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  1. #14
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
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    3,368
    The CBX27UH isn't variable speed - has a fixed speed ecm motor.

    Do you have a specific need for air conditioning at cooler outdoor temps (below 55f)? If not, wonder why they're providing the low ambient kit?

    I would ask them for an alternate estimate with an XP14 and CBX32MV.

  2. #15
    Join Date
    Jul 2012
    Posts
    37
    Quote Originally Posted by RyanHughes View Post
    The CBX27UH isn't variable speed - has a fixed speed ecm motor.

    Do you have a specific need for air conditioning at cooler outdoor temps (below 55f)? If not, wonder why they're providing the low ambient kit?

    I would ask them for an alternate estimate with an XP14 and CBX32MV.
    There should be no need for air conditioning if the temp is below 55. I guess I assumed the low abient kit had something to do with the heat pump and cold weather conditions. When I initially spoke with him he mentioned something about using a more economical unit and adding some components to it to make it do the same thing as a more expensive unit. What is the advantage/difference of the xp 14 and the cbx32mv?

  3. #16
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,244
    I would use a GREENSPEED 3 ton (See Page 11 of Attachment).
    I might may even be tempted to use a 4-ton (page 12) in a climate with > 6,500 Heating Degree Days.
    It seem like a 4-ton may be hard to justify at only $0.08/kW.
    Of course, this unit is quite efficient + New, so it comes with a pri$e.

    However, it is owners responsibility to try to determine Best Value.
    Life_Cycle_Cost (initial cost + operating and maintenance costs) comparison with the Lennox may indicate GREENSPEED should be selected.
    Ask each contractor how much it will cost to buy, run & maintain for 5 years.
    Need an opinion after you get to that phase ... you have my e-mail address in my profile.

    I am a bit ambivalent in attempting to validate whether your 48,000 BTU-hr is appropriate to your structure and locale.
    Off hand, it seems a bit high.
    What was the Air Change per Hour (ACH) selected?

    Is the design temperature you used in your calc in the range of -3'F? ASHRAE 99% design temp.

    Thermal Balance Point is 20'F assuming 48,000 BTU/Ht at -5'F
    ( Balance Point = meaning no aux. heat is needed > 20'F, except in defrost mode).
    Aux Heating needed will be about 8 kW at 0'F
    with use of a 3-ton Greenspeed.

    http://www.climate-zone.com/climate/...wa/des-moines/
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    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  4. #17
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,755
    Its an X13/ECM blower. Its not a VS blower. but it is very efficient.

    Non Lennox dealers pay a higher price for the parts then a Lennox dealer does.
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  5. #18
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,368
    Quote Originally Posted by burhead View Post
    There should be no need for air conditioning if the temp is below 55. I guess I assumed the low abient kit had something to do with the heat pump and cold weather conditions. When I initially spoke with him he mentioned something about using a more economical unit and adding some components to it to make it do the same thing as a more expensive unit. What is the advantage/difference of the xp 14 and the cbx32mv?
    Performance wise, won't see much difference between a 14HPX and XP14. Both have similar efficiency ratings. Both have scroll compressors with high/low pressure protection. Adding a low ambient kit won't make the 14HPX anymore like the XP14, which would also require a low ambient kit for low temperature cooling (rarely needed in residential). I recommended you at least look into upgrading to the XP14 simply because it's a better built, quieter unit. XP14: nicer cabinet that opens up easily for service, quieter operation, and a unit made in the US. 14HPX: same bare bones, louder operation, made in Mexico -- designed to be a base grade/budget replacement unit. They aren't bad units, but consider all of your options.

    CBX27UH vs. CBX32MV: both are fine air handlers and will match up well with either outdoor unit. The 27 can't do any special dehumidification without a relay kit. High efficiency, fixed torque motor, so if you have a restrictive duct system or filter starts to get dirty, your airflow will begin to drop, lowering capacity/efficiency. These motors certainly do better than PSC motors and can handle a reasonable amount of static pressure while still providing an acceptable airflow range. With the variable speed blower, it can be set up to run a ramping profile for better dehumidification in addition to doing dehumidify on demand with the right thermostat. It will deliver a constant CFM up to around .8" ESP and will adjust its rpm as needed.

  6. #19
    Join Date
    Jul 2012
    Posts
    37
    Ok one more question. Would it be a good idea to make this a dual zone system? The contractor has proposed to put a damper in each trunk line but I got to thinking about having them put automatic dampers in with two T stats, one upstairs and one down. It sounds like a great idea but I wonder what happens if the downstairs isn't calling for heat or AC and the damper is closed. It would seem that this would not be a good thing. Any opinions?

  7. #20
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,755
    That is what a bypass damper is for.
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  8. #21
    Join Date
    Apr 2010
    Location
    NC Sandhills
    Posts
    393
    You will like the Zoned (automatic) system much better than manual hand dampeners. It is code here that one system on a split level house must be zoned (automatic dampers and controls). I only like zoning with a by-pass when there is only 2 zones and the loads are fairly close. More than that I like to use variable speed w/ modulating dampers, no by-pass.

  9. #22
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,424
    agree with Rodney, go with the automatic zoned control system.

  10. #23
    Join Date
    Jul 2012
    Posts
    37
    Ok I am going with this contractor and he will be here on monday to measure for all of his pre fab stuff. I am going with a varible speed air handler cbx32 I believe. I spoke with him on the phone this morning and mentioned that I would like to add zoning eventually (not in the budget right now). He said he could make the single speed unit work but that I would be better off going with the variable speed unit. This put me at the upper end of my budget so I didn't ask about the xp14 upgrade. He also said that by going with the variable speed air handler I wouldn't need the bypass dampers. Does that sound correct?

  11. #24
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,755
    That would only be true if the smallest zones load was the same as the capacity of the unit in first stage.
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