Ron-thanks for the tip on the temp logger, I have some old computers that could be dedicated to this project so I should look into that. For now, I have a system that works good for me. I read and enter the data in the order it appears on the spread sheet. I have a lookup table in the spreadsheet so the TofP1 & TofP2 cells are filled with a lookup function. Then the SH, SC, and delta P cells are auto calculated. The COPstep4 is also calculated and gives a rough indication of how efficiency varies with time and tank temperature.

The odd temp results have been a puzzle to me for a long time. For example look at the 20 min data. The gas going from compressor to condenser is 130F at 292psi with a saturation temp of 140F. Seems to indicate that it is already starting to condense. The 16 F SC tells me the that it has fully condensed to liquid when it exits the condenser so that that seems about right.

It is possible that a bigger fan would raise the temp into condenser above the saturation temp which might help.

When I started this project I wanted to use a passive heat source, I just converted to one for a couple reasons. My unheated basement temp has been dropping with the cold weather. When the basement air temp got down to around 58F the evaporator started to get frosty, it was working, but that has to degrade performance. Now I could have just hooked up a bigger fan and I believe that would have moved enough air to prevent frosting. The original dehumidifier fan pulled 90 watts compared to 15 watts for the small fan I had been using and it was also too noisy for me.

So I made a long skinny water tank from a thin wall pvc tube that I had. It holds 2.9 gal of water which becomes a heat reservoir for the 2.5 gal water heater. To help transfer heat in, I added four 1/2 inch copper pipes which I expected to circulate water by convection. I made an evaporator from 1/4 tube like the one shown in the photo.
http://i764.photobucket.com/albums/x...ps2s2f4yzc.jpg

After running for a few days the water temp in the tube has settled to around 51F while the basement air has now dropped down to 55F.

My observation so far is that I don't think there is enough circulation through the copper tubes do much, but there seems to be enough heat transfer through the pvc tube to do the job.