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Thread: Silly questions that I should already know the answer to...

  1. #1
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    Silly questions that I should already know the answer to...

    Q1. What does it mean to set the cycles per hour on a thermostat? So how does that work? The default on cooling is 3. Does it shut the system off ever 20 minutes? Or is 3 the maximum number of times that it will come on? Can't seem to "see" how that setting would effect anything if the system has not met setpoint after running 2 hours. I know that at some time in the past I set the cycles per hour to something like 6 on a heat pump and it did not do well and had to change it back to 3. Any better insight on how this effects system operation would be great

    Q2. Could someone explain to me "Dirty Sock Syndrome"? Is it just stale air. First time I ran into it today, I think.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  3. #2
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    The cycles per hour only let the unit cycle on no more than three times in one hour. If the load is high and the unit needs to stay on to meet temp the CPH setting would not affect anything. If the load was low and the unit was meeting set point after running 5 minutes it would only allow three starts in an hour. So the temperature could drift up, but the compressor would not be banging on every ten minutes. That’s the way I understand anywho.

    Dirty sock syndrome is a “funk” that gets in a coil for some reason. No matter how much you clean with regular stuff it’s still there. I don’t have any experience with how to get rid of this.

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  5. #3
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    Dirty socks was named for smelling like dirty gym clothes. Caused by bacteria growth on the evap coil as a result of a lack of self rinsing condensate. Usually more than one:
    Improper charge
    Air flow/transitions
    Txv installation
    Oversize equipment short cycling

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  7. #4
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    The Tstat temp control operates at tenths of a degree (.1). The display is in whole numbers (70). The thermostat has a rounding function to decide what temp to display based on the sensed value in tenths of a degree. Some manufacturers may differ their rounding Calc, but here is an example:

    Though long, this is a simplified explanation. Typical rounding from math class says 69.5 rounds to 70. 70.5 rounds to 71. So when the sensed temp is between 69.5 and 70.4 the tstat displays 70 degrees. In cooling application when the sensed temp hits 70.5, cooling comes on for as long as it takes to get the temp below 70.4. When the sensed temp drops below 69.5, the system will stay off until temp goes above 69.5. CPH takes over between 69.5 and 70.4 with a 70 degree set point. With a CPH of 3, the unit will turn on 3 times during the hour. The goal is maintain temperature between 69.5 and 70.4.
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  9. #5
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    I like to think of setting cycle rates like setting the old heating anticipator on a mercury t-stat.
    If you set it for a longer time then it wouldn't create as much heat in the t-stat to help move the bulb so the system would stay on longer to reach the temp & shut off longer too.
    With cycle rates, the smaller the number, the longer the cycle & with an anticipator, the higher the setting, the longer the cycle.
    The biggest difference is that depending on the t-stat, a small number of cycles per hour can actually stop another cycle from coming on even when it's needed.
    Usually the default 3 cycles per hour works OK but I like to set mine to 4 just to be safe.
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  11. #6
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    I've sometimes found setting it to one cycle per hour to help with humidity control at the expense of temperature control. On the Honeywell thermostats I use it is never a very noticeable change.

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    CPH is to be based on your anticipated load.
    You can set it on 1 CPH and the stat will let the sensed temp drop typically 0.5 degrees F.
    Then it can rise to 0.5 degrees above stpt.
    At 2CPH it may have a swing of 0.8. At 3 CPH it may be a swing of 0.6
    According to HW, the aim is to give some amount of swing but with the goal of always showing the same temp on the stat. This shows how well the system can maintain comfort (per HW).
    It's a PITA I think, cause of calls about equipment running
    "when the tstat shows it's at stpt, but the equipment is still running! Come fix it. "
    With poorly sized equipment it's a often a poor match.
    If the temp exceeds the differencial, the stat will close regardless of cycle rate.
    The cycle rate is really in play when the space is at setpoint and the algorithms take over.

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  14. #8
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    On Honeywell thermostats, temp ALWAYS over rides CPH. So i you have it set to 3, it may still only run twice on a hot day, or it Could cycle 4 times.

    Its just an electronic version of heat anticipation.
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    Quote Originally Posted by beenthere View Post
    On Honeywell thermostats, temp ALWAYS over rides CPH. So i you have it set to 3, it may still only run twice on a hot day, or it Could cycle 4 times.

    Its just an electronic version of heat anticipation.
    Not sure I get that.

    If it is set to 3 CPH, how can it cycle 4 times?
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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    Quote Originally Posted by joemach View Post
    Not sure I get that.

    If it is set to 3 CPH, how can it cycle 4 times?
    CPH is simply you setting the swing of the room temp. You tell the stat that you dont want the temp to drop more than x 10ths of a degree.
    The largest swing is 1 degree, per HW.
    The stat trys to learn what the typical drop/rise in space temp is and give the requested number of CPH..
    But temperature swings outside the selected CPH rate, still will result in a contact closure in the stat.
    So, if you alternately blew a heat gun and a liquid-loaded refrigerant hose at the stat sensor. It would alternately heat and cool regardkess of CPH selection, (until you ran out of liquid.)
    Disregarding the last paragraph....that's how it was explained to me by HW about 12 years ago.

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    Quote Originally Posted by joemach View Post
    Not sure I get that.

    If it is set to 3 CPH, how can it cycle 4 times?
    You remember the old heat anticipator of thermostats? The higher you set it, the longer the run time and off time. CPH is just a digital method of heat anticipation. It is not a run this many times an hour exactly. It is also only accurate when the homes heat loss or gain, is at 50% of the equipment's capacity.

    The CPH algorithm attempts to conform to the CPH number, but is not locked into it.
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  21. #12
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    I have asked Honeywell (or Resideo I don't remember for sure) how their CPH algorithm works and let me tell you their explanation was not satisfying.

    Sent from the Okie state usin Tapatalk
    "Is this before or after you fired the parts cannon at it?" - senior tech
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

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  23. #13
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    Quote Originally Posted by R600a View Post
    I have asked Honeywell (or Resideo I don't remember for sure) how their CPH algorithm works and let me tell you their explanation was not satisfying.

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    Quote Originally Posted by Hurst11 View Post
    Enlighten us
    I wish I could.
    I don't remember the explanation but the manual has a better one.

    Sent from the Okie state usin Tapatalk
    "Is this before or after you fired the parts cannon at it?" - senior tech
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

  25. #15
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    Quote Originally Posted by R600a View Post
    I wish I could.
    I don't remember the explanation but the manual has a better one.

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    Quote Originally Posted by ehsx View Post
    "fuzzy logic" if this does that, then so-in-so does something else, but only if.....
    No they didn't get that much detail. They didn't seem to want to share. Its basically it makes you comfortable so don't question it.

    Sent from the Okie state usin Tapatalk
    "Is this before or after you fired the parts cannon at it?" - senior tech
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

  27. #17
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    Quote Originally Posted by beenthere View Post
    You remember the old heat anticipator of thermostats? The higher you set it, the longer the run time and off time. CPH is just a digital method of heat anticipation. It is not a run this many times an hour exactly. It is also only accurate when the homes heat loss or gain, is at 50% of the equipment's capacity.

    The CPH algorithm attempts to conform to the CPH number, but is not locked into it.
    Not much experience with the heat anticipator.

    So setting the CPH down to say, 1 would increase the run time & off time. Is that correct?
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  29. #18
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    Quote Originally Posted by joemach View Post
    Not much experience with the heat anticipator.

    So setting the CPH down to say, 1 would increase the run time & off time. Is that correct?
    Yes, thats correct.
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  30. #19
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    Quote Originally Posted by beenthere View Post
    Yes, thats correct.
    Great! Thank you so much.

    This has bothered me for a long time and never had the sense to ask.

    Load of stress off my mind.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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