[TriLUG] OT: thermodynamics of A/C question

[Steve Litt]

On Wed, 4 Jul 2012 04:29:06 -0700 (PDT), Joseph Mack NA3T said:
 
> My initial posting was to ask
> 
> "if you're moving a fixed number of BTU/day, is it better to 
> move them when the air is cooler, eg early morning 5am, 
> rather than running the A/C full blast mid afternoon, when 
> the outside air is hottest"
> 
> The assumption was that the A/C is a Carnot machine and in 
> the early morning the condenser would be operating at a 
> lower temperature. From the Carnot cycle efficiency formula, 
> I expected I'd get 50% more efficiency.
> 
> No-one had an answer to this, and none of us know if an A/C 
> operates at Carnot cycle efficiency (I suspect it doesn't), 
> but we've had fun discussing other aspects of A/C as a 
> result.

I saw lots of answers to this. I personally wrote that unless your house
is a heck of a lot better insulated than mine, you can't store up enough
cold in the night/morning to last you to the evening. And you know what
I mean by storing up cold.

I saw plenty of other answers, many suspecting that you WOULD be better
off running it at offpeak hours.

And then there were plenty whose basic response was that the
right question wasn't asked, and went into things like cooling only
certain room, fans, evaporative coolers and the like.

SteveT

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