Hybrid Open Loop with Large Storage Tank

[abh3]

I'm installing a 4 ton GSHP split system and had planned on an open loop. When I replaced my deep well pump the well guy said variable speed pumps are trouble and constant-flow/cycle-stopper valves are energy hogs, just pump and dump. I realize that my well system volumes and pressures aren't efficient for GSHPs and the cycling will shorten pump life. An enormous pressure tank may work to reduce cycling but is cost prohibitive, they all seem to be bladder tanks I've had nothing but trouble with over the years and only hold a fraction of what their size and cost might suggest. I have several large ponds on the property (3-10 acres) but the nearest is 500' horizontally and probably 25 feet vertically from the HP, I'm told pond loops or raw water open loop is out of the question.

What I had in mind was a large buried tank, 3-4k gal. minimum, with a pump providing around 10 gpm at low pressure to the HP. To fill the tank would be a float switch on a timed relay controlling the solenoid valve, the well would then start and run continuously until the tank was almost full. With a little thought it might be arranged that the tank would 'top up' when there is little other water demand. Used large tanks seem to be easy to come by in the area, I've got an excavator for installation and the well is capable of continuous operation. There might even be the possibility of capturing rain water from the gutter system and directing it into this tank though screening and filtration issues may be the downfall of that idea.

Could this be a viable setup or should I just give up and plumb 60psi water to the HP and let the well cycle itself to eventual death?

Thanks for listening to the delusional thoughts of a newbie.

[down2earth geothermal]

What you are talking about violates the basic KISS principles as it's rather complicated with 2 pumps, large buried tank etc.

What is your depth to static water in the well and also the sustained drawdown while pumping 10 gpm? Have you looked at the water quality to make sure it meets manufacturer specifications for open loop?

Variable speed pumps have come a long way and are a good solution. In some cases, you can add a variable speed control box to an existing pump such as Franklin's 3-wire: Franklin Monodrive Variable Speed Constant Pressure Controller

-Adam

[waterpirate]

I agree with Adam on the kiss principle. With that much water on the property I would have looked at another source for the pump. A shallow well adjacent to the pond would have provided pond water filtered by the local material but really supplied by the pond. I am asssuming banks and shores of overburden not rock. Shallow well+small pump dedicated for the geo at low pressure would have solved this puzzle. Was a closed pond loop looked at? Where are you going to dump the water in your current plan?
Eric

[abh3]

The first pump would be the existing 2 year old 2hp deep well pump that also serves six buildings of one kind or another and six RV spots, I need the flow/psi on my large system and hate the idea of changing out a pump that new. The second pump would be a low volume/pressure pump, probably Grundfos. I realize the complexity could be an issue but I've read a lot about the inefficient mismatch of open loop with residential water systems, I'm just trying to make something work without drilling another well just to get 10gpm!.

I'm not sure about the static depth of the well but drawdown isn't an issue, the well was originally for an orchard drip irrigation system designed for sustained use and was drilled until it reached a void in the Floridan Aquifer at around 350'. With all the irrigation on there were sometimes pressure issues for showers and so forth but we never ran the well low.

I have another post about the Monodrive XT, ITT has no such device (for single phase motors at least) so I hope the Franklin controller might be compatible with my pump motor. This could be the solution, I've called the well man but couldn't reach him before the weekend.

I'm told closed pond loops won't work as the nearest pond is 600' away and 25' downhill, supposedly frictional losses kill the idea. The open pond water loop might work but 600' of 1" or 1.25" pipe, a power pole to run the pump (plus $12/month service), drilling a shallow well or elaborate filtration for pumping out of the pond all adds up. Part of that doesn't meet my 'practical experience' test, the furtherest building here is 1000' from the well and has great pressure but that's what I've been told... If I could defeat reality I'd just tap into the 8" irrigation line already in place, prime it up and use raw pond water, maybe through a heat exchanger to keep it out of the coil, but the head is too much to overcome. I'm going to get the power co. to come out and take a look, if they'd provide service at the ponds with no upfront charge and $12/month for basic service, pumping pond/shallow-well water up here may be worth further consideration...

The water quality here is adequate for pump and dump according to local installers though they really like vertical/horizontal loops for huge amounts of money. I have a large excavator but I'm told that won't save any money, it's all the same price, vertical or horizontal loops, regardless of how much you can do yourself. I have my doubts about some of these guys, one outfit's approach to sizing the unit was to simply ask what ton HP I have now!

Dumping isn't an issue, lots of land and there's a disused 8" irrigation line buried within 70' of the HP that could carry the water down to the ponds...

Thanks for the help!

[waterpirate]

You sound like a prime candidate for a diy. If you can and have an excavator the horizontal loop can and will work with the correct design work done up front. I can appreciate your desire to not reinvent the well, lol! but.... Every option you have in front of you is going to cost something, and will have pro's and cons. The trick is to gather as much info in advance to commiting to any and weigh these options out. Also the amount of head loos you are going to see pushing 10gpm at a low end user psi is going to be next to nothing with a pipe as small as 1.25". Do not take anybodys word for it do your own math and see for yourself. Buy small pump,pipe, install yourself, finished.
Eric

[mac word]

If you have the pond avilable it would be much easier and less expensive to use a closed loop to the pond and back, using a high efficiency low profile lake/pond heat exchanger.

Send me your e-mail and I will forward a picture and a piping overview.

Mac

Send to mac@geosmartsupply.com

[AMI Contracting]

Pond loops might be easier but notessarily cheaper. Especially if you have to go 500' to the pond.
Variable speed well pumps are not energy hogs, quite the opposite is true.

[Mark Custis]

Once filled and purged of air the only head would be pipe friction.