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  1. #1
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    Digital scroll chiller



    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 itīs 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 6š C superheat, and the electronic capacity control of the compressor set-point at -10š 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 whatīs 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 (itīs 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 ?



  2. #2
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    Re: Digital scroll chiller

    Hi
    This is a common problem matching a capacity controlled compressor with an electronic valve control signals. I don’t know the Emerson valve and controller very well, but I always found the Emerson valve was slow to react to the pressure and temperature signal changes, which I suspect is due to the controller set up and the filtering time that the controller gives to the input signal changes. I would suggest speaking to Emerson directly to see if any of the settings in the controller could speed up the opening of the valve. I know the Danfoss electronic valve and controller and there are many parameters that can be changed to improve the erratic signal control that the suction sees during unload and load signals.
    Have you thought of trying an invertor (speed) controlled Maneurop scroll or Bitzer, this would give a far smoother suction pressure control and let the electronic valve control in a more stable fashion

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    Re: Digital scroll chiller

    Hi Glenn, thanks for your feedback.
    I did try Emerson already, but I was not able to find anyone giving me a sensible answer. I was hoping I could be given someoneīs name with hands-on expertise on this subject but all I got was the corporate "everything-we-do-is-perfect" answer instead.
    I am a fan of electronic valves myself, thereīs so much information and variables you can work with, but as I said before, this is the first time with a chiller and I suspect that since everything is so compact in terms of distances pressure variations are more abrupt than with a remote evaporator setup.
    Actually what I think is the valve is reacting too fast, not too slow. If you could give me a hint on which parameters you would work on with a Danfoss controller, I can figure out what to do with either Dixellīs or an Eliwell controller.
    Lastly, I regret having made the chiller with a digital scroll compressor but I need to make it work now. Actually the chiller does work fine if I do not fiddle with scroll capacity but it is a personal challenge to make it work as was meant to.
    If I could somehow figure out how to make the valve stay open at the same position while the compressor is not pumping, do you think this issue would still happen ?

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    Re: Digital scroll chiller

    I have used Sporlan EV controlled by Carel on two large air driers.
    Never had any problems.

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    Re: Digital scroll chiller

    Hi chemi-cool

    Are they digital compressor driers ?

    My own experience, so far: large setups, like supermarkets and large meat facilities with digital technology, both scroll and Discus compressors: great !

    Electronic valves: I have used both pulse PWM valves and stepper valves, both great. Also used electronic valves for non conventional uses, for example, hot gas and cool gas injection, never had any issues and I am happy to use them whenever the budget (and in my country at least) qualified maintenance people are available.

    It is this mix, digital scroll and electronic valve in a small sized chiller, that is giving us trouble trying to find the right setup.

  6. #6
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    Re: Digital scroll chiller

    Quote Originally Posted by otrotabi View Post
    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 itīs 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 6š C superheat, and the electronic capacity control of the compressor set-point at -10š 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 whatīs 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 (itīs 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
    The difference between genius and stupidity is that genius has its limits.

    Marc

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    Re: Digital scroll chiller

    No, itīs 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 itīs sort of a stabilized system issue.

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    Re: Digital scroll chiller

    Dear colleague ,

    Because of the symptoms presented by its control system with Copeland Compressor "Digital" and electronic expansion valve indicating that the valve closes after showing little superheat the possible causes are the following
    1 - The Evaporator is short because the commercial chillers are for air conditioning applications and / or the flow is low . . . Solution : select an evaporator for the operating conditions
    2- That you are using a liquid solenoid valve together with the electronic expansion valve . . . Solution : remove the solenoid valve

    Best regard
    Last edited by chemi-cool; 19-08-2018 at 08:28 PM.

  9. #9
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    Re: Digital scroll chiller

    Dear Carlos, thanks for your feedback.

    It is not a commercial chiller, actually it is a glycol chiller developed by us for a small brewery. The heat exchanger is correctly selected for the design condition of 30š ambient temperature, but when ambient temperature goes low (it is winter time here these days), compressor performance gets better and so (without capactity control) evaporation temperature goes low also.

    Using compressor capacity control should let us work in optimal conditions, high evaporation and low condensing, but digital technology is not working fine for this particular setup, we will move to an inverter in the future.

    Also though recommended by EEV manufacturers in case of power outage, we have chosen not to use a solenoid valve, using a scroll compressor any eventual liquid floodback should not mean a big issue.

    Regards

  10. #10
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    Re: Digital scroll chiller

    You have not mentioned condenser, is it water cooled or air cooled?
    You have to keep condensing pressure high with 404 and if you keep it high' it will help you to maintain evaporating pressure above freezing.

  11. #11
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    Re: Digital scroll chiller

    Hi chemi-cool, itīs an air cooled condenser.

    The whole point in this setup is to be able to work in the low condensing as long as ambient temperature is low, and this is why we are using an electronic valve and a variable capacity compressor. A ZBD114 compressor can work as low as 10š (about 100 psi) with 404.

    If you take a look at the compressor table, for a summer condition i.e -10/45š, COP is 2.1, but under a winter condition i.e. -10/15š, COP is 5.7. The problem is that the evaporator is sized for summer condition, so in order to balance the system you have to adjust compressor capacity, either a frequency inverter, or a digital compressor.

    We are not particularly worried about freezing, thereīs roughly 25 % glycol in the brine.

  12. #12
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    Re: Digital scroll chiller

    I don't argree with you.

    If your condensing pressure will be too low, gas will flow into the liquid line .

    You have to control head pressure and its not done by controlling compressor speed.

  13. #13
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    Re: Digital scroll chiller

    Dear colleague ,

    My recommendation to control the capacity of a Chiller is to use the Hot Gas Bypass at the evaporator inlet . The problem with variable speed in Scroll compressors is lubrication at low speed .

    I think your big problem is in the Shell-Tubes Evaporator that at low capacity the oil accumulates in the Evaporator and in the Condensation pressure that must be controlled . Regards ,
    Last edited by chemi-cool; 21-08-2018 at 07:29 PM.

  14. #14
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    Re: Digital scroll chiller

    Dear colleagues, I think we are deveating from my original post here and I do not want to turn this into a thermodynamics discussion. I was asking for help regarding specific setup for a digital scroll and electronic valve.

    I know there are different setups as you propose to make the chiller work and we have used them in the past and still do nowadays depending on the budget, however they are not the best in tems of energy efficiency.

    I thank for your feedback.

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