Are there geothermal water heaters? (not desuperheaters)

Discussion in 'General Discussions' started by BlueHawk, Feb 10, 2020.

  1. BlueHawk

    BlueHawk New Member

    Hi all – Are there geothermal water heaters? I mean full-fledged water heaters that supply all the hot water needs of a home, not desuperheaters.

    When I search online, all I get are desuperheaters. It seems like a geothermal loop should be able to power a dedicated, full capacity water heater, so I'm surprised that I'm not finding it. Shouldn't the geothermal liquid medium be able to heat water directly?

    Thanks for your feedback.
  2. ChrisJ

    ChrisJ Active Member Forum Leader

    Yes, it's a water to water heat pump.
  3. wing

    wing Member

    Absolutely such hot water heaters are available. In my opinion, in a heating dominated climate zone it is wise not to rely on the desuperheater for this purpose.

    Here is my hot water setup, a 119 gallon Caleffi SolarCon tank with single heating coil and 4500 watt electric backup.

    System has been configured to turn on a dedicated distribution pump to the hot water tank coil whenever the hot water tank thermistor calls for heat. Further, a hot water call will priority override any of other in floor heat or air handler distribution pumps until the hot water tank call is satisfied.

    And yes, Chris J is correct - a water to water heat pump with properly configured buffer tank and distribution pump system is the front end for a hydronic hot water heater.


    Last edited: Feb 11, 2020
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Waterfurnace has a small 1.5 ton and 2 ton water-water which can be ordered with a double walled and vented coax heat exchanger, so it is permissible for domestic hot water. We use it to make 100% of the domestic hot water via the geo system. It has become defacto the standard for us.

    Attached Files:

  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You are running your tank for your radiant hot water at 130F permanently to pull heat from it via an internal heating coil whenever the DHW tank calls for heat?
  6. wing

    wing Member

    That’s an interesting question.

    I don’t believe I will be able to get the water tank temperature to 130 degrees using load water from the heat pump - the water is just not hot enough. System is set up now to start up the heat pump when the temperature in the buffer tank reaches 95 degrees and shut down at 115.

    So my plan is for the water tank geo thermostat to shut down the DHW circulation pump at 100 degrees and let the 4500 watt electrical heating element in the hot water heater take over heating from 100 degrees to 120 degrees. More properly this will be a ‘geo assisted water heater’. I will miss out on the benefits of my geo system for these last twenty degrees of heat.

    Treated well water coming into the tank will be at 50 degrees.

    Is there a better way using only a single 5 ton water to water heat pump that is also distributing hot water to in floor slabs and air handlers ?
    Last edited: Feb 18, 2020 at 7:55 AM
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You only heat the water when it drops below 95F and then only heat it up to 100F? If it is 98F it does not get heated?

    Let me ensure you that you can heat water to 130 degrees with a water-water heat pump, It only works with a very large heat exchanger inside the tank, like the Stibel Elton plus.

    Here is an example.
  8. wing

    wing Member

    Thanks for the diagram docjenser.

    An improved control strategy for my configuration would be to have the DHW aqua stat make a separate call to the water to water heat pump during the period the DHW is in in priority override mode. Then revert after the DHW call with the aqua stat connected to the buffer with limits 95 degrees on 115 off.

    What temperature could my existing DHW (Caleffi 119 gallon solarcon with 4500 watt electric backup ) and heat pump (5T single stage Terra Therm THA 060) practically heat water to ? 120 ? 130 ?

    I profess being a little nervous feeding my radiant engineered wood floors over 1 1/2 inches of gypcrete with a burst of 130 degree water following satisfaction of the priority DHW call. I do have slab sensors to minimize any impact to the wood from too high of temperatures and they are set to shut down the heat call at 77 degrees slab temp. Any comments ? I have no ability to reduce water temperature to the slab manifolds as the DHW pump and manifold pumps are on the same manifold.


    Attached Files:

  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The problem is that you run your hot water off your radiant hot water. Thus your radiant has to be at least 120F. Look at the complexity just your radiant manifold has.

    Here is an entire diagram attached, for all the heating, DHW buffer tank and cooling equipment.

    Runs the radiant floors at 90 max, and the DHW at 125F. Do you have the 119 gal tank with the lower and upper coils in the tank, or the model with just the lower? You need both coils to transfer the heat from a 5 ton into the tank for DHW.

    Don't know your Thera Therm, Waterfurnace locks out at 138F leaving load temp, but we never run them higher than 130F. Their high temp model goes up to 145F, we use it for baseboard heat, and large amount of DHW, like big apartment buildings.

    You have a huge amount of complexity in your system, and it does not do what you need it to do, namely simply to heat you radiant to 90F and your hot water to 120F, simply by a single 5 ton heat pump.

    I don't have a slab sensor in my floor, I have an outdoor reset, so it increases the water temp by a few degrees when it gets a bit colder outside. And I don't have engineered wood, I have real wood, which is totally happy with an 84F surface temp on the coldest days of the year.

    Keep it simple. Geo systems need to be lean in order to be mean!

    Attached Files:

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