Building my first Single Stage

[Obijuan83]

After 10 years of inactivity I decided to come back.

I had an old Single Stage made by "Unseen" in the basement that was not working any more because of a leak.

I decided to try building my own Single Stage

I used:

Danfoss 1/3 hp with R404a
Condenser 140x140x90mm
Evaporator Asetec Vapochill LS
Desuperheater Coil
High Pressure Gauge
Filter/Drier
15ft captube

Case, I used an Freezepack made by Unseen back in 2008.

That was the compressor, condenser and evaporator in the old Single Stage...



This is the final result










As regards temps, idles at -55 C and with Pentium E5800 @5.0GHz at 1.7v after 27min of load keeps - 47 C.

[Charles Wirth]

Welcome back and good to see you got it running. If you need cadd files to cut new mounting I might be able to help with some measurements.

[Obijuan83]

Welcome back and good to see you got it running. If you need cadd files to cut new mounting I might be able to help with some measurements.

Thank you, my next goal is to make a new evaporator and new mounting clip

[aenigma]

Very nice, looks so very sexy! So good to see someone actually doing some refrigeration on here.

[Obijuan83]

Βecause of high ambient temps (37 C) and room temperature (30 C) efficiency of Single Stage suffers.

Without load idles at -32.5 C
High Pressure at 275psi / 48 C

Suction freezes till compressor



So I tried to cool the high pressure vapor with a chiller 1/8HP. I used the desuperheater coil to cool the 2 stage.

The temp now at evaporator is -47.5
High pressure is 180psi / 32 C

Suction doesn't freeze till compressor.

My question is, at that situation, I need to add refridgerant?

[aenigma]

Sounds like it's overcharged. Your head pressure shouldn't be that high. I'm thinking the cap tube is too restrictive so you overcharged trying to get more capacity.

[Obijuan83]

I asked if its undercharged at the situation with the added cooling.

The head pressure its only 180psi /32C and the suction doesn't freeze.

The cap tube is about 12 feet long and 0.031"

[aenigma]

I was talking about your first pressures. Same situation though, I think your cap tube is too restrictive.

[Obijuan83]

Ambient temperature doesn't matters?

[aenigma]

Ambient temperature matters, but if you were at 275 psi without the chiller/cascade/desuperheater that's indicative of an overcharge condition or the condenser isn't very efficient. Although I wasn't sure what you meant by 37c and 30c ambient and room temp since ambient and room temp is the same thing. A good thing to know is the air temp entering the condenser and the temperature exiting the condenser to find a Delta T. Finding the superheat and subcooling would be even better.

[aenigma]

Can you give the high and low side pressures? I would like to know the pressures you were getting before using the chiller on the desuperheater. Such high pressures on high side with somewhat high temps on evap and frost on compressor suction return has me wondering about the valveplate in the compressor.

[Obijuan83]

Here in Greece the outside temps are 37-40C but we try to keep lower temps inside home!

Propably the Condenser isn't that efficient at that ambient temps ~30 C but my question is when I use the first stage to cool the second stage , am I low on refridgerant at the second stage? If I add will I have better temps?

I asked that because one and a half month ago with 20 C ambient and head pressure 215psi /20 C, it achieved -55 C at no load

[Obijuan83]

Can you give the high and low side pressures? I would like to know the pressures you were getting before using the chiller on the desuperheater. Such high pressures on high side with somewhat high temps on evap and frost on compressor suction return has me wondering about the valveplate in the compressor.

Its difficult to measure low pressure atm but what makes you think that there is problem with valveplate? When I cooled enough the refridgerant at 175-180psi the evaporator temps are better (-47.5 C) that means low side pressure at 0psi and below I think.

[aenigma]

There are no real "stages" in this setup, so let's disregard that nomenclature. You got a much lower temp at 20c because it was cooler. Plain and simple you had a lower head pressure which means lower suction pressure. Either way knowing your inside ambient temperature, highside and lowside pressure and ideally condenser and evaporator inlet and outlet temperature would help a lot.

[Obijuan83]

Ambient temp is 29-30C
High side pressure before desuperheater is 180psi
Refridgerant temp before desuperheater is 20 C
Evaporator temp is 47.5 C

The condenser was not used, I mean no fan was working because of 30 C ambient.

The coolant that cooled the desuperheater has 16-17 C.

[aenigma]

Its difficult to measure low pressure atm but what makes you think that there is problem with valveplate? When I cooled enough the refridgerant at 175-180psi the evaporator temps are better (-47.5 C) that means low side pressure at 0psi and below I think.

I only mentioned the valveplate because these compressors have reed valves which are simple spring steel "flaps" like an air compressor has and if they get too hot or withstand too much pressure they can bend, crack or break which can cause high pressures on both low and high side. It's fairly rare, but it happens.

With R-404a you should be getting -46c with no load easily without the chiller desuperheater stuff. You saying it's difficult to check low side pressure makes me wonder if you pulled a vacuum before charging? If not then we found the problem.

[aenigma]

I looked at the pictures again and noticed you're using an evaporator heat exchanger for your condenser. The flow direction of the pipes traps refrigerant and oil. Might not be a big deal for a little system like this, but I thought I'd mention it.

[Obijuan83]

To be honest I pulled a vacuum but only for 45min. The low side gauge was at -30, not going any further. But i think that I did not fill the yellow hose with refridgerant when added the refridgerant, because I removed it from the vacuum pump and connected to the r404a bottle.Is that too bad?I mean the air inside the yellow hose.

[Obijuan83]

I looked at the pictures again and noticed you're using an evaporator heat exchanger for your condenser. The flow direction of the pipes traps refrigerant and oil. Might not be a big deal for a little system like this, but I thought I'd mention it.

What do you mean? The cap tube that is wrapped around flexible suction line?

If you mean that as evaporator heat exchange I would also like to ask if its better to wrapped it at contact to the suction line instead of the insulation of the suction line as it is now.

[aenigma]

Oh ok that's good you pulled a vacuum, I was just concerned there may be air in the system. After I vac my system I always close the manifold valves (low and high side valves) then disconnect the hose from my vac pump then connect it to my refrigerant tank, open my tank then crack open the line to the manifold/gauges to purge any air in the line set and tighten it back up. That makes sure there is no air in my line set.

I was talking about your condenser, the piping direction is wrong for a condensor, it's an evaporator HX. As for subcooling it's good to wrap the capillary tube around the suction line. Even better is to solder it to the suction line somewhat close to the evap outlet.

[Obijuan83]

I was talking about your condenser, the piping direction is wrong for a condensor, it's an evaporator HX. As for subcooling it's good to wrap the capillary tube around the suction line. Even better is to solder it to the suction line somewhat close to the evap outlet.

I dont understand what you mean that its not condenser but its evaporator HX,what is the problem with the piping?

[Obijuan83]

There are no real "stages" in this setup, so let's disregard that nomenclature. You got a much lower temp at 20c because it was cooler. Plain and simple you had a lower head pressure which means lower suction pressure. Either way knowing your inside ambient temperature, highside and lowside pressure and ideally condenser and evaporator inlet and outlet temperature would help a lot.

I used a second probe and got the following results.

48 C Inlet Condenser Temp (that means 315 psig)
38 C Outlet Condenser temp /Filter temp

(-10C Delta)

28 C Ambient temp
38 C Exhaust Air temp from Condenser

(+10 C Delta)

-33.5 C Evaporator temp
-32.5 C 1" before Compressor (that means 12.5 psig)

[Obijuan83]

I can understand that at these ambient temperatures, 28-30 C , and temperature before condenser 48C, the SS seems to be overcharged.

But, when I cool down the liquid line to 32 C before condenser (200psi) the evaporator temp is -47 and suction temp is -11C.

That seems to be undercharged, am I right?

[Obijuan83]

I tend to believe that my problem is not proper vacuum.

I pulled a vacuum only for 45min and when I charged via the high pressure, the hose connected to r404a bottle was empty an full of air. Could that cause not proper vacuum?

I have to add a low pressure gauge to measure superheat...

[Obijuan83]

Finally the problem was poor vacuum.

I did a proper vacuum procedure and now I have the following readings.

35 C Inlet Condenser Temp (that means 200 psig)
31C Outlet Condenser temp /Filter temp

(-4 C Delta)

27 C Ambient temp
31 C Exhaust Air temp from Condenser

(+4 C Delta)

-44.5 C Evaporator temp
-47.5 C /-1.5psi at low side gauge