofoam roof. At the time, we did express our concerns about having too much A/C, but the tech explained that with all of the window area etc, that these were the right numbers. I do believe he did due diligence with the calculations for a standard house, but didn't have any kind of a reference for a SIPs house. SIPs houses have VERY few thermal breaks in the insulation (corners only). So an R24 wall is a TRUE R24 for the whole length. VERY airtight.

    We even included a fresh air intake as recommended.

    Problem is the upstairs unit especially is oversized. South Louisiana, HIGH humidity. Have to set the upstairs on 71 during the summer to be decently comfortable. Downstairs stays on 75.

    Both of the units (TRANE), have had the evaporator coils rusted out.
    Upstairs after only 5 years, and the downstairs now after only 6 years.

    The Trane FSR is maintaining that the units are properly sized but that we need to add a dehumidifier to pull the excess humidity out.

    What kind of a recourse or recommended action do you suggest?
    Our Trane warranty is parts only for 10 years.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,085
    Unless you cna find a third party. To do an accurate load calc. That show they are oversized. And that will go to court if need be.

    Your best bet may be a whole house dehumidifier.
    And use another company, when its time to change out those units.

    6 tons for 3200 sq ft 6 year old house. Sounds oversized for a house that isn't a SIP house.

    Unless you have lots and lots of windows.
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  3. #3
    Join Date
    May 2002
    Location
    Houston Texas
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    6,323
    Quote Originally Posted by p-ry View Post
    We have a new SIPs (Styrofoam) house (6years).
    The HVAC contractor ran the numbers and came up with 3 1/2 tons downstairs and 2 1/2 ton upstairs. (3200 ft2) 6"Styrofoam walls and 8" Styrofoam roof. At the time, we did express our concerns about having too much A/C, but the tech explained that with all of the window area etc, that these were the right numbers. I do believe he did due diligence with the calculations for a standard house, but didn't have any kind of a reference for a SIPs house. SIPs houses have VERY few thermal breaks in the insulation (corners only). So an R24 wall is a TRUE R24 for the whole length. VERY airtight.

    We even included a fresh air intake as recommended.

    Problem is the upstairs unit especially is oversized. South Louisiana, HIGH humidity. Have to set the upstairs on 71 during the summer to be decently comfortable. Downstairs stays on 75.

    Both of the units (TRANE), have had the evaporator coils rusted out.
    Upstairs after only 5 years, and the downstairs now after only 6 years.

    The Trane FSR is maintaining that the units are properly sized but that we need to add a dehumidifier to pull the excess humidity out.

    What kind of a recourse or recommended action do you suggest?
    Our Trane warranty is parts only for 10 years.
    Six ton on any 3200 sq.ft. home built six years ago is probably oversized. I would bet your home has less than a three-ton load, the local Trane distributor did a load on a SIP home here in Houston and recommended a 4-tons system. I ran the load and came up with a total of 18,000 BTU's 11,500 of which was latent load, this on a 2800 sq.ft. two story home. We installed a single 2-ton two stage system with 2-zones and a whole house dehumidifier. They have been through two summers now electric bills are less than $100.00 average around 60 and they keep it around 79 during cooling season.

    Trane had a real problem with their TXC coil rusting out and I suspect that is what you have. Purchase the havc-calc program from this site, it has provisions for SIP homes and so your own load and submit this to your contractor. Ask to see their original load calc, I would say you were royally screwed and probably have little recourse at this time.

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    The OP's situation is a prime example how poorly understood the influence of infiltration has on a residential structure. A SIP house is indeed a tight house and does provide considerably higher actual R value for a given wall or ceiling section vs. conventionally framed, conventionally insulated 2 x 4 construction. SIP wall sections are also not subject to convective currents between stud cavities like conventional construction is, and thermal bridging is considerably less.

    Add all this up and you're looking at not only an airtight house, but one that sees much slower heat transfer rates across the building shell than with framing. I would also assume that anyone who troubles themselves to build a SIP house selects decent windows and doors. Again, added up we're talking about a house that sees much less influence from extremes in weather, while simultaneously heightened influence from interior heat and moisture sources.

    Therefore for a person to take on such a house and say in essence, "Well, I'm sizing the ENTIRE HVAC SYSTEM LIKE I WOULD WITH CONVENTIONAL CONSTRUCTION because it looks like you have a lot of windows" is way off target. How that comes across is: "I really have no idea how to run a decent heat load calculation on a SIP house, so I'll just throw in enough tonnage so I don't get that mid-summer call that the homeowner isn't cool enough".

    P-ry, unless your house has a massive bank of unshaded east, west, and south facing windows, I can't imagine your external heat gain into the structure in summer is high enough to warrant six tons of a/c for 3200 square feet. Your high humidity issues is because a tight house shifts moisture gain from infiltration to internal sources, such as cooking, showering, laundry, respiration, etc. Folks have a hard time understanding this because most folks live in homes that leak like a screen door on a submarine. They're mired in energy consuming solutions like humidifiers in winter and dehumidifiers in summer, when one of the main reasons a homeowner may have gone with SIP construction is to REDUCE the need for active forms of interior climate control vs. INCREASE the need. If your a/c is sized correctly, and you're provided with smart fresh air ventilation control, you likely won't have humidity problems in summer, and your house won't be bone dry in winter, even without a humidifer.

    Beenthere gave you good advise pertaining to your installer concerns. I merely wanted to address your post from a more global view, since such a view ignored is why your house and HVAC equipment is ailing so badly.
    • 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
    Nov 2004
    Location
    SW FL
    Posts
    6,287

    Frown SUBSTANTIAL MIS-SIZING

    Quote Originally Posted by p-ry View Post
    We have a new SIPs (Styrofoam) house (6years).

    Problem is the upstairs unit especially is oversized.
    South Louisiana, HIGH humidity.

    Have to set the upstairs on 71 during the summer to be decently comfortable. Downstairs stays on 75.

    What kind of a recourse or recommended action do you suggest?
    SIPS probably need ~ 1/2 of normal compared to regular stick-built.
    VERIFY.

    Even with 360 [down] / 220 [up] square feet of good, tinted glass only a Minimum size heat pump might be required.

    Ask for 2 ton Variable Speed AHUs & compressors.

    After the units are correctly sized, you may be able to increase temperature 3 to 5 degrees and still feel more comfortable.


    If they balk, hire an attorney who will hire an engineer.
    Sue for a very large amount Obviously.

    It seems to be a no-brainer on the technical side.
    The law side is Another Story!
    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

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,439
    It's raining and the outdoor temp is 65-75^F, the right sized a/c will keep the home dry? Get serious, regardless what size a/c you have, there are times that you need all latent cooling. A dehumidifier is the only solution.
    But keep on tring to make it work, us guys with dehumidifiers are smiling while all this chatter takes place. Turn off the a/c and have <50%RH regardless what the size of the a/c or the cooling load or the weather conditions.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #7
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,188
    I had to do a major battle for a homeowner who built SIPS with his hvac company
    3000 sq ft house and they wanted to put a 5 ton unit. instead they installed
    a 3 ton variable speed. He hired a guy to do his load calc that lives near
    Mandeville. My client has never had a utility bill over $100.
    Where do you live?
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  8. #8
    Join Date
    Nov 2009
    Posts
    7
    Lafayette, LA.

    I'm using Trane XL14i units with variable speed motors.
    Approx. 1800 ft2 downstairs and 1400ft2 upstairs.

    When we first moved in the downstairs unit would drop the temp from 78 to 75 in way under 30 mins (around 10 if I remember correct). I had them come out and adjust the variable speed to the lowest possible setting.

    The downstairs unit has another ongoing problem: occasionally when the motor first comes on after an extended time ( 1- 3 x ) day. The blower motor will shake rattle and sound like a loud compressor kicking on. The blower has been replaced and the new one does the same thing. I think the housing has warped and is placing stress on the shaft bearings.

    Sigh!!!

  9. #9
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,188
    You are righ down I49 from me. Drop me an email and I can hook you up with
    a very good hvac company in Lafayette, if you'd like.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  10. #10
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    Quote Originally Posted by teddy bear View Post
    It's raining and the outdoor temp is 65-75^F, the right sized a/c will keep the home dry? Get serious, regardless what size a/c you have, there are times that you need all latent cooling. A dehumidifier is the only solution.
    But keep on tring to make it work, us guys with dehumidifiers are smiling while all this chatter takes place. Turn off the a/c and have <50%RH regardless what the size of the a/c or the cooling load or the weather conditions.
    Regards TB
    We went through a very wet October locally where we had weather similar to what you describe. The interior of my home did not turn into a mold factory in spite of little to no run time for the a/c. The few times we did turn the system on was to knock the humidity level down a tad, which it did easily since my house doesn't leak like crazy. I did not need to overcool the house, no losing battle with infiltrating moisture, because infiltrating moisture has been reduced to manageable levels.

    You often state that the end goal of any dehumidification effort is to maintain indoor humidity levels below 50% relative humidity. I prefer monitoring indoor dew point, since what we deal with for indoor human comfort is a fairly close range of temperature, say 68 to 78 degrees. ASHRAE recommends indoor dew points be held 55 degrees or lower for buildings in hot, humid climates (and it's likely an acceptable high end point in any climate). So, at 68 degrees indoor air temperature, the maximum relative humidity level would be 63%, adhering to a <55F dew point target. At 78 degrees, you get 45% RH. At 75 degrees, which is a common design target, you get 50% RH.

    Mold growth requires the presence of food and moisture. The only place I had mold during our monsoon October was in the vicinity of a roof leak near our stone chimney. This is understandable since the drywall and framing members were saturated, providing plenty of moisture and food for mold growth. No a/c or dehumidifier would have prevented that onset of mold. Fixing the leak was the remedy, obviously.
    The concern for other potential mold growth risks occurs when interior moisture levels meet microclimate zones in the house that shoot the relative humidity levels up to a range suitable for mold growth to start. Typically this occurs due to flaws in the building envelope design and/or construction. Otherwise, any time a home experienced relative humidity levels above 50%, with all surfaces at normal human comfort room temperature levels, homes would fill up with mold quickly, and it would be everywhere, on every surface. The only time I've seen that happen were in empty apartment units during warm weather, closed up with no circulation, with a bad water leak saturating the carpeting. That was nasty, like those photos on the internet of the entire interior of a home looking like black leprosy. Otherwise I've only seen mold wherever a high presence of moisture has occurred, such as a roof leak staining drywall ceilings, or plumbing leaks in walls (from a/c condensate overflows as well as other sources).

    In conclusion, it would be unwise to bluntly state that dehumidifiers are never needed in residential applications, but the interim requires that other factors be addressed pertaining to effective humidity control in addition to forms of removing moisture from a home. Where we drag our knuckles is in the building science department, where it has become painfully obvious that there can be no segregation between building science and HVAC design and application anymore. The two are one system, pertaining to human comfort, health, and energy management.
    • 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.

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,439
    Quote Originally Posted by shophound View Post
    We went through a very wet October locally where we had weather similar to what you describe. The interior of my home did not turn into a mold factory in spite of little to no run time for the a/c. The few times we did turn the system on was to knock the humidity level down a tad, which it did easily since my house doesn't leak like crazy. I did not need to overcool the house, no losing battle with infiltrating moisture, because infiltrating moisture has been reduced to manageable levels.

    You often state that the end goal of any dehumidification effort is to maintain indoor humidity levels below 50% relative humidity. I prefer monitoring indoor dew point, since what we deal with for indoor human comfort is a fairly close range of temperature, say 68 to 78 degrees. ASHRAE recommends indoor dew points be held 55 degrees or lower for buildings in hot, humid climates (and it's likely an acceptable high end point in any climate). So, at 68 degrees indoor air temperature, the maximum relative humidity level would be 63%, adhering to a <55F dew point target. At 78 degrees, you get 45% RH. At 75 degrees, which is a common design target, you get 50% RH.

    Mold growth requires the presence of food and moisture. The only place I had mold during our monsoon October was in the vicinity of a roof leak near our stone chimney. This is understandable since the drywall and framing members were saturated, providing plenty of moisture and food for mold growth. No a/c or dehumidifier would have prevented that onset of mold. Fixing the leak was the remedy, obviously.
    The concern for other potential mold growth risks occurs when interior moisture levels meet microclimate zones in the house that shoot the relative humidity levels up to a range suitable for mold growth to start. Typically this occurs due to flaws in the building envelope design and/or construction. Otherwise, any time a home experienced relative humidity levels above 50%, with all surfaces at normal human comfort room temperature levels, homes would fill up with mold quickly, and it would be everywhere, on every surface. The only time I've seen that happen were in empty apartment units during warm weather, closed up with no circulation, with a bad water leak saturating the carpeting. That was nasty, like those photos on the internet of the entire interior of a home looking like black leprosy. Otherwise I've only seen mold wherever a high presence of moisture has occurred, such as a roof leak staining drywall ceilings, or plumbing leaks in walls (from a/c condensate overflows as well as other sources).

    In conclusion, it would be unwise to bluntly state that dehumidifiers are never needed in residential applications, but the interim requires that other factors be addressed pertaining to effective humidity control in addition to forms of removing moisture from a home. Where we drag our knuckles is in the building science department, where it has become painfully obvious that there can be no segregation between building science and HVAC design and application anymore. The two are one system, pertaining to human comfort, health, and energy management.
    How about addressing the fact that you control moisture by not allowing any fresh air into your home during wet cool weather. Most IAQ experts suggest a minimum of 60-100 cfm of fresh air when the home is occupied. That is an air change in 4-6 hours. What are you suggesting? Avoid all fresh air for how long? The trick is to provide fresh clean air when the home is occupied and maintain <50%RH during all weather conditions. Test for pollutants like formaldehyde etc. Homes with fresh air ventilation are healthier and more comfortable. It your choice, but not very healthy for all. The liability for avoiding for fresh air could be expensive. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Join Date
    Feb 2006
    Location
    Float'N Vally, MS
    Posts
    1,833
    Quote Originally Posted by p-ry View Post
    Lafayette, LA.

    I'm using Trane XL14i units with variable speed motors.
    Approx. 1800 ft2 downstairs and 1400ft2 upstairs.

    When we first moved in the downstairs unit would drop the temp from 78 to 75 in way under 30 mins (around 10 if I remember correct). I had them come out and adjust the variable speed to the lowest possible setting.

    The downstairs unit has another ongoing problem: occasionally when the motor first comes on after an extended time ( 1- 3 x ) day. The blower motor will shake rattle and sound like a loud compressor kicking on. The blower has been replaced and the new one does the same thing. I think the housing has warped and is placing stress on the shaft bearings.

    Sigh!!!
    Also contact the Power Company (Sleco ?) they may be able to help with design....
    These systems sound way over sized.
    Life is too short, Behappy!
    TFMM

  13. #13
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,346
    Quote Originally Posted by teddy bear View Post
    How about addressing the fact that you control moisture by not allowing any fresh air into your home during wet cool weather. Most IAQ experts suggest a minimum of 60-100 cfm of fresh air when the home is occupied. That is an air change in 4-6 hours. What are you suggesting? Avoid all fresh air for how long? The trick is to provide fresh clean air when the home is occupied and maintain <50%RH during all weather conditions. Test for pollutants like formaldehyde etc. Homes with fresh air ventilation are healthier and more comfortable. It your choice, but not very healthy for all. The liability for avoiding for fresh air could be expensive. Regards TB

    A little off-topic for the OP but here goes:

    Formaldehydes and etc. = don't bring stinky stuff into your house if you can help it, but if you can't, let it offgas outside your living space before bringing it into the house (new electronics, fabrics, etc.)

    Try to avoid stinky building materials as much as possible. There are healthier products out there; may cost a little more...your health is worth it.

    Fresh air ventilation requirements = Nobody is suggesting not to ventilate with fresh air. What is being offered is to more closely examine WHY ventilation is required. Human respiration and bodily function is primary, followed by dilution of indoor pollution, which may be best addressed by striking a reasonable balance between source control and ventilation (and supplemental filtration via hepa/carbon methods). An objection to this is that people won't stop bringing or keeping stinky stuff into their home, but how well do they understand what they're breathing when they purchase items that produce strong VOC offgassing?

    If the buying public was more aware of this, and more concerned, mounting pressure upon manufacturers of building materials, furnishings, fabrics, etc. might be enough to convince the manufacturers that the stinky components need to go. You can build a cabinet without putting formaldehyde in it. You can floor a house without spreading out a mat of off-gassing toxic fumes throughout the entire house. And you don't need to douche yourself with gallons of deodorants/perfumes to not smell objectionable to someone else. The way some folk splash on the cologne or perfume, I'd almost rather settle for the odor of sweaty socks...read that ALMOST. Bottom line: give source control more serious thought when considering ventilation needs.

    As for shoulder season ventilation, when little heating or cooling is required, this goes back to my earlier post regarding humidity levels, which is a primary concern when ventilating for any reason. Reducing infiltration of the building envelope not only reduces moisture and heat load gain or loss, it moves the introduction of outdoor air to a controlled source, be it the HVAC system or a ventilating dehumidifier. Some regions of the country, or some residential configurations within any region, may warrant the latter, but for my own dwelling in my own neck of the woods, I can't justify the cost of buying and installing it, when the passive means coupled to my existing mechanical system does the job handily.

    Generally, when I need cooling I need dehumidifying, and when I need heat I may need humidifying, depending on internal moisture generation levels. The house is by no means tight as a drum, but it has enough measures in place to reduce needless air exchange, funneling it down to a controllable level. It is not beyond my means to open a window or two when outdoor conditions permit to allow a really good purging of the interior spaces. This often can happen in "shoulder season weather" with no adverse comfort or IAQ effects. The rest of the time there appears to be enough remaining duct leakage on both supply and return side to assure a sufficient amount of make-up air so the house does not become a locker room.

    The overall challenge for this discussion is to strike a balance between indoor air quality/human health requrements, human comfort requirements, and energy consumption management. The OP built a SIP house with hopes to address the third item - energy management - and got stuck with way too much HVAC capacity, putting his IAQ at risk. He's NOT comfortable and his IAQ levels are NOT good. The building envelope is in his favor, but his mechanical contractor is not. Until HVAC contractors get smarter about building science and heat transfer dynamics in dwellings, this kind of crap will continue happening. It should not. The OP should not have been placed in a posiiton where his above average dwelling design was met with below average mechanical design.
    • 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.

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