DIY well geothermal water to water heat pump feasibility?

Bigruss

looking for someone to review and advise .

Have 11’ deep well ( 3’dia x 7’ constant water level ) next to house.

How many feet of 3/4” pipe would I need to install to “Heat - Only” 2000 sf one level home.

Jon_blaney

A system using a loop in a well will not work. There is inadequate heat exchange between the water and the surrounding earth. You would need to pump the water from the well, extract the heat, and return to some place else.

Heat loss drives equipment sizing. Equipment size drives gal/min required. Water flow drives piping. Does your well have an adequate flow rate?

DCContrarian

Before beginning I would check to see if this is even legal where you are. A lot of places a fussy about what you do with groundwater.

DCContrarian

This article tells how to calculate your house's heating load based on historical energy usage:

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

Let's say your well is at 50F in the winter and you can return water at 35F without having to worry about freezing. Let's say your house needs 50,000 BTU/hr. The formula for BTU/hr for water is (temperature change)*(gallons per minute)*500. With a 15F temperature change, and 50,000 BTU/hr, you'd need 6.7 gallons per minute.

Your well is 3' in diameter and 7' deep, so that's 49 cubic feet or about 500 gallons. At 6.7 gallons per minute it would take about an hour to cycle through all of the water in the well. Given that it's pretty small it probably won't have a lot of exchange with the surrounding water so it would get cold and stay cold and your heat pump would shut down.

What we don't know is whether your well can sustain extracting 6.7 GPM all winter long without losing water level. If it can, you could extract water and dump the chilled water elsewhere. You'd have to have a place to put quite a bit of water. It also would take a fair bit of electricity to pump out that much water.

Jamie Hall

Not much to add to all that. First point: will your well actually yield 7 gpm or better, pumped steadily 24 hours per day, 7 days per week? I honestly doubt it, but I haven't seen the well — obviously — and I don't know what kind of material it is constructed in (coarse sand next to a lake or river? Might manage quite well. Upland silty material? No hope).

Second, under those flow conditions, what does the water temperature stabilise at?

Third, as has been noted, where and how are you going to discharge the now cold water Groundwater recharge is strictly regulated in many areas, and surface water discharge even more so.

jumper

Trick is to discharge water so that it picks up heat from earth and gets back into well. Geothermal engineering?

Decades ago, when refrigerant was cheap, some guy buried lots of copper tubing in his yard to directly extract heat from earth. Story is that it took more than one winter to turn yard into solid ice.

Jamie Hall

The most reliable — and least subject to regulatory concerns — is not to use the groundwater directly, but to drill one or more deep wells (or a large horizontal grid, preferably well below frost level) and circulate water or some other liquid through them in closed pipes. They will pick up heat from — or release heat to — the ground. The deep well versions, if you are well below the water table in the area, will actually be transferring the heat from or to the groundwater going by, and if you get the numbers right the temperature of your circulating water returning from the well will be very nearly constant.

ethicalpaul

Well said @Jamie Hall

I hit water at 20 feet in my 550 foot well and I'm quite sure that's exactly what I was seeing. Incoming loop temp would slowly fall throughout the heating season but I never did actually need the food-safe antifreeze that I had added to it.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1805875#Comment_1805875

How many BTUs are you pulling out of the well? I've heard 500 feet per ton bandied about as a rule of thumb, curious how that compares with your experience.

ethicalpaul

I had a three ton unit on it. My engineer did a heat loss on the house. He sized the well for that size heat pump. It never had trouble heating and for cooling it was amazing

EBEBRATT-Ed

I am not much for heat pumps except for Geothermal. They work well. First ones I installed was back in the 90s. We had 5 or 6 WaterFurnace heat pumps in an animal hospital and they worked great. I think they were 3 ton units. Closed loop in the ground is the way to go

Expensive to install though

ethicalpaul

Upfront cost is high, but operation cost is nice and there is like 0 maintenance for 20 years (if you're luckyish).

But for the OP I would say that existing well isn't going to cut it.

hot_rod

years ago I went to a training and demo of a geo application with a directional boring rig

If you have the land area this may be an option to bore holes or trench loops

https://geosmartenergy.com/consider-horizontal-boring/

Intplm.

Those geothermal pits can get quite large.

If I had the land, I would do it.

Jamie Hall

One can, I think, sort of make an estimate of so and so many feet of pipe per ton, but it's going to be a ballpark. If all of your heat transfer is conduction through the pipe walls into or out of the soil, or rock, that's one thing — but if your heat transfer is convection to moving ground water as it might be in fractured rock or certainly in sands and gravels, you can get much higher capacity.

You'd really need a hydrogeologist (a rather exotic breed of cat) or a very experienced well driller to help with that.

For horizontal grid systems this isn't a factor, of course.

leonz

The general rule is 100 feet of drilled bore hole for every ton of heating or cooling needed.

The so called geothermally enhanced grout is a clay based grout and a net insulator. Using mason sand in a bore hole for a closed loop system would make a better less costly heat exchange method

Your hand dug well is not deep enough to do any useful amount heat exchange for heating or cooling.

Jamie Hall

Excellent point on the grout. It goes with my comment just above: if the system is depending on conductive heat transfer to dry or most ground, or to rock, without significant groundwater movement, then you really do need the "geothermally enhanced" grout, as you are dependent on conductance for the heat transfer. True, the stuff is not a very good conductor, but it does ensure large total effective heat transfer area. On the other hand, if you are depending on groundwater movement, you want a medium to coarse sand pack around the pipes — and no grout (and you'll be better off with a cable tool drill — or very careful development of the well, like a water supply well, if using a rotary or reverse rotary rig).

ethicalpaul

I have never personally measured the thermal conductivity of the grout, but the entire "Geothermal" energy industry, its drillers, and its engineers seem to be in concert against you.

https://www.thedriller.com/articles/87744-an-overview-of-geothermal-grouts

As someone who disagrees with several residential steam boiler modes of thought, I am sympathetic. But if sand works best, why don't they use it?

DCContrarian

The primary purpose of the grout is to keep surface water from contaminating the groundwater. It's high conductivity only compared to what is normally used for that purpose.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1805949#Comment_1805949

Details details. Quite correct. I just sort of assumed that the well would be drilled and completed properly. That is, drill oversize at least 10 feet into bedrock, if a rock well, or to a depth of at least 20 feet below the surface in unconsolidated materials. Lower casing in to that depth (never pound casing) and cement grout from the bottom up to the surface. Then drill through that to finish size as far down as needed…

ethicalpaul

So the reason they don't use sand is because that would allow surface (or near surface) water to flow into the well. It sounds like the grout is probably mandated by regulation then, no?

leonz

No, Baroid has convinced them thier grout is the be all, end all for geothermal.

leonz

The geothermal grout and closed loop systems are just another way to empty your wallet. if a 20 well closed loop system fails they may never find the leak.

ethicalpaul

My house had one well and that tube was extremely solid. if it did leak, I wouldn't have to look very far, but honestly that tube is going to outlive all of us and our children

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1805974#Comment_1805974

In some jurisdictions it is. In others, no. Unfortunately. However, it is generally regarded in the industry as good practice.

It is important to remember that what flows into a well in the way of near surface water — or other contaminants — will not stay in the well. It will migrate with the groundwater. Speaking from considerable experience, it can be devilishly hard to track down the source of such contamination, although it can usually be done (I once tracked a contamination plume back about a mile to an improperly built well…)

And guess who gets to pay the cost of the tracking down and the remediation? Right. The property owner. And we are talking low six figures in many cases.

Teemok

I had the Idea of pulling water up from one side of my 150' lot and reintroducing it on the other side. I live on an alluvial plain. 15' of silty soil down to 3-6' of 3/8-3/4 gravel that sits on a 20' clay layer. the first water table flows down following the natural slope of the clay in the gravel above it. It would be a 150ft diversion with a slight temperature change. I researched how to properly reintroduce the water back into the water table. Regulations made me think the better of it but I do think it would work……well

ethicalpaul

Pump and dump (open) systems like that can be hard on the heat pump depending on the water quality, I understand.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1805992#Comment_1805992

Usually that does work quite well — but you do have to be very sure of the regulatory environment — which can be squirrely. The other thing to make sure of is that the water quality you are pumping back in is at least as good as what you have pumped out — and be able to prove it.

Teemok

From evap. tests it doesn't seem to be loaded with much. I think heat exchanger type and maintenance would be key. I was concerned pulling that much out of the gravel it might eventually clog up. It will never happen. It was just a young man's musings.

hot_rod

I would look to IGSHPA for actual facts and data on what works, how and why.

https://igshpa.org

Geosman

Elemental iron and iron bacteria are the primay issues particularly with near surface aquifers or those from glacial deposits. I might suggest collecting a sample in a large mason jar and putting it on the windowsill for a few weeks. If iron is present, it will turn orange and settle out on the bottom. If the sediment starts to clump together, you are witnessing the beginnings of a colony of iron bacteria thriving on the elemental iron that just precipitated from the water. It is the iron bacteria and the precipitation of the iron that will eventually create "tree rings" of iron deposits on the interior of the piping system and on well pump impellers that eventually require cleaning or replacement. I have serviced many open loop systems over that past 50 years and find that blowing out the lines and heat exchangers with compressed air helps clear a majority of the iron deposits. As for the heat exchangers on the geothermal units. I find that by first blowing them with compressed air to clear all water and then allowing the system to run in the heating mode until the system trips on its low pressure or low flow sensor will allow ice crystals to form on the walls of the heat exchanger. When water flow is restored and the system run in the AC mode the leaving fluid is more akin to barbecue sauce with the release of accumulated iron from the walls of the heat exchanger. This method is much faster and safer than setting up an acid pump and circulating for several hours trying to dissolve iron deposits from the deep folds of a fluted spiral in a co-axial heat exchanger.

JUGHNE

I installed perhaps 8 water to air heat pumps in the 1990's.

They were all pump and dump. Some dumped into a return well, some dumped into a small creek in the trees.

Seldom a problem with discharge freeze up. Most are still in operation or have been replaced with the same system. The shortest lived one died at 16 years.

However we are above the Ogallala aquifer with excellent water quality.

I just hope and pray that we retain that quality as most people take it for granted. As I read here and other places about water quality and supply we are blessed by comparison.