An "Open" Argument

Discussion in 'General Discussions' started by Blake Clark, Oct 14, 2011.

  1. Blake Clark

    Blake Clark Member

    I'm feeling bold, so I'll make the following argument: There is no reason why an optimized open loop system cannot equal or better the pumping energy of a closed loop system. (Or at least come extremely close) A case in point is my own system with a static water level at 100 feet. I am pumping 7 GPM in a standing column configuration using 1.5 amps. Have at it closed loop advocates - I'll take on all comers;)

    My purpose for starting this thread is to challenge the notion that open loop systems are shackled by high pumping energy. There are many other arguments against open loops, water quality, permitting, etc and I'm not saying by any stretch that open loops are superior to closed loops - both have their place.
    Last edited: Oct 14, 2011
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    But in the end, you need all the proper controls and the costs start being equivalent to closed loop.
  3. Blake Clark

    Blake Clark Member

    Good strategy - agree, then shift the argument :) I might let others weigh in on costs, and I'll concede that a horizontal loop installed in an open field is probably cost competitive with a VFD drive, submersible pump, valves, transducers, etc. I'll argue, though, that many people installing open loops don't have that option, and 300 foot boreholes in granite are not cheap. And when comparing apples to apples, I'm convinced that the energy savings from an "optimized" vs "standard" open loop system will more than pay for itself.
    Last edited: Oct 14, 2011
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    In addition, the water temp is very constant through out the year. In my area loops are designed to go down to 30 degrees. Open loops are at 54 F. Increases HP efficiency by 15-20%!
  5. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    yak, yak, yak.....

    No two apples are ever alike. You Blake have demonstrated that you are not the average person with your solution to optimising the pump controls. To Doc I say check out the graph on my website to really understand how the temp swing in a closed loop equals the constant temp of the open loop.
    In the end there are no blanket answers or best cases for everyone. The heat exchanger chosen is purely based on economics for the spot on the rock where the project is to be executed.
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Maybe you could direct me directly to your graph, since the only one I could find does not display any loop data.

    We monitor our loop temps as well, and we go up to 63-64 degrees EWT in cooling mode. When the units go in reverse start we start the heating season with an EWT of around 55F and drop down to 30 degrees EWT at the end of the heating season. The average EWT for the whole season is between 35F and 36F.

    Web Energy Logger:
    Temperature and Energy logging by: Web Energy Logger

    Our open systems are 54F(+/- 1 degree).

    Temperature and Energy logging by: Web Energy Logger

    The 18 degrees average difference in EWT result in about 15% higher efficiency at the heatpump.

    May be you could enlighten me what I really need to :cool:understand....!
  7. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Sorry the chart is MIA, I hate IT crap!
    Meanwhile back at the discussion, the temps the loop field experiances is a function of the design parameters, not the loop. I can design a loop field to see 0 gain or drop. That has a direct relationship to rhe economics of the cost of construction.

    Your loop fields could use a little "bulking up" to experiance better performance. Are using design software to size your fields? If you monkey around with it you will see better performance. Our loop fields typically run highs of 75 and lows of 45.
  8. What is your water source?

    Conservation might be an issue.
  9. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

  10. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    I love a good yak. Got bbq sauce?
  11. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Let me remind you that the entire purpose in the loopfield design is to get the EWT within the operating range of the heatpump, which is at 30 degrees for heating.

    In order to give customers the best value for the money, you have to get the best balance point between larger loops with higher efficiency, and higher upfront installment costs for larger loops. IGSHPA and other literature recommends also 30 degrees F for that reason. So if I have a loop which a drops down to 30 degrees F at the end of the heating season, I know I have a perfectly designed loop, with a nie compromise between upfront cost and

    Now, after you had questioned whether we use loop software for our designs, lets take some loop software and run some scenarios. Lets take a 50000 BTU/H house in Boston, MA (which should be around you somewhere) lets take Climatemaster loop software, combine it with a 3 ton W-A Tranq 27, and it shows that at a 1.44 soil conductivity you need about 335 ft of trench of 18 inch pitch slinky buried at 6 ft to allow your loop to never drop below 30 degrees.
    If you want to reach a minimum of 35 F EWT, the design software indicates 600 ft of trench, which is almost double the loopfield size, but saving you only $40 annually.
    To achieve a min EWT of 41F (less then you claim to have) you would need about 2260 ft of slinky trench, essentially over 20 tons of loopfield capacity. It would save you about $72 in operating costs annually versus the regular sized one. However, in heating dominated climate like yours, max cooling season temp would not be higher than 58 degrees F, much lower than the 75F you claim.

    So your numbers you claim to have are ways off. A loopfield in your part of the country would need to be about 7 times larger (at about 7 times the upfront cost) in order to have min EWT of 41 F. Please do your homework next time when you suggest that we should make ours larger in order to experience better performance, when in fact we monitor our systems closely online and demonstrate that we are right on target with our design.
  12. Blake Clark

    Blake Clark Member

    I see folks have taken "open argument" literally. No one wants to discuss how to optimize open loop pumps :confused: Maybe if I titled the thread, "How to optimize open loop pumps":eek:
  13. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Certainly I did not want to hijack your thread.

    My argument was that the reason we do geothermal is that the season temps wing is less than the ambient air temperature, thus the higher efficiencies versus air sourced heatpumps in climates which have more temperature extremes.

    Open loops have almost no seasonal swing, thus an increased efficiency on the heatpump level due to higher average EWT.

    We have used open system in larger application with multiple heatpumps and variable speed well pumps, where the savings in upfront costs were significant (2 wells versus 20 for closed loop).

    We were dealing with a minimum pressure of 20 psi the well pumps needed to operate, which was costing us energy. But we too using discharge wells which help on the suction side if you discharge to water below the water level.
  14. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Sorry I got you rialed up, I assumed we were talking about vertical, you assumed we were talking about horizontal. The design is the heart of the loops performance and I am not an advocate of designing for 30 degree temps in heating nor 90's for cooling.

    In my world horizontal is for diy, or contaminated sites only. If we are going to drill mud rotary in uncosolidated formations, I can drill vertical faster and cheaper than you can excavate and lay pipe, but I digress. It is allways about the design and you and I will have to agree to dis agree on that

  15. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader


    The optimiseing of an open loop pump is governed by the things you have allready identified. Head pressure and volume, waste either one of those and the efficiency suffers. By far abd away the most ideal set up is to have a stand alone pump for geo only, lowhead and minimum flow requiredto do the job. The problems come when the pump must also serve another use point. Dual purpose means everything is and will be a comprimise to meet both demands.

    Maybe "engineer" will talk to you about his system that runs off a free flowing artesian well.
  16. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I'd like to change your last statement from "both have their place" to "all have their place".You won't get a permit for an SCW or an injection well in some states, so open loop becomes "pump and dump". Depending on where you are dumping the pump costs may be higher than on your SCW.With the exception of WP's AO, vertical loops are the most expensive and therefore our last resort.Once we buy solenoids, flow gauges, sediment filters etc. for open loop units, horizontal closed loop is seldom more than a thousand or two (less tax credit) higher to install. Op costs are similar. Closed loop wins the maintenence battle in my AO making it a no brainer (providing lot size permits horizontal install).
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Lets try this exercise with vertical loops. Same parameters, CM loop software tells you that you need 505 ft borehole for 30F min EWT (max of 71 in cooling mode). In order to get EWT up to 45F, you would need 1955 ft of borehole, almost 4 times as much. Then the max cooling mode EWT would be 51F. Annual operating savings would $91. Increased costs of installing another 1450ft of borehole? You tell me. In my neck of the woods you are looking at least at $22,000.

    Again, sorry for being off subject, but was trying to support the argument that open loops can run more efficient than closed ones.

    Then I was told that need to really understand how the temp swings in closed versus open loops, and that the nicely performing loopfields could use some bulking up for better performance.

    I simply dislike it when someone makes such unqualified statements, and uses numbers which do not add up.
  18. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    I will repeat this one more time and please try to remove emotions. It is all about the design AND the cost to install the exchanger. Your costs like most places on the planet, the cost to drill vertical are horrendous. When I drill it is not.

    It is hard to take your data or mine at face value as the actual site conditions are different, ie conductivity.

    There is a right choice for every situation and broad generalisations of any claim should be avoided.

    To say that any form of exchange can be more efficient than another is fair enough on any given day.

    To lighten up your tone a bit, I have been in a twelve step program for more than 2 years now. Every once in a while I like to treat myself. Although CM is one of the most popular units being installed, When it comes to software, education, and the IQ of their East Coast senior management they truly are a Climate Disaster.:D
  19. Blake Clark

    Blake Clark Member

    I ran into this a lot when looking at open loop designs - 20 psi seemed like a very common pressure point. Is this the lowest that the pump can operate, as you state, or the lowest pressure that the controls are designed to operate? I'm not sure I understand pumps as well as I think I do if there is a minimum pressure at which they can operate. If 20 psi is control related, I can give you a $1.99 solution that will shift the scale of any 4-20 mA control loop to whatever pressure you want it to be. I'd like to be able to give some of these tricks away - they're not doing any good in my head!
  20. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    We depended on our supplier who told us that the variable speed pumps we are using for our multi heatpump installation need a minimum of PSI on 20. The pump, not the controller. If we drop below that the pumps start to rev up and down the pressure pretty rapidly.
    Last edited: Oct 18, 2011

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