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Old 02-06-2019, 09:53   #1
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Testing icebox thermal efficiency.

Hi folks,

I'm about to add a holding plate system to my icebox, with spillover system into the fridge.

Before I start drilling holes for pipes and installing stuff, I figured I'd test to see if my insulation needed replacing.

There has got to be a way of testing it, like:
put x Kg of ice in the box, and time how long it takes to melt
Factor an outside air temperature of y degreees C
Factor square meters of internal ice box area
Plug these into an equation
Voila!

Anyone know a reliable method of doing this?

Thanks,

Matt
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Old 02-06-2019, 09:58   #2
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Re: Testing icebox thermal efficiency.

What you describe, exists.
However I don’t know the formula, sorry, but your on the right track
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Old 02-06-2019, 10:03   #3
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Re: Testing icebox thermal efficiency.

Nigel Calder has details of the ice melt test in a couple of his books (when he was all hot on vacuum panels). It's pretty straight forward; I've done it on a couple of boats. His books are worth having. But if you can't find it, let me know and I could probably dig it up.

edit - see http://www.swingcat.co.uk/what/fridg...lculations.pdf . . . it is not as simple as Nigel's writing but has the details if you read carefully and has some nice calculators.
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Old 02-06-2019, 10:46   #4
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Re: Testing icebox thermal efficiency.

Quote:
Originally Posted by Tailwheel View Post
Hi folks,

I'm about to add a holding plate system to my icebox, with spillover system into the fridge.

Before I start drilling holes for pipes and installing stuff, I figured I'd test to see if my insulation needed replacing.

There has got to be a way of testing it, like:
put x Kg of ice in the box, and time how long it takes to melt
Factor an outside air temperature of y degreees C
Factor square meters of internal ice box area
Plug these into an equation
Voila!

Anyone know a reliable method of doing this?

Thanks,

Matt
Not quite the way you run the test, but you are on the right track.

You can't tell when the ice has melted without opening the box, which destroys the test. Instead you put a block of ice in (as large as will fit), let it sit for at least 2 hours, (to cool the box off) then weigh it. Close everything up for, say, 12 hours, and then weigh it again.

Calculation #1 (Heat loss rate): ((Lbs of ice melted) * 144)/hours= BTU's per hour

Calculation #2 (Heat flux): (BTU/hour)/(Square feet of ice box internal surface area)= (BTU/hr/ft^2)

Calculation #3 (Temp difference) : DeltaT = Average external temperature(DegF) - 32

Calculation #4: R = DeltaT/(BTU/hr/ft^2)

This give R in [°F·ft2·hr/BTU] The higher, the better. A good minimum number for a fridge would be 15, for a freezer 20, but many people live with numbers less than this. Very roughly, doubling the R-value with half your power usage.

To convert to the metric equivalent R value, [°C·m2/W] divide by 5.68
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Old 02-06-2019, 11:09   #5
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Re: Testing icebox thermal efficiency.

Easiest way is to rent or buy $$ a Flir thermal camera a view you ice box with refer running. You’ll see the cold spots and can measure the thermal loss in real time. You could buy a cheaper one for around $400 and hope to re-sell for 250-300. Could also check buy and sell sites. Best place to see if someone will rent or loan you one is energy auditors in your area.
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Old 02-06-2019, 11:12   #6
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Re: Testing icebox thermal efficiency.

How old is the insulation?
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Old 02-06-2019, 11:13   #7
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Re: Testing icebox thermal efficiency.

Thanks guys, great feedback!
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Old 02-06-2019, 11:16   #8
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Re: Testing icebox thermal efficiency.

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Originally Posted by rbk View Post
Easiest way is to rent or buy $$ a Flir thermal camera a view you ice box with refer running. You’ll see the cold spots and can measure the thermal loss in real time. You could buy a cheaper one for around $400 and hope to re-sell for 250-300. Could also check buy and sell sites. Best place to see if someone will rent or loan you one is energy auditors in your area.
Only works (Sort of) if you actually have access to the REAL surface of the box. Which most boats do not. And you then assume that all surfaces lose heat at the same rate, a poor assumption since most boxes are irregular in outside shape and insulation is of differing thicknesses in different places.

Such a tool is great for localizing heat losses, but not for measuring the overall effectiveness of the insulation. It is geeky and cool and has pretty pictures, but not "easier", to my mind, and much less accurate. Of course if your definition of "easier" means "no math" I can't argue with you...

Takes longer to find the tool and resell it than to run the accurate test.
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Old 02-06-2019, 11:35   #9
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Re: Testing icebox thermal efficiency.

I thought one of the US-based custom marine fridge makers had a proper testing unit he was sending out on I think a rental basis?

They've all been pretty quiet for a few months now?
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Old 02-06-2019, 11:45   #10
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Re: Testing icebox thermal efficiency.

Quote:
Originally Posted by billknny View Post
Only works (Sort of) if you actually have access to the REAL surface of the box. Which most boats do not. And you then assume that all surfaces lose heat at the same rate, a poor assumption since most boxes are irregular in outside shape and insulation is of differing thicknesses in different places.

Such a tool is great for localizing heat losses, but not for measuring the overall effectiveness of the insulation. It is geeky and cool and has pretty pictures, but not "easier", to my mind, and much less accurate. Of course if your definition of "easier" means "no math" I can't argue with you...

Takes longer to find the tool and resell it than to run the accurate test.
He has the same boat as me and most likely a more or less large rectangle for an icebox. If I can see the thermal loss in an 18” finished wall shouldn’t be a problem with a square ice box less than an inch thick with an internal temp difference of over 30 degrees. I can also have a Flir camera in my hands within the hour from any local hardware store for around $500. Or I could use one from work $4000 camera (more accurate). Yes doing the heat loss calculations is a more accurate way to determine overall efficiency but still lacks the ability to identify areas of high thermal transfer and air leakage that could easily increase the effectiveness of your refer.
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Old 03-06-2019, 13:34   #11
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Re: Testing icebox thermal efficiency.

What the IR detector will tell you, assuming you can get a good read on all 6 sides, is what the external temp is, & where the leaks are. We know however you won’t be able to get at all sides & can guess where the greatest heat loss is. Neither of which will answer the larger question.

Either run the calcs or just assume the insul is older generation stuff & replace w the highest r-value closed cell foam insulation you can find.
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Old 16-06-2019, 19:12   #12
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Re: Testing icebox thermal efficiency.

Hey folks,

Thanks for all the help.

Did the ice melt test with a 2kg block of ice over 6 hours, which is a very rough first test, but it looks like I have an average R value of 22.3. I'll get a bigger block next time, leave it for longer and see how it goes.
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