Duct/Zoning Issues

Discussion in 'Maintenance and Troubleshooting' started by dmj2359, Feb 8, 2013.

  1. dmj2359

    dmj2359 New Member

    Having some minor problems with our new geo install, not specifically related to the geo aspects but seemingly more of general HVAC duct sizing/type/installation issue. With all the general HVAC pro's on here I'm hoping to get some opinions on a way to proceed.

    General system info: WaterFurnace 7 Series with IntelliZone2 and 3 zones. HVAC system duct plan can be viewed here. Zoning is broken down into: Master Suite, Balance of 1st floor, and 2nd floor.

    The first floor zones work great, the system has no problem maintaining the temperatures. The systems ramps up and down as needed and I've yet to see a compressor speed over 8 (of 12) even as the exterior temperatures dip down to 10F or so. The second floor however has been a constant problem. Although set at 68, it regularly drops to 64 or so at night when the outside temperature drops anywhere below 30 or so. This should not be an insulation (walls R-18 flash & batt closed cell spray foam, attic R-64 combination closed cell spray foam and blown fiberglass) or infiltration (scored 1.5ACH50 on our blower door test) issue. I believe the problem is a combination of the following issues:

    1. The flex duct installed in the attic is only isulated to R-8 (standard for the area) and in my opinion poorly installed. I can see a number of kinks where the suspension straps are installed, or where they cross trusses.
    2. Long duct run. The 10" x 10" riser up from the basement to the attic is long by iteself, even before the 10" and 8" flex duct runs in the attic.
    3. Variable speed system. Because the 7 Series is variable speed it generally cranks itself down to a low level where it runs all the time. This means that the 2nd floor zone is rarely running by itself, resulting in even lower flows due to the backpressure of the long run. It seems this should have somewhat been covered by the Manual J/duct sizing calculations.
    4. Because the flow to the vents is low and are not very well insulated the air coming out is fairly cooled by running through the uninsulated attic.

    The installer has brought out a vent hood meter and verified that each vent and return is moving some air (numbers are way lower than I'd expect, but I don't know what they should have been). I'm debating two possible paths forward.

    A. Reroute all the flex ducts to elimate kinks and shorten routes where possible. Lower them to the top of the spray foam and then mount blown fiberglass around them to improve insulation.
    B. Rip out all the flex ducts and replace with rigid ducting in the attic, using some combination of insulation to get them up to closer to R-25 or so.
    C. Something else I haven't thought of yet.

    I'm happy to provide any other info I might have if it helps in assisting with a solution. Thanks in advance.
  2. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I do not like flexible ducting for the same reasons you do not like it.

    I do not think that the R value is hindering your results as much as air flow is the problem. I have used miles of 4.3 R flex without any issues.

    I am off to find my duct slide wheel to find out what 10" X 10" will support. Might be a few moments to find it.

    Flex ducting by its design slows down the air flow.

    The "installation" may be the issue. ^^^goes of to find the person that does not return tools like the duct wheel to their home. I will beat him silly. Pogo says, "We have meet the enemy and he is us.".

    I do not use your zoning system. So I will need to learn it to be able to help. We do work in MD.

    Is there a by-pass damper or is the system equipped with an ECM blower drive?

    I will be back when I have the numbers 10" X 10" will support.

  3. dmj2359

    dmj2359 New Member

    The system does use an ECM variable speed drive.
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I have several Intellizones under my belt, but no 2s. The fact that your second floor zone falls way way behind despite the fact that the WF 7 never gets into high gear gives rise to several possibilities or combinations:

    1) Undersized or poorly installed ductwork - a proper, room-by-room load calculation coupled with reasonably accurate heat rise figure in heating mode will yield necessary air flow to each room, measurable with the flow hood. Ask to see a comparison between measured and calculated flows.

    2) IZ board set up - the system should run continually whenever any zone is calling...it sounds like the upstairs is calling and calling and calling, as indicated by a 4*F delta between measured and setpoint. Perhaps the zone is set up for "economy", ignoring Y1 calls from that zone alone, but when 2+ degrees shy, the thermostat should initiate a Y2 call, commanding compressor operation. IZ may be set up to assume the upper zone is smaller than it actually is, so it is not providing enough capacity. DISCLAIMER: the foregoing is based on IZ1 typical setups which may or may not apply to IZ2, but similar, in fact more advanced and flexible provisions should be available.

    3) Inappropriate installation / sizing / setup of a bypass damper. Personally, I despise bypasses and refuse to install them for several reasons I will not now elaborate. A true variable capacity system such as WF 7 should have absolutely no need of one. A screwed up bypass damper could easily starve an outlying zone while subjecting system to unnecessarily high compressor loading.

    4) Major duct leak in attic - this seems unlikely, but might explain the issue. Inspection or a duct leakage test might be in order. The blower door guy might also own a DuctBlaster from same company. As Mark noted, R8 insulation level is fine and likely has little bearing on your problem(s).

    5) I'm not real jazzed by some of the aspects of the upper floor - Beds 3 and 4 looked to be starved relative to Bed 2 and its bath, but I'd reserve judgement pending examination of a room-by-room load calc and actual airflows. Ask if the flow hood has been calibrated or otherwise assessed for accuracy.

    6) I haven't mentioned system size / whole house load until now, but given that system stays in low gear and problem is confined to one remote zone, I don't expect a problem there. It is odd that a heating problem appears in the upper floor of what sounds like a particularly tight and well insulated home - that further supports a duct or bypass problem. I assume windows are at least fair to middling as to winter energy performance?

    Is this system so new that it has not cooled during a summer? If it performs this badly as to the top floor in winter, summer will be a real bear!

    We do a fair bit of balancing work, especially in winter (the "off" season in Florida), and many duct systems are so screwed up that even the most rudimentary modifications are met with happy astonishment by clients.
  5. dmj2359

    dmj2359 New Member

    I *believe* the room-by-room calculation was done, but I don't have the paperwork to prove it. I do know they did not do a measured vs. calculated flow - reason stated was due to the zoning and variable speed fan would throw the numbers off. Seems like an excuse to me, it seems easy enough to force all the dampers open, use the AID tool to throw the fan into high gear and measure away, but I have been unable to convince them to do that. I have on my to-do list to pester them again about getting the proof of the full calculation.

    The system starts to run whenever any zone is running. All zones are set to comfort. I've even bumped up the size of the 2nd floor zone one notch (from the thermostat), which causes a slight increase in fan speed when that zone is running, but it hasn't made a noticeable difference in the temperature.

    There is no bypass damper. Each of the four trunks off the unit (2 for the main 1st floor zone, 1 for the master suite, 1 for the 2nd floor) have their own damper and there are no others.

    Possible. Due to the complicated roof structure, and the multiple attic heights getting around up there is interesting to say the least. I'm hoping to carve out a few hours this weekend to do a better inspection.

    Flow hood had a current calibration sticker on it. See comment on #1 above regarding room-by-room calculation.

    Windows were a slight upgrade over the standard builder grade - but with all the recent code upgrades they were actually pretty decent. I don't recall the exact specs. More importantly they were installed reasonably well. Decent job flashing, and low expansion foam all around.

    Correct - we just moved in before Thanksgiving 2012. This is a large concern of mine - I'd like to get it resolved while working in the attic is bearable, and right now if it gets too cold I can send a blast of heat upstairs by cranking up the pellet stove. No such option in the summer.

    My hope remains that it is a simple ducting issue and everything will be great afterwards!

  6. dmj2359

    dmj2359 New Member

    I got some updated information from the HVAC contractor. They provided me with the information they passed along to WaterFurnace to do the unit sizing (document here). The last page is my own addition, a screenshot from Excel with a breakdown of how the zones are broken across the different feeders. The HVAC contractor stated that a Manual D calculation was not done, but did not indicate how the duct sizing was then chosen. I'm still planning on an extended trip to the attic this weekend to see what I find. Will advise.

  7. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Good deal - you have a room by room manual J showing required airflows. That's hugely helpful.

    Dispense with the nonsense about how zoning and a variable speed air handler complicate a delivered air flow analysis. That's pure laziness wrapped in mumbo-jumbo.

    Given that your comfort issue pertains only to the top floor in heating mode, it should be a simple matter to replicate the circumstances (probably a persistent heating call from second floor only) and get someone in with a flow hood to take measurements. I'll venture a guess that the upper floor rooms are flowing no more than 1/2 - 3/4 required airflow.

    While you are mucking about, take some temperature readings. Implicit in any calculation of required CFM for heating or cooling is an assumed delta-T (temperature change) achieved by the system. It can heat lots of air a little bit (typical of heat pumps) or a little air a lot (typical of fired heaters, gas or oil)

    Upon reflection, that load calc exhibits some questionable values:

    1) design temperatures - 0*F heating, 95*F cooling does not make sense for anywhere I know in Maryland
    2) 55% humidity is OK in summer but wildly high for winter design
    3) The heating system is listed as a Carrier 15 kW heat kit providing 48*F temperature rise. You have a geo system and it won't make a 48*F temperature rise.
    4) The books seem to have been cooked to generate identical (966 CFM) required airflows in heating and cooling. That beggars belief!

    Something's rotten in Denmark, or at least in Maryland.
  8. dmj2359

    dmj2359 New Member

    This was my opinion as well, but so far I haven't gotten them to change their minds.

    My recollection (kicking myself for not writing it all down as it was being measured) is that the 2nd floor zone moves ~350 CFM total at fan speed 5 (of 7). I failed to have him measure when all dampers are open, which was a mistake because I think that is when the problem is the greatest.

    Will do - needed an excuse to buy a nice instant read probe thermometer anyways ;)

    The answer I got from the HVAC guys is this was their normal worksheet which was then sent to WaterFurnace to determine the unit size. I'm hoping to contact them to see what info they generated with it.

    I also did some further checking in the attic this past weekend. The 10" main flex duct feeds coming off the 10"x10" riser appear to be minorly kinked where they connect together. It could actually be more problematic as this connection is half-buried in closed cell spray foam and can't be fully inspected. I need to get a couple work lights up there to see what I'm doing but I plan to disconnect one of the 10" flex ducts so I can look at the inside of the connection to verify.

    Thanks for all the help so far.
  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I still have yet to find my "duct sizing wheel" I may have sold it with the motor home.

    I think 10" x 10" is not enough, but at this point I can not prove it. I do not think a minor kink in the flex duct buried in spray foam is the problem. Getting the kink out will not hurt.

    Let us get this solved before cooling season.

  10. dmj2359

    dmj2359 New Member

    Well, my constant complaining has gotten me somewhere. They are coming out to check things out again. Other than flow rates in all zone configurations, and EAT, LAT, and air temp at each duct is there anything else I should record/measure while they are here?

    Also, I'd be interested in have an independent company run a full room-by-room Manual J/D calc on the system and see if it's anything close to what was built. I should have all the pertinent data (floor plans, orientation, window data, insulation data, infiltration data) electronically, and as I'm just interested in the report outputs there's no requirement to go local - suggestions on where to start for this?

    Michael (Who is still thrilled when he sees the outdoor air temp at 21F and EWT at 48F)

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