Dumb geothermal question

RonLud

I read about the cycle times for running a geothermal hp. I'm seeing they run for an hour or longer before cutting off. I know there talking about 2 stage compressors, but still to run for an hour or longer .. it seems that there must be a very low volume of air or a low temperature range to make them run that long. What is the logic on having them run such long cycles ? Or maybe I'm getting bad information. How long should they run for an average cycle time ( just in general ) I know it's all relative to where you live and what the temp is outside.
Just trying to understand this.
Thanks!

Hot_water_fan

It depends. If it is a 100% 2nd stage, 40% 1st stage, it could run nearly nonstop during the winter. It runs longer because it’s usually more efficient and comfortable that way (quieter too). Nothing to be afraid of. 

RonLud

But if it's running continually, it must be blowing very low heat or very low volume.

Hot_water_fan

Correct, usually using lower CFM/GPM - quieter and more efficient. You can size better too, so instead of scorched air blown at high speed you get cooler air and lower speed. 

EdTheHeaterMan

Dumb geothermal question

There are no dumb questions!

Just dumb people asking questions


If you are using a heat pump with variable speed, inverter technology, then the system could run non-stop the entire season. If you had a car that only had two speeds: ON and OFF. ON=100MPH and OFF=STOP, then to go on a road marked 50 MPH you would need to turn the car ON for a few minutes and then OFF for a few minutes to average out to 50 MPH. Sounds crazy right? Nobody would drive that way.

Consider that you have a compressor that changes speed based on how cold it was outside (or hot out in the summer). As the outdoor temperature requires more heat to be added indoors, the compressor would go faster and the fan would move more air. As the temperature got milder, the compressor would slow down and the fan would slow down.

That is just like driving on the interstate with no other traffic. Conceivably you could drive until you needed fuel, without ever even hitting the break. Just increase the throttle if you are going up an incline and the car slows down. Reduce the throttle if the car goes faster on a downhill slope. There is technology available today, that will do this for heat pumps and air conditioners. Inverter technology is what they are calling it. I’m wondering if that is the heat pump you are talking about.

And to think that all those on and off cycles would be reduced to the beginning and the end of the season... How long would that relay last? ON and OFF only once a year. Those contactors would never wear out.

RonLud

That is probably true, but now let's add the problem of drawing your water from your house well. Providing 4.5 gpm from a 10 gpm pump, where the water is then let out into a natural runoff , ending in a lake. If you ran continually, then you run the risk of drying up your well. So, in my particular case the single stage on/off scenario is the one that works. If I were to dump it back down another well, then maybe your scenario would be better. But at this point, 3k to buy the hp, running for a year costs me 250.00 plus 40 more for running the well pump. So 300/year is not so bad a cost.
I just didn't understand how the new economical units worked.
Thanks for the explanation !

Hot_water_fan

Gotcha. Most geothermal isn’t open loop. You can still buy one speed heat pumps!

retiredguy

I do not know of anyone that would install or want a waste water geothermal heat pump where the water is pumped from a well , used for heat exchange, and the dumped into a stream or lake. All the geothermal heat pumps I have seen use sealed loops either horizontal loops or vertical loops.

RonLud

Depends on the cost.. 3k vs 20-30 k... big difference. But when mine was originally put in 40 years ago, only type available was the single stage. Burying loops wasn't even mentioned or an option given. Back then it was 1500 full install, including duct work. 15 years later that hp developed a leak in the copper coil. Replaced with similar for 1500 for the unit. 25 years later. Still running but full of mold... replaced with new miami unit for 3k and full ductwork for 3k more. They all run efficiently, like I said earlier 280/ year. The new one just has a lower air range on heat and cool .. about 20 degrees vs 25. Just got me looking at the more efficient units and wondering how they work, , I just can't waste that much water for one that runs a lot (even if it may cost less) and can't afford putting in loops or deep wells. I will just have to live with what I have.. and it's not a bad thing. With the exception of pulling from my well. But it clicked atc35 gpm (40 years ago)

EdTheHeaterMan

YOUR reason for not operating for long cycles makes more sense now. Your original post did not refer to an open well GEO HP. You are better off with shorter cycles with your situation. As the outdoor temp drops your cycles will be longer, but still have some off cycles until you get below the design temperature. (coldest day of the year being colder than normal). Understanding the logic of the new stuff compared to the ON / OFF equipment of 25 years ago will help in deciding what ot do if you do have a well running dry problem in the future.

Good thing they still make the simple ON / OFF equipment for your situation.

Dave Carpentier

A well would have a recovery rate. You can sip it in intermittent large gulps or continuous small sipping.
Would intermittent draw have a btu advantage ?
Hardware costs would be cheaper, of course.

Jamie Hall

Dave Carpentier said:

A well would have a recovery rate. You can sip it in intermittent large gulps or continuous small sipping.
Would intermittent draw have a btu advantage ?
Hardware costs would be cheaper, of course.

Well hydraulics is a fascinating topic all its own. Intermittent large draws vs. steady state draw at the same overall rate will make very little difference, except in the area really close to the well (like a few feet). What does happen, in the case of a totally consumptive use such as an open loop heat pump, is the steady state area of influence of the well will reach a stable size and geometry, dependent on the recharge rate from precipitation in the area. Again, in the case of a large consumptive use -- the quoted 4.5 gpm is equivalent to a system serving 80 people, more or less, for instance -- the area can be remarkably large. In most of New England the area of influence will be around 7 acres for that yield. In most of the rest of the US the area will be larger, until you get west of the 100th meridian, where the total precipitation recharge is negative and you are mining water.

Also, a word on well tests. Most residential wells are tested over a very short term -- a few hours at most -- and the results can be quite misleading. It is not, unhappily, uncommon for a well test to be a better measure of the stored water in the casing rather than the actual long term recharge rate. Back in the day when I was doing that sort of thing, I never reported a well yield from less than a 12 hour test for a residence, and a 72 hour test for a public or farm well.

pecmsg

@RonLud

How many GPM are you drawing?

leonz

RonLud said:

That is probably true, but now let's add the problem of drawing your water from your house well. Providing 4.5 gpm from a 10 gpm pump, where the water is then let out into a natural runoff , ending in a lake. If you ran continually, then you run the risk of drying up your well. So, in my particular case the single stage on/off scenario is the one that works. If I were to dump it back down another well, then maybe your scenario would be better. But at this point, 3k to buy the hp, running for a year costs me 250.00 plus 40 more for running the well pump. So 300/year is not so bad a cost.
I just didn't understand how the new economical units worked.
Thanks for the explanation !

=================================================================

Every 100 feet of drilled well depth gets you one ton of cooling or heating in a semi open loop system.

Depending on the depth of the well you could be looking at $200.00+- per foot for drilling cost including pipe, grout and labor.

The problem is not knowing whether you can benefit from a high water table using a single drilled deep well or 2 drilled wells for summer and winter pumping with well water.

This is done using one well which draws water and the second well is used to dump the water the year round allowing it to sink back into the aquifer or you have access to a deep well aquifer that will have a high natural artesian well pressure that will allow you to draw the water from the bottom of the well and let the warm water sink back into the well gradually to become cold again creating a semi open loop.
Some systems are designed using a reversing method where the water flow is reversed for summer operating and then valves closed and opened for winter water flow.

The well casing protected geothermal wells drilled in New York City, New York have the benefit of being drilled deep into the granite bed rock for 1,550+ feet and fracking them to break into water veins and creating standing water columns that are 1,400+ feet deep and they make lots of heat and cooling.

Then the CRAZIES with GEOTHERMALLY ENHANCED grout come into the playground saying the closed loop method with a big herd of vertical shallow wells closely spaced is so much better with butt fusing the elbows for the 2-pipe system in the bottom of the well are best.

After the elbows are butt fused to the twin pipe they attach a weight to the elbow and lower it into the well
all the way to the bottom of the bore hole and then the GEOTHERMALLLY ENHANCED GROUT is pumped in the well all the way to the surface collar of the well hole.

In most cases the closed loop cased wells are drilled with the casing left above the ground with the twin pipe sticking out of the casing to be butt spliced together to create the systems closed loop.

They have leaked in the past and destroyed the heating and cooling systems and because they have lost the fluid AND the drilled geothermal field has to be abandoned as they cannot find the leaking point and if they do find it with compressed air that borehole has to be dug up and abandoned and a new splice created to bypass it reducing the number of shallow wells by one well in the drilled well field for heating and cooling.

(ideally if one had a drilled deep well with a concrete plug in the cased well sump it can provide plenty of captive water for a heating and cooling system where the cold water is drawn from near the bottom of the well and this water is simply allowed to fall back into the well via a second sanitary seal and then sinks back to the bottom of the well to be cooled by the surrounding soil or rock temperature)

Then there are drillers that drill in small spaces using a radial drilling pattern at 45 degrees+- in a very small space with a very small track drill using soft copper refrigerant tubing loops to created geothermal heat exchange using a small vault for the connections using GEOTHERMALLY ENHANCED GROUT by creating a conical pattern of drilled holes drilled from one position that connect in the below surface vault.

By simply rotating the small track drills position by 10 degrees they can drill 36 holes and insert 36 pairs of refrigerant grade copper tubing loops or small diameter fused HDPE pipe in each hole to create the well field in a very small space. THE PROBLEM is how conductive the ground is to releasing heat and how quickly the ground can cool.

Some well drillers do heat and cold conductivity work to test the ground where the well field is to be placed to see what they will have to do to create the well field.

If your lucky enough to have access to an open water course with moving water, or a deep water location to employ open loop geothermal all the better as long as it cannot freeze and you will have plenty of heat and cooling.

Cornell University has been using the open loop method with 2 closed streams of water passing through
a heat exchanger on the shores of Cayuga Lake-MUCH to dismay of the locals as they are of the opinion that the open loop system is stirring up sediments that have created algae blooms.

(it does not help matters that the Village of Cayuga Heights Sewage treatment Plant is right next door and for years was dumping poorly treated effluent into the lake; BUT in recent years they have upgraded the sewage treatment plant with more settling basins and clarifiers with grant monies and loans which has helped created cleaner effluent flow from the sewage treatment plant there)

Back to the Cornell University and LAKE SOURCE COOLING PLANT:
One twin pipeline brings water from Cayuga Lake to the pump house on East Shore Drive through the twin bores drilled through the bed rock 30 feet+- below the lake surface to the basement of the pump house
where it is pumped through the heat exchanger to provide water that is 52 degrees Fahrenheit or less water to the closed loop from the University campus that is driven by simple gravity from the Humpreys Service building on Maple Avenue. The water from the closed loop University campus pipeline is drawn from Fall Creek at the Conell University Water Treatment Plant.
The system there uses removable screens that filter out debris to keep the heat exchanger clean.
I do not know what the screen sieve size is but I would imagine it is very small as we have a great deal of algae in the lake at the south end as it is shallow.
Angelica Boring of Angelica New York drilled the twin bores through the limestone bed rock on the lake
shore to the pump house basement.

I do not remember if they used a small diameter tunnel boring machine or an auger boring machine secured to a concrete foundation in the rock trench that was blasted and lined with sheet piling for the duration of the work as the drive for the twin bore holes was not very long.

I am not sure if the HDPE pipe that was Butt Fused or connected with mechanical pipe joints together for the lakes twin pipelines or if it was pushed into the rock bores all the way to the basement of the pump house and connected to the piping in the basement or connected to the boreholes in a cast concrete connection after the pipe was sunk and buried in the trench created by a dragline excavator to bury the twin pipes in the lake bed.

Last I knew the University of Hawaii was planning to use ocean water to cool its campus and The City of Toronto, Ontario, Canada was also planning to use the same methods citing the work done by Cornell University in Ithaca, New York.
The recently drilled 10,000 foot deep Well Bore Drilled by Precision Drillers Incorporated is another project Cornell is designing to use 130 degree water to heat the Cornell University campus buildings in the near future. This bore hole is not deep enough in my opinion but they may come back and drill it 5,000 feet deeper in the future or drill the second one deeper whenever they decide to drill into the bedrock again.

hot_rod

The concerns with pump and dump has to do with the potential for refrigerants to get into the aquifers via a HX leak. My state banned them, then came back with a 100’ max depth for the dump well?

EdTheHeaterMan

hot_rod said:

The concerns with pump and dump has to do with the potential for refrigerants to get into the aquifers via a HX leak. My state banned them, then came back with a 100’ max depth for the dump well?

What state is that BOB? The state of confusion?

hot_rod

EdTheHeaterMan said:

The concerns with pump and dump has to do with the potential for refrigerants to get into the aquifers via a HX leak. My state banned them, then came back with a 100’ max depth for the dump well?

What state is that BOB? The state of confusion?

Close, the Show Me state of Missouri

pecmsg

hot_rod said:

The concerns with pump and dump has to do with the potential for refrigerants to get into the aquifers via a HX leak. My state banned them, then came back with a 100’ max depth for the dump well?

Actually, it's the refrigeration OIL there concerned with and for good reason!

leonz

This reminds me of what happened to Coors at their brewery over 2 decades ago; the sanitary sewer pipes are buried in the brewery floor and the sanitary sewer line developed a crack and the solvent they used to clean the aluminum roll stock before it was punch pressed and coated with the plastic sealer ended up in their well water and they were pumping more well water into the same well to get it flushed out of the well water.

I would believe they lined the sanitary sewer line in the brewery floor with a CIPP pipe repair.

I don't know if they were able to use this well for brewery water again or not.

Jamie Hall

There are a whole lot of reasons to be unhappy with open or partly open loop geothermal systems, whether they involve discharge of the waste water into someone's lake or stream (you'd think we humans would learn...) or subsurface reinjection of the waste water in the vicinity of the extraction well.

Dave Carpentier

I might have a good property for closed loop but I've always assumed the price to be astronomical. If those directional boring guys can turn a 180 in 50ft width, then I could get about 700ft of pipe into the ground at about 8 or 10 ft deep. It would presumably be wet clay at that depth here.
Afaik, people used to just bury straight pipe ? Recent pics Ive seen are coils though.
Anyone know ballpark tons in 700ft of (deep) buried pipe ?

leonz

They cannot turn a HDD drill pipe using drilling mud and a drill bit 180 degrees; it is not physically possible.

HDD drilling involves using a launch pit for the drill string and drilling mud that is returned with the drill cuttings and suctioned out of the launch pit and sent through a drilling mud cleaner to be recirculated through the mud swivel to the end of the drill string and then back to the launch pit.

When the drill string reaches the end of the drilling length and exits into the reception pit they will pull pipe back through bore hole to the launch pit with the HDD rig that is secured into the ground with 2 augers drilled into the ground to hold the HDD drill in place.

If you have nothing but black clay in the ground a ground source heat pump will not do you much good.
and an air source heat pump may be your only option.

A geothermal installer that drills wells or does horizontal trench installations will spend time with you explaining the work and conducting tests of the ground to see how well the ground will exchange heat and create "useful" energy to heat or cool your home.

Normally they will bring in a trencher to dig a trench below the frost line to obtain the most available heat exchange using whatever heat exchange liquid like non toxic cryotek in the pipe loop.

If you expect to have them bury the pipe 10 feet deep you will be wasting your money as the distance between each length of pipe is what is important not the deepest depth as that HDPE pipe is going to radiate heat in the ground to cool it.

Dave Carpentier

Thanks Leonz. I've seen crews set up, and the guy with the head controller following along at the tip. I think they can turn a bit of an angle as they will come from depth and sweep up into a telecom box etc, but ya I didnt think of the actual pipe pulling process.
If clay is no good, then maybe Im SOL. If I recall right, the soil/muskeg is maybe 4ft deep, then clay to about 12ft and then shale. I suspect most of the top layer freezes.

hot_rod

Dave Carpentier said:

Thanks Leonz. I've seen crews set up, and the guy with the head controller following along at the tip. I think they can turn a bit of an angle as they will come from depth and sweep up into a telecom box etc, but ya I didnt think of the actual pipe pulling process.
If clay is no good, then maybe Im SOL. If I recall right, the soil/muskeg is maybe 4ft deep, then clay to about 12ft and then shale. I suspect most of the top layer freezes.

Really need a ground analysis to know. Local well drillers often know what the ground in their area is. Info at the ground source site

We did a 3 part series on ground source systems in our Coffee with Caleffi webinar series, part 1 here

https://www.youtube.com/watch?v=ytQT8cm0ng8&list=PLuuV0ELkYb5VE0I4evUZ30b5U78CRlRdg&index=107

Great detail regarding the options for putting tube into the ground with wells or excavated trenches.
Rent a medium size track hoe for a couple days🤔 A four pipe system can go into a 2’ wide trench.

leonz

Dave Carpentier said:

Thanks Leonz. I've seen crews set up, and the guy with the head controller following along at the tip. I think they can turn a bit of an angle as they will come from depth and sweep up into a telecom box etc., but ya I didn't think of the actual pipe pulling process.
If clay is no good, then maybe I'm SOL. If I recall right, the soil/muskeg is maybe 4ft deep, then clay to about 12ft and then shale. I suspect most of the top layer freezes.

=================================================================

Good evening Mr. Carpentier,

I hope I did not come off as being harsh. You may be able to find a well driller that has a Foremost Drill that can also mud drill and set well casing and then push marine grade sand mix cement into the borehole annulus with a tremie pipe filling the space between the casing and the well borehole to seal the well from any surface water contamination.

If the ground is stable the driller may be able to simply use a pipe cap on the first section of casing and lower the casing string into the hole with the tremie pipe duct taped to the last casing joint and when the casing reaches the bottom of the borehole they can begin pumping the cement down the tremie pipe to the bottom while a concrete vibrator is vibrating the sand mix cement as the tremie pipe is pulled up slowly while the sand mix cement is filling the annulus full of sand mix cement all the way to the surface.

The well would have a captive amount of water and your well would be protected by a small pump house and you could use the closed cell foam oxygen barrier PEX all PEX for the trench to the home and come up into the pump house and use a jet pump to move the water to the heat pump in pump house.

Using a jet pump eliminates having a deep well submersible pump in the well and any possible damage from a lightning strike killing the pump-been there done that multiple times thanks to the *&^%T^&*( well driller I had.

You could use a cast iron radiator in the insulated pump house to keep the pump house from freezing
by running the warm return water from the home into the radiator and then into the well head where it would sink into the cooler water below.

If 6 inch well casing is used you will be able to store 1.5 gallons per foot of well casing in the sealed casing and if you have a 500 foot deep well you could have 700 gallons of water for heat exchange-I did not use the full 750 gallon figure as space is needed for the warm water to drop to the bottom of the well.

A 2 pipe, 2 piece well casing cap and well head fitting would be used for the jet pump plumbing connection that holds the twin pipe in place.

If the jet pump and geothermal heat pump are wired into a disconnect in the pumphouse you could unplug them and plug them into a generator for heat in the event of a power failure to have heat.

RonLud

Thank you all for your input. My open loop system has been running since 1985, almost 40 years now. This is from a well that is 65 feet deep, with the pump placed at 40, with 18 feet of water above the pump. 6 inch well. Original calculation was 45 gpm. Never had any water supply problems (yet) but from what I've read, the linger you use a well, it will develope better pathways to recover the water your pulling. So my 45 could be higher now, or that could gave just been a line of bs.
But at this point, my hp seems to have a cycle time of 8 minutes (for heating.. thermostat set at 69 or 70) off time depends on how cold it is outside and my house's heat loss. But currently 20-30 minutes. Last night Temps got down to 40 and ut only ran once. But temp goes back up to 60's reheating the brick of my house. Summer is another story, it will run more often, thermostat set at 77-78 (same Cycle on time of about 7-8 minutes, but rest time is shorter, maybe 10 minutes. For me, this system works well, it's cost efficient and keeps us warm and cool.
My dump is into a natural runoff that eventually leads to what used to be a lake, but now more of a swamp. I doubt very much if my water ever gets there before it's absorbed into the runoff path it takes.

Jamie Hall

I envy your climate. It hasn't been above 40 here since late November, and it's been a warm winter (only got down to -15 once).

pecmsg

RonLud said:

Thank you all for your input. My open loop system has been running since 1985, almost 40 years now. This is from a well that is 65 feet deep, with the pump placed at 40, with 18 feet of water above the pump. 6 inch well. Original calculation was 45 gpm. Never had any water supply problems (yet) but from what I've read, the linger you use a well, it will develope better pathways to recover the water you’re The biggest issue with “pump and dump”pulling. So my 45 could be higher now, or that could gave just been a line of bs. But at this point, my hp seems to have a cycle time of 8 minutes (for heating.. thermostat set at 69 or 70) off time depends on how cold it is outside and my house's heat loss. But currently 20-30 minutes. Last night Temps got down to 40 and ut only ran once. But temp goes back up to 60's reheating the brick of my house. Summer is another story, it will run more often, thermostat set at 77-78 (same Cycle on time of about 7-8 minutes, but rest time is shorter, maybe 10 minutes. For me, this system works well, it's cost efficient and keeps us warm and cool. My dump is into a natural runoff that eventually leads to what used to be a lake, but now more of a swamp. I doubt very much if my water ever gets there before it's absorbed into the runoff path it takes.

The biggest issues with “pump and dump“ systems is when there’s a refrigerant leak refrigeration oil gets into the ground water and contaminates it. One by one municipalities are banning such systems.