Adding insulation is not typically an improvement in anything of recent
construction. That's a fantasy factoid lingering from the 1970s energy
crisis, endlessly repeated by people who've never measured the realized
benefit.
Richard - Unfortunately our boat is not of recent construction. The
original
icebox had just 1/2" of polyurethane insulation. When I installed the
refrig
unit, I added as much as I could on the outside. But, it is still not
as
much as is often recommended. Only way of adding more, is on the
inside.
But, if it won't make much difference in compressor run time, I would
prefer
not to do this because of cost of so-called "space-age" insulation or
space
taken by conventional insulation.
Perhaps this explains why I would like to measure present power usage,
then
add temporary sheets of foam using 2-way tape and measure again.
Thanks for all the input so far guys!
GBM
This topic (now moving away from recording to efficiency) has had a
great deal of exposure.
As one who has taken a sawzall to his original box (anyone wanna buy a
very cheap, perfectly good, 110/engine drive, dual split-system cold
plate[s - 2], quite large system?), without getting technical about it,
BTU are BTU. However many it takes is what it will require for the
cooling system.
An advantage to the older engine drives (techumseh compressors like
used to be on 60s era Ford products) is that they can make a ton of ice
in an hour, properly set up, so there's ample capacity if you have the
right cooling plates, regardless of how poorly insulated your box might
be.
However, if it's not adequately insulated, it will sweat - and
eventually rot stuff, usually behind the fascia, where you don't see
it. That's why, in our boat, the galley sole was skinned before I
bought it, and why the area under the reefer, inaccessible until we
tore it out, was mostly gone. Ample pix of that removal in the late
04/early 05 galleries if you wanted to see what happens.
So, back to the story. You can either live with it, add mechanical
(could be attached to a genset or the main engine - or rigged with a
110 motor and pulley, if you're dockside most of the time) cooling, or
(unless you don't mind losing the space occupied by the original
housing/insulation, in which case you could build it from the inside)
rebuild it from scratch, as we did.
At that point, your options expand but as you've identified, it's a
tradeoff between foam for cheap but fat, or vacuum for dear but thin.
I vehemently (well, not to be angry, just strong) disagree with the
"70's hype" bit. If you don't keep the heat out, you have to remove
it. There's a point of diminishing return, but my marker is to take an
infrared thermo (cheap at the cheapo tool places, and even sometimes at
the Shack) and point it at the face of the insulated, cold, box. Then
point it at another similar face nearby which isn't near the
reefer/freezer. If they're within a couple of degrees of each other,
that's probably as good as you'll get. The less techie test is to use
your hand. If the reefer feels notably cooler, you probably don't have
enough insulation. However, if you have a face plate trim which isn't
in contact with the box (another barrier, good idea) then it masks the
truth. If you have a top loader, your countertop is a good place for
the test, even though the least amount of BTU go through the top (heat
rises, so the convection component is very small there).
As to your "temporary" sheets of foam, part of the equation is
preventing air movements. You have to be very aggressive about sealing
joints and overlapping as many times as possible (longer path for air),
along with as precise a fit as you can manage. Again with my pictures
for examples - I used paper patterns for exact fits, and at that
spoiled some of my sheets, doing them over.
FWIW, my original thought was to add insulation to the inside of the
box, too, replacing the countertop as I went. Without the gory details,
that proved impossible. Had I known the reality which might have
avoided all the gory details, I might still have cut it out, because
the original insulation, even if it's not sweated (as yours nearly
certainly must have, as thin as it is), loses most of its R-value over
the years. Technology today helps, and epoxy encapsulation retards it,
but you'll still lose some R over the years with new stuff, space age
or extruded Poly-x. However, 30 years from now, I'll not care about it
in my boat :{))
I have a lead on what used to be a very much less expensive (than
Rparts or Glacier Bay, the usual suspects) source for vacuum panels if
you decide to go that route.
Hope that helped and not just repeated what you already know...
L8R
Skip
Morgan 461 #2
SV Flying Pig KI4MPC
http://tinyurl.com/p7rb4 - NOTE:new URL! The vessel as Tehamana, as we
bought her
"Believe me, my young friend, there is *nothing*-absolutely
nothing-half so
much worth doing as simply messing, messing-about-in-boats; messing
about in
boats-or *with* boats.
In or out of 'em, it doesn't matter. Nothing seems really to matter,
that's
the charm of it.
Whether you get away, or whether you don't; whether you arrive at your
destination or whether you reach somewhere else, or whether you never
get
anywhere at all, you're always busy, and you never do anything in
particular; and when you've done it there's always something else to
do, and
you can do it if you like, but you'd much better not."