Recently my 13-year-old Carrier A/C devolved a leak and I chose to replace the system rather than track down the leak and repair the coil. I had been reading about doing Manual J calculations and how contractors are scared to death to undersize. I had been talking to co-workers about this and it's an uphill battle getting them to think different than 1 ton per 500 sq ft. So I decided to take confidence in correct sizing and "put my money where my mouth is" and install a 2 ton sized A/C.
1,587 sq ft located in Oklahoma City, built 1999
Old A/C: Carrier 3 ton 12SEER system original to the house
New Condenser: Thermalzone (Rebadged Rheem/Ruud) 2 ton 14.5 SEER
New coil: 2 ton RFCL 13-16SEER with TXV
Temperature: The old unit cycled until it was above 105, clearly oversized for our area. New 2 ton unit can keep 76 degrees F inside with a 100 degree outdoor temperature, but runs continuously to do so.
Humidity: The humidity is higher in the day with the new system even though it runs more. 45% vs. 40% for the old system. I've already reduced the 3 ton blower to it's lowest speed.
As a test, I've captured the condensate in a bucket to measure humidity removal. The 3 ton system with piston metering pulled more humidity by day, less by night. The new TXV system pulls more humidity at night than day. Both units keep humidity about 45% at night.
Power: Old unit consumed 3,000 to 3,500 watts depending on outside temperature. New unit consumes 1,800 to 2,500 watts depending on outdoor temperature. Power use is on my in home wattmeter and includes blower consumption.
Delta T: Old unit got about 18 degrees most of the time, day or night. New unit gets 14 degrees in day, 18 degrees at night. Keep in mind the blower speed was lowered when the new A/C was installed.
Cycle time Cycles were running about 6 minutes with the old unit, new unit runs about 8-10 minutes per cycle.
Noise: New unit is much quieter, both units have 8 pole motors. Scroll compressor can barely be heard compared to the recip compressor of the old unit. With the new unit you can barely hear the fan, very impressed. Neighbor still has his 3 ton builder unit with the 1125 RPM fan and it's twice as loud as my old unit.
The coworker that helped me install it was impressed with how quiet the unit is and how much cooling it put out considering that it's only a 2 ton. He was a bit skeptical that the 2 ton could pull it off, but it's doing so with flying colors in my honest opinion. So, believe the load calculations and don't fudge the input number to get the result you want. Yes the numbers may seem low, but they DO work!
-Bob Blanchette can be reached at firstname.lastname@example.org.