Propane (R-290) for heat pumps?

[AC_Hacker]

Hey BradC,

What is going on here?

Can you explain what the Sub Cooler thingie is in this diagram (red circle)? I saw one of these in a photo of a heat pump from a book illustration from Poland that Piwoslaw posted.

Also, what is the possible function of the circuit shown in the illustration (green circle)? It looks like some kind of controlled leak...

-AC_Hacker

[BradC]

Hey, I can answer both of those!

When you store refrigerant in a receiver, you have the potential to lose a bit (or a lot) of any subcooling that you might have got from the condenser (or you did not get any to start with). As the TXV's are in the remote units, you _need_ 8 to 10C subcooling to ensure you have a solid column of liquid at the TXV, so they use some refrigerant in a tube-in-tube heat exchanger to subcool the liquid as it leaves the receiver. As they are aiming for maximum efficiency, even this loop is controlled by an EEV.

The "bleed" doohickey is the oil return from the oil-separator into the suction line. Under some conditions it's possible for refrigerant to condense in the oil separator, so the capilliary is there to ensure it evaporates before it hits the compressor. Once things are up to temperature, the bypass solenoid opens to make it easier for the oil to return.

Someone over are refrigeration-engineer.com pointed me at that diagram. I keep it open in a firefox tab as I find it fascinating. Someone has spent a lot of money engineering a solution that is as efficient as possible with the minimum number of parts, so I like trying to figure out what each bit does and why it must be required.

[MN Renovator]

You can see those EEVs in the two aussie50 vids on Youtube. I'll warn you though, he doesn't like inverter compressor systems so if you are easily discouraged, you might want to skip it. You can see the valves described in these videos along with the rest of what is inside.

Dead 16Kw Fujitsu Inverter Condenser Test and Dismantling - YouTube

Fujitsu Inverter Condenser In-Depth Autopsy (New Style Unit) - YouTube

[Xringer]

Interesting videos. That funny fellow has a big following on Youtube..

I noticed that some of the thermistors were clipped onto the copper lines,
while others used a brazed-on tube, which held a thermistor that clipped onto it.

I wonder why they don't just use clips or clamps to mount sensors?
Maybe it doesn't cost them much, when robots are doing the brazing.?.

Under one of those sensor 'tubes' was where my first Sanyo leak occurred..
http://i46.photobucket.com/albums/f1.../NCL/R032e.jpg
http://i46.photobucket.com/albums/f1...r/NCL/leak.jpg

Have to say, I'm not a fan of the sensor tube.. Seems like one more thing to go wrong.

[Thepprof]

I recently converted a Klimeair 12K unit from R410a to Propane. since there is no data available other than the standard gas charts. I just started adding propane to a empty,vacuumed system and with the best scenario I got Delta 10 at the air handler which works out to estimated 10K BTU and the next day started the unit again. Added more gas and now am getting Delta 8 or approximately 8K BTU at tge air handler. I noted that the difference through out the test that there was approximately 10 psi difference in the gas line vrs the liquid line. Since the capillery/piston tube is in the outside unit and I am a rank amateur and have found no one with serious experience and understanding I am currently at a standstill but since I now have reason to belive this unit is working as it is supposed to am considering taking it back to R410a and reinstalling it in the unit it came out of.

[Xringer]

If you do refill it with R410a, it would be interesting to see what the difference in power consumption is.
At least one of the R410A to propane conversions that I've heard about, used considerately less power (with propane).

Need more details on the Klimeair 12K, is it an inverter type mini-split?

[Ko_deZ]

Just so the question has been asked. Did you change the oil in the compressor? If I remember correctly, propane needs mineral oil, while R410a needs to run on a special synthetic oil. Getting that wrong will ruin the oil, and the compressor. If you want to revert to R410a, the oil may already be in bad shape, so you must change it anyway.

[Xringer]

I've heard that a few people have used POE oil with propane/R290 and had no problems.
But, I have not heard of anyone using that mix long term.
IIRC, some of the over-clockers have used propane with POE oil and it worked.

And, it seems like pulling a good vacuum on water-loaded POE does remove some of the H2O.

Fridge Compressor Vac Pump test on POE Oil - YouTube

(The last half of the video is the most dramatic)

I used a long vacuum run on my repaired Sanyo (leaker) and then used a filter-dryer
to try to clean up the R410A and the old POE before use.
That was last fall, and it's still running pretty well. But, only time will tell.

[Thepprof]

I recently posted several notes; regarding how to add Propane to my Klimeair minisplit. I literally got no feedback other than the probability that R290 is compatable with the oils in a R410a system. I thought my 12K unit was junk and rather than waste R410a which I did not have at the time used propane to get the unit up and running. I vacuumed, and then started adding propane to the unit set up in my shop. The first run resulted in the metering device frosting up big time. I cotinued adding gas and forced the frosted area up the 15 ft. of supply lines into the air handler. I ran these tests over several days and managed to get a steady 10 degree difference at the air handler and on one test managed a 20 degree difference. My other good unit shows a 30 degree difference on a 90 degree ambient day. I decided that the unit was actually a working unit and decided to convert it back to R410a. My refigeration guy would not touch the device because he could not do the usual sub/super heat process. Once again I took a shot in the dark. Turned the gas tank upside down to feed liquid into the unit and guessed at the amount. When I started the unit the metering device immediately frosted up. I once again slowly added R410a and pushed the frost up into the air handler. at 120 psi gas line pressure I'm getting 20 degree difference at the air handler. The Klimeaire rep finally told me that on a hot day I should shoot for 140 psi on the gas line. For those interested parties it seems that somewhere there is a chart relative to each device that you can use to top off the system at a given temperature. I'm assuming that this works if the device like mine is all new with no screwups anywhere in the system. I will have to get a new low pressure gage and increase the gas line pressure to 140 and see if I can once again get that aloof 30 Degree Delta T.

[dc€x]

I found an interesting study on propane vs. lubricating oils .This time a (large one) piston-compressor was concerned.

http://docs.lib.purdue.edu/cgi/viewc...8&context=icec

This story is worth reading when judging/evaluating the importance of superheating/subcooling/the meaning/necessity of extra HEX between evaporator and compressor in terms of R290 (this far).

No corresponding scientific stories available rgd. mini splits (this far)!