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Looking for comments on the vertical drilled system for Geothermal HVAC. Local power co seems to think this is best way to go on small lot in coastal South Carolina (basically sea level)
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Somewhat related, but has anyone tried to use the leach field trenches for running geothermal pipes?
Seems like the fluid would improve the thermal transfer. Also, the trench is already open...cuts down on the installation cost differential for geothermal systems.
Thanks
*Adam: You're right, wet soil will transmit heat much more quickly than moist or dry soils. However, leach fields are sometimes pretty shallow. Hopefully below frost depth, but the shallower they are, the cooler the soils will be in winter and the warmer in summer. Whereas you are hoping for steadier temperatures for the best performance. But if those leach fields trenchs are already open, you could save a lot of $$ on the install. Ask your inspector before heading too far down this path. What depth/length of leach field do you have? -David
*Windmill: I'm assuming you are talking about two or more vertical wells with a pump in one to extract shallow groundwater, send it through the HVAC, and discharge to the other well(s). The advantages of such a system include the limited amount of site disruption and yards of soil to be dug (as in a buried, below-grade loop of piping). And, if you get clever, you can pull from one region to heat - discharging cooled water to the other well. Then use that second well in the summer to cool because it will yield colder water and discharge the heated effluent back to the first well. In doing so, you'll be capturing some of the heat of summer for use the next winter. And some of the cold of winter to save on your A/C load in summer. If you have a heat/cool system.But my concern in such a system is in the lost work of lifting that water up out of the ground. Doing some rough calcs, for 100,000 BTU's with a 10F drop in water temperature and a 20-foot water depth, you'd use $0.03 of electric power at $0.12/kwh. A good deal compared to $0.50 for a therm of natural gas, but above 100 feet it would get significant. Fortunately, you have shallow ground water. You could theoretically prime your pipes with a vacuum pump and use a circulator pump of very low hp to move the water from one well to the other (keep the dip tube ends submerged) and avoid that loss of pumping the water up against gravity. (Only works if the water is less than 20-25 feet deep). -David
*Dave,Novel idea, but you must remember to keep the discharge tube end below the water table too or you will lose the "drop" to compensate for the "lift" in the source well.
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I too was investigating using Geothermal on new construction. My source was from a well, but the drillers had reached a dept of 205ft before hitting water at around 3-4 gallons per minute. Another 45ft didnt offer anymore. Is this enough for a 1200 sqft house with no more than 2 people and a geothermal system.
*I've had experience installing the horizontal loopsfor a 7-ton (2 units) Water Furnace installation. Ifyou're talking about using septic leach fields, even a 2000 sq. ft. home would need alot more trench thanwhat the average 100' leach field provides. I am currently investigating vertical loops for my own home. My question for GHP providers is why not push vertical loops more? Setup a truck to drill only the 150-200' depth required. In SE Ohio, most drillers are oil field rigs that destroy roads (and driveways) and can't even begin to enter city limits. Maybe somebody with drilling experience can respond. Good luck.
*I'm in the thick of putting in a ground source heat pump system for a three story office building. We are going with the loop field system. We need to drill 28 wells 350ft deep. HDPE pipe, 2" O.D. with a special U on the bottom is inserted into the wells to the full depth. A thinner 3/4" hose goes down with it. Grout is pumped thru the hose as it is pulled back out to completely seal the well and ensure the best possible thermal bond with the surrounding earth.Our total tonnage is 100 tons of cooling capacity. Figure about 450 sq ft of floor area per ton. We are using 32 heat pumps hung from the ceiling above the accoustic tiles for the different zones. It's costing $85,000 more than a conventional HVAC system to install, payback will take about 8 years, then it'll be gravy. We are going with Command Air heat pumps. Addison and Water Furnace are also good.Toughest drilling is thru collapsing sand formations and broken cobble rock. Around here it costs $8.50/foot to drill and install the pipe and grout. Figure on 100 lineal feet of bore hole per ton of cooling. The pump and dump systems (the ones where you actually pump out ground water and dump it back into a different well after it's circulated thru the system) gum up the heat exchangers with the fine silt. You valves will jam too. Better to go with a closed loop system. Phillips makes the HDPE pipe. Comes with a fifty year warranty and projected to last 200 yrs. Use methanol for the antifreeze, has better thermal transfer properties with less expansion. Cheaper than car antifreeze and better on the environment if you get a spill.Don't scrimp on the amount of wells. Space them apart to. at least 20', better is 30'. The wells have a tendency to warm up over the long run. It's called heat blooming. Comes from having lots more cooling loads thru the year than heating. Heat blooming shortens the service life of the ground loop system. Well depth/spacing /quantity is everything. Good subsurface conditions help--like flowing water strata deep down in.All in all a pretty good system once you take a careful look at all the pros and cons, and read and ask a million questions from everyone. Good Luck!!
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Roger: Here are the calculations: 3 gpm x 8.3 pounds/gallon x 10F temp difference (I'm assuming a drop from 60F to 50F) x 1 BTU/lb-F (heat capacity of water) x 60 min/hour = 15,000 BTU/hour = 4.3 kilowatts for you metric types.
Is that enough? I'm in a well insulated house but it was -40F this morning. If it were 1200 sqft, it would need 40,000 BTU/hour at that low a temperature. But a super insulated house would need only about 13,000, at -40F. So if the house is tight and your climate milder than an Alaskan winter, it's borderline. If you're in cheesehead land and aren't doing super insulation, you don't have enough water flow.
A bit about wells: They don't yield as much water when pumped continuiously as when pumped intermittently. Not nearly as much. A "cone of depression" develops around a pumped well and reduces the water level in and the flow rate to the well. For 100 to 300 gallons per day for domestic use, you only run the pump 2 to 7% of the day, giving the well a lot of time to recharge. But for heat pump use, that well will be pumped much of the day and flow will drop off.
Also to pump 3 gpm of water from 205 feet (90 psi) would take 1/2 hp or 350 watts. That's about 10% of the heat value of that water and electricity will cost you 3-6 times more than fossil fuels. So a quarter of your fuel savings might go into powering that deep pump.
Short answer: you need more water flow and would hope that it was from not so deep. Or look at using the thermal mass of the ground.
*Elwood: You've got a system that is all ready for one clever tweaking. To deal with that heat blooming, install some fin tube and fans to blow cold ambient air over the fins (during the coldest part of the year). Once primed with fluid, the radiator will cool the methanol and it will be denser than the relatively warm methanol coming up out of the ground. That density difference will drive a thermosiphoning of the methanol. No pump or controller needed. When there is heat to be lost, the methanol will flow. (You'll want a thermostat on the fan, just to save on energy). Similiar techniques (with antifreeze or with subliming crystals) are used in areas of permafrost to keep the ground frozen.If you can dedicate particular wells to heating versus cooling, you could even freeze some chunks of ground while warming up others in anticipation of the next season's need for heat/cold.Feel free to contact me. Sounds like a fun one. -David
*Trenches are 36" wide and down around 6 ft. Lucky me, frost line is about at the grass (Sacramento). Length is around 300 ft, but I was thinking of runing down each side of the trench.As it turns out, I went with a conventional system...next time perhaps. THere was a Electric Co incentive for energy efficient practices. I would up getting a check from them for $5500! But it required a "compliant" system...GHP didn't count. (The project engineer agreed it was ridiculous.)Per my research, the systems which use groundwater have notorious problems with contamination and scale buildup. Especially in hard water areas.Thanks for the info
*Rodger, You have a good start for a Geo system. I would trench down 3 or 4 feet for a slinky loop (put the leach bed or utilities in the same trench if you can) and put in series with a vert. loop in that 250" hole you allready paid for. Run the fluid thru the slinky loop first then the vert. loop. Fill in the well with mud or grout a Elwood mentioned. I would use 1'' or 1 1/4" pipe. I also like Command Air because they have the best price performance ratio. They make air to air, water to air, and water to water units for comm. and res. use, not just air to water like most other Geo only mfgrs. Their parent co. is Trane.
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To Dave Thomas or anyone with more thoughts on Geothermal. My question is about the "closed loop" system wherein a fluid (antifreeze) is circulated throughout the system. I don't believe that my community would allow for a drilled well system.
Comments, please
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David Thomas: are you a hydrologist? My second lap in college was all about geo- with emphasis in chemistry. Just curious.
*Windmill: A closed loop system has the advantage of not pumping groundwater up against gravity (only circulating the antifreeze at a low differential pressure) and, if used for both heating and cooling, that you are essentially storing summer heat for winter use and vice a versa. The down side is that you can't get as much heat out of a given length of well casing. You'll get heat from the soil and water as heat is conducted towards the well. There'll also be a convective aspect. As groundwater flows past your well, ambient temperature groundwater will replace the groundwater cooled by your system. But groundwater flow rates vary by orders of magnitude from one location to another. Permeable soils (clean sands vs. silts and clays) and steep groundwater gradients (usually occur where the ground surface slopes steeply towards a river, lake or ocean) correspond to higher groundwater flowrates. Best to get someone local to address sizing questions. Ask for AND CHECK references for people who have operated their systems for more than a year.Rich: I studied chemical engineering at Berkeley, have worked 10 years in environmental engineering (where the experience with wells comes from) and took my professional engineer registration in civil (cause they have more power than than chem engs).You know who the pioneers are? They are the ones with the arrows in their backs. -David
*Windmill - I had a geothermal system installed in northwest Florida ten years ago and have been quite pleased with it. It is a closed loop system with two 300' deep wells and a three ton WFI unit with desuperheater loop for hot water. The ground loop has plain water in it but perhaps a special liquid would be more efficient. Our house is 2700 sf and we keep it very comfortable for about $80 per month total electric bill (about 1/2 what our neighbors pay). I did get a leak in the freon/air coil but was fortunately able to repair it. I'm not sure I would recommend Water Furnace (WFI) as the freon cycle has been a little cranky and they were not a lot of help. You probably should look for a scroll compressor as I understand they are more durable.Good luck!
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I find the previous discussions fasinating since I am considering installing a geothermal system in a house we will be building this spring. I am from eastern Iowa and a common practice here is to use a single well for both the supply water and discharge. The supply water is pulled from the top of the water column and the discharge is placed in the bottom of the water column. This allows the discharged water to be swept away by the aquafer or mixed with other water to bring it back to the "normal" temperature prior to being brought back into the system. It also prevents the system from starving the well since nearly all of the water used for the heatpump is placed back in the same well. For extreme cases, a bypass valve is installed to divert the discharge to one of my two ponds if it becomes too cold or too warm. I am at the top of a hill and anticipate that the well will be 450 feet deep with the pump placed at approximately 180 feet. Using a single well system will save me about 4000 dollars on initial installation cost over a closed loop system. Also, with the climate around here the ground temperature surrounding a horizontal loop would rise or fall with the seasons and reduce the effectiveness of the system. The local utility said that the temperature of the closed loop system could drop as low as 20F during high heating demands. Also, the single well system helps prevent "thermal bloom" associated with the horizontal and vertical closed loops. The local utility company performed a heat gain/loss for me and provided a cost estimate of LP heat vs. geothermal. The predicted annual cost of LP, not including electricity to run the blower, was $850 and the cost for the geothermal, not including electricity to pump the water out of the well, was $250, this is for about 5000 square feet of heated space. I have not been able to quantify the effiency cost of thermal bloom on the closed loop system vs. the efficiency cost of pumping the well water. Therefore, I will probably have to just cancel them out and go with the intial savings of a single well system.
*Thanks for your comments. I am going down to Hilton Head in 2 weeks and plan to visit with the electric co. techie who gave me the initial recommendation to go with the vertical closed systemI'll fill the readers in when I return.
*I'm considering a closed loop vertical bore hooked to radiant slab in our new house. Can I use it to cool in the summer? An installer says that I'll have trouble with condensation if I circulate cool liquid in a slab during the summer. I don't get it. Anyone care to explain? I live near Denver. Summer temps can be 55-95 N/D with 15% humidity, or less. I figured that if I am uncomfortably hot and I go near a cool floor, I will become more comfortable. Espicially if I am barefooted. Also, the summer circulation will recharge the wells with heat for the winter.
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Jeff,
I have questions...What will this cost you for how many sqft of radiant slab...And what temperature will this system produce for circulating in the slab. And who makes the heat pump...and who is drawing up the total design?
Jack : )
*If your RH is really less than 15%, you could drop the temperature of the house air by 34F before you got above 50% RH - a good mark to shoot for comfort and to avoid condensation by a safe margin. Note that while heat rises off your radiant floor in winter, the cool air will stay low in summer. Unless you've got some way to kick that air around (fan or very low duct inlet), you'll have to lie on the floor to benefit. With that kind of a night/day temperature swing, can you cool the slab at night by running the heating/cooling fluid through a radiator outside? Get the slab down to 55 or 60F each night for very low electrical cost.
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I am planning to have a 3 BR house built on a 1/2 acre lot just outside Cincinnati, Ohio this year. My builder and architect are trying to change my mind about a geothermal HVAC system. I just read the latest issue of Fine Homebuilding and I am encouraged by the article on cohousing, which shows reasonably-priced houses with geothermal HVAC systems. The article mentions that the HVAC system was designed by a firm in Raleigh, NC. I can't find them on the internet. Does anyone know how I can find someone experienced to design such a system for my house here in Ohio???
*Hello I was reading all of your posts on geo thermal heating and cooling and would like some advice on finding the best choice of what system to use. We have a lot of land with our house and I was wondering if a horizontal system would be best. I know the cost of a well getting dug can be a nice price tag. I like information on systems so I can take a look at. Plus your thoughts on them as well. I think the system we have now is an electric thermal coil in the ceiling. No ducts. I want the system to work for both winter and summer. So what is my best choice? Your input will help me thank you......
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Harvanator: A few background questions (for more useful response later): Where are you located and what are the costs for available utilities?
-David Thomas, Kenai Alaska; Elec=$0.083/kwh, NG=$0.38/therm (cheap), oil=$0.92/gallon, and propane=$1.05/gallom.
*The house is located in South Jersey. I will post the utilities cost when I get a chance at home. From The Harvs
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Looking for comments on the vertical drilled system for Geothermal HVAC. Local power co seems to think this is best way to go on small lot in coastal South Carolina (basically sea level)