Regulating Voltage to a Fridge

[coopec43]

Originally Posted by ramblinrod

Here are some things that may be causing your problems:

1. Insulation: There should be at least 2" of well sealed Styrofoam SM, (or better) on all sides, bottom, and top of box.

2. Lid Seals: There should be no air leaks.

3. Opening: Shoul

In Australia they recommend a minimum of 4 inches: preferably 5 inches even in Tasmania!

A Fridge Mechanic (who has worked a lot on boat fridge/freezers in the tropic port of Darwin) says a lot of people have placed the foam between the freezer box and the hull which is a mistake as air must be able to circulate around the freezer.

Apart from that the sea water temperature is often around 32°C (89F) in Darwin and the heat is conducted through the hull and foam into the fridge. Keeping the fridge contents cold is therefore impossible.

[john61ct]

so much wrong where to start

[ramblinrod]

Originally Posted by coopec43

In Australia they recommend a minimum of 4 inches: preferably 5 inches even in Tasmania!

A Fridge Mechanic (who has worked a lot on boat fridge/freezers in the tropic port of Darwin) says a lot of people have placed the foam between the freezer box and the hull which is a mistake as air must be able to circulate around the freezer.

Apart from that the sea water temperature is often around 32°C (89F) in Darwin and the heat is conducted through the hull and foam into the fridge. Keeping the fridge contents cold is therefore impossible.

We have to be a little careful here.

2" of well sealed Styrofoam SM is "adequate" in most cases.

Is 4" or 5" better?

Well, on paper.

One of the issues is that perhaps 90% of the heat transfer from the fridge may not be due low insulation R value.

It could be due to the insulation not being sealed well, gaps in the door lid, frequent or long duration opening, adding warm items, etc.

On a day the fridge isn't used and sits their all closed up, the 100% increase in insulation will likely result in energy consumption reduction of only 20% or even less.

During a normal day of use, the difference may not even be really detectable.

Regarding insulation thickness, one has to consider the value of the boat space consumed.

If the insulation has to be added to the inside, reducing fridge capacity below what is needed, that's not so good.

Or, if adding insulation to the outside interferes with storage space for provisions or gear, that also is not good.

So like everything else related to boat design and modification, there are pros ands cons to every decision.

Under normal circumstances, putting extra insulation against the ice box where one can afford to give up the space, can't hurt anything but the pocket book, to purchase the additional insulation.

An exception I can think of, is between an ice box and dark hull.

It is not desirable to seal the space between the hull and refrigerator box insulation, as the trapped air space can act like a solar collector holding significant heat well above cabin temperature, against the fridge insulation.

This higher than normal temperature gradient can result in greater heat transfer into the fridge.

An air gap between the hull and insulation, that permits convection air flow, to carry that heat away from the fridge insulation, is preferable.

For a white of light coloured hull; no real issue in my opinion.

If one can't keep fridge contents cold with 89F ambient, I think something is wrong.

Lots of boats have air cooled fridges running just fine with 110F ambient cabin / condenser space temps, and higher.

The point about insulation right up to a hull below the waterline transmitting heat to the ice box could be valid if the vessel is air conditioned. If not, then the cabin temp is likely to peak well above 89F when the water temp is 89F (avg) so it would be better to fill the gap.

Notwithstanding, even with only 2" of Styrofoam SM (well sealed) the temp in a reasonably sized ice box should be fairly easily maintained with an 89F water temp. outside the hull.

I would not claim your fridge mechanic was wrong, but that perhaps he was correct only for your very specific circumstance, that may not translate well as a general statement applicable to most other conditions.

[coopec43]

Rod

Rigid polyurethane is a better refrigerator insulation than Styrofoam (polystyrene foam). Just about all the refrigerators world-wide would use polyurethane.

One of the best commercially available choices of insulation material for fishing vessels is polyurethane foam. It has good thermal insulating properties, low moisture-vapour permeability, high resistance to water absorption, relatively high mechanical strength and low density.
5. Thermal insulation materials, technical characteristics and selection criteria

And

Polyurethane rigid foam is the insulating material which is most widely used throughout the world for refrigerators and freezers. The insulation efficiency of .

[john61ct]

Polyiso for most of the thickness, thin sheet of XPS (styrofoam is a branded instance) lining the inside

ha proven to provide the best R value per space occupied, out of reasonable priced options.

aerogel, vacuum panels better but pricey AF

and as noted R value is not be all and end all,

effective vapour barrier surfaces, quality opening hatches / door seals, food safe, longevity in use, many other factors

[ramblinrod]

Originally Posted by coopec43

Rod

Rigid polyurethane is a better refrigerator insulation than Styrofoam (polystyrene foam). Just about all the refrigerators world-wide would use polyurethane.

One of the best commercially available choices of insulation material for fishing vessels is polyurethane foam. It has good thermal insulating properties, low moisture-vapour permeability, high resistance to water absorption, relatively high mechanical strength and low density.
5. Thermal insulation materials, technical characteristics and selection criteria

And

Polyurethane rigid foam is the insulating material which is most widely used throughout the world for refrigerators and freezers. The insulation efficiency of .

2" of Styrofoam SM will give an R value of "10", whereas 2" of polyurethane foam board has an R value of "12.5".

Styrofoam SM is cheap and available at any building supply store.

As mentioned, a 100% increase in R value over 2" of Styrofoam SM will have minimal affect during normal use.

So a 25% increase in R value is not likely to noticeable at all. If boat are easily accessible and about the same price, polyurethane foam board would be a good choice, but I wouldn't go out of my way or incur additional expense.

If one is using 4" of Styrofoam SM, the diminishing returns of higher R value makes the change to polyurethance even less worthwhile.

[coopec43]

Originally Posted by ramblinrod

2" of Styrofoam SM will give an R value of "10", whereas 2" of polyurethane foam board has an R value of "12.5".

Styrofoam SM is cheap and available at any building supply store.

If one is using 4" of Styrofoam SM, the diminishing returns of higher R value makes the change to polyurethance even less worthwhile.

What you are saying goes against all the advice I was given when I constructed my fridge/freezer. (Any decent boat fridge/freezer on a boat would use polyurethane)

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
http://www.kollmann-marine.com/insulation.aspx

[ramblinrod]

Originally Posted by coopec43

What you are saying goes against all the advice I was given when I constructed my fridge/freezer. (Any decent boat fridge/freezer on a boat would use polyurethane)

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
http://www.kollmann-marine.com/insulation.aspx

I don't know what to say.

Was the person advising you selling polyurethane foam panels?

From the information you posted, about the 3rd sentence from the bottom...

"One of the most common materials used as insulators today are polyurethane or styrene"

First, polyurethane and polystyrene are different materials, so they are two of the most common materials used as insulators today...

There are plenty of fridge and cooler manufacturers that use polystyrene, in fact probably more polystyrene are sold.

For one-off fabricators of small systems I would expect Styrofoam SM (aka a specific brand of extruded polystyrene foam board) to be the vast majority.

There are all kinds of insulating solutions that are superior to both polystyrene and polyurethane foam, and if one is going for one-up-man-ship on specs and energy conservation on paper, that's fine, but again, in everyday use, it won't make a lot of difference.

A 25% increase in R value, may only translate to a 2% energy reduction in real world use. IOW, one may be wiser (faster, easier, cheaper) to go for a little more solar vs beef up the fridge insulation.

That said, extra or better insulation can't hurt refrigerator performance, so if one already has it, or decides they want it and can afford to give up the space, why not?

[coopec43]

Rod

"One of the most common materials used as insulators today are polyurethane or styrene"

First, polyurethane and polystyrene are different materials, so they are two of the most common materials used as insulators today.

..

You'd have to ask the author about his/her wording but apparently both materials are used in refrigeration (don't ask me why)

Why is polystyrene used as an insulating material in refrigerator?
Polyurethane rigid foam is the insulating material which is most widely used throughout the world for refrigerators and freezers. The insulation efficiency of polyurethane foams is a key property for the low temperature preservation of food during processing, storage and distribution to the consume

Many top-mount refrigerators have a section of styrofoam above the freezer control dial. This is not packing material and should not be removed. Styrofoam may also be located around the vent and in the roof of the refrigerator and should not be removed.

Insulation
The first step that can be taken to reduce the power needed to run a fridge is improving the insulation. In many cases this is woefully inadequate – ideally a marine fridge will be encased in four-inches of insulation. Smaller units – those below around 100 litres – may be able to get away with less than this. However a freezer should ideally have some six inches of insulation.
https://uk.boats.com/how-to/efficien...-how-to-guide/


I can't imagine ANY production yacht builder using 4+ inches of insulating material as they like to make their yachts look as spacious as they can.

[john61ct]

In an open forum, choose who you listen to

or even who you invest extended time engaging in discussions with

very carefully.