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Author Topic: DIY water chiller - reading suggestions?  (Read 3154 times)

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #120 on: August 31, 2021, 03:55:52 AM »
I haven't seen the slightest change in suction side temperature at the HE regardless of pressure differential (flow).  It seems completely fixed to inlet water temperature of the HE. 

That makes me question the TXV regulation for my HE setup since bulb temperature is the primary control, and will be stuck at around 70F, calling for full open and never changing.  I don't see how that can work very well.  It's still an adjustable orifice but that's about it.  I suppose the pressure feedback would do a little benefit.

In some cap tube charts I was shocked that a 10 degree increase in evap temperature results in a 20% change in same size tube length.   I was looking at a chart from Tecumseh, where medium and high temperature columns used the same size tube. I have a few articles to read through still; I'm not ready to cut tubes yet.

Today I ordered a used 8000 BTU R410 compressor on ebay for $60 to use as refrigerant recovery pump.  I have the terrible feeling I may be getting very good at it, if I have to sneak up on the right cap tube length.

Thanks for your help and patience!

Bruce








32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #121 on: August 31, 2021, 05:21:02 AM »
I'll make some calls today to see if I can get some info.









« Last Edit: August 31, 2021, 12:25:43 PM by 32 coupe »
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32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #122 on: August 31, 2021, 05:53:08 AM »

Bruce,
If you do decide you want service valves I think I have some of the brass ones here.
They used to be brass but a few years ago they went to steel. (Works really well in the
boat environment.  Not !)

If you like I can look tomorrow and see what I have. I know I have a few new ones.


Metro 6/1 turning a ST 7.5 KW gen head
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Ashwamegh 2/25
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New Holland TC 30

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32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #123 on: August 31, 2021, 12:35:40 PM »
I think your readings are off.
You said you got the best performance when your suction pressure was 125 give
or take....that means your SST is about 40......BUT you said your water temp
is 74 and the SST follows the water temp.....something doesn't add up....
Or I just don't understand .....

Metro 6/1 turning a ST 7.5 KW gen head
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32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #124 on: August 31, 2021, 02:14:56 PM »
Bruce,
I spoke with 3 design engineers this morning.
I will try to call you later today.

Gary

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
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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #125 on: September 01, 2021, 03:51:29 AM »
True confession:
I got my wires crossed on the full load rated amps for my 230V LG window AC unit; it's 4.61 amps total at 230V, not 5.8! That's the amps for my well pump.  I slipped a cog.  So I have to re-test and see what's up exactly at that max amps.  I'm pretty pissed at myself for this serious screw up. 

At 4.6 amp draw, and a lower refrigerant charge to go with it, I think I'm in the sweet spot for pressures, just not getting the BTU's I should.   I'll have to retest carefully, but I expect only half the cooling I need.

I realized the stock cap tube should be fine even with my BPHE as it's sized for compressor hp, so then thought to double check the figure I "knew", which is the amps for my well pump, not the window AC unit. 

I hope I'll be able to incompetently bumble my way through this, but I really need a minimum of 10 degrees of water chilling at 2 GPM for it to work. That's 10,000 BTU.

32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #126 on: September 04, 2021, 10:53:53 PM »


Bruce,
You making any progress ?


Metro 6/1 turning a ST 7.5 KW gen head
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Ashwamegh 2/25
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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #127 on: September 05, 2021, 05:02:14 PM »
Hey Gary,
I overdid on a volunteer project and have had to lay low.  My health is pretty shaky.

While waiting for parts and supplies, I've been trying to get up to speed on the relationship between pressures, temperatures, and refrigerant flow rate, and efficiency.  I've come a long way, though my memory problems makes it a challenge.  COP or efficiency is a matter of keeping superheat close to the safe minimums. I must achieve a lower superheat and lower suction side temperature (60-65F max) in order to have the COP I need (to get 10K BTU's out of the water with 4.61A current)  plus keep the compressor cool. 

It's still unclear if just increasing refrigerant flow alone will result in low enough suction vapor temperature for compressor cooling, and for a low enough superheat to get a decent COP.

Swep is a company that makes brazed plate heat exchangers.  They have some very helpful design articles.

This is a a good summary that relates well to my situation of too restrictive (stock) capillary tube, poor performance at rated power (my added italics):

"When a SWEP BPHE is used as an evaporator, a secondary gas or liquid is cooled as it loses heat to the refrigerant. The refrigerant boils and is converted into a gas, absorbing more energy. A SWEP evaporator provides a good, stable boiling process with a small temperature difference between the refrigerant and the secondary fluid. A low temperature difference means that a higher evaporation temperature is possible, which corresponds to a higher pressure. Reducing the pressure difference between the low-pressure side (evaporator) and the high-pressure side (condenser) will reduce the energy use in the compressor. The higher evaporation pressure will also increase the density of the refrigerant gas. For each stroke, the compressor will therefore transport more refrigerant through the system. Lower electricity consumption and higher refrigeration capacity will increase the total system efficiency (COP). "

They also have a good article on capillary and TXV valves.  Alas, they don't specifically address my water temperature being so high.  Another problem with high water temperatures is that the suction side vapor temperature is above the normal 60-65F maximum temperature for cooling the compressor.  The return vapor is run inside the housing for pump cooling, and is the primary means of pump cooling.

I did think of a plumbing cheat that might be useful;  by adding a bypass valve on the water to and from the BPHE/evaporator, this would allow the BPHE water (and suction side) temperature to be lower, while keeping the temperature going to house  above 58F (to avoid manifold condensation and mold).  This might allow the use of a standard TXV and operate at lower (high side) pressure.  The normal TXV line pressure and temperature balance will be outside the normal design range otherwise.  This also gets suction temperature below the 60-65F that is specified to provide compressor cooling.  Right now, if water temp is 78F, so is the suction side, and that's BAD news for the pump temperature and life.  This could also be helpful for a capillary tube expansion valve, in that it allows for the return vapor temperature to be within specs for compressor cooling.  One  issue with this water bypass method is that water flow may have to be changed to the same direction of flow as the refrigerant to lower suction vapor temperature.  Right now, suction temp tracks inlet water temp...too high!

I found that there are no manual/hand expansion valves rated for R410a pressures. They were used and are still being made for R22 level pressures.

I did find a teflon packing, high pressure needle valve that could be used in addition to an intentionally short cap tube to make up an R410a rated manual adjustable expansion valve.  Most high pressure needle valves use viton o-rings/seals and refrigerants eat Viton.  EPDM is fine, but they don't seem to use that.

Today's project is to build my reclamation pump with the used R410a compressor and filter/dryer.  I'll still use ice water in a bucket around the reclamation tank.


« Last Edit: September 05, 2021, 05:40:07 PM by BruceM »

32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #128 on: September 05, 2021, 07:10:10 PM »
Bruce,
I personally would not play with the "manual valve". I don't think you would ever be able to get it right.
The tolerances are just too small plus you don't have a known starting point. Would be easy to flood the
compressor with excess refrigerant.

Also RLA is usually the maximum.  Most units will run well under that number. With that 4.6 number I
would be looking at around 4 amps more or less. As an example I am running a small water circulation
pump on my Ashwamegh.  Today I got it running and with a load and 3' of head it is drawing .27 amps.
RLA is listed at .35......Most of those small compressors I'm around run under. When they get close to
listed RLA I am looking to see if there are other problems.

As usual take I what I say with a grain of salt !

Gary

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 #129 on: September 06, 2021, 01:02:40 AM »
Put together the recovery pump and fittings. capacitor, switch and cord.  Simple enough, runs, not bad for $60.

I decided to test the recovery pump.  It worked nicely, only a few minutes to pull out 1.5 lbs of refrigerant into a tank in a bucket of ice, and pull a soft vacuum. I then put in a couple psi of nitrogen so when I cut the lines it wouldn't be sucking in air.

I ordered  the Emerson 1 Ton R410a TXV with bleed that Bronco found for me at SurplusCityLiquidators.com.  If I can get the suction temp down to where it will operate, it could help improve performance in a wider range of ambient temperatures.  It's well worth trying.  The equalize line is a PITA, but can't be helped.

For education, I want to  try a shortened cap tube first.  On JB Industries cap tube reference chart, page 4, is the dual tube, R410a, 1.5 HP unit like mine.  They show dual 34 inch. 0.049 ID tubes.  I"ll check the OD and length of mine when I cut it out tonight to check that it matches. That's for AC use with a temperature of 45 degrees.   The next colder entry is 25F (refrigerator), and is 44 inches. So about 10 inches for 25 degrees colder.  Going warmer SST by 20 degrees (65F when incoming water is 75F) should be 8 inches shorter if it stays fairly linear.  So I might shorten it 6 inches and see how it performs as I sneak up on the proper charge. 

The sun and reflected heat problem in the afternoon at the present location is BAD news, and the low volume fan is a problem for mixing output and input air when the wind is from the north, which isn't uncommon in the summer.












BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #130 on: September 06, 2021, 04:04:53 AM »
My dual capillary tube was originally 63.5 inches.  Close to 0.046" ID.   It's now 62 inches.

Alas, 60 inches is the minimum distance for linear response to length and less than that, it acts more like an orifice, so small changes can make a bigger difference in flow.  The JBind.com R410 dual tube data shows:

3/4 hp line (106 to 70" 34% shorter, for  25F to 45F entries
1 hp line goes from 83" to 42" - 50% (!) shorter, from 25 to 45F respectively. This DOES NOT FIT!
1.5 hp line (44" to 34"- very short and thus quite non linear) only changes 25%.

A variation between 25% and 50% shorter for 25F warmer is not very helpful.  I see the same range of variation in other refrigerants and in single tube charts, when looking for entries around 62 inches, going shorter.

Not helpful. Every little detail is an educational project.





BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #131 on: September 06, 2021, 05:33:20 PM »
https://icemeister.net/backroom/wp-content/uploads/2015/04/AndySchoen_A-Modern-Method-of-Properly-Sizing-Capillary-Tubes.pdf

Tecumseh has some data here on non-R410a refrigerants, showing a consistent 28-29% shortening of tubes in the 60 to 72 inch length range going from 25 to 45F evaporator temp.   Less for shorter, more for longer.  So at least consistent with the theory of optimum length 5 to 10 feet and with reason, unlike some of the JBind data.

I'd like to see a 15 degree reduction instead of 20F in evaporator suction side temperature (SST), so will shoot for 21% reduction, but because of my shorter length, perhaps 18%.  So 11 inches shorter. 


BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #132 on: September 06, 2021, 08:08:13 PM »
Cap tube shortened  by 11 inches, reinstalled, pressure test and purge with nitrogen. Now pulling a vacuum for a few hours before recharging.  I'm getting a bit better at standard procedures.

One finding of note:  The BPHE has become an oil reservoir, exactly as Bronco suggested, with flow from the bottom.  When I removed that fitting, oil was dripping out. I quickly capped it, but I should probably add POE oil to compensate, or perhaps reorient the BPHE for the less efficient, less reliable refrigerant entry at the top with lines sloped downward to the compressor. 








BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #133 on: September 06, 2021, 11:14:19 PM »
Baffling findings. 

Limiting charge to 4.6 amps, I get only 1.3KBTU of cooling.
High pressure:290 psi
Suction: 47 psi
Water in: 75F
Water out: 73.7F
Suction temperature: 75F, so a rediculously high superheat, and thus pathetic BTUs.

This lowering of suction pressure is the opposite of what was supposed to happen according to my reference.
https://lando-chillers.com/the-effect-of-capillary-tube-length-on-the-performance-of-refrigeration-system/












32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #134 on: September 06, 2021, 11:58:51 PM »
I don't know what's going on but do know the suction pressure is way too low.

Are the cap tubes freezing as before ?

Are you sure your amp meter is correct ?

If you add more gas does the amp reading rise excessively ?

???????

« Last Edit: September 07, 2021, 01:07:55 AM 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 !"