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Old 01-10-2015, 17:52   #91
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Re: Why no Residential Fridges?

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Originally Posted by Cadence View Post
The PFD sounded like Gullable's Travels.

Yep. First one that got me was when he said "After contacting some leading fridge manufacturers and discovering that no one has ever made and tested a chest fridge, I decided to make my own test."

You mean Dometic, Norcold etc have never tested any of their products?

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Old 01-10-2015, 17:56   #92
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Re: Why no Residential Fridges?

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I'm not sure if the one you posted is the same as the one the person above is referring to, but let's run with it. From the site, "418W / 24 hours", which isn't a measure of energy, but let's assume they meant 418Wh per 24 hours (17W average duty). And we have 4.6 cuft of space, so we're spending 90Wh per day per cubic foot.

Top-rated (by Energy Star) models are in the 600kWh/year range, or 1650Wh/day for about 25cuft. That's 65Wh per day per cubic foot. Not sure if that is considered a "far cry" or if it is considered to be one in the right direction.
Wait... You used a standard number and not the number posted on Rich's website. His website shows 35Ah/day or 420W per 24 hours (at 12V). That pretty much exactly the same as the fridge I listed.

If he posted those numbers on his site, I trust he actually tested them. I'm pretty sure the standard numbers posted by manufacturers are in the perfect environment at 15 deg C ambient.
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Old 01-10-2015, 18:23   #93
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Re: Why no Residential Fridges?

For those that want to convert a 120V fridge to 12V, there is a fellow from Poland selling the Secop BD35 (Danfoss's Chinese OEM) with controller for $245 plus shipping (worldwide) Not a bad deal.

The 35 amps per day on Rich's site for the 4.0 cf fridge is at 70 degrees F. You'll find that the energy costs/ run time increases as cabin temperatures rise to the 80's and 90's. I suspect that at 90 degrees it will be in the ~48-50 amp range.

Oddly Secop uses the same BD35 compressor in a 120V model. Only difference is the controller.

Pretty much all the small fridge compressors in the 12V, 120V and 220V range are of the same basic design. That is, a positive displacement, electric driven piston compressor in a hermetic sealed can with an oil bath for cooling/lubrication.. So overall efficiency for a given compressor will be about the same. What makes the most difference is the thickness of the box insulation.

Least that is how it seems to me. But then I'm just a crazy blonde hippy who does a bit O'engineering on the side to keep the cat in kibble.
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Old 01-10-2015, 18:30   #94
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Re: Why no Residential Fridges?

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Wait... You used a standard number and not the number posted on Rich's website. His website shows 35Ah/day or 420W per 24 hours (at 12V). That pretty much exactly the same as the fridge I listed.

If he posted those numbers on his site, I trust he actually tested them. I'm pretty sure the standard numbers posted by manufacturers are in the perfect environment at 15 deg C ambient.
One of us is confused. (It may well be me; I am easily confused.)

The person I quoted upthread seemed to be arguing that a specialized fridge would be much more efficient (a "far cry"). My suspicion is that the domestic house fridges are already very efficient, and there'll be little gain by going specialized -- and, in fact, there may be a loss in a lot of cases.

I'm not sure if that's what you thought I was talking about, but yes, the 420Wh per day minifridges you linked are about 50% less efficient per unit volume than the big residential fridges, on paper.

p.s. Watts are a unit of power, but what we care about is energy. Watt-hours would be the most convenient units for our comparison purposes.
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Old 01-10-2015, 18:34   #95
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Re: Why no Residential Fridges?

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One of us is confused. (It may well be me; I am easily confused.)

The person I quoted upthread seemed to be arguing that a specialized fridge would be much more efficient (a "far cry"). My suspicion is that the domestic house fridges are already very efficient, and there'll be little gain by going specialized -- and, in fact, there may be a loss in a lot of cases.

I'm not sure if that's what you thought I was talking about, but yes, the 420Wh per day minifridges you linked are about 50% less efficient per unit volume than the big residential fridges, on paper.

p.s. Watts are a unit of power, but what we care about is energy. Watt-hours would be the most convenient units for our comparison purposes.
Yes I know we were going back and forth on the same thing.. Dispelling the myth of "far cry", but I thought it only fair to use real numbers.

I understand the difference between Wh and Watts.. I used them interchangably as it was clear in the context of the sentence what I was talking about!
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Old 01-10-2015, 18:47   #96
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Re: Why no Residential Fridges?

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Yes I know we were going back and forth on the same thing.. Dispelling the myth of "far cry", but I thought it only fair to use real numbers.
Okay, so I was the confused one: I thought you were disagreeing with me.

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I understand the difference between Wh and Watts.. I used them interchangably as it was clear in the context of the sentence what I was talking about!
Unfortunately, my brain hurts every time I see mangled units.
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Old 01-10-2015, 18:54   #97
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Re: Why no Residential Fridges?

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The 35 amps per day on Rich's site for the 4.0 cf fridge is at 70 degrees F. You'll find that the energy costs/ run time increases as cabin temperatures rise to the 80's and 90's. I suspect that at 90 degrees it will be in the ~48-50 amp range.
...
Least that is how it seems to me. But then I'm just a crazy blonde hippy who does a bit O'engineering on the side to keep the cat in kibble.
No such thing as "amps per day"

Someone who does a bit O'engineering should at least know the difference between Amps and Amp hours.
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Old 01-10-2015, 18:58   #98
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Re: Why no Residential Fridges?

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I understand the difference between Wh and Watts.. I used them interchangably as it was clear in the context of the sentence what I was talking about!
My comment re SC's posts above is apropos. No one who truly understands the difference would use them interchangeably (sp!).
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Old 01-10-2015, 19:06   #99
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Re: Why no Residential Fridges?

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My comment re SC's posts above is apropos. No one who truly understands the difference would use them interchangeably (sp!).
Ya ok.. I'll take your word for it!
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Old 01-10-2015, 19:07   #100
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Re: Why no Residential Fridges?

Come children. Don't get into a pissing contest.
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Old 01-10-2015, 19:15   #101
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Re: Why no Residential Fridges?

No contest.. I concede he uses the term Watt hour and watts better.

Funny I didn't see a bridge around here though!
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Old 01-10-2015, 20:49   #102
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Re: Why no Residential Fridges?

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Originally Posted by StuM View Post
No such thing as "amps per day"

Someone who does a bit O'engineering should at least know the difference between Amps and Amp hours.
Amps per day is perfectly acceptable in this discussion. Most cruisers analyze their system needs based on that measure.

From someone who used to do a bit O'engineering.
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Old 01-10-2015, 21:00   #103
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Re: Why no Residential Fridges?

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My comment re SC's posts above is apropos. No one who truly understands the difference would use them interchangeably (sp!).
It's always fun seeing how some people can't see the forest through the trees and then smacks their head right into it.
Thanks for your Assessment of SC's engineering ability, actually on second thought....not really....
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Old 01-10-2015, 21:19   #104
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Re: Why no Residential Fridges?

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Wait... You used a standard number and not the number posted on Rich's website. His website shows 35Ah/day or 420W per 24 hours (at 12V). That pretty much exactly the same as the fridge I listed.

If he posted those numbers on his site, I trust he actually tested them. I'm pretty sure the standard numbers posted by manufacturers are in the perfect environment at 15 deg C ambient.
The posted numbers on power usage are the average of a 4 days test in a 70-deg climate controlled test room.

(sounds better to say Test Room than a temp controlled office bathroom...).

Of course the power usage will increase with ambient temps, and one day when I have time I should break our our data logger and get some test data in 5-deg increments up to 100-degs. Man would that tell all you need to know about the value of insulation! Which, by the way is the weak point of ALL of these drop in dorm type boxes. They all SUCK, ours or anyone elses just have about 1" of Polyisocyanurate insulation or an approximate R-value of 7...ha ha ha..that's crazy bad!

The industry seems to like 70-degs, so that's what we used to be able to compare to other units. Notice the manufacturers of these don't even talk about insulation or the R-value of their boxes? Why...because other than Government Regs, these units are not made for efficiency but for convenience and a price point. Would anyone buy one with 3 or 4" thick walls of insulation? Not a chance. Then again who in their right mind would buy a front opening refrigerator/freezer if Efficiency was one of their big buying considerations? Answer...no one, which is why front opening boxes are almost all you see on power boats (hint generator running all the time).

From test we have done, a front opening door can cost you about 30% efficiency on a refrigerator and up to 40% on a freezer. I know they are convenient but they SUCK power. The biggest issue is frost insulating the evaporator and killing your Box/evaporator heat transfer.

Life and Boat gear is a compromise...budget, space, needs, wants.
There is a market for these down and dirty easy/cheap units, which is why I make them. I also don't pretend they are what they are not. Do I push them and hype them to cruisers setting out on a world cruise...no I don't and I'm not here. But they work great for some folks and in September we shipped 16 of them, which is good because replacing 21 through hulls on my boat is expensive!
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Old 01-10-2015, 22:48   #105
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Re: Why no Residential Fridges?

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If you compare the fridge that Rich sells and the one I posted on Defender, they draw almost the same. Of course this is just literature, but I tend to trust Rich as he seems to underspec his gear. Ask anyone who owns one of his water makers.
If you want to get real world numbers on the cool blue system just look on here and on sailnet under my name to find the info I wrote a rather lengthly series of posts on the power draw at various water and air temperatures suffice to say have been keeping ice cream solid since February with 200 watts solar to run the whole boat no shore power or engine charging 2.5 cf top freezer and 7 cf fridge lower front load liveaboard.
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