Suction line heat exchanger

[jeff5may]

Mikesolar,

Thank you so much for the retrofit articles! I wish we could sticky these. They are a must for anyone attempting projects with flammable refrigerants. The articles put safety first and discuss proper handling techniques for these potentially dangerous gases. Very well authored.

dc€x,

I have just recently become aware of Coolpack and have used the software a few hours, but I still haven't become proficient enough with it to get much meaningful data. AC_Hacker has started a tutorial thread about it. Hopefully he can teach us noobs something.

I am aware of the HC refrigerants and their applications except DME. Really? Dimethyl ether? This stuff has been taken out of everything it used to be in except spray paint and vcr tape head cleaner spray due to people getting high with it. I googled it and found that ASHRAE has labeled it R-E170. Wow, higher COP than R12? Maybe someday we will have sub-mini-splits running off ether!

Honestly, I believe the 3 winners in this new arena will be propane, butane, and co2. All are common and inexpensive, and they actually work well. I've experimented with propane (r-22 replacement) and butane (r-12 replacement), with good results with both gases.

The guentner knowhow article I cited a few days ago titled "Subcooling but Correctly" briefly covers the TX valve operating at its limits. It's near the end of the article. Basically, it says that with extreme subcooling (enough that the liquid line could sweat), the valve bangs against its seat when it shuts, much like when flash gas is fed into it. Either condition is to be avoided. I read the same thing somewhere else also but I can't find it now.

[jeff5may]

I found a suitable HX on ebay for $35 plus shipping.

http://i1326.photobucket.com/albums/...psf7ab4dcc.jpg

3/8" line wound around 1" pipe with reducers at each end. 11" overall length, Sized for 10 degF subcooling, 20 degF superheat at 1.5 ton capacity.

All major manufacturers recommend the same superheat/subcooling values as this example for a sizing reference. Most say this is all the transfer you should need. Some say to go up one size for extreme performance. Who am I to argue?

I believe I am ready to build a SLHX for my unit. Since the compressor is rated at 10500 btu, I will borrow from this example and wind 10 turns of 3/8 inch copper refrig. line around a 1" pipe as a liquid side exchanger. For the suction accumulator, I'll chop an evacuated and purged propane bottle down to about half its original size, plumb the shell, then braze it all up. Wish me luck, please.

[Mikesolar]

What I did is to get the next size up tube from the suction line, put 2 reducing tees at either end and braze the sucker up. The tees had to have the stops drilled out so the original suction line would go right through. 8" was long enough for good heat transfer.

[jeff5may]

Mikesolar,

So did you get your heat pump tested/working? Haven't seen anything new on your thread. What transfer temps are you getting out of the suction exchanger?

[Mikesolar]

I hate to disappoint but I haven't got it running yet. I am waiting for a hall effect flow meter to arrive which I will hook up to the top of a manual 4-way diverting/mixing valve that I am making out of PP (see attached photo). This will have two pumps one for the evap and one for the condenser going to/from the tanks in the next picture. Meanwhile the dog shows off her ribbons.

The parts will be mounted on the plywood so I can test a variety of heat pumps.

[buffalobillpatrick]

I know this is an old thread but that don't change it's importance.

Actual Testing, not simulation:

http://fire.nist.gov/bfrlpubs/build00/PDF/b00014.pdf

See fig 4.4 R290 heating mode ICHX vs Basic (without ICHX)

ICHX looses about .4 COP

BUT, this also shows same .4 COP loss for for 4*C superheat.

This conflicts with many other papers tha show great gain in COP with 30-35*C superheat.

SO FOR NOW I DON'T BELIEVE IT!


See figure 4.2 R290/R600a isobutane 70/30% mixture sucks!

[buffalobillpatrick]

http://inpressco.com/wp-content/uplo...r48226-229.pdf

SLHX is very beneficial in this testing.

[jeff5may]

Scientific research in general is not as concrete or absolute as you might think. Most scientists and engineers are paid to provide research and published papers that support a certain bias or agenda. Numbers are twisted and parameters are modeled to produce a certain outcome, if not dictated outright.

Concerning r22 and propane, the pt curves are much like r12 and r134a. Close enough for me to call even, but far enough apart for engineering field days.

[buffalobillpatrick]

http://www.danfoss.com/NR/rdonlyres/...ompressors.pdf

p122

"For R290 experience shows the need for a
capillary flow rate almost similar to R404A. At
least this is a good starting point for optimization.
As with R134a, R404A and R600a the suction
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
systems.
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
improvements.
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."

[Mikesolar]

Originally Posted by jeff5may

Scientific research in general is not as concrete or absolute as you might think. Most scientists and engineers are paid to provide research and published papers that support a certain bias or agenda. Numbers are twisted and parameters are modeled to produce a certain outcome, if not dictated outright.

Concerning r22 and propane, the pt curves are much like r12 and r134a. Close enough for me to call even, but far enough apart for engineering field days.

Jeff, that is absolutely wrong and is one of the worst generalizations I have heard in a long time. And this argument about scientists is one reason why the climate change deniers will never believe them.

YOU HAVE TO SEPARATE OUT THE SCIENTISTS AND ENGINEERS ABOUT WHOM YOU SPEAK. YOU HAVE JUST, POTENTIALLY, INSULTED MY WIFE WHO FIGHTS DAY IN AND DAY OUT TO KEEP BIAS OUT OF PUBLISHED PAPERS. (take that with a grain of salt)

Distinguish between proper wide spread peer reviewed papers by people with good reputations and the corporate apes that masquerade as scientists. They are the ones with the usually "undeclared" bias.

That said, everyone has a bias, and most scientists do some research to prove a theory. Their neck is on the line if they fake anything. It will almost NEVER be published in a legitimate paper.

The above paper in BBP post, if you read it, is by engineers at a large Indian university. They are not being paid by some nameless nebulous think tank with deep pockets filled from beyond the big curtain.