Steve Lusardi wrote:
Jon,
Effectively, I am building an old fashioned ice box and these plates will be
atached to the walls of the well insulated box. The air flow inside the box
would be convective, just like in your freezer at home. All the plates would
be in parallel. These cold plates are holding plates and I suspect they are
filled with brine, as they were probably used as a refrigerator. In order to
use these plates in a freezer efficiently, the solution will have to be
changed to one that changes state at a lower temperature. You stated that
the expansion valve must have the same freon on both sides of the diaphragm.
I hadn't thought of that, but it makes sense. I know I must use the most
appropriate freon for the task, which means that I will have to buy new
expansion valves to match that choice.
They CAN be refilled, but that's not for the amateur.
Good info. I understand the
difficulty in calculating the heat load, but I don't think the ice box
itself has much to do with it. I would think the volume of the cooled fluid
medium is the 90% answer. The rate that medium has in warming up is not very
relevent, because the system will not be operating then. It is also
unreasonable to think that these holding plates will freeze solid at he same
time, but if each has its own control valve it shoudn't matter.
Steve
OK, I gather the compressor will only be run a couple times a
day, and the brine (or whatever state-change fluid) needs to
keep it cold between runs? Is that the basic idea?

Very concentrated brine can probably be made up with something
like calcium chloride that will freeze out at some really low
temperature. I don't know if you can get to -40, but definitely
well below 0 F. The cooling capacity of these brines drops as
the water content drops, though. Oh, yeah, litium bromide would
definitely work! But, it might be way too hazardous to use near
food. If there was any leakage, you'd get REALLY mellow on all
that lithium.

Anyway, I'm not a pro at this, but I think you will have real
trouble making it to -40 with an R-22 system and any appreciable
heat load. It will eventually get there if you can keep the
doors shut, and there aren't any air leaks.

One other thing I discovered some years ago is that some foam
insulations get saturated with ice. You know this has happened
when a chunk of foam suddenly weighs about 40 Lbs! It is HELL
to get the water back out of the foam, too.

Jon