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Messages - BruceM

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31
Everything else / Re: DIY water chiller - reading suggestions?
« 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.

32
Everything else / Re: DIY water chiller - reading suggestions?
« 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. 


33
Everything else / Re: DIY water chiller - reading suggestions?
« 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!


34
Everything else / Re: DIY water chiller - reading suggestions?
« 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.










35
Everything else / Re: DIY water chiller - reading suggestions?
« 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/












36
Everything else / Re: DIY water chiller - reading suggestions?
« 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. 








37
Everything else / Re: DIY water chiller - reading suggestions?
« 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. 


38
Everything else / Re: DIY water chiller - reading suggestions?
« 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.





39
Everything else / Re: DIY water chiller - reading suggestions?
« 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.












40
Everything else / Re: DIY water chiller - reading suggestions?
« 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.



41
Everything else / Re: DIY water chiller - reading suggestions?
« 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.

42
Everything else / Re: DIY water chiller - reading suggestions?
« 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








43
Everything else / Re: DIY water chiller - reading suggestions?
« 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.















44
Everything else / Re: DIY water chiller - reading suggestions?
« 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. 

 









45
Everything else / Re: DIY water chiller - reading suggestions?
« 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.






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