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  1. #1
    Join Date
    Oct 2011
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    7

    Is my Lennox XP-21 heat pump operating efficiently?

    I live in SE PA and recently had a Lennox XP-21 heatpump installed with electric strips for backup heat. I received my first full month's electric bill and it was a bit higher than I expected (2100 kWh - last year before the HP it was 899 kWh) so I am wondering if there are any obvious things I should check to ensure that the HP is running efficiently.

    For example, is there a way to determine if the electric backup strips are being used too much (if at all)? How can I know if the HP is running in the 1st stage or 2nd stage?

    I have the thermostat set at 67 during the day and 65 at night. Is it more energy efficient if I leave it at the same temp all the time? I've received conflicting information about the setback two contractors and there seems to be two schools of thought in these forums.

    The outside temperatures have been ranging from the mid-30s to upper 40s and the compressor seems to be only running a couple minutes at a time several times an hour. Also, I've never seen my thermostat indicate that the Aux Heat is running (but I'm confused if the Aux heat on the thermostat means that the strips are on or if it means that the compressor is running in the second stage).

    Any guidance?

    (PS Please forgive any technical misstatements in my question - I'm a homeowner who is very interested in understanding how my HP works - not a Pro!)

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,308
    Leave it set at one temp. When you raise the temp setting on the thermostat your also bringing in the aux heat and costing yourself more money. Unless it has an outdoor stat/sensor and is programmed to lock out the aux heat above X temp.
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  3. #3
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by dpals View Post
    I live in SE PA and recently had a Lennox XP-21 heatpump installed with electric strips for backup heat. I received my first full month's electric bill and it was a bit higher than I expected (2100 kWh - last year before the HP it was 899 kWh) so I am wondering if there are any obvious things I should check to ensure that the HP is running efficiently.

    For example, is there a way to determine if the electric backup strips are being used too much (if at all)? How can I know if the HP is running in the 1st stage or 2nd stage?

    I have the thermostat set at 67 during the day and 65 at night. Is it more energy efficient if I leave it at the same temp all the time? I've received conflicting information about the setback two contractors and there seems to be two schools of thought in these forums.

    The outside temperatures have been ranging from the mid-30s to upper 40s and the compressor seems to be only running a couple minutes at a time several times an hour. Also, I've never seen my thermostat indicate that the Aux Heat is running (but I'm confused if the Aux heat on the thermostat means that the strips are on or if it means that the compressor is running in the second stage).

    Any guidance?

    (PS Please forgive any technical misstatements in my question - I'm a homeowner who is very interested in understanding how my HP works - not a Pro!)
    Establishing how much electricity is used for other than heating can determined from comparison of monthly electric bills over a year or two.
    April - May and Sept - Oct likely have very little or no heating and cooling requirements.

    I would use ANY setbacks.

    2100 - 899 = 1200 KiloWattHours needs to be compensated for Heating Degree Days (HDDs) between the two years.
    1200 kWH would be a 4-ton heat pump running for ~ 300 hours.

    Such a simplification is not going to go anywhere in ascertaining the proper operation of 1st and 2nd stage at ~40'F.
    Much more detail and analysis/testing/observations is REQUIRED, if instrumentation is not added.
    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. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323
    Apparently, it may have been SIGNIFICANTLY Colder in YOUR Area this November than last year.

    Station: …….. Philadelphia, Wings Field Airport, PA
    ----------- 75.27W, 40.14N
    Station ID: …….. KLOM ……..
    …….. ……..
    Month
    starting …….. HDD …….. This year
    10/1/2011 …….. 329 …….. 275
    11/1/2011 …….. 467 …….. 716 1.533
    12/1/2011 …….. 717 ……..
    1/1/2012 …….. 858 ……..
    2/1/2012 …….. 729 ……..
    3/1/2012 …….. 454 …….. Annual
    4/1/2012 …….. 366 …….. 3,920
    5/1/2012 …….. 92 ……..
    6/1/2012 …….. 46 ……..
    7/1/2012 …….. 1 ……..
    8/1/2012 …….. 13 ……..
    9/1/2012 …….. 98 ……..
    10/1/2012 …….. 275 ……..
    11/1/2012 …….. 716 ……..

    Short Cycling as described seems to indicate the use of strips .. but that's a W.A.G.

    Run times need to be Specifically defined and noted for Outdoor Temps
    Any increase in vent temperatures indicates use of either 2nd stage or Aux Heat (strips)
    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
    Oct 2011
    Posts
    7
    Quote Originally Posted by dan sw fl View Post
    I would use ANY setbacks.
    Can you clarify? Did you mean to say "I would *NOT* use any setbacks"?

    Quote Originally Posted by dan sw fl View Post
    Much more detail and analysis/testing/observations is REQUIRED, if instrumentation is not added.
    I am going to do some detailed observation but I'm not clear what I should observe! Like I said, I've never seen the Aux Heat or Emerg Heat indicators appear on the thermostat. I check the vent temps periodically and have never seen them above 85F (today with an outside temp of ~32F the temps are ~81F). What else can I monitor besides the daily electricity usage and the items I mentioned above?

    Really appreciate your response!

  6. #6
    Join Date
    Oct 2011
    Posts
    7
    Quote Originally Posted by beenthere View Post
    Unless it has an outdoor stat/sensor and is programmed to lock out the aux heat above X temp.
    I do have an outdoor sensor but I noticed that my thermostat settings are set to only use the outdoor sensor for display only. Setting 0340 on the ComfortSense 5000 thermostat is set to "#1 Outdoor temperature sensor used for display only". It is not set to #2 "Outdoor temperature sensor used to control heat pump-lock-out settings. Should I change it to #2 and then also set the Compressor Lock-Out and Aux Heat lock-out to specific temps?

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    I'd set the aux heat to be locked out above 25, and let the compressor run to -10.
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  8. #8
    Join Date
    Nov 2004
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    SW FL
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    Quote Originally Posted by dpals View Post
    Can you clarify? Did you mean to say "I would *NOT* use any setbacks"?

    I am going to do some detailed observation but I'm not clear what I should observe!

    Like I said, I've never seen the Aux Heat or Emerg Heat indicators appear on the thermostat.

    I check the vent temps periodically and have never seen them above 85F (today with an outside temp of ~32F the temps are ~81F).
    What else can I monitor besides the daily electricity usage and the items I mentioned above?

    Really appreciate your response!
    ___NOT __ was left out in Post #3, as you have observed.
    Do _NOT_ use Setbacks.

    Exact Start & Stop times over several 4 hour periods.
    Outside temp, inside temp and vent temp - once an hour.

    You may notice increase in electric usage on the utilities power meter.
    + " " " " " fan speed / air flow in 2nd stage.
    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

  9. #9
    Join Date
    Oct 2011
    Posts
    7
    Thanks for the guidance!!

    Per the above, I've done some detailed monitoring of the system that last few days and here are my summarized results:

    Outside temp Run Time Time Between Cycles Vent Temp
    29F 10 minutes 10 minutes 83
    29F-31F 9 minutes 11 minutes 84
    34F 9 minutes 11-12 minutes 85


    Some other notes:
    - I've used 84, 86, 102, and 98kWh in electricity over the last four days (and the variations seems to roughly correspond to the weather fluctuations and house activity).
    - the vent temps are varied by a few degrees throughout the house (i.e. 2nd floor vs. 1st floor)
    - I still haven't seen any indicators on the thermostat beside "Heat On" so I don't know how to tell if my HP is in the second stage or is using the aux strips
    - I have changed the thermostat settings to a constant 68F (no setbacks)
    - I've confirmed that I have the 3 ton system (which is AHRI reference number 5268807)


    Does this provide enough data to form an opinion? Thanks!

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by dpals View Post
    Thanks for the guidance!!

    Per the above, I've done some detailed monitoring of the system that last few days and here are my summarized results:

    Outside temp Run Time Time Between Cycles Vent Temp
    29F 10 minutes 10 minutes 83
    29F-31F 9 minutes 11 minutes 84
    34F 9 minutes 11-12 minutes 85

    Some other notes:
    - I've used 84, 86, 102, and 98kWh in electricity over the last four days
    (and the variations seems to roughly correspond to the weather fluctuations and house activity).

    - the vent temps are varied by a few degrees throughout the house (i.e. 2nd floor vs. 1st floor)

    - I still haven't seen any indicators on the thermostat beside "Heat On" so I don't know how to tell

    - I've confirmed that I have the 3 ton system (which is AHRI reference number 5268807)

    Does this provide enough data to form an opinion? Thanks!
    A few more small pieces of this Complex Puzzle:
    AHRI
    HSPF 9.5
    33,200 at 47'F
    21,000 at 17'F

    So, ~ 27,000 BTU/HR at 32'F if using 2nd stage
    3-ton unit running for 12 hours (overall daily use) will be ~ 35 kWHr

    Guessing the total airflow rate is 1,200 CFM, the heat rise should be about 20'F
    Q = 27,000 BTU/HR = Constant * CFM * Heat Rise
    1.08 Constant
    1,200 CFM
    20.83'F Heat Rise
    68' +20' = 88'F anticipated vent temperature
    which is not too far off of the measured 85'F at 34'F outside air.

    Is this a new house?

    What is the square footage?
    seems to be << 1,900 sq. ft.

    Did you look up monthly electric bills over the last two years?
    Monthly bills are generally available on-line from your electric utility.

    Based on what I currently understand (which is probably far from a complete viewpoint),
    it appears that your heating energy use is only a small portion of your overall electric energy use.

    I think I would set CPH (Cycles {Counts} Per Hour) = 2
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    Last edited by dan sw fl; 01-05-2013 at 06:12 AM.
    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
    Nov 2004
    Location
    SW FL
    Posts
    6,323

    IOM



    A more specific definition of air handler and controls set-up is needed.

    Lennox_CBX40UHV_IOM.pdf
    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

  12. #12
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,713
    call your installer back and ask for a seinor tech to come and check the unit and record info http://www.gwd-ac.com/MEG/LinkClick....Lk%3D&tabid=96 this is a sample form only ask if they have there own form to fill out and give you
    We really need change now

  13. #13
    Join Date
    Oct 2011
    Posts
    7
    RESOLUTION UPDATE: It was a loose screw!

    I realize this thread has been dormant for a while but I thought it would be helpful to provide an update: The technician did come out and check the unit and found that one of the electric strips was always on. After removing the strip, he found that a loose screw was lodged in the strip and the screw was completing the circuit and causing the strip to remain hot independent of the thermostat / control unit. He said it was drawing 9 AMPs of 120 volts all the time. The strip has been now been replaced.

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