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Author Topic: DIY water chiller - reading suggestions?  (Read 4036 times)

broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #105 on: August 30, 2021, 12:44:41 AM »
The slinger ring is pretty much standard on window bangers these days, it helps deal with condensate and as you found they get some free evaporative cooling out of it which allows the manufacturer to use a smaller(and cheaper) condenser coil. As you suggested you need to be careful with your water source as mineral will build up pretty quickly and stop up the coil but it will also deteriorate the aluminum fins.

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #106 on: August 30, 2021, 01:49:02 AM »
Wow, thanks for the great links, Bronco. A fantastic resource for the refrigeration experimenter! They state the range of evaporator temperatures for these TXV's as going up to 50F, but my evaporator temp is 60-68F. That makes me worry about the temperature compensation bulb/valve aspect not working for my "high temp chiller" setup. It seems these TXV's  might be not able to regulate via temperature outside it's design range.  Is that a problem?  I've also learned (I think?) that I need a bleed type TXV to avoid excessive compressor start currents as this was designed for capillary.

 I noted in my reading today on cap tubes and their sizing charts that they tend to specify a 20% shorter tube length for an evaporator temperature increase of 10F, so I know the evaporator temp is important for proper flow rate.

Gary, Yes, rain water collection would be disappointing here.  For a distilled water source, I might build a solar water distiller.  They are pretty simple.
 
Regarding shading the condenser unit:
My PV panels are fixed with seasonal tilt...so my hours of operation for the chiller will be the nasty, high noon scenario. 
Shade with a canvas type cover that could be put up in June after the big spring winds might work.  If I used one that attached to the shop wall it would also get rid of the afternoon west wall heating/radiation.

I sure appreciate the help on this project, it's continues to be very educational, and I enjoy that.

Best Wishes,
Bruce

« Last Edit: August 30, 2021, 02:27:56 AM by BruceM »

32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #107 on: August 30, 2021, 02:06:31 AM »

Yes, thanks for the link.
I knew those parts were available.  Just couldn't find them.  Bookmarked that site for sure.

Bruce,
I think one of those valves would work fine. Your water temp is not your chiller plate temp.......



Metro 6/1 turning a ST 7.5 KW gen head
Changfa 1115 turning a ST 15 KW gen head
Ashwamegh 2/25
John Deere 110 TBL
New Holland TC 30

"I was sitting here reading this thinking what an idiot you are until I realized it was one of my earlier posts !"

broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #108 on: August 30, 2021, 02:32:52 AM »
You are quite welcome.

As Gary said, your evap temp isn't your fluid temp. It is your saturated suction temp. I am guessing when you get everything dialed in you will be in the 40-45 degree range. I don't think your saturated suction temp will get above 50 degrees and if it does you are going to have bigger issues.

The two 1 ton valves are the same valve except one has a bleed circuit and the other does not. I would recommend the one with a bleed circuit for your application. It allows the pressures to completely equalize on the off cycle which a rotary compressor will appreciate.

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #109 on: August 30, 2021, 02:58:48 AM »
Fantastic, Bronco, thanks for your patience and help.
I measured the temperature of the suction line about 10 inches from the evaporator/BPHE, in the 60's F.  You're saying it should be 50F or below?   I better retest that, well insulated.   

Here's my earlier test data repeated:

High Side:415 psi cloudy to 440 sunny  (122 Saturation temp)
Low Side: 128-132 psi                         (45 Saturation temp)
Suction temp near evaporator 68F
Liquid line temp a foot before capillary tube: 109F
Superheat: 23F
Subcool: 13F
Running amps: 5.8 (EDIT: ERROR, well over rated 4.61A, even adjusting for low voltage) with sunny at max pressure 440psi.  I forgot to measure fan separately. It's less than 0.3A  I need to recheck this with my RMS amp meter; my clamp on meter was showing steady low amps until I moved the wire  deeper in the meter hook, and it gained an amp.  So my amps checking was crap due to clamp on meter unreliability.

Water flow rate 2 GPM
Water temp in:  67.6F
Water temp out: 56.6F
Delta temperature: 11.1F







« Last Edit: September 07, 2021, 10:01:04 PM by BruceM »

32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #110 on: August 30, 2021, 04:47:25 AM »

Bruce,
I think you are looking at 2 different things........I could be wrong on this.....

You stated your low side psi was 125 (give or take) and your saturation was 45 degrees......
I don't think that is the same as your suction line temp 10" from the chiller core...
My understanding is that the guage psi/saturation temp is the temp in the middle of the coil.
You can't measure the middle of the coil in your case.

So your saturation temp IS 45.......

If I'm wrong on this let me know.

???????????


Metro 6/1 turning a ST 7.5 KW gen head
Changfa 1115 turning a ST 15 KW gen head
Ashwamegh 2/25
John Deere 110 TBL
New Holland TC 30

"I was sitting here reading this thinking what an idiot you are until I realized it was one of my earlier posts !"

broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #111 on: August 30, 2021, 04:58:43 AM »
I measured the temperature of the suction line about 10 inches from the evaporator/BPHE, in the 60's F.  You're saying it should be 50F or below?   I better retest that, well insulated.

You do want that line well insulated but No, you wouldn't want your suction line temp down to 50 or below at a 45 degree saturated suction temperature. Water being a much better heat transfer medium than air will tend to keep your suction line temp to within a few degrees of your fluid entering temperature.

I think your ideal pressures and temperatures once the system has been running for a little while would be a 45 degree saturated suction temperature(132 psi), and your suction line temp measured a few inches from the heat exchanger at about 55 degrees(10 degrees superheat). I would expect fluid entering temp to the HX at around 65 degrees and leaving temp at around 55. That would put your slab somewhere in the 65-70 degree range.

When you first start the system and the slab temperature is say, 72 degrees, you will see that your suction pressure, suction line temperature, discharge pressure, liquid line temperature, and fluid temperatures will be elevated above the "ideal" running conditions noted above as the chiller will be taking the maximum load it can. As the chiller displaces the heat from the slab and the slab temp starts to drop to say 69-70 you will see the operating conditions start to get closer to ideal. When the system has been running for a couple of hours and the slab is down to around 67-68 degrees you should see the "ideal" conditions noted above.

A TXV would make dialing in ideal conditions easier and would do a better job of keeping the system close to ideal during the slab pull down but isn't completely necessary. I don't think you are far off and my only real concern with your current conditions being the discharge pressure. If you can find a way to keep the discharge temperature down with shading that will reap significant gains in both efficiency and heat removal. My real concern is where is it going to be on a 100 degree day?

There is a lot more to system setup than just hitting target pressures and temperatures as all along the way you need to be thinking about component longevity, most importantly the compressor. A difference of a few psi, a few degrees, and a few 10th of an amp can make a big difference in longevity.


broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #112 on: August 30, 2021, 05:02:13 AM »

Bruce,
I think you are looking at 2 different things

Correct. Saturated suction temp is derived from a pt chart for a given refrigerant at a given pressure. Suction line temperature is physically measured. The difference between the two is superheat.

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #113 on: August 30, 2021, 07:01:00 AM »
It's not trivial to have a good understanding of the interaction between refrigerant charge level. SH, SC, and the resulting water chilling performance,  I'm working at it, and making some progress, but have a way to go.  Thanks for the thoughtful explanations and patience with me, Bronco (and Gary). 

I'll do a careful evaporator suction line temperature measurement at 3 inches and hope for something much lower than what I got 10 inches away and not well insulated.






32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #114 on: August 30, 2021, 01:38:43 PM »
Bronco,
Thanks, thats what I thought. In my world I rarely have to use a chart. Gauges and my thumb will usually
get me there. Plugged dryers, plugged water lines are what I mostley see. When I have a more serious
problem then I use SH and SC and have to look them up because I can't remember.....getting old ....


Bruce,
A txv would be nice BUT you have already shown that that system has a too small of a condenser coil.
You did that with the water.....the numbers you got were just about perfect..When I see those small compressors
they normally run in the 325 to 375 or so psi range......as Bronco said for longevity it is much happier at 350 than
440........I could be wrong but I don't think a txv will solve the condenser coil problem.....water will, again you
have shown that.....

I would not waste any more time on the charge until you get the condenser worked out.

In one post you mentioned if it were you designing it you would have gone witb a 1.5 ton coil.... still too small.....
I'm thinking  2 or 2.5 to get it close in your area....AZ is 🔥 so is FL.

Look at home units. Condensers that are high efficiency are huge by old standards.  More coil, more cooling.
(Yes, I know 410 is different than 22 but you get the idea)

Work on your condenser.....thats where the problem is......and well insulated lines will make a significant change.
Think cooling back to the compressor.....

Just my 2 cents.....




« Last Edit: August 30, 2021, 01:44:37 PM by 32 coupe »
Metro 6/1 turning a ST 7.5 KW gen head
Changfa 1115 turning a ST 15 KW gen head
Ashwamegh 2/25
John Deere 110 TBL
New Holland TC 30

"I was sitting here reading this thinking what an idiot you are until I realized it was one of my earlier posts !"

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #115 on: August 30, 2021, 04:51:24 PM »
Bronco, One more TXV specifications question if you can bear it, please.
Is the temperature range specification stating a maximum of  50F  for the TXV referring to the saturated suction (low) side temp, not the actual line temperature?  That seems an odd convention to me for a mechanical bulb sensing the physical line temperature, but every technical field has it's own conventions. 

I'll mull over options for the condenser issue while I work on the control electronics and some electrical help for a friend.

If the TXV valve would stop the high side overpressure issue, that would make it worth the effort.  Alas, I'm not seeing a climb in the low pressure side with the rise in ambient temperature near the condenser unit, as I do for the high side, and the low pressure side is where the TXV pressure sensor is.  I continue to read and try to understand the interactions. 

 








« Last Edit: August 30, 2021, 07:09:11 PM by BruceM »

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #116 on: August 30, 2021, 10:45:04 PM »
I did some more testing today looking at chilling performance while adding water to the condenser, and operating in cloudy, somewhat cooler.  In all cases, lowering the pressure causes a huge loss in chilling.  Reducing the charge made it worse.I only got back to near the 11K BTU by increasing charge back to high pressures (430+ high side, 132 low).  Again, I watched cooling slowly improve as charge and pressure increased.   

The other observation is that my previous 68F at the suction line at the evaporator was correct and is only achievable after long running; it starts about 74F. The evaporator suction line temperature right near the BPHE stays within a few degrees of water input temperature, so it will never be much lower than 68F in real use. 

That concerns me about using a TXV, since they are designed for a window AC unit, with around 38-45F temperature at the evaporator suction line.  That's a long, long way from 68-78F.

It also concerns me about evaporator performance; I'm wondering if the ONLY way to have evaporator performance is to reduce the superheat.  In this case,  I'll have no choice but to run at high pressure, as I am now.  I think perhaps high superheat is OK in this case, since clearly I'm extracting all the available coolth of the refrigerant, and I just need more refrigerant flow and by shortening the cap tubes I can achieve that at a lower high side pressure.

I'd love the regulation of the TXV for better performance across a range of ambient temperatures, but unless they have one for much higher temperatures at the evaporator I'm concerned.

I may try shortening the cap tubes substantially and see how that works out.  From charts I've seen, a 10 degree change of evaporator temperature makes a 20% change in length.  I need about 30 degrees and 60% shorter....maybe. I'll study some charts more to see how linear it might be over a larger range.














« Last Edit: August 31, 2021, 12:24:01 AM by BruceM »

broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #117 on: August 31, 2021, 01:51:39 AM »
Bronco, One more TXV specifications question if you can bear it, please.
Is the temperature range specification stating a maximum of  50F  for the TXV referring to the saturated suction (low) side temp, not the actual line temperature?  That seems an odd convention to me for a mechanical bulb sensing the physical line temperature, but every technical field has it's own conventions.

Yes, the specification is for saturated suction temp. And I believe that is not necessarilly a hard limit, they just can't guarantee as tight of control on the superheat outside of that range so it may work acceptably up to 55 degrees SST.

A TXV only trys to maintain the superheat setting, that's why the sensing bulb is attached to the suction line. The spring pressure inside the valve working against the pressure in the power head is designed to know what the suction pressure is and the sensing bulb senses what the suction temperature is and the valve will modulate open or closed to maintain the superheat setting that is adjusted with the stem under the brass cap. The operating/target load temperature range is set by compressor capacity and the inherrent pressure for either low/medium/high temp application. If the valve is set for 10 degrees superheat it doesn't care if it is maintaining 10 degrees superheat at -10 degrees or +45 degrees.

That is a pretty generic wide range valve. Valves can be built for specific temperature ranges depending on the application. Those wide range valves come in handy for field service or if say a manufacturer onky wants to have an inventory of a few txvs vs. one specific for each application.

broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #118 on: August 31, 2021, 02:18:55 AM »
Your observations from today definitely lead me to believe it is refrigerant flow issue. You aren't getting enough liquid to flood your HX causing high superheat and high discharge pressure. Another side effect is high discharge temperature which will kill a compressor in short order, especially a rotary. Couple that with getting 13 degrees of subcooling with that small condenser and you definitely have a restriction, as in the cap tube is your limiting factor. Shortening it would definitely get you more flow.

I would ditch the cap tube at this point and go to a txv. You are fighting an undersized condenser and cap tube. It will be much easier to dial in your charge and the whole system in general with a txv. I think you could eventually get there by shortening the cap tube but it will likely take multiple attempts and if you go too short there is no putting it back. If you want to continue experimenting with the cap tube I would suggest getting a pair of service valves so you can pump the system down and isolate the cap tube and HX. Then you only need to evacuate that part of the system as you experiment. You will also need to change the drier at some point as each time you open the system up there will be some moisture and contamination that you will not be able to get out which the drier will collect and eventually clog. I change driers anytime I open a system for service. As a word of caution, if you do add service valves and want to pump the system down you will need to soak the condenser with cool water and monitor the discharge pressure. 410a builds head pressure very quickly and can be very difficult to completely pump down without exceeding the discharge pressure limits of the compressor and condenser coil.

broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #119 on: August 31, 2021, 02:31:14 AM »
Also, a 60% reduction in cap tube length would most likely have you flooding liquid back, high suction, and low discharge pressures. I think you are only about 10-15% too long. You are getting enough liquid to get you to within your target SST just not enough to flood your HX and get your superheat down.