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  1. #1

    XP21 Heatpump and Lennox 7000 stat

    I have just had a Lennox XP21 (5 ton) heat pump installed with a Lennox 7000 thermostat. The air handler is a CB31-MV 65 equipped with 20 kw lennox electric strips. The thermostat has been set to 2 stages of heat pump and 1 stage backup. After 6 days I have noticed that the low balance has reset itself from -10C to factory default of -4C. This has happened 3 times for no apparent reason. Also there is a random demand for electric back-up heat at all times and temperatures. Sometimes it is 5kw and sometimes 10, 15 or even 20 - this lasts for anywhere from 30 seconds to a minute and then goes off while the heat pump continues to run. As a result, I am using more electrics now than I was was with my older XP15 single stage heat pump. The installer does not seem to have any answers other than monitor it. Are there any suggestions as to what may be the problem and will adjusting the high balance point lower and or changing the stage delay diiferential and timers make any difference? Also would rewiring the elctric backup to come on in 2 stages as per the available thermostat settings make any difference?

  2. #2
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,845
    Well, you have an R-22 airhandler, that I don't believe is an ARI match, with an R-410A heatpump.
    As you stated, the backup, or aux heat is only 1 stage, so they will sequence on by the air handler sequencer operation, or they maybe controlled by an "Even Heater". So, how do you know how many are coming on? Why aren't they staged?
    If the factory defaults are resetting, you may have an issue with the thermostat.
    "The only true wisdom is in knowing you know nothing" Socrates

  3. #3
    Thanks for the reply. The air handler has been in use with an XPA15 heat pump for about 7 years. Lennox assures me it is compatible with the XP21. I can watch the load draw for the elctric heat elements and see a 5, 10, 15 or 20 kw draw as they come on. The installer said they always wire these as 1 stage and my question is why? Why not have 2 stages of heat pump and 2 stages of electric back up heat as per the lennox 7000 thermostat? It has only been the low balance point that has reset to factory default and only 3 times. It has stayed at -10C for 3 days now with no change. Any other info or suggestions are appreciated as I had so much trouble with the last heat pump that I am trying to preclude a repeat of the headaches.

  4. #4
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,845
    If you got the approval from Lennox then, how can anyone argue with that?

    The staging, well... I guess, they just don't know how to wire it. It's really not that difficult. I wish I could advise your tech how to do it, but we can't give DIY info on this site.

    I can tell you that thermostat does offer 2 stage aux heat and emergency heat, as you probably know. The air handler can be configured for 2 stage aswell, very easily. I don't know what else is connected though. Humidifier, humiditrol, is the electric heat a smart heater, or a Lennox Even Heat?
    "The only true wisdom is in knowing you know nothing" Socrates

  5. #5
    MGenius33, I'm not sure exactly what the heat strips are called but the manual says ECB29/31 and there is 20kw (4 x 5kw units). The installers say there is no advantage to wiring the strips in stages and allow the thermostat to control them. They basically have refused to even consider it. I don't know if there is any efficiency advantage to having them controlled in stages but I want to get everything I can out of this unit. Because the compressor is hard wired to use second stage only below 40F, can you see an advantage to me persuing the wiring issue? Also can you give any comments on setting the stage diff and delays to get the most out of the single stage electric heat? On the positive side the temperature has gone above 40F and the XP21 operating with only first stage is very quiet and seems efficient. And, the current draw is much less then when opertating second stage heat so should be economical. I'm anxiuos the see how it works in the summer. Thanks in advance for any advice.

  6. #6
    Join Date
    Jun 2010
    Location
    Western Nebraska
    Posts
    246
    Quote Originally Posted by LEC View Post
    MGenius33, I'm not sure exactly what the heat strips are called but the manual says ECB29/31 and there is 20kw (4 x 5kw units). The installers say there is no advantage to wiring the strips in stages and allow the thermostat to control them. They basically have refused to even consider it. I don't know if there is any efficiency advantage to having them controlled in stages but I want to get everything I can out of this unit. Because the compressor is hard wired to use second stage only below 40F, can you see an advantage to me persuing the wiring issue? Also can you give any comments on setting the stage diff and delays to get the most out of the single stage electric heat? On the positive side the temperature has gone above 40F and the XP21 operating with only first stage is very quiet and seems efficient. And, the current draw is much less then when opertating second stage heat so should be economical. I'm anxiuos the see how it works in the summer. Thanks in advance for any advice.
    LEC,

    Do you have a discharge air sensor in the supply plennum? It will have a rectangular mounting plate with a brass locking nut and two wires (one red one green) running to the air handler. If so, your unit may have Evenheat. Evenheat only looks at discharge temp not staged calling.

    Hope this helps.

  7. #7
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,791
    Tell the installers that by staging the heat strips. it allows for the heat pump to run longer, and use less electric for the strip heaters.
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