Results 1 to 4 of 4
  1. #1
    Join Date
    Sep 2007
    Location
    Brisbane, Australia
    Posts
    44
    Rep Power
    0

    Question R404A TX valve used on an R22 system... What could go wrong?



    G'day,

    I recently found that a medium temp system that is on R22 has had an R404A TX valve fitted to it. I noticed because the part code used was TES2 (Danfoss R404A TE2 valve) instead of a TEX2 (Danfoss R22 TE2 valve).

    Does anyone know what the impact of this would be?

    My quick calculation is that if the system gets to -5C SST the bulb will be reading 65psig (R404A) and the valve outlet will be seeing 46psig (R22) which will have the effect of the valve closing significantly more than it should and thus starving the evaporator.

    Does that sound about right? The higher bulb pressure will "beat" the spring pressure much more readily and result in less refrigerant and thus higher superheat.

    The recommendation will be to change to the correct valve, but I believe the unit is operating just fine so I suspect it may not go ahead. The bigger concern will be if I've got this arse about and the valve will actually OPEN more, risking liquid flood back....


    EDIT: Actually, I think I do have it arse about... 5K superheat should see a -5C SST give +0C on the outlet (57.5psig R22) but instead it will be reading 74psig (0C R404A) and thus try to open the valve further.
    Last edited by The Red Krawler; 21-06-2017 at 02:37 AM.



  2. #2
    Join Date
    Jan 2007
    Location
    India
    Posts
    60
    Rep Power
    12

    Re: R404A TX valve used on an R22 system... What could go wrong?

    Hi
    hen you use R404A Valve instead R22 ; the valve opening will be more than it would be .switching over to R22 valve will increase the super heat

  3. #3
    Join Date
    Sep 2007
    Location
    Brisbane, Australia
    Posts
    44
    Rep Power
    0

    Re: R404A TX valve used on an R22 system... What could go wrong?

    To update anyone who finds this in a Google search or whatever:

    Using an R404A valve on an R22 system will indeed result in a lower superheat than desired. In this case, around 2K evaporator superheat.

    I've taken a gamble and just adjusted the valve to suit 5K superheat (approximately 3/4 of a turn in). It maintained 5K through the full cycle on -> off at set point so we'll see how we go.

    If any work is done to the unit in the future that requires reclaiming the refrigerant it will either be switched to R404A, or have an R22 valve fitted. Hopefully the former - R22 is starting to get REALLY expensive!

  4. #4
    Join Date
    Aug 2014
    Location
    UK
    Age
    69
    Posts
    402
    Rep Power
    16

    Re: R404A TX valve used on an R22 system... What could go wrong?

    Hi RK
    So now you have seen the folly of people using an expansion valve designed for one refrigerant but used on a totally different refrigerant.
    When R407F was introduced into the market as the great supermarket replacement gas for R404A to prevent Ozone depletion engineers were running around the supermarkets retro-fitting this new gas, but using the old original expansion valves , which may have been R22 ,R404A, R407C valves etc. All were now being used on
    R407F . Not many of these valves were adjusted to run with the new refrigerant.
    Expansion valves and their relevant power element gas charge , are designed to give a constant static superheat across their design operating range normally about 5K. When you change the refrigerant in the system to a different type you also change the static superheat of the expansion valve , where this ends up depends on the pressure/temperature of the refrigerant and any glide with the gas.
    We did many calculations on the various valves that could be used in supermarkets and what would happen to the existing valve when the new refrigerant was installed.
    From this Danfoss decided to produce a dedicated R407F/A range of expansion valves , as the static superheat of the mismatched valve was causing high superheats and excessive run times of the plants. So reducing Ozone depletion but increasing Global Warming Potential by the increase in energy consumption.
    As you know there are so many refrigerant varieties on the market now that the only way to get the plant performance from these gases is to fit an electronic valve and insert the gas type into the controller ,so that it works with the true pressure/temperature curves for the installed refrigerant.
    I had one customer who did a retrofit to a plant in Scotland and after he did it the room temperature of the coldstore was controlled not by the thermostat but by the Sun rise and Sun set .
    Unless a dedicated designed thermostatic valve is available for the refrigerant type in the plant, an electronic type should be used to allow the plant to run as efficiently as possible
    The static superheat change change depending on what the evaporating temperature is of the system. You may end up with 10 -15K superheat or maybe run on a negative superheat ie flooding liquid back.
    Static superheat is the factory setting. superheat = static superheat + opening superheat = operating superheat

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •