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  1. #1
    Join Date
    Mar 2008
    Location
    Jackson, NJ
    Posts
    176

    Compressor Lockout - Recovery

    Hey Gang,

    Can somebody explain how compressor lockout and recovery work?

    From what I understand:
    Compressor lockout is the temperature dictated by the stat that basically forces a hybrid system to run backup heat.

    Now .. backup heat ... I'm assuming this behaves differantly if you have electric strips vs. a gas furnace?

    The reason I ask is this. I have read on this forum a number of times where folks say they have their electric strips come on during the recovery phase in their heating cycle. It appears, to me the layman, that the strips either come on in tandem to the heat pump or they are coming on solo. There is never a mention of the lockout temp on the stat.

    So what happens with a hybrid Heat Pump / Propane system? My assumption was, recovery or not, if the temperature outside was above my lockout setting the heat pump would run as long as it needed to in order to catch up. The gas furnace would only fire if the temperature was under my lockout set point.

    Am I right?

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,326
    Lockout can be interpreted in more than one way.

    High temp lockout: if outdoor temperature exceeds a given setpoint, compressor will not run if heat pump system is in heat mode. This is to prevent excessive head pressure building up in the indoor coil, stressing the compressor and system.

    Low temp lockout: if outdoor temperature goes below a given setpoint, compressor will not operate if heat pump system is in heat mode. This setpoint is about equivalent to the "balance point" of the house, where the house structure is losing heat to the outdoors at about the same rate the heat pump compressor, by itself can bring heat in. Below that point, running the compressor does not accomplish much, so it is locked out and the back-up heat source is the sole provider of heat.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    Dec 2007
    Location
    East central Indiana
    Posts
    477
    In the case of gas/heat pump combinations, a "fossil fuel" kit is normally used. This is done for at least 2 reasons I know of. 1. To prevent the heat pump and gas furnace from operating at the same time, in which case the furnace would be blowing hot air over the indoor coil (no big deal in the case of electric furnaces, because the "draw through" application is used). 2. To prevent the heat pump from operating below a certain temperature (it would be rather pointless to use the heat pump below a certain temperature, because without the gas furnace being able to run simultaneously, the heat pump simply wouldn't be able to keep up).

    Now, if it's pretty cold outside, and if the heat pump still isn't on low temp lock out, the stat will sense when the heat pump is "falling behind", and will turn on the furnace (with the fossil fuel kit turning off the hp at that point).

    I'm probably goofing up somewhere, but when I make my own fossil fuel kits out of relays and temperature switches, that's what I design them to do.

  4. #4
    Join Date
    Mar 2008
    Location
    Jackson, NJ
    Posts
    176
    Quote Originally Posted by shophound View Post
    Lockout can be interpreted in more than one way.

    High temp lockout: if outdoor temperature exceeds a given setpoint, compressor will not run if heat pump system is in heat mode. This is to prevent excessive head pressure building up in the indoor coil, stressing the compressor and system.

    Low temp lockout: if outdoor temperature goes below a given setpoint, compressor will not operate if heat pump system is in heat mode. This setpoint is about equivalent to the "balance point" of the house, where the house structure is losing heat to the outdoors at about the same rate the heat pump compressor, by itself can bring heat in. Below that point, running the compressor does not accomplish much, so it is locked out and the back-up heat source is the sole provider of heat.
    Thank you !!!!

  5. #5
    Join Date
    Sep 2007
    Location
    KY
    Posts
    79
    Quote Originally Posted by ECIndHVAC View Post
    In the case of gas/heat pump combinations, a "fossil fuel" kit is normally used. This is done for at least 2 reasons I know of. 1. To prevent the heat pump and gas furnace from operating at the same time, in which case the furnace would be blowing hot air over the indoor coil (no big deal in the case of electric furnaces, because the "draw through" application is used). 2. To prevent the heat pump from operating below a certain temperature (it would be rather pointless to use the heat pump below a certain temperature, because without the gas furnace being able to run simultaneously, the heat pump simply wouldn't be able to keep up).

    Now, if it's pretty cold outside, and if the heat pump still isn't on low temp lock out, the stat will sense when the heat pump is "falling behind", and will turn on the furnace (with the fossil fuel kit turning off the hp at that point).

    I'm probably goofing up somewhere, but when I make my own fossil fuel kits out of relays and temperature switches, that's what I design them to do.

    you do know that they make thermostats that will control hybrid/duel fuel systems without any kit or relays don't you? just need capable stat and outdoor sensor.
    I'm lost, I've gone to look for myself.

  6. #6
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by ECIndHVAC View Post
    when I make my own fossil fuel kits out of relays and temperature switches, that's what I design them to do.

    you are setting yourself up for a liability case!

    use a certified fossil fuel kit or stat to avoid this!



    .

  7. #7
    Join Date
    Dec 2007
    Location
    East central Indiana
    Posts
    477
    Quote Originally Posted by chlosum View Post
    you do know that they make thermostats that will control hybrid/duel fuel systems without any kit or relays don't you? just need capable stat and outdoor sensor.
    ...well, if the boss insists on 35 dollar stats and refuses to use fossil fuel kits, then what's a guy to do?

  8. #8
    Join Date
    Mar 2008
    Location
    Jackson, NJ
    Posts
    176
    Quote Originally Posted by chlosum View Post
    you do know that they make thermostats that will control hybrid/duel fuel systems without any kit or relays don't you? just need capable stat and outdoor sensor.
    I've got one of those honeywell IAQ's and a outdoor sensor.

  9. #9
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,188
    Quote Originally Posted by ECIndHVAC View Post
    ...well, if the boss insists on 35 dollar stats and refuses to use fossil fuel kits, then what's a guy to do?
    Kindly inform him that he's an idiot and sell the customer the proper thermostat that will cost less than the relays and time spent doing it.
    Perhaps you should have read the instructions before calling.

  10. #10
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by ECIndHVAC View Post
    ...well, if the boss insists on 35 dollar stats and refuses to use fossil fuel kits, then what's a guy to do?
    post a wiring diagram for your homemade fossil fuel kit in the pro section

    i am curious what your homemade fossil fuel kit does when heat pump goes into defrost!



    .

  11. #11
    Join Date
    Jul 2008
    Location
    Dutchess County, NY
    Posts
    152
    Quote Originally Posted by Jopopsy View Post
    Hey Gang,

    Can somebody explain how compressor lockout and recovery work?

    From what I understand:
    Compressor lockout is the temperature dictated by the stat that basically forces a hybrid system to run backup heat.

    Now .. backup heat ... I'm assuming this behaves differantly if you have electric strips vs. a gas furnace?

    The reason I ask is this. I have read on this forum a number of times where folks say they have their electric strips come on during the recovery phase in their heating cycle. It appears, to me the layman, that the strips either come on in tandem to the heat pump or they are coming on solo. There is never a mention of the lockout temp on the stat.

    So what happens with a hybrid Heat Pump / Propane system? My assumption was, recovery or not, if the temperature outside was above my lockout setting the heat pump would run as long as it needed to in order to catch up. The gas furnace would only fire if the temperature was under my lockout set point.

    Am I right?

    Ok first off..what kind of thermostat do you have? you stated that there was no mention of a lockout set point on your stat... some stats have hidden programming built in and are accessed by holding several buttons down for several seconds... anyway, the stat should have been programmed by your installer which would have included a lockout point for your HP compressor or if you have a zoned system that uses a zone board the lockout point could be set there. either way you would need an outdoor air sensor for this feature, so you can trace the wire back to see where it is going. Your compressor is also locked out if you ever put your stat in emergency heat mode. The reason for a lockout is that you never want to have both primary and auxilliary heating running at the same time. But you want your efficient HP to work for as long as you can get it to run efficiently ...right around 30° is where I find it not to put out enough heat for it to run any longer so you turn it off or "lockout" the HP and go to auxilliary oil/propane/electric/ etc. but When the outdoor temperature is between the two temperatures, both the Compressor and Auxiliary Heat operate with some stat models.

    You also asked about recovery time.. again what kind of thermostat are you using? Recovery is displayed when the heating or cooling system is activated before a set point For example: Set the Wake time to 6 am, and the temperature to 70°. The heat will come on before 6 am, so the temperature
    is 70° by the time you wake at 6. The message “Recovery” is displayed when the system is activated before a scheduled time period.

  12. #12
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347
    Quote Originally Posted by Sonicview View Post
    you want your efficient HP to work for as long as you can get it to run efficiently ...right around 30

    that number can vary by 10 or more degrees higher or lower, it has a lot to do with outdoor humidity level
    as well as the electricity and gas rates and whether the customer wants to be more efficient or more comfortable



    .

  13. #13
    Join Date
    Sep 2007
    Location
    KY
    Posts
    79
    Quote Originally Posted by ECIndHVAC View Post
    ...well, if the boss insists on 35 dollar stats and refuses to use fossil fuel kits, then what's a guy to do?
    seems to me that if you have enough knowledge and exp. to rig your own fossil kit that you could get a new boss...
    I'm lost, I've gone to look for myself.

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