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Old 02-10-2018, 19:07   #1
cruiser

Join Date: Dec 2006
Location: Yarroweyah, Victoria. Australia
Boat: "Arapaho"
Posts: 398
Testing fridge insulation.

Insulation qualities vary considerably as does their longevity, so age etc should not be determining factors.
Deciding if a marine refrigerator cabinet’s insulation is defective or not, can be very difficult.

The following method involves some ‘reverse engineering’ but will provide a reasonably accurate assessment.

Firstly have your cabinet pre-cooled to say +3C then with no refrigeration operating or product added, add a noted weight of ice block(s), sufficient to maintain cabinet temperature at +3C. Try to locate the ice central and high in the cabinet.
Check over a 24 hour period to ensure cabinet temperature is maintained. Also note ambient temperatures hourly.

Then:
1. Weigh Ice at the end of the 24 hour period to determine the kilograms of ice melted.
2. Multiply the kilograms melted by 93 to establish how many watts of heat entered the cabinet.
3. Average ambient temperature for the 24 hour period. (C)
4. This will establish the number of watts penetrating the cabinet in a (your average C) environment.

Next:
1. We establish the number of watts of heat per hour that should be entering the cabinet if the insulation is not defective.
2. This is achieved by adding your cabinet details and the average ambient temperature to a ‘Heat load’ estimator, as below.

Conclusion:
1. For an example let’s assume the ice melt test determines that it required 3.5 kilograms of ice to maintain cabinet temperature, that is 325 watts per 24 hour period
2. Having entered the cabinet dimensions etc and the average ambient, the Heat load estimator should indicate a heat load equal to or greater than that determined via the ice melt method.
3. If the Heat load estimate in watts is similar or more than the ice-melt outcome, then the insulation is fine.
4. If the Heat load estimate in watts is far less than the ice-melt outcome, then the insulation is defective and should be replaced. .

Typical heat load estimator: (Click to expand)

Click image for larger version

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The estimate above for this cabinet with 100mm of good urethane insulation and in an average 30C environment would see heat penetration of 14.34 watts / hour or 344.00 watts per 24 hours.
This would relate to approx 3.7 Kilograms of ice melt per 24 hours, therefore if the ice melt was say 4.00 Kilograms or less then the insulation is not defective.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems
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