Reefer Design

[Doe818]

A question for the reefer gurus here. If you were planning a new install of fridge and freezer (separate or spill over) on a custom new build to be set up for 2-6 people for long distance cruising in tropical waters, what would be your choice of system? You would have easy access during the build, lots of space and could build the system you want (albeit whilst trying to save money of course).

[colemj]

If no constraints, I wouldn't build one at all and instead get a premade drawer system. Make sure it is insulated well and has an efficient compressor with sufficient space around it or a system to introduce air and remove heat.

Mark

[Noreastern]

We are also in the planning process of installing reefer/fridge as part of our refit on our 38' Pearson Invicta. Our restraints are size of box and house battery bank size and of course budget.

Box we are planning to build our self's because the space we would like it to go in is odd shaped. With six" of Dow Blueboard insulation all around the inside box will be 12" wide 24" long and up to 20" deep. If spill over is where the freezer box also cools the reefer this is the system we are looking at.

So far we like the Sea Frost BDXPX system with water cool option and two sided cold plate stainless steel freezer bin that will fit into reefer box.

We would rather have separate reefer and freezer boxes with separate refrigeration systems but that option takes up to much space and over our budget.

[Freedom45]

I installed two Engel drop ins(MB40), use one as freezer and the other for fridge.
So far working great, low amp about 2.5 amps(12v) each. Not cheap, not huge but fit perfectly where my old box was.

Chuck

[Richard Kollmann]

Doe818, You must make several decisions before selection size and type refrigeration unit for a box conversion to refrigeration/freezer.

Cruising area temperatures? Tropics.

Number of people onboard? 2 to 6

Desirable amount of insulation R30, approximant planned R value of insulation? __________.

Where will energy come from to support refrigeration? _________.

What is the desired size of refrigerator area you need after box is completed? _________.

What is desired size of Freezer area you need? _________________.

A 4 cubic ft (133 Liter) combination box in a tropical climate with 2 people will need about 10 amp-hrs per cu ft refrigerated space per day and 20 amp-hrs per cu ft of freezer space per hour per day. These amp-hrs will be again increased by at least 2 amp-hrs per cu ft by addition person above 2 on board per day do to cold liquid consumed and ice per day.
Actual energy consumed will depend on the temperatures you desire in the two separate refrigerator freezer areas. The above 4 cu ft box example would be at constant mid to high 30s F refrigerator temperatures and +10 to +15 degree F freezer temps.

It is difficult to design a spillover system that provides stable controlled temperatures.

I suggest you do the math on my web site slide show for the concept you come up with, then select a compressor with capacity needed and its largest evaporator for your special design. Also for more info on spillover click on FANS for spillover systems.

[SV THIRD DAY]

A common mistake we see in refrigerator and freezer box design is that often times the goal is to build the biggest box that will fit in your space, rather than the size of box you actually need. The "bigger is better" mindset needs to be weighed against the realities that bigger will mean a larger daily power usage. For example a 2.5cubic foot freezer can hold 120 pounds of frozen food, do you really need more capacify than that? However, when I recommend not going larger than 2.5CF as a good practical freezer size people often look at me as if I'm from Mars. Coming from their 5, 7, or 9 CF freezer unit in their garage, 2.5CF or less seems nuts. But we cruised Mexico for 4 years with a crew of 4 (with our two teenagers) with a 1.5CF freezer box and felt we had plenty of freezer volume.

The Number ONE complaint out there in the cruising fleet is the difficulty in keeping up with their daily power usage and at the top of the usage list by FAR is the boats refrigerration needs.

If you have the luxury of building the boxs, consider 4" of polyisocyanurate (approx R26) as an absolute minimum. I'm in the process of rebuilding my freezer box now and being in the business of marine refrigeration (Technautics CoolBlue Marine Refrigeration) I'm builidng my 2.4CF freezer box with 6" of polyiso insulation and from my real life testing data I know I will be able to keep ice cream rock hard, make ice, and not stress about the power usage even down in the hot climate and waters of the Sea of Cortez...where we intend to head back to as soon as these kids get out of school and we give them the boot...ha ha ah .

Here are a few inspiration photos of boxs we helped clients make from scratch.
The first client spent the big bucks and used vacuum panel insulation, but honestly at a cost of about $2500 for a normal size box I can't recommend that when it can be done well for so much less cost, unless money isn't an option to you OR you simply don't have room for enough insulation.

The second photos went with 4" of polyiso for his box. (tw0-2" layers)








Having played the water cooling game on my last boat, I would recommend looking at systems that are designed for air cooling even in tropical environments because once you introduce water cooling into the system, you add maintenance and power costs.

The above systems are both spill over types, but you will always have better temperature control of the two boxes if you went with two independant systems, one for the freezer and one for the refrigerator box. PLUS you will get some system redundancy in the event that one system was to go down while out cruising. With the expense of the new construction, I would go with two seperate units and ask the refrigeration system supplier you ultimately decide on to cut you a good deal one two systems, I know we give a pretty good discount on the second unit for clients.

Good luck and by all means, check out the wealth of data and information on Richard's website http://www.kollmann-marine.com/ because the more you know going in, the happier you will be with your system in the end.

[Roy M]

Or, go nuts and spend more money and time building a custom unit with vacuum insulated panels and a box configured exactly to your needs. I admit it, it costs much more than I anticipated, but it is sooooo cool. No pun intended (BS). You only get to go through life once. Do what you think is right for you.

[Boatguy30]

Well, many different views. Third day pretty much has it right with the exception that the Cool Blue systems involve a bit of alchemy in their claims. A alloy roll bond evaporator is much more efficient in BTU transfer than stainless and anti freeze or whatever they put in them.

Certainly do not go larger than 2.5 cu ft. I had that on a previous boat and made the next one about 1.1 or so. Partly due to space, but would not have gone over 2 cu ft.

Jeff

[SV THIRD DAY]

Originally Posted by Boatguy30

Third day pretty much has it right with the exception that the Cool Blue systems involve a bit of alchemy in their claims. A alloy roll bond evaporator is much more efficient in BTU transfer than stainless and anti freeze or whatever they put in them.

Hey Jeff, CoolBlue has never claimed that a holding plate has a better BTU heat transfer rate than a thin roll band evaporator... I'm not sure where that cruise rumor is coming from. There are other design items that give the coolblue system an edge up on efficiency...but BTU rapid heat transder in the box is certianly not one of them. This faster heat transfer is the mian advantage that evapororators have over holding plates. Well that and their light weight.

[Boatguy30]

My point was to make the amp/hr claims they do at the boat shows they would have to be using some mystery energy conversion. Their claims at one time far exceeded the the Danfoss tech specs. they also either directly or indirectly claimed that the holding plate was somehow magically more efficient, whilst the physics is the exact opposite.

Anyhow, seems like this guy is on the right track. Blue board foam and danfoss all the way. Maybe when Roy gets done paying off his vacuum panels he can get off on that cruise he built his boat for 40 years ago.

[Roy M]

Alas, Roy has been using his boat for these many years, and now it is getting a long needed overhaul, so it can continue to further reaches of the cruising spectrum. And, spending money effectively is considered by some an investment in the future, which is why I built my boat out of West System during the first Arab oil embargo (very costly, indeed), used linear polyurethane (when it was a novelty only used on aircraft and high-end cars) to protect it, and have been enjoying the fruits of that investment these many years. My decision to use top grade, high efficiency insulation, and some other cool features, merely reflects a pattern of personal decision making that has suited my needs, both for my boat and for my customers'. So far, so good. You pays your money and takes your chances.

[Noreastern]

This is the space for our reefer/freezer system first picture on the left. Dinette will be to the right. Obviously we are still in the starting stages of design. Second picture is where the old huge icebox was (above the engine compartment!) with less then 2" of Styrofoam insulation. This will now be where the nav station is located in our plans.

[Doe818]

Awesome, thanks for everyone's input. My last boat had separate fridge and freezer. Both of them ran the thin ally type evaporators on separate air cooled BD35'S. Both were top loaders. The freezer was huge and I hear you on smaller units because most of my life jackets ended up in the freezer trying to kill some volume and I sometimes struggled to keep the whole box frozen. The comp on the freezer ran just about all the time. The fridge was excellent but it was under the galley prep surface so it was somewhat annoying when cooking if someone decided they needed a cold beer and everything had to move off the counter.
Richard, I'll have a look at your site, but to answer some of your questions, we would try and get to R30, no real reason we shouldn't as we have a blank canvass with multiple options. The power will come from a +/- 600 amp lithium bank with solar support (approx 35-40 amps peak) and 200 amp alternators. Re size of boxes, perhaps 2.5-3 for the freezer, 4 or 5 for the fridge.
Re drop in manufactured units like the drawer systems or ones with doors, how is the insulation on those? Are they gimmicks or the real deal? Is it silly to have a top loader freezer and a door / drawer fridge?

[Doe818]

Rich, will drop you a pm as need to chat about other stuff too.

[SV THIRD DAY]

As nice and convienient as front loader refrigeration units are, they just can never stack up to a top loading unit. What happends is that each time you open the door the cool (and dry) air will spill out onto the floor and is replaced with warm (and moist) air. It would be bad enough to just deal with the extra heat load the new warm air brings into the box, but the moisture brought in causes front door opening units to grow frost on the plate/evaporation unit at a much higher rate than traditional top opening boxes.

We have conducted field testing of two identical box volumes comparing the front opening and top opening boxes. We found that there could be as much of a 30% efficiency difference between a top open and front open box of the same size, I would hate to give away those Amps after working so hard to have a well insulated box and efficient refrigeration unit.

The drop in units in trying to maximize internal volume vs overall size so that more people can fit them in their space, sacrafice insulation. I don't know of any premade box drop ins, front or top loading that have the R30 insulation. To give you an idea, we manufacter a line of what we call "EcoFridge" DC refrigerators and freezers that are popular in off the grid homes, cabins, and believe it or not lately the Dooms Day Prepper market.

The unit below for will use 30AH/day at a 70-deg ambient temp (4.4CF refrigerator box kept at 35degs). If you take this unit up to a 90-degs ambient temp, it will use70AH/day. Basically, you have poor insulation in a box like this and could cut the power usage way down with proper insulation.
www.offthegridrefrigeration.com




Rich