heat exchanger for small chiller

I plan to build a 1 ton chiller for cooling computer equipment. I'll probably use a mixture of water, propylene glycol, and anticorrosion compounds as the coolant. It will likely be implemented as two independent 1/2 ton systems, allowing for redundancy and better capacity control. I'll probably start by building only one of the systems, but leaving enough room in the box for a second system. (Or I might make two separate chillers and make it possible to connect them together to use as one chiller.) I aim for a normal operating temperature of 20C liquid (efficiency during the summer - condenser positioned to vent heat outside) but might turn it as low as 5C during the winter (as I can recover heat from the condenser to warm the room - it doubles as a heat pump!). It will mostly cool processors using directly mounted blocks, but I'll also have a mini air handler for cooling laptops. (Note that the air handler will operate in reverse - sucking hot air from the laptops and then cooling it down before blowing it back into the room.)
Now, what's the cheapest heat exchanger (can consider heat exchangers made from copper tubing inside plastic tubing) for what I'm doing? I am thinking about copper tubing as the evaporator with plastic tubing to channel the coolant. (And note that the condenser will be a standard air-cooled type - I don't mind having to physically move the machine to switch from summer (vent heat outside) to winter (vent heat inside) operation.)
BTW, what common refrigerant makes for the cheapest heat exchanger? R134a operates at a low pressure, but requires a larger heat exchanger IIRC. R410a can use smaller heat exchangers, but operates at higher pressures requiring thicker tubing. (I'll try to stick with a common HFC if possible.)

Seems you have done already some research: R410 is indeed the best choice but don't worry abouth the pressure. These small tubes can widhstand very well the higher r410a pressures.

Star882 is a bot. It has posted in all kinds of newsgroups.

lmao ya real hard core AI bot, its so life like it even has a real life!

Star go to ebay and keep an eye out for some 1.5Ton Coax condencers, they have 5/8 water side and 3/8 sweat for refrigerant side, nice and cheap.

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Originally Posted by absrbrtek

Star882 is a bot. It has posted in all kinds of newsgroups.

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Maybe star has a photo of that cute girl and 'his' LG heat pump clothes dryer