Author Topic: DIY water chiller - reading suggestions?  (Read 3255 times)

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #135 on: September 07, 2021, 12:53:05 AM »
Cap tube into BPHE is cold with some condensation but not frosting.

Yes, increased charge raises amps above the 4.6 rated max, I took out some charge to get  back down to 4.6, and I'm using my best clamp on amp meter. Checked it against a RMS 120V power meter to be sure it was fairly accurate.

But the real baffler is why didn't suction side pressure come up.  Suction temp near BPHE is still exactly the water inlet. Suction pressure is WAY low, as if starved for charge, but no frost, and amps show full charge, increasing with an increase in charge.

Hopefully I'll see my next step when I feel better.










32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #136 on: September 07, 2021, 04:04:41 AM »

Every thing would indicate a low charge except amp draw.

The cap tubes should not be cold except at the plate.

Low head pressure.....low suction pressure......

I'm baffled.

I would gently add gas and see where the amp draw goes.......does the compressor have its own data
plate ?    ...........




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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #137 on: September 07, 2021, 07:20:39 AM »
I like to your theory, Gary. It fits.  I suspected it myself until I saw the current being 4.8 amps.  I thought that I didn't put in nearly enough R410A; I found my bathroom scale was not seeming to read correctly, then caught it changing values significantly on subsequent re-weighs.  But still, the faceplate calls for 20 oz, and I did not put in that, or the 4 oz for the dryer, and 2 oz for the extended copper lines.  (I'm ordering a postal scale.)

What I'll do tomorrow is some new wiring to allow for inline RMS current sensing in addition to my clamp meter and then keep adding in some refrigerant and see what happens.  I won't stop until the current goes substantially high (5.6A) and stays there.  Today I stopped immediately and backed off when it got to 4.8 amps... perhaps I should have just waited longer???  As I let some high side liquid back into the recovery tank, the current did come down, slowly.

I'll retest and see what happens with more refrigerant, and I won't stop until it gets well over 5 amps, and will let it run and see if it goes down after a bit.

Thanks for your good thoughts!


BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #138 on: September 07, 2021, 09:56:05 PM »
Good news; The problem was both meter and apparently a blip of higher current during filling, plus not realizing that my inverter 230V was more like 217 a the unit due to my use of an extension cord for a temporary hookup. 

So, my hat's off to Gary; he diagnosed it correctly as undercharge with bogus high amps. 

 Alas, the suction side temperature has not come up enough, yet.  But BTU performance is somewhat improved at normal max power; 8.5K  BTU to the water at 4.8A/217V.  As the outside temps got warmer from the sun heating the west wall of the shop and thus the air around the condenser unit, I lost 1K BTU.  As the math turns out, BTU's are easy with my setup at 2 GPM; every degree of cooling is 1K BTU.  (8.5 degrees = 8.5K BTU)

The ambient air into the condenser fan was 95F, and the high side temp was 115F.  Room for improvement there. 

High Pressure: 390-400, low side 115 to 120.  High side temperature 115F. Sub cool near zero. 
Suction  temperature at BPHE: 70F  Superheat= 29, the horn in my efficiency side.

Since low side pressure and temperature have not come up, I'm reluctant to shorten further.  I think my next move is to add the water bypass valve, to allow water temp in the BPHE to drop lower, thus lowering my suction side temperature, superheat and hopefully improving my BTUs. 


32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #139 on: September 07, 2021, 10:52:29 PM »

Looks like you are getting close.
 
400 psi head is not bad but if you could shorten the tubes a little more and run the
head near 350 to 375 I think it would make a big difference on compressor life.....

Did you run water on the condenser?  We know that will lower the head.

Tell me about your bypass idea. Yes, lowering the water temp will help lower pressures and temps.

Metro 6/1 turning a ST 7.5 KW gen head
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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #140 on: September 08, 2021, 03:33:47 AM »
I found some old test notes: 
With the stock cap tube, 5.0amps (at 218V) 350/110 PSI, 95F high side temp, evap suction temp 69F. Must have been cooler.
Still, only 5K BTUs, despite the slightly higher BTUs.
5K BTU is 1465 watts, with 1090 corrected watts input, is a very poor COP of 1.3 .


With the shorter cap tube, 4.8 amps at 218V, 8000 BTUs (at higher temperature), 2344 watts of cooling over 1046 watts of power is better but still poor COP of 2.2 . 

So I'm making some improvement.

The high side pressure now tracks my condenser liquid temperature, which tracks the sun baked, 10F over ambient air at ground level in the sun plus 15 degrees.  The bugger is the low side pressure isn't coming up as much as I'd like, since it's pegged at the incoming water temperature.

Perhaps I should consider another shortening for educational purposes.

The water bypass method is to plumb in a bypass for the BPHE, so that only some of the water goes through it. This would allow the suction side temperature to lower even if it's still tied to water temperature. I'm  not sure if this is a viable means of improving COP/BTU's, but it could get the temperature of the EXV bulb to within it's design range.  It may not be necessory if shortening does the trick.

I'm interested in the concept; it's similar the method used industrially to keep up efficiency, when cooling a large tank starting at a high temperature and going all the way to a cold one.

A BPHE with fewer plates also comes to mind.

mobile_bob

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Re: DIY water chiller - reading suggestions?
« Reply #141 on: September 08, 2021, 04:08:03 AM »
i am placing my be on the deletion of the cap tube and the installation of the expansion valve.

i like things that i can adjust to tailor things to get the result i want.

cap tubes to me seem about the same as having to adjust an engines valves by having to grind the end off a pushrod, not enough and the engine loses power, too much and it clatters.

poor analogy? i know... hey its late and i am getting old!

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #142 on: September 08, 2021, 04:39:49 AM »
I found some research papers to study, about superheat, subcooling and COP. I skimmed some of it and it seems I'm off the mark entirely on reducing superheat to get a better COP.  An academia mind bender, no doubt.

I'll do some tests  tomorrow morning when the air temps are cooler and see how that performs. That will improve my pathetic subcooling and increase COP and BTUs.  I'll try some water as well.

I agree with you on having adjustment, Bob.  It's just that I need very hot days to get valid data and so I'm trying to learn all I can before the TXV gets here.  Thus the jury rigged power, etc.  Today I had to take time to repair my old Eaton air compressor pump which the Lister CS drives.  The output valve was leaking, and the downstream check valve failed, also.  Luckily I had a spare check valve on hand, and was able to clean up the compressor disk valve after welding up a special spanner.   Things never fail until you're rushing on another project...

Lucky for me, damned hot this week and sunny. 



« Last Edit: September 08, 2021, 04:48:43 AM by BruceM »

mobile_bob

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Re: DIY water chiller - reading suggestions?
« Reply #143 on: September 08, 2021, 05:12:03 AM »
Bruce

i understand the wanting to learn all you can about the system while you are waiting, very well.

don't think for a minute i am trying to teach you anything, you already know more than i do on this subject, that is why i am following with interest.

sometimes i just can't help myself and i have to chime in with unsolicited input.

one way or another i am confident you will get this worked out, and we will all learn from your efforts... that is what makes for a good forum.

having to learn everything on ones own got really old, sure nice to have a place where one can draw on other experiences or live vicariously as i do.  :)

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #144 on: September 08, 2021, 06:11:59 PM »
Got some 80F (condenser fan input) data this morning on Lister power.

High side- 340 psi,  temp 95.9F   Low side- 102 psi, temp 72F
Water in/out 72.4F, 63F
230V x 4.3A (rms)= 989 watts

BTU is 9360.  (2734W)  Below my minimum cooling required, but getting close, and there's some head room on amps.
COP = 2.76.  Better than a hot afternoon at 2.2 but still not good.










32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #145 on: September 09, 2021, 12:31:53 AM »

I'm curious about your temp readings....

Hi side 340 (I like that ).....temp 95F...where are you reading that ?

Low side 102 F (might be just a tiny bit under charged) @72 F....where are you reading this ?

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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #146 on: September 09, 2021, 02:25:48 AM »
Hey Gary, My high side temp is measured just before the cap tube indoors, the suction side a few inches from the BPHE. Both are insulated for their 6.5  foot length.

My high side was the standard 15F over air inlet, which is often 10F over ambient on a sunny afternoon from ground heating. The sun is intense at 5600 ft. 

I tried several experiments this afternoon.  One was putting up a tarp awning for shade.  That did very little, since the ground was already warmed up.  It dropped current slightly.  No measurable change in BTUs.  When I add water to the rimmed condenser fan bath, current drops 0.4 amps and BTUs increase just slightly.  Not surprising as the same performance gains are in the morning at cooler temperatures.  But it is not huge. 

I next tried changing the water flow direction through the BPHE. This made no difference in water cooling, but it lowered the suction side temperature to match the cooler outgoing water temperature, today about 64F.   This is better for cooling the compressor so I'm leaving this change for now.  It made no change in BTUs, still 9000.  This lack of improvement with reduced Superheat  agrees with  an academic research paper using a computer model that suggests that lower superheat is not helpful for improving COP.

Next I decided to blow my last nitrogen before my neighbor gets me a refill on Friday. I shortened the cap tube  10 inches this time, just to see if again I get some improvement on BTUs and COP.  A quick braze, installation, then pressure test on nitrogen, followed by nitrogen purge till my little tank gave it's all and it's back in now and I"m pulling a vacuum.  Having flare fittings on both ends of the cap tube is nice. 

I don't see why I shouldn't be able to get a COP of 3 like all the other guys do.  Fingers crossed for tomorrow.





« Last Edit: September 09, 2021, 06:57:51 AM by BruceM »

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #147 on: September 09, 2021, 06:18:46 PM »
Results are great on the total of 21 inch shortened cap tube (stock 63 inches, dual tube). 
My BTU's have gone from 9000 to 13000 at 4.5 amps/1035W  total (fan plus compressor).  Water in: 69.8 after running for a while, water out 56.8F.   My COP has gone from 2.76 to 3.68 ! (3809W/1035W)

What a difference the proper expansion valve flow makes!

My suction side temperature is 54.5F, still closely tied to the water out (I'm using the "wrong" water flow to make it lower.)
This is good because most compressors specify 60F for the minimum suction temperature for compressor cooling.  The vapor enters the hollow pump cavity to provide essential cooling.

Ambient Conditions: 80F, morning shade.  Measured at fan inlet, also 80F,  Fan outlet 94F.
Amps: 4.5A  I stopped here as incrementally charging as spec is 4.6 at 230V.  I can operate at a lower charge and amps, to allow head room for hot afternoons if not using a TXV.

High pressure: 356 psi,  Low 127 psi. (low gauge reads 10 psi low at 200 psi equalized)
Temps near BPHE: liquid line 94F , suction 54.5F  (water out 56.8, wrong flow direction used to lower suction temp).

I expect the amps to climb with heat, and I'll check that this afternoon.  That would be where the TXV would help, as the increased liquid line pressure will throttle back flow, reducing amps.  Even though the superheat bulb won't do much. The unknown is if this Emerson TXV will allow the much higher flow rate I need with air to water cooling, instead of air to air, as it was designed for. A 1.5 ton unit might be needed, if so.  First I'll see how much the temperatures affect current draw this afternoon.

I'm relieved that I'm finally getting the BTU's I need, and a decent COP for an 80F morning.

Edit- Addendum of follow on testing with increased outdoor temperature.

While still in shade, and condenser fan inlet now up to 90F, (10F increase), and current climbed 0.4 amps.  I reduced the charge until 4.5Amps again, noted the low side pressure just below 100 (indication of too little charge)  and got only 8,000 BTU of cooling.  So now I see the need for a custom tailored TXV to get an optimal COP, you really need to adjust the expansion valve flow rate to control amps, not starve it for refrigerant charge.  This means I'm now too short on the cap tube for inlet air temps over 85F.

Next week I'll try to make it work with the surplus Emerson TXV.  Hopefully the Emerson unit will be sufficient; pressures rise with temperature and motor draw, and that should decrease TXV valve flow. Otherwise, I'll have to go with electronic controlled valves.  Some are quite cheap, but I've not designed or seriously researched stepper motor drives before.  I could control the expansion valve based on motor amp draw and outgoing water temperature.  The latter to intentionally limit the low water temperature to avoid condensation at the PEX manifolds.






« Last Edit: September 09, 2021, 11:43:16 PM by BruceM »

32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #148 on: September 10, 2021, 03:32:30 AM »


Or.......not enough condenser.......


Metro 6/1 turning a ST 7.5 KW gen head
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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #149 on: September 10, 2021, 04:42:24 AM »
From what I've read, refrigerant liquid temperature roughly 15F above ambient is normal for a condenser. That's what I'm getting when I check the temperature at the back of the fan compared to the high side liquid temperature, though in some conditions my inlet air temp gets 10F above ambient.   I did look for surplus condenser coils but came up empty.  I do have the original air evaporator which I could add in parallel. But that might only buy 5F.  I'm not sure it's worth it.

I wish I'd started with a bit more excess BTUs; it's easier to lose them than gain them.






« Last Edit: September 10, 2021, 04:52:50 AM by BruceM »