Estimating Refrigerant Charge with TEV TXV

There are many posts on how to charge a system in RE, some of the latest ones are shown below. If you know of a good one feel free to mention it. TKS!:

Charging System With TEV
http://www.refrigeration-engineer.co...ad.php?t=14050

How to calculate refrigerant charge required?
http://www.refrigeration-engineer.co...ad.php?t=13478

Good Article About Superheat and Subcooling
ttp://www.refrigeration-engineer.com/forums/showthread.php?t=13284

Related but has new material: Superheat and Subcooling
http://www.refrigeration-engineer.co...ad.php?t=13119

How to Measure Superheat and Subcooling
http://www.refrigeration-engineer.co...ead.php?t=3716

In order to estimate the amount to charge you have to calculate the volume of the system that is filled with liquid and multiply by density of saturated liquid at the same conditions plus the vapor volume times the density at its conditions (usually a small value).
Using saturated conditions simplifies calculations and gives a good approximation.

If you don't have manufacturer data on evaporator and condenser you must estimate. Modern DX HE have low internal volume and if I had to guess would use 70% vapor and 30% liquid in the condenser and reverse these figures in the evaporator.

Te only new "concept" is to calculate the minimum height of liquid in a receiver at maximum load.

You do this equating potential energy of a fluid = kinetic energy at the highest value in a place with reduction of the area of flow like when you have a "vena contracta" in the outlet valve.

Rule of thumb use a 0.5 factor times the outlet pipe inner area (this means you should double the mass velocity value). Please don't post if the height you get is higher than the receiver! this could mean two things either you have the wrong receiver or the rule of thumb is only good for sucking!

The equation will solve to something like V squared = V V =2 g h

The height of liquid is h, g is acceleration due to gravity, and use consistent units.

Once you have a height calculate the volume of liquid of a (usually) cylinder shape times density of saturated liquid at high pressure conditions and the volume of the rest of the cylinder times its density of saturated vapor at the same conditions. This gives you the amount of refrigerant in the receiver at maximum load (minimum liquid height).