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Old 09-12-21, 10:21 AM   #4
Robl
Helper EcoRenovator
 
Join Date: Oct 2020
Location: Cambridge, UK
Posts: 31
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I've run the rig a few times now logging data, and analysed the data a bit better now, taking into account losses of the 27litre water tank to air - I did this by only running the circulation pump allowing the 27l tank to cool down, and then curve fitting to get the losses. I find 15W/degC relative to air, so when running hottest I get 300W extra loss, which is significant given the system is small.

I tried working out the superheat, which started at around +20C, then added some more R290, then I got +10C superheat. I added some more again - I think too much, not sure if I had any superheat at all at this point, and the efficiency dropped. I've added a picture of the calculated COP versus DT, and all the runs are similar except for the one with the highest charge, which gave to worst result.
Today I planned letting out some gas, to get back to the better performance - only to discover some must have leaked out - my pressures were a bit lower again, and the efficiency was good again. Hmm, clearly something isn't quite gastight. I have 4 heatexchanger connections that rely on nitrile rubber washers, and I left the manifold guage set on, I think it will be one of those things.

There's some vibration on the thin capillary tube, at the end, after the section soldered to the liquid line. It makes a white noise sound which I can deaden by touching it - I presume there's bubbles of gas in here? Is this a sign of something I can improve somehow? Should more of the cap tube be soldered to the liquid line, or the length be more/less? All the 4 charge levels I used made this happen, I think in a similar way. There's a pic of where this is coming from attached, I circled the pipe in red.
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