Thermodynamics, Please (Refrigeration question)

Thelonious II has the stock E381 large refrigerator I want to make temporarily smaller, so as to use fewer amps per day.

What's the best way to do that?

Filling the fridge with frozen jugs of water seems logical--until the ice melts and all that water turns to ambient heat.

I could stack the unused areas with styrofoam, reducing the volume that way.

But is that better than leaving a void?

My plan is to keep the refrigerator off much of the time. If I run it only during the 45-minute daily battery recharging, the evaporator plate compartment will cool a can or two of beer just in time for sunset.

So--leave the refrigerator empty, fill with foam, use frozen water jugs?

Maybe it doesn't matter, if you only turn the thing on for an hour a day.

Does your refrigerator have a thermostat or does it just have cold and colder settings that basically set the cycling time?

Thinking without Googling, I think you should fill the excess volume with something light like styrofoam and test that against empty space. If you could build a wall with styrofoam and some tape that doesn't leave residue it might be slightly better to reduce the air exposed to the cooling parts. For grins, take a starting temperature reading of the outside skin of the boat in the area of the refrigerator, or an indoor temp near the refrigerator, and see if ambient temperature affects the results inside the refrigerator.

I think the water bottles idea is worth testing, though. The water would seem to represent a load worse than empty air, but maybe the insulating or moderating affect of the bottles would be beneficial. Think about how cool it is near the water!

I've forgotten most of what I learned in thermodynamics but I do remember that cold is the absence of heat and heat is molecular motion. You should be able to solve your problem based on these principles and get back to us with your solution. Good luck!

Paul
E29 "Bear"

Yes, I think that was pages 457-488. I'll look it up.

Actually, gents, I have concluded that it doesn't matter in my case, since I'm only going to run the refrigerator an hour a day for spot cooling.

Smaller volume to cool would only apply if I were trying to maintain a temperature.

Craig, I have a manual switch (level 1-10), rather than a thermostat. It's set on 1, which maintains 38 degrees F. That actually makes ice, since the vertical ice trays lie against the cold plates. In think in SoCAl, which has cool nights, it uses less than 2 amps an hour. About 5 amps when its running.

Christian Williams said:

Yes, I think that was pages 457-488. I'll look it up.

Click to expand...

I went sailing the day those pages were discussed.

However, I would suggest that Styrofoam blocks randomly thrown in to reduce the volume won't help much, but placing them against the box walls effectively improves the box insulation, keeping the heat out.

If the compressor runs for the full 45 minutes the amp hours become strictly time dependent. If the added insulation allows the compressor to shut off sooner you have a savings.

The link to the missing pages:

http://www.personal.utulsa.edu/~kenneth-weston/chapter8.pdf

That said, insulation between areas of heat vs cold seems to be the best solution. I'd second that adding a smaller volume of cool would also be a contributing factor if the smaller volume is also insulated.

I'm relying on my "ice" box full time as a liveaboard and have had adding insulation on the honeydew list for quite some time. In the interim I've been using iced tea containers and ice packs to take up 2 cubic feet of a 6 cubic foot space. Anecdotally the answer to the question "does this help?" is "nope, but it makes me feel better than trying to freeze cold air."

Currently, (no pun intended) the energy draw from the compressor is helping cycle battery banks against the charge of the solar panels. No such thing as a free lunch I guess...but a cold tea with lunch is just 's well.