Texas Buffer Tank

Discussion in 'Maintenance and Troubleshooting' started by woodbutcher, Jan 6, 2017.

  1. woodbutcher

    woodbutcher Member

    When my geothermal system was installed twenty years ago, no buffer tank was included. Desuperheated water was circulated thru the house water heater, and I didn't know it would make a difference. Geothermal HVAC was new to this area, and very few companies did install/service for them. A few years ago I read about the need for a buffer tank in this forum. Someone posted a diagram that made installation simple enough for me to add one to my system, but first I spoke with the technician who works for the closest company( 40 miles away) that services geothermal equipment. I also spoke to a plumber about the plan. Neither of these people were willing to do the work, citing warranty violation. I installed a 38 gallon electric water heater (not connected to power) and I plumbed the T&P into a house drain where all the condensate drains are connected. Is water from the desuperheater hot enough to open the T&P valve and cause my buffer tank to dump water into the drain?
  2. woodbutcher

    woodbutcher Member

    I live in northeast Texas. My unit is a 4T Bosch split system with American Standard airhandler with vertical loops buried 205 ft. Power cost here is $.115 per KWH and we average 1,200 KWH per month. I don't have the tools to give accurate readings or estimates for air temps or load, so my question about buffer tanks might be in the wrong forum.
  3. mrrxtech

    mrrxtech Member

    Do you have a water to air geothermal with hot water option from the Desuperheater, or is this a water to water geothermal?

    If the T&P valve is the relief on your water heater, I wouldn't expect water from a geothermal heat pump to cause the relief to lift. The Desuperheater hot water system has a 2 bimetallic switches to shut down the desuperheater pump at a designed temperature in order to prevent scalding someone taking a shower, 125 degrees is the return side bimetallic switch set point on my Carrier Unit.

    I just found these clip on probe Volt Amp meters on ebay, got a few coming in the mail for compressor efficiency determination.


    I have 2 of these type of temperature monitors I found for under $4 each, tucked under the insulation of my loop inlet in outlet at the Geothermal Unit. I have an extra for measuring air temp in and out.


    Going DIY means going cheap for me. Why pay too much, save the money to pay for the electric bill.
    Last edited: Jan 6, 2017
  4. woodbutcher

    woodbutcher Member

    Thanks for the reply. I don't know the answer to your first question. I do know that I have the hot water option for the desuperheater, there is a switch that turns on the pump. I assumed that my system is water to water. Thanks for the links.
  5. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Your T&P shouldn't be hard plumbed to a drain. The point of them, is to make leaks noticeable.

    On your domestic, your desuperheater supply is very unlikely to blow through a T&P valve.

    Now you talk about a buffer tank, so I'm going with a radiant side. Your radiant side needs an expansion tank. If you don't have one, that's why you're blowing through your relief valve.
  6. woodbutcher

    woodbutcher Member

    Yes, you're right. The T&P valve has a tube on it that drains it into the pan under the tank which is plumbed into the drain for the condensate. I'm actually not having a problem with the T&P. It seems to work fine. Thanks for the info.
  7. Stickman

    Stickman Active Member Forum Leader

    From my ClimateMaster manual:

    "The temperature set point of the HWG is field selectable to 125F or 150F"

    My T/P relief valves are labeled to open at 210F.
  8. mrrxtech

    mrrxtech Member

    120 is the recommended highest set point of an electric water heater element in order to protect the young and elderly who would be most likely to get burned in the shower. Based on this info the 125 degree setting would be the setting to use.

    Geothermal Units aren't known for the high temperature output that you see with a gas or propane unit. That's why they use a higher air flow rate than a gas unit. They move more BTUs with the higher air flow and a lower Delta Temperature across the unit.
  9. woodbutcher

    woodbutcher Member

    Thanks, that was my concern also.
  10. mrrxtech

    mrrxtech Member

    Those switches used in geothermal units are the same as the ones used in the HVAC industry, they are very inexpensive and use a mounting bracket to hold them against the copper inlet & outlet pipe. I could make my own or use a tiewrap, since they only need to be touching the line, the heat will transfer without having a fancy bracket.

    Here's the results of a search on ebay using Bimetalic+Temperature+switch and 120 degrees. The switch needs to be normally closed then open above 120 to shut off the circulating pump. the discharge switch on my Trane is Normally Open closing at 145 degrees. I jumpered this switch out since it took forever to get the line heated up to 145 degrees using heat conduction in the line. Since this switch needed to be closed to start the circulating pump I jumpered it out so the pump always starts with the compressor.

  11. woodbutcher

    woodbutcher Member

    Thanks so much for your idea for mounting the switch and for the link. As it turns out, there doesn't seem to be a problem with the desuperheater temp or the T&P valve. I was looking for the cause of a larger than usual water bill. I don't see anything that makes me think that was the problem.
  12. mrrxtech

    mrrxtech Member

    How about an underground leak, a running toilet, or a neighbor using a hose to borrow water when the hose isn't frozen.

    You're Welcome Butch.
  13. woodbutcher

    woodbutcher Member

    Yep, those are possibilities.
  14. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Beware yet more WrecksTech potentially dangerous nonsense:

    "Those switches used in geothermal units are the same as the ones used in the HVAC industry, they are very inexpensive and use a mounting bracket to hold them against the copper inlet & outlet pipe. I could make my own or use a tiewrap, since they only need to be touching the line, the heat will transfer without having a fancy bracket."

    Accuracy of contact-based thermal sensors very much depends on how they are attached to the tube or surface being measured. The "fancy bracket" is integral to proper heat transfer between tube and sensor. An overly small contact point not augmented by a conductive bracket and, even better, some insulation, will easily be overwhelmed / rendered inaccurate by ambient air temperature, particularly if ambient air is driven by fan or wind.

    Competent HVAC technicians are schooled in proper techniques for affixing temperature sensors, and it is time well spent to insure safe, proper, and efficient operation of HVAC systems. Anything less is professional malpractice.

    If you persist in dispensing DIY advice geared toward driving every issue to the absolute least first cost do please at least also kindly know and convey the importance of the underlying physics and thermodynamics:

    To wit - an open attachment of a sensor to a tube made merely by a single nylon wire tie carries a real risk of the sensor being led astray by dominant ambient air temperature.

    If the "fancy bracket" (usually a stamped metal clamp or section of copper strap) is unavailable, a temporary but quite serviceable mechanical and thermal connection between sensor and tube can usually be deployed using a short bit of kitchen aluminum foil folded over a couple times and wrapped over the sensor / tube junction with (despite the exorbitant "extra cost") 2 or, (perish the thought) maybe even 3 nylon wire ties and a scrap of pipe insulation to isolate the whole assembly from ambient air.

    Sadly, I've become convinced that, despite your enthusiasm for geothermal HVAC, your posts, too often unencumbered by facts, present a clear and present danger to new members of this site.
  15. The buffer tank is not so much a required part, but helps get the most out of it. The more stored hot water the better. The unit only creates hot water as a by product of compressor operation, not on demand (in a typical unit), so it's really just for hot water assist. I have at least one customer who turns tee propane off his heater all summer, and only has to turn propane on from maybe November to February or so when the unit doesn't run enough to satisfy his hot water needs.
  16. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Desuperheater is pretty much useless without a buffer tank. Otherwise a heat element or a gas burner is trying to keep set point temperature, and the DSH pump will rarely turn on, since the tank is always hot.

    But first of all, welcome here. Why do you respond to 18 month old threads?

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