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  1. #1

    Confused Infinity Dump zone through unoccupied zone remote sensor

    Background:

    I have new construction (built Dec 2011) two story modern home (house is very tight) in Houston TX. The house has high end argon filled low E windows, regular bat insulation on walls and R30 open cell foam on roof, the roof design is an non vented attic, meaning that the ducting on the upper floor is in semi conditioned space.

    The house has 2 carrier systems, one system on each of the floors. The layout of the house has living / kitchen open plan downstairs along a bedroom, and 3 bedrooms upstairs separated by a large loft / landing that is open to downstairs. The manual J for upstairs call for 19kbtu heat and 2.1 ton cooling.

    On the upper floor we currently have a 58CVA110 with a CA16 48 4 ton single stage condenser and a 5 ton CNPV coil, the above is controlled with an infinity controller and has two zones (no bypass damper design), all damper are infinity modulating. The load analysis was incorrectly done, and now the contractor is replacing the current system with a 58CVA90 with a CA16 36 3 ton single stage condenser along with a 4 ton CNPV coil.

    Our issue was that the old system was oversized for the ducting that was installed, we had high noise and when we used the infinity controller to adjust zone airflow limits we started to come up against high static and airflow limited shutdowns. The contractor changed the setting on the infinity controller for the condenser from 4 ton to 3 1/2 ton and this helped some but it could not hide the fact that the equipment was oversized and the ducts undersized.

    The duct setup upstairs was such that we ended splitting 4 main supply ducts to make a 60 and 40% zone.

    The 4 supplies are:
    - 2 x 12" flex duct
    - 1 x 10" flex duct
    - 2 x 8" flex duct

    We split the two zones upstairs to 1 zone with 1x12" + 1x8" + 1x10", the 2nd zone has 1x12" and 1x8"

    - Now along with resizing to the smaller furnace and condenser the contractor is proposing that they add a remote sensor at the open loft landing area (contains 1 x 8" + 1x10" supplies) and set it as its own zone in unnoccupied mode. This way they suggest that when the 2 separate bedroom zones are calling for cooling that area will be used as a dump for excess airflow. Bedroom zone 1 would have 1x12"+1x8" and bedroom zone 2 1x12".

    What do the pros in the forum think about this application of the infinity system? Do you think that we would still get the high airflow noise and static when the zone initially calls and until the damper to the unoccupied zone opens to relieve?

    I have been suggesting that the only real solution (aside from gutting the ducts and redoing...) is to have a 3 ton two stage condenser. I am being met with resistance and told that the next solution would be to take out infinity controllers and do a bypass damper (not thrilled with this option)

    Thanking you in advance for your advice and time

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,821
    Put in the 3 ton unit.
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    How many times must one fix something before it is fixed?

  3. #3
    Thank you for your answer, do you mean put in the 3 ton 2 stage because you don't believe the infinity dump zone will operate correctly?

    Appreciate your help

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,821
    Weather the dump zone works or not. You would still have an over sized higher energy using unit.
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    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,826
    You don't need a 'dump' zone with the Infinity system at all, except where some yo-yo steps way outside the load analysis, as they did with you. But let's take the issues one at a time.

    1. What design criteria was used to get to 2.1-tons on cooling? This is important because the jump from 2.1-tons to 3.0-tons is a lot of air. So I'd suggest the designer take a look at the needs of cooling system 1 or 2 lower on design. What this means in operation is that the indoor temperature may climb an equivalent number of degrees when the system reaches design temperature. But if your load analysis was predicated on design for your area +6F to reflect maximum anticipated high temperature, then you may be better served with a 2.0-ton system. That .1-tons leaves a lot of room for analysis questions.

    2. You need to have a duct analysis done at the same time. Manual 'D' should be used as the criteria and the system analyzed to determine if it was installed for a 4.0-ton system or was under sized for a 4.0-ton system and is well suited for the smaller 2.0-ton system. If the ducts are too large, a smaller system may not work properly and as is and duct modifications may be necessary.

    3. You could solve many of these issues if you spring for a new Greenspeed modulating unit (heat pump). They're pricey for sure but you'll get the 3.0-ton capacity you may need or think you need for the highest temperatures but will modulate down to as little as little as under 1.0-tons at its lowest setting. Matched to the variable speed air handler or furnace, the system will 'loaf' most of the time.

    The theory of the Infinity zone system is that it uses all of the zones in concert with each other to achieve both the greatest comfort level while protecting the equipment from wide variances of static pressures. I'm somewhat surprised that the User Interface didn't recommend a new duct system with the 4.0-ton system in there. Oh and while I'm thinking of it, if the contractor you're now using is the same one who put in the 4.0-ton system previously when the load analysis called for 2.1-tons, I'd be quite wary of his/her knowledge of the dynamics of either the system in general or specifically the Infinity control system.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  6. #6
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,649
    Load says 2 ton. Loads typically oversize. Why are you putting in 3? I'd put in 2, and ABSOLUTELY 2 stage.

    Sounds like you are dealing with a contractor that has no clue about airflow or communicating equipment. This means, unfortunately, you will need to become the expert and hold fast when met with resistance. You can teach ignorant but not sure you can teach stupid, and not sure how much uncompensated effort you'll have patience for in either case.

    I'd recommend you do a search on Skips posts, he knows as much about infinity, communicating equipment, and communicating zoning as anybody you are likely to meet. Print and highlight the applicable info so you have something to refer back to when doubt creeps in. I don't think you can build a collaborative effort here, you have to dictate.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  7. #7
    Thank you all for your help and suggestions. The contractor says his manual J comes at 2.8 tons (I know he tweaks the temperatures and does not use the default for Houston in Manual J). I had a 3rd party do a manual J and it came to the following for that particular floor (keep in mind that about a 1/4 of the total sqft for that floor is open to below. Does the load analysis point you more towards a 3 ton ton rather than 2?

    Weather: Houston Bush Intercontinental, TX, US
    Winter Design Conditions Summer Design Conditions
    Outside db 33 F Outside db 96 F
    Inside db 70 F Inside db 75 F
    Design TD 37 F Design TD 21 F
    Daily range M
    Relative humidity 50 %
    Moisture difference 65 gr/lb
    Heating Summary Sensible Cooling Equipment Load Sizing
    Structure 18604 Btuh Structure 16996 Btuh
    Ducts 1371 Btuh Ducts 904 Btuh
    Central vent (0 cfm) 0 Btuh Central vent (0 cfm) 0 Btuh
    Humidification 0 Btuh Blower 0 Btuh
    Piping 0 Btuh
    Equipment load 19974 Btuh Use manufacturer's data n
    Rate/swing multiplier 1.01
    Infiltration Equipment sensible load 18079 Btuh
    Method Simplified Latent Cooling Equipment Load Sizing
    Construction quality Semi-tight
    Fireplaces 0 Structure 2633 Btuh
    Ducts 1064 Btuh
    Heating Cooling Central vent (0 cfm) 0 Btuh
    Area (ft) 1708 1708 Equipment latent load 3697 Btuh
    Volume (ft) 15370 15370
    Air changes/hour 0.34 0.18 Equipment total load 21776 Btuh
    Equiv. AVF (cfm) 87 46 Req. total capacity at 0.70 SHR 2.2 ton

    PS. Thank you for the words of encouragement and advice, this issue with my contractor has dragged on since Dec 2011 when we moved in our brand new home, I made the mistake of educating myself on HVAC design after rather than before building than house....

    Carrier rep has even come to the house and has (predictably remained out of touch and silent about what he saw), they tried to get this oversized system to work (by using th infinity controller and switching supplyies for different zones) with the undersized ducts for several months until finally admitting to getting the load analysis wrong. We are at the stage where we are curently trying to settle to a solution.

  8. #8
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,649
    What ESP numbers does the stat give you at the equipments various stages?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  9. #9
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    WIth a zone system, you can underszie a little sice rarely are all zones at maximum heat gain or loss at the same time due to the positon of the sun and occupancy requirements. Also, if you have dense materials in your home like tile floors, plaster, stucco, brick, stone, the thermal mass will help you "ride out" peaks in outdoor temperature.

    A 3 ton 2 stage, even in 1st stage is still about 2.2 ton of capacity.

    That being said... this is Houston, not NY, so at design temperatures, the actual capacity will be much lower than nameplate. So a 2 ton will only be maybe 1.8 tons.. and a 3 ton maybe 2.7 with low stage being right at 2 tons. The humidity also can't be discounted. If the air leakage is higher than estimated and attic insulation underperforms, you'll have issues in design conditions. Factor in the loss of capaicty over time with aging equipment and dirty coils and you could be possing it with a 2 ton. I have little faith in new construction to meet what's calculated unless you've doen an actual blower door and checked insulation with an IR camera.

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