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  1. #1
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    Sep 2012
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    Orlando, FL
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    AC Help in Florida - 5 DIfferent Recommendations

    Really need some expert advice. In the process of replacing 2 complete systems in our 2 story house. Total sq. ft is 3215, lower is 1814, upper is 1401. Current systems are 18 plus years old, Carrier 2 1/2 ton each. Both air handlers are located in a mechanical room on the 2nd floor and all duct work runs through our attics.

    Thought I was going about this the right way, read a lot on here. Had a company come out and perform an energy survey to include a Man J, blower door, duct testing, etc. Hers score of 114 with recommendations to seal ducts, add insulation and various other minor things. They also provided a couple of system recommendations. Also had 3 other companies come out and provide recommendations. All companies have excellent reputations and carry a variety of manufacturers. 3 Man J's came up with cooling load requirements of between 44,000 and 52,000.

    So here is the dilemma, each company come up with completely different recommendations. Company A: 2 1/2 ton up and down, B: 2 1/2 down 3 up, C: 2 down 2 1/2 up, D: 2 1/2 down 2 up. Company D also made a strong recommendation to do a single 5 ton zoned system using a Carrier 2 stage, variable speed unit.

    After all this I am even more confused as what to do.

    Thanks

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    The one that did a blower door test would have the actual infiltration rate of the house where others would be guessing on this rate, unless you shared it with the others, infiltration load has a significant effect on the outcome of a manual j calculation.

  3. #3
    Join Date
    Nov 2004
    Location
    SW FL
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    6,248
    Quote Originally Posted by scooterfj62 View Post
    Really need some expert advice. In the process of replacing 2 complete systems in our 2 story house. Total sq. ft is 3215, lower is 1814, upper is 1401. Current systems are 18 plus years old, Carrier 2 1/2 ton each. Both air handlers are located in a mechanical room on the 2nd floor and all duct work runs through our attics.

    3 Man J's came up with cooling load requirements of between 44,000 and 52,000.

    So here is the dilemma, each company come up with completely different recommendations.
    Company A: 2 1/2 ton up and down, B: 2 1/2 down 3 up, C: 2 down 2 1/2 up, D: 2 1/2 down 2 up.
    Company D also made a strong recommendation to do a single 5 ton zoned system using a Carrier 2 stage, variable speed unit.

    After all this I am even more confused as what to do.

    Thanks
    You run into a MIRACLE THAT these recommendations and calculations are So Closely Aligned and yet you ascribe them to be "completely different".
    The recommendations are definitely within the science and art of equipment selections and what one should expect.
    One ought not to seek Five recommendations if one does not have a thought process to determine what will suit him most appropriately.

    5 +/- 0.5 Tons ... +/- 10% is remarkably close. In fact, in comparison you won't find an air balancer in nearly any industry to provide a set-up to anything less than 10%.
    One would be rethinking ANY Bid where a building is specified to be balanced to < 10%. Saved

    _____________ 44,000 to 52,000 BTU/Hr ..
    also known as 48,000 +/- 4,000 BTU/HR ... within +/-8% is definitely within accuracy expectations of this art and science.

    The glass is MORE THAN half FULL, not half empty.

    Confused?
    IF the "equipment selection glass" is not half full, you are faced with hiring - a sixth unknown someone- to Tell you which recommendation to accept.

    I guess that 6th someone may be the ~123 responses to this thread to be posted over the next 5 weeks
    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

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,271
    Quote Originally Posted by jtrammel View Post
    The one that did a blower door test would have the actual infiltration rate of the house where others would be guessing on this rate, unless you shared it with the others, infiltration load has a significant effect on the outcome of a manual j calculation.
    What was the real infiltration rate of the home? (Question for origiinal poster) This is a misleading number in that it is a measure of the leakage area in the home, not the variable real leakage rate the home has. The average air leakage is based on the assuming the air leaks are located equally on all surfaces. The estimate is at average winter temps and average wind. During calm winds and moderate outdoor temps, fresh air leakage is near zero. During high wind and the coldest temps, the air leakage could be double. Nothing wrong with blower doors but the info is limited when it comes to sizing and providing adequate fresh air to be healthy. Most of the summer infiltration loads are latent and when combined with the occupants latent load overwhelm the a/c's capacity during low cooling loads.
    Part of any evalution of the home should include a fresh air ventilation recommendation. This home owner is trying to get educated about updating the home as best as possible. There are no explanations about the needs for fresh air and supplemental dehumidification. Sign of the times.
    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"

  5. #5
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    Sep 2012
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    Orlando, FL
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    37
    Quote Originally Posted by dan sw fl View Post
    You run into a MIRACLE THAT these recommendations and calculations are So Closely Aligned and yet you ascribe them to be "completely different".
    The recommendations are definitely within the science and art of equipment selections and what one should expect.
    One ought not to seek Five recommendations if one does not have a thought process to determine what will suit him most appropriately.
    With all due respect, in my profession I deal with Facts, if it calls for a number 2 widget, that's what it gets. I did not realize this was as much "Art" and some "Science". When all 4 of the companies came up with different recommendations, but alas with your help within acceptable limits, is when the confusion set in. Also I initially had 3 companies come out based on the equipment they carried, Trane, Lennox and Carrier. I didnt like the Lennox guy as he was a professional salesmen and not a tech. Then with the recommendation of many professionals on this list, I found a company in the area that would do a complete energy audit, for a fee of course, and hired them to do one. As part of their audit, they too made 2 recommendations.

    So in the end, what I have is 2 different recommendations, equipment aside. A unit for each floor, or one larger unit with zoning.

    Confused?
    IF the "equipment selection glass" is not half full, you are faced with hiring - a sixth unknown someone- to Tell you which recommendation to accept.
    So what your saying is with the recommendations being all equal and within acceptable limits, go with my equipment/contractor preference? What about the single unit zoned system from either Carrier or Amana?


    Quote Originally Posted by teddy bear View Post
    What was the real infiltration rate of the home? Part of any evalution of the home should include a fresh air ventilation recommendation. This home owner is trying to get educated about updating the home as best as possible. There are no explanations about the needs for fresh air and supplemental dehumidification. Sign of the times.
    Regards TB
    The infiltration numbers are somewhere in the attached reports. Would the "fresh air ventilation recommendation" come from all the contractors or just the guys doing the energy audit?

    Man J with Blower Door.pdf1st Man J.pdf

  6. #6
    Join Date
    Jul 2007
    Location
    Delaware
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    Are you going with the company that gave you the FREE energy report?
    Always here

  7. #7
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    Jul 2012
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    Western KY
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    Eeny meeny miney moe. They are all pretty close. I like 2 systems on 2 story homes myself, if upstairs goes out I can sleep downstairs till its fixed, no real scientific reason. Pick the guy you were most comfortable with and get-r-done.

  8. #8
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    Sep 2012
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    Orlando, FL
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    Quote Originally Posted by energy star View Post
    Are you going with the company that gave you the FREE energy report?
    There was nothing "FREE" about the energy report. I paid for it.

  9. #9
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    Sep 2012
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    Orlando, FL
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    Quote Originally Posted by Tommy knocker View Post
    I like 2 systems on 2 story homes myself, if upstairs goes out I can sleep downstairs till its fixed, no real scientific reason. Pick the guy you were most comfortable with and get-r-done.
    With the cost of the systems we are looking at, there is a significant cost savings with going with one zoned system. But with that said, cost is not the driving force, its comfort, reliability and what's best suited for the house.

  10. #10
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    Jul 2007
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    Delaware
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    Quote Originally Posted by scooterfj62 View Post
    I found a company in the area that would do a complete energy audit, for a fee of course, and hired them to do one. As part of their audit, they too made 2 recommendations.
    Oh.....
    Always here

  11. #11
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    IF you did zoning with a single system, I'd go with a 4 ton unless it was an inverter drive like a Carrier Greenspeed. I like the one that's 2-1/2 up 2 down. The downstairs will have a LOT less latent load due to reverse stack effect.

    If the equipment is alreay right next to each other, going with a single premium zoned system, if installed correctly, could give het best comfort. You might save enough as well to install a whole house dehumidifier. The dehumidifier would remove enough latent load that you could easily do the whole house on a 4 ton system.

    Given hte location of the equipment, I would ask the CArrier or Byrant dealer about a single Greenspeed or Bryant equivalent zoning system. Further, if you want, you could split the downstairs "Depending on ductwork" into 2 or 3 zones as well. Nice ot have if you have a home with these things called interior walls. They are not very common anymore since open concepts are so plular. But if your lucky enough to have walls inside you home downstairs, you could zone the kitchen, dining room a sun room, etc, spaces that have uniquue cooling loads during different times of the day, use and occupancy. Carrier zoning is modulating as well. SOe with Greenspeed, its' a fully modulating system. SO when installed correctly, if a zone needs 1/2 ton to maintain it's temperature, it gets exactly a 1/2 ton of capacity. WIth a conventional system, it might get 1 ton for 10 minutes, then 0 for 10 minutes and the dampers would open and close, causing hte tmeprature to vary.

  12. #12
    Join Date
    Jul 2012
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    Western KY
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    Quote Originally Posted by motoguy128 View Post
    IF you did zoning with a single system, I'd go with a 4 ton unless it was an inverter drive like a Carrier Greenspeed. I like the one that's 2-1/2 up 2 down. The downstairs will have a LOT less latent load due to reverse stack effect.

    If the equipment is alreay right next to each other, going with a single premium zoned system, if installed correctly, could give het best comfort. You might save enough as well to install a whole house dehumidifier. The dehumidifier would remove enough latent load that you could easily do the whole house on a 4 ton system.

    Given hte location of the equipment, I would ask the CArrier or Byrant dealer about a single Greenspeed or Bryant equivalent zoning system. Further, if you want, you could split the downstairs "Depending on ductwork" into 2 or 3 zones as well. Nice ot have if you have a home with these things called interior walls. They are not very common anymore since open concepts are so plular. But if your lucky enough to have walls inside you home downstairs, you could zone the kitchen, dining room a sun room, etc, spaces that have uniquue cooling loads during different times of the day, use and occupancy. Carrier zoning is modulating as well. SOe with Greenspeed, its' a fully modulating system. SO when installed correctly, if a zone needs 1/2 ton to maintain it's temperature, it gets exactly a 1/2 ton of capacity. WIth a conventional system, it might get 1 ton for 10 minutes, then 0 for 10 minutes and the dampers would open and close, causing hte tmeprature to vary.
    No no no no no!! Give that Greenspeep a few years, for bug extermination, before jumping on that band wagon. There's parts in that thing that cost more then most systems!! Maint on that thing will be a huge problem!!! Looks good on paper BUT. Our sales engineers have been forbidden to sell them, for now.

  13. #13
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    Oct 2010
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    Anderson, South Carolina, United States
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    Quote Originally Posted by Tommy knocker View Post
    No no no no no!! Give that Greenspeep a few years, for bug extermination, before jumping on that band wagon. There's parts in that thing that cost more then most systems!! Maint on that thing will be a huge problem!!! Looks good on paper BUT. Our sales engineers have been forbidden to sell them, for now.
    Inverter technology has been out for years and is probably more reliable than a recip or scroll compressor. Plus parts will be under warranty for 10 years and if someone is gonna pay big bucks for a top of the line system they probably will opt for a 10yr labor plan as well

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