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stevehull · 11-26-15, 03:08 PM

Details on my "pump & dump" (open-loop) geothermal situations.

Water sources are two 250 ft deep wells in multi-strata sand/shale/clay layers. Water table typically about 30-40 feet from surface. Ground water temp ~ 60 F. Water of minimal hardness and with low iron.

Two 1.5 HP 240 V submersible pumps each about 150 feet down - each can pump 30-35 GPM. One is a back - up the other is actively used. The pumps feed into two 60 gallon bladder air tanks in parallel. This is so that if one fails, the other tank will prevent short cycling (early/premature death) of the submersible pump. Pump cut-off/on at 40/60 PSI. Bladder tanks set 5 psi below that and large bladder tank capacity markedly decreases pump cycle frequency.

Cheap kWhr electricity ($0.08 in summer, $0.07 in winter). About double the number of cooling degree to heating degree days so the lower winter kWhr rate helps.

At least 10 kW of PV to go onto shop next spring/summer. Wind is plentiful here but it can't compete with $1.25/watt for PV (self install). Putting up a 10 kW wind turbine on a 100 ft tower is NOT a self install issue.

Local utility does month to month net metering paying about 1/2 of retail back when you supply surplus to grid.

Three WaterFurnace water to air heat pumps (two sorta new and one very old). The two new (8 and 4 years old) units are true two stage with variable ECM motors. One is a 24K BTU (stage 2) 18K BTU (stage 1) for a guest house (1600 ft sq) with COP of 5 and EER of 35. The old farm house has a 36 KBTU/24K BTU (stage 2/1) for about 2900 sq ft (COP 5, EER 35). The old 1 ton unit is a resurrected unit I patched together that heats/cools shop (COP 3, EER 25). All water lines from geo units go to livestock waterers that supply ~ 100 head. Output of waterers then drain passively to ponds that are then used for irrigating pastures. Have warm water in winter and cool water in summer 24x7 for livestock. Ponds are back up for that.

Prior WaterFurnace open loop installed in 1991 in prior home (2 ton and 3 ton) and savings put at least two kids through college. No repairs to either unit in almost 25 years (exception air filters).

The issue I am contending with now is to continue to use pump and dump or to put in some vertical or horizontal loops. About 25% of my heating/cooling cost is well pump operation. It is expensive to pump up water to 40/60 psi, much less to a lower pressure. That is why I am considering putting the geo units on a 20/30 PSI setting (or lower) and using a water psi booster pump for those few occasions when I need high pressure in house (showers, for example).

Horizontal loops are expensive here due to caliche rock ~ 3 feet down. But plenty of acreage to do this on. Have dug many a trench with an excavator crawler - hard to go 8 feet down through 2 feet of caliche. Ponds are not deep enough for loops in them. Vertical loops can be done, but thick caliche rock (very hard) requires substantial drilling rig ($$).

Tax credits, farm depreciation and rebates from the local electric coop made geo incredibly affordable. Now looking at using the standby well for a DX system - wonder where I heard of that . . . .

Steve

11-26-15, 03:08 PM	#1817
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	Details on my "pump & dump" (open-loop) geothermal situations. Water sources are two 250 ft deep wells in multi-strata sand/shale/clay layers. Water table typically about 30-40 feet from surface. Ground water temp ~ 60 F. Water of minimal hardness and with low iron. Two 1.5 HP 240 V submersible pumps each about 150 feet down - each can pump 30-35 GPM. One is a back - up the other is actively used. The pumps feed into two 60 gallon bladder air tanks in parallel. This is so that if one fails, the other tank will prevent short cycling (early/premature death) of the submersible pump. Pump cut-off/on at 40/60 PSI. Bladder tanks set 5 psi below that and large bladder tank capacity markedly decreases pump cycle frequency. Cheap kWhr electricity ($0.08 in summer, $0.07 in winter). About double the number of cooling degree to heating degree days so the lower winter kWhr rate helps. At least 10 kW of PV to go onto shop next spring/summer. Wind is plentiful here but it can't compete with $1.25/watt for PV (self install). Putting up a 10 kW wind turbine on a 100 ft tower is NOT a self install issue. Local utility does month to month net metering paying about 1/2 of retail back when you supply surplus to grid. Three WaterFurnace water to air heat pumps (two sorta new and one very old). The two new (8 and 4 years old) units are true two stage with variable ECM motors. One is a 24K BTU (stage 2) 18K BTU (stage 1) for a guest house (1600 ft sq) with COP of 5 and EER of 35. The old farm house has a 36 KBTU/24K BTU (stage 2/1) for about 2900 sq ft (COP 5, EER 35). The old 1 ton unit is a resurrected unit I patched together that heats/cools shop (COP 3, EER 25). All water lines from geo units go to livestock waterers that supply ~ 100 head. Output of waterers then drain passively to ponds that are then used for irrigating pastures. Have warm water in winter and cool water in summer 24x7 for livestock. Ponds are back up for that. Prior WaterFurnace open loop installed in 1991 in prior home (2 ton and 3 ton) and savings put at least two kids through college. No repairs to either unit in almost 25 years (exception air filters). The issue I am contending with now is to continue to use pump and dump or to put in some vertical or horizontal loops. About 25% of my heating/cooling cost is well pump operation. It is expensive to pump up water to 40/60 psi, much less to a lower pressure. That is why I am considering putting the geo units on a 20/30 PSI setting (or lower) and using a water psi booster pump for those few occasions when I need high pressure in house (showers, for example). Horizontal loops are expensive here due to caliche rock ~ 3 feet down. But plenty of acreage to do this on. Have dug many a trench with an excavator crawler - hard to go 8 feet down through 2 feet of caliche. Ponds are not deep enough for loops in them. Vertical loops can be done, but thick caliche rock (very hard) requires substantial drilling rig ($$). Tax credits, farm depreciation and rebates from the local electric coop made geo incredibly affordable. Now looking at using the standby well for a DX system - wonder where I heard of that . . . . Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990