freezer cold room pull down slow

[nick clark]

30 hp bitzer unit coldroom temp required -20
new system suction 20 psi discharge225 psi
sight glass clear , frosting back to compressor
pipe run is25 m , evaporator temp -16
have changed valve ,same problem this is on r404
any idea out there nick on behalf of jason

[taz24]

30 hp bitzer unit coldroom temp required -20
new system suction 20 psi discharge225 psi
sight glass clear , frosting back to compressor
pipe run is25 m , evaporator temp -16
have changed valve ,same problem this is on r404
any idea out there nick on behalf of jason


At 20psi suction and frosting back on the suction line I would sugest you measure the superheat and pherhaps you could open your valve a bit.
At 20psi the refrigerant is evaporating at about -35deg C.
The frost on the suction could be cold gas returning and not liquid.
Check the superheat settings and set the valve up if required.
You could allow your back pressure to rise to 2b (30psi) and still freeze the room correctly.

Cheers taz.

[nick clark]

many thanks , will pass on info to jason , he also told me there is no heat x fitted , i feel this would help ?
nick

[Samarjit Sen]

Hi nick clark,

Has the selection of the equipments and the controls been done properly. As I am very much involved in such projects, I have seen a small mistake makes a lot of difference in refrigeration.

Please recheck the equipments and the selection of the TEV.

[nick clark]

yes ,same set up used before on coldroom same size
regards nick

[suny]

yes ,same set up used before on coldroom same size
regards nick

May be a defective TEV

Suny

[nick clark]

hi suny , changed tev just the same nick

[suny]

An error may give you big problem. Did you top up with R 404a. If so you will have this problem. Then reclaim & chrage again with fresh gas.

Suny

[nick clark]

hi suny large plant so pump down to change valve
no loss of refrigerant nick

[Samarjit Sen]

yes ,same set up used before on coldroom same size
regards nick

It means of assessing the load, you have just copied the the equipments from a similar Cold Room. This is a dangerous thing to do. In refrigeration, I always every project as a new one and do all the calculations in details. Even the selection of equipments and controls. In this way, God willing I never had any problem in attaining the temperatutre nor the pull down period.

Please do recheck the compressor, condenser and the evaporators and of course the TEV and the pipe lines.

If I could be of any help, please do let me know.

[Samarjit Sen]

Please check the product load. Maybe it is quite different from the previous one.