Morphing Air Conditioner into Autocascade System

[mytekcontrols]

Well I hope nobody busts my chops over this, since it isn't actually a PC Cooler. However I thought it would serve as a good example, or should we say slightly different approach to recycling a cheap window air conditioner into a very usable Autocascade Chilling System.

I built the basic refrigeration unit in about 2 days (this is the advantage of trying to use as much of what already exists "as is"). And although this unit was intentionally limited "by design" to only operate down to -30C, it could have just as easily been tweaked for -80C or better.

Using an Autocascade for -30C refrigeration may seem unnecessary, but there are advantages. For instance; ultimate temperature was achieved in only 10 minutes from a warm start condition. Also running pressures were very comfortable at 20 psi suction and 100 psi discharge. You could easily leave your hand on top of the compressor all day long, since it was not hot. Where as utilizing a conventional refrigeration system for -30C, would require operating the compressor suction at a very low pressure or in a vacuum with very little mass flow through the compressor, very hot compressor temperatures, and a very long cool-down period for the evaporator (not to mention hardly any load handling capability).

Now in my application I didn't have an easy way to measure heat load capacity, but judging by the 10 minute cool-down and the large mass being used for the evaporator, I would say it would be good for at least 200 watts or more.

For a complete look at what I am talking about, check out this link: Alcohol_Cold_Trap.pdf

This will give you a complete piping schematic, heat exchanger and cap tube sizing, as well as the refrigerant charge that I used (with exact amounts of each component specified).

For -80C operation, I would recommend increasing the length of the cap tubes by perhaps 3 feet (increases pressure differential and gives us a lower evaporator pressure), eliminate the R-22 and increase the R-123 to 6 ounces instead of the original 3 ounces.

Enjoy