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Brians256 · 03-07-2003, 12:35 PM

You aren't going to get something much cheaper than that $23 unless you go dumpster diving and strip out heating elements from junk.

The more that I think of it, though, I'm convinced that a better solution is to use a TXV in series with a capillary tube. The problem with TXV's is that they don't have the ability to finely control high constrictions. But, restrictions can be summed. So, if you add a restriction after the TXV, you should be able to have the best of both worlds.

I can think of another (really interesting!) way to do it, but, it would require some really hefty microcontroller work. Basically, you could PWM the TXV valve based upon superheat feedback. This way, you could overcome the inability of the TXV valve to fine-tune it's constriction. Basically, you could do the same thing that fuel injectors do in a car. Squirt a little bit every time slice, and regulate the time period based upon the load. I wonder if the idea is patentable!

It's better for our purposes than using a variable speed DC motor on the compressor (which the refrigeration companies are moving towards for energy savings).

03-07-2003, 12:35 PM	#34
Brians256 Pro/Staff Join Date: Oct 2001 Location: Klamath Falls, OR Posts: 1,439	You aren't going to get something much cheaper than that $23 unless you go dumpster diving and strip out heating elements from junk. The more that I think of it, though, I'm convinced that a better solution is to use a TXV in series with a capillary tube. The problem with TXV's is that they don't have the ability to finely control high constrictions. But, restrictions can be summed. So, if you add a restriction after the TXV, you should be able to have the best of both worlds. I can think of another (really interesting!) way to do it, but, it would require some really hefty microcontroller work. Basically, you could PWM the TXV valve based upon superheat feedback. This way, you could overcome the inability of the TXV valve to fine-tune it's constriction. Basically, you could do the same thing that fuel injectors do in a car. Squirt a little bit every time slice, and regulate the time period based upon the load. I wonder if the idea is patentable! It's better for our purposes than using a variable speed DC motor on the compressor (which the refrigeration companies are moving towards for energy savings).