CPVC from geothermal unit to water heater pre-heat tank failing

Discussion in 'Solar and Geothermal Water Heating Forum' started by Brian_in_Virginia, Dec 1, 2019.

  1. Brian_in_Virginia

    Brian_in_Virginia New Member

    Joined:
    Dec 1, 2019
    Location:
    Arlington, VA 22205
    Hi all,
    Newbie here. I'm hoping I can get some advice about the CPVC leading from my geothermal units to the storage tank for pre-heated water. My system is set up so the geothermal dumps excess heat (during the summer cooling period) into tap water so the water heater has less work to do. A few weeks ago I had an elbow fail. First it was a slow drip that I thought could wait two days until my HVAC folks were scheduled. By that eve, it was a stream and two "pinholes" in the top of the elbow were streaming water about 2 feet across the floor (very small holes). I turned off main water and made the repairs myself (on a Sunday...). I duplicated the section I had to cut out. Now the same lines are leaking in two other locations. Luckily at least this time the leaks are behind the shut-off valves and I am able to isolate only these pipes.

    This link is to my google share site and it has pictures and a few pictures and short videos (3 videos, less than 4 minutes total). https://photos.app.goo.gl/qMrKuNezJA6wnc5W9

    I'm not sure it comes through in pics or video, but the pipes closest to the HVAC units have areas that feel oily or slippery. It feels like some contaminant was spilled on the CPVC.

    I'm hopeful someone can give me advice...
    - Is a plumber or HVAC person the best to address this?
    - Should I be worried about CPVC throughout house?
    - Does it make sense that so many elbows, connectors, etc., were used?
    - Is this shoddy workmanship?
    - Is it possible/likely that HVAC refrigerant and/or other HVAC maintenance liquids were spilled on the pipes and caused them to deteriorate?
    - What should I be asking? ;-) Any advice in general?
     
  2. WorthFlorida

    WorthFlorida When the wife won't let you get a Harley!

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    Are there any chemicals in the loop to the geothermal ground and the storage tanks? Is there antifreeze in this system? I would say a plumber is the better person to look at this issue.
     
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  4. SShaw

    SShaw New Member

    Joined:
    Nov 17, 2019
    Location:
    Virginia
    I recently had a geothermal heat pump installed with a domestic hot water assist option (desuperheater.) I was told that copper pipe should be used between the geothermal heat pump and the buffer tank to reduce the risk of pipe/joint failures. The water can get very hot, especially if there is a problem with the desuperheater water pump. My pump is set to stop circulating when the water hits 130 degrees. So, replacing the pipe with copper should help. I'd also suggest checking to see if your unit has a temperature limit for the desuperheater pump and make sure it's set appropriately and working correctly.
     
  5. Brian_in_Virginia

    Brian_in_Virginia New Member

    Joined:
    Dec 1, 2019
    Location:
    Arlington, VA 22205
    Thanks for the reply and the question. I'm not sure what the fluid is within the geothermal loop. I think it's water mixed with something to help heat transfer, but I don't know. I'm confident the storage tanks are isolated. Fresh water comes into the HVAC, there's heat transfer, and slightly warmer fresh water goes to the tanks. I have had a plumber take a look, but I wanted a second opinion.
     
  6. Brian_in_Virginia

    Brian_in_Virginia New Member

    Joined:
    Dec 1, 2019
    Location:
    Arlington, VA 22205
    Thanks for the reply. I also received the same recommendation. I'll likely have the pipes replaced with copper until well away from the units. I'm thinking refrigerant or oil used when working on the units affected the CPVC. Either that or the vibration of the units weakened the CPVC joints. I'll also check if there is a temperature limit, but I didn't think mine would ever got that hot. In the summer it dumps some excess heat info the water rather than the ground, but I don't believe it transferred that much heat. It didn't produce hot water, rather only pre-heated the water going into the water heater to improve efficiency.
     
  7. SShaw

    SShaw New Member

    Joined:
    Nov 17, 2019
    Location:
    Virginia
    A closed geothermal loop will have antifreeze fluid added to it. Usually methanol or glycol is used. The fluid is necessary to prevent the water in the loop from freezing. The fluid actually hurts heat transfer a little.

    As you know, the desuperheater (DSH) hot water "loop" is totally separate from your ground loop. The DSH loop doesn't have any fluid added to it. It's an open system connected to your incoming domestic water supply. As such, the antifreeze in your ground loop shouldn't have any effect on your DSH piping issue.

    The DSH will produce only about 10% of the BTU output of the heat pump, so it will heat the water slowly compared to a water heater. However, it's not correct to say that the water will never get very hot. The water will slowly get hotter the longer the heat pump and DSH runs. Plus, you have 2X heat pumps tied into one tank, so your setup should heat up faster. As I noted in my first post, my DSH is set to stop circulating at 130-degrees and the water often gets that hot. A typical water heater will be set at 120. DSH buffer tanks can run at 130-140 degrees.

    The DSH pumps get hot themselves, so the water can be very hot right at the unit--hot enough to burst PEX pipe. So, the recommendation is to use copper piping, at least for a few feet from the unit.

    DSH setups can work any time the heat pump is operating--both in the summer and in the winter. In the summer the DSH will draw waste heat from the heat pump that would otherwise be dumped into the ground loop. In the winter the DSH reduces the output capacity of the heat pump by about 10%. If yours is setup to operate only in the summer, you are not getting the most out of it.

    From the video, it looks like you have two heat pumps tied into one buffer tank. I can't tell for sure, but the DSH output pipes from the two units appear to be simply tied together without check valves. I'd be concerned about that. I believe check valves are recommended to prevent back flow through a DSH pump that's not operating. Without check valves, I think it would also be possible for the DSH water to flow through the other heat pump and bypass the buffer tank.
     
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