Geothermal Tunnel Linings - WorkshopAgenda 08.30 Registration & Coffee, Breakfast

09.00 Introduction & Welcome

09.15 Principles & Benefits of tunnel geothermal energy Duncan Nicholson, Director ARUP Geotechnics

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09.45 Installing geothermal pipe in Tunnel linings Ralf Winterling, Technical Director REHAU Ltd

10.15 Energy lining segment design and construction Case History Dr. Jan-Niklas Franzius, Zblin AG

10.45 Discussion and questions

Tunnel Geothermal Linings- Principles, Benefits, and Potential Issues

Duncan Nicholson 15/02/2011 Presented at Geothermal Tunnel Lining Workshop

Contents

Background Geothermal tunnels

cold tunnels and hot tunnels Connecting tunnels to buildings Impaction of ground conditions Market and distribution

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Benefits Potential issues

below surface: pipework connections, fire safety and structural integrity

above surface:- access installation:- impact on tunnel construction programme

Background Ground Sourced Heat Energy

Open Systems Water wells Extract water 500kW / hole

Closed Systems Vertical or horizontal loops Extract heat 3.5kW / hole

Source: Commercial Earth Energy Systems (Canada Natural Resources)

Geothermal Piles and Sprayed Lining

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Geothermal Piles at

One New Change,

Arup (2009)

Austrian Sprayed concrete lining at Lainzer Tunnel,

After Brandl (2006)

Other Infrastructure Projects Loops are used in;-

Diaphragm walls Base slabs Linings of the station tunnels, eg metro NATM tunnel lining, Channel Tunnel heat-exchange pipes

Crossrail

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Diaphragm wall, Brandl (2006)

Crossrail Redevelopment above stations: Thermal diaphragm walls Thermal piles

Geothermal Tunnel Concept

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Access points at 500m centres for each tunnel

Position of pipes inside tunnel segment

Thermal Loops Inside Segment

Box out section for the pipe connections.

Hot TunnelsHot Tunnels:

Tunnel air temperature higher than ground Heat Energy mostly from tunnel

Mainly for building heating helps to cool the tunnel Not efficient for cooling building Tunnel

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Hot tunnel locations :- cable tunnels, foul sewers, Deep/long rail and road tunnels

Not efficient for cooling building Tunnel Heat source

Ground Heat source

Cold tunnelsCold Tunnels:

No tunnel heat source Tunnel air temperature low Provides building heating and cooling Heat energy mostly from soil mass not tunnel

No tunnel

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Cold Tunnel locations Short road and rail tunnels Cold climates Good natural air ventilation

No tunnelheat source

Ground Heat source

Cold Tunnel Example Janbech Tunnel

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Details to be given by Dr Franzius from Zblin

Linking Header pipes to surface

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Existing access points

Shafts, stations, entrances,

Dedicated access points

Boreholes

Vertical Drilling Connect cross passage or tunnel

202 casing with 110mm pipeVerticality tolerance

1 in 200 (+/-100mm at 20m depth)

2 boreholes per access point for header and return~ 40K for a pair~ 40K for a pair

Inclined Drilling14m

Connect to cross passage /tunnel

225 liner with 2 x 110mm pipe inside .

1 borehole per access point

Verticality tolerance 1 in 200 +/-100mm at 20m depth Up to 35o from vertical

Cost 33K

Directional Drilling Connection surface site 50-100m from tunnel 300mm liner with 2 x 110mm pipes Magnetic guidance system

Accuracy +/-0.1o

49K for 100m

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Impact of Ground Conditions

Tunnels in Clay: Heat stays, - local conduction Access boreholes - easy to construct

Heat conduction

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Tunnels in Sand: Heat dissipates with ground water

flow Access borehole are difficult to

construct water bearing sand. Grouting required

Ground water flow

Thermal transfer Heat transfer mainly from hot air inside tunnel to

heat buildings.

Heat transfer from plastic pipe 30w/m2

Assume pipe loops at 0.5m centres in rings

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Assume pipe loops at 0.5m centres in rings Power out put is 15 x 40m = 0.6KW/m of tunnel.

For 6m dia tunnel 1000m long = 600kW.

Thermal Transfer Modelling - SetupOuter radius: temperature fixed at 15C

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Heat extracted from pipes at rate equivalent to 30W/m2 of tunnel surface

Inner surface: receives heat from tunnel air q = (Tair Tseg).

Heat Transfer - Hot Tunnels

Heat extraction rate = 30W/m2(Constant)

Tunnel air temperature = 25oC

Pipe temperature = 17.6oC

All heat extraction comes from

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All heat extraction comes from the tunnel

For pipe flow rate of fluid = 0.27l/s

Flow temp = 14.6C approxReturn temp = 20.6C approx

Market for Tunnel Geothermal Low grade energy source use locally

Residential buildings heating demand Office blocks cooling and heating demands

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Old buildings - refurbishment New buildings - renewable source requirement

Helps at Planning Stage with Part L

Cools tubes / ground reduces ventilation costs

Typical London Residential Building

Typical 5 Storey refurbished buildings heating needs 40-50W/m2 of floor.

Say 16 flats /building unit Space heating 40kW. Hot water 25kW.

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Hot water 25kW.

Similar to 50 to 100m long tunnel section.

Market for Tunnel Geothermal

Building options: Existing buildings: residential housing dominated by space

heating over the cold season, topped with DHW Existing building: office/retail complex, heating and cooling New buildings - heating and cooling

Base Load and Peak Load

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Base Load and Peak Load Combined GSHP and gas boiler

GIS mapping of potential users along tunnel alignment

Buildings Identification Stage GIS

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Distribution of Tunnel Geothermal

ESCO typeso Privately-owned ESCOs - More efficient at running district heating schemeso Private ownership - Only really works for large schemes (billing complexity)o Publicly-owned schemes - Difficulty growing (profit reinvestment constraint)

Renewable Heat Incentiveo The indicative tariff is 1.5p/kWh for heat generated

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o The indicative tariff is 1.5p/kWh for heat generated

Main Heat Supply Optionso 1: Tunnel owner retains ownership of assets, identifies customers and sells heato 2: Tunnel owner becomes ESCO, - installs tunnel / access pipework and sells heat

directlyo 3: Tunnel owner sells heat rights to an ESCO who installs access pipe work

Benefits of Tunnel Geothermal

Benefits

Tunnel geothermal energy is renewable, low carbon, sustainable.

Compatiable with Ground Source Heat Pumps Cheaper that vertical borhole loop options. Similar cost to thermal piles

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Similar cost to thermal piles

Payback time can be viable in many cases Provides an option for Cooling the Tube or

adjacent tubes.

Cost Benefit Analysis Gas comparison

1970s Council Block

Central Boiler Room

800kW Gas boiler

Base Case

400kW Gas boilerGSHP (cost of above ground works only)

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400kW Gas boiler400kW Heat pump

ground works only)

GSHP (including cost of below ground works)

400kW Gas boiler400kW Heat pump+ Ground Works

Cost Benefit AnalysisAnalysis of differential costs/revenues above the central gas boiler retrofit baseline

Capital Costs Above Ground: Installed gas boilers/heat pump- 800kWth total thermal system

size, 400kWth heat pump. Below Ground: hard dig trench & man hole; borehole connection; tunnel lining

pipework installation.

O&M Costs

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O&M Costs Maintenance of building systems Sinking fund

Fuel Costs

Revenue RHI @ 1.5p/kWh heat generated CO2 @ 12/tonne. Approx saving of 80 tonnes CO2/yr

Key Financial Figures

Basecase

GSHP Excluding Below

Ground Works

GSHP Including below

ground works

CapEx () 80,400 144,200 269,000

O&M Costs (/yr) 4,200 15,000 15,000

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CO2 Sold at 12/tonne Sinking fund factored- 15years for Heat Pump, 25 years for boiler

Fuel Costs (/yr) 26,800 22,000 22,000

Revenue (/yr) 0 13,400 13,400

Added Benefit Cooling the Tube

Extracted significant heat from tunnel Reduce cost on cooling/ventilation system

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Potential Issues and Risks

Pipe joint Rotation

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Joint rotation effects Max ring deformation = 1% of dia.

Joint rotation is 1.45 degree

Joint opening = 150mm tan 1.45

= +/- 3.8mm

Combined box out lengths = 0.3m

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Combined box out lengths = 0.3m

Loss of lining area due to plastic pipes

Lining thickness = 300mm Plastic pipe diameter = 20mm % reduction in Area = 20/300 = 6.7% Not significant

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Not significant

Fire Safety Assessment

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Single segment Single ring Small circuit

Large circuit

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Exposed pipework, eg header pipesNeed to satisfy fire / smoke requirements set out by rail operatorsMitigation measures to be assessed if needed

Connected Building

Access Point

HP

Heat pump

Structure Integrity - Fire

Pipework inside segments could impact on the structure integrity of the linings

Pipework performance under fire needs could be detrimental to linings

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Above Surface Access

Restrict on drilling Drilling risks Connection inside tunnel

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Impacts on Tunnel Design and Construction

Impact on segment erection Impact on space use inside tunnel Impact on construction cost Impact on tunnel maintenance

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Impact on tunnel maintenance

Conclusions

1. Thermal tunnels are an extension of GSHP systems2. Hot and cold tunnels effects heat outputs.3. Effect of ground conditions water4. Tunnel pipe work installed during construction5. Access from Shafts - Boreholes provide flexibility6. Consider Market surface building needs

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7. Commercial case Cheaper than borehole loops 8. Detailed tunnel design issues

- Concrete stresses- Joint rotation- Fire impacts- Surface connections- Seasonal heat load peak demands tunnel heat input

Thank you for your attention

Any Questions?

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Any Questions?

Buildings Indentification

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NPV

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Upper Value: CO2 sold at 50/tonne; sinking fund not considered

Lower Value: CO2 not tradable; sinking fund factored- 15years for Heat Pump, 25 years for boiler