Author Topic: DIY water chiller - reading suggestions?  (Read 8268 times)

mikenash

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Re: DIY water chiller - reading suggestions?
« Reply #75 on: August 28, 2021, 08:05:25 AM »
Hey Bruce I was reading what you were saying about threads and sealing issues.  Are you comfortable that your fittings do have the threads you think they do?  I don't know if it's the same over there - but here there is often confusion, especially in hydraulic or pressure systems, with JIC threads being mistaken for NPT

Similar threads but different sealing systems. If you wanted to google JIC (Joint Industry Council so another SAE thread) I'm sure there'd be endless detail online

Sounds like a fascinating project.  Well done

broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #76 on: August 28, 2021, 01:31:54 PM »
Sorry I have been absent on this Bruce. Been pulling 16 hour days keeping up with the heat and working on a chiller repair.

From the calcs I ran with your existing temp differential and flow looks like you are doing about 6500 BTU of sensible work. With a chiller since there really isn't any calculable latent work being done in your setup I will just stick to sensible loads. That window unit is specified at 12,000 btu total load and I would guess at least 15% of that would be latent heat so it won't surprise me if at best you get around 10,000 BTU out of it. That should still get you right at your target of a 10 degree TD. 

With the evap temperatures you are running I would expect to see a higher suction pressure and you are bouncing right against the upper limit of where I would feel comfortable on discharge pressure. I would try to stay below 120 degrees condensing temp on the discharge. Can you monitor your liquid line temperature a few inches from the condenser outlet? That will give you an idea of how much subcooling you are doing. That will help give a better idea of how long the liquid is spending in the condenser for troubleshooting.

I think you are going to find that the cap tube is limiting your refrigerant flow as I would expect a lower differential between suction and discharge on a 90 degree day. That unit does have some constrains as far a condenser size though. Just for troubleshooting sake before you get too far with the refrigerant charge could you throttle the water flow to 1.5 gal/min and see what it does to all of your measurements after giving it 5-10 mins to settle out? I think that may help with your superheat at the compressor but will also be a good set of data points for comparison to 2GPM.

I do think you are still a little shy on refrigerant but I think the cap tube is going to limit you. You will likely end up having to find a happy medium between TD and flow rate to control your head pressure which is ok. Any idea how much refrigerant you have in so far?

Here is part of the chiller setup I am working on.  ;D New evaporative condenser and storage tank. Should be done in about 2 weeks.

« Last Edit: August 28, 2021, 01:34:30 PM by broncodriver99 »

BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #77 on: August 28, 2021, 03:36:42 PM »
Hey Mike.  I'm quite suspicious that the McMaster.com 1/2 BSP male to 1/4 NPT female bushings I got are the wrong parts, or that the female threads on my brazed plate exchanger were out of spec for BSP.  It was the BSP to BSP that were not a proper snug fit. No problem on the NPT side fitting the flare connectors. 

Fun to see that monster of a chiller, Bronco, and I appreciate your thoughts.  I'd love to be able to adjust the evaporator refrigerant flow restriction to see how that affects water chilling BTU performance; something like a high pressure needle valve, but I've not found such a beast. Capillary tube shortening is doable but I'd need a reclamation pump and would need to add a flare coupler.  A lot of time and work for each iteration... not ideal for experimentation.

Multiple rain showers through the night, and heavy cloud cover  this AM so I'll just have to wait and see.  Cool temperature performance is not very helpful when the intended use is for days in the high 90's F during our wildfire season in June and July.






32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #78 on: August 28, 2021, 04:00:35 PM »
Hey Bruce,
Could you slow water down with one of your swing  valves ?

In a perfect world an expansion valve on the liquid line at the HX would be the way to go.
Then you could adjust the superheat at the expansion valve.
When I went to the supply house the other day I priced one, about $180.00.....
They will build them in house with Sporlan parts.
I looked online and they are alot less but I'm not positive which one would be best for you.

With that said I would try to slow the water flow.......

Gary



Everyone seems to be in agreement that the head pressure is close to its upper limit.
Like I said when we talked the company that builds systems locally runs them harder than
that but I've never liked that but hey what do Iknow ??? He will run them around 450 but at
point the compressor will draw max RLA......in an ideal world the  RLA should be under tag specs
for RLA.

I wouldn't run the head over 425 and at that point I would keep a close eye on amp draw........



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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #79 on: August 28, 2021, 05:57:10 PM »
Hey Gary,
Yes, easy to slow the flow by existing ball valve restriction, though I don't see the value in doing so; the temperature is suitable if a few degrees high, I'm just lacking BTU performance I was shooting for.

I'm presently seeing only 4.8 amps or 1104 watts. 
This unit is rated for about 5.8 amps/1350 watts.

So by increasing refrigerant or increasing refrigerant flow at the evaporator, I hope to increase the amps and squeeze some more BTU out of it.

I'm not sure about TXV type valves (regulating evaporator refrigerant flow based on evaporator pressure and outlet temperature) for water chillers.  Maybe Bronco can tell us if they are commonly used in that case, and what the temperature of the evaporator outlet of a chiller might be for an R410a system???  One problem being I think most chillers would be shooting for much colder water temperatures than I am.   60F water at the house manifolds is about as low as I'd dare go, so a few degrees below that (57F) coming out of the BPHE would be the lower limit, and anything up to 72F is OK.

A TXV valve might be a good, if spendy, solution.  I did find small hydraulic needle valves but I think buna-n seals are a bust for refrigerants.









 








32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #80 on: August 28, 2021, 06:28:46 PM »
Yes, txv valves are on the ones I see. The thing is they have a bulb that goes on the suction side
and the txv will "adjust" the charge as its running to keep the suction side "cold line" where it needs
to be. That is why with a txv you adjust the charge by subcooling rather than superheat. (I think I got
that correct) Yes, most are 410 units. And the txv valves are adjustable.

I don't think the "needle valve" is a good idea.  Don't think you could ever get it right. You are probibly
talking about an adjustment of a few thousands of an inch to swing one way or the other.

You amp measurements.....is that the compressor alone ?

I would try playing with the charge just a little to see how close you can get the suction to
where you want it without running the head and amps too high.

On an air unit I always look for coil saturation.  On a chiller you only have the td across the
core to go by. (Plate in your case)

And yes slowing the water flow will change your readings. More heat loss.

Maybe try slowing the water first to see how much the guage readings change.......



« Last Edit: August 28, 2021, 06:44:25 PM by 32 coupe »
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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #81 on: August 28, 2021, 07:06:14 PM »
I didn't realize that the TXV's were adjustable.  That makes them very appealing for getting the best performance.
Much more appealing than diddling about hacking cap tubes.  I agree, a needle valve is really not very practical.

I'm waiting for it to warm and clear up;  there's still lots of clouds.  It's only 82F at 11AM.

My floor is 72.9 degrees this morning,  room air temp is 74.1, so only 1.2 degrees between floor and room air  (head high) with 24 hrs to equalize. 

32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #82 on: August 28, 2021, 07:56:13 PM »
You have many avenues to go with.......

For simplicity sake play with the water flow first....see what that does.....

Then play with the charge ..........it's a small system.....I have seen where when
they are as close as you are an ounce or two of refrigerant will chance things
considerably.

After all that go to the txv.........the nice about that is that with the txv you could
probibly get the head pressure in the 300 to 325 psi range......the compressor is
not heavily loaded and running much cooler and you are still getting coil saturation.

With said......I only remember adjusting a txv a time or two. They work great right
out of the box....they allow much more leeway on the charge parameters,  the txv does
the job !

The txv comes in flair or weld fittings. I have done both but recommended the flair type
simply because you keep the heat away from it.

They also have a bleeder type . It's the way to go.....if you look at txv's you will see them and what
they do

I would think any 12k btu txv for 410 would do the job..

Over and out !
« Last Edit: August 28, 2021, 08:06:03 PM by 32 coupe »
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mobile_bob

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Re: DIY water chiller - reading suggestions?
« Reply #83 on: August 28, 2021, 09:54:35 PM »
just asking because i want to learn too

does txv = expansion vavle?

is it basically what is or was used on automotive systems?

we used expansion valves back in the r-12 days, (no idea what is used today, i got out of the automotive a/c business after r-12 went out) and some of them were adjustable.

my belief, right or wrong, was the capillary tubes were simply a move to reduce costs, as they worked and reduced the need for a more expensive expansion valve.

also is there a reason to run such high head pressures?  a benefit to the system?

i mentioned the reduction in water flow in order to get more time to remove the heat from the water flowing through the heat exchanger, rather than running higher pressures.

intuitively it would seem to me that if i could get better heat rejection by adjusting the water flow, and reduce the head pressure, the compressor wouldn't have to work as hard?  but then again maybe i am way off base, maybe there is a need for having more refrigerant in the system and running higher pressures?

if such a system could accomplish the goals set out, and run with a partial charge, with pressures like 40psi on the low side and 150 psi on the high side on a hot day, i would be tickled.

does it have to do with needing enough charge or refrigerant in the system to return the lube oil to the compressor?

there is a lot for me to learn, and i am very interested in this project! so hopefully you guys don't mind me asking a few questions along the way.

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

32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #84 on: August 28, 2021, 10:33:07 PM »
Hey Bob,
Yes, txv = expansion valve

Yes, older cars had txv's and the cap tube does a similar job for less money.
I don't remember the older systems much but as I said in an earlier post the
txv's I'm around today are adjustable and with that you have a broad range of
settings to play with. With the cap tube you got what you got.

Yes, adjusting water flow will make a definite difference in system performance.

The difference in pressures is because of the types of freon. 410 runs at much higher
pressures than 12 or 22.

Don't know if any of this helps . And I'm the first to admit that I don't know much.

At lot of variables at play here.
 
If I had to guess in this case I would think a restriction in the system  High head , low suction.
Only the cap tube could do that........cap tube too small or too long . I am not a designer so
can't help with that.

Gary



« Last Edit: August 28, 2021, 11:21:30 PM by 32 coupe »
Metro 6/1 turning a ST 7.5 KW gen head
Changfa 1115 turning a ST 15 KW gen head
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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #85 on: August 28, 2021, 11:59:11 PM »
Not very hot and highly variable sun today but I did some experimenting anyway.
84F with occasional 90F during sunny stretches.

I managed to get 11.1 degrees of water cooling at 2 GPM, so my performance goal is now met, though the high pressure is a bit higher than I'd like when a get a sunny stretch.

I started with low pressures, both high and low side, and crappy performance.  As I kept adding in refrigerant in sub ounce increments, pressures slowly rose and so did water cooling performance.  It never stopped doing so but it took a long time to see the water temperature drop further, but it did, after some minutes.

Pressure on the high side is now above where I'd like to be when the sun comes out and it gets hotter.  I think this indicates that I should get a TXV valve, or shorten the capillary tube (which I'm less interested in), so pressure could be lower.

Here's the data:

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 (full specified running amps for compressor and fan) 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

One thing I noticed is no more frost on the capillary tube. A little sweating but that's it.  At the higher pressure it's no longer flashing in the tube. A good thing; the flashing is happening inside the BPHE where it should be. 

I can see the value of a TXV for lower pressures and better efficiency and will look into sourcing one, but I'm in no hurry now as I have met the goal and can afford to remove a little R410a to get the high pressure down 10 lbs without screwing up performance much.  I stopped adding tiny burps of liquid when the time to see improvement took minutes, and improvements were diminishing.  I need to do some more measurements on cooling the house.  I ran out of sun before I could start that process; I want to monitor incoming and outgoing water temps plus slab temp over about 4-5 hrs of running (my intended use, to use my sunny day PV surplus). 

I'm very happy with performance as it is, but would be glad for advice regarding my high side pressure.  When the temperature rises, it's a bit much by my references.  But it really does work best like this.

Suggested online sources for TXV's would also be appreciated.

Best Wishes,
Bruce









« Last Edit: August 29, 2021, 12:03:03 AM by BruceM »

broncodriver99

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Re: DIY water chiller - reading suggestions?
« Reply #86 on: August 29, 2021, 12:35:57 AM »
It definitely looks like the cap tube is limiting you. But, my math shows you in the neighborhood of 11,100 BTU of heat removal which isn't bad at all. I definitely don't like that head pressure but with the small condenser in the window unit it isn't terribly surprising. That chiller is taking a lot of load right now. Maybe run it for a couple of hours and see where it settles out. I would bet your temps come down some more and as the slab cools a little your head pressure will as well. I would probably shoot for about 10 degrees of subcooling and a 10 degree td on the liquid side but that would be when the slab is down to operating conditions. You can control the load on the chiller by adjusting your water flow. Maybr try it just to see what it does with your head pressure.

32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #87 on: August 29, 2021, 12:36:51 AM »
My local builder would be happy with that.

Amazing isn't it ?  Those small systems are touchy......doesn't take much.
 
Shade on the condenser will make a BIG difference . In Florida as much as a 20 degree difference.
Hard to believe but I have proved it many times.

You might try letting out a tiny amount of gas. You may get the TD closer to 10 degrees
and relieve some of the head pressure.

Considering what you are working with I think you are about as close as you are going to get.
Try to get better more accurate amp readings on the compressor alone. This will be your most
critical thing to watch at this point.

And yes as the load (slab) temp drops so will the temps and pressure in the system.


And........GOOD JOB !!!!!+



« Last Edit: August 29, 2021, 12:39:38 AM by 32 coupe »
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BruceM

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Re: DIY water chiller - reading suggestions?
« Reply #88 on: August 29, 2021, 01:50:37 AM »
I had a celebratory tequila and water on ice for spending so much time near running motors but getting the job done. So now I'm a bit goofy.

I think my location for the condenser unit sucks- I see a big rise in air temp when the sun's heat is reflected off the shop and garden shed walls.  Good protection from hail, but I'd be better moving it further from the building.  And perhaps adding both shade and evaporative cooling! 

The existing fan has a circular rim designed to spin condensate from the base pan up into the condenser.  Normally the evaporator would provide that distilled water. No rain water here in June or the previous months, so hard to supply soft water for such a process, though is could be done.

I don't want to reduce the water flow rate water as the chilled water temps must remain above the condensation point, which would cause mold issues at the manifolds. Today's temps were about as low as I can go.  Normally, this approach is only for supplemental cooling, because of that limitation.

I've got quite a bit of addition work to do for control electronics, and power to the unit (just an extension cord jury rigged for 230V now), and line protection.  But it sure is great for morale to see water chilling at planned levels.  The return water temps today are the lowest I would use cooling for.  Normally opening windows at night suffices and the superinsulation plus slab and wall/tile mass lets me ride through the next summer day.  I only need cooling for smoke events where I can't open up at night.

For my intended use period, evap cooling could be VERY helpful; 20 degree air temp reduction is common in June as humidity is perhaps 7% during the day when I'd be running the cooler on PV power.  So perhaps I need to move the the cooler, put a shade cover over it and think evap cooler pads in the air inlet fed by my well water. 

I was surprised that the air volume through the condenser is not very high.  It's just a  bladed fan, not a squirrel cage blower as was used on the evaporator side.  From what I saw today on high pressure PSI variation with temperature, there is a lot to be gained from lowering temperature.  Pity I can't run it at night, when air temps are reliably 65F ! Then I'd have to add a pump to INCREASE water flow rate.






32 coupe

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Re: DIY water chiller - reading suggestions?
« Reply #89 on: August 29, 2021, 02:16:35 AM »

Bruce,
I am so happy to see it work for you.

I went back and looked at your numbers and I do believe you are just a little over charged.

I try to run the suction side on most 410 units just under 125 psi and the guage evap temp
around 38 to 42.......on a 80 + degree day . I wasn't sure what the numbers would be because
of the build changes you made but they look like what I see in the field on air to air and water
to air units.

Funny how some things get lost in translation.......if we knew the cap tubes were frosting it
would have been a direct sign of low charge.......but hey, you know now !!

I think I'll have Knob Creek Whisky Sour to celebrate for you .

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