DIY water chiller - reading suggestions?

[BruceM]

This year's fires and record heat have forced my to re-consider adding a water chiller to my in floor heat system for some modest cooling.  Since the house is only 1100SF and superinsulated, and based on tests with my neighbor's home using well water, about 12,000 BTU would just do it, and that's within my daytime PV/inverter power of 1500W at 230VAC.  I only need to pull out about 4 degrees per day, my hot day heat gain which I normally can overcome with just opening windows at night.  But not when smoky or clouds hold in the heat at night.

I've read all about refrigeration systems and understand the principles, but lack hands on experience. 

Water chillers are grossly overpriced for their BTUs, using titanium clad heat exchanger assuming corrosive, oxygenated water.  My heating system is closed loop, so that's a non-issue and so I'd like to use a tube in a tube or stainless plate type exchanger between refrigerant and the in-floor, recirculated water.  This will require new tubing on the low pressure side.

I'd love to find a book or other resource so I can learn how to estimate the amount of refrigerant required after evacuating the assembled system. I would prefer to use a non-inverter mini split outside unit, or modified evaporator window AC unit  with 3/8 pipe run of about 6 feet to the plate heat exhanger. Issues I need to learn include  when to purge after brazing,  how to calculate refrigerant charge and lubricant, how to adjust the evaporator valve for optimal efficiency.

Any suggestions for good texts or websites?

BruceM


I'm looking for the practical experimenter's guide to homebrew refrigeration, I suppose. 

[mike90045]

way over my head.

But chilling the floor, will the coolness travel up into the house ?

[BruceM]

The notion that heat only rises is erroneous.  Hold a hot pan just above your hand and feel the heat radiating downward .  Transfer is better with  lots of convective air flow, but using the floor provides so much area that it's not a problem; there is adequate room air movement to transfer heat from the room air, walls and ceiling to the cooled floor surface.

The use of in floor heat systems for cooling has been well proven.  My house is superinsulated and the house temperature is within a few degrees of the tiled, insulated slab floor.  In heating season, the floor is never actually warm except near the manifolds.  For cooling, you must use water above the dew point, and it will not dehumidify so is appropriate for my high desert climate but not for others.  New Mexico state paid for most the early research; they used unglazed night sky cooling panels to help pull heat out of commercial buildings at night.  I did experiments with night sky and evaporative cooling a few years ago.  I could never quite get water temperatures to the high 50F's, always mid 60's. You need water temperature a bit over near 15F cooler than the desired slab temp to get good transfer. 

I'm having trouble finding a 12000-15000 BTU condenser unit drawing under 1500 watts continuous without variable speed inverter drive.

 

[broncodriver99]

Bruce,

I am a Refrigeration/HVAC tech. The trade and technologies within have changed a lot in the last decade. The only book I can recommend is "Modern Refrigeration and Air Conditioning". I am not sure when it was last updated so may be a little thin on some of the inverter technologies but is very good for basic principles. I will say that most Mini Split units will have a proprietary communication protocol between the indoor and outdoor units. They usually require at least a signal from a hall effect sensor on the indoor blower motor to run and will need temp sensor data from the indoor coil as well. You may be able to figure it out having an electronics background but you will need to replicate that signal to get the unit to run. I have had a similar system planned for years but instead of cooling a slab, building an ice bank. I have most of the pieces and parts salvaged from jobs over the years.

I haven't seen a non-inverter mini split in at least 15 years and don't believe they are available unless used so you may have to use a window banger instead. As far as purging practices the best practice is to always be purging especially with the modern refrigerants and oils, they don't like ANY moisture. I use a 2 stage regulator with 2 different low pressure settings to help prevent burning through so much nitrogen. The first is a purge setting which moves a fair amount of nitrogen through the system to displace the air and then switch to a braze setting which flows just enough nitrogen to keep the air out of the system. You want to be bleeding nitrogen the whole time you are brazing and you never want to leave the system open. Always seal it up and add some nitrogen to keep it dry. As far as estimating refrigerant charge that is going to be a big task as there are a lot of variables. The simplest thing to do is install a refrigerant sight glass in the liquid line and charge to a full sight glass with a target of at least a few degrees of sub cooling of the liquid. This is all dependent on the refrigerant you use and operating conditions. The charge is calculable using pipe volumes and density data for the specific refrigerant but in the end you will end up adjusting the charge for proper operation. I would be surprised if the system you are planning is more than 1-2 lbs of refrigerant.

[BruceM]

Thanks for the very helpful post, Bronco.   I've got "Modern Refrigeration and Air Conditioning", but the 18th edition published in 2004.  It is a good one.  I'll check for a newer one.  Storing surplus summer PV power in an ice bank is a great project that I'd love to read about.

You hit the nail on the head with the inverter type issue for my application. The reverse engineering required is something that I'd rather not do, and the EMI generated by such systems is something I'd like to avoid, despite the lovely soft starting they employ.  So it looks like I'm stuck with a window unit.

Does the method of observing the dryer window for refrigerant charge assessment work for R410a? I think most new window AC units are now R410a...but I'm nof sure.  If it would work, I'd put in a dryer w/ observation window to make charging easier.  I have to research sub cooling and measurement as charge assessment.  I recall the term but not how it's done and how to interpret it.

I do remember the important use of nitrogen to avoid oxidization on the tubing interior during brazing/silver soldering.  I'll see if I can rent that from my gas/welding supplier.

I also want to thank 32coupe for his PM and speaking with me on the phone about my project.  I sure appreciate the technical support!

Bruce

PS-  here's an article on in-floor cooling for Mike.  https://www.arcticheatpumps.com/radiant-floor-cooling.html

[32 coupe]

Sight glass works on most stuff. But everything.

Dometic freezer units have a sight glass installed from the factory but they tell you
 not to charge by filling the glass.

When they are correctly charged liquid will "trickle" through the glass.

That's 134a running an expansion valve to a plate or coil at low temps.

May not be applicable to your application but good brain exercise.

[broncodriver99]

Thanks for the very helpful post, Bronco.   I've got "Modern Refrigeration and Air Conditioning", but the 18th edition published in 2004.  It is a good one.  I'll check for a newer one.  Storing surplus summer PV power in an ice bank is a great project that I'd love to read about.

You are quite welcome. Hopefully one of these days I will have time to put it all together.

You hit the nail on the head with the inverter type issue for my application. The reverse engineering required is something that I'd rather not do, and the EMI generated by such systems is something I'd like to avoid, despite the lovely soft starting they employ.  So it looks like I'm stuck with a window unit.

The EER of window units has come a long way in the last couple of years so it may not be as much of a sacrifice as you think. I think the simplicity would outweigh the gains had by an inverter, especially on a one off unit.

Does the method of observing the dryer window for refrigerant charge assessment work for R410a? I think most new window AC units are now R410a...but I'm nof sure.  If it would work, I'd put in a dryer w/ observation window to make charging easier.  I have to research sub cooling and measurement as charge assessment.  I recall the term but not how it's done and how to interpret it.

Yes, in most cases. R-410A is a Zeotropic blend but it's properties are near Azeotropic meaning it acts nearly like a single component refrigerant with almost no glide. It really depends on your metering device. If you use a TXV setup then yes, you will likely always have a full sight glass when the system is running and stabilized. If you use a capillary tube or piston device you may have flash gas sometimes depending on the operating conditions. Capillary tubes and pistons are generally a compromise of best overall performance in a range of operating conditions for the sake of ease and cost of manufacture, where a TXV will always try to adjust to the most efficient operation but is a more expensive device.

Subcooling is the difference between your calculated condensing temperature(derived from A PT chart) and the measured liquid temperature. If your condensing temperature is 100 degrees and your measured liquid temperature is 85 degrees that is 15 degrees of subcooling. Most systems shoot for 10-15 degrees of subcooling. TXVs really prefer subcooled liquid as it guarantees no flash gas which can make them hunt and get stuck in a cycle of over and under correction. A capillary or piston system is usually charged using superheat at the compressor as well as pressures and amp draw to dial in the charge. Ultimately unless you are chasing the absolutely most efficient system possible either type system will work as refrigeration will work in a very broad range of conditions and accomplish what you are looking to do. If you go the window unit route a good starting point for charge would be to calculate the refrigerant volumes for whatever tubing lengths you add to the system and then add that to the factory charge stated on the data tag and that should get you to within a couple of ounces of the proper charge.

I do remember the important use of nitrogen to avoid oxidization on the tubing interior during brazing/silver soldering.  I'll see if I can rent that from my gas/welding supplier.

I also want to thank 32coupe for his PM and speaking with me on the phone about my project.  I sure appreciate the technical support!

Bruce

PS-  here's an article on in-floor cooling for Mike.  https://www.arcticheatpumps.com/radiant-floor-cooling.html

Responses in Red

[BruceM]

Thank you, Bronco, for the clear and detailed answers.  You'd make an excellent instructor. It's a huge help.
Thanks again to 32Coupe, also.

I'll report back as I get further along.
Bruce

[32 coupe]

Check out  www.seafrost.com

Scan down the page to the spec charts.

Look at running amps, locked rotor and btu output.  The numbers are interesting.

They obviously are not "the answer" but gives you an idea in that area.

[BruceM]

Hi Gary, I downloaded the manual and the charging section is quite helpful. Thanks!

[mike90045]

..... PS-  here's an article on in-floor cooling for Mike.  https://www.arcticheatpumps.com/radiant-floor-cooling.html

thanks !

[BruceM]

I ordered a refurbished 230V wall unit, 12000 BTU by LG to use as my compressor/condenser unit.  It's R-410A as are almost all new units.  I hope to use the dryer and evaporator capillary tube/piston valve and remove the evaporator and interior fan, replacing them with a brazed flat plate heat exchanger about 5 feet from the unit.  I'm assuming I should move the capillary tube or piston valve to close to the new evaporator location, about 5-6 feet from the new condenser unit.  I'll learn more after I take the LG unit apart.

Advice wanted:
1. For home use, is a dual stage vacuum pump worth it?  Dual stage is nearly double the price, though still doable.
2. What about the acrylic HVAC rated glues for copper/brass as listed below?  They eliminate the need for nitrogen/brazing, which saves me quite a bit of $ but makes me a bit concerned about reliability.  I do have oxyacetylene for brazing. Many HVAC techs seem to skip nitrogen purge and fill for brazing but with the newer POE oils that seems hazardous in a small system like a modded 1 ton wall AC unit modded to be just a condenser unit.  I have no practical experience here, only book learning.

https://www.amazon.com/ComStar-Copper-Solder-Plastic-Container/dp/B004Y753FM/ref=sr_1_1?dchild=1&keywords=comstar+copper+lock&qid=1628299152&sr=8-1

I've used this successfully on lower pressure copper without a problem, where a torch was not practical. 
I'm skeptical about HVAC use because of pressure and vibration.  When I move the evaporator valve/capillary tube to near the plate exchanger/evaporator that joint will see R-410A high pressure.

Because the LG 12000 btu wall unit is R-410a,  I'm looking at higher pressure rated brazed heat exchangers.  I found a chart for one vendor that gives me a range of acceptable sizes specifically for R410 evaporator use.  A 30 plate Vevor 12x5 unit should not affect my low pressure/head  circ pump much, and would handle almost triple the BTUs. Overkill but a bargain.
 
https://www.vevor.com/products/5x12-brazed-30-plate-heat-exchanger-1fnpt-316l-stainless-steel-w-bracket?_pos=13&_sid=477567439&_ss=r

 I'll have to bush down the 1 inch F-NPT fittings but for the price, it's worth the hassle.  If the flow restriction is low enough, I can simplify the plumbing and avoid bypass valves for winter operation.  I'm adding a digital flow meter to my in floor system flow rate so I'll be able to see the impact is. 

I've got a reclamation tank on order and plan to use the operating compressor for high side reclamation to an evacuated tank in ice water.  This avoids the reclamation pump expense.

Thanks in advance!
Bruce M

[broncodriver99]

A dual stage vacuum pump is definitely prefered but not completely necessary. Dual stage pumps will ultimately pull a deeper vacuum and are faster. Find the ratings for the pump you are looking at and make sure it will pull down to at least 100 microns. Is there a harbor freight out your way? I broke a vacuum pump on a job a few years ago and needed one quick, grabbed a small cheap one from harbor freight and figured I would just toss it if it crapped out or have it as a backup but it has held up surprisingly well. It is definitely not near as fast as my larger and more expensive pumps but will get the job done. Should work fine on a small system like what you are working on.

I would not trust those glues at all. There is no information on chemical interaction with the refrigerant or refrigerant oil nor the pressures and temperature cycling it will experience in your water chiller system. If you want to avoid brazing you can always go the flare joint route. Just make sure you get flare nuts and fittings rated for refrigeration as they are forged and rated for higher pressure. They also eliminate the need to purge as you wouldn't be doing any brazing. You would still need some nitrogen to pressure test and for keeping the system dry until you are ready to evacuate and charge with refrigerant.

As far as techs skipping a nitrogen purge for brazing, that is just poor practice and asking for trouble in modern systems, especially a cap tube system. It is something that is in every piece of literature and recommendation associated with servicing equipment with modern refrigerants and oils. It ultimately comes down to experience with when and where a purge may not be necessary but it is best to just purge anytime one has to braze.

I would make sure that heat exchanger is rated for refrigerant. It looks like a fluid to fluid exchanger to me. Flat plate exchangers rated for refrigeration usually have fittings for either a welded or brazed attachment for the refrigerant lines. I believe the plate design may differ as well and they are usually rated for 650psi design pressure. You are better off to closely match your evaporator with your load than go with something so oversized. You may have oil return issues due to lack of refrigerant velocity and could also run the compressor a little warm as the suction gas will likely be much warmer with an oversized evap. Do you have a link to the chart showing capacities?

[32 coupe]

I agree with your assessment of the "chiller core".
Looks like water to water/oil ?

[BruceM]

I spoke with 32coupe on the phone since my last post.  Great encouragement and help for a refrigeration novice like myself.  He's sending me a care package with fittings, swage/flare tool, etc.  Amazing and much appreciated.

Bronco:
Per your suggestion I'll pass on the glue and stick to old school brazing or refrigeration pressure fittings, thanks. 

Here's the chart I found for  R410a evaporator flat plate exhanger, on pdf page 12, printed page 10.

https://www.kaori-bphe.com/uploads/editor/files/Catalogue_EN_Imperial-Unit.pdf

The recommended units for 1 ton or 12000 BTU,  R410a evaporator are 2.8 x 8"with 34 plates, or 2.8 x 12.2"  wth 20 plates.

Exhangers specifically for refrigerant I've found have small inlets on both sides, and are too small for 12000 BTU as the typical small water chiller flow rate is low and pressure loss is not an issue. 

I appreciate the warning bout oversizing the evaporator, Bronco.  I'd hate to accidentally create a slowly filling oil trap from too low flow rate.  I could tilt the exchanger unit to insure gravity oil flow to the return port if you think that's a good idea.

The price of R-410A is stunning; $79 (shipped) for a 2 lb cylinder.  Higher than R22.

I wish I could change over to propane refrigerant, but I suppose that's a no-no.  The application is ideal for propane as it's right outside the propane water heater closet, and the closet is ventilated for propane use. 

One more technical question-  how do I determine the ideal or target superheat degrees for my water evaporator/exchanger?  I can find this for typical air conditioner AC, computed using air and wet bulb temps but not for a water chiller.