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Old 07-04-2014, 16:05   #16
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Re: Efficient home frigde/freezer on a boat?

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Skipmac,

Did you insulate the box with Areogel? Sorry, I tried looking at your past post, man, you've got a lot. Those are impressive numbers for a box that big, at those temps.
I looked at aerogel but just could not get comfortable with the stuff. It sounded really good reading the specs online but seemed like there were issues with handling and working. Plus I never did understand exactly what it was like so ended up using expanded polystyrene, Dow Blue board as the insulation. However did a lot to help the insulation..

First I sealed the inside of the plywood cabinet with epoxy, then lined the entire space with aluminum foil, shiny side out. Then started adding layers of the foam. Due to the odd shape of the cabinet and the hull I ended up with varying insulation thicknesses; 6-8" next to the hull, 6" on the bottom, 4-6" along the sides, 5" on the top. To be fair, the test was static, no opening or closing and after a couple of days to allow the whole box to cool down. Even if real world use raises that 5-10 amphours/day I would still be pretty happy with the results.
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Old 07-04-2014, 16:11   #17
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Re: Efficient home frigde/freezer on a boat?

Hello, it's done in Greenline 33 Hybrid in europe, and USA, every appliance off the shelf household appliances.

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Old 07-04-2014, 16:12   #18
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Re: Efficient home frigde/freezer on a boat?

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So... sorry to be a skeptic but...
Nothing to be sorry about...folks were skepptical that the earth revoled around the sun for thousands of years.

Technautics has converted hundreds of 120v smalll dorm style refrigerators for years. It's not that difficult and I have one running on my boat at the moment connected to an Amp meter, Hour meter, and temperature data logger.

Our standard procedure when doing a unit that we haven't done before is to run the unit for a week or so all hooked up to the data logger with the stock 120v comrpessor. We then swap it out to a 12v compressor (like a Danfoss of various size or Cubigel) and then run the unit for anther few weeks. The typical amp usage difference is about 1/3 the power. The trash 120v compressors may be marked as "Energy Star" I call them a falling Star once you see just how inefficient they turn out to be compared to a compressor designed for energy efficiency from the get-go.

No rocket science envolved...just basic Refrigeration skills, an easy DIY Project or buy one converted. I'm not sure how you got the impression we give a bid, go out to the boat to do anything??.....that would be Crazy when we can do everything at the shop.
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Old 07-04-2014, 16:15   #19
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Re: Efficient home frigde/freezer on a boat?

I wonder how important it is to move the heat exchanger out of the living space,
like is done for air conditioning? I don't see any home fridges that do this.
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Old 07-04-2014, 16:22   #20
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Re: Efficient home frigde/freezer on a boat?

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Ahhh! Forgot to put that one in. It was on my spreadsheet. A good choice.

I should mention that my numbers are very specific to my own situation. I have a blank canvas. No systems yet. So, these costs were to produce power for incidentals, plus refrigerator, varying power sources and refrigerator types.

Everyone really has to do their own calculations sine maybe you already have a 2KW solar array or 2,000 gallons of fuel in a bunker somewhere.
No 2,000 gallon stash and hoping I won't need it.

So far only 190W of solar so a little short there as well.

I did have more or less blank canvas as I stripped out the old box and very old cold machine. The only limitation was to fit the new system into the same cabinet space in the galley which seriously complicated the construction process but in the end was able to make it work.

I do have to make one confession, I'm still on the hard finishing my refit so no real world, open and close, food in and out test. The power draw I in that situation remains to be seen.
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Old 07-04-2014, 16:43   #21
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Re: Efficient home frigde/freezer on a boat?

No one seems to mention disconnecting the defrost element. Isn't this the big power eater?
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Old 07-04-2014, 17:44   #22
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Re: Efficient home frigde/freezer on a boat?

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The one thing that may have been missed on the propane fridge is: they seem to often be brokedown on travel trailers/motorhomes (cost?), the danger of the always "on" propane aplliance in the cabin, the trouble of getting propane all the time (they use it pretty fast).
Doors:
I've had front door, refrig with front and top doors, and top loading only. Frankly I couldnt determine any differnce in power use from the doors. Maybe if you have kids that will open the door and stand there for 5 mins it would matter. It does make a diff frost wise though... must defrost more often on a front door model.

Absolutely important points.

You can never get away with posting the bare minimum on a forum.

You really shouldn't use a propane refrigerator below decks, although plenty of boats did come wirth them installed and never had a problem. My installation kept the "business end " outside on deck. Multihull.


And yes, those old propane refrigerators broke down often, which was also due to poor installation from the rv conversion company. I am very pleased with my large Norcold which has run continuously for 5 years, costing $20/mo. Zero problems. Love it, which is why it made my list.
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Old 07-04-2014, 17:50   #23
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Re: Efficient Hhome Frigde/Freezer on a Boat?

I have a 3.5 CF dorm fridge mounted next to the galley. As Rick/Third Day says a 12V unit uses way less amps when running. My fridge will pull 14 amps at 12.5V when running. A 12V will use 4-5 amps I'm guessing, though the better ones have variable speed which helps lots with the COP. So at first blush 12V would seem to be the way to go.

But she says.... You have to factor in run time into the equations also. My fridge in 90-93 cabin temps (summer in the CA Delta) will run 2.5 minutes+/- every 14 minute, or about 10 minutes per hour. So 14 amps +1 amp for inverter lose (93% conversion efficiency) is 15 amps. So 15/6 equals 2.5 amps per hour used. Which I would guess will be about the same for a 12V unit. This as the amount of work done and compressor design is similar.

Just as a 1 KW and 4 KW electric heating elements will use theexact same amount of amps heating 10 gallons of water, just at different rates. A 12V and 120V compressors are doing the exact same amount of work for a given box size. So the 120V would run less to the 12V running more.

I know that my 230 watts of solar panels will run the fridge day and night, while also running lights, propane solenoid, charging laptop ,etc. I figure I get about ~65 amps a day from my solar panels. I'm figuring about 50-55 amps for the fridge a day, which jives with manufacturers data.

My fridge 7 years ago was about $140. Add in a $44 700 watt inverter, two solar panels and a PWM unit and for about $800 installed, its pretty cheap. If the fridge dies, $200 gets me a new one.

As someone mentioned the front opening fridge is not too bad, though don't leave the door open too long. I find that defrosting the freezer evaporator once a month or so really helps keep things working well. A 1/4" of ice on the evaporator will raise the fridge temp 10 degrees and the compressor will run more.

Agreed that disconnecting door heaters and auto defrost will save more energy. I use a electric hair dryer with the genny, which takes 5 minutes to defrost my small freezer section.

Anyway that's what this poor sailor does.
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Old 07-04-2014, 18:07   #24
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Re: Efficient Hhome Frigde/Freezer on a Boat?

Quote:
Originally Posted by sailorchic34 View Post
I have a 3.5 CF dorm fridge mounted next to the galley. As Rick/Third Day says a 12V unit uses way less amps when running. My fridge will pull 14 amps at 12.5V when running. A 12V will use 4-5 amps I'm guessing, though the better ones have variable speed which helps lots with the COP. So at first blush 12V would seem to be the way to go.

But she says.... You have to factor in run time into the equations also. My fridge in 90-93 cabin temps (summer in the CA Delta) will run 2.5 minutes+/- every 14 minute, or about 10 minutes per hour. So 14 amps +1 amp for inverter lose (93% conversion efficiency) is 15 amps. So 15/6 equals 2.5 amps per hour used. Which I would guess will be about the same for a 12V unit. This as the amount of work done and compressor design is similar.

Just as a 1 KW and 4 KW electric heating elements will use theexact same amount of amps heating 10 gallons of water, just at different rates. A 12V and 120V compressors are doing the exact same amount of work for a given box size. So the 120V would run less to the 12V running more.

I know that my 230 watts of solar panels will run the fridge day and night, while also running lights, propane solenoid, charging laptop ,etc. I figure I get about ~65 amps a day from my solar panels. I'm figuring about 50-55 amps for the fridge a day, which jives with manufacturers data.

My fridge 7 years ago was about $140. Add in a $44 700 watt inverter, two solar panels and a PWM unit and for about $800 installed, its pretty cheap. If the fridge dies, $200 gets me a new one.

As someone mentioned the front opening fridge is not too bad, though don't leave the door open too long. I find that defrosting the freezer evaporator once a month or so really helps keep things working well. A 1/4" of ice on the evaporator will raise the fridge temp 10 degrees and the compressor will run more.

Agreed that disconnecting door heaters and auto defrost will save more energy. I use a electric hair dryer with the genny, which takes 5 minutes to defrost my small freezer section.

Anyway that's what this poor sailor does.
At $120 for an apt refrig... it would be hard to not try one if it fit!
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Old 07-04-2014, 18:12   #25
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Re: Efficient Hhome Frigde/Freezer on a Boat?

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Anyway that's what this poor sailor does.
And you do it right. People confuse power draw with energy consumption. Ah, the life of an engineer...

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Old 07-04-2014, 18:35   #26
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Re: Efficient Hhome Frigde/Freezer on a Boat?

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Originally Posted by sailorchic34 View Post
I have a 3.5 CF dorm fridge mounted next to the galley. As Rick/Third Day says a 12V unit uses way less amps when running. My fridge will pull 14 amps at 12.5V when running. A 12V will use 4-5 amps I'm guessing, though the better ones have variable speed which helps lots with the COP. So at first blush 12V would seem to be the way to go.

But she says.... You have to factor in run time into the equations also. My fridge in 90-93 cabin temps (summer in the CA Delta) will run 2.5 minutes+/- every 14 minute, or about 10 minutes per hour. So 14 amps +1 amp for inverter lose (93% conversion efficiency) is 15 amps. So 15/6 equals 2.5 amps per hour used. Which I would guess will be about the same for a 12V unit. This as the amount of work done and compressor design is similar.

Just as a 1 KW and 4 KW electric heating elements will use theexact same amount of amps heating 10 gallons of water, just at different rates. A 12V and 120V compressors are doing the exact same amount of work for a given box size. So the 120V would run less to the 12V running more.

I know that my 230 watts of solar panels will run the fridge day and night, while also running lights, propane solenoid, charging laptop ,etc. I figure I get about ~65 amps a day from my solar panels. I'm figuring about 50-55 amps for the fridge a day, which jives with manufacturers data.

My fridge 7 years ago was about $140. Add in a $44 700 watt inverter, two solar panels and a PWM unit and for about $800 installed, its pretty cheap. If the fridge dies, $200 gets me a new one.

As someone mentioned the front opening fridge is not too bad, though don't leave the door open too long. I find that defrosting the freezer evaporator once a month or so really helps keep things working well. A 1/4" of ice on the evaporator will raise the fridge temp 10 degrees and the compressor will run more.

Agreed that disconnecting door heaters and auto defrost will save more energy. I use a electric hair dryer with the genny, which takes 5 minutes to defrost my small freezer section.

Anyway that's what this poor sailor does.

With that, the thread can close. Perfect, perfect, perfect!!
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Old 07-04-2014, 19:04   #27
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Re: Efficient Hhome Frigde/Freezer on a Boat?

Yepers....
Yep forget about auto-defrosters when you are trying to be energy efficient...them be power suckers.

I've ran these units both ways (120v throuh and inverter and then 12v) living at anchor in the hot world of Mexico and what killed us was the 1.0 to 1.5A draw 24hrs/day of having to leave the inverter ON to cycle the refrigerator. That is 24 to 36AH PER DAY for nothing. That doesn't really matter in marina living or hoping from marina to marina power cord, but when you are trying to live out on anchor off of solar....whew boy...let me tell you....every 25AH matters. This is where economics comes in....it was cheaper for me to run the honda generator and live with the power usage of my $150 refrigerator at the time in my cruising budget life than convert it to a 12v unit. This is why there are many correct answers to questions..it just depends who is asking and how they want to cruise.
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Old 07-04-2014, 20:05   #28
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Re: Efficient Hhome Frigde/Freezer on a Boat?

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Yepers....
Yep forget about auto-defrosters when you are trying to be energy efficient...them be power suckers.

I've ran these units both ways (120v throuh and inverter and then 12v) living at anchor in the hot world of Mexico and what killed us was the 1.0 to 1.5A draw 24hrs/day of having to leave the inverter ON to cycle the refrigerator. That is 24 to 36AH PER DAY for nothing.
Oh agree that the big 1500/2000 watt inverters can have some pretty high standby losses. Agree with you there for sure. 25 amps is a huge amp leak.

Me I use a small cheap Wagan modified sine wave inverter. Its no load standby loss is <0.3 amps per hour. That's only 7 amps per day and not so bad, less then 45 minutes for the solar to make that up.

I had thought of hard wiring a relay to a dedicated inverter run from the fridge t-stat, but find the standby load is not really a big factor with the smaller inverters. Plus the inverter has two USB power ports for charging phones and tablets, etc. Pretty sweet really.

FYI wagan is the OEM for some of the west marine inverters. I find it less expensive getting the inverter from the OEM. Plus they are cheap enough that I keep a spare in a sealed plastic bag, for when/if the running wagen inverter dies.
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Old 07-04-2014, 20:35   #29
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Re: Efficient home frigde/freezer on a boat?

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The more energy efficient solution is to get a bigger single refrigerator/freezer. You will use double the power installing a second unit. Increase the size of the single unit.

Further, the cold air loss is negligible with an upright when contrasted with the pain in the %ss of digging through a deep pit to find things. This is an old wives tale. See, this has to do with the physical property "specific heat." When some cold air drops out of a refrigerator, it raises the temp of the air inside just a little bit. But, the food, liquids,refrigerator interior surfaces,shelves, etc... do not change temperature, unless you are sitting there like an idiot with the door open trying to look at what you want to eat.

So, you are only introducing a moment or 2 of compressor work by changing the air because while the air raises slightly in temperature, the things that are most difficult and energy consuming to cool (the food, shelves, lining of the refrigerator), do not need additional cooling from you opening the door.

Expense and energy consumption are basically the same foir both. So why have to suffer through digging in pit?

Lastly, the amount of time you have to keep the damn pit open, coupled withthe need to take half of the stuff in the pit out and put it on the counter while digging COMPLETELY negates any advantage of air not spilling out. Opening a front loader, instantly grabbing the item and closing the door wastes less energy than piling all the food on the counter, where all those higher specific heat items soak up heat.

It's a wives tale, imo, made up by people who do not actually live on boats and who probably are just weekenders getting a sandwich out of an empty pit refrigerator. In real life on boats, the energy lossses from digging are substantial.
Yes!

A fridge full of air carries bugger-all in heat. You can easily calculate it with specific heat of air (which is low) and the density of air (also very low compared to water). I ran those numbers a few years ago in a similar discussion and came up with something like that you can completely drain all the cold air out of the fridge 10 times, and that still doesn't consume as much energy as putting in one warm can of coke.

Some people fill up the empty space in their fridges, trying to reduce the cold air leakage from the door opening. Total waste of time.


Freezers are enormous power hogs, not because of the air in them and opening the doors, but because of the large temperature differential between the interior and your cabin, which means a lot of energy is needed to pump out the heat which soaks through the insulation. A big chest freezer on a boat would be insanity; would bankrupt your power budget. I have a separate freezer on my boat, and I love it. It is a very efficient Isotherm job which cools to sea water without a pump (and the seawater where I sail is cool, which makes it even more efficient). But despite all this efficiency, it uses something like 4x as much power as the larger fridge. It is the biggest power consumer on board.
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Old 07-04-2014, 20:59   #30
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Re: Efficient Hhome Frigde/Freezer on a Boat?

Here is some scientific testing data to shed some light on the issue of top loaders vs front loaders.

Here are the test conditions:
Two 7CF boxes 1/3 freezer and 2/3 refrigerator both with 4" of Polyisocyanurate foam insulation. Test one had the box positioned as a traditional top opening box and for test contition two the same box was stood up on it's side for a front opening. The doors were opened for 1 minute every other hour from 8AM until 8PM. Both boxes had the same amount of contents (about 3/4 full) with standard food items to simulate real life as much as possible. Ambient temp...74 degs.The test were conducted for a 7 day period each.

Here are the results:
Top opening box used an average of 27AH/Day
Top opening frost thickness 1/4" at 7 days

Front opening box used an average of 36AH/Day
Front opening frost thickness 3/4" at 7 days

Now is a 30% power difference and an increased need for defrosting worth the EASE and JOY of not having to dig for you food in the damn boxes from hell? Well...that is your call and for the record I have a front opening refrigerator and a top opening freezer aboard my boat. The freezer suffers MUCH more from being a front open than does the refrigerator since you are trying to maintain a much larger temperature delta.

With Technautics Marine Refigeration being around since 1968 (before I was born) and the the founder Randy Simpkins being a reserach scientist, we have as many notebooks filled with refrigeration test data as Romney has Notebooks of Woman...ha ha ha...lots of cool stuff.

With the trend to larger and larger boats and systems, people want 5...7...even 10Cf freezer boxes which is crazy. I think an ideal freezer box size is 2-3CF. Heck we cruised/lived aboard now for 6yrs with two kids aboard with one smaller than that and are fine but then again we didn't have frozen lobster tails in the freezer...we just caught them under the boat....
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