Date:         Wed, 12 Aug 2009 15:16:16 -0600
Reply-To:     Richard A Jones <jones@COLORADO.EDU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Richard A Jones <jones@COLORADO.EDU>
Subject:      Re: cognitive dissonance and refrigerators
In-Reply-To:  <200908121917.AOH35853@Colorado.EDU>
Content-Type: text/plain; charset=ISO-8859-1

> Many RV fridges are spec'ed +/-3 in one direction and +/-6 in the
> other.  Ours is +/-8 either way.

My camper manual with my '87 Westy specs 7 degrees.  I took a
level and checked and decided that I would not consider the van
level enough to sleep in WAY before 7 degrees, so that was
my measure.  I only shut down the fridge when parked on very
steep slopes such as a trailhead parking lot, etc.

> If you're expecting performance like a compressor fridge, you're
> doomed.  You get to pick between home-fridge performance (compressor
> units) or silent long-duration (weeks) operation on propane
> (absorption units).

Most RVs, including the BIG RIGs, have absorption fridges--side-by-
side units.  Lots of rural houses around the world have absorption
fridges.  Servel is owned by Dometic now.  We used Servel fridges
in mtn cabins growing up.  Anyway, absorption fridges and
freezers can work great in all conditions.

The real problem with the 182-sized fridge is size.  The bigger
the fridge, the easier to keep cold.  Surface area goes up by
the square but volume by the cube.  Most RVs have fridges that
are "somewhat" or "a lot" bigger than the 182--and so they
work better.  A small fridge like the 182 has cooling sized
to work in the middle temp range.  At the extremes, it has
a disadvantage--it can't stay cold or gets too cold.  The
cooling is sized to the volume not the surface area.

A fridge that is a 1 unit sphere has area of 4pi and volume
of 1.3pi.  Make it 4 units and the area is 64pi but the
volume is now ~85pi.

The same math says that a Vitri that is double the size of
what we are installing would work better--use fewer amps,
have steadier internal temp, or be better in some way.  Or
maybe just have thinner insulation!

Richard