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Thread: txv v.s. fixed

  1. #27
    Join Date
    Jun 2003
    Location
    Jacksonville, FL.
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    4,313
    Originally posted by RoBoTeq
    Define "better". I for one would rather have the simplicity of a fixed metering device on a system that does not require to have a constant superheat. Do I have to give up my pro status?
    Yep. I expect your resignation on my desk by midnight!
    WHY?

  2. #28
    txv by far

  3. #29
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,981
    Originally posted by smokin68
    Robo, you really need to stick to the ARP section, you're giving politically correct replies in the res section.
    Are you really going to back an orifice over a txv? I know you know better,as does everyone else.
    I am not stating that fixed metering is more effective then a TXV, just that if its not needed, then it is "better" to have the more reliable fixed metering.

    I went through this with my parents home in Ocean City, Maryland. As the name implies, their home is very close to the Atlantic Ocean and 8 feet from a brackish bay. I was certain that the system would benefit from a TXV due to the humidity.

    Well, I installed a fixed metered coil in a VS air handler with the intent of installing a TXV. I forgot the TXV on weekend I went to my parents house and so installed the system with the fixed metering, again, with the intent of changing it to a TXV.

    I've been monitoring this system for 3 years now. It reduces the humidity fantanstically with only using the VS blower on a lowered speed.

    Bottom line; I'm not going to "fix" what ain't broken.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  4. #30
    Join Date
    Dec 2002
    Location
    North Central Ohio
    Posts
    230
    Question,
    would a piston setup with a VS blower and a condensor fan cycling control protect the compressor from slugging and allow operation at a low ambient condition also?

  5. #31
    Join Date
    Mar 2006
    Location
    Delaware
    Posts
    448
    TXVs are CLEARLY better. Even inthe long term. I come across bad ones SO rarely, reliability is clearly not an issue. The improved performance and added compressor protection by having constant superheat is a clear bonus. And heck, TXVs don't even cost that much! Electricity does.

  6. #32
    Join Date
    Nov 2000
    Location
    Eastern PA
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    68,981
    Originally posted by supertech 1234
    Question,
    would a piston setup with a VS blower and a condensor fan cycling control protect the compressor from slugging and allow operation at a low ambient condition also?
    For low ambient operations I always suggest using a TXV. This is one of the conditions I was referring to that a TXV is worth investing in.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  7. #33
    Join Date
    Feb 2005
    Posts
    95
    Fixed metering devices have three advantages they prevent runaways, they are cheap, they are cheap, oh yeah I almost forgot they are cheap.
    Experiance is learning what doesn't work.

  8. #34
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    Originally posted by -80guru
    No doubt about it txv rules, fixed restriction drools.
    LOL!

    Cheap is as cheap does.

    Performance is as performance does.

    Give me performance and precision. Give me compressor longevity (TXV is cheaper to replace than compressor). Give me lower operating costs. Give me dehumidification like nobody's business!

    Sure, a fixed restrictor gets the job done. So does a fast food burger vs. prime rib. Burger's cheaper, goes to the same place. But it's unremarkable. Pedestrian. Pedantic. Pond scum. Paltry...okay, that's enuf...
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  9. #35
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    Originally posted by jamessaluda
    I have to agree with the fixed. even though you cant acheive the required superheat{ which is a game invented by the goverment} service for the tech and consumer is much more feasible.
    Ummm, last time I checked, wich is usually several times a day, servicing a system that has a TXV is simpler than it is with fixed metering....

    What could be simpler than charging by subcooling and verifying superheat?

    Charging a fixed metering system has more varriables that leave room for error.

    Sadly, many "techs" don't have a good grasp on the refrigerant cycle and how things like airflow, and other system problems, affect the refrigerant cycle. These "techs" don't understand how a TXV works, and how it reacts to other problems in the system, so they often end up blaming the problem on the TXV. Most "failed" TXVs didn't actually have anything wrong with them....

    In my area, I probably work on disproportionatly more TXV equipped systems than people do in most other parts of the country because high SEER equipment has been popular here for many years. I have also been working for companies that sell far more systems with TXVs equipped than with fixed metering.
    I find less than 1 failed TXV per year. I would call them extremely reliable based on my experience...
    If more government is the answer, then it's a really stupid question.

  10. #36
    Join Date
    Nov 2000
    Location
    Eastern PA
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    68,981
    I agree with the charging comparisons. Whether you are checking superheat on a fixed metered system and verifying the subcooling is in line or checking the subcooling on a TXV system and verifying the superheat is correct, the same basic measures are being taken.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  11. #37
    Join Date
    Feb 2005
    Location
    Toms River, NJ
    Posts
    428
    Will someone please tell goodman to start using TXV's so Robo can stop embarrassing himself....


    Dave in NJ

  12. #38
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453
    I tend to agree with Robo, here. Properly set up, a piston system will last forever, and I have NO data that says more compressors have been replaced from pistons than with TXV's. In my experience, I have replaced just as many compressors on TXV systems as I have on piston systems.
    I also think TXV's generally are set for too high a superheat value. Like 15 or better. If a TXV was so good at keeping superheat steady, then why aren't they set at 5 or 10, which would keep the coil colder and make the supply air cooler. I have replaced several TXV systems ( mostly Lennox ) where the HO could not get the house comfortable. Put in a new piston system and the HO was very happy.
    For technical purposes, the TXV handles load changes faster, and I'll admit, under certain circumstances can protectthe compressor better. However, due to the higher superheat that they are set for, the piston would be cheaper on the HO's electric bill, without having the possibility of repair / replacement.

    Richard

  13. #39
    Join Date
    Mar 2006
    Location
    Delaware
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    448
    Note: TXVs don't control evaporator temperature per se, they control superheat. Coil temp is determined by air flow, compressor delivery, etc., but the coil temp will float to maintain fixed superheat. At least it's being controlled by the parameter that helps the system maintain peak efficiency, and that's superheat. fixed orifices simply cannot do this. And then there's the energy savings by controlling superheat. I agree, lower superheat would be great, but lowering it with present control valves could get close to having liquid come through, and 10-15ºF superheat is still pretty good, not a lot to be gained by going lower.

    >>I tend to agree with Robo, here. Properly set up, a piston system will last forever, and I have NO data that says more compressors have been replaced from pistons than with TXV's. In my experience, I have replaced just as many compressors on TXV systems as I have on piston systems.
    I also think TXV's generally are set for too high a superheat value. Like 15 or better. If a TXV was so good at keeping superheat steady, then why aren't they set at 5 or 10, which would keep the coil colder and make the supply air cooler. I have replaced several TXV systems ( mostly Lennox ) where the HO could not get the house comfortable. Put in a new piston system and the HO was very happy.
    For technical purposes, the TXV handles load changes faster, and I'll admit, under certain circumstances can protectthe compressor better. However, due to the higher superheat that they are set for, the piston would be cheaper on the HO's electric bill, without having the possibility of repair / replacement.

    Richard

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