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Ninety percent of
today’s boat refrigeration systems perform poorly in
the tropics.
- The reasons
for the poor performance are many:
- Lack of
insulation
moisture in the
insulation
equipment
selection
- Ability to
supply the amount of daily power needed to
operate the system
- Systems that
are incorrectly installed.
An
acceptable refrigeration system is one that performs as
well as the standard household refrigerator. Items in
the freezing section stay frozen and ice cube production
will satisfy your daily needs, and there is adequate
temperature in the refrigerator to keep items such as
milk and lunch meat for a week without spoiling. If
you’re not achieving these goals, then you do not have
an adequate refrigeration system.
Who
needs to worry about his boat refrigeration insulation?
Boat builders, those owners repairing an old boat with
deteriorated or wet insulation or the live-aboard for
cruising in the tropics. On older boats there are
tell-tale signs that the insulation is poor, moisture
forms on the outside of the box, ice melts too fast, and
the refrigeration unit is large enough to do the job,
but the box just isn’t getting cold enough and the
service man can find nothing wrong with the
refrigeration unit. All of these points to one problem
– poor insulation!
INSULATION
TODAY
What
do we know about Insulation used for boat
refrigerator/freezers in the past.?
For
the last 15 years Urethane, polystyrene and
Isoyanurates foam insulations were
the best choice having an advertised
"R" value of from R- 5 to R- 8.
All insulation loses its ability to hold back
heat due to the following factors:
· AGE
- from
15 to 20 years the deterioration may be as much as 50%
loss.
·
Moisture
in the insulation destroys its insulating qualities.
·
In
addition to convection and induction, heat infiltration
through the insulation radiant heat must be reduced,
this can be achieved by surrounding the box with
reflective foil
·
Effective
insulation totaling an R value of 30 is enough for a
freezer, to double this amount will only provide a small
improvement in the total heat reduction.
· To
compensate for lack of insulation,
install larger equipment or run the refrigerator
more hours per day.
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Keep
moisture OUT!
The
worse thing that can happen to an insulated box is to
have moisture penetrate into the layers of insulation
which renders it useless as moisture is one of the best
conductors of heat. A good insulation system for any
refrigerator/freezer would be insulation that is
encapsulated in plastic. If you cut open a new
commercial refrigerator, you will find that all the
insulation is covered with blankets of plastic that
prevents any air from moving into the insulation. Air in
the humid climates will deposit its moisture on any
surface that is 10 degrees cooler than the ambient air.
This means that a refrigerator operating over a long
period of time with air leaks into the insulation will
continue to accumulate moisture until the insulation
reaches its saturation point. It is true that the new
closed cell foams resist the moisture but there is still
a loss in the "R" value over a long period of
time. Therefore, if you are building a new box, make
sure that the insulation is cocooned in a plastic of
4-6 mil. similar to that, which is primarily sold
for paint drop cloths. This can be purchased at any
hardware store. There should also be one reflective
layer of aluminum foil somewhere in the insulation with
the shiny side toward the sun. This can also be found in
your home refrigerator. If you are building your own
box, the standard Reynolds wrap Aluminum foil will work.
Most
manufacturers of boats aren’t concerned with the
amount and quality of insulation. Many times production
techniques dictate the quality and the amount of
insulation used in the ice-box. The liner is normally
fabricated from fiberglass and the interior looks very
nice. This is then attached to the counter top that is
turned upside down in the production shop and coated
with a layer of spray foam. Spraying the foam on in this
manner means that when the liner is dropped into the
hole it will have air spaces on all sides. The only
insulation that has a good "R" value is the
insulation that is poured into sheets where the density
can be controlled. This results in a good "R"
value but liquids and spray on foams just do not provide
as high an "R" value.
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Ways
to check your box’s insulation
There
are two ways to evaluate your box’s insulation. You
can conduct an ice melt test to see how much ice will
melt in a given period of time at a given box and
ambient temperature. Or you can drill ¼ inch pilot
holes in a few spots out of sight through the paneled
wall into the insulation cavity. You should be careful
when you do this that you only drill through the
partition material and not into the insulation. After
the holes are drilled, use a probe such as a piece of
coat hanger wire to feel the amount of space between the
wall and the insulation and you can also determine if
there is moisture in the insulation with this method. If
an air space is found, use cans of spray foam to fill up
the cavity through the drilled holes. Several holes will
be required top and bottom to assure that you’ve
filled all the empty spaces. Be careful that you don’t
let the spray foam leak out into the bilge or other
areas. You can build a dam with cardboard and duct tape
to contain the foam.
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Adding
foam to your box
The
most important area to consider when adding foam is the
liner and cabinetry surrounding it especially if it is
fabricated with a thin material. You will need to add
some supporting braces to these areas since the foam
will grow over a 24 hour period and will apply pressure
to any areas with less strength than ½ inch thick
plywood. To reach the far corners such as those against
the hull, it may be necessary to place an extension,
such as a small piece of copper tubing onto the spray
can nozzle. If you find moisture in the insulation after
probing, about the only thing that you can do to improve
the box’s performance is to open up the wall or
countertop and remove all the old insulation. This is a
major project but is necessary if you want a good
refrigeration system or even a good ice-box.
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Hints
for improving refrigeration
The
quality of insulation determines the amount of energy
required per day to keep the box at the desired
temperature. Upgrading the quality of a box’s
insulation should be a top priority when replacing or
updating a refrigeration system. One simple insulation
trick that can improve refrigeration is the placement of
a type of insulating blanket over the food product in
the box. This will reduce the amount of heat
infiltration from the top. One easy method is to fill
zip lock bags half full with Styrofoam packing peanuts
and place them on top of the food product. This will
hold in the cold and help prevent the infiltration of
hot air when the box is opened. You can easily add or
subtract bags as the food is used or replaced.
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Future
Advanced Insulation Panels
What
do we know about the new insulating panels offered to
the boating industry?
There is one new insulation product that offers improved
infrared heat shielding. The distributors provide the
materials so that the installer can build his own
panels. There are procedures on how to remove the air
from the panels, although they would not be considered
vacuum panels. This material is advertised to have an R
value of R 30 per inch. The
question seams to be how much of the thirty rating is
infrared and how much is conduction and convection of
heat.
The
newest and most talked about insulations are the true
vacuum panels. They are semi rigid skinned panels with
all the possible moisture, air and gas removed. The
manufacture of vacuum,
insulated panels is a complex process. The following
defines what is involved in producing a (VIP) vacuum
insulated panel:
·
The
structure of the VIP must withstand almost 15 lbs. per
sq. inch. This means a 20 by 20 inch panel has almost
6000 lbs applied to both sides. The interior core and
skin/membrane joints must not fail over the life of the
panels.
·
The
outside skin/membrane should conduct as little heat as
possible and a thin reflective film is required to
reject the infrared heat rays.
·
The
outside skin/membrane must retain the vacuum and prevent
small molecule gases from entering for the life of
the panel.
·
The
core inside is what is expected to control the panel’s
life, as the core ages it deteriorates giving off gas
which is a heat conductor that in turn reduces the
vacuum.
We have known for years
that some materials are better insulators than others
and that an airspace that has had all air, gas and
moisture removed from it is the best insulation. This
application is used in the manufacture of thermos
bottles. There are two basic types of these sealed
panels. One is a vacuum sealed insulated core with open
cell foam and the other is a sealed panel of closed cell
foam core with little or no vacuum inside. There are
questions as to which panel is the best, or most cost
effective. Each panel type has different chemical
compositions and construction properties. The degree of
vacuum varies from moderate to no vacuum.
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A
Major Concern
A
major concern with the vacuum panels is that they might
leak and lose their vacuum. A boat is constantly in
motion and subjected to temperature changes. A leak in a
panel with open cell foam would be bad news. With
special handling and proper mounting the panel
manufactures believe these types of failures can be
avoided but if these panels are used as the liner wall
they will be exposed to sharp object damage.
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What
We Know
After
reviewing comments from 40 boats without any actual
performance data the vacuum type panels do reduce the
thickness of insulation required. We do know that six
inches of standard foam has kept our freezer working
well in the tropics on boats for the last 10 years, but
we lack any data on vacuum insulated panels under
tropical conditions. We know that boating with good dry
insulation where the sea-water temperature rarely
exceeds 70°F, you can get by with 2 to 2-1/2
inches of insulation in the refrigerator, but if
you are boating in the tropics with a daily high of over
90°F, and the sea-water temperature is 85°F you would
need from 3-4 inches of good quality closed cell foam or
a product with an “R” value of at least 7 per inch
for a good performing refrigerator. To maintain a good
freezer in the tropics, you would need from 4-6 inches
of good quality insulation.
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Is
the Price Worth it?
If
a conventional sealed insulated box costing $300 to $400
for materials can work just as well as a $6000 to $8000
vacuum panel one why spend the money to go VPI?
For some it’s the ability to save precious
space and in some cases avoid extensive retrofit.
There
are VIP panel manufacturers with more realistic pricing
such as VacuPanel Inc. Phone: (937)376-8233 web site
www.vacupanel.com.
If
you are familiar with my book you know that I am
conservative and that I recommend no item or piece of
equipment that does not have one million hours in
service and a failure rate of more than five per
thousand operating hours. So far I have not been able to
find any performance data on vacuum panels that meets
that criteria, but here are my thoughts:
-
If
there is enough space, stay with the conventional
method and upgrade the
-
If
space is tight, I would use the less expensive
Vacupanels with an impact resistant box liner.
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