Over condensing?

[samisonfire]

I have heard the expression "over condensing" but have never come accross a problem that has been caused by it so i don't actually know what the effects of it are?

Can anyone shed any light on this for me please?

I'm thinking that if the refrigerant is over condensed then the head pressure is dropped thus causing low suction pressure?

Fan speed controllers are used to maintain a certain head pressure and therefor eliminate over condensing, but why are they only installed on certain refrigeration equipment?

I would be very grateful if someone could help me with this.

Thanks, Sam

[taz24]

I have heard the expression "over condensing" but have never come accross a problem that has been caused by it so i don't actually know what the effects of it are?

Can anyone shed any light on this for me please?

I'm thinking that if the refrigerant is over condensed then the head pressure is dropped thus causing low suction pressure?

Fan speed controllers are used to maintain a certain head pressure and therefor eliminate over condensing, but why are they only installed on certain refrigeration equipment?

I would be very grateful if someone could help me with this.

Thanks, Sam

Hi Sam.

You are right in what you assume re head pressure
but the big problems comes if the head preasure drops too low then the TEV's don't work correctly and the whole system falls over.

Think of a condenser on a roof in the depth of winter and with wind chill the condensing temp just fall through the floor which then cause's the liquid to log in the condenser. That results in the suction pressure dropping also.

Cheers taz

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[Grizzly]

Well said Taz.
Hi Samisonfire.
I think I am correct in saying technically you cannot "over condense".
But you can loose control of the liquid line temp, resulting in insufficient "Lift" ( Pressure Temperature diff between the LP and HP sides of a system).
A particular problem on start-up for some systems.
So when you have lost control of your "Head Cooling" you could say your system is over condensing.
Grizzly
Grizzly

[lana]

Hi there,

As mentioned by the experts :
THERE IS NO OVER CONDENSING!!!!!!????

If ambient temperature drops OR a huge (Surface area = Infinity) condenser is used, the condensing temperature corresponds to ambient temperature and condenser Delta T.
When consenting temperature drops below design then TEV starves the evaporator and suction pressure falls.

Head pressure control keeps the condensing temperature near the design value.

Cheers

[desA]

Some very interesting comments. Thank you taz, grizzly & lana.

I learned something today.

[mad fridgie]

without getting to complex, what is intersting, if you drop your SCT by 5C and SST by 5C, your COP soes not change much. So if you do not care about RH or freezing of the evap, then let the system reach equalibrium (as long as in range of the comp) Practically your SCT would drop but your SST would not drop as much, thus actually increasing the COP.
A bit of food for thought

[coolhibby1875]

without getting to complex, what is intersting, if you drop your SCT by 5C and SST by 5C, your COP soes not change much. So if you do not care about RH or freezing of the evap, then let the system reach equalibrium (as long as in range of the comp) Practically your SCT would drop but your SST would not drop as much, thus actually increasing the COP.
A bit of food for thought

never seen so many abbreviations used in a thread ever pmsl

[Gary]

Balanced port TXV's were developed for this very problem. They require less dP to function properly, thus the head pressure can be lowered.

[samisonfire]

Thanks for your help everyone.

When you guys have said about insufficient lift and starving the TEV does this mean that the head pressure has dropped so much that there isn't enough pressure to push the refrigerant through the valve?

What the symptoms be for "over condensing"?

Low suction pressure
Low discharge pressure

[samisonfire]

Sorry, i pushed the wrong key!!!!

What would be the symptoms for "over condensing"?

Low suction pressure
Low discharge pressure
High superheat?
High subcooling?

If i came across a system that had low suction pressure, low discharge pressure and it was in low ambient conditions i would try restricting the air flow across the condensor to see if that improved the performance of the system before carrying out a leak test, but i am trying to learn the techniques of using subcooling and superheat to fault find so i think this is probably a time where those techniques would come in useful.

Thanks, Sam

[multisync]

Someone said to me that a-20c freezer room with a TEV + receiver was over condensing and that is what is causing the suction line to freeze..

Anyone care to comment on this remark?

[taz24]

Someone said to me that a-20c freezer room with a TEV + receiver was over condensing and that is what is causing the suction line to freeze..

Anyone care to comment on this remark?

I think that the suction being below 0 is more than
likely to cause it to freeze, but what do I know

Cheers taz

.

[taz24]

Thanks for your help everyone.

When you guys have said about insufficient lift and starving the TEV does this mean that the head pressure has dropped so much that there isn't enough pressure to push the refrigerant through the valve?

What the symptoms be for "over condensing"?

Low suction pressure
Low discharge pressure

Yes.

Manufacturers may have different figures but I was
always led to belive that you need a minimum
of about 7 bar accross you valve for it to opperate
correctly.

taz.

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