TEST BORING, GROUND TEMPERATURE AND FORMATION THERMAL
CONDUCTIVITY TESTING
PART 1 – GENERAL QUALITY ASSURANCE/ LOCATION OF WORK
1.1 SCOPE
A. Local and State laws and ordinances as they pertain to geothermal vertical bore construction shall be strictly followed.
B. The Geotechnical Subcontractor must have a minimum of two years company experience in test boring and thermal conductivity testing of vertical bore ground heat exchangers. Experience must include not less than 10 successfully completed thermal conductivity testing events. A list of previous tests shall be made available upon request.
1.2 LOCATIONS
Provide Geothermal Conductivity Testing as specified herein at the following locations to be determined by the Design Consultant.
PART 2 - VERTICAL HEAT EXCHANGER INSTALLATION
2.1 SCOPE
A. A vertical heat exchanger (VHE) with a completed bore depth of 210 feet shall be installed according to these specifications. The completed VHE shall be located as shown on site plan or as directed by Owner or Owner’s agent. A completed VHE shall consist of the vertical bore with an approved polyethylene u-bend assembly installed to the completed bore depth with an approved thermally enhanced bentonite grouting material installed in the bore annulus.
B. Contractor shall take all necessary precautions to protect the site from any damage resulting from the drilling operation. No drilling waste or ground water shall be introduced to any existing stream, river, lake, pond, or in any manner which violates local, State and Federal laws and regulations.
C. Contractor shall be responsible for all permits and following all applicable codes and regulations. Where any discrepancy exists between local codes and regulations and this specification, the more stringent of the two documents prevail.
D. Contractor is responsible for obtaining potable water as necessary to perform the work.
2.2 EQUIPMENT
A. The vertical bore can be advanced by either mud-rotary, air-rotary, airpercussion, or sonic coring method, which ever is most feasible based on geological conditions.
2.3 POLYETHYLENE U-BEND ASSEMBLY
A. The polyethylene u-bend assembly shall be manufactured from a polyethylene extrusion grade material having a minimum cell classification of PE345464C per
ASTM D-3350 and shall fully comply with the ISGHPA standard 1C "Ground Heat
Exchanger Materials". The u-bend shall be factory assembled and pressure tested to 100 psi prior to insertion into the vertical bore. The u-bend pipe diameter shall be 3/4 inch (19 mm), 1 inch (25.4 mm) or 1-1/4 inch (31.8 mm)
IPS-OD as determined from the table below:
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U-Bend Pipe Diameter Completed Bore Depth 1 in. (25.4 mm) Polyethylene 201 to 300 ft B. U-bend piping shall have factory printed lengths on the sidewall to indicate length of the pipe at any point. The printing shall read zero on one end and the actual heat exchanger total length on the other end.
C. U-bend pipe shall be factory assembled, fusing two continuous lengths of pipe to a U-bend fitting at one end. Manufacturer shall hydrostatically test the assembled U-bend piping at the greater of 125 psi or 1 ½ times the maximum working pressure for a period of four hours. Pipe shall be capped on each end prior to shipment.
D. U-type fittings shall be shop fabricated under quality controlled conditions of the same material designation. These fittings shall be factory fused to the pipe. No field fusions of pipe installed within a bore, encapsulated by grout or cement, will be acceptable.
2.4 GROUTING MATERIAL
A. Unless otherwise specified by State regulation, the annular space between the vertical bore wall and the u-bend assembly shall be filled with a thermally enhanced bentonite grouting material with a minimum solids content of 20%. The grouting material shall be mixed in strict accordance to the manufacturers mixing instructions. Grouting material shall be placed using a pressure pump with a tremie pipe system. The material shall be installed from the bottom to the top of the vertical bore.
B. Providing State regulation allows and in the event that a geological formation is encountered that prevents the grouting material from forming a solid seal, either a 3/8 inch (9.5 mm) or 3/4 inch (19 mm) granular bentonite material may be used through that specific formation zone. Upon completion of that specific zone, the grout slurry shall continue to be used until reaching the surface of the vertical bore.
C. The minimum thermal conductivity of the installed grouting compound must be not less than .75 Btu/hr-ft-° F as determined when tested in accordance to ASTM
D-5334.
2.5 EXECUTION
A. The diameter of the vertical bore shall not be greater than 6 inches (152.4 mm) and shall not be less than 4.5 inches (114.3 mm). The final diameter shall be determined by the drilling contractor's available equipment.
B. The completed bore depth shall be as specified herein, with an acceptable deviation of not greater than +/- 5%. The completed depth shall be determined by the placement of the u-bend pipe. The distance from the bottom of the u-bend to the surface shall constitute the completed bore depth.
C. Extreme care shall be taken not to crush, cut or otherwise damage the pipe.
No field fusions shall be utilized to repair damaged u-bend pipe.
D. Prior to installation into the borehole, the u-bend shall be filled with water and pressurized to 100 psi and monitored for five minutes to verify leak free integrity.
E. Retractable weighting devices shall not be utilized. If weighting of the u-bend is required to aid in the installation, steel or iron bars may be attached at the base of the u-bend pipe to overcome buoyancy. Any weights must be prepared as to prevent damage to the pipe.
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F. Prior to installation of the pipe into the bore, a temporary 1” to 1 ½ HDPE tremie pipe shall be attached to the U-bend, so that the discharge end of the tremie is near the base of the u-bend to ensure complete borehole grouting.
G. After installation into the bore, both ends of u-bend pipe shall then be taped or capped to prevent the introduction of soils or other debris. Do not purge or otherwise drain water from pipe.
H. Grouting material shall be mixed according to manufacturers written instructions.
I. To prevent collapse of the bore wall, the bore shall be completely grouted within two hours of insertion of U-bend pipe into the borehole.
J. Grout material shall be pressure pumped through the tremie pipe and placed in the bore annulus from the bottom to the top. Grouting process shall conform to
State Regulations, the manufacturer's instructions, and "Grouting for Vertical
Geothermal Heat Pump Systems -- Engineering Design and Field Procedures
Manual", as published by the International Ground Source Heat Pump
Association (IGSHPA), Oklahoma State University (OSU), 2000.
K. Retract the tremie pipe as the bore is filled with grout.
L. Since some settling may occur after initial placement of the grout material, the
Drilling Contractor shall monitor the borehole and continue adding grout as required to ensure complete bore sealing to grade. Grout shall be allowed to slightly mound at grade to ensure complete filling of the bore annulus.
M. At minimum, 5 feet of each pipe shall extend above grade.
PART 3 – BORE DEPTH CONFIRMATION AND UNDISTURBED GROUND
TEMPERATURE TEST
3.1 SCOPE
A. The Bore Depth Confirmation is required to obtain a +/- 1% accuracy in final installed ground heat exchanger depth.
B. The Undisturbed Ground Temperature Test is to determine the average design ground temperature of the formation for the completed bore depth before circulation or other agitation of water contained in loop pipe.
C. Temperature of the water contained within the u-Bend pipe is obtained before connecting to a conductivity testing unit, circulating, inputting heat or otherwise disturbing the water.
3.2 EQUIPMENT
A. The temperature testing device shall have the capability of collecting the water temperature at depth and transmitting that data to a digital display viewable above grade. No other method of obtaining Undisturbed Ground Temperature is approved. The combined accuracy of the temperature display and thermocouple shall be +/- 0.5 o
F.
B. The Depth Confirmation device shall be a coil of wire or cable having footage indicators factory printed on it in 1’ minimum increments. Length of coil shall be at least 20’ longer than the depth of bore to be tested. A weight at the end of the wire/cable shall be utilized to facilitate lowering of the cable to the installed depth of the pipe. Maximum diameter of the weight and wire/cable shall be sufficiently small enough to facilitate unrestricted insertion to final depth. Weight must be securely fastened to wire/cable so as to prevent detachment of weight resulting in obstruction of pipe.
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3.3 TESTING SEQUENCE AND ELAPSED TIME BEFORE TESTING
A. A mandatory minimum delay of five days must be allowed between vertical heat exchanger grouting and Ground Temperature testing.
B. Ground Temperature testing shall occur before Depth Confirmation to minimize fluid disturbance within pipe.
3.4 GROUND TEMPERATURE TESTING PROCEDURE
A. Without flushing, evacuating or otherwise disturbing water, insert thermocouple probe into water filled pipe.
B. Unless otherwise specified, record fluid temperature at the greater of 100’ or the midpoint of bore depth. Allow temperature to stabilize before recording.
3.5 BORE DEPTH CONFIRMATION PROCDURE
A. Utilizing a tape measure, Record length of pipe extending above grade.
Measure/record only the pipe to be utilized for insertion of Bore Depth testing device.
B. Insert Bore Depth testing device into pipe and lower weighted wire/cable to installed depth of pipe. Prevent restriction and insure device is lowered completely to U-bend fitting.
C. Record depth indicated on wire/cable, subtract length of pipe extending above grade.
PART 4 - FORMATION THERMAL CONDUCTIVITY TEST
4.1 SCOPE
A. The Formation Thermal Conductivity test is designed to determine the average thermal conductivity of the formation for the completed bore depth.
4.2 EQUIPMENT
A. The testing device shall be designed so that a constant, measured rate of heated water is circulated in an uninterrupted fashion through the U-bend assembly.
B. The testing device shall have the capability of automatically collecting data at pre-determined intervals. Collected data shall be available to the design engineer in an electronic format compatible with Microsoft Excel®.
At minimum the following data must be collected: a) Time b) Fluid supply temperature to U-bend assembly c) Fluid return temperature d) Current to heating device e) Voltage to heating device f) Fluid flow
C. The accuracy of the temperature measurement and recording devices shall be not less than +/- 0.5° F.
D. The combined accuracy of the power transducer and recording device shall be not less than +/- 2%.
E. The testing device shall be designed so that a constant rate of heat input into the vertical U-bend assembly shall be not less that 51 Btu/hr (15 W) per bore
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foot. The selected heat rate shall not be greater than 85 Btu/hr (25 W) per bore foot.
F. The testing device shall be designed to prevent as much heat loss to the environment as possible. Each exposed end of the U-bend assembly shall be insulated with a closed-cell insulation to prevent heat loss or gain.
G. Flow rate shall be sufficient to maintain a Reynolds number equal to or greater than 2300. Additionally, rate shall be sufficient to provide a loop temperature differential of 6 to 12° F.
4.3 DATA ACQUISITION FREQUENCY, DURATION AND QUALITY
A. Data shall be recorded at a maximum interval of 5 minutes. Unless otherwise specified, data shall be recorded at this interval for 40 hours without interruption.
4.4 POWER QUALITY
A. Power shall be applied continuously. The standard deviation of input power shall be less than or equal to 1.5%, and peaks less than or equal to 10% of average power applied for the duration of the test. Any power interruption resulting in a delta fluid temperature deviation of 1° F or greater, when compared to a trend line of the full data set, shall render the test a failure and require retesting.
4.5 RETESTING IN THE EVENT OF FAILURE
A. In the event a test should prematurely fail, the Undisturbed Ground
Temperature shall be allowed to naturally return to within 0.5° F
O f the initial temperature as measured in Part 3 above.
PART 5 – DATA ANALYSIS AND REPORTING
5.1 ANALYSIS
A. Data shall be analyzed using the Line Source method and shall follow
ASHRAE standards as defined in the 2003 HVAC Applications handbook.
5.2 REPORTING
A. The final report shall include the following
1. Detailed test bore report including the following information: a. Each formation type encountered (drill log) b. Each formation depth (in feet) c. Depth of any significant cracks, fissures, voids or caverns encountered d. Static water depth (if encountered) e. Manufacturer, blend and bag quantities used of both grout and sand f. Diameter, SDR rating and length of pipe used g. Date of installation
2. Undisturbed ground temperature readings
3. Test initiation date
4. Test duration and declaration of any interruption to data gathered and/or power during the test
5. Calculated thermal conductivity
6. Estimated thermal diffusivity
7. Average input power, standard deviation and peaks
8. Average flow
9. Graphical representation
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a. Plot of supply/return temperatures for entire test duration b. Plot of temperature vs. logarithmic time with slope calculation c. Average temperature plot and trend line for entire test duration d. Plot of heat rate applied (W) e. Plot of temperature differential
END OF SPECIFICATION
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