Is it possible...

Discussion in 'Geothermal Loops' started by wigaloi, Aug 13, 2012.

  1. No 24 x 9 is not enough on the return side for a 4 ton geo system rated at 400 cfm per ton. Most geo's are running 450 cfm per ton with a 1/2" w.c ESP
  2. Improper duct design and sizing and sealing accounts for an average of 46% drop in efficiency with the average HVAC system today across one corner of this country to the next.
    We see this on a daily basis.
    I also do not see a barometric damper, Ductwork is a science and when you then add a zoning system into the equation it gets to be even more of a mess. Add in the average contractor with little to no design experience and there goes all of your energy savings.
    I am truly sorry for your problems
  3. wigalo

    wigalo New Member

    Yeah, that's what I was thinking. I was hoping that since the return inlet is so large that it made up for the plenum getting smaller after the air filter.

    As you can see, it looks to be a major undertaking to get a larger return intake in because of the supply on the left hand side.

    Would it be worth having the ducting adjustments made and the unit moved over to get a larger return air intake? The downstairs unit has the same setup.
  4. wigalo

    wigalo New Member

    I have the Hvac guy coming out on Monday, so I went back to develop a plan for the revised return. I was incorrect on the measurement. The return plenum is 8x30, not 9x24. Based on the CFM charts online, it has a 1675 cfm capacity.

    So while my cold air return trunk line is undersized for both units (12" flex). It doesn't look as though we'll need to do any major moving of the Hvac unit to get a larger return in.

    We have 5 returns downstairs and 6 up. can the return ducts be run like a supply...i.e. 18" down to 16" down to 10" at the end of the run(with the appropriate t's to individual returns) OR should each return grill be run back to the plenum individually. since I'm paying for this twice, I want to make sure that it's done correctly this time.
    Last edited: Dec 20, 2015
  5. wigalo

    wigalo New Member

    There is a bypass valve on both units. (arm with adjustable weight) you can't see it in the pic because it's in the attic
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Increase the size of the round pipe or just add more.

  7. We typically run the returns independent of each other. It is more materials to do so but you then have the most efficient and super quite design. Glad to hear your R.A duct is larger than previously stated. Just make sure when you size for your return cfm that you are using .05" on the ductulator to get the proper size duct as well as using 450cfm per ton for your system total cfm.
    We actually size our returns at .03" w.c
  8. wigalo

    wigalo New Member

    Back again. Going through another uncomfortable summer. I think we finally found a tech who knows what their doing.

    Like everyone else he went through all of the normal checks. Superheat was out of spec so he focused on the txv valve. It was wide open as it should have been.

    He then shut the fan off while keeping the compressor on and that's when he spotted a problem. The frost buildup was extremely uneven. It caked on the top and bottom of the coil, but the middle had 1/2 the frost build up.

    He concluded that the coil was clogged (internally). Makes sense to me. He didn't think that he could blow it out so he is ordering a replacement from cm tomorrow. I'll keep you posted in the upcoming weeks to let you know if this was the solution to one of my major problems after 6 long years.

    I hope this helps someone else.
    Last edited: Aug 5, 2016
  9. wigalo

    wigalo New Member

    I think after all these years the problem has been resolved. As it turns out the charge on both units was extremely low. About 1.1 pounds on the upstairs unit. No leaks after vacuum and pressure testing, so the tech thinks that has been the problem this whole time. He was baffled because the pressure readings were in spec and is thinking that's why all of the other techs missed it.

    He actually evacuated the refrigerant and weighed it on his way to replacing the txv valve when he realized the low level. He filled it up and just like that a 20* split instead of 6* yesterday when it was 90* outside. Instead of it taking a 4 hour run time to move a degree, it only took 15 minutes.

    In addition, earlier this spring I had an outfit come out and fix my ducting for the downstairs unit. Prior to that, still another outfit came out and recharged the downstairs unit and by coincidence the downstairs compressor stopped engaging while the tech was working on the upstairs heat pump. Turns out, there was a leak, which my new guy found and rebrazed. Filled her up and again, magic.

    Props to To owner Chris and his Tech Dennis of "Absolutely Fabulous HVAC" out of Tacoma, WA. For fixing in a short amount of time what 5 other"Geo Experts" (including one member of this forum) weren't able to do over the last 6 years.
  10. wigalo

    wigalo New Member

    79* today and a/c is keeping up in every zone Screenshot_20160829-190130.png for the first time ever and it hasn't been running continously.
  11. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Absolutely bizarre to go from a 6 to 20 *F indoor air temp split after several other techs had evaluated.

    Pressures alone aren't enough. Need to know superheat and / or subcooling. (When in doubt, charge for 10*F each)

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