08-12-14, 02:44 AM | #241 |
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Efficiency, toxicity, explosiveness, cost and flammability must all be considered. On the extreme ends of flammability hazard is hydrocarbons while toxicity would be ammonia and SO2.
As awesome as it would be, we don't have the almighty fluid. HFO-1234yf and HFC-32 are in consideration, however they're not perfect as they have A2L flammability classification even though they're not as dangerous as hydrocarbons. They require much higher concentration, higher ignition energy to ignite and do not propagate explosively like gaseous hydrocarbons. I don't believe there's a silver bullet. The use of existing stock and reclaimed HCFC-22 remains legal for service. There are plethora of approved replacements, but I'm not sure which one we should settle down on yet. I don't believe there's been extensive testing done using tailored equipment. New equipment have migrated to R-410A. R-32 could possibly substitute it. Any blend and new refrigerants are subject to patent dictated pricing including the R441A/HCR188C . |
08-12-14, 10:58 AM | #242 | |
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11-12-14, 12:36 PM | #243 |
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Just found info R290 vs. R22:
R290 (Propane) has about 35% less liquid viscosity than R22 (1 / 1.5555) Due to Molecular Mass of R22 (86.5) is almost double that of R290 (44.1) Refrigerants - Physical Properties So it seems that R22 fixed oriface expansion devices will flow about 35% more R290 Also: Liquid R290 has about 20% better thermal conductivity than R22 |
11-12-14, 12:40 PM | #244 |
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It doesn't quite work that way. R290 will work just fine in a R22 system.
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11-12-14, 12:44 PM | #245 |
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http://mail.airah.org.au/downloads/2004-05-01.pdf
3 - Conclusions The refrigerating capacity of a R22 compressor that was switched to propane was reduced between 13% to 20%. These values, though more or less as expected from refrigerant properties, are somewhat affected by differences in volumetric efficiency that, at intermediate pressure ratios are lower for propane. On the other hand, unlike expected by the analysis of isentropic cycles, there is an increase in COP of the compressor of 1% to 3%. In the case of the scroll compressor differences in capacity are shorter (up to 15%) and even reversed and COP values are around 1% to 2% higher with propane. A noticeable result is in the volumetric efficiency of both refrigerants, showing considerable differences. In the origin of the observed behaviour, three main factors can be thought to have an influence: the reduced irreversible heat flow due to the lower discharge temperatures of propane, the increased electric efficiency of the system working against a reduced load and the reduced pump losses in the inlet and discharge valves |
11-12-14, 12:52 PM | #246 |
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My comment :
" So it seems that R22 fixed oriface expansion devices will flow about 35% more R290" possibly holds true at the same pressures, but R290 generally operates at lower pressure, which may make the liquid flows more even. ? @50C R22 is about 38PSI higher than R290 Last edited by buffalobillpatrick; 11-12-14 at 12:54 PM.. |
11-12-14, 01:54 PM | #247 |
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BBP,
Good analysis w/ good technical explanation. I've done more than a few searches for studies of efficiency differences (COP) between R-22 & R-290, and R-290 comes out ahead in every study I've found. Hacking a R-22 system straight across to R-290 works fine. The metering device may not be optimum, if you are using cap tubes. If you have an adjustable orifice device, like an adjustable TXV, you should be able to dial it right in. Your study implies quite a few parameters that are different. There are some free HX sizing programs in the Internet that will take into account the multi-variant factors, and you can dial right in the optimum components you need. As I recall, THIS_ONE did a pretty good job. -AC
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11-12-14, 02:21 PM | #248 |
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Yes, I like the GEA Flat Plate HX online sizing software. I have used it several times over the last 5 yrs.
I have already bought 2X of the 4-Ton coax (snake) HX's from Surplus City. Oversized for my 2-Ton R410a Copland scroll compressor. As I will be using Propane, in my DIY W/W heat pump, I am trying to figure out how the oversized Condenser & Evaporator will effect Subcool & Superheat? I have a 2-Ton R22 TXV with 0-50*F Superheat adjustment. Am trying to figure out if SLHX, IHX will help COP or not? Most of the many website I have researched say SLHX will help some, as Propane needs very high Superheat at Compressor inlet using POE oil (33-35*C or K, note: as this is a delta temp, C or K are interchangeable) and more Subcool should also help as fewer bubbles will be present at TXV. Also lower temp. refrigerant entering Evaporator will pick-up heat faster. Last edited by buffalobillpatrick; 11-12-14 at 02:36 PM.. |
11-12-14, 06:34 PM | #249 |
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When I was going through the same process, I made a decision to go with thick mineral oil. The pag and ester oils just don't play with r290 as well as the old stuff. Also, the stink oil in camp gas bottles is mineral oil based as well. I figured that the oil thinning issue and the superheat conundrum would both be solved at once. The system has been doing well since I got rid of a few design bugs.
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11-12-14, 07:10 PM | #250 | |
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