6k sub cooling

[SkyWalker]

hi guys we got a system running 6k subcooling when the saturated condensing temp was 17.1 BAR/ 46c. R407c

now as I have learnt from Gary on this site that a system (TEV) should have no more than 8k sub cooling when SCT is between 38-43C, if SCT is lower then block condenser to increase, BUT this system is higher and it has a fan speed controller which I believe is pre set to 17BAR and it cant be changed?

what do we do in this situation? and does the 6k subcooling at this SCT sound correct?

or did gary say at least 38-43C if its over it may not matter, im not sure, eeeeeeeek ?????

[Magoo]

Hi SkyWalker.
Generally with a standard condenser you will average a nominal 5 'K subcooling, and a couple of degress between receiver and TX valve. Check the liquid temp entering the TX valve. If greater then you have sub cooling created by liquid line loses, caused by vertical height separation, length of liquid line and bends etc., or undersized liquid line. Commonly called flashing off in liquid line.
A quick check is to install a liquid line sight glass at the TX valve. If the glass never clears the TXV will always hunt and play up.
The TX valve is just a pressure reducing valve based on a given flow rate at a given temp., to supply 'x 'flow rate at a given pressure differential . self regulating by pressure and compensated by external temps converted to pressure.

[smc200276]

Surely if you have a receiver, you can't achieve any sub-sooling as the refrigerant contained in the receiver is at saturation point? Don't you need a sub-cooling circuit after the receiver to be able to achieve any significant sub-cooling?

Please correct me on this if I am wrong - I definitely don't claim to be any kind of expert in this area.

[NoNickName]

Is it overcharged? What is the ambient temperature?
High subcooling in itself does not represent a malfunction: infact it may be desirable to have a high grade of subcooling for certain refrigeration circuits, as the performance of them is a function of subcooling, among other things.

[mad fridgie]

Surely if you have a receiver, you can't achieve any sub-sooling as the refrigerant contained in the receiver is at saturation point? Don't you need a sub-cooling circuit after the receiver to be able to achieve any significant sub-cooling?

Please correct me on this if I am wrong - I definitely don't claim to be any kind of expert in this area.
I am with you on this one, so called sub-cooling is actually a function of pressure drop. True sub cooling is measuring the liquid pressure and then temperature.

[NoNickName]

There is only way to measure subcooling: temperature corresponding to condensing pressure, minus liquid temperature.
Any further cooling, wherever it happens, is to be added to subcooling.
Often, in refrigeration equipment, suction gas exchanges temperature with liquid, to further subcool it. 20-30K of subcooling are not unusual.

[oldesky]

There is a long thread on RE about the argument of subcooling in the receiver and there has been a range of views. Likewise the argument and similar result on Hvac. Professor Wilbert Stoecker a well known expert on refrigeration states in his book "Industrial Refrigeration Handbook" that there is no actual subcooling in the receiver. Unfortunately I do not have my copy with me to give you his exact quote. Maybe someone else on RE does

[Collie]

I am with you on this one, so called sub-cooling is actually a function of pressure drop. True sub cooling is measuring the liquid pressure and then temperature.

Can this temp measuring not be done along the pipe at the outlet of the condenser but before the receiver?
As the gas should have fully condensed into a liquid with no traces of vapour by the last few runs in the condenser coil, sensible cooling will still be occuring and therefore sub-cooling? im just thinking out loud on this, feel free to put me straight lads :)

[mad fridgie]

Can this temp measuring not be done along the pipe at the outlet of the condenser but before the receiver?
As the gas should have fully condensed into a liquid with no traces of vapour by the last few runs in the condenser coil, sensible cooling will still be occuring and therefore sub-cooling? im just thinking out loud on this, feel free to put me straight lads :)
Hi this was referenced to liquid out of the reciever.
You can have genuine liquid sub cooling down a liquid line, you can have a seperate sub cooling coil. If your condenser is not free draining (basically no reciever) then liquid sub cooling can occur) Really what is truely important is lthe liquid pressure and temperature at the expansion device inlet.