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  1. #1

    Cycles Per hour what does this mean?

    Hello,

    Can someone explain to me what cycles per hours mean? I noticed that my system can be set for 2,3,4,5, or 6. Thanks for any help

  2. #2
    Join Date
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    Quote Originally Posted by rickytz7111 View Post
    Hello,

    Can someone explain to me what cycles per hours mean? I noticed that my system can be set for 2,3,4,5, or 6. Thanks for any help
    Air changes per hour, which remove latent heat and humidity. Most HVAC units if design properly will make 4-5 cycles per hour, but is there a written formula for cycles per hour NO, each home or conditioned space is different.
    "Everyday above ground, is a good day".
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  3. #3
    Join Date
    May 2007
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    DC Metro Area (MD)
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    What aircooled53 said.

    How many times the system cycles/runs per hour while maintaining temperature. A setting of 3 is typically recommended.

  4. #4
    Join Date
    Jan 2004
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    CPH isn't air changes per hour.

    At 3 CPH, you will have on off cycles. A on time and a off time makes 1 cycle.

    EG: First cycle,10 min on 10 min off, second cycle,10 min on 10 min off, third cycle,10 min on 10 min off; would be 3 CPH.
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  5. #5
    Thanks for the replys. Right now my ac system is set for 3 cycles per hour. Is it ok for it to come on for close to ten minutes and then shutoff for 10 minutes? I was told that it should run closer to 20 minutes before it shuts off. I have been timing it for the past hour or so and i'm getting anywhere from 7-12 minutes of off time and run times of about the same. Is that ok? I just want to make sure the system isn't oversized for the house. It's about 91 degrees outside and about 60% humididty. I have it set for 76 degrees in the house. Do all of these reading seem normal? I have a allegiance 14 AS 4 ton system cooling a 2500 sq ft house. Thanks in advance for the help.

  6. #6
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    That sounds about right. Is the stat satisfied after the cycle? The house temp what is called for at the stat? If it is set at 76, is the house 76? Then you are good....
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  7. #7
    Join Date
    Nov 2004
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    SW FL
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    Smile R.H. = Guidance for comfort and performance

    Quote Originally Posted by rickytz7111 View Post
    Thanks for the replys. Right now my ac system is set for 3 cycles per hour. Is it ok for it to come on for close to ten minutes and then shutoff for 10 minutes? I was told that it should run closer to 20 minutes before it shuts off.

    I have been timing it for the past hour or so and i'm getting anywhere from 7-12 minutes of off time and run times of about the same. Is that ok?

    I just want to make sure the system isn't oversized for the house.

    It's about 91 degrees outside and about 60% humididty. I have it set for 76 degrees in the house. Do all of these reading seem normal? I have a allegiance 14 AS 4 ton system cooling a 2500 sq ft house.
    Run times are Very Short.
    What is the Relative Humidity (RH) inside?
    Is that measured with a very reliable instrument (hygrometer)?

    IF R.H. > 52%, try CPH =2. Monitor for a week or so.
    Did the R.H. drop some?
    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
    The humidity gauge is just a $15 accurite I think. I have 2 diffrent gauges in the house they are reading between 54-56%. The run times seem a little short to me to dan sw fl. I just wasn't sure with this new system if it was suppose to run that way?

  9. #9
    Join Date
    Nov 2004
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    SW FL
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    Question See you next week

    Quote Originally Posted by rickytz7111 View Post
    The humidity gauge is just a $15 accurite

    I have 2 different gauges in the house, they are reading between 54-56%.
    Accurite is likely sufficiently accurate.

    R.H. > 52%, so try CPH =2. Monitor for a week or so.
    Did the R.H. drop some?
    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
    Jan 2008
    Posts
    56
    Here is why cycles per hour are important. You can cycle the equipment on and off to maintain tight control of your indoor temperature. But that won't improve your comfort. In fact, it might increase your humidity by maintaining an accurate "sensible heat" reading that would cause you to turn the thermosat down. because it's not comfortable.

    If you let the sensible heat (thermostat setting) wander a bit and prevent the system from switching on and off, you will get improved humidity removal. You won't notice the extra temperature swing because the comfort is improved due to better humidity removal.

    The system spends the first portion of it's run cycle building pressure, dropping the coil to operating temperature and building up moisture collected from the home on the coil. It also spends the early portion of that cycle discharging moisture that remains on the coil back into the home until the coil gets cool. If you cut the system off as soon as the system drops the temperature, the system is turned off at the time it was just starting to do some efficient work. When you turn it off and on to micro-manage the sensible heat temperature, you hurt humidity removal, damage comfort and increase operating cost. All without benefit.

    Smart thermostats can limit cycles per hour. They do this by letting the temperature setpoint wander a bit from the thermostat setting. The advantage is the system runs longer. A system that runs longer spends more time operating in it's most efficient portion of the cycle. It removes more humidity. It costs less to run.

  11. #11
    The RH did drop. I had my ac set at 78 this morning when I left for work. When I came home for lunch the humidity was 67%. I thought that was way to high. So I lowered the stat down to 76 and I have had it there the rest of the day. The humidity is right at 54% right now at 8:30 pm. It was about 55-56% this afternoon. Just to answer some questions the stat is getting satisfied and the house is really cool but it just seems like it is cycling on and off to much. I just check it again and this time it only ran for 6 minutes. Could the stat be messed up? It seems like it goes up 1 degree really quick to make the ac kick back on. My accurite does seem to go up as quick from what I have been paying attention to.

  12. #12
    Join Date
    Jan 2004
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    Lancaster PA
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    Chance its slightly over sized.
    What area do you live in.
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  13. #13
    I live in Arkansas. It's in the low 90's in the day and the mid to upper 70's at night. By me changing the cycle to 2 cycles per hour does that mean that it only run and stop twice during that hour? One last thing if it oversized what can be done about that? Thanks again for all the help

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