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Old 01-29-13, 07:31 PM   #1
jeff5may
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Default Suction line heat exchanger

Ok, so the window AC unit I turned into a heat pump is doing such an awesome job that I have decided to build another, similar unit. The first unit and this unit will have similarly sized heat exchange coils, only this one will be based off a 9k btu compressor vs a 15k btu in the first. So in theory, I should be able to squeeze more COP out of this one. which leads me to this thread...

While researching propane-based refrigeration cycles, I kept coming upon mentions of using suction-line heat exchangers (SLHX). The research and application papers I read said that considerable performance and efficiency gains could and/or should be had by using them in the refrigeration cycles of propane-based setups. Somewhere along the line I decided that I would try one in action and see if it would help. Before I do, though, I need to become more familiar with them and gain some insight and confidence.

I have a ton of questions about these gadgets. The main idea behind these things is that they take waste heat from the liquid line and warm the cold suction line with it. This is supposed to subcool the liquid line (a good thing?) and superheat the vapor line (another good thing?) while increasing suction pressure (i know this is good.) and mass flow (definitely good.). This sounds like some sort of free lunch to me.

I will be running a TXV on this new unit (harvested from the first unit), so it alone should net me some performance vs. the cap tube running in it now. Keeping this in mind, will the txv work with or against the hx? Should I put the sensor bulb on the evap or compressor side of the slhx? Would it make much difference?

Next come the plumbing questions. Should I extend the liquid line or the suction line? Vertical or horizontal orientation? How big is too big?

I know I will probably learn more than I accomplish from this endeavor... that's kind of the point. I hope somebody can help clear up the muddy water a little before I jump in.

jeff

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Old 01-30-13, 08:14 PM   #2
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Quote:
Originally Posted by jeff5may View Post
I hope somebody can help clear up the muddy water a little before I jump in.
Can you cite links to the literature that you've come across?

I think I may have seen such a device in a photo of a Heat Pump that Piwoslaw posted a long time ago.

I'm pretty sure BradC has some information on what you're trying to do... maybe Vlad, too.

Also, it's not clear from your description if you plan to separate your compressor function from your condenser/fan function, but I think it will make your life a lot more comfortable if you do. There's a reason they call air conditioners "window shakers". I really think that they're best left outside, bolted to a concrete pad.

Best,

-AC
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Old 01-31-13, 01:22 AM   #3
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Do you mean the HX "W", called "ekonomizer"?
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Old 01-31-13, 05:41 AM   #4
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Some quick papers:

http://www.irc.wisc.edu/file.php?id=49

LCYE - Suction line accumulators, with heat exchanger

Numerical simulation of the effects of a suction line heat exchanger on vapor compression refrigeration cycle performance - Springer
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Old 01-31-13, 10:18 AM   #5
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I have lots of theory SLHX, but no experience at all. Therefore I'm watching eagerly!
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Old 01-31-13, 11:19 AM   #6
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Do you mean the HX "W", called "ekonomizer"?
Piwoslaw,

It would be useful to English-only readers if you edited in to your diagram post what all the labels are.

Best,

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Old 01-31-13, 02:49 PM   #7
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Piwoslaw,

It would be useful to English-only readers if you edited in to your diagram post what all the labels are.
Did you have to spoil the fun?
Changed it. Sorry about that.
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Old 02-01-13, 12:33 AM   #8
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Piwoslaw,

Yes, the part labeled "w".

I had written a descriptive post, but the site ate it when I tried to post it.
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Old 02-01-13, 07:02 AM   #9
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I use them all the time, in 2 ways. The simplest is as the diagram shows and could be fine provided you do not wish to have a reversing system to do cooling as well (or defrost, but there are other ways of doing that). The second one is to get a suction accumulator with a pancake HX inside it. The added benefit of this system is to take up the extra refrigerant when in reverse mode so the pot doesn't get flooded.

The pic I showed on the other thread shows my HP with both types on it. The main reason I am using it is that it will extend the operating range down another 5-8C

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Old 02-01-13, 11:16 AM   #10
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I use them all the time, in 2 ways.
So what is your rationale for using the size that you chose to use?

Did you just eyeball it, or was there some design criterion that you used.

-AC

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