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Static pressure question for Lennox cba38 variable speed and el17xp1 single stage heat pump 3ton

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I have a 3 zone system controlled by Honeywell hz432. I ask the contractor that I needed a bypass as when 1 zone is on and 2 off the zone supply is loud.

  1. Am I right to say that it’s pushing 1200 cfm to one zone when the other two are closed?
  2. Contractor states that they did a static pressure test and got .12 above the air filter and .39 in the supply plenum. But this was with all zones calling for cooling. With that alone they said I don’t need a bypass. My thinking is that they need to test each zone separately while one is open and the other two zones are closed. I have two 12” zone dampers on two zones and 1 10” damper in the third zone. Right now when tow zones are closed and one is calling for cooling it’s loud and sounds like a rain storm as the zone get cooled.
    Am I right that they need to do these tests before concluding that I don’t need a bypass?
  3. I have a Honeywell hz432 and I read in the manual that it can modulate the variable speed air handler when 1 zone is open and two zones are closed reducing airflow otherwise reducing the amount air that needs to be bypassed. Can this be done with the cba38. The manual says to wire the ds/bk terminal on the zone board to the ds terminal on the air handler?
  4. If it’s possible could this negate the need for a bypass. I ask because the home never had a bypass and it was originally powered by Lennox signature series variable speed air handler and 2 stage heat pump 3 zones fully communicating system. Unfortunately I never got to experience it operating with 1 zone open and 2 closed with the original zoning board as I had to replace it with the Honeywell hz432 and honey 9000 tstats

So is the contractor right? Or are they just trying to close the deal with the least amount of work to finish the job?

Can the hz432 modulate the blower speed with the wiring I mentioned above?

Without a bypass will the blower and compressor fail given the amount of static pressure with one zone getting all cfms?

What is the range of proper static pressures for 1 zone open and two closed?

Comments

  • HVACNUT
    HVACNUT Member Posts: 5,874
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    A bypass can be added. But it sounds like the ductwork itself and the diffusers weren't designed correctly for a zoned system. Even with a constant torque motor, there's limitations. As is, its trying to push 3 tons through a 1 ton duct. Definitely use the DAT sensor. Are there returns in each zoned space?

  • GW
    GW Member Posts: 4,734
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    I'm very rusty on my Lennox nomenclature, but that seems like this is a full variable speed air handler. In that case I would always wish to install a communicating zone controller, not a Honeywell or EWC, etc. When we do "X-13" ECM motors, then we rely a little bit on the extra static lowering the actual CFM. But 3 zones, that's a bit more than 2 zones, gotta be more on the ball.

    ".12 above the air filter and .39 in the supply plenum."—-he is telling you the static of the ducts only? Not sure how that helps much. In any case, supply ducts seem like they could have been a smidge larger.

    DS—- I Just grabbed this off of lennox' web site, for the AHU you have: "Harmony III control - This will allow the
    control to vary the voltage signal to the in-door b lower motor to control required CFM. " Back when i did Lennox 15 plus years ago, we always used the harmony 3 panel when we zoned.

    My opinion is —Bypass is a bandaid. Get the correct panel to modulate the blower motor.

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • pedmec
    pedmec Member Posts: 994
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    You will also need a variable speed full communicating condenser. if you don't and the blower speed is lowered you risk the chance of freezing the evaporator. From what you stated the condenser is only a two stage condenser (maybe that's the old one?). That means its going to run at 67% capacity at its lowest. Basically 2 tons of refrigeration. With only one zone calling you might only have 1 ton of airflow but 2 tons of condensing which will lower you back pressure until the evaporate starts to freeze.

    what model condenser do you have?

    Zman
  • GW
    GW Member Posts: 4,734
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    @pedmec OP said el17xp1 single stage heat pump 3ton.

    I'm assuming OP doesn't want to go to battle to reinvent the wheel with new outdoor equipment. DATS will kill the outdoor unit when temps get too warm/cool. AS we all know, zoning is a blessing (control different parts of the home) and a curse (going to have some shorter cycling, no matter what) all in one package.

    Also—-I am not skilled on the Honeywell HZ zone control operating a DS signal on the Lennox. That very well may be the answer.

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Pxsfir
    Pxsfir Member Posts: 4
    edited June 9
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    Btw I live in the Tampa Bay region in case that changes anything. Thanks for all your comments outdoor unit is EL17XP1 1 stage indoor unit is CBA38 variable speed. It’s 3 zones each zone is a separate floor. Honeywell HZ432 controlling 3 dampers in the attic to 3 zones. Contractor did a static pressure test again see attached. They recommended a by pass damper. First pic is all 3 zones open, 2nd pic is the 1 zone open (zone 3) and 2 closed. This happens to be the smallest zone. Hope this provides useful information. Last pic is not clear what was measured either it was an early snapshot of zone 3 or some other open zone just included it here for extra data

  • GW
    GW Member Posts: 4,734
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    Your screenshots don't make sense to me. I may be blowing smoke, but I assert that some hvac guys can't do a proper static measurement. I wasn't there of course

    The return is 'negative' and the supply is 'positive'. But these pics have two 'negatives'. Seems like they didn't move the hose to the negative and vise versa for the supply. Basically, you ADD the supply and the return to get total static.

    1st pic shows .40" which seems OK (are we talking ducts only?). 2nd shot shows 1.8" which is off the charts high. I can not place the + and the - numbers, I don't run these static numbers though the phone app they are using.

    That 2.4" figure is nuts. The more I look at the numbers, the more it doesn't make sense.

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Pxsfir
    Pxsfir Member Posts: 4
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    I’m not sure why they are both negative. But they definitely where placed in the return below the filter and the supply.


    I’m wondering if replacing the Honeywell Hz432 with a Lennox control board will take care of the issue in zone 3 as that’s the smallest zone. The original hvac was a Lennox signature series variable speed air handler and 2 stage outdoor unit installed in 2014 and in 2022 the Lennox control board failed and replaced with the hz432. Now in 2024 it was replaced but with no bypass installed. I’m wondering if the original contractor didn’t install a bypass because of how the Lennox zone board allows you to configure air speed per zone based on percentage jumper settings.

    Any thoughts?

  • GW
    GW Member Posts: 4,734
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    "I’m not sure why they are both negative. But they definitely where placed in the return below the filter and the supply." OK we are all over the map- if you want the total static, you need one probe (or reading) on the supply side and another probe on the return side. I'm getting more confused by your technician's readings. And, exactly where these reading are taken is important too, if you want the real numbers.

    Yes, that system worked normally when the Lennox zone controller was in place. Then along comes a tech that didn't know what he didn't know (happens all the time, me too). It went down hill when the Honeywell was installed. IF that Honeywell has a digital signal (Lennox calls this the DS wire/terminal) that works with lennox, then you may be all set when someone that knows what they are doing comes and corrects it. I simply stick with what i know works, when it comes to Lennox variable speed. Also, there's a jumper on the AHU's board that needs to be snipped when you run the DS.

    I learned 20 years ago you can't zone with a variable speed unless you have communicating zone panel. Basic ECM (X13, or, 'constant torque'), yes. Variable speed ECM, no.

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Pxsfir
    Pxsfir Member Posts: 4
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    Hi Gary

    Thanks for the feed back. It’s all about the technician I agree. I think that installing the Honeywell HZ432 was the first contractor mistake. On the other hand if they knew about how the HZ432 worked with variable speed air handlers and had experience with the DS/BK terminal things could have been different when the HZ432 was installed in 2022.

    From the HZ432 manual:
    "The DS/BK terminal is used with a variable-speed fan. Connect the DS, BK, ODD, or DHUM terminal on the HVAC equipment to this terminal. When 1 zone is calling (or 25% on systems with more than 4 zones) this terminal will be de-energized of 24 VAC. This reduces blower speed on most variable speed blowers."

    I asked the tech after he took the static pressure readings about wiring the DS/BK terminal and he said he wouldn’t as it will reduce velocity when the blower slows down. I tried calling Honeywell about the DS/BK terminal but they won’t answer questions because I’m not a HVAC contractor. I wanted to ask them if the signal is PWM which is what your calling digital and if that terminal works with Lennox.

    I’m of the opinion that most contractors at least ones I’ve dealt with here don’t understand zoning.
    When you say you stick with what you know what works are you referring to a Lennox Zone Board? Because I know there are a few versions out there Harmony 3 or 4, iHarmony and what Lennox is now calling the LZSV and LZS2.

    Based on what I read the Lennox zone boards is superior then the HZ432 as it let you configure each zone by percentage of CFMS so with that said the HZ432 DS/BK terminal at best only reduces blower speed if it is a digital signal vs how the Lennox Zone board.

    Question do the Lennox Zone boards need to be paired with Lennox S30 thermostats and anything else that’s necessary (I have Honeywell zoned dampers) as these are very expensive or can it work with Honeywell VP 8000 or Honeywell 9000.

    My challenge now is getting the current contractor to properly address the static pressure by either adding a bypass or wiring the DS/BK on the HK432 or by installing a Lennox zone board or a mix of the properly installed zone board and a bypass. My thinking is the original system didn’t have a bypass because it didn’t need it because it was a total Lennox signature series communicating system. But that’s assuming the original contractor knew how to configure zoning.

    If you were me what would you ask my contractor to do? Keep in mind the unit specs in the subject.

    Maybe it’s time to call another contractor and get a 2nd opinion?

  • GW
    GW Member Posts: 4,734
    edited June 12
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    ok yes, trying to work the DS seems simple and low costs, I just don't have any experience with it.

    Harmony 3 is what I have used in the past. i have never installed a harmony4. We have been Carrier-Bryant (evolution/Infinity) for the last 12 or 14 years.

    Yes, just normal stats with harmony 3, which is why i likes that control so much

    I just logged on to my Lennox acct— seems like they changed the name

    "Lennox LZSV, LZS Zone Control Panel (Formerly Harmony III), Up to 4 Zones, 24 VAC" (wow the price has jumped too)

    Some tradespeople are stubborn, and or don't have time to take on something new. I am in that category too (we all are if we are being honest). Whoever installed the Honeywell made the first mistake. Whoever installed the new outdoor unit didn't know what they were walking into. It's a big old finger-pointing circle.

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • mattmia2
    mattmia2 Member Posts: 9,842
    edited June 12
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    I can't qoute just a line anymore but:
    ""The DS/BK terminal is used with a variable-speed fan. Connect the DS, BK, ODD, or DHUM terminal on the HVAC"

    Usually dehumidify is just a contact closure that reduces the blower speed t another setting on the control board, usually only 25% slower or so so unless somewhere else you can set the function of this terminal, it is probably just a contact closure that says run at a slower speed. You would have to look at the air handler manual to see if you can set how much slower that is.

    This also needs to control the outdoor unit somehow so it shuts off when the evaporator gets too cold. There may be a kit for the air handler that does that or there may be an option with the zone control.

    Edit: Even with a bypass damper you will need to control the condenser so the evaporator doesn't get too cold.

    In the original system with the lennox control the zone control controlled the blower speed.

  • GW
    GW Member Posts: 4,734
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    yes the DATS will kill the outdoor unit for 5 or so minutes

    Discharge Air Temperature Sensor

    normally set to 42 degrees or so

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com