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  1. #14
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    Thread Starter
    Thank you all for your input and discussion, it is appreciated and helpful to have a place where home owners can discuss their own understanding and get objective input.

    I know I have an up-hill battle on my hands related to getting things done right at this point, it might be something I have to deal with more directly after closing but I'll push as much as I can as a buyer. I did want to ask one final question as a possible option to improve the latent capability of what they plan to install. The configuration they have designed is AHRI Ref # 202387194 with is a 4 ton condenser coil with 5 ton evap coil. I did some digging and there is a reference design (202387188) that uses the same condenser and furnace but has a fully matched 4 ton evap coil, lower SEER and EER (15/11.7 vs 16/12) but I believe this would do a better job with humidity management? If my assumption is correct I will as a fallback push them to install this 4 ton evap coil in place of the 5 ton which will also bring down the % of load to something more reasonable.

  2. #15
    Join Date
    Nov 2004
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    SW FL
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    Quote Originally Posted by VegaTX View Post
    I am more resigned to the fact that I will require a whole house dehumidifier just as I had to install in my current 2014 built 1.5 story home to deal with excessive humidity, just a matter of how much capacity which to me hinges on them sizing the AC right.
    ___
    They don't have one in their design and stated to me on a discussion call that "The most you will encounter will be around 60% in the shoulder months" as though that is acceptable design.

    I don't think I have any supporting code requirements to pressure them to install one in their design if the humidity is problematic as I expect it to be so I will likely install one after moving in (as I did with my current home).

    The unit they have installed is a 4 ton 2 stage paired to a 5 ton coil (my understanding is this increases sensible efficiency but robs latent) with a 90000 BTU variable speed furnace (122% cooling capacity and 253% heating capacity based on design conditions, it will go higher once they fix what I requested they fix in their calculations).

    If they recalculate the load based on my corrections to the design (no west facing windows doors, ducts in conditioned space) the likelyhood is high the actual cooling load would necessitate a 3 ton 2 stage system.

    That said, the argument now gets to the CFM requirements of the home being 1540 CFM which is too much for a 3 ton unit so they have to oversize;
    I guess it doesn't make full sense to me being 3 zones and a 2 stage unit already.

    I know going from 3rd to 1st floor has some long trunk runs so there is airflow degradation to account for and going too high in CFM on a smaller unit to overcome distance will reduce delta-t.

    I am hopeful that this HVAC company will correctly configure the variable speed blower for the home needs and system. Considering they did Manual J on incorrect design data (no actual review of architectural plans based on wrong orientation and larger sqft than designed) I have my doubts on how well this install will be.

    I had to adjust the taps on my existing homes unit after we moved in as they left it at default max 2200 CFM instead of lowering to 1600 per design conditions.
    The contractor is definitely _100% Hacker_.!

    Hackers = Illegimate scums who create the industry's
    ______________________ reputation as Jus Plain Dumb Folks
    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

  3. #16
    Join Date
    Nov 2006
    Location
    Athens, Ohio
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    Quote Originally Posted by VegaTX View Post
    I keep getting "I have been doing this 15 years"
    That's a lame excuse from someone unwilling to learn. Stick to your guns. You may have to find a contractor who has actually learned something.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  4. #17
    Join Date
    Mar 2016
    Location
    Dayton Oh
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    Larger coils raise suction pressure and create more sensible cooling and less latent. But they get a higher seer rating. Larger coils remove less humidity.


    Sent from my iPhone using Tapatalk

  5. Likes dan sw fl liked this post.
  6. #18
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by jbhenergy View Post
    Larger coils raise suction pressure and create more sensible cooling and less latent. But they get a higher seer rating. Larger coils remove less humidity.


    Sent from my iPhone using Tapatalk
    I hate make this more complicated,but--. Large coil high efficiency a/cs can be setup to remove high latent and be efficient by adjusting the air flow to get a cold enough coil to get an adequate latent capacity. The minor problem is that the amount of moisture on the coil is greater to get moisture to drip the drain. At the end of the cooling cycle, the moisture on the coil evaporates back to the home. But while running very efficient at sensible/latent cooling. Short cycling is when you pay a penalty.
    The air flow adjustment is critical.
    Until the coil is loaded and dripping down the drain, no dehumidification. Coils can hold up to 1 lb. per ton of residual moisture at the end of cooling cycle. Fan "on" dries the coil in <1 hour. Fan "auto" or off during may take 2 hours.
    Short on/off cycles like 15 mins. on, +40 mins. off may result in little or no moisture remove until the %RH is higher.
    For evenings and rainy days, a small whole house dehumidifier is best solution to supplement the a/c to maintain 50%RH.
    Most do not understand the limitations of any a/c. VS a/c is better reducing the number of short cycle. During early morning hours and rainy days there is low/no sensible cooling to have a cooling unit control indoor %RH. Over-cooling is uncomfortable and increases the amount of moisture that must be removed to maintain moderate %RH levels. Also condensation on ducts and building barriers between inside/outside moisture.
    A proper setup a/c with small whole house dehumidifier will get you the temperature %RH that you want.
    If all understood this concept, all green grass climate homes would have an a/c+dehu.

    Thanks for the chance to explain the concept.
    A good discussion.
    Regards Teddy Bear
    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. #19
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by teddy bear View Post

    I hate to make this more complicated, but--.

    Large coil high efficiency a/cs can be setup to remove high latent and
    be efficient by adjusting the air flow to get a cold enough coil to get an adequate latent capacity.


    If all understood this concept,
    all green grass climate homes would have an a/c+dehu.

    Thanks for the chance to explain the concept.
    A good discussion.

    Regards Teddy Bear
    I don't know ANY Competent Technicians who will set-up an air handler
    and Limit the manufacturers air flow requirement BELOW the minimum
    for AN OVERSIZED, IMPROPERLY SELECTED COIL.

    So this comment may actually be addressing issues that would be
    implemented as DIY efforts or for the Hackers to provide for ill-informed owners.

    The sensible capacity WILL BE REDUCED by the amount of air flow restriction to some degree.
    … _______ 350 CFM/ Ton MINIMUM … ~ 10% Less than a Normal set-up
    SENSIBLE HEAT RATIO would be in the range of 0.71 given 77'F / 65'F DB/WB 52% Return Air.
    Ideally, 54.2'F / 53.0'F Leaving Dry Bulb / Wet Bulb

    If one wishes to have additional dehumidification,
    Select a 6-Row industrial coil.
    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. #20
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by dan sw fl View Post
    I don't know ANY Competent Technicians who will set-up an air handler
    and Limit the manufacturers air flow requirement BELOW the minimum
    for AN OVERSIZED, IMPROPERLY SELECTED COIL.

    So this comment may actually be addressing issues that would be
    implemented as DIY efforts or for the Hackers to provide for ill-informed owners.

    The sensible capacity WILL BE REDUCED by the amount of air flow restriction to some degree.
    … _______ 350 CFM/ Ton MINIMUM … ~ 10% Less than a Normal set-up
    SENSIBLE HEAT RATIO would be in the range of 0.71 given 77'F / 65'F DB/WB 52% Return Air.
    Ideally, 54.2'F / 53.0'F Leaving Dry Bulb / Wet Bulb

    If one wishes to have additional dehumidification,
    Select a 6-Row industrial coil.
    The interesting part is that the minimal air flow recommended is about right for the about right to get adequate dehumidification with their high SEER equipment. It is about 30^F coil temperature below the return air temperature.

    75^F, 50%RH, 55^F dew point return air equals a 45^F cooling coil temperature will get you a 49^F dew point supply air temperature. About 3,000 btus of latent cooling per ton. Not bad, this will keep most homes with 80 cfm of 70^F dew point fresh air infiltration/ventilation plus 4-5 occupants on a design day.
    During the evening or rainy day with a 70^F outdoor dew point, not so much. Add 3-5 lbs. per hour dehumidifier to the home and we are all set.

    Caution with a/c ducts in unconditioned space, need top notch insulation or by-pass air to avoid condensation on the outside of the ducts.
    There could be problem with excess fresh air or high occupancy. We are seeing some a/c manufactures are pushing as low as 37^F coil temperatures which could be a problem with condensation on the supply ducts.
    All on a fine line.
    Thanks for raising the issue.
    Regards Teddy Bear
    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"

  9. #21
    Join Date
    Apr 2016
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    6
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    Thread Starter
    Been a fun month with my AC woes on my new build with this contractor the builder has. I finally got them to provide a latest revision to the calculations to find they still have the orientation wrong, the wrong insulation value for the encapsulated roof (R19 instead of R22, which is funny because they note R22 in their notes), wrong ceiling height on 1st floor....just a mess. They still refuse to correctly calculate duct gain/loss based on the location (continue to note all duct is in the encapsulated attic and none in the conditioned space which is wrong so still a high gain/loss for the ducts).

    They did adjust their latest to a 3 ton 2 stage system and after some review of the document I see how, they are playing with the SHR. They only went down by 1756 total load (33005 now) but they changed from a SHR of .70 to .79 so it would require 2.9 tons of cooling; the actual SHR of the home (their calculations) is .84 based on my calculations (total sensible/total load).

    So now I am curious at the reasoning behind playing with the SHR to justify a particular AC size? What is acceptable with this, as the actual home is .84 and the equipment design (AHRI 202363357) is .84 (and now it is only 109% instead of 129% total capacity) but why pick .79 to arrive at 2.9 tons (or before which was .70 to arrive at 3.5 tons and end up at a 4 ton unit)?

    I am still pushing them to get the homes characteristics correct in their calculations before I accept any new units while escalating the issue with the builder (might have to push for an ACCA accredited HVAC company to do it right).

  10. #22
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    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Let us hope that they do not setup for anything less then .25 latent/.75 sensible heat.
    Less latent cooling and you will be marginal dehumidifying even during peak sensible cooling. Even adding a dehumidifier to this poor setup will not work well.
    Keep us posted on how this all works.
    Regards Teddy Bear
    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"

  11. #23
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    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by VegaTX View Post

    Been a fun month with my AC woes on my new build with this contractor the builder has.

    I finally got them to provide a latest revision to the calculations to find
    they still have the orientation wrong,
    the wrong insulation value for the encapsulated roof
    (R19 instead of R22, which is funny because they note R22 in their notes),
    wrong ceiling height on 1st floor....just a mess.

    They still refuse to correctly calculate duct gain/loss based on the location
    (continue to note all duct is in the encapsulated attic and
    none in the conditioned space which is wrong so still a high gain/loss for the ducts).

    They did adjust their latest to a 3 ton 2 stage system and after some review of the document I see how, they are playing with the SHR. They only went down by 1756 total load (33005 now) but they changed from a SHR of .70 to .79 so it would require 2.9 tons of cooling; the actual SHR of the home (their calculations) is .84 based on my calculations (total sensible/total load).

    So now I am curious at the reasoning behind playing with the SHR to justify a particular AC size? What is acceptable with this, as the actual home is .84 and the equipment design (AHRI 202363357) is .84 (and now it is only 109% instead of 129% total capacity) but why pick .79 to arrive at 2.9 tons (or before which was .70 to arrive at 3.5 tons and end up at a 4 ton unit)?

    I am still pushing them to get the homes characteristics correct in their calculations before I accept any new units while escalating the issue with the builder (might have to push for an ACCA accredited HVAC company to do it right).
    How many coil rows are there for the equipment that you are using in YOUR ACCA Manual S CALCULATIONS.?

    S.H.R. is not a MAJICAL, Single Value.
    S.H.R. is dependent on the number of coil rows, air velocity and ACTUAL varying INDOOR MIXED-AIR CONDITIONS.

    S.H.R. of ~0.79 may be typical for a Semi-Dry or Dry climate.

    5 Ton air handler paired with 4-ton condensing unit will also tend
    to provide an even higher S.H.R. value.


    The Indoor Air will not be consistently at a majical 51.0% R.H.

    Indoor air may be in the range of ~47% to ~62%
    depending on
    __ whether you are in Houston TX, Death Valley CA, Saudi Arabia or ...
    + whether your infiltration is 0.20 or 0.70 A.C.H. Natural
    + whether you have a few/several fish tanks & plants.

    The achievable S.H.R. is NOT the value calculated in Manual J.

    Heat loss & heat gain for ducts in an encapsulated space
    should Obviously reflect a significantly lower value.
    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

  12. #24
    Join Date
    Apr 2016
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    Thread Starter
    I don't know specifics on the coil rows, don't have access to that information myself or know where I can locate it. At this point in reviewing the old design 4 ton 2 stage with a 5 ton evap coil the new correct load would have put that system at 129% of sensible and 149% of total at design conditions. I did overhear the builder talking with the HVAC designer and their concern with reducing to the 3 ton 2 stage system is humidity. He is afraid that by reducing the system size we will have humidity issues which is confusing to me but he mentioned the stacking effect with this being a 3 story home (3rd story is finished attic) as the reason for concern. In the end I'll be installing a dehumidifier since they aren't putting one in as I expect it will likely be needed regardless but I would expect the more appropriately sized system to handle the latent load better due to longer run times.

    The only real change in their design is adjusting the SHR as the total load didn't reduce that much, outside of that it is possible they just decided to select a system that isn't grossly over-sized for the design conditions as was asked (though I did ask them to justify why it was over-sized to crickets in response).

    The unit and some ducts are in an isolated section of the encapsulated attic facing the rising sun, they are separated from the attic section facing the setting sun by actual conditioned space. A lot of the duct is actually in conditioned space (running between floors in open web floor truss) but their accounting of that is lacking so it is all classified as in an encapsulated attic.

    The new unit they have purposed (which seems more appropriate to me, 3 ton cond+3.5 ton evap) with the new load calculations at design conditions shows it is:

    Sensible Cap: 28440 (104% of load)
    Latent Cap: 7560 (145% of load)
    Total Cap: 36000 (111% of load, 79% SHR)

    Houston
    Outdoor design DB: 97.2
    Outdoor design WB: 76.6
    Indoor design DB: 75
    Indoor RH: 50%
    Entering coil DB: 76.8
    Entering coil WB: 63.8
    Cooling Infiltration ACH: .07 (It is a very tight house)

  13. #25
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    This a recap of the amount of fresh air infiltration/ventilation you need in a 3,500 sq.ft. home is 150 cfm minimum to purge indoor pollutants and renew oxygen when occupied.
    Even air tight homes leak enough during winds of +10 mph. As winds calm, the fresh air needs to supplied by a mechanical fan with a merv 13 air filter.
    The moisture in the fresh air is about 5-6 lbs. per hour plus the moisture from the occupants while maintaining 50%RH.
    Typically 5-7 lbs. or 5-7,000 Btus of latent cooling per hour is need to maintain 50%RH. Anytime the outdoor dew point is +70^F, expect this amount of latent cooling load, hot days, evenings, and rainy days.
    The specs on any a/c are stated in sensible/latent Btu per hour capacity at the ARI rated conditions and typical desired temperature and %RH conditions.
    Match your Manual D calcs. to the a/c specs. The required air flow and capacities will be listed.
    Add a whole house dehumidifier that supplements the a/c during evenings and rainy days plus the moisture from the occupants.

    Name:  capacity chart.JPG
Views: 47
Size:  48.5 KB

    This is available on rated a/c.
    Regards Teddy Bear
    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"

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