I purchased a house 8 years ago that has an open loop geothermal.  It shares a common well for domestic water use and the GSHP.  The well has plenty of flow and the water is discharged to a river.  I know this is not the best system, but is is what I have and the payback to covert to closed loop does not make sense.  My well pump is currently failing (it can't make 40 psi) so I need to replace it.  I noticed several years ago that my well pump uses just about as much energy as the GSHP so it really cuts into my efficiency.  From what I've read, the GSHP does not require high pressure, but flow.  In other words any pressure coming out of the GSHP is just wasted energy.  Of course you need the pressure for the domestic water.  So I'm thinking of sizing the new pump to provide my water flow needs at low pressure (maybe 15 psi) and then adding a boster pump for the domestic water.
So I guess my questions are:
1.  Will this work?
2.  How do I size the pump since most pumps are made to deliver higher PSI?
3.  Would I be better off investing in variable speed or 3 phase and converter to save energy?
4. Who makes the most efficient pumps?

Here is what I know about my well:

5" casing, the well is drilled 235' deep, water level (while pumping) is 66' below ground
current pump sitts 120' deep

1) yes
2) based on manufactures curves using15 psi from ~66ft + the total GPM you need for all uses
3) good question

Your best money spent is finding out what the tonnage of your system is and converting that to gpm based on 3 gpm per ton. Then determine what your domestic water needs are based in gpm. Add those two numbers together and you get the gpm of pump you need. Then determine the horsepower you will need based on a pumping water level of 100' to be safe and allow for fluctuation. Purchase a variable speed pump that fits this design and install.

The easy way out is to replace pump with what is in the well now, but you will not address the power consumption issue. Depending on the well guys experience at time of initial install the pump could be oversized, which was common early on.

Might I suggest a franklin electric quick pak model 35-280 which will deliver 35 gpm at 280 feet of head, assuming your gpm's do not add up to more than 35.
Hope this helps
Eric Sackett
weberwelldrilling.com

Without a check valve, regulator and two stage (say 15 psi and 60 psi) control, a variable speed pump will not address the energy waste in pressuring all of your water to 60 psi.  And you will still have the issue of the pump usually operating outside of its efficient range.

It would be interesting to look at sizing the submersible pump closer to the common case (heat pump only) and let the gpm delivered to the heat pump fall a little below the optimal gpm for the short  periods when domestic water (via the  booster pump)  is being used.    For example:


heat pump - ideally needs 12 gpm, 8 gpm is ok for short periods
domestic - 10 gpm

size pump for 15 psi  + 30 psi (head) = 45 psi at (10+8) = 18 gpm.

Heat pump requiring 12 gpm will lock out quickly at 8 gpm. 
Is it better to have to reset the heat pump after everyone showers and flushes in the morning than to have a few extra psi available? Of course the auxiliary coil will run until you reset the geo, that's sounds like an energy saver......
Sounds like excellent advice.
j

A heat pump requiring 8 gpm and running more optimally at 12 gpm will not cut out at 8 gpm.

I would love to see the data on just how much energy we are going to waste making 60 psi, verses running to seperate pumping operations for two applications. A quick refresher tells us that a variable speed only consumes the energy neccassary to meet demand. So if you do not need it, your not spending making it. Also if full pressure bothers you the install of a simple pressure reducing valve enroute to your gshp will allow you to make it any pressure you want. At some point this exercise becomes a model for waste by not observing the K.I.S.S. principle. You will only succeed in building a system that is overly complicated and a PITA to work on and service.

I agree, two pumps does sound complicated, but the pump runs a lot more for the GSHP than for domestic use so if there is a decent amount of savings by lowering the pressure it would be worth it.

As far as pump motor efficiency, in the research I've done on the net and talking with motor people, there seems to be a consensus that permanent magnet motors and 3 phase motors are the most efficient.  So I'm looking at:
Grundfos SQ  series    or   Franklin 3 phase pump with 75 controller box
Anybody have and idea which is better?
Thanks,

Added note here an open loop Geo requires 1 1/2 to 2 GPM per ton depending on water temperature  < 50 degrees is 2 GPM above 50 is 1/12 GPM if you are going to size a pump it would behoove you to know the size of the GEO.

Just my 2 cents

It has been my experiance that both of the pumps you have referanced will provide the variable economy to supply both your gshp and your domestic needs. In my kneck of the woods the grundfos product proved to be much more finnicky when it came to rural electric applications, specificaly power fluctuations and brown outs killed the control boxes and the and electronic package in the pump itself. The franklin product is a much more durable and robust product with direct support via the franklin network/hotline to not have problems with your system. If you have a steady reliable power source all the time I.E. near town I have had good results with the grundfos.

My water temp is 51 and I have a 4 ton unit.

With a booster, the submersible pump only needs to push against ~45psi. Without it, ~90 psi. That takes about twice the energy, no matter what type of pump you use. At perhaps 4000 hours/year, that is worth saving. Over pressurization isn't free.

The  submersible can certainly be a variable speed pump designed for and set to 15 psi (at the surface).

Might get away with 2-2.5 GPM per ton. Go too low and there is a risk of freezing, which could be expensive if low temp lockout doesn't catch it.

I somewhat agree with jonr that reducing load and pressure on the deep pump is worthwhile. Requiring a well pump to supply open loop geo might multiply its daily flow by 10 to 50, a huge increase. Any steps taken to reduce workload on that pump should be beneficial, so having it supply just 10-15 psig to geo and then boosting the pressure more for domestic use isn't an altogether bad idea. A small cheap Flotec pump could do the boosting since it should only run for a few minutes per day if connected to a decent sized tank.

I also question the need for a full 60 psig for domestic water. I use 30-40 at my well pump, and top floor shower is 20 feet above pump, which equates to another 8 psi loss, yet our showers and fixtures on that level flow fine.

Pressure and flow are very subjective. what is acceptible to you, is sub-par to others. I think that a water system that delivers 60psi to the end user is just o.k. 30 to 40 psi is totally unacceptable to me.
A booster pump coupled with the storage tank to reduce energy consumption is wastefull on two levels. We are running and purchasing another totally seperate mechanical system, and we are giving up heated square footage for this tank. I would love for someone to put a time recorder on their well pump with an average family of four and see how much energy we are really talking about. Also the water has to pumped into the tank so do not forget to add that cost to the cost of running the booster. Also add the cost of the controls to keep the storage tank full to a useable level. Just a few thoughts.

All good points.

By your question of well pump run time I infer your point to be that well pumps run very sparingly to supply domestic water, and I agree with that - Average well pump probably runs less than an hour per day for in house use.

Jonr's point that pressurizing 1000+ gallons of water per day to 60 psig for use by a geo system that requires a mere 5 psid is well taken - that represents a significant power usage, compounded by the relatively low efficiency of small pumps and the risk of prematurely killing a pump residing deep underground.

The points you make about extra complexity and space required are all good, but actions taken to lengthen the life of and greatly reduce the power used by an expensive pump that lives hundreds of feet underground may be justified.

These are just a few of my thoughts and I willingly admit to very limited experience with deep well pumps and the complexity of a dual pressure system - I'm fortunate to have a flowing well able to meet my geo systems needs without pumping, indeed I substantially restrict the outlet to keep flow down to reasonable levels and discharge temp up to a comfy 90 for the pool it feeds. My $200 1/2 hp shallow well pump boosts enough of the artesian water to 30-40 to keep 3 houses well-supplied. I did once drop pressure to 25 and one tenant complained, so I know the lower limit for my system.

I will stick by my contention that 30 psig should suffice for most domestic use; need for 60 suggests a search for scaled lines or fittings might be in order - consider de-restricting showerheads if shower vigor drives the 60 psig setpoint - just my opinion.