Insulation

 

     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, and 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.

     The most important and the most misunderstood aspect of refrigeration is the quality and the amount of the insulation. When you purchase a boat you have no control over the amount or quality of insulation that is installed in your box. The best boxes are those that have been rebuilt and insulated by their owners. There has been considerable improvements in the quality of insulation through the years. In the early days we used sawdust and then cork, Styrofoam and fiberglass, but these are all poor insulators. Today we have insulation materials of a much higher quality. One of the most common materials used as insulators today are polyurethane or styrene which have an "R" value of between five and eight per inch. "R" value is an established rating method used by the insulation industry. These common insulation's are referred to as closed cell which means that they are resistant to moisture infiltration. 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 a conductor 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 which 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 showing. 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 which 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 a high "R" value.

    If icebox presently has refrigeration it is easy to determine if the current insulation is adequate by comparing heat loss temperature of insulation’s exterior surface. If when box temperature has stabilized at desired temperature for several hours insulation’s exterior surface temperature should not be more than five degrees colder than surrounding cabin ambient air insulation is less than desirable. If this temperature is greater than eight degrees wet condensation will develop on insulation’s exterior surfaces and you will not need a thermometer to identify poor insulation. Question normally asked is how much insulation is enough for my boats refrigerator? The answer is simple if boat remains in climates with seawater temperatures 75 degrees F or cooler two to three inches of dry insulation are adequate for a refrigerator.  In warm climates insulation with an R value of 30 is desirable. I do not believe there is a noticeable difference between insulation of R30 and R50. The main difference between refrigeration or no refrigeration on a boat is whether boats energy power grid can handle refrigeration and not the amount of insulation around refrigerated box.

     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.

     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 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.

     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 replenished.

     Fifteen years ago Glacier Bay’s marine division produced reports on how Vacuum Insulated Panels (VIP) better met future insulation applications for boat refrigerators saving space while increasing insulation R value. Soft drink manufacturers were interested in VIP for vending machine energy saving insulation. The VIP industry was not a new industry as many companies were already assembling shipping containers using silica materials for structural cores.  The two concerns with VIPs are life expectancy of core material and membrane cover leaking. In the beginning it was believed that all cover membrane material with the exception of glass and metal could over time leak reducing effective insulating quality. Dow did for a short time did produce a metal aluminum VIP but they lost vacuum and were discontinued. Most panel manufacturers of  VIP use Instill as core material. Glacier Bay's BARRIER Ultra-R  VIP’s uses Aerogel core material.

     Most pleasure boats have small refrigerated boxes so it is difficult to quantify the difference between three inches of polyurethane insulation versus one inch VIP with one inch blue board backing it up. On a six cu ft box I believe a one inch VIP and one inch blue board can be compared to four inches of polyurethane if both boxes are in use daily.

     There are no records of success or failure of VIPs in boat refrigerated boxes but there are a number of reported VIP failures on boating forums. Most companies that sold VIPs to boaters no longer do so..

      If you have questions about insulation you may post them on my forum.