Combo desuperheater?solar hot water

Discussion in 'Geothermal Heat Pump Applications' started by Corey, Jul 26, 2011.

  1. Corey

    Corey New Member

    I built a solar hotwater heater prior to putting geo-thermal. Basically I have a 300 gallon tank of 110 degree solar heated hot water in my basement. The water to be preheated come in from my well, goes through 300 feet of PEX in the tank,gets preheated and goes to my water heater. Works great when the sun is out. Not so great with cloudy winter days. What i want to do is use the desuperheater in my Waterfurnace Envision to heat the water in the tank. I understand it will only warm the tank water 40 or 50 degrees and will overlimit at the temps the solar heater can generate, but shold do great when cloudy days prevent warm up. To check things out I hooked up the inlet/outlet lines on the desuperheater to a cold bucket of water, flushed the system, turned on the desuperheater,but no circulation of water with the geo unit on. I can see the pump in the geo unit that is supposed to circulate water, but no go. The best I can get from Water furnace is that the line going into the desuperheater has to be pressurized. I got the feeling they really didn't want to talk to me about this crazy application. They said " about 5 lbs of pressure ought to do it".I can put a circulator in line with a pressure switch, no big deal. I guess I don't understand the mechanics of this system. If there is a pump in line, why does the inlet water have to come from a pressurized source/ What is the purpose of the pump that is in the system? How does the system work? When the desuperheater is on, does it check the inlet water temp for a few minutes and heat it if it is below a certain temp while shutting down if it is above the high cut off temp? If so, does it periodically recheck the water temp and decide if it needs to be heated? I think it would be a great complimantary system and it drives me crazy to have these 2 units 10 feet apart and not be able to connec them. Any ideas?
  2. geome

    geome Member Forum Leader

    Has air been purged from the DSH lines?
  3. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I don't understand the pressure situ either.
    This configuration should work ok, but may offer more contribution with yet another buffer tank if you have room.
  4. Corey

    Corey New Member

    I purged the system by flushing it with a hose connection right from the home water source and ran it till I didnt see bubbles
  5. Altnrgy

    Altnrgy Member

    Water Furnace is correct. Fractional HP wet rotor circulating pumps, like the 1/25th common to DSH’s, need a few PSI to operate properly which equates to somewhere between 3'-8' of water above the pump in a non-pressurized system. Without that they will cavitateand loose prime. I've hooked up many atmospheric solar water heating systems and wood fired boilers thus have become very familiar with this aggravating phenomenon.

    Be warned, as the water heats up you need more pressure then you did when it was colder. Grundfos actually details this in the literature that comes with the pump. I've got one system that lost prime every time the fluid got above 160F. Drove me crazy until I moved the pump to lowest possible place in the system this getting a few more feet of water on top of the pump and it workfine now.

    For your testing put the 5 gallon bucket of water at least 5’-8’ above your pump, purge the lines like you’ve been doing then see what happens.

    You'll get this whipped!

    Cheers, T

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