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Old 07-04-2014, 21:18   #31
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Re: Efficient Hhome Frigde/Freezer on a Boat?

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Originally Posted by SV THIRD DAY View Post
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....
You can easily calculate the difference. Just take the volume of the fridge (less the volume of the contents if you want to be precise). Take the temp differential, specific heat of air, mass of air derived from the volume, and there's the amount of energy needed to cool down the fresh warm air in the fridge. That's a very simple calculation.
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Old 07-04-2014, 21:28   #32
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Re: Efficient Hhome Frigde/Freezer on a Boat?

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You can easily calculate the difference.... That's a very simple calculation.
Of course it is, beginning thermodynamics 101...and that calculation will give you a different value than a real life field test.

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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..
A 30% energy difference is a bit more than a can of coke. That's why scientist types do tests to verify the calcualtions in the real world of unaccounted for variables. Plus it's much more fun to set stuff up in the lab and do some cool testing with data loggers and pretty graphs. The beer and ice cream was also eaten at the end of the test...try eating the Hp calculator and pocket protector.....gulp.... We have 4 test boxes running at the moment and my partner keeps asking why the Cookies and Cream Ice Cream carton keeps decreasing in volume??? The best part is that the steaks and beer we have been buying for the tests goes down as an R&D cost for our crazy Uncle Sam. There is a method to the madness after all...
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Old 07-04-2014, 21:31   #33
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Re: Efficient home frigde/freezer on a boat?

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Originally Posted by nimblemotors View Post
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.
With a fridge, you're cooling the inside of it, with AC you're cooling the living space, so just as you'd put the fridge condenser outside the fridge, obviously there would be no point in having an AC condenser inside the living space.

I've seen it argued that having a fridge condenser in the living space heats it up. The fact is it would only be by a very small amount, since the heat being removed from inside the fridge originally CAME from the living space. The only additional heat generated would be from the compressor motor.
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Old 07-04-2014, 21:36   #34
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Re: Efficient home frigde/freezer on a boat?

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Originally Posted by SV THIRD DAY View Post
Here is some real life date...although these smaller refrigeration units are not what you are looking for, you will see the same type of power problems.
EcoFridge 12v/24v Solar Powered Upright Refrigerator and Freezers

We have converted dozzens of 120v refrigerators to 12v and almost every one we test results in a 1/3 the power draw once we put in the 12v compressor over the 120v.

Two big reasons:
1. Even the best energy start 120v compressor is horribly less efficient as the moden 12v compressors. They are popped out without regard to true energy efficiency but just want to get the "energy start" rating...IE doing the bare minimum necessary because people don't really buy a 120v refrigerator these days based on energy usage data..but on price/looks and features.

2. Anytime you power something through an inverter you have an efficiency loss

Now none of this really matters with a 2000W solar array, but for mose boats without a crazy amount of solar powering their refrigerator and freezer is the No 1 battery sucker on their boat. We won't even talk about the energy loss every time you open the door and the cold air spilled out on your feet replaced by warm moist air.....that right there has caused a 30% efficiency loss in our testing.
My 90 litre 240 volt freezer draws 60 Watts when it's running. That's real life, checked with a clamp ammeter. (It's also on the spec sheet on the freezer.) Are you saying that you could power it with a 20 Watt 12 volt compressor?
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Old 07-04-2014, 21:54   #35
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Re: Efficient Hhome Frigde/Freezer on a Boat?

If I recall correctly, the 12V compressors actually include an AC motor. The little black box is a DC to AC inverter. There would be efficiency losses there too. What with the heat rejection on the cooling fins on the little black box in all. Really there is no free lunch. Since the basic mechanical design of the compressor is practicelly the same between the DC and AC units, the overall BTU's rejected per watt would be very similar for the same box design.

The VFD units would give better COP at low speed, but the difference is not that much in real life.

Before I installed my 120V fridge, everything I read said that it would not work at anchor. I figured that at the price point it was worth a try. Imagine my surprise, when I find that it actually works pretty darn well on the hook with a pretty low energy use, within the same magnitude as a 12V unit for 10% the price or less.
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Old 07-04-2014, 21:56   #36
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Re: Efficient home frigde/freezer on a boat?

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Originally Posted by 44'cruisingcat View Post
My 90 litre 240 volt freezer draws 60 Watts when it's running. That's real life, checked with a clamp ammeter. (It's also on the spec sheet on the freezer.) Are you saying that you could power it with a 20 Watt 12 volt compressor?
I have no idea 44'CruisingCat, far to many variables not knows yet to answer that question. Clamp on meter Amp Draw vs daily Amp Hour usage is a big difference and I always look at things in a daily power usage because real time Amp draw leads a lot of folks astray. I also don't know anything about the efficiency of your unit. We also have to be sure not to mix and match units or 12v DC and 120v or 220v AC in looking at the numbers.

I do know that the 120v AC compressors popped out by the cargo container load and put in these small dorm type refrigeration units that I'm talking about are horribly inefficient when compared to a 12v compressor is your better than the ones I have seen and tested? Don't know. A 90L freezer is 3.2CF and with an efficient 12v compressor unit and adequate insulation that can easily be kept cold enough to freeze ice cream for 25-30AH/day.
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Old 07-04-2014, 22:01   #37
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Re: Efficient Hhome Frigde/Freezer on a Boat?

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If I recall correctly, the 12V compressors actually include an AC motor. The little black box is a DC to AC inverter. There would be efficiency losses there too. What with the heat rejection on the cooling fins on the little black box in all. Really there is no free lunch. Since the basic mechanical design of the compressor is practicelly the same between the DC and AC units, the overall BTU's rejected per watt would be very similar for the same box design.

The VFD units would give better COP at low speed, but the difference is not that much in real life.

Before I installed my 120V fridge, everything I read said that it would not work at anchor. I figured that at the price point it was worth a try. Imagine my surprise, when I find that it actually works pretty darn well on the hook with a pretty low energy use, within the same magnitude as a 12V unit for 10% the price or less.
There is really no such thing as a DC compressor...they all operate on 3 phase AC converted from 12v. Of course a 120v refrigerator will work...I used one for 2yrs of cruising Mexico in 100 degree heat and that sucker used over 150AH/day in the Sea of Cortez. The el cheapo China 120v compressors put in the dorm refrigerators are a far cry in efficiency from a Danfoss or Cubigel unit. But at $150ea....you can toss them overboard rather than clean them out and come ahead of a 12v unit due to the cost of the compressor. Our cost on the Danfoss or Cubigel compressor is oddles more than the whole dorm refrigerator to start with....different ball of wax...and different approaches. As an el cheapo cruiser/live aboard myself I'm into doing things cheap...but I did just spring for a total of 1380W of solar...so ****...I could run a meat locker aboard now...ha ha ah
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Old 07-04-2014, 22:07   #38
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Re: Efficient Hhome Frigde/Freezer on a Boat?

Hum, So how much would it cost to convert a 120V fridge to 12V, say in the 3 to 4 CF range. Just a ball park figure would be fine. I know what Rparts charges for their parts. I'm betting its a bit north of a boat buck. I should note that my cheap $140 fridge is on its 7th year of continuous use. I've not noticed an increase in amps used per day either.
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Old 07-04-2014, 22:14   #39
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Re: Efficient Hhome Frigde/Freezer on a Boat?

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Hum, So how much would it cost to convert a 120V fridge to 12V, say in the 3 to 4 CF range. Just a ball park figure would be fine. I know what Rparts charges for their parts. I'm betting its a bit north of a boat buck. I should note that my cheap $140 fridge is on its 7th year of continuous use. I've not noticed an increase in amps used per day either.
We sell the units for $995 or convert ones that clients bring us for the $995 less the cost of the refrigerator...so $845.
So you can do the math and add all the components from Rparts and easily see what we are charging for labor, R134, etc. I converted the 120v unit I bought in Mazatlan Mexico when we got back from Mexico and then my wife saw this nice one and Costco so it is what we have now:


She likes the design and the fact that it doesn't try to have a small freezer box gives more refrigerator room and cuts down on power usage. We have a standard top loading freezer aboard.

It's not that hard of a DIY project at all...and I'd be willing to talk anyone through the process if they wanted to give it a try on their own. My intent here wasn't to make sales but to pass on info.
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Old 07-04-2014, 22:42   #40
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Re: Efficient Hhome Frigde/Freezer on a Boat?

That is actually a really fair price all in all.


I did a tiny bit of research and the Danfoss 12V and home 120V/220V compressors are actually manufactured by a company named Secop (the OEM) and just branded for Danfoss. Three guesses where the danfoss/secop small compressor production line is located. Secop is listed on the Danfoss datasheets at the very bottom, in small print. (since 2008 btw).

I'm betting there is a better price point going direct to secop.....

Wuqing, China
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Old 07-04-2014, 22:48   #41
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Re: Efficient Hhome Frigde/Freezer on a Boat?

2006 actually....but it was the final 2008 move, knows as "the disaster" of Danfoss moving the production to China that lead Technautics to stop using them and moved to Cubigel made in Spain. We had compressor after compressor with problems. In fairness to Danfoss, they have worked through that mess.

Here's the irony....

Cubigel was bught last year by....ta da...a Chineese Compay....ha ha ha
But at this point they say they are keeping production in Spain as part of the Spanish government allowing the sale...how long will that last?

The fun of world Markets.

(oh...and trust me...Danfoss/Secorp is damn good about price control and not allowing people to go around their distributers that will lose their distributorship for undercuting the set price....ahem...we tried for years to break the mafia...no luck. So if you figure it out...hell....I will convert your refrigerator labor free just as a prize...ha ha ha)
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Old 07-04-2014, 23:28   #42
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Re: Efficient home frigde/freezer on a boat?

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I've seen it argued that having a fridge condenser in the living space heats it up. The fact is it would only be by a very small amount, since the heat being removed from inside the fridge originally CAME from the living space. The only additional heat generated would be from the compressor motor.
If you are expending the energy to move heat, why would you not want to also move it outside the living space? Assuming you want to cool the living space. The issue is whether it is enough heat to worry about it, maybe not. Surely depends on how much warm stuff is put in to cool compared to just maintaining the temp. Our freezer at home gets frozen stuff put in, and you just keep it frozen, so not that much energy just to maintain it (if you keep the door closed and have good insulation )
making ICE on the other hand..

I believe R/V's put the condenser on the roof or a panel vented to the outside, and don't big boat systems use seawater for the heat exchanger, or is that just A/C they do that?

Grocery stores put their heat exchangers on the roof.
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Old 09-04-2014, 14:55   #43
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Re: Efficient home frigde/freezer on a boat?

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The issue is whether it is enough heat to worry about it, maybe not.
Yep, that's the real issue. IMO it's not enough heat to worry about. Compared to cooking or just boiling a kettle, it's a drop in the ocean.

It's amusing to see people saying it won't work, when we've been using one for the past 4 years living aboard full time, and cruising 20,000 miles.

On power consumption - we were off the boat for a few days, and left only the fridge, freezer, LED anchor light and an LED cockpit light running.

The solar charge controller went into absorption and float mode each day, and total amp/hours to the batteries was in the order of 50 per day. Not excessive IMO.
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Old 08-05-2014, 14:09   #44
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Re: Efficient Hhome Frigde/Freezer on a Boat?

Cruisingcat: How many watts of solar do you have?
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Old 09-05-2014, 12:17   #45
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Re: Efficient Hhome Frigde/Freezer on a Boat?

Very good read, thanks all!

In the end I'm probably going to spring $1,500 or so for an exact fit marine-type 12/120V fridge. If the compressor alone is $800, then I guess I'm getting a fair deal for the whole package.

My own situation is that I'm replacing an el-cheapo, no-name brand 120V fridge the PO put in when they ripped out the marine fridge. It's a power hog and already starting to rust. It doesn't really fit the opening where the original 7cu ft built-in was removed, so it doesn't really look right.

I don't have a separate freezer, so having on as part of the fridge is a big plus. Looking good is a plus. Not having to run the inverter all the time is a plus.

I did toy with the idea of replacing the fridge with something similar, only one notch higher quality, then fitting some trim to make it look built-in. It worked fine all last season, and I found I could go 24 hours or more on my house bank before recharging. So I can't argue against that option, especially budget-wise. I guess it all depends on your boat, your equipment, your usage patterns and your budget.
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