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.
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.
You run into a MIRACLE THAT these recommendations and calculations are So Closely Aligned and yet you ascribe them to be "completely different".
Originally Posted by scooterfj62
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.
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
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
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.
Originally Posted by jtrammel
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.
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"
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.
Originally Posted by dan sw fl
So in the end, what I have is 2 different recommendations, equipment aside. A unit for each floor, or one larger unit with zoning.
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?
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.
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?
Originally Posted by teddy bear
Man J with Blower Door.pdf1st Man J.pdf
Are you going with the company that gave you the FREE energy report?
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.
There was nothing "FREE" about the energy report. I paid for it.
Originally Posted by energy star
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.
Originally Posted by Tommy knocker
Originally Posted by scooterfj62
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.
Originally Posted by motoguy128
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
Originally Posted by Tommy knocker