Replaced my A/C this weekend, results of downsizing by 1/3.

Recently my 13 yr 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 500sq 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.

House: 1587sq 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

Results:
Temperature the old unit cycled until it was above 105, clearly oversized for our area. New 2 ton unit can keep 76F inside with a 100 degree outdoor temperature, but runs continuously to do so.
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 2,500watts 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 WAY 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 IMHO. 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 !!!

Views: 568

Comment

You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Comment by Tom Delconte on December 10, 2013 at 8:09am

Nicely done Install !

Comment by Curt Kinder on September 9, 2012 at 9:41am

Absolutely agree - we routinely drop tonnage by 0.5 to 1.0 following a careful Man J, generally including a Blower Door test to nail down infiltration figure

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Tom Conlon commented on Kurt Shafer's blog post What is your opinion about members promoting products here?
"I just checked the site Guidelines Kurt, and any true "promotions" should be posted in…"
12 hours ago
Tom Conlon posted a discussion

Whole House Fans - Love 'Em or Not?

I just searched this forum for "Whole House Fan", but I didn't find much about them (except …See More
12 hours ago
Richard Beyer replied to Mike Kandel's discussion Our Homes Suck – And That's Why Our Kids Have Sinus Problems
"Don, Thank you for the praise! I only wish that some of these profiteers could answer my questions…"
15 hours ago
Richard Beyer replied to Mike Kandel's discussion Our Homes Suck – And That's Why Our Kids Have Sinus Problems
"Todd, This report (attached link) below on poor people living in subsidized housing show's…"
15 hours ago
Mike Kandel added 4 discussions to the group Building Performance Institute (BPI)
17 hours ago
Mike Kandel posted discussions
17 hours ago
Nate Adams commented on Jim Gunshinan's blog post My Energy Upgrade California—The Numbers Are In
"Jim, Glad to help! OK, a touch of soap box. So long as we don't tell people EE is free and…"
17 hours ago
Kurt Shafer commented on Kurt Shafer's blog post What is your opinion about members promoting products here?
"Bob, Good idea. I see that you are a window energy reduction expert. You might consider adding…"
18 hours ago
Robert (Bob) Bacon commented on Kurt Shafer's blog post What is your opinion about members promoting products here?
"Kurt, I would explain what energy/efficiency problem this device solves and explain the science the…"
18 hours ago
Ben Jacobs replied to Mike Kandel's discussion Our Homes Suck – And That's Why Our Kids Have Sinus Problems
"I agree that in many homes the indoor air sucks.  However, a lot of this problem is caused…"
20 hours ago
Kurt Shafer commented on Kurt Shafer's blog post What is your opinion about members promoting products here?
"Tom, thank you for your odd reference to a leaky duck. It is a bit off topic since I was not asking…"
21 hours ago
Tom Delconte commented on Kurt Shafer's blog post What is your opinion about members promoting products here?
"Shameless self promotion here sucks like a leaky duck!"
22 hours ago

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service