low ambient - low liquid level ?

[kfjoe]

Please can anyone explain why there would be less liquid refrigerant in the sytem during low ambients?
I understand there is additional liquid in the reciever for use during low ambients,but i am getting myself confused as to why.

I understand a lower ambient will reduce the saturation(condensing) temp and pressure , does this mean there is more liquid in the condensor during low ambients ?

any help appreciated thxs

[Dan]

I understand there is additional liquid in the reciever for use during low ambients,but i am getting myself confused as to why.

The additional liquid in the receiver during the warm months is usually referred to as a "winter" charge or "flooding" charge.

Compressor units are often equipped with winter control valves or flooding valves that let liquid stack up in the condenser when the weather gets cold in order to maintain design condensing pressures. Basically, they use refrigerant to shrink the area available for vapor.

Even without such valving, it is possible to see more liquid in the condenser during cold weather. It's especailly apparent when the condenser is actually colder than the evaporator temperature, such as an outdoor condenser in freezing conditions attempting to maintain a 40 deg F evaporator in an a/c system.

[Gary]

The high side pressure corresonds to the temperature at which the refrigerant is condensing from a vapor to a liquid.

When the condenser if filled with liquid, there is only a small portion at the top that is condensing vapor. It is as if the rest of the condenser didn't exist.

In effect, it reduces the useful size of the condenser. The liquid filled portion of the condenser acts as if it is part of the liquid line.

[Peter_1]

Originally posted by Gary
In effect, it reduces the useful size of the condenser. The liquid filled portion of the condenser acts as if it is part of the liquid line.

And as a giant subcooler.

[kfjoe]

Thxs for the replys.
Its just a basic cold store with a air cooled condensor , no head pressure regulators etc. just a standard reciever ,suction accum,cpr, tev system and 2 hp controlled condensor fans.

Basically i cant quite get my head around why during low ambients and therfore low head pressures there is a shortage of refrigerant( flashing in sight glass ) and yet at normal ambients and head pressure the sytem looks fine.

I am probally missing something very basic

[Peter_1]

To little Dp over the TEV, to little refrigerant flow and if you lower the upper horizontal line (condensing line) in a lop-P diagram, the chanche that you come "with your sightglass" in the liquid/vapor "area" becomes more likely.

One of my technicians explained it this way:"The compressor sucks more gas 'through' the TEV then there is feed from the condensor"

I think the phenomena you describe wouldn't happen if you should use a condnsor pressure controller for each fan or is it doen this way?

Almost the same happens when you use an on/off controlled pressure condensor with to large differential.

You see bubbles in the sightglass and a lot of techs then say "there is not enough liquid in the system" They fill it up till all the bubbles are gone. The next summer the problems start with HP cut-outs.

I had once somebody with me which was in his training from school. The liquid receiver had a capacity from +/- 50 kg. I asked him to fill the system while I was doing other things. I suddenly noticed that there where already 2 cylinders of 60 kgs standing beside him. He was already filling his 2nd which was almost empty. When I asked him what he was doing he said "Well..; filling till all the bubbles are gone" It was difficult to explain that he saw the bubbles due to flashgas instead of shortage of liquid.