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  1. #27
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    LF at various times

    I think I want to measure duty cycle (also called Load Factor, or "LF") on some time period longer than 1 hour. I already have 1-hour duty cycles, putting them into a graph would make the info far easier to read -- but maybe my spreadsheet skills are too basic, I think it would take me a lot of work.

    My thinking is that 100% 1-hour duty cycle is not measuring the threshold of sizing. My system which has run 2+ hours without stopping, seems always able to maintain the 78-degree thermostat setpoint (because of my duct qualities, temperature is often 2 degrees cooler in bedrooms and bathrooms). Very typical behavior is running 55 minutes out of each hour, for several hours in a row. I believe this illustrates the system barely making the setpoint, then it would want to restart sooner but the 5-minute off-time is enforced by something in the system (you can tell I am not a pro, with language like that!).

    For the interest of the original poster, here are some of my hourly load factors:
    Jul 01 9-10pm 73% LF i.e., ran about 44 minutes out of 60.
    10-11pm 70% LF
    11-12pm 53% LF
    12-1am 55% LF
    1-2am 58% LF
    2-3am 58% LF

    I looked at other days and believe July 1 is completely typical (it helps that S.Texas has a lotta typical summer days). It may seem curious to some, but mid-morning is when this system sees lowest LF. I don't know how to explain, but I am reporting the data as I observe it. Will admit possibly I am off by one hour due to daylight savings time, but no really big experimental flaws that I know of. So have a heart and don't call me a "clown" or "Homer Simpson" if my experimental data does not cleanly fit one's expectations. It simply is observed data.

    It may help to know that my #1 purpose with these measurements is to provide a non-Manual-J method of finding out whether my system sizing is appropriate, with *my* usage patterns, *my* duct and other flaws as installed, etc. In other words, an observed LF below 100% is incontrovertible proof the system is doing the job I ask of it. Any LF significantly below 90% is proof IMO that system could be replaced with a smaller one and be properly sized. It is not my intention to be controversial, and I intend to have a proper Manual J report made to "prove it" via conventional wisdom before I buy a new AC. But to get original, direct evidence seems pretty darn good to me. That might explain why my data is in a big spreadsheet and maybe not formatted to communicate best.

    Best wishes -- P.Student



    [Edited by perpetual_student on 08-17-2005 at 10:03 AM]

  2. #28
    Join Date
    Jul 2004
    Posts
    253

    Re: LF at various times

    FYI, my two stage Bryant Evolution system has run an average of 13 hours a day for the last 3 months. I live in southeast Georgia. Approximately 75% of the runtime is on low-speed.


    Originally posted by perpetual_student
    I think I want to measure duty cycle (also called Load Factor, or "LF") on some time period longer than 1 hour. I already have 1-hour duty cycles, putting them into a graph would make the info far easier to read -- but maybe my spreadsheet skills are too basic, I think it would take me a lot of work.

    My thinking is that 100% 1-hour duty cycle is not measuring the threshold of sizing. My system which has run 2+ hours without stopping, seems always able to maintain the 78-degree thermostat setpoint (because of my duct qualities, temperature is often 2 degrees cooler in bedrooms and bathrooms). Very typical behavior is running 55 minutes out of each hour, for several hours in a row. I believe this illustrates the system barely making the setpoint, then it would want to restart sooner but the 5-minute off-time is enforced by something in the system (you can tell I am not a pro, with language like that!).

    For the interest of the original poster, here are some of my hourly load factors:
    Jul 01 9-10pm 73% LF i.e., ran about 44 minutes out of 60.
    10-11pm 70% LF
    11-12pm 53% LF
    12-1am 55% LF
    1-2am 58% LF
    2-3am 58% LF

    I looked at other days and believe July 1 is completely typical (it helps that S.Texas has a lotta typical summer days). It may seem curious to some, but mid-morning is when this system sees lowest LF. I don't know how to explain, but I am reporting the data as I observe it. Will admit possibly I am off by one hour due to daylight savings time, but no really big experimental flaws that I know of. So have a heart and don't call me a "clown" or "Homer Simpson" if my experimental data does not cleanly fit one's expectations. It simply is observed data.

    It may help to know that my #1 purpose with these measurements is to provide a non-Manual-J method of finding out whether my system sizing is appropriate, with *my* usage patterns, *my* duct and other flaws as installed, etc. In other words, an observed LF below 100% is incontrovertible proof the system is doing the job I ask of it. Any LF significantly below 90% is proof IMO that system could be replaced with a smaller one and be properly sized. It is not my intention to be controversial, and I intend to have a proper Manual J report made to "prove it" via conventional wisdom before I buy a new AC. But to get original, direct evidence seems pretty darn good to me. That might explain why my data is in a big spreadsheet and maybe not formatted to communicate best.

    Best wishes -- P.Student



    [Edited by perpetual_student on 08-17-2005 at 10:03 AM]

  3. #29
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,374

    Load Factor definition

    Originally posted by perpetual_student
    I already have 1-hour duty cycles, putting them into a graph would make the info far easier to read -- but maybe my spreadsheet skills are too basic, I think it would take me a lot of work.

    For the interest of the original poster,
    here are some of my hourly load factors:
    Jul 01 9-10pm 73% LF i.e.,
    ran about 44 minutes out of 60.
    10-11pm 70% LF
    11-12pm 53% LF
    12-1am 55% LF
    1-2am 58% LF
    2-3am 58% LF

    July 1 is completely typical (it helps that S.Texas has a lotta typical summer days). It may seem curious to some, but mid-morning is when this system sees lowest LF.

    It may help to know that
    my #1 purpose with these measurements is to provide a
    non-Manual-J method of finding out
    whether my system sizing is appropriate,
    with *my* usage patterns,
    *my* duct and other flaws as installed, etc.

    In other words, an observed LF below 100% is incontrovertible proof the system is doing the job I ask of it. Any LF significantly below 90% is proof IMO that system could be replaced with a smaller one and be properly sized.

    I intend to have a proper Manual J report made to "prove it" via conventional wisdom before I buy a new AC.
    But to get Original, Direct evidence seems pretty darn good to me.

    [Edited by perpetual_student on 08-17-2005 at 10:03 AM]
    Great work process on DEVELOPING PROOF!

    ____ much better than just believing Manual J which
    can have a lot of Assumptions by one who performs calc.

    Send 1-hour Duty-Cycle spreadsheet for 5-1/2 days ( .xls or .wlr format), house drawing with window specs and current equipment to racingdan11 at comcast.net

    It is NOT a lot of work to graph a significant amount of data IF it is conveniently formatted into COLUMNS.

    I will make a full load analysis evaluation and comparison for your equipment sizing and my Manual J features/performance benefit. I wonder how much Manual J ___8th edition oversizes___ and this is an appropriate opportunity to provide solid evidence.

    The hourly weather data for July 1st ( to 6th) might be obtained via internet or other source (i.e. local TV Station).

    I somewhat doubt that running 43 minutes out of 60 minutes really constitutes a true Load Factor of 73%.
    It is NOT likely to be running at 100% R.L.A.
    ALL of the 43 minutes 9 PM -10 PM.

    http://www.ise.ufl.edu/capehart/papers/diversity.html

    Talk to you soon. racingdan11 at comcast.net
    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

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