Reefer box construction - vapor barrier?

[jordanbigel]

Originally Posted by mvweebles

From the picture, looks like you may need to curve along the hull. 1/4" will be too stiff. You can double or trople the thickness of 1/8" at mounting points.

The plan is to build a vertical form on the left to block off the hull and make a squared box and start insulating from there in - we will also glue foil to the side of the hull and then pour 2 part foam into the space between the vertical form and the hull.

[GreenWave]

Originally Posted by Bellinghamster

The polyiso foam I used was foil faced both sides and I taped the exposed edges with 2" foil tape so they were completely sealed panels. Staggered overlaps in the corners and filled any gaps with expanding foam (from a can, i.e great stuff if equivalent)

This is how I plan to redo my freezer box. It currently has foiled wrapped insulation that is breaking down (probably been in there for 10+ years).

[wingssail]

Originally Posted by mvweebles

I wish 6" was practical. Household counters are 24-inches deep. Boats are often a few inches less. If the cavity is 24Dx36Wx30H, you would end up with a fridge with dimensions of 12x24x18, not much larger than a large milk crate.

This type of guidance comes from the old days of flood acid batteries and very limited power generator options. Another strategy would be accept some inefficiency in exchange for carrying capacity - upsize the refrigeration unit, and add an extra solar panel and LiFePO4 battery.

6" inches is practical if you are willing to live with a smaller box. We had limited space but we wanted efficiency, so we used about 6" of insulation and accepted the reduced size of 13x16x17 including the small freezer section. We don't keep a lot of beer or pop in the refer but other than that we don't find it inconvenient. The evaporator box freezer section makes ice and can hold about 15 -20 days of frozen meat. We find this is fine. On a recent 90 cruise we were able to go a month between restocking and had enough refer space to have fresh food for that length of time (with frozen meat).

We rebuilt our box with a outside layer of reflective aluminum bubble wrap and then overlapping 1" blocks of pink closed cell foam and a final layer of 1/8 fiberglass totaling over 6". We originally had some air gaps near the top of the box which we filled with spray foam which made a very big improvement. We angled the hull side to get a few more cubic inches of usable space and accepted that the angled back makes stacking some stuff inconvenient. Now we think a better seal at the lid will also help, indicated by frequent (once per month) defrosting required.

This small, well insulated, box uses about 75AmpHours of electricity per day in 90-100 degree ambient temperatures (with water temps at 70 degrees) but more in warmer water which indicates the insulation is still not perfect.

This box is over three years old and has continued to work with no increase of daily power usage. Most of all what I like about it is my daily scotch rocks with a huge chunk of ice.

[rbk]

Originally Posted by jordanbigel

The thing is that there seem to be 2 opposing viewpoints - some people think the secret sauce is absolute air-tight seal of the insulation (which I am still not clear on how to achieve) and others suggest, as you do, that you want it to breathe.

I think there is logic to the first viewpoint - if no air gets in, no water can get in.

And, the Dupont article "weather barrier myths" is about insulating a house, not a freezer box. I am not sure the issues are the same, in fact, I'm certain they are not the same, but I still don't know which camp is right.

I have read several other threads (man, I have read a lot of threads on this topic) where some people have repeated this idea that they have to breathe, and others, again, suggesting the secret is to make it air-tight. I even read one thread (from like 2005?) where a guy said he sealed up all the insulation air tight, then a few days later he read that it has to breather or it will trap moisture, so he spent a day removing the sealing on one side or something like that. Sigh.

IF you have large (sufficient) amounts of insulation to create a large enough temperature gradient and keep the dewpoint far enough out while ensuring there is no surface for vapour to condense on (air gaps) then you can use an insulation that breaths to the exterior of the box. If this is not practical (in which most cases it is not) then you need a vapour barrier installed on the warm side (exterior in this case). The Insulation moves the dewpoint more toward the exterior (but does not eliminate it) and the sealed vapour barrier stops warm moisture laden air from reaching coming into contact with the dewpoint and condensing. Another option that most do not consider is the use of VIP's (Vacuum insulated panels) Not cheap and they can break a seal but are extremely efficient as a thermal break and vapour barrier, with the right tools you could make and maintain your own VIP's.

[LakeSuperior]

Originally Posted by jordanbigel

The plan is to build a vertical form on the left to block off the hull and make a squared box and start insulating from there in - we will also glue foil to the side of the hull and then pour 2 part foam into the space between the vertical form and the hull.

The poured foam against the foil will nullify the radiation barrier. Skip the foil.

[rbk]

Originally Posted by LakeSuperior

The poured foam against the foil will nullify the radiation barrier. Skip the foil.

Yes and no. If the foil is glued directly to the hull then yes it is useless. If there is an air space 1"+ on the hot side of the foil then it can reflect heat away. Foil does not reflect cold only heat. Just to clarify for all, they are not radiation barriers they are radiant barriers.

[LakeSuperior]

Originally Posted by rbk

Yes and no. If the foil is glued directly to the hull then yes it is useless. If there is an air space 1"+ on the hot side of the foil then it can reflect heat away. Foil does not reflect cold only heat. Just to clarify for all, they are not radiation barriers they are radiant barriers.

“Glue the foil to the hull!” There was no mention of an air gap!

[rbk]

Originally Posted by LakeSuperior

“Glue the foil to the hull!” There was no mention of an air gap!

True but the type of insulation behind it is irrelevant. Totally agree that the proposed method has no benefit from the foil.

[jordanbigel]

Seems clear, the foil against the hull idea is pointless and an air gap would be difficult to get to follow the curve of the hull, which is why we are planning to pour in that space.

I suppose the same applies to the side facing the oven, though that is not radiant heat, I think it is inducted (by induction) which is different?

[rbk]

Originally Posted by jordanbigel

Seems clear, the foil against the hull idea is pointless and an air gap would be difficult to get to follow the curve of the hull, which is why we are planning to pour in that space.

I suppose the same applies to the side facing the oven, though that is not radiant heat, I think it is inducted (by induction) which is different?

No still radiant heat. Radiant heat radiates from the source, possible conduction but conductive is through direct contact and your stove should not be touching anything really, also your stove cutout should be lined in some sort of reflective material (usually stainless steel) to reflect the radiant heat back at the stove. Induction is a form of heating using electromagnetic fields and nothing to do with this thread.

[jordanbigel]

Originally Posted by rbk

No still radiant heat. Radiant heat radiates from the source, possible conduction but conductive is through direct contact and your stove should not be touching anything really, also your stove cutout should be lined in some sort of reflective material (usually stainless steel) to reflect the radiant heat back at the stove. Induction is a form of heating using electromagnetic fields and nothing to do with this thread.

Yes, of course - it's gimbaled in a slot which, as you suggest, is lined with stainless steel. Thank you for clarifying!

[mvweebles]

Originally Posted by wingssail

This small, well insulated, box uses about 75AmpHours of electricity per day in 90-100 degree ambient temperatures (with water temps at 70 degrees) but more in warmer water which indicates the insulation is still not perfect.
.

Wingssail - 75AH seems like a lot for such a small, well-insulated box, even in hot weather. I realize you state this is indicative of imperfect insulation, but still.....that sees to be a relatively large amount of energy over the long haul. I do not have a good baseline......yet. Thoughts?

[wingssail]

Originally Posted by mvweebles

Wingssail - 75AH seems like a lot for such a small, well-insulated box, even in hot weather. I realize you state this is indicative of imperfect insulation, but still.....that sees to be a relatively large amount of energy over the long haul. I do not have a good baseline......yet. Thoughts?

Two thoughts:

My power measurement is imperfect. It's based on observation of the amp load when the refer turns on, about 4 amps, and the percentage of time when it is on over the course of a day, 75-80% in cool (not cold) sea water surroundings. So 24*4*75%=72 amps.

My insulation may not be perfect, based on what I'm reading here. For example there is no air gap between the hull and the foil, and my lid seal is poor, but my refer used to take over 100 amps per day before I rebuilt the box. If others are doing better, well good for them. I tried and this is what I got. I can live with it and what would another rebuild get me, 5AH lower?

I hear some fantastic numbers from people but I wonder how realistic they are.

[jpwdesigns]

I've built 1 custom boat fridge and redid the insulation on another boat fridge. Don't over complicate it. You want to avoid air gaps between insulation and the fridge liner. 4" of the pink/purple-ish ridged foam from home depo is great. You can glue it with liquid nails, wood glue, epoxy, contact cement (if you use the spray 3m stuff don't get too close when you spray). Your question about the moister barrier, use some plastic drop cloth stuff from the paint isle in home depo or equivalent. Tape it up with some foil tape and try to make sure there's no way for air to get out or in to the insulation. Just do your best on that, it's not a rocket engine. Then if you use a modern condenser/compressor you'll find this setup VERY efficient. Don't sweat it too much if you don't have 4-6" of foam, just get as much as you can. 2" of the pink xps stuff is still better than whatever you had before most likely.