Geothermal Open Loop

imatellerslie

my house and am also going to have a new well drilled in the next week or so. I am considering using an open loop for the geothermal system, which will require a second well to return the water to the aquifer. It's cheaper to do it this way than with a closed loop, and I think I'll get higher efficiency this way as well, since the ground water temperature will be higher in winter and lower in summer than a closed loop would give me.

I was just wondering if any of you guys have any experience with these systems, and might be able to relate any problems you've had with open loops (clogging of the return well, heat exchanger scale or corrosion, etc.)

GMcD

Open Geothermal

Hopefully someone's done a water quality test, a percolation test, and checked any environmental permits requirements. Depends on the local hydrogeology- is the ground water deep? Flowing? Standing water table? Normally for most clean groundwater direct systems a 5 micron filter ought to be OK on the supply side. As a designer of commercial systems, we like to put in a plate type or shell and tube heat exchanger to separate the groundwater from the geothermal unit if big volumes of water are going to be used- allows for a gauranteed separation of anything that can go wrong with the groundwater, cleaning and maintenance, and future flexibility if supplemental cooling or heating was needed to insure the groundwater return temperature was within limits. The local environmental issues may dictate that the returned ground water be within certain temperature limits, worth checking. Watch the selection of your well supply pump to make sure it has enough head for the lift as well as the pressure drops of any filters and the heat pump unit, check the operating curves to see what your operating band performance is going to be.

imatellerslie

My well driller said...

that the well will likely be 350'-400', and will tap into flowing water. I've checked with both the county and state authorities, and they indicate that an open loop system is permissible. I read in the regulations that the water temperature isn't a problem unless I am putting water at 120F or greater back into the ground, which is not going to happen. Mostly, I'm concerned with problems with the water quality, which is unknown now since the well is yet to be drilled, and problems with the return well being unable to accept the water volume necessary. I think I'm going to need 10 or 15 gpm, since I'm going to have an 11 ton system.

How much does the intermediate heat exchanger affect the efficiency?

Thanks for your response Geoff

don_19

open

From my experience if you think long term a closed loop
is the only way to go.

I much rather spend the money on a closed loop distribution
and relent on the high price equipment.

For all the reason you stated above, collaspe or clogged return wells,scale, corrosion is not a issue with the coopernickal coil.

Sure you will need a low temp equipment on the close loop
and you will lose alittle efficency.But!!!
When ever you let oxygen in to a system the minerials will grow.Then they began to grow,wonder what efficency you are getting out of that equipment now.

Think of it this way,you got alittle circ driving the closed loop,that save on your electric,verse a well pump that eating your efficency up.Also you elimate ever having
to deal with collaspe or return wells.
You dont have to call your service man to come out in shock
the coil because it tripping out on safety and not getting the proper heat transfer.

Not only will you have a distributiom system that will be long term,but its more complatible to your equipment and will not abuse the equipment like a open system will do.

Open system on a geo,is like putting a non condensing boiler
on a low temp infloor system.
Wheres the Bang?

Earthfire

pump and dump

the best way to do a pump and dump is to use two pumps and alternate their operation and keeps the receiving well operating longer.The soil usually does not accept water injection as readily as it supplies it to the well If you are in loose sandy soil water acceptance in the return well is not a problem. Also the cost of operating a submersible pump for the hour that the system requires can run the power bill UP. A closed loop system with either horizontal or vertical loops is the most economical and maintenance frendly system to own & operate.

imatellerslie

Thanks for your perspective Don...

I tend to agree with you. I am just trying to get some data points to see if my concerns are valid. I had originally ruled out the open loop concept because of these concerns, but decided to reconsider when it came time to put in my new well.

imatellerslie

Can I alternate wells if...

I'm using the well for potable water? I assumed I could only pump one direction if I'm using the same well for potable and geothermal supply.

don_19

I

> I'm using the well for potable water? I assumed

> I could only pump one direction if I'm using the

> same well for potable and geothermal supply.

don_19

And

> I'm using the well for potable water? I assumed

> I could only pump one direction if I'm using the

> same well for potable and geothermal supply.

don_19

And

> I'm using the well for potable water? I assumed

> I could only pump one direction if I'm using the

> same well for potable and geothermal supply.

don_19

And

> I'm using the well for potable water? I assumed

> I could only pump one direction if I'm using the

> same well for potable and geothermal supply.

don_19

And

> I'm using the well for potable water? I assumed

> I could only pump one direction if I'm using the

> same well for potable and geothermal supply.

Earthfire

domestic water

should have its own well the demand for domestic water and heatpump water are different and trying to control the pump from two different demand points can be a nightmare.

don_19

I wish

I could give answer,but in my neck of the woods,we have to have different well for heat and domestic.

Have you look at the geothermal dx system? WWW.amgeo.com
Claims of 40%-70% on utility cost.No water issue at all to worry about.

imatellerslie

If I have to dig a separate well for geo, it's a no brainer...

to go with a closed loop instead. My understanding is that I can use the same well for both systems. I know that sizing of the pump has to be done carefully, and intended to make sure that my pressure tank is quite large, to keep the pump from cycling too much. I suppose it's also feasible to get a variable speed pump.

Earthfire

geo heatpump

what recommendations has your heatpump installer supplier made as to the ground loops? The local installer would be most familiar with what looping method would give you the best long term operational and economic efficiencies in your area.And by installer I'm not talking about the drillers that shoots a hole, drops pipe, and leaves never to be seen again, I'm talking about the guys that handle the installation and service of the inside unit and know what it takes to keep them going for the long term.

imatellerslie

I was looking at the dx system from ecr technologies...

I really like the way they control the refrigerant. Unfortunately, the only authorized installer for my area is a little far from me, and apparently busy enough that he's not too interested in my business.

imatellerslie

I haven't picked an installer yet...

I have talked to several, and had two promise me proposals, but none has crossed my desk. When I talked to these guys, I was only considering a closed loop system, so I haven't discussed the open loop with any local installers.

Earthfire

drillers

There are drillers and there are drillers. Installing a geo loop field is not rocket science, but the driller must have proper grouting equipment and the knowledge of proper grout and grout installation procedures. In my area most well drillers have not made the investment necessary to do the job correctly. I would recommend coordinating the loopwork with the equipment installer. How big is your lot?, a horizontal loop field may be a viable solution, if you have the space

don_20

We

feel your pain.I also know all to well that a closed loop system can eat up the budget real quick.

Open system if you got to go that route,and not knowing
your part of the country,I would go with the submersible pump.
But keep the coil pressurize at all times,no bleed down system they are the worse.
And go with the lowtemp equipment,it will save you some discomfort when the water quality issue start coming to a head.

imatellerslie

If I use the closed loop approach...

I'm going to use a horizontal loop. I'm not sure how much area I need for the field, but I have 4 acres, so I'm hoping it's enough.

imatellerslie

How do you

keep the coil pressurized at all times? I read that scaling is alleviated significantly by doing this, but I don't know how its accomplished. Control valve on the discharge of the heat exchanger? When the compressor starts, valve opens, well pump responds to pressure drop and runs? I guess that would actually be pretty easy.

don_20

Thats correct!

Earthfire

Area

4 acres should give you more the enough room for a horizontal system

GMcD

Intermediate heat exchanger

It's hard to quantify an efficiency number for what a heat exchanger will do since the overall system performance and long term maintenance are also issues to consider, but a good plate type heat exchanger will not have a significant efficiency impact at all. A shell and tube HEX is a little less efficient, but, again in the overall system function, minimal.

In reading some of the other responses, I agree that a separate closed loop geothermal is certainly a very good option and will insure maximum safety for your potable water and groundwater quality issues, but all that polyethylene for a closed loop can eat up budget $$. The rule of thumb I generally use for horizontal fields with a bury depth of 6-8 feet is to allow about 250 feet per ton for straight pipe, and about 65-75 feet of slinky coil per ton, again, dependent on the ground temperatures and soil conductivity. Horizontal ground coils should be separated by 6-8 feet, so you can do the math and see that 4 acres ought to be plenty of room to do a horizontal field for 11 tons. The key issue is to make sure you've done an energy balance on the geothermal system: the heating energy you suck out of the ground in winter must be replenished by the heat energy being dumped back in the ground from summer cooling. If you are using the geothermal system for a heating dominated function, the risk is that an improperly sized closed loop geothermal field will cool off over the long term and degrade performance, plus you'll end up operating the geothermal fluid at points where you'll need anti-freeze solutions and more nastiness. My own rule of thumb is to design a closed loop geothermal system for a balanced heating/cooling load and supplement the overage as needed- in a heating dominated climate, use a small boiler or other heat source to supplement the winter heat loads, and in a cooling dominated climete, use a small cooling source to supplement the cooling demand. All this is dependent on your local soil conditions, soil conductivity etc. Another trick is to use solar water panels to dump excess heat into the ground in summer time to store more heat in the ground for winter extraction, which may save the need for a supplemental boiler or heat source. If you are having a well driller there anyway, to drill potable water wells, you may as well have him drill some vertical closed loop geothermal wells on the way by, if your budget can take it. Takes up less ground area, and the rule of thumb for vertical geothermal closed loops is about 200 feet depth per ton, with wells at least 15 feet apart.

imatellerslie

There are something like

4700 heating degree days and only 1100 cooling degree days where this system is going in, so your concerns hit home with the closed loop. It's amazing how many ways a conversation can reveal new avenues for thought. Thanks for your help.