A/C time to reach maximum efficiency

[54regcab]

How long does a typical A/C have to run until it's full efficiency is realized? I suspect it's somewhere around 10 minutes per cycle? Does anybody have a link to a efficiency vs. time on chart?

[allan38]

I've been taught it takes 10 minutes for the system to stabilize, I've found it to be generally correct. The longer the run time, the more humidity is removed thus longer is typically better. Starting an AC system from a dead stop takes a good spike of electrical current, thus longer run times give higher energy efficiency due to lower average electrical current.

I've never seen an actual study of the topic, perhaps ASHRAE has one somewhere.

[amd]

^The spike probably lasts 1/10 of a second or less.

[behappy]

How long does a typical A/C have to run until it's full efficiency is realized? I suspect it's somewhere around 10 minutes per cycle? Does anybody have a link to a efficiency vs. time on chart?

Too many variables in your question to answer it properly.
A system with an expansion valve on the evaporator will reach efficiency faster than a system with a piston or cap tube.

A couple of years ago I was doing a performance test on my neighbors El Cheapo HP with a piston in it. The system would cycle off before it got close to "efficiency".

[lynn comstock]

http://www.energystar.gov/ia/new_homes/features/RightSizedAC1-17-01.pdf

[54regcab]

http://www.energystar.gov/ia/new_homes/features/RightSizedAC1-17-01.pdf

Exactly what I was looking for, thanks. It seems to me that keeping the A/C in the 5 min+ operating range is more important that selecting a high SEER unit. Is there some merit to slightly undersizing to reduce utility costs? I wouldn't mind it being 80 degrees inside for a few hours on the 100+ days we occasionally get around here if it meant saving $20/mo on my summer electric bill.

Is there a chart like this for the heating side or do furnaces reach full efficiency relatively quickly?

[teddy bear]

Attaching a graph of a 2 ton a/c with a very cold coil. For this data collection, the fan is on low "on" during the off cycle. It shows that no moisture goes down the drain the first 30 mins as the coil/pan loads. After a 1 hour continuous run, 2 lbs. of moisture went down the drain. I measured 4 lbs. per hr. of moisture removal. You can see the time it took to revaporate the 2 lbs. of moisture left on the a/c coil at the end of the cooling cycle. This is 13 SEER A coil. Horizontal coils hold more condensate than vertical coils.
Regards TB

[pstu]

Exactly what I was looking for, thanks. It seems to me that keeping the A/C in the 5 min+ operating range is more important that selecting a high SEER unit. Is there some merit to slightly undersizing to reduce utility costs? I wouldn't mind it being 80 degrees inside for a few hours on the 100+ days we occasionally get around here if it meant saving $20/mo on my summer electric bill.

Is there a chart like this for the heating side or do furnaces reach full efficiency relatively quickly?
What you have described is precisely the "best practices" wisdom that ACCA promotes for air conditioning. I am a homeowner in S. Texas, what is a furnace<g>?

Best of luck -- Pstu

[lynn comstock]

... I am a homeowner in S. Texas, what is a furnace?

A furnace is a lousy boat anchor. :)