|11-05-14, 05:46 PM||#51|
What I'm talking about is the papers written by individuals employed by a certain industry or interested or vested entity. Some of these authors are in positions sheltered from repercussions, but most aren't. Logical papers can be written, that stand up to institutional scrutiny, with research to back the thesis, to support nearly any agenda. After a while in the system, ambitious professionals have learned what they can write about that will get noticed, and what not to write about that might end their careers. The peer review process is a walk in the park at the end.
The whole process reminded me of an episode of mythbusters while I was in school. Some of the stuff good researchers were spending their public-funded time on was just a joke. But it wasn't.
Last edited by jeff5may; 11-05-14 at 05:50 PM..
|11-06-14, 10:44 AM||#53|
Not the entire process. I was a helpers helper, working on a small part of a larger project. At least half of what I did got rejected. It was something to do with communication electronics. I was etching and drilling PC boards.
|11-07-14, 10:43 AM||#54|
Join Date: Mar 2014
Location: Florissant, Colorado
Thanked 58 Times in 54 Posts
From my research: Propane (R290) performs best with very high Superheat (33-35*C) at the compressor input.
Attaining this much Superheat without a (SLHX, IHX, LSHX) many names, would require that the TXV throttle down the refrigerant flow so that the last section of the Evaporator would not be evaporating any more refrigerant, but just be adding sensible heat.
This throttling down of refrigerant reduces Mass-flow in system, thus capicity drops.
It seems that attaining this much superheat at the compressor input should be accomplished with a SLHX.
Another great benifit in performance, is increasing Sub-cooling at the TXV, so bubbles are elemonated.
Finding SLHX optimum size testing has been difficult, I have seen examples from 1/3 as big as the condenser on down. ?
" Use of liquid-suction heat exchanger in the VCRS reduces the possibility of liquid
carry-over from the evaporator which could harm the
compressor, by superheating the refrigerant vapours after
evaporator, by the heat of hot liquid refrigerant available
after condensation. The refrigeration capacity of the
system is increased by 9% to 32% for different flow rates
of the refrigerant in the range of 12 to 16 LPH, which is
obtained due to the sub cooling of the liquid refrigerant in
the LSHX, leading to the efficient throttling. For lower
flow rates of the refrigerant the effectiveness of the LSHX
is maximum as compared to higher flow rates, because the
time available to exchange heat is more in case of the low
flow rate. The optimum effectiveness (0.65) is obtained at
40 °C of initial water temperature. Use of LSHX in the
vapour compression refrigeration system, increases the
COP of the refrigeration unit for different initial
temperatures of water by 10 % to 40 % . The compressor
work gets reduced by 3% to 11%, by using the liquid
suction heat exchanger in the vapour compression
refrigeration system that means less power consumption
by the refrigeration unit has been observed. The LSHX
sub-cools the liquid refrigerant before passing to the
expansion valve which leads to the rise in evaporator
capacity which is much more than the heat rejected in sub-cooling.
Thus the LSHX is found to be a device which is
useful for avoiding flashing of refrigerant in expansion
device that raises the amount of liquid refrigerant in
evaporator. Ultimately, it increases the refrigeration effect
and COP of the system (10 % to 40 %). The optimum
effect of the LSHX is seen at different flow rates of the
refrigerant for lower initial temperature of water (30 to 35
Last edited by buffalobillpatrick; 11-07-14 at 11:08 AM..
|11-07-14, 12:15 PM||#55|
The tiny amount of testing I have done has me sold on them with r134 and propane in cold climate heating applications. The unit I tried one out in put more heat inside at the same outdoor temperature and added a few more degrees to the bottom end of the useful range. How much, I can't say for sure, but it definitely did a better job than before it was modified.
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|11-13-14, 06:30 PM||#56|
Has anyone seen inside the newer Zoneline heat pump PTAC units? I saw a brand new one at work today. They have a quiggle-ator in them! This device not only serves as a suction/liquid heat exchanger, but also as a charge compensator. It looks like a compressor muffler, and has cap tubes in the top and bottom of it. The wide part of the muffler is brazed to the outdoor hx line that leads to the reversing valve. I found a faraway pic of a smaller unit on display:
If I can remember, and find some time, I'll go back and stare at the rat's nest between the compressor and outdoor hx. I'll take some pics and try to untangle the maze.
These units also have a heat pipe sandwich with the indoor hx in the middle. They call it "super-dry" or something similar. The main purpose of this rig is to increase dehumidification.
Since one half of the heat pipe sandwich is upwind from the evaporator, it will always be warmer than the other half downwind. The heat pipes have R410A in them, and are connected at the top and bottom. When the unit is working as an air conditioner, the downwind hx condenses refrigerant, due to the temperature drop of the evaporator coil. This forces a pressure drop which carries over to the upwind hx. Due to the decreased pressure, the refrigerant boils out of the upstream hx and pre-cools the ambient air before it reaches the evaporator coil.
GE says this gimmick nearly doubles the amount of water the evap coil can condense from the air. They claim a 10 degree or better reduction of wet bulb temperature at the evaporator coil surface.
Now correct me if I'm wrong, but this sounds like the opposite of what we are trying to do with a suction line exchanger. Doesn't this thing shunt some of the load around the evaporator? Also, wouldn't forcing a 10 degree drop in evaporator temperature raise the effective temperature split and kill efficiency and COP?
|11-16-14, 12:27 AM||#57|
Follow up video:
I stood and looked at it up close for a few minutes (until someone ran me off) and I can't be 100% sure how this thing is plumbed. There are no active metering devices, all metering is done with cap tubes. I believe some of them are shunted in cooling mode.
|01-21-15, 12:31 PM||#58|
Join Date: Mar 2014
Location: Florissant, Colorado
Thanked 58 Times in 54 Posts
r290 pressure level and critical temperature are
almost like R22. However, the discharge
temperature is much lower. This gives the
opportunity to work at higher pressure ratios,
means lower evaporating temperatures, or at
higher suction gas temperatures.
Refrigerant R290 is used with polyolester oil in
Danfoss compressors, so material compatibility
is almost identical to R134a or R404A situation
from oil side. R290 is chemically inactive in
refrigeration circuits, so no specific problems
should occur there. Solubility with ester oil
is good. Direct material compatibility is less
To keep the
refrigerant flow speed within the recommended
range of 3 to 5 m/s it may be necessary to adopt
the cross flow sections
Special care has to be taken when
designing the accumulator in the system. When
using R22 or R134a the refrigerant is heavier than
the oil used, while with R290 the refrigerant
is less heavy, as can be seen in the data table 1.
This can lead to oil accumulation if the
accumulator is too large, especially too high,
and has a flow path which does not guarantee
emptying sufficiently during startup phase of the
line heat exchanger is very important for system
energy efficiency of R290, which it was not for
R22, see fig. 5. The figure shows increase of COP
with superheat from few K up to +32 °C return
gas temperature, where a range from +20 °C
to approx. +32 °C is usual for small hermetic
This large increase in COP for R290 is caused by a
high vapour heat capacity. In combination with
the need for keeping the refrigerant charge close
to maximum possible in the system, thus giving
no superheat at evaporator outlet, the suction
line heat exchanger has to be very efficient for
preventing air humidity condensation on the
suction tube. In many cases an elongation of
the suction line and capillary gives efficiency
The capillary itself has to be in good heat
exchanging contact with the suction line for as
long a part of total length as possible.
At high superheat, with good internal heat
exchange, the theoretical COP of R290, R600a
and R134a is higher than for R22. At very low
superheat the COP of R290, R600a and R134a is
lower than for R22. The R290 behaviour is similar
to R134a, with respect to internal heat exchange.
Generally the same rules for evacuation and
processing are valid as for R22, R134a or R404A
systems. The maximum allowable content of non
condensable gases is 1 %.
Too high level of non condensables increases
energy consumption because of higher
condensing temperature and a portion of the
transported gas being inactive. It can additionally
increase flow noise
The 3rd paragraph on Suction Line Accumulator, oil being heavier than Propane & probable accumulation of oil in Accumulator makes me VERY hesitant to use the LARGE 60oz one that I have bought!
I have a large Refrigeration Research BH750 for use as SLHX, 7.5hp (19K btu/h)
The suction line pipe in the middle of it is 15" long x 1.625" ID (31.1 cubic inch)
I'm thinking of positioning it vertical with evaporator output 3/4" pipe into bottom, so it would also be a burp / slobber reciever tank.
This would be a 6.76x increase in pipe volume for 15", thus the refrigerant would slow down by about the same ratio.
Good idea or bad ???
Last edited by buffalobillpatrick; 01-21-15 at 03:33 PM..