new 12000btu 3.2 kw chiller unit as a school project - Page 2

A couple options for raising head pressure during cold ambient would be, installing a head pressure control valve(Headmaster) and or a fan cycling pressure switch. The Headmasters can be quite expensive, you should at least add the fan cycling switch. I recommend a switch adjustable from 100-400psi with 40-150psi pressure differential. Look for Ranco or Danfoss.

The high pressure cutoff for your application with r410a can be 350-400psi. Use a manual reset type.

You don't need a huge receiver.. 30mm x 300mm is fine. If copper costs too much then use a steel pipe rated for the pressure.

A 50 plate hx is fine. Oil won't be a problem in the -30c range. If going lower then add a small amount of propane to facilitate oil return. You can go ahead and add it either way.. the small amount won't hurt anything. Just pre-charge to 40psi with propane "gas".. the rest r410a liquid.

Note.. you'll need to run a methanol blend for the coolant when operating that low in temp. You can run a non-flammable mix up to around -30c.. after that it needs more methanol to keep from slushing/freezing. Iwaki or Little Giant pumps can handle the fluid and temps perfectly fine. I use Prestone De-Icer washer fluid to -30c. PEAK is another good brand.

I wouldn't allow pressure that high Drew unless hes using a retail receiver rated for that pressure. 300 to 350 psi is adequate for his needs and shouldn't be an issue for his homemade receiver.

Just my 2 cents...

@SD...The main reason I suggested a 350-400psi cutoff is because all the r410a systems I've worked on had discharge pressures well above 300psi. If CS can keep discharge pressure below that then all the better. Maybe use an adjustable cutoff switch and start at 300psi .. increase if needed.

I did take into consideration the smaller diameter tubing of 30mm/1.125". The working pressure for 30mm drawn copper is close to 900psi... annealed from brazing process is still well over 500psi.. burst pressure will be many times that. The end caps of course are the weakest link.. but at approx 1in² the force applied is still only 350-400psi. The problem is when ppl start to use much larger diameter tubing and improper end caps. I always keep the receivers thin(1.125"OD) and tall... if they need to be short then I'd use a retail unit.

CS.. that's great you already have a frequency drive there. Hopefully it will have quick enough response time during starts. The slightly higher hpco might be needed in this situation. A fan cycle switch can still be incorporated as a backup to prevent excessive pressure spikes.

You won't have any problems feeding the 50 plate hx bottom to top at -30c. Obviously the system will be capable of temps below that so I highly recommend the shot of r290(propane) regardless. Keep the suction line 3/8"/9.5mm and incorporate a nice size "u" bend to help meter off excess liquid. If you only need occasional sub -40c use for like pc benching then I wouldn't worry about an oil separator. Just cycle the compressor with pump off every few hours and the velocity/elevated temps will carry the oil back to the compressor.

Maybe start at 300 to 350 psi and if its not tripping on a regular basis then great otherwise adjust it up to 400 - 450...

No biggie either way..

Nice metal work there CS! Do you have a shear and brake?

That's too bad about the 3 phase controller. We have opposite situation at my work.. we now need 3 phase controllers and have a bunch of single collecting dust.

The braze joint looks ok.. just a bit lumpy. Just so you got some to flow down into the joint. It's all about preparation and heat control.. a good quality filler rod helps too.

No fan shroud for the condenser? The fan bracket screws are nutted I hope.

Are you going to add a reservoir?

If you're adding a solenoid valve then make sure to position hpco after the condenser.

You can clean the Danfoss out with mineral spirits too if you like... just make sure it all drains out and evaporates.

Any propane will do... I use Coleman camping fuel or Bernzomatic for torch.

Is the 24/7 chiller for pc then?

Heh very nice work there. I just ordered a pan break and shear for the holidays, so excited.

looks large enough for two compressors a 20 plate hx and an oil sep...
hmmm