walk-in freezer

[jhoeyjdp]

Good evening everyone, Im working here in Dudai UAE. as a cold room tech. I have a strange problem regarding my walk-in freezer, 10 hp.3phase 380v. 50hz copeland compressor air cooled condenzer single evaporator coil 404a refrigerant.
the stange problem is if winter seasons its working well, i can reach the set point -20*c but this summer the temperature here is above 42*c. My problem now is I can't reach the set point -20*c its only -17*c maximum, i clean the condenzer and the condenzer fan speed is ok, ***** charge is normal, sunction is 18psi, dis-charge is 320psi, refrigerant sight glass showing sometimes bubbles speed passing through is ok but sometimes bubbles running slow. Please I need your help...Thank you.

[tonyelian]

hi
1-size of ur room
2-compressor capacity@-27
3-capacity of evaporator
4-kind of product
5-room movement
6-product entry fresh or frozen
more info more help

[kkboy]

How thick are the freezer room panels. Is the room built inside or outside.
What you could try is set up a spinkler system in front of condensser with a water mist. if this improves your tempreture you would have to seriously look at if the design... is large enough.
What ambient is your condenser designed for?
How long has the system been installed? what product are you trying to freeze? Do they open the door constantly to get stock out?

[kkboy]

Have you tried adding a small amount of gas the pressure you have given a a little low for -17 and the head pressure is slightly lower for a 42 degree day. 323 psi is 50degrees condenssing temp. if its 42degrees on condenser then you want about 340psi discharge and if is -17 in the room suction pressure should be about 23psi.

[lana]

Hi there,

What is the head pressure control setting in winter?
If it was working fine in winter, what was the working pressures then?

Try to measure sub cooling and super heat.

Cheers

[jhoeyjdp]

How thick are the freezer room panels. Is the room built inside or outside.
What you could try is set up a spinkler system in front of condensser with a water mist. if this improves your tempreture you would have to seriously look at if the design... is large enough.
What ambient is your condenser designed for?
How long has the system been installed? what product are you trying to freeze? Do they open the door constantly to get stock out?

*kkboy thanks for your concern, the room is built inside, i try to put spinkler water to the condenzer but still d'same, the condenzer ambient is above 50*c, the unit is 5yrs old,the product are prozen fish,and the door is not open constantly, I try to add few amount of *****,but still d'same,but something wrong with the sight glass,its not normal sometimes, the liquid is passing very pass with tiny bubbles,which is good, but the bud things is sometimes is showing empty, I think some thing wrong with the TXV....Please advise...Thanks.

Healthy Regards
Jhoey

[ref717]

Kabayan!, same problem here with our air cooled chillers. High ambient temperatures and humidity makes the condenser overworked, the refrigerant discharge gas cannot normally release its latent heat in the condenser, therefore you'll have low subcooling which leads to poor system performance.

The best that you can do are : always keep your condenser fins clean, keep correct refrigerant charge, give adequate ventilation on your condenser and keep away from direct sunlight, check and/or adjust your TXV to suit your requirements.:)

anung Co. ka bro.?

[benijoseph]

All air cooled con will have problems when amb goes up if it not designed tropical , IF the unit was working normaly early days of its installation then the problem is in its comp efficency or poor quality of gas ,

rgds.

[kkboy]

I would do a compressor valve check by pumping suction pressure into a vacuum. If thats ok. open your tx valve up. Or try changing gas to R507 (AZ50)

[Peter_1]

Reduce your HP by adding a PHE on water which will help your aircooled condenser only when it becomes too hot.

Or/and your panels are not thick enough, so more energy is entering your freezer room.

[Scramjetman]

Pretty hard to tell without more detail, but the symptoms of flashing in the sight glass tells me:

1. Insufficient subcooling with the right charge of refrigerant or
2. Not enough refrigerant or
3. Both of the above.

If the TX valve doesn't have a full head of liquid arriving at it, it will be all over the place and out of control- opening and shutting trying to settle the superheat temperature down. It will be near impossible to achieve full power in the system unless stable valve control exists.

The question is, where to start?

Step 1.
Connect your gauges and have a pressure temp chart for the refrigerant handing to consult.

Step 2.
Operate the system and use your water spray to get the head pressure for your refrigerant such that the refrigerant in the condenser is fairly steady and no more than 55°C (check your chart for the corresponding pressure) Also make sure it doesn't get too low. You need at least 100psi (700kPa) difference between your suction pressure and head pressure or you will lose control of the TX valve as well.

Step 3.
Let the system settle for 15 min or so then check the sightglass is now full. If not, first measure the superheat temperature. If the superheat temperature is more than 8°C in this state, add refrigerant slowly until the sightglass is full ( keep monitoring the superheat temp - if it gets below 5°C, stop adding refrigerant and let the system settle down)

Step 4.
Set the TX valve for 6°C of superheat (search for and read some threads on superheat and subcooling and how to do this).

If your condenser can't keep the refrigerant at or below these pressures and temperatures, you have a condenser sizing issue and need to put in a condenser that can manage this under summer conditions.

[Peter_1]

...
Also make sure it doesn't get too low. You need at least 100psi (700kPa) difference between your suction pressure and head pressure or you will lose control of the TX valve as well.
....

I have some systems running with only 4 bar (60 psi) DP across the TEV (Danfoss) without any problem.
Danfoss even gives stable capacities for a DP of 2 bar DP (30 psi)
But, orifices were selected for this lower DP

[Scramjetman]

True, and I've seen systems on conventional TX's running consistantly as low as 80psi differential. At this point, though, we are right on the edge of losing control because the tx is a pressure driven device. Once the differential pressure gets too low, it goes out of control. You don't want a high capital cost plant destroyed because we were trying to wring every last kW (or btu) out of it by pushing the differential pressure down to the redline. It's all about risk and reward. It doesn't take much floodback to wreck a compressor. You don't want to lose control of the valve for even 5 seconds. That's enough to kill the plant.

[Peter_1]

If DP becomes too small, it doesn't loose control but it simply doesn't open any any longer or not enough, just preventing floodback. That's my practical experience on our systems.
We're also not on the edge but 100% higher than that edge (4DP instead of 2 DP)
Even with a low DP, the valve still maintains its preset SH. It's only a matter of 3 pressures on a diaphragm, that's all and I don't see how it then can go out of control. It remain in fact very stable.
It's good to know that this works in a real life situation so that we all can benefit from this energy reduction.

That client called me last week that he lowered the evaporating temperature with 3 to 4°C because the blast cooler on this system is most prone loosing its needed cooling capacity. It became outside very hot the last days and to increase capacity, he had to lower this temperature to increase DT over the evaporator.

But I'm sure as soon temperature drops again in September, he will increase this temperature again with some degrees. Increasing your LP benefits much more then decreasing the HP with the same degrees.
This client has the software of Bitzer on his PC and it has become a routine of him to look for the COP on his compressors on a regular base. We explained him what COP is and how he can calculate this with the software.

This has become for many years a perfect practical case for us.