System Design Charge

[cool-hvacer]

Hi all...

I posted a similar question earlier, but that thread kinda diverged...

Let me rephrase it slightly. If you just designed a chiller system what would be the method you would use to calculate the proper refrigerant charge.

Just for the heck of it, let me throw in a few details....
* Air cooled condenser
* TXV
* Receiver
* condenser flooding for head pressure control
* single hermetic compressor

The other thread had somewhat converged to
30% condenser volume +
100% liquid line volume +
80% receiver volume +
70% evaporator volume

All converted to the mass of refrigerant (at the proper temperatures). Any comments!?!? Everyone in agreement?!?!

And the first time you charged this thing, would you just plug in that amount, and then fine tune with superheats / subcooling?!?!

[cool-hvacer]

No takers?!?!?!

I would have thought this would have been a very basic question, as anyone/everyone who has designed a new system would have to come up with a number to put on the name-plate.

[nike123]

No takers?!?!?!

I would have thought this would have been a very basic question, as anyone/everyone who has designed a new system would have to come up with a number to put on the name-plate.

That number doesn't come from calculation. It comes by fine tuning of system components and testing of performance in all operating conditions in predicted operating envelope.

It cannot be calculated with satisfactory accuracy for that pourpose. You could only calculate amount of refrigerant needed to have on stock for service job rough estimation purpose or simmilar tasks.

http://www.defra.gov.uk/environment/...pport-gen5.pdf


And what about answering to thread which you, somehow, abandoned?

[cool-hvacer]

Not abandoned..... Before I can give better measurements, I have to visit the facility where the equipment is located - its quite remote!! Actually, at 14 000ft altitude, so that also makes things a little more interesting.

For the charge question:

I could counter your assertion by asking if its a brand new machine, how do they come up with the number that they put on the nameplate, but I guess that they could operate the equipment in their plant after they first manufacture, and tune it properly / measure proper refrigerant charge there before they send it out....?!?!

Oh ya - Thanks for the link...

[nike123]

Not abandoned..... Before I can give better measurements, I have to visit the facility where the equipment is located - its quite remote!! Actually, at 14 000ft altitude, so that also makes things a little more interesting.

Only for condenser size! If correctly sized, there is no problem! But that we will see after measurements are done at air side of condenser.

For the charge question:

I could counter your assertion by asking if its a brand new machine, how do they come up with the number that they put on the nameplate, but I guess that they could operate the equipment in their plant after they first manufacture, and tune it properly / measure proper refrigerant charge there before they send it out....?!?!

When I visited plant which manufacture chillers by order (Geoclima) they showed me their test room and told me that for every new custom order they need to test equipment and fine adjust charge.

Also, because of huge difference in volume of gas phase and liquid phase (check this thread) it is practically impossible to to calculate correct amount of refrigerant since small mass of evaporated/flashed refrigerant makes huge difference in occupied volume of equipment parts.