Suction line heat exchanger

[jeff5may]

Originally Posted by BradC

The other thing about 410A vs 22 or 290 is it has quite a high latent heat capacity so you need less mass flow for the same refrigerating capacity.

I'm a bit confused. Can you help clear some things up for me?

I thought that r22/propane and r12/isobutane were kind of equal opposites. The hc's have large latent heat but small density, the fc's have small latent heat but high density, when compared to each other. R410a plays the middle, having high density and medium latent heat. When the terms are combined, R410a comes out a winner at medium-high latent heat-density.

Does this make sense?

Also, you stated the r290 running in the 410a compressor would have reduced capacity versus the nameplate. Would the compressor also be consuming less power in this condition? What ill effects would the compressor running out of its range have besides being underemployed?

I'm speaking ideally here, not practically. Just trying to gain some clarity and straighten out my thoughts on the different refrigerants. The research on the subject isn't exactly in common english.

[Mikesolar]

Brad, I have Coolpack as well but it is really hard to get my head around mostly because they assume you know all the acronyms and what the proper ranges should be which takes more time than my ADHD brain will allow, haha.

I was looking for, and asking others, on RE about the performance difference between R410 and R22 (or R290) on the same pot but didn't get good answe r so if you have any insight, it would be welcome.

[BradC]

Originally Posted by Mikesolar

Brad, I have Coolpack as well but it is really hard to get my head around mostly because they assume you know all the acronyms and what the proper ranges should be which takes more time than my ADHD brain will allow, haha.

Did you see the 25 second Coolpack walkthrough I put in my Gas and gear thread?

[Mikesolar]

Originally Posted by BradC

Did you see the 25 second Coolpack walkthrough I put in my Gas and gear thread?

Nope, probably my ADHD, haha. I will look at it.

[BradC]

Originally Posted by jeff5may

I'm a bit confused. Can you help clear some things up for me?

I haven't forgotten these questions, I've just not had time to sit down and think about how to answer them yet. All great questions, it just takes me a while to come up with a way of communicating the answers that don't need my wife to interpret for you.

[jeff5may]

I found another article which describes the effect I am trying to achieve:

http://www.pattonnz.com/site/patton/...Exchangers.pdf

It suggests that with R290, a 40% in capacity can be theoretically achieved (ignoring changes in mass flow) and realistically 12% (considering mass flow) can be had with a SLHX that is 100% effective. Similar increases in COP are also suggested.

The charts the author provided show the effectiveness vs. gain is close to linear. I've been told the reduction in gain isn't as much from ideal as the author suggests, due to R290's inherent high latent heat. The liquid subcooling has more to do with heat flow than the vapor superheating, the mass flow doesn't decrease as much as expected.

[jeff5may]

Yet another article that ties things together a bit better:

http://www.guentner.eu/know-how/tech...chash=d9123254

Actually, the site has a number of energy-saving design articles in the know-how section.

http://www.guentner.eu/know-how/

[jeff5may]

BradC,

Take all the time you need. I've found coolpack and downloaded it, but have no idea how to use it to any useful extent yet... time will tell if this will change. I'll ask questions about it on the new coolpack thread. If I can figure out how to use it, the program seems robust and precise. It could be a godsend, preventing a lot of wasted trial and error.

A big point I gathered from the Guenther article is that too much heat exchange in the SLHX is a bad thing.

Compressors specify a maximum SST (suction socket temperature) which could be exceeded by too much heat transfer into the suction line. This would make your compressor roast itself due to high discharge temps. 99.9% of hermetic compressors use cool suction gas to cool the motor windings, warm suction gas could cause motor overheating. Most likely the refrigerant would be above its critical point also, causing all manner of thermodynamic mayhem in the condenser.
On the other side of the exchanger, too much subcooling causes more problems. Expansion valves are designed to have SOME gas flashing inside the body. Extremely subcooled liquid hardly flashes, causing the valve to eventually lose its seal. In the evaporator, the lack of flash gas causes low quality and velocity (laminar flow pattern). The evaporator heat exchange suffers until the liquid speeds up and starts to churn inside the pipes (turbulent flow). The effective area is greatly reduced, causing reduced capacity and COP.

So now I'm with Mikesolar on the notion that a massive exchanger isn't so useful. In fact, it can be a bad thing. But how big is too big?

[dc€x]

Originally Posted by jeff5may

BradC,

...coolpack and downloaded it, but have no idea how to use it to any useful extent yet... time will tell if this will change. I'll ask questions about it on the new coolpack thread.

Guenther article is that too much heat exchange in the SLHX is a bad thing.

specify a maximum SST (suction socket temperature) which could be exceeded by too much heat transfer into the suction line. This would make your compressor roast itself due to high discharge temps. 99.9% of hermetic compressors use cool suction gas to cool the motor windings, warm suction gas could cause motor overheating. Most likely the refrigerant would be above its critical point also, causing all manner of thermodynamic mayhem in the condenser.
On the other side of the exchanger, too much subcooling causes more problems. Expansion valves are designed to have SOME gas flashing inside the body. Extremely subcooled liquid hardly flashes, causing the valve to eventually lose its seal. In the evaporator, the lack of flash gas causes low quality and velocity (laminar flow pattern). The evaporator heat exchange suffers until the liquid speeds up and starts to churn inside the pipes (turbulent flow). The effective area is greatly reduced, causing reduced capacity and COP.

So now I'm with Mikesolar on the notion that a massive exchanger isn't so useful. In fact, it can be a bad thing. But how big is too big?

You have exellent attitude,jeff5may, approaching this "awkward" matter.
Find below one humble coolpack-wersion (not created originally by me).

Pls,note always the Coolpack knows nothing about lubrication oil behaviour(viscosity/mischibility/dilution etc.) in the refigeration process .These are key factors as well.


One COOLPACK-simulation below for LL/SLHX-solutions :
+7/+50 degC setup
2K subcooling
5K superheating
compressor with isentropic efficiency 0.7 (=very good compressor,usually in heat pump contex ranging between 0.60 - 0.65 appoaching 0.7 when bigger compressors concerned).
Rgd. new PERMAMAGNET-compressors (BLDC) the efficiency is still higher
(heat loss through windings modest).

HEATING COPs through COOLPACK:

R404A: -COP = 4.053
R410A: -COP = 4.193
R407C: -COP = 4.324
R1270 (propylen) -COP: = 4.41
R290 without LL/SLHX: -COP = 4.454
R22: -COP: 4.519
R134a: -COP = 4.519
R290 with LL/SLHX efficiency 50% => 85 degC hotgas: -COP= 4.54
R600a without LL/SLHX: -COP= 4.59
R12 -COP =4.608
DME: -COP = 4.82
R600a with LL/SLHX efficiency 70% => 85 degC hotgas: -COP= 4.92

Coolpack is originally designed for cooling =freezing purposes.
The Guenter article is for R404A and maybe not the best example for heating purposes.But the idea of deviding the circuit into many sections (HX:s for different phase-/physical transitions) is most necessary if highest gain is in sight.

Heating COP to be derived from cooling COP by adding +1 (unit) into the coolpack value.

As you said there is a upper limit in LL/SLHX efficiency you should not exceed
=> CRITICAL temp. of the refigerant (no phase transition!).
Another thing is that HYDROLYSIS of the oil (MO-POE-PAG etc) may start
(hotgas T> +120C /POE ?) if oil contaminated enough by H2O.

The "flash-gas" item you told is something new and strange to me.
I have before always had the idea the expansion valve should be "safe" if no cavitation forces are prevailing in the TXV-body.
Any referenses available on the subject?
Any difference in behaviour between capillary/TEV/EEV-systems ?

PS: You may wonder about the R1270 in my list above.
You have this available at Lowe`s and Walmart at <$ 8 per can (400g).
Guess which stuff is "originally" concerned and for which purpose ?

As US/Canadien citizens you are sitting on a treasure without knowing(?) about the cheap refrigerat resources (even) better than R290 (propane).
As a Finn I feel furious due to non-access to these "crown jewels" of
yours!

[Mikesolar]

Here is the link to a guide for the SAFE changeover to R290 (and maybe R1290) as well as a suitability guide. There are 2 documents but they are too big to post.

GIZ. Publications