1/2+ hp Single Stage Build

[Obijuan83]

After my first attemp on phase change cooling its time for something bigger.

So I ordered an Embraco-Aspera Refrigerator Unit



It cost me 135 Euros + VAT.

NEK2150GK 1/2+ hp
Condenser (3/4 hp)
Fan 250mm 16w
Receiver-Drier
Steel Base

I will add

Sight Glass
Desuperheatercoil
Low/High pressure Gauses
Low/High filling/service ports
Accumulator

[Obijuan83]

My question is the lenght of captube.

I want 250W-300W load capacity

I will use 0.031'' cap tube

How many feets of captube will I have to use?

I will try 8.5' of 0.031 captube, sounds ok?

[Charles Wirth]

Really nice condensing unit, guesstimating cap tube length... I don't use cap tube so my guess would be wrong.

[Obijuan83]

What do you use TXV?

More photos adding gauges and valves.

[Obijuan83]

Little progress, suction remaining...

[Charles Wirth]

Interesting with the gauges on the high and low side.

I use Sporlan txv on the first stage, my second and third stage are also Sporlan.

[aenigma]

Beautiful condensing unit and that's a very interesting "receiver" that I assume you added? Using capillary tube you don't want a receiver, you want it to exit at the very bottom of the condenser and have very minimal climb after the outlet since you're dealing with liquid there. Liquid doesn't climb very well. With that receiver setup you will have a harder time adjusting the charge with cap tube since you are fighting gravity, but it would be pretty good with a TXV since it adds a decent amount of volume in the liquid line.

If you're going with cap tube then it's all trial and error, so start with more than you think you need and keep adjusting. I see you have a king valve which is good. Hard to see from the pictures where it goes but I am assuming it's on the high side liquid line after the receiver? If so then that is great since you can close it to pump down to about 0psi low side in order to adjust cap tube length and re-braze without losing any gas. Just make sure to vacuum the low side afterwards so you don't have any air in the system.

Your condensing unit is perfect for easy trial and error cap tube adjustment if it weren't for the liquid line receiver/sight glass. Either go with a TXV or get rid of that "receiver" piping and sight glass and don't let it fight gravity.

[Obijuan83]

Thanks for the comments.

The purpose of the coil before the filter is to act as a heat exchanger when I want it. I mean, I will use another single stage with a coil as evaporator (the coil of the second unit will be bigger diameter of the first coil and both of them will be inside a can full of coolant).

Do you think it will have effect(not as cascade but better temps and load?)

[Obijuan83]

I found an excellent software that can estimate the cap tube lenght and diameter if you give parameters as compressor model, condensisng temp, superheat and subcooling.

Do you think I' ve set right parameters?

[aenigma]

Oh I see, a same refrigerant cascade. I've made them before and they do get much colder, although I can't comment on how well it will handle a load with such low head pressures since I never really tried it with a load. As for the cap tube tool I haven't had any luck with them before and that seems to be recommending quite a small length of cap tube. I prefer using the whole roll of cap tube and then making adjustments after getting it charged and testing it.

Having valves to isolate the suction line and liquid line makes making those adjustments very easy since you don't have to reclaim the refrigerant, just put the system into pump down until the lines before and after the cap tube are at about 0psi, cut a bit of cap tube if it's too long then vacuum that line and open your valves and test the system again. It's a little extra work installing the valves, but it's well worth it.

[kayl]

been a while since i have been in the game dont know what sort of wattage you need to hold these days, maybe start around 3.3m 0.031" to cut down, think 2.7m will be high capacity but it too high your compressor will freeze over at the suction port at idle.

[aenigma]

been a while since i have been in the game dont know what sort of wattage you need to hold these days, maybe start around 3.3m 0.031" to cut down, think 2.7m will be high capacity but it too high your compressor will freeze over at the suction port at idle.

Same here kayl, that's why I say start long then cut down. Beats cutting too short then having nothing to work with afterwards. Nice to see you around again! Seeing your -100C Club Member name makes me think I should have actually made some threads on my systems 20ish years ago instead of only posting to help haha

[Obijuan83]

Finally up and running.

2.7m captube lenght.
Remove the desuperheater-coil



These are working temperatures.The low side gauge measures the pressure/temp at suction(superheat)

[Obijuan83]

One strange thing: The static Pressure on both gauges when the SS is closed even when its cold (all night not working) is 175 psi. Is that pressure normal?

When i fire it up pressure goes till 260psi and then when achieve -47 C after 80-90sec sits at 200-205psi.

But 175psi static pressure sounds too high, what do you think?

Is it highly overcharged?

[aenigma]

I'm assuming this is still using R-404a? If so then all you do is use the P/T chart for R-404a to determine static pressure at a given temperature. For r-404a a static pressure of 175psi indicates the ambient temperature is about 80f/26.7c and if it is then that's normal. Static pressure won't go any higher than the saturated liquid pressure of the refrigerant.

[Obijuan83]

Its true that ambient temp is 27-28C, so you think that the 175psi static pressure is ok.

Ok the question is if I start remove gas (with static pressure at 175) till it get to 160psi , the the static will rise again at 175psi?

With this amount of r404a I get -47 C no load, -39 C at load ~ 250W and suction gets cold till compressor (3-4cm from it)

[aenigma]

Yeah that static pressure is fine. R-404a is a fairly high pressure gas so it's normal to have a higher static pressure than something like R22 or R290 for example. If you were using something like R-410a your static pressure would be about 240 psi! If you take gas out to lower the static pressure you're just undercharging the system. If there is any liquid in the system then static pressure will always match the saturated temperature, so if you let gas out until it reaches 160psi and stays there you are effectively removing any liquid refrigerant that is present in the system so it's not at saturated pressure anymore. If however you were to add even more refrigerant right now and overcharge it your static pressure will still be the same. If you put a gauge on your R-404a tank you will find it will be at the same pressure as your systems static pressure.

[Obijuan83]

So you are saying that at that amount of refrigerant inside the unit there is gas at liquid state so thats the ambient temp/pressure on the High side gauge.

How can I determine that the unit is not overcharged? The suction line freezes till compressor at idle -47 C and at load e.g E8600 @ 5350MHz @ 1.85v holds - 38 C and suction freezes 5cm from compressor.

I am a little confused because my previous SS had a Static Pressure of 90-100psi and it seemed to be well charged, had -45C idle and at load E8600 @ 5250MHz @ 1.85v -28.5 C. It was a Danfoss 1/3Hp , small Condenser , + 30cm longer cap tube (3m 0.031 cap tube)

Why that big difference?

100psi Static Pressure (26C ambient)



170psi Static Pressure (28.5C ambient)

[aenigma]

If it were overcharged your compressor would be icing up and you would be getting liquid returning to the compressor. You can try removing a little gas to fine tune the charge under a load since cap tube systems are very reliant on a proper charge. I was just saying that your static pressure is fine since that matched the P/T chart of R-404a perfectly. Under a load having a little frost on the suction line before the compressor is great, it means the compressor is getting adequate suction gas cooling, but it is possible it's slightly overcharged when trying to achieve the lowest temps possible.

As for your other system being at only 100psi static, was it also using R-404a? There are many variables that could explain it. The biggest thing I am noticing is that your liquid line on the old system is lower and doesn't go straight up, straighten out then go through a sight glass and then down into the drier filter. That is most likely the reason right there. With your new system you are fighting gravity to get the liquid refrigerant travel up the liquid line to the capillary to get a proper liquid seal which requires much more refrigerant. If possible with a cap tube system you want your liquid line to be at the lowest point of the condenser so liquid doesn't have to travel uphill otherwise you have to overcharge it and it makes fine tuning more difficult.

[Obijuan83]

So you think that if I lower the line that exits condenser climbing at the sightglass to a lower point would be better?

[aenigma]

Yes, you always want the liquid line exiting the condenser to be straight as possible. Liquid doesn't climb up very well, so you end up having to overcharge it to get enough liquid at your drier exit/cap inlet as it is now. Sight glasses are not used on cap tube systems, that's just extra volume where liquid can settle and upset the cap tube charge.

[Obijuan83]

Yes, you always want the liquid line exiting the condenser to be straight as possible. Liquid doesn't climb up very well, so you end up having to overcharge it to get enough liquid at your drier exit/cap inlet as it is now. Sight glasses are not used on cap tube systems, that's just extra volume where liquid can settle and upset the cap tube charge.

That is the importance of having this forum alive...thanks aenigma and his advice for lowering the liquid line exiting the condenser.

I gained 3C and the SS unit went from -47C to -49.9C (no load) only lowering the liquid line with the sight glass.

This temp is after 4hrs of benching...






Also at load it can hold better I think, wprime -40C @. 1.85v

E7500 @ 5.0GHz 1.9v Superpi 1m

[aenigma]

Awesome, glad it helped! For fine tuning to get better temps it would be good to get some evap in and out temps with a load so we can see if your charge and cap tube is right. Seems pretty sweet so far though.

<edit>

By the way, what evap are you using?

[Obijuan83]

By the way, what evap are you using?

Asetek Vapochill LS evaporator ( I think )

Maybe with human ambient temps 20-22C (these days 28-30C) it will achieve even lower temps...(I hope)

[aenigma]

Ah ok, not sure what that looks like inside. I was just curious. I have an evap that was on my old autocascade made by teyber I believe. It's a stepper kind of thing. Tons of mass and super restrictive so pretty lousy for a heat load haha