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No matter how the coils looked, they were 20 year old coils. They build up a layer of material that doesn’t easily wash away. This results in a reduction of heat transfer. If there is blockage in the coils then you also have a reduction in air flow across the coils. An older fan motor can also generate more heat than when new. While you may not feel the heat, this heat is transferred to the air moving through the unit. New motor won’t generate that much heat. There are way too many variables to consider other than the difference between a 20 year old brand and a new brand of the same capacity being the reason for the difference in cooling.
Would you say then, if the old unit was "new" it would perform close to the same as the new unit assuming both had been installed properly AND there were no leaks or other wear out issues?
That is, any two 3 ton units should perform nearly the same IF the conditions are the same?
And, the difference in price between any two same tonnage units for sale today would only vary in price due to reliability and SEER?
undercharged, overcharged, txv valve not adjust correctly, refrigerant line issues, contaminates in the lines (including air/moisture) incorrect blower motor speeds, improper ducting**; any of these would contribute to reducing BTU CAPACITY (but unit would still seem to 'work') - ie, 'take longer to cool' , so your BG 3ton unit may only be performing like a 2.25 ton capacity, and take longer to cool. Proper measurements MANDATORY to determine ACTUAL BTU performance.
Also to note is that your 'builder grade' unit may have even been MISMATCHED (ie, 3 ton condenser w 2 ton coil, etc) - without us knowing model# of condenser and model# of air handler (and coil), it's anybody's guess as to what you actually had there. Mismatched systems can 'work', but capacity will be nowhere near the design ratings.
Same on the premium system, but it's more likely the system was properly matched (extended warranty would be VOID on a mismatched install).
** interesting to note that the ducting may actually be same & improper for BOTH the BG and the Premium installs, but often a Premium system will likely include a variable-speed blower motor that can compensate and maintain full BTU capacity, whereas the BG system is set speed and Can't compensate, hence capacity loss on the BG system (assuming all other factors are proper). Same with line sets (what works optimally for one model/brand may not for the other).
On top of that, BTU performance is actually a 'curve', and not a static rating for all conditions. Manufactures detail a performance chart (or table) at measured conditions - so all that has to be fully taken into account to de a real comparison.
This thread started out saying both systems were same seer and same tonnage - somehow it's evolved with now a 20-year old 10 seer unit (prolly R22) as the comparison - no measurements on anything??? impossible to compare...
Newer units also have options such as multi stage and multi speed compressors. A higher end unit of the same size will cool better than a older low end unit.
Trying to compare different brands and models of same size is like trying to compare cars that have a 3 liter motor. Higher end cars will typically perform better than the base car with the same size motor.
Also like someone else said, not all a/c units are rated at the advertised size. A 3 ton (36,000 btu's) lower end unit might only perform at 31000 btus, where a higher end unit could be closer to 36000.
A HVAC contractor explained it to me this way....A lower end unit will cost you less, but will not last as long, or make you as comfortable as a higher end unit. Meaning it may take longer to cool down the house, and it will likely be noisier.
Case in point with my house. My 1993 unit was 3.5 tons. After they did an evaluation of the house, they decided a 3 ton unit was the appropriate size. I went with a higher end multi stage/speed unit and higher SEER rating. I am much more comfortable in the house, and our energy bills went don over $1100 per year.
A lower end unit will cost you less, but will not last as long, or make you as comfortable as a higher end unit. Meaning it may take longer to cool down the house, and it will likely be noisier.
Why would this be the case if both units were the same tonnage?
Had a very basic Trane XR14 2-Ton heat pump installed early last year. The corresponding air handler installed was set very, very low out of the box. I phoned the installer when summer came around (it wouldn't keep up) and he changed around the DIP switches on the blower. Literally the difference between the unit running 20 hours one day, and 8 hours the next. Comfort level from 6 to 10 overnight.
Old unit, new house 1997 10 ton three tons.
New Unit, 2017 14 ton three tons...so about 20 years.
The old unit was way less efficient.........think about a 20 year old car vs. a new one. Even if you compared a 97 Camry to a 17 Camry, same trim level the old car would be worse at everything! AC is the same thing, also consider your comparison was the the end of life of the 1997 and then started up the brand new one. I'd bet the comparison would be a lot closer if you installed a brand new 1997 unit (leftover) vs. a tired 20 year old unit.
Why would this be the case if both units were the same tonnage?
Like I outlined in a previous post, tonnage is not always the same even though they are both "3 tons". One might be actually producing 31000 btus (instead of 36000=3 tons) and a higher end unit might actually produce 36000 btus. The btus produced are what matters, not the advertised size. Get away from the idea that advertised tonnage is all that matters. There is so much more to it than that. The higher end units will perform better on all fronts, than a lower end unit. That means they will cool better, be less noisy, and use less energy while doing it.
Also, higher SEER ratings will make the unit perform more efficiently and cool the house better than a lower SEER unit will. Speeds and types of compressors also come into play and can make a huge difference on the performance of the units.
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