This document compares the performance of three different geoexchange loopfield designs: a traditional U-loop system, an Earthlinked direct exchange (DX) system, and a Kelix Thermacouple system. The U-loop consisted of two 500-foot boreholes while the DX used five 100-foot boreholes and the Thermacouple used a single 306-foot borehole. Monitoring of the systems found that while the Thermacouple and DX designs had shorter borehole lengths, the U-loop was able to reject more total heat over time, suggesting borehole resistance impacts efficiency. Overall, shorter borehole designs like the Thermacouple and DX can be viable alternatives but ground performance, not manufacturer claims,

1. Comparison of Three Different
Geoexchange Loopfields
Daniel W. Felten, P.E., CGD
World Energy Engineering Conference
October 2011

2. Background
 ECS purchased abandoned
factory in 2007.
 Terraclime Geothermal
began business operations
in 2009
 Redeveloped 3rd floor
(7,000 SF) for our offices
 Needed our first
geothermal project to get The “Mill”
going!!! Florence, MA

3. Geothermal Demonstration Site Design
 Industry standard “U-Loop” has been around for
decades. It works, but…
◦ High drilling costs (150 to 200 ft of borehole per Ton)
◦ Grouting with high TC grout costly
◦ Land “hog” with 2 to 3 Tons (500 ft) every 20-25 ft
◦ Many competitors installing U-Loops
 Thermacouple and DX offered enticing claims with
limited penetration in the market…

4. Thermacouple Claim:
A Thermacouple earth energy system…allows the
earth to exchange up to 5 tons of thermal energy…”

5. Reducing Drilling Requirements
◦ Kelix Thermacouple
could reduce drilling
depth by more than
60% (if claim true)
◦ One 306 foot Kelix
can provide “up to”
5 Tons of
heating/cooling

6. Earthlinked DX System Claim
“Typically, the earth loops are 100 feet per ton of
capacity.”

7. Reducing Drilling Requirements
◦ Direct Exchange
(DX) uses
refrigerant in copper
earth loops
◦ One ton per 100
feet of borehole
◦ 3 inch diameter
borehole means
quicker drilling and
less grouting, less
disturbance

8. Final Systems Configuration
 5 Tons Direct Exchange (DX)
◦ Single stage Cu ground loops
◦ Manufacturer - EarthLinked Technologies
 5 Tons Water Based “U-Loop”
 5 Tons Water Based Concentric Tube “Kelix
Thermacouple”
 Outside water systems interchangeable
◦ U-Loop 2 x 500’ / Thermacouple 306’
 Water Based Manufactures: Carrier & WaterFurnace
 Data Acquisition using Web Energy Logger (WEL)

9. Drilling U-Loop
 Two 500-foot
boreholes, 6”
diameter, 1000 feet
total
 Bentonite sand grout
 HDPE Tubing
 25% EtOH
 2.5 days to
complete
 5 Tons Total
 $12/Ft = $12,000

10. Installing Loops Damaged U-Loop
U-Loop Installation

11. Installing KELIX Thermacouple
 One 306-foot borehole, 6”
diameter
 Geo Supergrout
◦ Cementicious TC=1.0
 4” diameter outer casing
 1.5 days to complete
◦ recent modifications has reduced
install time to 0.5 – 1 day)
 5 Tons Total
 $14/Ft X 306 ft = $4,384
 Plus, $5,500 materials
 Total Cost = $9,884

12. Thermacouple (Casing and Head)

13. Thermacouple Field Fabrication

14. Thermacouple – Finished Wellhead

15. Drilling DX Boreholes
 Five 100- foot holes, 3”
diameter
 Geo Supergrout
 Copper Earthloops
 One day to complete
 $2000/Ton = $10,000

16. Smaller DX Drill Rigs

17. DX Earthloop (Earthlinked)

18. Drill Tooling and DX Earthloop
Copper
Earthloops

19. DX Manifolds

20. DX Exposed Manifold
Manifolds
Five 100’ Earth Loops

21. DX Linesets (Interior) DX Linesets (Exterior)
DX Installation (at the Mill)

22. Real Time Monitoring and Data
Acquisition-Web Energy Logger (WEL)
 Real Time Monitoring
and Data Acquisition
◦ Temps
◦ Pressures
◦ Flows
◦ Watts
 Performance
Reporting
◦ COP/EER
◦ Troubleshooting

23. Data Acquisition & Analysis
 Each system is instrumented at key locations
◦ Ground Loop (temps and flows)
◦ Air Handler (temps)
◦ Geo System (temps, pressures, amps)
◦ Ambient air & earth temps
 Data acquired at one minute intervals (NOTE:
DON’T TRY THIS AT HOME!)
 Systems were started up July 2009

24. http://welserver.com/WEL0201/

26. DX System Performance Summary
DX Modification Progression
COP Heat < 3 •Original installation, R407c
•Pressure Oscillations due to component
sizing mismatch, refrigerant characteristics
COP/EER Cooling •R407c changed to R22
~3.3/11.3 •Flow control changed
Cooling capacity 5 •Glide eliminated
Tons confirmed •System pressure losses remain due to
distribution & volume

27. DX (Direct Exchange)

29. Mill Systems Performance Summary
Water Based Systems
Water Systems Comments
Carrier COP/EER •R410a Two-Stage compressor option
< 6/20+ provides max performance benefit by
rejecting condensing heat @ 90F into
ground @ 56F operating in 1st stage
WF COP/EER •R410a & Two Stage similar max benefit
~6/20+ •North side building provides cooling
advantage

30. Water (25% Ethanol)
COP
3.5 – 4.1 (heating)
5.5 – 6.1 (cooling)
(ground systems interchangeable
with geothermal systems)

31. Thermacouple Cooling Performance

32. Comparative Analysis - Cooling

33. Normalizing Data - BTU vs. ∆ EWT
 U-Loop
◦ Initial EWT = 56 F
◦ Max EWT = 69
◦ Delta EWT = 13 F over 72 minutes
◦ Total BTU Rejected = 93,000 BTU
◦ Rate = 6.5 Tons
 Kelix Thermacouple
◦ Initial EWT = 65 F
◦ Max EWT = 85 F
◦ Delta EWT = 20 F over 72 minutes
◦ Total BTU Rejected = 77,000 BTU
◦ Rate = 5.3 Tons
50% greater EWT rise with 20% less BTU rejected

34. Normalizing Data

35. Capacity Evaluation
 Normalized to a Delta EWT = 13F
(eg., how many BTUs does it take to get a 13 degree delta)
◦ U-Loop: 93,000 BTU (@ 6.6 Tons)
◦ Kelix: 35,000 BTU (@ 5.4 Tons)
 Thermacouple Equivalent Capacity (relative to U-
Loop) = 0.376
Kelix Capacity = 0.376 X 6.6 Tons = 2.5 Tons
Equivalent to 120 feet/Ton
U-Loop at 152 ft/Ton
Thermacouple is ~20% more efficient?

36. Is this a valid analysis?
15 minutes
•These two geothermal systems
rarely cycled for 72 minutes
•The majority of cycles for both
systems were under 15 minutes

39. It’s the ground, stupid…
 We can force heat into/from the ground using
earthloop “improvements”
 The shorter the borehole, the greater the thermal
gradient required
 The “improvements” are really about eliminating
borehole resistance

40. Decreasing Borehole Resistance and
Increasing Efficiency
 Thermacouple
◦ Greater turbulence with lower pressure drop (reduced
pumping penalty)
◦ Minimizes “cross talk” between inlet/outlet piping (PVC
inner pipe)
◦ Better Grout: TC >1.0 vs 0.8
◦ More Conductive Casing: Fiberglass vs HDPE
 Direct Exchange
◦ Highly conductive copper earthloop
◦ Better Grout
◦ No pumping penalty (other penalties may apply…)

41. Decreasing Borehole Resistance and
Increasing Efficiency
 U-Loop systems work well and are easy to install
 DX and Thermacouple are viable alternatives for
smaller sites and/or higher drilling costs
 The manufacturer claims should be ignored -
ground performance drives the system design
 Need to develop equivalent models for DX and
Thermacouple

42. System Comparisons