Page 1 of 3 123 LastLast
Results 1 to 13 of 28
  1. #1
    Join Date
    Feb 2019
    Posts
    31
    Post Likes

    New AC: Phoenix, AZ. Questions about Manual J Load, SEER, EER

    First post here. I have already learned a lot from reading other posts. Thank you all for your advice.

    I live in Phoenix, Arizona. I am looking to replace/upgrade two Carrier CKC-350 HVAC units. The house was built in 2004, and the HVAC is original. My upstairs unit is sized at 3.5T and my downstairs unit is sized at 3T. Until a refrigerant leak became evident last year (2018), we were content with these Carriers for our summer cooling. Internet search says original SEER of these Carriers is 10 SEER; I had a home energy audit done in December 2017 which stated the two Carriers were 7 SEER. The home energy audit gave us helpful advice about duct sealing, air sealing, attic insulation, and shade screens for windows; we have not installed any improvements yet.

    I have met with two contractors. One peddled Trane, the other peddled Lennox. From both contractors, the high SEER HVAC units of their preferred manufacturer are NOT available in 3.5T, so they are quoting me to install 3T downstairs (same) and 4T upstairs (0.5T larger than original) . For 16 SEER, both contractors quoted 3T downstairs and 3.5T upstairs like my original/present system. Neither contractor did a Manual J Load calculation before issuing me formal quotes. Upon questioning the second contractor about this, he stated that he would do the Manual J Calculation when I am prepared to finalize the sales contract. (I have not contacted the first contractor about Manual J Load.) I have never gotten a Manual J Load for my house: not from home inspection, not from home energy audit, not from AC tuneups/repairs, not from new AC quotes (as of yet).

    We would like to pursue energy efficiency, so, at the surface, high SEER is very appealing. But I gather that SEER is like MPG: calculated from a standard formula for a "standard" condition. Living in Phoenix, I have seen our 2.5% Design Temperatures are approximately 107F DB and 71F DB; we cool our house to between 78F to 80F. How do those outdoor design temperatures and preferred interior temperatures impact my "real world" SEER?

    I am gathering that if I did perform the energy-efficiency improvements to my house (air sealing, duct sealing, more attic insulation, shade screens on S,W,E windows), that my Manual J Load would decrease. If so, that means I am being quoted (for high SEER units) for oversized (4T vs 3,5T) HVAC units for my upstairs. That will adversely affect my "real world" efficiency, yes?

    I read on here that having a coil rated at a higher capacity than the condenser is wise/typical for Phoenix, and the second contractor did that. But I am a bit concerned that I was given quotations (after in-house i visits) for "oversized" upstairs HVAC before a Manual J Load calculation -- and with knowledge that my 2004 HVAC units are 3T & 3.5T.

    As I understand it, "Two-stage, Multi-Stage, and Variable Capacity" units are "more efficient" than Single-Stage. Does the "stages of cooling" directly impact SEER? I don't understand how a single-stage unit (Lennox EL16XC1) can have a higher SEER and higher EER than a Multistage (Lennox XC16) but then supposedly the Multi-Stage is "more efficient" (and costs more).

    With the understanding that "Variable Capacity" should be the "most efficient", the Lennox XC25 does have the highest SEER, but the EER is the second-lowest of the four Lennox systems in my quote! And this XC25 is quoted as a 4T upstairs unit since XC25 is not made in 3,5T. I am concerned that this proposal for XC25 will fall far short of the 20/23 SEER when installed in my house, but I am not sure.

    I am thinking I might get the best "bang for my buck" by installing the (properly sized) EL16XC1 and doing some household energy-efficiency improvements rather than splurging on a (perhaps oversized) Lennox XC25. Thoughts?

    Thank you very much for any advice and clarification about "real-world" SEER for Phoenix, Arizona, as well as EER, Manual J Load, and the true energy-saving benefits of multi-stage or variable cooling or other household energy-saving improvements.
    ================================================== =================================

    I was quoted the following specifications for four Lennox systems:
    EL16XC1
    Brochure: Up to 17 SEER
    Single-Stage
    Quote: SEER 17.4,16, EER 13.5, 13.5

    XC16
    Brochure: Up to 17.20 SEER
    Multi-Stage
    Quote: SEER 16,16, EER 12,12

    XC21
    Brochure: Up to 21 SEER
    Two-stage
    Quote: SEER 18,19, EER 14,14

    XC25
    Brochure: up to 26 SEER
    Variable Capacity
    Quote: SEER 20,23, EER 13,13

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,732
    Post Likes
    Quote Originally Posted by clmssun View Post
    First post here. I have already learned a lot from reading other posts. Thank you all for your advice.

    \ I live in Phoenix, Arizona.

    I am looking to replace/upgrade two Carrier CKC-350 HVAC units.

    The house was built in 2004, and the HVAC is original.
    My upstairs unit is sized at 3.5T and my downstairs unit is sized at 3T.


    Until a refrigerant leak became evident last year (2018), we were content with these Carriers for our summer cooling.

    Internet search says original SEER of these Carriers is 10 SEER;
    I had a home energy audit done in December 2017 which stated the two Carriers were 7 SEER.
    The home energy audit gave us helpful advice about duct sealing, air sealing, attic insulation,
    and shade screens for windows; we have not installed any improvements yet.

    For 16 SEER, both contractors quoted 3T downstairs and 3.5T upstairs like my original/present system.

    Neither contractor did a Manual J Load calculation before issuing me formal quotes.
    Upon questioning the second contractor about this, he stated that he would do the Manual J Calculation
    when I am prepared to finalize the sales contract. (I have not contacted the first contractor about Manual J Load.)

    I have never gotten a Manual J Load for my house:
    not from home inspection,
    not from home energy audit,
    not from AC tuneups/repairs,
    not from new AC quotes (as of yet).

    We would like to pursue energy efficiency, so, at the surface,
    high SEER is very appealing.

    But I gather that SEER is like MPG: calculated from a standard formula for a "standard" condition.

    Living in Phoenix, I have seen our 2.5% Design Temperatures are approximately 107F DB and 71F DB;
    we cool our house to between 78F to 80F.

    How do those outdoor design temperatures and preferred interior temperatures impact my "real world" SEER?

    I am gathering that if I did perform the energy-efficiency improvements to my house
    (air sealing, duct sealing, more attic insulation, shade screens on S,W,E windows),
    that my Manual J Load would decrease.


    If so, that means I am being quoted (for high SEER units) for oversized (4T vs 3,5T) HVAC units for my upstairs.
    That will adversely affect my "real world" efficiency, yes?

    I read on here that having a coil rated at a higher capacity than the condenser is wise/typical for Phoenix,
    and the second contractor did that.

    Thank you very much for any advice and clarification about "real-world" SEER
    for Phoenix, Arizona,
    as well as EER, Manual J Load,
    and the true energy-saving benefits of multi-stage or variable cooling or other household energy-saving improvements.

    ================================================== =================================

    I was quoted the following specifications for four Lennox systems:

    XC16 Brochure: Up to 17.20 SEER
    Multi-Stage -- Quote: SEER 16,16, EER 12,12

    XC21 == Brochure: Up to 21 SEER
    Two-stage -- Quote: SEER 18,19, EER 14,14
    DESCRIBE YOUR RESIDENCE - EXAMPLE

    3,800 SQ FEET .. 2-STORY .. 500 - 600 SQ FEET OF GLASS

    R-13 WALLS
    R-30 CEILING

    $ 380 to $460 / MONTH 3,400 +/- 20% KW-HOURS for 6 months
    --------------------- MAY - OCTOBER

    $ 0.125 / kw-hr

    _________ 1,000 KW-HRS other months

    Evaluation of your BUILDING THERMAL ENVELOPE improvements should
    include SPECIFIC BENEFITS _ $$$ REDUCTION for each
    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

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    78,340
    Post Likes
    With your dry climate. You won't get the full benefit of 2 stage or modulating. Since you don't need much to any moisture removal in your home.

    Over all comfort would still be improved by the long run times in first or lower stages when your area is between 60 and 90% of outdoor design temps.

    Energy efficiency improvements to your home would probably be better money then going to modulating or 2 stage equipment.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,732
    Post Likes

    CLIMATE CONDITIONS - 1% 108.3'F / 69.4'F 4626 CDD

    Equipment cooling capacity needs to be derated at 110'F

    Also, CDD for 2011 to 2018 needs to be reviewed.
    __ Cooling Degree Days / Month and Annual __
    ___ CDD 65
    Attached Images Attached Images  
    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

  5. #5
    Join Date
    Feb 2019
    Posts
    31
    Post Likes
    Thread Starter
    Thank you for the replies. I will reply later today with more specifics about my house.

  6. #6
    Join Date
    Jan 2014
    Location
    New England
    Posts
    6,294
    Post Likes
    Ask them for the AHRI number to prove a match and to check your SEER and EER. At least you realize it’s the indoor combo that gives the rated SEER as you mention up to. You would need the AHRI number also for any rebates your state or local utility company may have.

    Make sure your system gets registered also.

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,732
    Post Likes
    Quote Originally Posted by clmssun View Post
    Thank you for the replies. I will reply later today with more specifics about my house.
    INPUT FORM _ EXAMPLE

    Provide info in shaded boxes on applicable lines from 11 to 26, 30, 39 & 42

    Lines 21 -22
    If unknown value,
    _ Provide description:
    1. Single or Double Pane
    2. Amount of tint - light, medium, heavy
    3. Any interior shading
    ___ blinds, roller shades, ...
    4. Any exterior shading - insect screens, amount of overhangs
    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

  8. #8
    Join Date
    Feb 2019
    Posts
    31
    Post Likes
    Thread Starter
    Dan in SW FL,

    Thank you very much for Manual J Load Calculation sheet! I have all the information for it, I just need to figure out how to perform the calculations in the pdf (I am using Linux right now); I may just load it up on Windows with a different computer.

    This will be hugely helpful for me as I navigate this purchase. Thank you for sharing!

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,732
    Post Likes
    Quote Originally Posted by clmssun View Post

    Dan in SW FL,
    ________ Thank you very much for Manual J Load Calculation sheet!

    I have all the information for it,
    I just need to figure out how to perform the calculations in the pdf (I am using Linux right now);
    I may just load it up on Windows with a different computer.

    This will be hugely helpful for me as I navigate this purchase.

    Thank you for sharing!
    The attachment is NOT A LOAD CALCULATION sheet.
    I definitely do not see the value of an INPUT FORM BY ITSELF as being hugely helpful.

    The attachment in PDF format is an INPUT FORM { post # 7 }
    for an EXCEL spreadsheet which has three additional separate sheets.

    MY CALC enables me to perform Heat Transfer and Cost Analysis in a few minutes
    after the input values are established.

    PDF files do not have ANY Computing capability.

    Providing values for the 16 shaded boxes will enable me
    to perform a BLOCK LOAD on the 2 stories.

    Also, the Operating Cost per month or Year can be calculated based on:
    heat loss and gain load calculations similar to Manual J methodology,
    given Local utility rates,
    Temperature BIN DATA,
    determination of THERMAL BALANCE POINT for heat pumps,
    my selected equipment SEER and an average time-temperature weighted C.O.P.,
    AND
    AVERAGE HDD & CDDs per month or year as listed by ASHRAE.

    Providing the glass areas per floor enables one to
    perform a BLOCK LOAD on Each floor.

    My gmail address is racingdan11.
    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

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,732
    Post Likes
    Quote Originally Posted by clmssun View Post
    Dan in SW FL,

    Thank you very much for Manual J Load Calculation sheet! I have all the information for it, I just need to figure out how to perform the calculations in the pdf (I am using Linux right now); I may just load it up on Windows with a different computer.

    This will be hugely helpful for me as I navigate this purchase. Thank you for sharing!
    What is your Air Change per Hour Natural as determined by Blower Door test.?
    ………. … _ _ _ _ A.C.H. _ _ _ _ _

    Please provide photos of the performance label /fenestration properties for the windows
    and any sliding glass doors.

    http://www.nfrc.org/energy-performance-label/
    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

  11. #11
    Join Date
    Feb 2019
    Posts
    31
    Post Likes
    Thread Starter
    Dan,

    I sent data about my house to your Gmail. Thank you for all your help.

    With regard to "Air Change per hour Natural" from my Blower Door Test, all I can find so far is Blower Door Reading 1705 CFM50 and then Equivalent NACH 0.24.

    I apologize for not knowing all the verbiage of this kind of survey. Thanks again.

  12. #12
    Join Date
    Feb 2019
    Posts
    31
    Post Likes
    Thread Starter
    Quote Originally Posted by beenthere View Post
    With your dry climate. You won't get the full benefit of 2 stage or modulating. Since you don't need much to any moisture removal in your home.

    Over all comfort would still be improved by the long run times in first or lower stages when your area is between 60 and 90% of outdoor design temps.

    Energy efficiency improvements to your home would probably be better money then going to modulating or 2 stage equipment.
    Thank you. This is something I am trying to clarify and better understand.

    I do note the higher SEER and greater rebates from the local utility company for "multistage", two-stage, and "variable capacity" units, but I am not sure that I would really all the benefits. (But why would a Phoenix electric company offer a larger rebate if the climate here is not conducive to benefits from multistage, two-stage, or variable capacity?)

    What is the difference between "two-stage" and "multi-stage"?

    The "two-stage" and "variable capacity" units require a "communicating" thermostat, but the "multi-stage" does not.

    Are "two-stage" and "variable capacity" already accounted for in SEER? Or do "variable capacity" and "two-stage" pave the way for better efficiency regardless of SEER?

    I see that the four Lennox units have a different sequence of "SEER" than "EER". I am pretty sure that the hot dry climate of Phoenix is well outside the "standard" SEER climate; I also understand that EER is not variable with climate. In my hot dry climate, should I pay more attention to SEER or EER?

    Thank you again for all the advice.

  13. #13
    Join Date
    Apr 2012
    Location
    Millsboro, DE
    Posts
    181
    Post Likes
    No one is permitted to select equipment based on SF/Ton, but it's a great BS meter when you do the math: 3,800 SF/7 Tons = 543 SF/Ton.

    Today's range is 1,000 to 1,350+. Yes I know your home was built in 2004, hopefully to then current standards. The thing we all worry about with older homes in how leaky it is, and you've nailed that: Your home might be "Tight" and comply with today's standards in that regard (going out, will check MJ on using blower door results).

    You don't need dehumidification in Phoenix (negative grains of moisture!!!), and it amazes me contractors try to sell it there. The design airflow will be at the high end of the Manufacturer's range, to minimize dehumidification. Stick with single speed (16+/-), 4 or 5 tons total should be OK, and get rid of the 0.35 windows, they make them below 0.20 today, especially if it's a sunny lot. Insulation upgrade is recommended, we're seeing R49 used by better builders here. Keep in mind you'll only do this once and our GM is right: Forget the bells and whistles, put your bucks into the structure; you can easily exceed today's requirements with what you'd intended to spend on structure PLUS the 5 figures you'll save on the new equipment.

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •