Well modifications for Geothermal

[marcusj]

Bill,

Thanks for your thoughts. I agree that it would be desirable to separate the geothermal water form the household water. However, there really is no distinction here between shallow and deep wells. I'm a mile from Lake Michigan and everything is sand. There is plenty of water and it is all less than 75'. My well is 50'. The issue is the water quality. There can be iron, sulphur, and tannins as speedbump experienced in Florida. My water is marginal and I'm having it tested before I run it through the geothermal unit. I may try another slightly deeper well, but if I go to that expense and get better water quality, then I want the better water for the house as well so I'm back to a combined usage for the well. You mentioned one well with two pumps - that never occurred to me. Is that common?

 

[Bill Arden]

You mentioned one well with two pumps - that never occurred to me. Is that common?

I've seen hand pumps and jet pumps connected to the same pounded well.

If you have a basement or a well pit to reduce the static water depth, you could use a T and then two check valves with two Jet pumps.

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For a well where a jet pump won't work, you could add check valve at the tank and a second pump to boost the pressure for the house. This would require using a contactor to run both pumps at the same time when the house tank needs water.

This second configuration would not be very standard since you would have to find two pumps designed to produce low head pressure.

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Either way the one pump would use a contactor and would run continuously when the heat pump is.

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exactly how much electricity will be saved will depend on the final pressure that the heat pump will need to achieve the required flow rate.

You might want to turn down the water pressure on the existing system and see how low it can get and still get the required flow.

If the needed pressure is higher than 30PSI, you would be better off just getting a CSV and use one pump.

 

[Sponsor]

 

[Speedbump]

However, there really is no distinction here between shallow and deep wells. I'm a mile from Lake Michigan and everything is sand.

I drilled a Well at a weekend place I had in Silver Lake Doones in 1976. There was a lot of sand, but I went through a lot of clay getting there. The clay seperates the shallow water from the next vein. I think you will find the same through out the entire State. The well flowed a lot of water without the use of a pump, so we let it go to keep it from freezing. It also brought the Deer into the camp to drink.

bob...

 

[Alternety]

Just a little point on resource use. Fresh water is scarce and getting scarcer. We are using up aquifers in many places faster than they can be replenished. An open loop heat pump is rather discourteous to those living on the same aquifer or wherever water may be obtained when the wells dry up.

If you dig some trenches and install a continuous loop for your heat pump you will achieve several things. You will not waste huge amounts of water. Your pumping costs will be very small. The circulation pump will be much smaller that the well pump. It is overcoming only friction losses rather than head from the water source. Many states forbid open source or reinjection wells. I suspect that open source will eventually be banned just about everywhere. If climate patterns change, your previously robust aquifer may run into more serious problems.

Of course a loop needs the space to install it and it is a cost.

There are also some heatpumps that bury tubing that carries the refrigerant directly. They would need less digging I suspect.

 

[marcusj]

speedbump: I've talked to two drillers in the area and both were pessimistic about going any deeper. One reviewed the well logs and said nobody was deeper than 75'. It does not mean I can't try, but it's not a sure thing for the money.

alternety: With all due respect, I don't agree that it is either discourteous or wasteful to install an open loop system. The water is going right back to the same aquifer without any changes to it except a few degrees in temperature. Furthermore, a closed loop is not necessarily cheaper to operate. While circulation may be less expensive than pumping water out of a well, the closed loop system is less efficient. According to the manual for my ClimateMaster, it has a heating capacity of 48,300 btuh open loop (COP 4.7) versus 38,700 btuh in a closed loop setup (COP 4.0). I think these savings more than overcome any pumping costs. To me, the real issue open loop versus closed is the maintenance needs of an open loop system versus the initial cost of a closed loop setup. However, I do agree that open loop systems will likely face increasing regulation or restriction - the concerns you just raised (whether justified or not) will likely cause more government bureaucrats to feel the need to step in.

 

[Bill Arden]

I see Open loop as a "stepping stone" to a deep drilled closed loop system.

The efficiency of trench based systems can also be increased by trenching it below the water line.

I've tried to convince directional drilling company's to do a "star" installation from a pit, but they tend to think in terms of "price per foot" due to the way they have to set up and drill 15 feet across a driveway.

Like I said, there was a study here in MN and it found that "shallow well" open loop systems that basically took "surface water" were not harmful to the environment. and since the water flowed back into the ground it did not really use any water.

Edit: I am currently looking at a system where you pound down a clamshell point then opens to let out the tubing as you pull it back up.

 

[Alternety]

marcusj: I was going to address efficiency which I figured would be a bit less, but I had no numbers. Your data is more than a bit less. I do not have hard data at hand, but here was my thinking.

The factors that I thought of that affect COP would be the thermal conductivity of the ground surrounding the loop, the length of the loop, flow rate, and how deep it is buried (i.e., temperature).

I believe temperature should be close to ground water if you go down 10 or 15 feet (my memory of gradients - it may be wrong). It is kind of difficult to ascribe such a COP difference as a general case. Below a certain depth (in the range of 10 or 15' I believe) the ground temp is a pretty stable average of seasonal air temperatures. The place where you are most likely to get a reduction in heat flow would be the transfer through the adjoining fill material. Back filling with a suitable material would help. Perhaps a little water delivered subsurface to keep conductivity up.

Of course it you have not got the dirt depth, it won't work real well. Then the loops would have to go into vertical wells; pricey.

It should be possible to adjust loop length to compensate for heat transfer rate.

As was pointed out, most of the water probably does get back to a shallow aquifer. It is kind of a function of geology. With your shallow well the odds are pretty good. Deep aquifer recharge may be more affected by runoff and evaporation, and blocking strata. Conditions vary widely even within a short distance.

It is becoming more common for wells to run dry as the water level decreases due to drought and over use. Distance and subsurface geology determine the effect on other wells. I took a quick search and the national average per capita water consumption seems to be a bit less than 200 gallons. Your heating is equivalent to about 12 wells each supporting a 4 person family. You may very well have no impact. As a general approach it is not a good idea. Even in the east and south, drought water restrictions would make you stop extracting water for that use.

I had a home in Pennsylvania where a neighbors well went dry when a new single family well was put into service in the next lot. I currently live in the west where water rights (surface and subsurface) are a much more common source of contention than we would have understood in the east. The water in rivers is owned by governments and private concerns. That has become an issue with the east coast as drought persists. Currently the local Indian tribes here are trying to stop all new wells near salmon bearing creeks. In many parts of the west you may not have an intrinsic right to water under your property. I live in an area where the only ground water is from small cracks in what is essentially solid granite from a few feet below the surface to the core of the earth. If I was aware of anyone doing this I would do everything that my neighbors and myself could do to stop it. But that is clearly a situational thing.

If you are interested you could do a bit of googling about US aquifers; including the upper midwest (for a real treat look at Las Vegas and similar regions). Weather patterns can cause some serious problems with recharge and use rate. Surface water discharge does not necessarily get to deep aquifers at a real high rate. Those big green crop circles you see all over the country put the water on the ground but they are depleting the aquifers at an alarming, and unsustainable, rate. Your shallow situation is probably pretty good.

My intent in commenting was to bring attention to the situation in general not your specific case. You seem annoyed with the idea that the government might control such water use. Letting everyone do what they wish with resources is accelerating a number of world wide (including us) crises and potable water is just one of them. It will be a general crises; timing is the only thing in question. In a sense water is just like oil. We are using a finite supply. With fresh water there is new material added but our use rates exceed recovery rates. Run down to the end of the Colorado River and see if you can spot it.

 

[marcusj]

alternety: The closed loop proposals I received were all for horizontal loops that went down ~6'. That was already pretty expensive. To go down 10-15 feet is really not practical given the size and number of trenches. I think at that point, you might as well go to vertical loops. The vertical loop price around here was another 33%. Pricey, as you mentioned.

I think we have a difference in perspective on open loop systems. You mention the per capita water consumption and computed that my heating is equivalent to about 124 family wells. I still don't view an open loop system as "consumption". If done properly, the water should go right back where it came. I am transferring energy to or from the water, but not consuming the water itself. This is substantially different from irrigation or other uses, and my family water consumption should remain the same. Perhaps we can agree that any regulatory efforts regarding open loop systems should be aimed at making sure water is not consumed, but rather returned to the aquifer from which it came. For some shallow wells in sandy soil (like my case) that may be very easy to achieve. In other cases, it may be a second well is required to return the water. In some instances, it might prove prohibitively expensive. In any event, that sort of regulatory effort serves the public interest without resorting to an all out ban.

By the way, I view this installation as a very green approach utilizing, but not consuming, the very accessible water available on our property and dramatically reducing our energy consumption.

 

[Alternety]

I agree. A point on well numbers; what I meant is 12 wells running at a rate to support families of four. I will go back and fix that 12 4 sequence.

 

[marcusj]

Funny, I read that as 124 without thinking twice. Open loop does run through a lot of water, but that did seem high.

 

[iamjcl]

Just a little bit of info to add to this thread, as well as an invitation to correct my thinking or improve my system's efficiency:

I've got 4 FHP geothermal units running in my home in south Georgia. Open loop, with a freshly-replaced pump / motor, pulling water from around 120', into a (roughly) 150 gallon pressure tank. Well only provides geothermal water, and irrigation (normally at times when geothermal demand is low - overnight).

Need here is almost entirely for cooling, as opposed to the northern climates mentioned above.

I would submit that my system, at least, is no more efficient (maybe less) than a decent air/air system. Here is why:

I'll use one of the units to do the math:

H20 temp out of well is 77 degrees Summer or Winter.

34,000 BTU unit. Draws 11 amps at about 225v, or about 2475 watts.
Pump useage with just this one unit running (no compressor cycling) is 65 seconds on, then 180 seconds off, or .27.

The well pump draws 10.6 amps at that roughly 225 volts, so 2385 watts, x .27 = 644 watts for 1 continuous hour of AC use.

So thats 2,475 watts for the heatpump, and 644 for the well, = 3,119 total.

Thats 13.75 EER for the FHP heatpump unit alone.

That equates to a 10.9 EER for the heatpump / well combo (the number that matters).

You can get a 12,000 BTU window unit at Home Depot with the same EER for about $225. Not the same thing as central air, I know, but its the same efficiency as I read it - maybe I'm missing something?

I have a Mitsubishi inverter-driven mini-split in a single room in the same house, and it has variable capacity delivery, ranging from about a 14 EER at low capacity, to a worst-case of 7.8 EER at "wide open" compressor speed.
The average is better than any of my 4 geothermal units, and its a simple unit - no issues or maintenance items.

I'm kind of stuck with this setup, and just recently replaced 3 of the 4 units with the newer models from FHP (The old ones were just as good - in fact, the example above uses actual measurements from the remaining old one).

I'm sure I could improve the pump setup somehow, but it seems to me the savings would be marginal.

As it stands now, I've just let all 4 units run wide open, and then monitor current draw on each compressor as I close down the water supply valves on each one. I can close down only slightly before amp-draw begins to creep up. I then back off to where amp-draw is the same as it was when the water flow was at pump capacity. The amp draws are very slightly less when there is only 1 or 2 units running as opposed to all 4, strangely.

I wonder if flow regulating water valves on each unit would help ?

As it stands now, I've got the slow-closing Taco valves on the water exit of each unit, with a gate valve to adjust as well.

FWIW, these are the basic FHP units - single stage, nothing too fancy.

Thanks for any insight or correction on my observations, or possible ideas to use LESS POWER!

Thanks

 

[Masterpumpman]

OK, I've heard enough!

I've just read comments from good meaning people and then from Valveman! Valveman's solution is the best by far.

A Cycle Stop Valve is the simplest, most dependable and least expensive.

Try it, I promise you'll like it.

Forget the variable speed (computer managed) pumps, they are a marvel nightmare!

Porky

 

[Bill Arden]

I would submit that my system, at least, is no more efficient (maybe less) than a decent air/air system.
H20 temp out of well is 77 degrees Summer or Winter.

There is one big difference between ground source based systems and air ones.

Air source heat pumps (or window units) need a LOT more energy when it gets hot out. As we head into "Time of Use" electrical pricing it is important to realize that you will have to pay a lot more for that increase in electricity when it's hot out.

There are a lot of ways to increase the efficiency of a heat pump.
1. variable restricting valves to optimize the pressure ratio.
See "thermostatic valves".
2. Increasing the output air temperature when interior humidity levels are already low.
3. Larger Air ducts. The mini-split systems do have an advantage here since they are in the room.

 

[iamjcl]

I may well be wrong here also, but I think most EER specs for air / air units are stated for 95 degree ambient outside temp.

I know my Mitsubishi mini-split is spec'd at that temperature.

Even here, where its hot, it is not that often above 95 (at least in the shade - where my mini-split outside unit is). In fact I have a temp. sensor on the outside unit air-intake side, and its rarely above 95.

I assume (maybe incorrectly) that if its less than 95, the unit is more efficient than spec, and if it is hotter, its sucking up more power than spec.

I also make this assumption on my water-source units - hence the attempt to cut back on water consumption as much as possible without negatively impacting current draw (assumed efficiency) of the units.

My water is a constant 77 degrees, so the only variable that I can see (if I'm seeing it right) relating to efficiency is flow rate, and the power needed to generate that flow rate.

I can't tweak the heat pump units themselves (beyond making sure they are clean, etc...), so delivering the amount of water they need as cheaply as possible is what seems to be within my power to change.

 

[Valveman]

The only way to reduce the pumping cost is to reduce the pressure required. I assume you have about a 1.5 HP, 20 GPM pump from the 10.6 amps and the run time. If this pump is on for 65 seconds and off for 180 seconds, that is using .36 of 1.5 HP, or about ½ HP load. Pumping into the pressure tank with a 40/60 setting is using twice as much electricity as it would if pumping directly to the heat pump with only 10 PSI. You also didn't say what the GPM demand of the heat pump is but, I am assuming about 11 GPM. You can pump 11 GPM from 120' at 10 PSI with a 1/3 HP pump.

I didn't check you calculations but, if you are currently using 644 watts for the pump, it will cut that to about 350 watts for using the 1/3 HP pump. Since the water is only used for the heat pump or the irrigation, you can then add a ½ HP jet pump to pick up the water coming out of the heat pump, and boost the pressure to 50 PSI for the sprinklers. This means you would be using the warm water to irrigate with but, it will be going through some piping and the sprinklers which will cool it off a little. I have been irrigating with the warm water from my heat pump without any problems. I just let the irrigation water run through the heat pump, no matter if the heat pump is on or not. This is double use of the same water, which will not only cut the power used to supply the heat pump but, will also reduce the power used to irrigate.

I have a mobile home with 3 window units right next to my house with the 3 ton heat pump. The house has twice the square feet of the mobile home but, has better insulation. The highest cooling bill I have had for the house is about $130, while the mobile home can easily use $250. It is probably the length of time the units run that makes the most difference. The heat pump easily catches up and is off more than ½ the time, while the window units never seem to catch up and shut off, except for a little while early in the mornings.

 

[iamjcl]

Valveman,

Thanks for taking the time to comment.

I think the pump is a 2HP unit (franklin motor / controller, goulds wet-end).

It seems to me that the pump being over-sized (for 1 or 2 units running at the same time, anyway) is mitigated by the expansion tank, correct?

In other words, thats why it cycles?

In my example above, I point out that it takes 644 pump watts to supply x amount of water to the 2.8 ton heat pump.

With a valve system, wouldn't it still take 644 watts to lift x amount of water? It just might not cycle so much, I understand, but still use similar amounts of power?

The other thing is that when all 4 units are running together (much of the time during mid-day during the summer) the well essentially never cycles off, so I don't see how a valve could help that situation.

Now the idea of running all my sprinkler water through the heat-pumps, even if they are off, is an excellent Idea.

Only issue I see with my situation is that the smaller piping / back pressure introduced by the long plumbing system of the heatpumps would reduce the flow rate at the end of the line, and the sprinklers may not get proper pressure / flow? I suppose thats where the jet pump comes in? That would go at the "end-of-line", at the hot water exit of the system, and "pull" extra water from the pressure tank / well system at the other end ?

I hope I'm understanding this right.

Thanks for the insight!

 

[Valveman]

I didn't mention anything about using a valve. I would run a 1/3 HP directly to the heat pump coil. And now that I think about it, you could add the jet pump before the heat pump coil, and that way you are pumping cool water instead of hot. Just when the heat pump alone is running it would be at 10 PSI through the heat pump, and when the jet pump kicks in you would be running 50 PSI through the heat pump, so you would have 45 PSI coming out to the sprinklers.

I don't understand what you are talking about as far as friction loss on the long pipe. Mine goes into the heat pump on one side and comes out on the other (only about 2' of pipe). There is only about 5 PSI of friction loss at high flow through the heat pump. The jet pump is to build enough pressure for the sprinklers, because the 1/3 HP well pump will only deliver 10 PSI, it has nothing to do with friction loss. Delivering water to the heat pump at 10 PSI instead of 40 to 60 as you are doing now, is what will reduce the horse power. It takes as much power to produce 50 PSI, as it does to lift water 115'. So it takes twice as much energy to lift water 120' and add 50 PSI, as it does to just lift the water 120' alone.

The way your pump is cycling now will shorten it's life considerably. Using a 2 HP pump that is on for 65 seconds and off for 180 seconds means you are using about a 3/4 HP load to handle the heat pump. If you reduce the pressure from 40/60 to 10 PSI, the horse power required will reduce from 3/4 HP to about 1/3 HP. A 1/3 HP will use ½ the power you are using now, and will last much longer because it is not cycling 352 times a day as your 2 HP pump is doing now.

Using the water as it comes out of the heat pump and pressuring it up to 50 PSI with a jet pump, will be using 1/3 + ½ or 5/6th of a horse power, instead of the 2 HP you are using now. This will also reduce horse power required for the irrigation.

 

[iamjcl]

Valveman,

Thanks for the response - pardon my inexperience and or ignorance.

The pipe friction / loss is me assuming that the water running up to the top floor (30' above ground level, on top of the 120' from the well water surface), all around a fairly large house, and then out the other side of the house, is more than 2' of pipe.

I don't have all the heat exchangers neatly in a line - the HP units are all package units, and they are scattered in attics and lower floor storage areas.

That said, I don't understand one thing you point out about needing only about 1/3 or 1/5 HP for the cooling system: When all 4 units are on (frequently, if not most of the time in the summer) the well pump NEVER cycles off. If it does, its not for very long before coming back on.

That leads me to believe that the pump is properly sized for the potential maximum required water flow - does this make sense, or am I missing something entirely ?

It seems to me that any potential I have to save power on the well system is when only 1 or 2, maybe 3 cooling units are running simultaneously. The more units running, the more water I need, and the closer to "ideal" the current 2 hp pump becomes.

Maybe I don't have a clear understanding of the pressure -vs- flow rate concept.

If I recall, I think my systems are supposed to get around 3-4 gpm per ton.
I have 11 tons of water-cooled cooling, which equals 33-44 GPM needed when all units are running. My wet-end is spec'd at 30 GPM using 2HP (which I am). Again, it seems the pump is properly sized when all units are running - it is only over-sized when 1, 2, or maybe 3 are running together.

How can I save power again ?

 

[Valveman]

OK, now that we know the flow required, it changes everything I said. 11 tons at 3 gallon per ton equals 33 GPM minimum. The piping up to the top floor and back down will have some friction loss that needs to be added in. Hopefully you used large enough pipe to not have much friction loss. Take a pressure reading at the lower floor when all heat pumps are running. Then take a pressure reading after the heat pumps. The difference is the friction loss that must be overcome. The 30' rise to the top floor should be counter balanced by the 30' drop back to ground level, so the friction loss of the pipe and heat pump coils, as well as the 120' of lift in the well, is all that you have to overcome.

Again, the only way to save any power is to reduce the pressure required. Using the pressure tank and controlling the pressure at 40/60, it takes 2 HP to handle the load. If you do away with the pressure tank, let the pump come on with a relay from the heat pumps, you can reduce the pressure required to less than 10 PSI. Then a 1 HP pump will give you 33 GPM from a total head of about 120'. That will cut your electric bill in half from using the 2 HP. Then when you are only using 1 zone of heat pump, the restricted flow rate from the heat pump zone valves will reduce the 1 HP power consumption to about ½ HP load. This will also be less than the 3/4 HP load you are using while the pump cycles as you described.

Then you will still need a jet pump to boost the pressure when you need to irrigate. The size of the jet pump depends on the flow rate for the irrigation. If you use the discharge water from the heat pump to irrigate with, it will use less water and horse power. Any of the 33 GPM you are using for the heat pump can be used again for irrigation. If the irrigation is an added demand for the pump, you will need 33 GPM for the heat pump, plus X GPM for the irrigation which will take additional horse power. The irrigation system can trigger a relay that starts the jet pump and the well pump, if the well pump is not already running to supply the heat pump.

Another idea would be to use a 3/4 HP well pump to handle heat pump zones 1 and 2. Then use the jet booster pump to increase flow when needed for heat pump zones 3 and 4 or the irrigation. Only in this way you would not be able to run more than 2 heat pump zones while the irrigation is running.

I use a small booster pump to assist my well pump when extra demand is required. In this way I am running the smallest pump possible when only low flow zones are being used, and the extra pump only comes on and uses additional power when absolutely needed.

 

[iamjcl]

Its starting to make sense now.

So the pressure tank is creating a "load" on the well pump? I guess it is pushing against the bladder, much like pushing the water even farther uphill than the 120' depth?

So going with a smaller pump, regulating the flow somehow (cyclestop valves maybe, or is this the wrong application), and putting a booster pump in after the well pump to "pull" (reduce back pressure) water out of the primary well pump when the irrigation is needed?

I'm sorry I just replaced the well pump / motor / controller about 2 months ago!

Thanks for your time - its been very informative to hear your ideas and suggestions.