Coolroom Freezer WIRING CONFIGURATION

[acura]

Hi Guys im from AC industry now doing some coolroom work . Have come across alot of various wiring setups eg. Mechanical tstat to dixell controller , Solenoid pumpdown . Is there any issue with running every basic Coolroom/Freezer setup with a solenoid pumpdown setup ?. thanks

[lawrence1]

acura
The disadvantage with pumpdown is that the liquid line can sweat after the solenoid when it is closed,,,the unit will cycle off then via the lp control.
This method pumps the refrigerant out of the evap and can be less effecent in off cycle defrost.
I usually do not use a solenoid but just cycle the compressor off and that way the refrigerant assists in a better defrost and there is no liquid line sweating.You will need a relay to switch the compressor via the dixell/carel controller.

[Grizzly]

The correct answer is it very much depends upon the system design and the required running temps.

This method pumps the refrigerant out of the evap and can be less effecent in off cycle defrost.

Would you like to elaborate some more lawrence?

How is liquid migration dealt with?
Cheers Grizzly

[chemi-cool]

acura
The disadvantage with pumpdown is that the liquid line can sweat after the solenoid when it is closed,,,the unit will cycle off then via the lp control.
This method pumps the refrigerant out of the evap and can be less effecent in off cycle defrost.
I usually do not use a solenoid but just cycle the compressor off and that way the refrigerant assists in a better defrost and there is no liquid line sweating.You will need a relay to switch the compressor via the dixell/carel controller.

Not true, if the SV is located near the TEV, there are no sweating of the liquid line, beside that, if it bothers you, you can simply insulate it.

Pump down protects the compressor from liquid returning and restart the system with less currant draw.

I don't see how lack of SV can affect off cycle defrost but I'm willing to learn something new.

[FEISTY]

Agreed, chemi-cool. I try and modify ever walk-in system I encounter that is running on a low pressure control for temperature to a thermostat and use the low pressure control with a solenoid valve for pumpdown and low press. safety. I can prove by my records of replacement that you will extend the life of a compressor by startup and shutdown at lower pressure/lower current load. I know this has been a point of " push-pull " discussion for quite a while here but the numbers don't lie. The customers are happy also with reduced costs for new compressors.

[lawrence1]

Grizzly,
There is more latent heat in liquid at say 5c then there is saturated vapour at 5c.The liquid boils off in the evap and transfers heat better to the fins.
Difference in defrosting times is minimal but i find the evaps have no residue ice.
The largest condenser/evap manufactures here specifies that the pumpdown cycle is not used during defrost and that the evap should be flooded.

[coolhibby1875]

acura
The disadvantage with pumpdown is that the liquid line can sweat after the solenoid when it is closed,,,the unit will cycle off then via the lp control.
This method pumps the refrigerant out of the evap and can be less effecent in off cycle defrost.
I usually do not use a solenoid but just cycle the compressor off and that way the refrigerant assists in a better defrost and there is no liquid line sweating.You will need a relay to switch the compressor via the dixell/carel controller.

i would not reccomend this way as its a freezer, by not pumping down the system on defrost, you have refrigerant in the evap like you say so when the heaters come on the gas presure increases to silly presures, then when the compressor starts its starting under an increased load which is not good for the compressor, or your electricity bill!! as for sweating after the solenoid valve i have never seen this ever!!

[Grizzly]

Lawrence I already understood your original post, well partially at least.
Because previously on the forum "We" all had a long discussion about this.
Basically if I remember correctly, You have a manufacturer (Buffalo possibly I can't really remember).
Anyway they have evaporators that have restriction orifices in the liquid lines.
This design is based upon the theory that you are explaining.
And several of you Knowledgeable Countrymen argued successfully what you are saying at that time.
Likewise myself and others over in this part of the world argued the opposite.
At the end of it all we agreed to differ, because as I said originally it really does depend upon system design.
The system you explain is very rare over here and therefore the use of liquid line solenoid valves is the norm.

I guess acura may well benefit from your advise more because of where he is based.

Your system is a mystery to me but I am willing to accept to some it makes perfect sense.
Cheers Grizzly