Michigan Geothermal compressor life with radiant heat

Discussion in 'Maintenance and Troubleshooting' started by jrj, Oct 14, 2017.

  1. jrj

    jrj New Member

    My 4000 sq ft home (including walkout basement} is heated with a TMW060, 5 ton Climatemaster unit and radiant floor heating. I installed the entire system myself. The compressor failed after 4 years, and I was wondering if I should adjust my system to extend the life of the compressor

    Load water is distributed by 4 individual pump/manifold setups all directly connected to the geothermal unit via a 1" "trunk" line. All pump/manifold setups run everytime there is a call for heat. I originally planned on running zones independently as necessary, but realized it was never necessary for my home to be evenly comfortable.

    I do not have a buffer tank, and here is why.

    I live in SW Michigan. We have nuclear power here, and pay only 1.7 cents/kw between 9pm and 7am, and 14 cents/kw during the day. Because of this, I run the entire system constantly from 9pm-7am, and turn it off during the day, except when necessary due to very cold weather. This seems to work very well, except for the compressor failing after 4 years. I understood that the more a compressor starts and stops, the harder it is on the unit, so I thougth just running it for 10 hours at night straight would be best for the compressor. The temp gauges on the manifolds usually range from 80 on the cold side and 110 on the hot side.

    Any ideas on how to extend the life of the compressor? Thanks!
     
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    The buffer tank is to reduce short cycling; guarantee constant flow; and reduce high temperatures returning to the heat pump. In summary, the pump flow for the heat pump is not the same pump flow for your floors. Unless you have one zone and a constant demand.

    A 30 degree drop is fairly high for a radiant system. I use 10C (try 15F) otherwise you get cold spots on the floor.

    If I had to guess - you are getting too high of return water temperatures to the heat pump.
     
  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    30F delta T on the load side indicates that your flow is quite low, meaning you likely only have 2.5 gpm flow through your heat pump, likely one of the problems.

    First thing of action is the check you flow rate and ensure that there is enough flow to the system. Larger pipes are likely needed. 1" header is usually is not enough to ensure enough flow to a 5 ton heat pump. Describe your radiant system, and your loop field and pumping solution. Pipe sizes etc.
     
  4. C. J. Edward

    C. J. Edward New Member

    What was the failure of the compressor?
    Did it fail electrically?
    Mechanically stuck?
    Runs but wouldn't pump?
    Who diagnosed the failure?

    Chillers (even heat reclaim like you have) like constant steady-state conditions. Including water flow rates. Change upsets them.

    The chiller flow and the loop flow are two different exercises as the dynamics are so different. Separating the two functions is always a good idea. Plus; if you have zoning you can vary the loop flow while keeping the chiller flow rate constant. And finally; with a buffer tank you can always ensure at least a small amount of work for the unit to do.

    Compressors do not die - except of extreme old age: they are generally murdered by adverse conditions.

    I would add a decent sized buffer tank - 80 gallons or so. If you use an electric water heater it can also serve as redundant heat in case the heat pump is not working for want of repairs. Just leave the breaker off. Use a buffer tank / unit circuit pump and use a separate space heating loop pump. Make sure the water flow through the heat pump unit is correct and constant. Stable conditions make for happy machines who then contentedly live long lives.

    CJ
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  5. geoxne

    geoxne Active Member Forum Leader

    That is good advice.
    I usually do not recommend your typical electric water heater. It may work for smaller HPs but they usually only have 3/4" ports (with a ridiculously small dip tube on the cold water inlet) and not enough ports to provide hydraulic separation between circuit flows. A true buffer tank has at least 4 big ports. Such as-
    http://www.lochinvar.com/_linefiles/SBT-02.pdf
    With some research you may find an electric tank that does it all such as-
    http://www.waterfurnace.com/literature/geotank/AG1600TW.pdf
     
  6. C. J. Edward

    C. J. Edward New Member

    I used to fully agree with your hydraulic separation concept but on commercial jobs I have seen a single H connection very effectively decouple the flow rates. The first time I Screamed about it in the specs but, even though I still want to use a buffer tank, and would on my own design, the hydraulic separation can be done with an H connection and no tank.

    I don't mention that to be argumentative or to be 'right' - I'm just chatting. In fact; I would always prefer to be wrong and so know more tomorrow than I did yesterday. <g> And an H connection would not serve all the OP's needs anyway. He also needs thermal mass / flywheel effect to stabilize his heat exchanger operation.

    But let's go back: 3 tons s0 let's call it 9 GPM chiller (condenser in this case <g>) flow rate. Wouldn't a 3/4" port be adequate for such a small flow? And also; it is common to find space-heating-option water tanks with multiple ports. Wait; I just checked - 9 GPM through a 3/4" diameter gives about 6.5 FPS velocity. That's not too bad. At about 8-9 FPS I would want to up the port (and pipe size) size. At about 10 FPS you start to lose heat exchanger performance. On my just-a-water-heater solar storage tanks I avoid using the dip tube in favor of a brass tee at the drain connection and a brass tee at the P/T valve connection

    CJ
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  7. geoxne

    geoxne Active Member Forum Leader

    15 GPM then for the OP per J.C.s calculations. I wouldn't pipe a 5T unit with less than 1 1/4" pipe. We are selling and installing high efficiency systems that deserve high efficiency piping and pumping.

    An H bypass does not work well for geo HPs as you would be mixing down supply temps, lowering system temperature and unnecessarily raising LEWT (Load Entering Water Temp). If you want to learn something check out the "Bypass Tee" piping concept with a buffer tank innovated by Docjenser on this forum.
     
  8. geoxne

    geoxne Active Member Forum Leader

  9. geoxne

    geoxne Active Member Forum Leader

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