prEN 17522

Design and construction of borehole heat exchangers

This document covers standardization in the field of geological and environmental aspects, design, drilling, construction, completion, operation, monitoring, maintenance, rehabilitation and decommissioning of borehole heat exchangers for uses of geothermal energy.
The direct expansion and thermal syphon techniques are excluded from this document

Planung und Bau von Erdwärmesonden

Dieses Dokument befasst sich mit der Normung von Erdwärmesonden für geothermische Anwendungen unter geologischen und Umweltaspekten und deckt dabei die Bereiche Auslegung, Bohrung, Ausführung der Sonde, Fertigstellung der Anlage, Betrieb, Überwachung, Wartung, Sanierung und Stilllegung ab.
Techniken mit direkter Ausdehnung und Thermosiphonen werden in diesem Dokument nicht behandelt.

Conception et construction des échangeurs géothermiques

Le présent document concerne la normalisation des aspects géologiques et environnementaux de la conception, du forage, de la construction, de l’exécution, du fonctionnement, de la surveillance, de la maintenance, de la réhabilitation et du déclassement des échangeurs géothermiques utilisables en géothermie.
Les techniques de détente directe et de thermo-siphon sont exclues du présent document.

Konstruiranje in izdelava vrtinskih toplotnih izmenjevalnikov

General Information

• Status: Not Published
• ICS: 07.060 - Geology. Meteorology. Hydrology
• ICS: 91.140.10 - Central heating systems
• Technical Committee: CEN/TC 451 - Geothermal and water boreholes
• Drafting Committee: CEN/TC 451/WG 2 - Borehole heat exchangers
• Current Stage: 4599 - Dispatch of FV draft to CMC - Finalization for Vote
• Ref Project: oSIST prEN 17522:2020 - Design and construction of borehole heat exchangers

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN 17522:2020
01-julij-2020
Konstruiranje in izdelava vrtinskih toplotnih izmenjevalnikov
Design and construction of borehole heat exchangers
Planung und Bau von Erdwärmesonden
Ta slovenski standard je istoveten z: prEN 17522
ICS:
07.060 Geologija. Meteorologija. Geology. Meteorology.
Hidrologija Hydrology
oSIST prEN 17522:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 17522:2020
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oSIST prEN 17522:2020
DRAFT
EUROPEAN STANDARD
prEN 17522
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2020
ICS 07.060
English Version
Design and construction of borehole heat exchangers
Planung und Bau von Erdwärmesonden

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

CEN/TC 451.

If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations

which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC

Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 17522:2020 E

worldwide for CEN national Members.
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oSIST prEN 17522:2020
prEN 17522:2020 (E)
Contents Page

European foreword ...................................................................................................................................................... 4

4.1 General................................................................................................................................................................ 7

4.2 Geological and hydrogeological risks ...................................................................................................... 7

4.2.1 Artesian aquifers ............................................................................................................................................. 7

4.2.2 Stacked aquifers with different groundwater potential ................................................................... 7

4.2.3 Groundwater and soil chemistry ............................................................................................................... 8

4.2.4 Gas occurrence ................................................................................................................................................. 8

4.2.5 Ground stability ............................................................................................................................................... 8

4.2.6 Swelling and shrinking minerals or soils ............................................................................................... 8

4.2.7 Contrasting geological sequence (Alternated bedding) ................................................................... 8

4.2.8 Karst geology .................................................................................................................................................... 9

4.2.9 Frost susceptibility ......................................................................................................................................... 9

4.2.10 Groundwater protection area .................................................................................................................... 9

4.3 Anthropogenic risks ...................................................................................................................................... 9

4.4 Environmental aspects ............................................................................................................................... 10

4.4.1 Influence on groundwater ......................................................................................................................... 10

4.4.2 Environmental Impact Due to Construction Works ......................................................................... 10

5.1 General.............................................................................................................................................................. 11

5.2 Borehole heat exchanger ........................................................................................................................... 12

5.3 Horizontal piping .......................................................................................................................................... 13

5.4 Manifolds ......................................................................................................................................................... 13

5.5 Thermal plant ................................................................................................................................................. 14

6.1 General.............................................................................................................................................................. 14

6.2 General Properties ....................................................................................................................................... 14

6.2.1 General.............................................................................................................................................................. 14

6.2.2 Plastic materials ............................................................................................................................................ 15

6.2.3 Connection methods .................................................................................................................................... 16

6.2.4 Metallic materials ......................................................................................................................................... 17

6.2.5 Heat transfer fluid ........................................................................................................................................ 17

6.2.6 Backfilling material ...................................................................................................................................... 18

6.3 Component selection criteria ................................................................................................................... 19

6.3.1 General.............................................................................................................................................................. 19

6.3.2 BHE loops ......................................................................................................................................................... 19

6.3.3 Horizontal pipes ............................................................................................................................................ 19

6.3.4 Manifolds ......................................................................................................................................................... 20

6.3.5 Heat transfer fluid ........................................................................................................................................ 20

7.1 Steps of Design ............................................................................................................................................... 20

7.2 Sizing ................................................................................................................................................................. 21

7.2.1 General.............................................................................................................................................................. 21

7.2.2 General methodology .................................................................................................................................. 22

7.2.3 Thermal properties of the ground .......................................................................................................... 24

7.2.4 Thermal Response Test (TRT) ................................................................................................................. 25

7.2.5 Calculation procedure ................................................................................................................................. 31

7.2.6 Simulation ....................................................................................................................................................... 32

7.2.7 Hydraulic design ........................................................................................................................................... 33

8.1 General.............................................................................................................................................................. 34

8.2 Site Preparation and planning ................................................................................................................. 34

8.3 Drilling .............................................................................................................................................................. 34

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8.3.1 General ............................................................................................................................................................. 34

8.3.2 Drilling diameter .......................................................................................................................................... 35

8.3.3 Drilling fluid ................................................................................................................................................... 35

8.3.4 Monitoring and Documentation of the Drilling Process ................................................................. 35

8.3.5 Backfilling........................................................................................................................................................ 35

8.4 Borehole Heat Exchanger Loop ............................................................................................................... 36

8.5 Borehole Heat Exchanger Loop Installation ....................................................................................... 36

8.6 Backfilling and Grouting procedure ...................................................................................................... 37

8.6.1 General ............................................................................................................................................................. 37

8.6.2 Grouting procedure ..................................................................................................................................... 37

8.6.3 Other backfilling procedure ..................................................................................................................... 37

8.7 Horizontal Piping .......................................................................................................................................... 38

8.8 Testing of BHE – Leakage Check, Flow Check, Grouting Check, Geophysical

Measurements ............................................................................................................................................... 38

8.9 Manifolds ......................................................................................................................................................... 39

9.1 General ............................................................................................................................................................. 39

9.2 Heat transfer fluid ........................................................................................................................................ 40

9.3 Filling of the System ..................................................................................................................................... 40

9.4 Drying of New Buildings ............................................................................................................................. 40

9.5 Commissioning .............................................................................................................................................. 40

9.6 Documentation .............................................................................................................................................. 40

10.1 Operation ......................................................................................................................................................... 40

10.2 Monitoring....................................................................................................................................................... 41

10.2.1 General ............................................................................................................................................................. 41

10.2.2 Temperature .................................................................................................................................................. 41

10.2.3 Pressure ........................................................................................................................................................... 42

10.2.4 Flow rate .......................................................................................................................................................... 42

10.3 Maintenance ................................................................................................................................................... 42

12.1 General ............................................................................................................................................................. 43

12.2 Heat carrier fluid .......................................................................................................................................... 43

12.3 Borehole heat exchangers ......................................................................................................................... 43

12.3.1 Backfilled boreholes .................................................................................................................................... 43

12.3.2 Water filled boreholes ................................................................................................................................ 43

12.4 Horizontal pipes ............................................................................................................................................ 44

12.5 Documentation .............................................................................................................................................. 44

Annex A (informative) Insulation of horizontal piping................................................................................ 45

Annex B (informative) Example simulation time ........................................................................................... 46

Annex C (informative) Commissioning Checklist ........................................................................................... 49

Annex D (informative) Examples of thermal conductivity and volumetric - heat capacity of

the underground ........................................................................................................................................... 51

Bibliography ................................................................................................................................................................. 53

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oSIST prEN 17522:2020
prEN 17522:2020 (E)
European foreword

This document (prEN 17522:2020) has been prepared by Technical Committee CEN/TC 451 “Water

wells and borehole heat exchangers”, the secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
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oSIST prEN 17522:2020
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1 Scope

This document covers standardization in the field of geological and environmental aspects, design,

drilling, construction, completion, operation, monitoring, maintenance, rehabilitation and

decommissioning of borehole heat exchangers for uses of geothermal energy.

The direct expansion and thermal syphon techniques are excluded from this document

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

EN 12201-1:2011, Plastics piping systems for water supply, and for drainage and sewerage under

pressure - Polyethylene (PE) - Part 1: General

EN 12201-2:2011, Plastics piping systems for water supply, and for drainage and sewerage under

pressure - Polyethylene (PE) - Part 2: Pipes

EN 12201-3:2011, Plastics piping systems for water supply, and for drainage and sewerage under

pressure - Polyethylene (PE) - Part 3: Fittings

EN 12201-5:2011, Plastics piping systems for water supply, and for drainage and sewerage under

pressure - Polyethylene (PE) - Part 5: Fitness for purpose of the system

EN ISO 15875-1:2003, Plastics piping systems for hot and cold water installations - Crosslinked

polyethylene (PE-X) - Part 1: General (ISO 15875-1:2003)

EN ISO 15494, Plastics piping systems for industrial applications - Polybutene (PB), polyethylene (PE),

polyethylene of raised temperature resistance (PE-RT), crosslinked polyethylene (PE-X), polypropylene

(PP) - Metric series for specifications for components and the system (ISO 15494:2015)

EN ISO 22391-1, Plastics piping systems for hot and cold water installations - Polyethylene of raised

temperature resistance (PE-RT) - Part 1: General (ISO 22391-1:2009)

EN 1057, Copper and copper alloys - Seamless, round copper tubes for water and gas in sanitary and

heating applications
EN 12449, Copper and copper alloys - Seamless, round tubes for general purposes

EN 1965-2, Structural adhesives - Corrosion - Part 2: Determination and classification of corrosion to a

brass substrate
EN 12168, Copper and copper alloys - Hollow rod for free machining purposes

EN ISO 1127, Stainless steel tubes - Dimensions, tolerances and conventional masses per unit length (ISO

1127:1992)

EN 10216-5, Seamless steel tubes for pressure purposes - Technical delivery conditions - Part 5: Stainless

steel tubes
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3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
aquifer

underground geological formations containing water that can be partially mobilised by gravity and

which of permeable and/or cracked or fractured rocks that allow enough transmission of groundwater

to create a significant flow and catchment of a significant amount of water
Note 1 to entry: An aquifer can be fully or partly saturated.

Note 2 to entry: Its upper limit is called the “top of the aquifer” and its base is called the “bottom of the aquifer”

3.2
aquitard

body of rock or stratum of sediment that retards but does not prevent the flow of groundwater from

one aquifer to another
3.3
borehole heat exchanger
BHE

consists of the borehole with a loop, to circulate a heat transfer fluid, and a borehole filling

3.4
BHE loop

part of the pipe system in the borehole, which contains the fluid for heat transfer

3.5
heat transfer fluid
HTF
fluid circulated through the BHE for the heat transport
3.6
BHE system
one or more BHE connected in one hydraulic circulation system
Note 1 to entry: It does not include the heat pump or circulation pump
3.7
ground source heat pump system
GSHPS

BHE system including the horizontal piping, manifolds, the heat pump and circulation pump

3.8
BHE field

area with several BHEs systems that are not connected in the same hydraulic circulation system

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3.9
backfill
material used for refilling any borehole or trench
3.10
grout

backfilling material composed of cement and water mixture and other additional components (clay

minerals, etc.)
3.11
fluid
gas, vapour, liquid or combinations thereof
4 Geological and Environmental aspects
4.1 General

The design shall check whether the location of the planned installation is situated in any areas defined

in spatial planning documents. These could be areas of special protection of natural resources (water

protection, nature protection) or areas of specific risks (endangered areas, landslides, contaminated

sites, etc.).

If the installation would be situated on such protected areas, it shall be verified that the design is in

accordance with the specific geological conditions.

It shall be checked whether there are hydrogeological conditions (artesian aquifers, shallow

groundwater table, perched groundwater, etc.) that could require special consideration or even impact

or risk assessments.

The designer shall assess whether the available geological and hydrogeological information is sufficient

for the project in question.
4.2 Geological and hydrogeological risks
4.2.1 Artesian aquifers

When the drilling penetrates into an artesian aquifer, the groundwater level rises over the orifice of the

borehole. Uncontrolled upwelling and pressure loss would occur from use of improper drilling

techniques or equipment selection. In certain cases, the upwelling (into shallower aquifers) might not

be directly evident. This represents the main risks when artesian aquifer is penetrated.

Drilling in the artesian aquifer is a risk. Special specifications regarding drilling methods and BHE

construction shall be implemented.
4.2.2 Stacked aquifers with different groundwater potential

Drilling through sealing layers between aquifers could result in leakage from one aquifer to another and

result in impact on chemical characteristics of groundwater or hydraulic conditions. This could also

cause an undesired drop or increase of groundwater level in one or more aquifers. Consequences could

be decreased productivity of water sources or deteriorated formation conditions.

Groundwater flow conditions and qualities can also be affected adversely where drilling penetrates two

or more groundwater layers. In this case, the possibility of uncontrolled water exchange between the

individual aquifers via the borehole needs to be taken into account. A hydraulic short circuit should be

avoided for groundwater protection reasons, especially where one of the penetrated layers contains

highly mineralized or contaminated groundwater.

If drilling would cross through several aquifers, at least the aquitards shall be sealed.

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4.2.3 Groundwater and soil chemistry

The chemical composition of the groundwater (high sulphate concentration, high salinity, etc.) could

adversely affect the sealing properties and stability of the backfilling.

Drilling or excavating near mineral water springs or wells could adversely affect the mineralogical

composition of groundwater.
4.2.4 Gas occurrence

Under certain geological conditions, gas of geogenic origin can accumulate in cavities and trap

structures in the subsurface. When drilling in these areas, the gas could leak uncontrollably through the

borehole and pose a safety risk (toxic or explosive gases) or an environmental risk (greenhouse gases).

Gas deposits could occur in areas with volcanic activity or above geological layers containing coal, peat,

hydrocarbons, sulphides, etc. If the risk of drilling gas at the project site is known or can be predicted

based on geological research, certain safety measures (e.g. explosion protection concept, special backfill

material) are required or the drilling depth shall be limited or the drilling shall be terminated.

4.2.5 Ground stability

Unstable ground could be found especially in the following geological situations:

— intensively fissured, faulted and breccia zones, provoking formation of natural or anthropogenic

cavities;

— soft fragile rocks representing unstable ground (e.g. volcanic or sedimentary rocks).

4.2.6 Swelling and shrinking minerals or soils

Presence of evaporates or swelling clays presents a risk of subsidence or swelling in the case of

connection of shallow or deep aquifers with evaporitic or clay layers because of unsuitable or hardly

feasible underground operations.
4.2.7 Contrasting geological sequence (Alternated bedding)

Geology is highly diverse, and could range from structures represented by unconsolidated sand, clay

and gravel going to very complex situations including unconsolidated or consolidated sedimentary

(sandstone, limestone – fissured and frequently karstified) or crystalline (metamorphic and igneous)

rocks. An adequate knowledge of the geological conditions and associated hydrodynamic properties of

the selected site represents the base for any BHE drilling project. Adequate prior analysis of site

conditions raises the probability of an efficient and long-lasting product; this also contributes to the

management and protection of groundwater resources (quantity and quality) to be exploited through

future projects (e.g. water wells of different purposes and configurations).

The lithological description of the geological sequence be drilled and the structural characterization of

the site area are both compulsory in order to provide sufficient information for the preparation of a

BHE design and provision of adequate drilling machineries and auxiliary equipment for efficient

construction works; whilst avoiding, minimizing and/or controlling the potential geologic risks during

drilling.

Depending on the complexity of the project and of the geological conditions, the standard set of topics

to be described should refer to the following aspects (if appropriate):

— occurrence and description of the regional geologic structure(s) - sedimentary basin, folded

structures and/or faults;

— the lithological (specific) description (from bottom to top or reverse) of the litho-stratigraphic units

(formations, beds, layers, or horizons) to be drilled;
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— occurrence and characterization of local tectonic (structural) discontinuities – faults, fissures,

fractures (particularly in case of hard rocks);

— occurrence and characterization of dissolution voids and channels (in case of carbonate and

evaporite rocks);

— hydrological aspects (groundwater chemistry, redox potential, depth of sweet/salt level, level of

phreatic groundwater, regional groundwater flow for every aquifer, hydraulic conductivity,

porosity / thermal parameters);

— inventory of other users in the vicinity (groundwater extraction wells, groundwater energy wells,

borehole heat exchangers).
4.2.8 Karst geology

Karstified zones can represent strong heterogeneity of the ground and risk of caverns. High probability

of occurrence of caverns leads to several risks: collapsing of borehole, subsidence of the ground, losses

of drilling fluids, problems with backfilling, turbidity and solids in groundwater, unstable temperature

of groundwater (too low in winter, too high in summer), hardly predictable, unreliable modelling.

Geological and hydrogeological conditions in the depth of karst area are often not sufficiently known to

make a reliable prediction without additional investigation.
4.2.9 Frost susceptibility

Because the temperature of the fluid in the BHE can be below 0 °C, there could be a risk of freezing the

soil causing upheaval of the horizontal part and affect the sealing properties of the borehole filling an

...