Open Loop Questions

Discussion in 'Open Loop' started by o08, Nov 8, 2011.

  1. o08

    o08 New Member


    I am new to this forum. I am interested in installing an open loop system in the mountains in Southern Vermont for a new construction log cabin. The cabin will be 1300 sq. ft not including a walk out basement.

    The water to the home will be fed by a drilled well that is yet to be drilled. I've been quoted at $8.50/ft and $15/ft casing for the well, which seems fair to me. Now, I already have a home on the property whose well is located about 700 feet from where the new well will be dug. It is an artesian well that constantly overflows into a hole in the basement from which the water is dispersed into a dry well. I'm not sure the depth of this well but for the 50 plus years, we have had the home, it has never stopped overflowing.

    The cabin will be located about 80 - 100 feet from a cold water mountain stream for which I want to utilize for the "dump." The stream flows at about 100 gpm year round, slowing in dryer conditions and when it is wetter, it can be significantly higher. For the first question, will the dump from the geothermal change the water temperature of the stream such that it would affect the cold water habitat that the stream supports? Will the dump affect the composition of the stream in relation to iron level increases? Do I have to worry about freezing of the dump line in the middle of the winter? The particular spot I want to dump is into a natural pond at the base of a series of waterfalls from which I would like to utilize as a cold water bath in the winter. Would the dump make it so that this pond area never freezes? Is it logical to situate the dump to take advantage of the natural downward slope?

    Now regarding the flow rates of the new drilled well I am uncertain. However, the same driller I will hire recently drilled two wells about 2000 -3000 feet from where I am located for a proposed 150 unit condo construction at the base of a ski mountain. His wells drilled about 400 feet deep provided water at 90 gpm. I am fairly certain I will have more than enough flow. They checked the performance on our existing well during the drawdown tests and we were not affected. So I anticipate a good gpm flow rate. The rock formation in my particular are is bedrock.

    The only remaining concern within this open loop option if the flow does indeed happen to be more than 15 gpm is the hardness of the water. I have had my existing water tested and we do have minerals that flow through but otherwise, the water is very balanced and is not acidic at all. There would be a certain amount of iron in the water. Is a small amount of iron so corrosive that it would negate the upfront cost benefits of doing this open loop system for the cost of repairs later on?

    The water comes up year round at 52 degrees. As I understand it, the efficiency of this temperature is somewhat greater than that of a closed loop system where the water can get colder. Would I be able to apply the added benefit of saving on the efficiency cost towards future repairs?

    Last question. I want to utilize this mountain stream as a source of power. I have about 70 feet of head and 100 gpm. If I dump higher up in the stream, could I use the added gpm to help power the micro-hydro system or would the cost to pump the water up hill negate this increased power potential? Is it possible to harness the flow of the dump at all with a micro hydro type attachment to the end of the dump pipe? If not, for the experts and innovators of these systems, is an attachment of this sort something that is in the works? It seems that if I am discharging 7-8 gpm, there is quite a bit of energy to be harnessed from this dump and could possibly cut the electric cost of running a heat pump.

    I had a second quote from another contractor for geothermal and he insisted on closed loop with an estimated cost coming in at $40,000. It seems like paying more than $30,000 in up front costs for a closed loop system particularly concerning the ideal location for a dump site is really not worth it.

    Thank you for your time and I apologize for a lengthy first post.

  2. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    We need to talk


    It has been a while since I have been to VT.

    You want lots of answers to a lot of questions so I will give your post a go. If I miss anything let me know.

    Your description of the new home tells me you are in the 2 to 3 tons of cooling range. I do know you will be in a heating dominant setting. What to do about auxiliary heat and back up heat will need to be addressed.

    Will you kill the fish down stream? No.

    I am not sure I see why there would be increase in iron. I developed a spring in Ohio that was so acidic it ate the copper we planed on using for a heat exchange system. I have photos here on the geoexchange some place of that job.

    Freezing of the dump line depends on where it is and how cold it gets vs. GPM flow.

    The work around for "bad" water is a flat plate heat exchanger. That solution requires an additional pump. The pump and the heat exchanger are small beans compared to replacing a unit or a coaxial heat exchanger.

    To evaluate the mini-hydro stuff I need boots on the job site, but I am willing to "blue sky" with you on that issue.

    Geo is not cheap. Ask the guy for a quote on a propane system and compare the two.

    I would take you water to water and include radiant heating, boosted domestic hot water, and passive radiant cooling with dew point control and the rest of the stuff you want. I will not be the lowest bidder, but you will get what you want for this new home.


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