Factory / Engineer level question

Discussion in 'Geothermal Loops' started by HVAC Technician, Aug 30, 2011.

  1. If we are desuperheating our water, wouldn't it make sense to design a system that at least in cooling mode would just recirculate water to a 100 gallon water preheat tank?

    Seems to me that one, you could heat up some hot water fast, say 15 - 40 minutes WITHOUT using city or well water. (I see some economies here because you would start off NOT using additional water).

    Adding what I will call main water coil cooling would just be a matter of adding an additional valve or two. Having two heat exchange coils in one unit open up some interesting possibilities, but they would have to be properly designed in from the factory.:rolleyes:
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    I ain't no engineer and got fired from the factory, but....
    What you are describing if I am reading your post correctly is done all the time. It is called a desupraheater with buffer tank. The other option is a dedicated water to water unit for domestic water.
  3. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I get it, vs DSH you want to replace brine in primary heat ex, with DHW.

    My concerns:
    As your heat exchange water, became warmer (for DHW) you would begin to tank (pun intended) EER.
    You would also be adding valves (things to fail) for a modest benefit if a DSH is already available.
    Therefore (IMHO) I could see benefit perhaps when heating a pool (lower set point, higher volume with higher bill to justify extra heat pump cost) but not 50 gals of water.
  4. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    As per Ami, the heat pumps aren't the biggest fans of the temperature swings they would see for EWT.

    Also, seperating brine/potable fluids would likely need an additional pump.I've seen hybrid units used in this manner though. Just dedicated for hot water, not radiant.
  5. clarification

    Suggesting ideas helps me to think things through.

    Desuperheating as we currently do it is sort of a fixed system. Main water flow is "calibrated". Separate desuperheater turns on and off some way.

    It takes a fair amount of time to heat that residential water up.

    What I posed is why not ONLY remove heat during AC mode through the desuperheater coil for the first 15 - 30 minutes of run time. In theory at least we would not have to pay open loop pumping cost.

    (I am not familiar with all the different brands out there and how they differ in purpose and function)

    While I believe that geo has a 'bright' future, I do not feel that we are remotely close to exploiting it to the max.

    I work with 500 + tons of refrigeration cooling everyday and it is like pulling hen's teeth to get engineers and 'bean counters' to understand that we are wasting expensive free 90 + degree heat that I have a lot of on my site 365 days a year.
  6. ChrisJ

    ChrisJ Active Member Forum Leader

    Just a homeowner with a Hydro-temp (Almost scared to say that) HP that does just what you are saying (I think). When stat calls for cooling, instead of the closed loop pump turning on, my DHW pump starts( B & G 1/6 HP) topping off my DHW temp to 120* before switching over to loop pump.

  7. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    I get it now. Yes the wasting of that energy with no recovery is a crime. Even if you plumbed the 90+ degree water into another vessel and did only indirect feeding of the domestic supply you would reduce the ewt that the domestic supply will save. I have worked on a bunch of projects like this over the years on a residential scale, trying to get as close to net zero as possible. Never applying it to a commercial cooling tower scenario. On that scale the usage should match the output/savings possible.
  8. If so, that is cool. You should be getting good efficiencies. There is very little energy loss in closed loop systems in general because your pump size is small; therefore pumping costs are minimal.

    The losses in open loop systems have to include (that much larger well pump) and that cuts into overall efficiency because your cost in those systems is compressor + time on of the well pump.
  9. clarification

    I am not thinking about "brine". When I think about 'brine' I think about (absorption systems). That is a whole separate story.

    Just for the sake of discussion, I would assume (per my original discussion) that we would switch in or add additional or primary cooling (often from wells) to kick in at @ 112 degrees. These days that could be designed into a computer board with two or three sensors giving a digital 8 -10 volt DC input to an electronic valve or for that matter a 24 volt AC valve. (I don't care if it is direct 24 volts AC or digital).

    Remember that all this stuff is getting cheaper. That application could be as little as one three way electrical or electronic valve.

    You could also specify a spring loaded "fail safe valve" to make sure we do not overheat or damage our compressor when something malfunctions.

    I personally work with a lot of digital valves these days. Many brands like belimo (german made) are quite solid and dependable.
  10. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    By "brine" I was referring to water and antifreeze mix in a closed loop system, but my posistion would remain the same.
    You picture a 3 way valve that's dependable, fine. That still does not address the reduced efficiency as the water in your DHW tank heats up.
  11. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    Wait, you are desuperheating the refrigerant.

    You are taking away from the magic of changing states in the refrigerant cycle.

    Some times it could be considered free, other times you are robing yourself of the main goal: heating your space.

    I tend not to be concerned with DHW production as I include it in my heat loss calcs.



    It has been busy here.
    Last edited: Oct 29, 2011
  12. GeoHeatNZ

    GeoHeatNZ New Member

    Hi there , what you would need is a second heat exchanger in series (refrigeration) with the one connected to ground source , so when in cooling and dhw not up to temp ground loop pump switches off and dhw pump comes on . Water in tank gets to temp then ground loop pump takes over.

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