Freezer not achieving -20

[jmc88]

I was working on a a -20 room that was run on R417a and it had only been achieving -12. The previous engineer that had been out to it couldnt get it lower than that so he recommended it be retrofitted for R404a. I went out and retrofitted it to R404a, new oil, exv, drier etc but the system can only achieve -15. Apparently the system has worked prevously but i have my doubts as to whether it was achieving -20 and pumping down etc or just struggling by to reach around -18 running non stop as thats what thy said the room used to be at.

My running pressures are suction- 7 psi and discharge- 210 psi. The only way to get my suction pressure/temp up is to adjust the expansion valve out but any further out that 1 1/2 turns from factory setting causing the evaporator/compressor to flood with liquid. Any adjustment in from factory setting loses cooling so there isnt much adjustment i can make to it.

I am getting sub cooling of 4C but superheat of 21C but i can still get a high/false superheat reading with liquid slugging at the compressor after a slight adjustment of the exv??!

I am pretty sure the charge is correct, 10.5 kg, i had it running for a day with 9.5kg in also before adding an extra kilo to no effect. (I recovered 11kg of R417a before the retrofit)

I have tried various things to try and get the temp down but i cant get it any further than -15

Ive checked all the obvious things at the evap, correct air flow through evap, clean coil, evx bulb is in correct position, I even disconnected the exv and blew through down through the evap with nitro down to the suction to see if there was any oil or sludge or anything sitting inside the evap but there was nothing.

Anyone else any ideas?

Here is the details of the system, is it sized incorrectly??

Evaporator

Searle KM80- 6L
R404a
Capacity- 9.74 X 0.6 correction for minus 30 /6C td ..5.84Kw on R404aAir Volume= 2m2/s
Surface area= 34.5 m2
internal volume= 8.4 dm3
inlet- 5/8th outlet- 1 1/8th
Distributor= 6 x 1/4 pipes

Room Size

6570 x 3940 x 2130 high
Approx 2000 cubic feet

Expansion Valve

TES 2
R404a

Orrifice -No.4 = 4.5 KW



Compressor

input = 3.6 KW
RPM = 1450




Condensing Unit

Prestcold
MALGV 95 JA B4
Assembly no. 34800523
Comp replacement- 6711302
Run amps- 13 A
Comp- 3.6 KW 440/480 60HZ
Fan- 0.18 KW 440/480 60HZ
FLA- 0.7 LRA- 2.4
High pressure- 31 Bar
Low pressure- 19 bar
Serial- 0101 AH

Liquid Reciever

Copeland
Serial- USB 12586
Model- M114
Int vol- cub ins 696
litres- 11.4 litres
Test pressure- 32.3 bar

Pipe sizes

Suction- 1 1/8th
Liquid- 1/2

Approx 20M pipe run, approx 15-20 bends. Evaporator is located above condensing unit.

[HVACRsaurus]

Probably not the issue, but does the evaporator have a liquid/suction heat exchanger (tube in tube)? Seen plenty of these things leak internally & make all sorts of trouble!

[desA]

Comparing R22 (R417A is the drop-in 'equivalent') to R404A on a simulator, I see a 14% drop in evaporator performance - when compared at same compressor power.

To get same evap performance, the compressor runs at +16.7% higher duty. Condenser needs to perform at +8.8%.

Perhaps some problems with system component balancing can be expected & that your -15'C is actually pretty good, considering. May need to think about how to boost other parts of the system to compensate for the imbalance e.g. condenser fan speed-up?

[jmc88]

Probably not the issue, but does the evaporator have a liquid/suction heat exchanger (tube in tube)? Seen plenty of these things leak internally & make all sorts of trouble!

No it doesnt have one

[jmc88]

Comparing R22 (R417A is the drop-in 'equivalent') to R404A on a simulator, I see a 14% drop in evaporator performance - when compared at same compressor power.

To get same evap performance, the compressor runs at +16.7% higher duty. Condenser needs to perform at +8.8%.

Perhaps some problems with system component balancing can be expected & that your -15'C is actually pretty good, considering. May need to think about how to boost other parts of the system to compensate for the imbalance e.g. condenser fan speed-up?

Thats interesting to know about the lack of performance but the room still wasnt achieving temp while running on R417a which makes me think it is something else??

[monkey spanners]

You should get a bit more duty out of it now its on R404A compared to R22 (think R417A is about 20% less duty than R22), as an example as i can't find your model, a copeland H8-LL-40X 4hp unit will do 4.7kw @ -25C on R404A and 4.6Kw on R22.

But R404A has to flow greater volumes of liquid to do the same duty so you will need to go up a size on orifice to get the right duty. Liquid line and components can in some cases need to go up a size too.

e.g. n.4 orifice R22 = 8kw at 5c but only 6kw on R404A

Other things to check as i'm sure you know are airflows and coil cleanliness, a lot of the prestcold condensers can look clean on the outside but have a lot of dirt between the coils.

Jon

[desA]

I suspect that the original kit was designed for R22.

[jmc88]

You should get a bit more duty out of it now its on R404A compared to R22 (think R417A is about 20% less duty than R22), as an example as i can't find your model, a copeland H8-LL-40X 4hp unit will do 4.7kw @ -25C on R404A and 4.6Kw on R22.

But R404A has to flow greater volumes of liquid to do the same duty so you will need to go up a size on orifice to get the right duty. Liquid line and components can in some cases need to go up a size too.

e.g. n.4 orifice R22 = 8kw at 5c but only 6kw on R404A

Other things to check as i'm sure you know are airflows and coil cleanliness, a lot of the prestcold condensers can look clean on the outside but have a lot of dirt between the coils.

Jon

From the danfoss website it looks like a TES 2 on R404a with an evaporating temp of -30, orrifice no.4 is 4.5 KW. It looks like I would need a no.5- 5.7kw for the required duty of the evaporator?

The compressor details- Aces- PLG400/0062S/0 serial 8199
The compressor was changed in may from the original compressor. The original was 3.6kw input 3.5hp, i presume the new one is a similar match


Re, cleaning the condenser coil, I know what you mean, it looked clean from the outside but i blew through it with OFN and the coil was filthy. Managed to get the condensing temp down 4 degrees after blowing through.

[monkey spanners]

I think even a n.5 might be too small, i'd give either Peter Bell or Victor Ballard a call at Climate centre technical, give them the evap model, compressor/condensing unit model, room temp and they'll size the orifice for you at the required temp. Also if you have any worries about the duty required they will size the room and compair to what you've got.

Jon

[chemi-cool]

What about R-422D?
Its a good replacement for R-22, no changing oil and you hardly loose any capacity.