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buffalobillpatrick · 03-18-14, 12:05 AM

PROPANE

http://docs.lib.purdue.edu/cgi/viewc...20superheat%22

See figure 6 highest Eff. with superheat (SH1) 21-35K

http://ww.mycoolingtower.com.au/down...2004-05-01.pdf

Fig 5 right side scroll with R290 goes off the top of chart at about 22K

The purpose of IHX or SLHX is to move heat from the condenser to TXV section into the evaporator to compressor suction line, this increases Eff. by increasing superheat.

references that I copied from this site:

"A word on R290 and superheat. If your TXV came set up for R22, the factory superheat setting is WAAAY too low! R22 likes 6-7K superheat in practice, whereas manufacturers are recommending 14-20K or more superheat for R290 systems. It seems that the propane dissolves in oil, making a kind of oil soda in the condensor side. This actually aids in heat transfer, since liquid propane soda has much better thermal conductivity than just oil. The problems happen on the other side of the TXV when this oil soda rapidly expands. Instead of fogging like R22 and oil, the propane soda fizzes and foams like warm beer! If your superheat setting is too low, the stuff spews right through the evap coil, transferring nearly no heat and killing your temperature split. If you listen to the evaporator, you can hear it! Sounds kind of like a car radiator that is about to spew from overheating."

another reference:
"4 Superheat MUST be in 20F zone because propane is tend to condense and compressor is getting liquid in suction line. This can dramatically shorten life of compressor.

5 I found that many recommend liquid line-suction line HX because it helps maintaining superheat and increases COP (substantially compare to R22)"

another reference:
Then I read this:

"...the high solubility of mineral oils in propane could represent a problem, especially for applications such as heat pumps displaying high suction pressures... the experimental results reported in the present work can therefore be explained by means of the strong influence that the propane solubility could have on the sealing effect of the lubricant between piston and cylinder... the solubility is shown to strongly decrease by increasing the superheating; as a consequence, the viscosity of the oil strongly increases with superheating until reaching a maximum at around 30-40K superheating... the suction superheat would have a positive influence on the volumetric efficiency."

and from the other article:

"Refrigeration capacity and COP differs only slightly from R22
data. However, the suction superheat with R290 has essentially
a greater influence (see Fig. 4). In other words: R290
profits in capacity and efficiency from useful superheat, the
use of a heat exchanger between the suction and liquid lines
is therefore an advantage.
R290 has mainly favourable thermodynamic properties and
low energy requirements during compression. Pressure levels
and volumetric refrigeration capacity values are very similar
to R22, however, there is a large difference in enthalpy,
density, mass flow and isentropic compression exponent
(operating temperatures)...

R290 has an extraordinary high solubility with conventional
lubricants and Ester oils. This characteristic is of course
desirable for the oil circulation in the system. However, it
can lead to a considerable decrease of the oil viscosity in
the compressor especially at low oil temperature and high
suction pressure. In addition to this, there is a strong degassing
effect in the crankcase and lubricating spaces
which is, amongst other things, due to the enormous volume
change with the evaporation of R290. This leads to
high oil carry over (foaming), reduced performance and
stronger wear on the moving parts (also see para. 3.2)...

Expansion valves should be specifically designed for R290.

The use of R22 valves is of course possible but at higher
evaporating temperatures it can lead to insufficient superheat
(different pressure / temperature relationship). A corrected
superheat setting would then be necessary.

Attention!
The minimum discharge gas temperature should be at
least 20 K (try to attain 30 K) over the condensing temperature.
(see information in para. 2.1)"

BBP

03-18-14, 12:05 AM	#167
buffalobillpatrick Master EcoRenovator Join Date: Mar 2014 Location: Florissant, Colorado Posts: 599 Thanks: 814 Thanked 59 Times in 55 Posts	PROPANE http://docs.lib.purdue.edu/cgi/viewc...20superheat%22 See figure 6 highest Eff. with superheat (SH1) 21-35K http://ww.mycoolingtower.com.au/down...2004-05-01.pdf Fig 5 right side scroll with R290 goes off the top of chart at about 22K The purpose of IHX or SLHX is to move heat from the condenser to TXV section into the evaporator to compressor suction line, this increases Eff. by increasing superheat. references that I copied from this site: "A word on R290 and superheat. If your TXV came set up for R22, the factory superheat setting is WAAAY too low! R22 likes 6-7K superheat in practice, whereas manufacturers are recommending 14-20K or more superheat for R290 systems. It seems that the propane dissolves in oil, making a kind of oil soda in the condensor side. This actually aids in heat transfer, since liquid propane soda has much better thermal conductivity than just oil. The problems happen on the other side of the TXV when this oil soda rapidly expands. Instead of fogging like R22 and oil, the propane soda fizzes and foams like warm beer! If your superheat setting is too low, the stuff spews right through the evap coil, transferring nearly no heat and killing your temperature split. If you listen to the evaporator, you can hear it! Sounds kind of like a car radiator that is about to spew from overheating." another reference: "4 Superheat MUST be in 20F zone because propane is tend to condense and compressor is getting liquid in suction line. This can dramatically shorten life of compressor. 5 I found that many recommend liquid line-suction line HX because it helps maintaining superheat and increases COP (substantially compare to R22)" another reference: Then I read this: "...the high solubility of mineral oils in propane could represent a problem, especially for applications such as heat pumps displaying high suction pressures... the experimental results reported in the present work can therefore be explained by means of the strong influence that the propane solubility could have on the sealing effect of the lubricant between piston and cylinder... the solubility is shown to strongly decrease by increasing the superheating; as a consequence, the viscosity of the oil strongly increases with superheating until reaching a maximum at around 30-40K superheating... the suction superheat would have a positive influence on the volumetric efficiency." and from the other article: "Refrigeration capacity and COP differs only slightly from R22 data. However, the suction superheat with R290 has essentially a greater influence (see Fig. 4). In other words: R290 profits in capacity and efficiency from useful superheat, the use of a heat exchanger between the suction and liquid lines is therefore an advantage. R290 has mainly favourable thermodynamic properties and low energy requirements during compression. Pressure levels and volumetric refrigeration capacity values are very similar to R22, however, there is a large difference in enthalpy, density, mass flow and isentropic compression exponent (operating temperatures)... R290 has an extraordinary high solubility with conventional lubricants and Ester oils. This characteristic is of course desirable for the oil circulation in the system. However, it can lead to a considerable decrease of the oil viscosity in the compressor especially at low oil temperature and high suction pressure. In addition to this, there is a strong degassing effect in the crankcase and lubricating spaces which is, amongst other things, due to the enormous volume change with the evaporation of R290. This leads to high oil carry over (foaming), reduced performance and stronger wear on the moving parts (also see para. 3.2)... Expansion valves should be specifically designed for R290. The use of R22 valves is of course possible but at higher evaporating temperatures it can lead to insufficient superheat (different pressure / temperature relationship). A corrected superheat setting would then be necessary. Attention! The minimum discharge gas temperature should be at least 20 K (try to attain 30 K) over the condensing temperature. (see information in para. 2.1)" BBP Last edited by buffalobillpatrick; 03-18-14 at 06:07 PM..