On Sat, 11 Aug 2007 19:56:22 -0400, Jeff wrote:

* Vic Smith wrote, On 8/11/2007 5:25 PM:
...
I'm thinking for guys like me there is a BCAH calculation for
beer/coke amp hours. I just don't know what it is.
You weren't clear about cooling anything except beer in your reefer.
Let's say I want to spec out reefer cooling 6-8 12 ounce cans per day.
How would you recommend going about calculating BCAH, and sizing the
reefer to accomplish that?

There are books written to address this topic. It runs something like
this:

A BTU is raising a pound of water one degree. If you have a 6-pack,
that's 4.5 pounds of water. Removing heat to bring it from 70 degrees
to 38 means a removal of 144 BTU. Figure 5 BTU of heat removal per
watt-hour of energy in, so we end up with only a cost of 2.5 Amp-hours
to chill the beer.

BUT, what if the beer started at 100 degrees, what if there's two
6-paks, what about the heat losses of the box? These can all be
calculated, but a one cu ft box with 3 inches of insulation will loose
about 1000 BTU per day, and that would cost 16 Amp-hours. Thus, the
total load for a small fridge can be 20 Amp-hours, easily handled by
a small Danfoss like the BD35.

One point here is the the fridge could be a lot larger - you could go
to 4 cu ft and still have a loss of only 2000 BTU. Or, if you put in
6" of foam you can keep the loss down to 1200 BTU on a 3 foot box.
(These numbers from a table by Grunert.) Also, the "cool down" cost
can be estimated just by considering the weight of the food/drink
consumed each day. Since this is largely liquid (beer/coke/water)
keeping a little bit of butter or cheese cold costs very little. Once
you're in for the basic investment, there's little additional cost to
keeping some eggs, and maybe some bacon, etc, since they get added
cold at the start.

Contrary to the "common wisdom" opening the door is not a major cost,
the heat content of the air that comes out is rather low. You can
even make the case that digging around in a top-loader creates more of
a loss than quickly opening the door of a front loader.

What it comes down to is the cost of chilling your favorite beverage,
and the heat loss of the box itself.

Thanks, Jeff. You've given me a great starting point.
Forgot my BTU's, probably because I always used them in steam calcs.

--Vic