Open loop water flow into a pond

Discussion in 'Open Loop' started by ryoung9, Sep 14, 2011.

  1. ryoung9

    ryoung9 New Member

    Hello, new to GEO but I've been doing a lot of reading and have reviewed all of the relevant threads/posts here on this subject but still haven't come to a solid conclusion, so I'm hoping someone can give me a good sanity check here.

    I'm in the conceptual design stages for a new business where the use of renewable energy will be a main part of the attraction. Here is the basic concept:

    6000 sf of mostly open space on two levels with lots of south-facing windows to take in the rolling Iowa countryside. I would like to put in a pond as well to further enhance the scenery, but some of the initial analyses I've had done indicate that the watershed feeding the target area would only support a pond with a half acre to one acre surface area. I was hoping to have something more along the lines of an acre and a half to two acres total surface. Thus the consideration for an open loop geothermal system, to provide the extra water supply to support a larger pond.

    At this point, I'm not overly concerned about power consumption (I'm planning a combo wind/solar installation to support everything), water supply, or water quality. Those are issues I can deal with later after I've passed the proof of concept stage.

    Assuming good insulation (R30-50), with all the windows, based on what I've read I would be looking at a total of somewhere between 5 and 10 ton geo to heat and cool the entire place all year round. Assuming 2gpm per ton (a little on the high end?), I'm looking at an open loop system producing 10-20gpm or roughly 15-30,000 gallons per day, which again based on my research thus far is way more than would ever leak or evaporate out of a 2-acre pond. Based on what I've read, a two-acre pond could have something like 1/8 inch or 7000gpd seepage/evaporation loss (I'm also thinking of drilling a return well to divert any excess water back into the aquifer/water table).

    However, the actual amount of water coming out each day would depend on how hot or cold it was, i.e. how much the system was actually running, right? So that is my question. What should I expect in terms of ACTUAL water production per day throughout the year, particularly in the spring and fall when the system wouldn't be running as much? On the lowest days, would I still be able to generate enough to keep my pond full? Would a qualified, experienced contractor be able to figure all this out or would there just be too much guess work involved to come up with a reliable, self-sustaining system?

    If this is too complex, then I could always go with the smaller pond and with a closed loop system in it, but I'd really like to make the bigger pond work.

  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Where are you?

    Expected equipment run times for regions can be just looked up in charts. Actual run times can be predicted in a design phase.

    But, overlapping two complex systems like pond maintenance and building HVAC could result in conflicts. I have a technical background in natural water systems (of all things) and manmade ceases to exist when it starts supporting natural wildlife. You'll need to try to decouple the demands from each other or build in some redundancy.

    Lots of complexity that could be estimated with some basic calcs for a go/no-go decision.
  3. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I'd say that less than 1 in 100 HVAC contractors know geo. Chances of finding a good geo outfit also with intimate knowledge of pond sizing dynamics would seem to be vanishingly small.

    If you are planning to meet all electrical loads with an RE (renewable energy) system the you had best be INTIMATELY rather than "not overly" concerned about power consumption since RE systems have very high capital costs per unit of power needed.

    If your understanding of likely load is really within the broad range contained by "5-10" tons, the you are truly in the very very early design phase of this project.

    With geo and even more so with RE, one quickly learns that steps taken to reduce load are far cheaper, up to a pint, than gratuitously enlarging the geo / re system so as to meet a perceived load.

    Hours of daily operation are highly dependent on occupant behavior - stat setpoints and willingness to open windows in mild weather figure heavily into installed system performance.
  4. ryoung9

    ryoung9 New Member

    Thank you both

    Yes, I am really only in the feasibility phase of this and am reluctant to waste an engineer's time until I am able to determine whether it's so crazy it might just work :)

    I'm not sure I follow when urthbouy says decouple the demand - I think what you're saying is don't make the success of the pond dependent on the geo system, right?

    I might just take this to the local engineering college and see if this is a problem they'd be interested in tackling.

  5. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    "Would a qualified, experienced contractor be able to figure all this out or would there just be too much guess work involved to come up with a reliable, self-sustaining system?"

    We can predict annual water discharge based on 20 year weather data, but we can't predict the weather (any better than a meteorologist) or day to day usage.

    Much of your post is at odds with itself. Generally where renewable energy is a "main attraction" it is accompanied by conservation. Expending energy to create a pond that is not self sustaining would seem to be in conflict with that.

    If you wish however to have the pond regardless of cost, you need simply to run a hose to the geo drain on those days that your heat pump is not running.
  6. ryoung9

    ryoung9 New Member

    Yes, conservation too

    Oh, I'm definitely not trying to oversize the system just for the sake of it. Conservation is also a big part of what this project is all about. We're hoping to use this as a way of demonstrating and educating our "users" not only on energy conservation but conservation of other natural resources including land and water as well. We are going to do a pond (assuming all else works out) and we are going to do geothermal, I just want to see if we can use one to enhance the other.

    Now, I know there will be critics who might say "pump and dump" is actually ANTI-conservation, which is why we are also considering a return well for any excess water generated by the geo system IF we do go open-loop. I also know there will be those who will say "it's not nice to fool (with) mother nature" by attempting to tie these systems together, but I am not claiming to be a conservation "purist" or "extremist" by any means. In the end there will be many tradeoffs in terms of how and how much energy and other resources are used. The ultimate goal, regardless of what we end up actually implementing, is to use this as an opportunity to demonstrate and educate people on these issues and tradeoffs as much as possible.

    We also know that everything we're looking at will require a significant amount of up-front capital investment and a significant amount of faith in a business model that will enable us to successfully recover that investment over time. This is just a much larger-scale version of the conversation on NPR this morning over the transition to CFL and LED lighting, in terms of the leap of faith required to spend $30 on a single light bulb.

    I appreciate a robust discussion as much as the next guy and greatly appreciate the range of perspectives available here, but I don't want to take this thread too far off topic. I think I've got my basic answer here, which is that there is a lot more fine-grained work to be done in order to determine when and how much additional runoff will be generated by an open-loop system.

    Thanks, all.
  7. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I do not build....

    ...ponds but I know how to use them. For geothermal and fishing. The former I know the later I am learning.

    How do you fill farm ponds in your area? We fill them with rain water in Ohio, and/or get lucky and hit a spring.

    If one had a pond for a heat sink why deplete aquifers? Just build the pond to the size you can. Deep is better than broad with closed geo pond loops.

  8. ryoung9

    ryoung9 New Member

    Same here

    That's pretty much how ponds get filled around here, too, from what I can tell. The rule of thumb is one acre of surface area to every 10-20 acres of watershed feeding the target spot. I have 8-10 acres of watershed, so I'm looking at a pond .5 to 1.0 acres in size with just runoff. Not likely to hit a spring. The other rule of thumb is that you need at least an acre to support a reasonable fish population, so I'd like to make sure we can at least hit that and possibly go a little over.

    I've seen all the debates here about whether open loop is really more efficient, both in terms of energy consumption as well as heating/cooling efficiency, and from what I can tell they're getting closer but open loop still has the overall edge. Then again, there's more maintenance with open loop. I'll probably end up making the decision based on what my pond experts estimate for "natural" size.

    Thanks for the input.

  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    Some one told me many years ago that one does not learn by talking. It took me about 20 years to get what she meant.

    I am old enough and have enough experience to tell you what I think, especially at the price you pay for my rant.

    I do not think you have seen all there is to know about ponds, either open or closed loops as they apply to geo-exchange HVAC. You have not seen the work I do since it is not published therefore I think your conclusion is not without fault.

    I, how ever do not know what you know, so I will grant you your professed knowledge.

    Build your pond to fish.

    Do not build your pond for geo-exchange if you are going to mix aquifers. Dig it deep enough for your geo-exchange wan ta bees to happen, that will grow fish. Then install a closed loop geo system and take what the pond will give you. The entire Earth is a geo-heat sink. We do not need IA to take drinking water VA needs.


  10. ryoung9

    ryoung9 New Member

    Thanks, Mark

    Yeah, the more I think about it, the more inclined I am to go with the closed loop and just make sure the pond is deep enough to support a good fish population and good thermal exchange. If the pond were dependent on the geo system, it could end up being not much of a pond if the geo system should ever cease to operate or exist someday (change in water supply/quality, new regulations on open loop, new technology, etc.).


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