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Old 01-14-2014, 08:34 PM   #1
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refrigerator question number 2

I will soon need to replace the upright refrigerator in my boat.
In looking over the manufacturers that make these uprights Isotherm, Tundra, Norcold and Novacool, they all seem about the same. They all use the same Danfoss compressor and they all range in size from 7 to slightly over 8 cubic feet.
The power consumption is also the same ranging from 4 to 5 amps? Only one manufacturer stated a possible usage of about 60 amps a day which would come out to the unit running about half the time.
The prices range from a low for the Norcold about 1200 dollars to a high for the Isotherm unit about 2200 dollars. So with all of the units using the same compressor why is there such a large difference in price for units roughly the same size?
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Old 01-15-2014, 08:34 AM   #2
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Are they the same Danfoss compressor? How about the control circuits? How about the insulation and quality of construction?

It's pretty much impossible to say how much current a refrigerator will draw because it cycles on and off to keep the internal temperature at the point the thermostat is set to. Where and how it's installed and the external ambient temperature have an effect on run time as well. That means it's not really possible to compare efficiencies for similar products from different manufacturers.

Norcold has a poor reputation among boaters. Isotherm, Tundra and Nova Kool have good reputations. When comparing similar products, often the lowest priced is poor quality and the highest priced may be overpriced. Somewhere in the middle is probably the best value.

Parts and service availability is something else to consider.

I have a Nova Kool in my boat and had a small Isotherm in a previous boat. No problems with either.
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Old 01-15-2014, 10:49 AM   #3
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Good question about the Danfos compressor. I'll need to so some research.

My Norcold is 15 yrs old and never a problem. It is a power hog and why I need to replace it. So how do I determine a units power consumption efficiency?
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Old 01-15-2014, 11:08 AM   #4
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Submit a photo of the bottom of the fridge and a list of the ingredients of any bottle on the middle shelf.

"... power consumption efficiency?"

You will have to measure the power consumed over a given period and the number of BTUs removed in that period. There are several ways to do that, one as simple as weighing a block of ice at the start and finish of the experiment.
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Old 01-15-2014, 12:13 PM   #5
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Some manufactures will give the average daily power consumption. Here's what Isotherm says about one of their units:

Current Draw:
Compressor Running: 6.2 Amp @ 12 Volt DC (half at 24 Volt DC)
Average: 2.3 Amp @ 12 Volt DC
Average draw measured at 43F in refrigerator, 72F ambient temperature

Nigel Calder goes into pretty good detail with what Rick B was referring to: using ice and weighing it over time. Accurate but hard to do on a unit you're looking at.
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Old 01-15-2014, 12:30 PM   #6
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Daily power consumption without reference to heat flow and volume, doesn't mean much and is certainly not a measure of efficiency.

Current is not power and it doesn't directly relate to efficiency of the system.

I could keep a beer cool all day in a beer bottle sized fridge with a Peltier element in Seattle in Winter with just a few Watts.
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Old 01-15-2014, 01:27 PM   #7
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Quote:
Originally Posted by timjet View Post
I will soon need to replace the upright refrigerator in my boat.
In looking over the manufacturers that make these uprights Isotherm, Tundra, Norcold and Novacool, they all seem about the same. They all use the same Danfoss compressor and they all range in size from 7 to slightly over 8 cubic feet.
The power consumption is also the same ranging from 4 to 5 amps? Only one manufacturer stated a possible usage of about 60 amps a day which would come out to the unit running about half the time.
The prices range from a low for the Norcold about 1200 dollars to a high for the Isotherm unit about 2200 dollars. So with all of the units using the same compressor why is there such a large difference in price for units roughly the same size?

You might also look at Vitrifrigo (sp?). They make a model that fits the same footprint as Norcold's most common model and I think are about the same or lower in price.
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Old 01-15-2014, 07:10 PM   #8
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I suspect manufacturers power consumption figures are about as reliable as car makers mpg figures, ie not.
One domestic brand here got caught fiddling fridge settings on models provided to a testing agency, to take special advantage of testing methods. The agency now buys their fridges from retail shops.
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Old 01-15-2014, 11:09 PM   #9
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Refrigerator

My Isotherm has been a nightmare. Based on my experience, I would be very careful in chosing Isotherm as an refrigeration unit. The interior of my refrigerator came apart prior to the 2-year warrantee expiration.
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Old 01-16-2014, 09:14 AM   #10
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>There are several ways to do that, one as simple as weighing a block of ice at the start and finish of the experiment.<

YES ,

When I worked for Mike Adler , who built mechanical /eutetic machinery for cruising sail, boats , his method for estimating refrigeration was simple.

Get a 20# block of ice and a fishnet and scale.

Put the 20# block in your cool space , wait 24 hours and then weigh it.

Wait another 24 hours and weigh it again

IF you lost under 5# of ice the second day DC refrigeration could be done.

Over 5# a day either rebuild/re-insulate the box or select the far more powerful engine drive /eutetic plate installation.
For offshore cruisers where a freezer was more important , mechanical was the only choice , it takes a load of energy to hold a big box at +5F or less.

The DC fridges that blow the air into the cabin are a better choice than those that vent it into a usually closed fridge space.

A really good well built reefer can operate in summer conditions ( 80F-90F) for about 50-60A a day .
The poorer they are built/insulated the higher the bill, with house stuff and a cheap inverter at 100-125AH a day.

Efficiency is how often you need to operate a power source to recharge, and how fast and quietly its done.
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Old 01-16-2014, 11:48 AM   #11
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My Isotherm has been a nightmare. Based on my experience, I would be very careful in chosing Isotherm as an refrigeration unit. The interior of my refrigerator came apart prior to the 2-year warrantee expiration.
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Bummer Randy. I bought my Isotherm in 2002. It was still going strong in 2012. Our amp usage went from over 140 with the Norcold to about 80.

I hope yours was an isolated problem.

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Old 01-16-2014, 12:11 PM   #12
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Refrigerator

Rob, we replaced the old Norcold on our Krogen Manatee with a Summit FF874SS 8.1 cuft top freezer. Stainless steel door fronts and black trim. Specs 50.25"H-23.63"W27"D, 158 lbs, 370 KWH@year, 1.2amps, $619 free delivery. Had it three months and no complaints, very quiet, has auto defrost which first mate loves, I have a 900 watt inverter to use at anchor but we generally run the generator when underway or anchored.
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Old 01-16-2014, 12:22 PM   #13
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Daily power consumption without reference to heat flow and volume, doesn't mean much and is certainly not a measure of efficiency.

Current is not power and it doesn't directly relate to efficiency of the system.

I could keep a beer cool all day in a beer bottle sized fridge with a Peltier element in Seattle in Winter with just a few Watts.
But are you adjusting for bottle slip?

I know a lot of boaters concerned with efficiency but forget every time they reach in to grab a cold one...it slips a little, thus taking greater time to get a better grab so efficiency numbers plunge. I do know of some that paint all their bottles with Kiwi Grip prior to placing them in the fridge to prevent this...but I do remember a post where someone determined from a grainy photo that the efficiency can greatly be improved by watching the FLIP top line and making sure that your fingernails don't exceed 1.34mm in length so the airflow doesn't create to much of a bow wave and startle the bottle/can before you get there.

Seriously...Norcold I think retooled recently an make a much better product.....the electronic bits and pieces usually don't drive a price up...it's the big components and materials used...plus sometimes "just a name" that costs more.

If I could find an off the shelf apartment fridge that had the room and would fit...that would be my choice...even if it wasn't as efficient....but I'm shy on spending a fortune on a marine unit ...I'd rather those bucks go somewhere's else for now. I don't complain about my home fridge (well when I had a home)...so why should I complain about one on my boat?
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Old 01-16-2014, 02:22 PM   #14
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No, I didn't account for bottle slip but I did use the constant for label thickness and adhesive type.

I would need to know if the beer was in bottles or cans in order to calculate the permeability of the refrigerated space so I can figure out the RS/GV ratio. That is the ratio of the volume of uncooled air in the galley that is displaced by refrigerated air exchanging per unit of time of door opening. Of course that depends on how familiar the user is with the contents and general arrangement of the refrigerated space. Teenagers and picky operators tend to upset the results by standing there with the door open while they make up their minds or rummage through the contents.
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Old 01-16-2014, 02:58 PM   #15
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No, I didn't account for bottle slip but I did use the constant for label thickness and adhesive type.

I would need to know if the beer was in bottles or cans in order to calculate the permeability of the refrigerated space so I can figure out the RS/GV ratio. That is the ratio of the volume of uncooled air in the galley that is displaced by refrigerated air exchanging per unit of time of door opening. Of course that depends on how familiar the user is with the contents and general arrangement of the refrigerated space. Teenagers and picky operators tend to upset the results by standing there with the door open while they make up their minds or rummage through the contents.
Ah...simple solution, Night vision, remote cameras inside the fridge and a large flat screen mounted to the door...that way the contents can be studied prior opening...of course only the best fridges have that as an ABYC required standard and not an option.
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Old 01-16-2014, 03:00 PM   #16
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Double pane clear lexan door with a vacuum between the panes would work well.
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Old 01-16-2014, 03:06 PM   #17
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Double pane clear lexan door with a vacuum between the panes would work well.
How about those glass panes that go clear to solid with electrical input? Rig something like that?

If I could see the food and beer every time I walked past...mmmmmmm
but I doubt I would pass my next USCG physical

But to stay on topic for the OP...I can't seem to find too much that justifies the huge cost difference. Anyone??
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Old 01-16-2014, 03:47 PM   #18
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How about those glass panes that go clear to solid with electrical input? Rig something like that?

If I could see the food and beer every time I walked past...mmmmmmm
but I doubt I would pass my next USCG physical

But to stay on topic for the OP...I can't seem to find too much that justifies the huge cost difference. Anyone??
Depends on your crusing style I suppose.
THe PO had/has Dual Subzeros. They are now 25 years old and work well. Freezer stays just below 0F +-5 and Fridge stays where I want it near 40
Connected to SP or with the gen on, no problem, but they use about 17 amps per hour, incl about 3.3 for inverter.


But I'm getting rid of them and in this instance will end up paying more for marine because power consumption is my number concern. I want to be able to go 5 days with no power generation. Since we'll be living full time on the boat in the next few years and I'm living on it already 75% of the time, the high acquisition cost will pay back in fuel savings within 2 years.

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Old 01-16-2014, 04:05 PM   #19
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... they use about 17 amps per hour, incl about 3.3 for inverter.

I should probably just give up nagging about it but the above is meaningless.

How much power does it consume?
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Old 01-16-2014, 04:07 PM   #20
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Well the ice test is out. I'm not going to buy all 4 units and keep only the one that wins the ice test.

Tundra and Vitriofrig are the same and made by Dometic, at 8.5 cuft the largest of the bunch drawing 4.5 amps. Since it's the largest it may have the thinnest insulation??

Isotherm is the smallest at 6.8 cuft drawing about 3 amps with a Danfoss / Secop compressor type BD35F X 2.

NovaKool at 7.3 cuft is right in the middle and draws 5.2 amps

Norcold at 7.0 is next to the smallest and draws 3.2 amps and would appear to be the most efficient along with the Isotherm.

The amp draw as I understand it is per hour and must be multiplied by how often the compressor runs in a 24 hour period to get total amp draw per day.

So based on the figures above the Norcold and Isotherm are the most efficient when the compressor runs.

The Norcold retails for $1359
The Isotherm retails for $2182.

There's got to be more than just a name for that difference in price.
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