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  1. #1
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    Need some help from the experts.



    Hi folks,

    I have 2 NF9FX Danfoss compressors with R404A gas.

    These units are cpu cooler devices know as the Prometia Mach II GT. This unit is geared for a 200 Watt max load on the evaporator and temps are around -35 C unloaded and -20 C something loaded.

    I know of some thread in another forum where the person increased the size of the condenser and cap tube from .028 to .031 and made the unit hold a quad core i7 load at -35 C -200 Watts. His unit is still single stage.

    I would like to know if my units can be cascaded to produce an even higher - C temp with current R404A in each unit and with the upgrades this gentleman made.

    Thanks



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    Re: Need some help from the experts.

    The working pressure inside the Mach II GT unit is 331 PSIG on the high side, 174 PSIG on the low side.

    Thought this might help.

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    Re: Need some help from the experts.

    Quote Originally Posted by acdcmike View Post
    The working pressure inside the Mach II GT unit is 331 PSIG on the high side, 174 PSIG on the low side.

    Thought this might help.
    I think that maybe should read test pressures, you wont get low temperatures at 174psi.
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    Re: Need some help from the experts.

    Quote Originally Posted by Brian_UK View Post
    I think that maybe should read test pressures, you wont get low temperatures at 174psi.
    Hi Brain,

    Do you mean I won't get lower than the standard temp of -50 C available from the unit now? Those are the pressure readings on the units case from the company.

    The unit actually produces -50C at no load, the readings I gave before are for the Mach 2, not the GT.

    My question is can these units be cascaded to give any sort of increase in - C temps?

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    Re: Need some help from the experts.

    Those readings are just maximum test pressures that can be applied to the unit without causing damage.

    R404a at 174psig equal a temperature of +26C.

    +
    -50C is about the limit for R404a without running the compressor under vacuum conditions.
    Last edited by Brian_UK; 02-02-2010 at 11:10 PM.
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    Re: Need some help from the experts.

    Quote Originally Posted by Brian_UK View Post
    Those readings are just maximum test pressures that can be applied to the unit without causing damage.

    R404a at 174psig equal a temperature of +26C.

    +
    -50C is about the limit for R404a without running the compressor under vacuum conditions.
    Thanks Brian,

    I pulled this off of a site.

    Advantages of R404a over R134a Refrigerant

    The Prometeia Mach II GT is charged with R404a refrigerant, which is a blend of non-flammible Hydrofluorocarbon (HFC) gasses Pentafluoroethane / 1,1,1-Trifluoroethane / 1,1,1,2-Tetrafluoroethane. R404a is a near-azeotropic 'zero ozone depletion' HFC refrigerant specifically used for low-temperature refrigeration applications. The term Azeotropic describes "a liquid mixture of two or more substances that retains the same composition in the vapor state as in the liquid state when distilled or partially evaporated under a certain pressure." The boiling point at 1ATM pressure of R404a is -46.5C, whereas the boiling point for R134a is -26.1C. Vapour pressure at 20C for R404a is 167.2 PSIG, and for R134a it is 84 PSIG.
    The original Mach I/II/II ST models ran with R134a, so the switch from R134a to R404a essentially means that the Prometeia Mach II GT can attain lower evaporator (cold head) temperatures and shorter start-up times. The trade off being that the Danfoss NF9FX compressor has to work a little harder. Compressor noise levels between the two refrigerants are no different, and the added stress is apparently mitigated by changing the working pressure inside the Mach II GT unit; 331 PSIG on the high side, 174 PSIG on the low side. (I thought it was at this pressure, sorry I'm a newbie in A/C)ECT believe that the Danfoss NF9FX compressor can run with R404a coolant in this very specialized application without problems, and claim not to have had a single RMA case due to the change from R134a to R404a.

    Just wanted you to see this.

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    Re: Need some help from the experts.

    I would like to add that I know cascading is an art and that there are few that can do this without any prior hands on knowledge.

    I'm hoping that someone here in this forum can give me a concrete answer as to whether or not I can cascade the guy's with some mods to get higher -C temps. I'm right in the middle of a system build and I cannot go any further until I know. I need tyo buy condensers, cap tube, and other products to finish the build but everything will be based on whether or not I can cascade.

    Thanks

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    Re: Need some help from the experts.

    Quote Originally Posted by acdcmike View Post
    I would like to add that I know cascading is an art and that there are few that can do this without any prior hands on knowledge.

    I'm hoping that someone here in this forum can give me a concrete answer as to whether or not I can cascade the guy's with some mods to get higher -C temps. I'm right in the middle of a system build and I cannot go any further until I know. I need tyo buy condensers, cap tube, and other products to finish the build but everything will be based on whether or not I can cascade.

    Thanks
    Thanks anyway folks.

    Got an answer in another forum from a well known cascading cooler guy and I will be cascading my units.

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    Re: Need some help from the experts.

    Fair enough, as long as you have a route to follow, keep cool.
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    Re: Need some help from the experts.

    Quote Originally Posted by acdcmike View Post
    Thanks anyway folks.

    Got an answer in another forum from a well known cascading cooler guy and I will be cascading my units.
    I have a question.

    The Danfoss NF9FX Process Connector is something I'm just not finding gen on.
    Can oil from an oil reservoir be returned to this connector?

    Turns out I cannot cascade my compressors and expect higher temps, it's only a 9cc compressor. I did bring up a viable idea to the boys in the other forum though, and that was to put them in parallel. I've been reading for a while now and I'm gaining much knowledge in refrigeration. I'm at the point where I put a diagram together and it seems to be pretty good in their eyes.

    I'm a licensed electrician with a cert in electronic controls and I always wanted to have HVACR under my belt but never could find the time.

    I really wish I could post the drawing I made but I don't have enough posts in yet.

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    Re: Need some help from the experts.

    I guess I can post attachments.

    This is what I have so far;
    Attached Images Attached Images

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    Re: Need some help from the experts.

    I'd like to add some shots of my build as well. I am committed to learning and building this system.
    Attached Images Attached Images

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    Re: Need some help from the experts.

    There is one more question I'd like to ask.

    I read somewhere that you should use a vertical accumulator if the suction line is going to be more than -10C.

    Should I change the horizontal to a vertical?
    I'm pretty sure the suction temp will be more than -10C.

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    Re: Need some help from the experts.

    Quote Originally Posted by acdcmike View Post
    I have a question.

    The Danfoss NF9FX Process Connector is something I'm just not finding gen on.
    Can oil from an oil reservoir be returned to this connector?

    Turns out I cannot cascade my compressors and expect higher temps, it's only a 9cc compressor. I did bring up a viable idea to the boys in the other forum though, and that was to put them in parallel. I've been reading for a while now and I'm gaining much knowledge in refrigeration. I'm at the point where I put a diagram together and it seems to be pretty good in their eyes.

    I'm a licensed electrician with a cert in electronic controls and I always wanted to have HVACR under my belt but never could find the time.

    I really wish I could post the drawing I made but I don't have enough posts in yet.
    Hi,

    I'm quoting my own post.

    I know that the lubrication system of a hermetically sealed compressor is inherent and no external lubrication is required, unless fresh gas charging is done.

    If oil and vapor always leaves the discharge connector it can cause some issues all around. In paralleled compressor systems, hermetic or not, oil seperators need to be used right?

    The addition of a regulator will assure that both compressors are getting equal amounts of oil from the reservoir right?

    If oil can be added to a hermetically sealed compressor before fresh gas charging, can the oil recirculate through the process connector after fresh gas charging?

    Would a steady recirculating flow of oil at the process connector damage the compressor in any way being that the oil flow is regulated?

    I noticed that most regulators have a three bolt pattern and are bolted to the compressor near the bottom.
    Is the a regulator that can be added to this style of compressor?
    Is there an adaptor kit to go from three bolt to copper line?
    Will the regulator still work if it's at the top of the compressor?
    Would I see the oil in the regulator sight glass?

    Thanks folks.

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    I updated my drawing

    Hi folks,

    Made a few changes to my drawing. I added gauges and changed the accumulators to verticals.
    Attached Images Attached Images

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    Re: Need some help from the experts.

    I'm wondering if I posted in the right place?

    Any takes on my questions folks?

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