MICRO-AIR Artic Air 24 Guía de instalación descargar pdf (Pagina 59)

Transmission Properties.” This test approximates the conditions seen by boat cold box

insulation. There are other test methods which involve an air gap between the heat source and

the insulation being tested. These methods will usually overstate the R value added by a radiant

barrier if the results are applied to cold box performance. Thus high R value claims for certain

insulation types may not be untrue according to the test procedures followed, but may not give a

correct picture of the performance of the insulation in a boat cold box.

If a radiant barrier is installed so that there is an air gap between the barrier and the heat

source, some thermal benefit can be gained. An example of an effective use would be as a

blanket covering the food in a partially full box. If a radiant barrier, which is usually a shiny, foil-

like surface, is sandwiched between another solid material, such as fiberglass or plywood, the

heat energy it sees is largely in the form of molecular motion and the heat is rapidly conducted

through the foil.

Insulation Types and Performance

There are some very old boats that have cold boxes built with fiberglass bat insulation, but the

most common type is two part pour-in polyurethane foam. As this foam cures, the cell size

depends on the curing temperature, and is typically not well controlled. This inability to control

the temperature leads to voids that often develop in areas of the pour in foam. It is not unusual

with stock boats to find no insulation at all between the box hull-side liner and the hull, or under

the counter top.

Even if a good thickness of insulation is present, polyurethane foam insulation tends to adsorb

water. Cold boxes that started out with good performance may lose up to two thirds of their

original insulation value if the foam becomes wet from condensation. Other foam types that

share this moisture absorption problem include sheet polyurethane, polyisocyanurate foams, and

molded bead, or expanded polystyrene. Note that this is not just an open or closed cell foam

issue, but depends on the moisture adsorption properties of the resin used to make the foam.

One way to evaluate your existing box insulation for wetness is by drilling a small hole

somewhere at the bottom of the box and checking the insulation space with a cotton swab. If the

swab comes out wet, the original insulation value of your box is compromised. Such a result

would mean that you should consider completely rebuilding your box.

Extruded polystyrene is the best type of foam insulation to use because it doesn’t adsorb

water and will maintain its insulating value indefinitely. Two common brand names are Dow

Square Edge STYROFOAM

, often called blueboard, and Owens Corning FOAMULAR 150

Additional information and sources for the Dow product can be found at

http://www.dow.com/styrofoam/index.htm. You can also reach Dow by phone at 1-800 232

2436. Information and sources for the Owens Corning product can be found at

http://www.owenscorning.com/around/insulation/products/foamular.asp

The Owens Corning phone number is 1-800-GET-PINK.

How much insulation do you need? The tradeoffs are between energy consumption, usable

box volume, and cost. For tropical conditions we recommend a minimum of R-20 for a

refrigerator and R-30 for a freezer. Extruded polystyrene has an R value of about 5 per inch.

This would correspond to an insulation thickness of 4 inches of foam in the reefer and 6 inches in

the freezer.

For a 5 cubic foot reefer, the daily heat loads on a 90ºF average day would look something

like this as insulation thickness increases:

Page 59

1 2 ... 54 55 56 57 58 59 60 61 62 63

Comentarios a estos manuales

Sin comentarios

MICRO-AIR Artic Air 24 Guía de instalación Pagina 59

Comentarios a estos manuales