Overview
EN ISO 17628:2015 - Geotechnical investigation and testing - Geothermal testing - Determination of thermal conductivity of soil and rock using a borehole heat exchanger (ISO 17628:2015) specifies an in situ test method (Geothermal Response Test, GRT) for determining the thermal conductivity of soils and rock using a borehole heat exchanger (BHE). The standard covers installation and testing of vertical or inclined boreholes (examples given up to about 400 m length and diameters up to ~200 mm) using liquid heat transfer media that do not undergo phase change. EN ISO 17628:2015 is intended to provide reliable ground thermal parameters for the design of geothermal exchange systems and thermal storage.
Key topics and technical requirements
- Geothermal Response Test (GRT): measurement of temperature response to a known thermal forcing or extraction in a BHE to derive ground thermal properties (thermal conductivity, borehole thermal resistance).
- Borehole heat exchanger installation: requirements for drilling rigs, installation methods, BHE materials (U‑tubes or coaxial), annular space filling materials and heat transfer fluids.
- Test equipment and procedure: instrumentation, test execution, data recording, test duration and procedures for obtaining reproducible temperature response data.
- Data evaluation and reporting: methods to evaluate thermal conductivity and borehole resistivity, presentation of measured values and interpreted results.
- Site and safety requirements: pre-installation information, environmental protection, safety standards and site reinstatement following testing.
- Documentation: prescribed field reports, installation records, annular filling records and example forms and graphical presentations (annexes included).
Applications
EN ISO 17628:2015 is used to obtain accurate, site-specific ground thermal parameters critical for:
- Designing ground source heat pump systems and borehole field layouts
- Sizing geothermal heat exchangers and thermal storage systems
- Reducing design uncertainty for heating and cooling installations
- Supporting feasibility studies and energy performance modeling
Using standardized geothermal testing methods improves system efficiency and contributes to carbon-emission reduction goals by enabling optimal use of geothermal energy.
Who should use this standard
- Geotechnical and geothermal engineers
- Energy consultants and HVAC designers
- Drilling and ground‑works contractors installing BHEs
- Research laboratories performing in situ thermal testing
- Project owners, building services designers and local authorities assessing geothermal projects
Related standards
Normative references commonly used with EN ISO 17628:2015 include:
- ISO 14688-1 (soil identification and description)
- ISO 14689-1 (rock identification and description)
- ISO 22475-1 (sampling methods and groundwater measurements)
- EN 16228‑1 / EN 16228‑2 (drilling equipment safety)
Keywords: EN ISO 17628:2015, geothermal testing, borehole heat exchanger, thermal conductivity, Geothermal Response Test, ground source heat pump, in situ thermal testing.
