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  1. #1

    Recommended Thermostat Cycle Rate Settings

    I recently installed a Honeywell Prestige thermostat for my Bryant 4-ton electric heat pump. The heat pump has 1 compressor stage and 1 auxiliary heat stage (electric heat strips). The thermostat has settings for the cycle rate for each stage. The default settings are 3 cph for the compressor stage and 9 cph for the auxiliary heat stage. Should I leave the cycle rates at the default settings of 3 and 9, or change them to something else? What do you guys recommend?

  2. #2
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    3 for both.
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  3. #3
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    For electrical heating , 6 is reasonable. 3 for the compressor is fine

  4. #4
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    I usually set the CPH numbers high like 6 for both. In most cases 3 should be fine but if for some reason more cycles are needed its better that they're available.
    Gary
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    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  5. #5
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    What is the purpose of limiting the number of cycles per hour? Why would the setting be different for a heat pump compared to a furnace?

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    Its suppose to be based on the efficiency. But generally, both furnaces and heat pumps should be set to 3.

    6 is too high for the strip heaters also. In homes where the people are in the air stream, they get annoyed at the cool warm cool warm air flow they feel.
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    Quote Originally Posted by garyed View Post
    I usually set the CPH numbers high like 6 for both. In most cases 3 should be fine but if for some reason more cycles are needed its better that they're available.
    6 is a bit high for Heatpump or A/C

  8. #8
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    Quote Originally Posted by beenthere View Post
    Its suppose to be based on the efficiency. But generally, both furnaces and heat pumps should be set to 3.

    6 is too high for the strip heaters also. In homes where the people are in the air stream, they get annoyed at the cool warm cool warm air flow they feel.
    Honeywell recommends 9 for electrical aux heating. cool warm cool warm air flow is caused by low CPH. In a heatpump, 3 CPH is good for compressor, which means the compressor maximum starts 3 times in an hour. However, when the outdoor temp is very low, room temp drops very fast. Then it is quite important to have aux heater running to maintain the supply temp when the compressor is not running.

    On the other hand it costs more energy, but to maintain a decent comfort level and also protech the compressor, that is the only way.

  9. #9
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    Quote Originally Posted by leoxxl View Post
    Honeywell recommends 9 for electrical aux heating. cool warm cool warm air flow is caused by low CPH. In a heatpump,
    Nope. Lower CPH setting doesn't cause cool warm cool warm. Higher CPH does.

    Set electric aux to a CPH of 3. To 2 if you want to satisfy the heat call with the aux heat on, and shut off the compressor.
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  10. #10
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    Quote Originally Posted by beenthere View Post
    Nope. Lower CPH setting doesn't cause cool warm cool warm. Higher CPH does.

    Set electric aux to a CPH of 3. To 2 if you want to satisfy the heat call with the aux heat on, and shut off the compressor.
    Hi Beenthere
    Here is my understanding of CPH, correct me if I am wrong. CPH stands for Cycle per Hour, and it is a part of the internal logic of the thermostat. For example, if CPH=3, that means 1 cycle is 20 minutes. Assume it takes a heatpump 30 minute to warm up the room temperature (say 10F) to setpoint (say 75F), during this 30 min of period the compressor will keep running because during the first 20min when the thermostat checks the room temp hasnt reached the setpoint, so that it wont shut the compressor off just because the CPH setting is 3. As soon as the room temp has reached setpoint 75F after 30min, the compressor contact of the thermostat becomes open which makes the compressor lose power, thus the compressor stops at the end of the 30th min when it reaches the setpoint temp. Then, we assume that the room temp droped in 5min, but the thermostat still will not start the compressor off untill the next cycle which is the 41th minute.

    Here comes to the key point. when CPH =3, the thermostat doesnt just cycle the compressor every 20 minutes without comparing the room temp and setpoint temp.

  11. #11
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    Quote Originally Posted by leoxxl View Post
    Hi Beenthere
    Here is my understanding of CPH, correct me if I am wrong. CPH stands for Cycle per Hour, and it is a part of the internal logic of the thermostat. For example, if CPH=3, that means 1 cycle is 20 minutes. Assume it takes a heatpump 30 minute to warm up the room temperature (say 10F) to setpoint (say 75F), during this 30 min of period the compressor will keep running because during the first 20min when the thermostat checks the room temp hasnt reached the setpoint, so that it wont shut the compressor off just because the CPH setting is 3. As soon as the room temp has reached setpoint 75F after 30min, the compressor contact of the thermostat becomes open which makes the compressor lose power, thus the compressor stops at the end of the 30th min when it reaches the setpoint temp. Then, we assume that the room temp droped in 5min, but the thermostat still will not start the compressor off untill the next cycle which is the 41th minute.

    Here comes to the key point. when CPH =3, the thermostat doesnt just cycle the compressor every 20 minutes without comparing the room temp and setpoint temp.

    Temp OVER RIDES CPH.


    If the room temp drops in 5 minutes, the thermostat will start the heat pump or what ever type of heater it is. With the only exception being that if the compressor safety time is set to more then 5 minutes. But that isn't a part of CPH.

    CPH, is not a fixed number of cycles. It is only an attempt of controlling cycles. Don't give CPH more credit then it is due.

    If you want to test it. If you have a CPH thermostat. Go to it, set it to 2 CPH. Then set it a few degrees higher then room temp, let the heat run for 2 minutes, set it below room temp, let the equipment shut off, then raise the set temp a few degrees above room temp again, keep repeating. With the exception of a 5 minute lock out time. It will always bring the heat back on without regard to CPH.
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  12. #12
    Sounds like I need to leave the compressor stage CPH set at 3. I would like to minimize the usage of the electrical heat strips to save $$ on my heating bill. With the CPH higher at 6, does this mean that the heat strips would run more frequently for a shorter period of time in a given one hour period, or with a lower setting of 3 CPH would the heat strips run less frequently but for a longer period of time in a one hour period?? For a comprimise, I have set it at 5.

  13. #13
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    Here is a quoted Trane manual Pub. No. 18-HD32D1-2
    "Cycle Rate
    Cycle rate is the selected number of system cycles per hour at 50% load. If the cycle rate were set to 3, each ON/OFF cycle would be 20 minutes long when operating at 50% load. The total ON and/or OFF times depends on the actual indoor space load. A shorter cycle rate may be desired for Heating mode to maintain tighter control to indoor setpoint. A longer cycle rate may be desired for Cooling mode to allow the system to remove moisture from the air and improve indoor comfort."

    So, a cycle rate should be set to YOUR HOME and YOUR COMFORT. Keep in mind, all houses are different and in different locations. Some are built tighter with better insulation R value, and some can barely maintain temp. Some have humidifiers, some are dry and shrink resulting in leaking windows and doors. Some have more appliances that run more often creating more heat.
    Your preferred cycle rate may change with humidity level, and total load conditions etc. As Beenthere states, "temp overrides cph". CPH is at 50% load conditions, normal on/off cycles that are consistent. These rates are just simple parameters to HELP operate the COMFORT SYSTEM in your HOME. A cycle rate cannot change your home, nor your comfort system...

    Most customers that complain about cycle rate do not have a humidifier, nor a tight, well insulated home, or their system is improperly sized or configured/functioning/leaking ducts etc..
    "The only true wisdom is in knowing you know nothing" Socrates

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