Refrigeration Insulation Test

[rtooh]

Evening Forum - some time ago I clipped an interested thread and saved it to my computer for future consideration. Well, the time has come to use the thread to evaluate the R value of the my ice box's current insulation. I have one question though before conducting the test:

While ice freezes at 32 degrees F, a block of ice I might purchase at the store will be well below that temperature, perhaps at 22 degrees F for instance. So, is measuring the change in weight of the block a true representation of the thermal gain of the closed system? How can you quantify the thermal gain that took the block from 22 degrees F to 32 degrees, at which point the block's change in mass can be converted to thermal gain?

Perhaps I'm missing something. I'd love to hear other's thoughts on this question...

[Scott Berg]

You're measuring the amount of ice that melts, it can't melt till it hits 32/0... how much ice is melted is the key. Lots of variables but you'll learn a lot. BTW, I'll make it easy; damn near every box I test needs more insulation <grin>

[rtooh]

Originally Posted by Scott Berg

You're measuring the amount of ice that melts, it can't melt till it hits 32/0... how much ice is melted is the key. Lots of variables but you'll learn a lot. BTW, I'll make it easy; damn near every box I test needs more insulation &lt;grin&gt;

Thanks Scott, but given that it’s a timed test, I need to know when to start the clock (when the ice starts to melt). I guess I could leave the block in the space for a couple hours as suggested and then check for drips. If I have them, I measure the the block’s weight and start the timer. If I don’t, I wait another hour and check back. I guess though two hours should be plenty of time for the ice to start melting.

Sounds like you’ve done this multiple times. Any advice for a newby?

Finally, I wonder if dry ice would be a better cooling agent since it would last longer and turn to gas as it absorbs heat. I guess you’d need to replace the 144 in the calculations with a dry ice specific number. Huh. Have you ever thought of doing that?

[OzeLouie]

There are many factors that can effect your search for refrigerator cabinet insulation properties or the lack of!!
Suggest having a heat load calculation done for that specific cabinet so you know what it should be if the insulation is ok.
To obtain this you would need to know and advise the interior dimensions, insulation thickness (and type if possible). Also inner lining material, and the average environment temperature. This would provide you with an hourly cabinet heat load in Watts/hr if the insulation is ok.

Then test as follows to ascertain your actual insulation quality for comparison

Using blocks ice to absorb cabinet heat, allow to settle at storage temp, say 2degree C and note/ weigh how much ice is left by Kg.
Establish ice cooling expectation by multiplying the Kg of ice left by 90. Each Kg of ice should now be able to absorb approx 90 Watts of heat before complete thaw and cabinet temperature rises. Keep cabinet closed and time, monitor cabinet with remote digital thermometer and note how many hours before ice fails to maintain cabinet temperature and temp rises.
Divide total watts of hold-over ice by the hours cabinet temp was maintained and you will know the actual heat load watts / hour of you cabinet and now able to compare with what it should be. Suggest within 80% would be acceptable.

Hope this helps and is not too complicated, besides re-insulating is a sod of a job especially if found later to be unnecessary!!!

[OzeLouie]

Originally Posted by OzeLouie

There are many factors that can effect your search for refrigerator cabinet insulation properties or the lack of!!
Suggest having a heat load calculation done for that specific cabinet so you know what it should be if the insulation is ok.
To obtain this you would need to know and advise the interior dimensions, insulation thickness (and type if possible). Also inner lining material, and the average environment temperature. This would provide you with an hourly cabinet heat load in Watts/hr if the insulation is ok.

Then test as follows to ascertain your actual insulation quality for comparison

Using blocks ice to absorb cabinet heat, allow to settle at storage temp, say 2degree C and note/ weigh how much ice is left by Kg.
Establish ice cooling expectation by multiplying the Kg of ice left by 90. Each Kg of ice should now be able to absorb approx 90 Watts of heat before complete thaw and cabinet temperature rises. Keep cabinet closed and time, monitor cabinet with remote digital thermometer and note how many hours before ice fails to maintain cabinet temperature and temp rises.
Divide total watts of hold-over ice by the hours cabinet temp was maintained and you will know the actual heat load watts / hour of you cabinet and now able to compare with what it should be. Suggest within 80% would be acceptable.

Hope this helps and is not too complicated, besides re-insulating is a sod of a job especially if found later to be unnecessary!!!

I should have mentioned that if the cabinet had been used as a freezer in the past, or the cabinet insulation was originally from the era 1995 to 2005 then it is more likely that the insulation is faulty.

[Lepke]

I have a large, double door ac reefer. I measured power consumption, added 1" foam on 3 sides and the top in the cabinetry, and consumption went down by half measured over 24 hours.