Buffer Tank Temp Rise

Discussion in 'General Discussions' started by tstolze, Feb 12, 2012.

  1. tstolze

    tstolze Member

    Thought I would post this image of our buffer tank over the last day, I am thinking we can point those who want to try a single tank setup to this image.

    As you can see the temperature rise or heat transfer really noses over the hotter the tank gets. Once over 120 the rise is almost nonexistent in our setup, of course when the tank gets down into the 70's the rise is really steep, although not shown in this graph.

    Our system is a 2 ton 2 stage setup, during this time we have run in 1st stage only. I am sure larger systems that have bigger exchangers in them will have a faster recovery, but I think the fall off would be very similar.
     

    Attached Files:

  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I guess that around 17.5 hours in the past there was a fairly significant hot water draw event.

    What I don't understand is the 90 minute interval where the desuper appears to have been extracting heat from the tank.

    I occasionally experience short intervals like that when a system has run for hours in high stage and then downshifts to low stage, but from the description, that doesn't sound like the case here.
     
  3. tstolze

    tstolze Member

    Correct on the water draw event.

    The interval you are describing is actually a time when the heat pump was not running, looks like it shutdown about the 17 hr mark and back on between 14-15 hr mark. The buffer tank sensor was pushed between the insulation and the tank about the level of the top element. The heat pump was off shortly after the usage "V", you see a slow drop, then when the unit came back on you see the leveling of temperatures. The little blip near the 4 hour mark is the Bryant/Climate Master infamous 5 minute compressor shutdown after 4 hours of continuous use. I would really like to see a workaround for the so called feature.
     
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I agree that dumping the compressor for 5 minutes after a mere 4 hour run is a needless waste.

    It is headed for 22*F tonight here in Jax and I fully expect my system to stay on pretty much all night servicing all 4 zones.

    I get the same behavior on long hot afternoons in July.

    I think WF throws a code w/o shutting down after 18 continuous hours. That's quite reasonable. A very long run could indicate a welded contactor, so some vigilance is in order.
     
  5. StevieB

    StevieB Member

    CM shutdown

    I think you two answered a question I had about my unit seemingly shutting down the compressor with a call for heat. A five minute shutdown after a four hour continuous run....HUH! I checked and no codes, no loss of Y1, no apparent reason. I never did see it in the paperwork. I was worried it may have been high headpressure but I think there should have been a code for it and could require a reset. Is this it? A feature?
    Thanks, Steve
     
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Seems like a welded contactor would cause a unit to shut off on pressure switch fairly soon after fan cycled off.....though it may restart lock-outs.
     
  7. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I agree that a compressor would trip on overload a few minutes after any stoppage of heat removal from its high side (air or water as applicable) so I'm not completely convinced that an alarm based soley on excessive runtime is useful

    Perhaps the intent is to alert user of some other problem - bad thermostat or window left wide open in winter...I dunno, I'm grasping at straws.

    In a somewhat related vein, when I program thermostats (always Honeywell) I clamp the overly broad default allowed setpoint range from 50 / 90 to 68 cooling low limit, 77 heating high limit. That protects equipment from fools, drunks, and pranksters.
     
  8. tstolze

    tstolze Member

    I did the same thing when setting up my stat from Bayweb, believe I entered numbers +/-5 degrees from our normal heat/cool settings.
     
  9. comment

    ======================

    Want to be careful here comparing apples to apples. My 2008 Carrier GTPX only delays 5 minutes on an initial "power on / checkout of the unit circuit board". I am talking about the self check out / test feature. My Vision Pro 8000 Honey well thermostat also has an additional built in default 5 minute wait after shut off ( to make sure a compressor has plenty of time to equalize and doesn't start under unequalized stress). So could have a theoretical delay of almost ten minutes under certain conditions. I normally leave the unit powered and I changed the 5 minute time default delay on my Honeywell T'stat to 4 minutes. My unit will run forever unless something breaks or a safety trips.

    Are you saying that the unit automatically shuts off for 5 minutes based on a certain run time? That sounds screwy. My experience tells me that these units should run until power is interrupted something actually goes wrong with them.
     
  10. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    All Climatemaster units (which makes units for carrier) deactivate the compressor for a few minutes every 4 hours. The fan keeps going, so you don't notice it unless you have a thermometer on your supply air. This comes from the circuit board, not the thermostat. So far, no one at CM could explain it to me.
     
  11. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Why subject the compressor and the system to an unnecessary stop / start cycle every 4 hours?
     
  12. geome

    geome Member Forum Leader

    I believe the geothermal unit test time and the thermostat timer would run concurrently (with both timers starting at the time power is turned on.) If so, 5 minutes would be the maximum delay.
     
  13. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    A friend had daughter and son-in-law staying with her elderly father and was on the hook for the utilities.
    She delightedly reported back to me that the son-in-law complained that while the thermostat I installed for her seemed to work okay, he couldn't set it past 72*.
    :D:D:D
     
  14. geome

    geome Member Forum Leader

    Could be worse. My father-in-law would "solve" a non-responding thermostat the same way he "solves" non-responding TV remotes (due to bad batteries) - push it HARD until it breaks. (That's why I use a thermostat cover during his 3-day visits.) :)
     
  15. tstolze

    tstolze Member

    I have no idea why CM does this, just to be clear it is the compressor only, everything else keeps running.
     
  16. StevieB

    StevieB Member

    That's what mine does. I picked up this feature with CTs on the compressor circuit.
    I could not figure out why til I read this thread. Never did see it in the factory papers.
    Steve
     

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