DIY water chiller - reading suggestions?

[BruceM]

32coupe suggested this morning that I use flare fittings at the flat plate exchanger, and that made me think again about a suitably sized, 1/2 Female BSP fitting heat exchanger I saw on ebay. 

I found some BSP thread, flare fittings and BSP bushings at McMaster.com, fairly cheap.

I ordered  1/2 female BSP brazed plate exchanger (3x8 by 40 plate) for $56. Thanks for the help, and good suggestion, Gary! 

The water side is low pressure so I can make 1/2 npt hose barbs fit the female BSP with plastic epoxy (a two part urethane) or Permatex gray gasket maker as thread sealant. As I recall, NPT male fits BSP for that size, just leaky without goop.  This is only 12 psi max. 

Thanks for the timely warning on over-sizing the evaporator, Bronco!

[32 coupe]

Those British threads.......

Do it like they do in India. Take an old rag, dip it in some green paint, wrap it around the fitting and
assemble ....presto bang oh......no leaks !!!

Sound familiar ?

White teflon paste seems to work well for me.

[BruceM]

Hey Gary, Yeah, any serious pipe goop would do on the low pressure side.  I just didn't want to frig the refrigeration fittings, re: BSP vs NPT (1/2).  No price penalty for the BSP on flare fittings, so I'm happy to do it right.  Better than drlling  brass plugs and braze in the copper tubes! 

Hopefully tomorrow I'll figure out the cause of my in -floor heat (soon to be +cool) 12V circulation pump deficiency; I'm only getting 0.8 GPM flow and it used to be over 2 GPM.  I need to correct this for the cooling or the water would get too cold.

[broncodriver99]

Agreed, just about any pipe dope will work on the water side. On the refrigerant side you will need to use a high pressure sealant rated for refrigerant use. There are several loctite formulas that work. I have always used loctite 554 or leak lock by highside chemicals.

[BruceM]

Thanks for the tip on proper refrigeration rated sealants.  I ordered some Nylog Blue which Amazon had so I can get it quickly.  My brazed plate heat exchanger should be here tomorrow, and my vacuum pump and gauges Monday.

I got the LG 12000 BTU, 230V window unit late yesterday, test ran it and took it apart this morning for reverse engineering.  It's dual capillary tubing instead of a valve for the evaporator.  There are no valves for operating as a heat pump. It is really just a cooler, when I peeked behind the evaporator coil I found a resistance heater.  That makes it a dual cool/heat unit in Korean/American marketing language.   The specs are bogus (high) on power draw, it reads 4.5 amps on my clamp on meter.  The compressor is in fact made in China.  No BTU rating on it but the model number is so I'll check the specs.

It uses a common 80W, 2 speed induction fan motor, and the wires are marked for high and low speeds. I'll only need the high.  The compressor is a  single speed 3 wire, capacitor start induction motor, not much to sort out there, just what I wanted.

I will replace their electronics with my own, with a circ pump water flow sensor and outgoing,  temperature used to turn off the compressor. 

My neighbor is very interested in this project for his (similarly constructed) home, and has offered to get a rental cylinder of nitrogen for me  so I can use it for purge, braze, pressure test. 

So far, it's looking good, with no bad surprises.

[broncodriver99]

Yep, can't beat them for simplicity. The capillary setup is what I was expecting you to find.

The more I think about this I don't see any reason you can't just un-sweat the capillary tubes from the evaporator coil and put them together into a piece of 1/4" soft copper, lightly crimp it shut around them and sweat that up. You can then just run 1/4 copper to the HX and have a flare connection there. you would end up having to do that anyway to make the connection at the HX, better off to just leave the cap tubes in place in the AC unit. That is exactly how most ductless mini split systems work, with the metering device in the outdoor unit. You will need to insulate that line well, at least 1/2" wall thickness insulation. It looks like you can also cut the suction line right before the Y joint where the two lines come from the evaporator and use that as your tie in point. As long as the copper isn't an oddball metric size you can also just have a flare connection there. That gets you down to one solder joint or two if you decide to sweat the suction line.

[32 coupe]

!

[BruceM]

Thanks, Bronco.  Gary also suggested that extending after the cap tubes is commonly done on a phone call.  I can see it if insulated well.  I got the electronics removed today. I replaced the two PCBs with just two switches for compressor and fan, adequate for testing.

Can capillary tube can be cut with a pipe cutter? My best guess otherwise is to cut it with an Exacto saw blade (super fine, tiny back saw made of stainless steel) while flowing nitrogen out that cut.

[broncodriver99]

Cap tube needs to be cut with cap tube cutters. Tubing cutters, if they can even close small enough, will collapse the tube and leave a burr inside the tube.. The inside diameter and length of the tube are specifically sized for proper refrigerant flow. You dont want to alter the inside diameter in any way. If you are trying to cut it right at the coil to avoid unsweating it that shouldn't be a big issue.

Your saw will probably work fine but I wouldn't just cut right through it, you could end up with a burr. I would cut around the entire diameter to the point that you are almost through and then snap the cap tube off. That will give you a clean cut with little to no distortion to the tube ID. You can use a fine file to do the same thing. I tend to keep some super small drill bits on the truck to clean out any burrs and just do it by hand or a pin vice can be used.

[BruceM]

I had no idea there was such a thing as capillary tube cutters until you mentioned it; thanks Bronco.

[BruceM]

I'm searching for a chart or table to size the suction line extension (6 foot ) for my 1 ton (12000 BTU). All the published tables I can find don't go that low.  The LG unit has 1/2 OD suction line leading to the stock evaporator. 

[broncodriver99]

I would stick with 1/2". 12,000 btu is right at the threshold between 3/8 and 1/2 for 410a.

[BruceM]

Thanks!  I'd love to have the reference name.  I did find a vendor chart:

https://www.hillphoenix.com/wp-content/uploads/2020/02/Gen-suction-and-liquid-line-sizing.pdf

It shows 1/2 inch for a 6 foot suction pipe for R404a, and since R410a is usually a bit smaller, it makes sense that 3/8 is on the edge for 410. 

[BruceM]

I did find a R410a refrigeration pipe size calculator that goes to 0.8 tons online:
https://efficientcomfort.net/asp/LineSetCalc_Web/LineSetCalc_Web.asp

It says 1/2 inch  even dialing down to 1 foot and 0.8 Tons, or 1 ton at 94 feet. It won't ever 3/8, so I'm suspicious.
I'll try to find some 1/2 ACR tubing in the area tomorrow. 

 

[32 coupe]

3/8 should be fine