Digital scroll chiller

[marc5180]

We are trying to develop a chiller with a Copeland ZBD114 digital scroll compressor. The chiller is meant to be used 365 years a day in a small brewery. We have chosen to use a digital compressor in order to try to modulate evaporating pressure and save our customer some bucks.

Since it´s supposed to be the ideal marriage, we have also included an Emerson EX5 electronic stepper valve as the evaporating valve. We have previously used both new technologies before with great success but since now we have not built something like this previously.

We are using R404A and we have programmed the electronic valve controller to maintain a 6º C superheat, and the electronic capacity control of the compressor set-point at -10º C .

When the compressor starts modulating, it comes to a point where the evaporation pressure starts to go down very quickly. It took me a long while to figure out what´s happening but as far as I can tell, the problem is that, when the compressor is on the OFF part of the modulation cycle (20 seconds cycle) the evaporation pressure goes up as expected, the pipe temperature that measures return gas temperature does not change (it´s an NTC sensor) and the electronic valve pressure sensor reads low superheat and closes. Then the ON part of the modulation starts and the valve is closed, so the system pressure goes down.

Has anyone experienced this issue ? Hy anyone worked with or developed a chiller using a digital scroll compressor ?

Which controller are you using for the EEV? Is it the EC3 D73 by any chance? If so, then when the compressors cycle off, does the ‘enable’ (0-10v/4-20ma) also drop out?
Also what do you have the minimum valve opening position at upon startup set to?


Have you got a controller to be able to go in and check the settings that the

[otrotabi]

No, it´s an Eliwell XVD, but I also have a Dixell XEV22 to work with if that would mean a solution.

Actually the valve controller has no way of realizing the compressor is not cycling in this setup, the digital input is enabled throughout the whole cycle. I have not found any parameters (but maybe there is a way I can not find so far) to allow me to keep the valve open while on the OFF cycle.

I am using the suggested 85 % as the opening position valve, but problems are not happening during startup, actually it´s sort of a stabilized system issue.