Quote Originally Posted by mvtop View Post
So how to improve what I/we (group project) have now,

i'm thinking that i need to add some length to the cap tube to slow things down a bit. I think i'm running a 32" tube now.
I would expect to get better performance with the heat exchange once i rework the coil again. Reduce refrig. charge

anything else?

thanks
Mvtop
If you lengthen the tube then the following may happen:
The controlling element is the compressor and not the tube, it is the compressors suction volume and suction conditions that dictate the systems mass flow rate. The other components just adjust themselves to fit to the compressor. So if you increase the length of the tube then:-
Before the knee - i.e. at flows hight than at the knee - the condenser will begin to back up liquid and reduce its effective cooling till the pressure is high enough to force the mass flow through the tube.
The consequences are a higher head pressure, a starved evaporator and more power consumption.

After the knee - i.e. at mass flows less than at the knee - the increase in the tube will make the quality move towards zero and the pressures will remain almost the same as now. You will see an increase in cooling effect, there will be more liquid in the evaporator because the the charge will need to be a little bit more. The corrollary is that more liquid is then in the system and during startup even more is built up in the condensor and the discharge pressures are higher.

Its a sort of win at one end and loose at the other.

If you are thinking about redoing the evap coil have you considered putting the coil inlet at the bottom and outlet at the top, it seems more common to do it that way - in all the systems I have seen anyway.

Chef