Comments on: 3 Reasons Your 3 Ton Air Conditioner Isn’t Really 3 Tons

By: Dave Roberts

Dave Roberts — Fri, 24 May 2013 17:26:27 +0000

Nice article Allison.
Nice article Allison. Similarly, a “SEER X” isn’t always a SEER X. A scan of the AHRI data shows the reported values within a nominal SEER family of products varies significantly. See Figure 9 in http://www.nrel.gov/docs/fy13osti/56354.pdf

By: bob

bob — Fri, 24 May 2013 08:14:58 +0000

Actally higher cfm increases
Actally higher cfm increases total capacity up until the coil is so warm its not removing any humidity at all. Pull the expanded performance data off your faorite brand of ac or copelands website.

By: bob

bob — Fri, 24 May 2013 01:13:42 +0000

You can trade sensible and
You can trade sensible and latent capacity by varying the airflow on the indoor coil. Lower cfm gives more latent, higher is more sensible. The best way is to have a blower than can vary the speed in real time to meet load requirements. Often latent loads are high when sensible is low.

By: Allison Bailes

Allison Bailes — Thu, 23 May 2013 18:26:04 +0000

Ernest M.:
Ernest M.: Yes, a lot of people in the HVAC industry don't understand this. For those wanting to see what your company offers, here's a direct link: Total Performance Diagnostic.

: Thanks for posting the link to Isaac's Manual S spreadsheet, here's the direct link:
Home Energy Partners Manual S spreadsheet.

Bob: Yep. I added a sentence about that near the end that should have been there to begin with.

Bob S.: So true!

Curt K.: Yeah, I thought I'd leave the discussion of sensible and latent for another article and focus mainly on the sensible here. Not because it isn't important, though.

By: Curt Kinder

Curt Kinder — Thu, 23 May 2013 18:08:47 +0000

Another consideration,
Another consideration, although somewhat implied by the discussion of indoor rating conditions, is sensible heat ratio.

A 4 ton system typically supplies just 3 tons of sensible cooling, and loads in really hot places (such as Tucson) tend to be more sensible.

All that said, we are today merrily installing a 3 ton system on a house that loads out to 3.25 tons. Client has committed to some envelope and insulation improvements.

By: Bob Seaton

Bob Seaton — Thu, 23 May 2013 17:41:01 +0000

“One needs to know
“One needs to know everything,” responded don Quixote, “in my profession.”

By: bob

bob — Thu, 23 May 2013 16:36:18 +0000

Even with all these capacity
Even with all these capacity reducing factors AC units are still oversized on average by 50%.

By: Ryan Moore

Ryan Moore — Thu, 23 May 2013 16:16:53 +0000

Home Energy Partners out of
Home Energy Partners out of Ashville, NC put together a great Manual S spreadsheet that automates a lot of the calculations. They have posted a video explaining how it works. Check it out at: http://homeenergypartners.com/2013/04/manual-s-speedsheet-2013/

By: Ernest Murry

Ernest Murry — Thu, 23 May 2013 14:22:35 +0000

Allison,

Allison,
This concept of cooling performance is even less understood in the repair and maintenance field than it is in the building performance world. Measuring actual system performance in the field (in real time and in real world conditions) has been nearly impossible.
We have great hopes that our Total Performance Diagnostics will save consumers and the nation a lot of energy by identifying poorly operating systems so they can be repaired or replaced.

ernie