arup_presentation_tunnel geoheat source uk 21 02 11
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Tunnel Geothermal Linings- Principles, Benefits, and Potential IssuesDuncan Nicholson15/02/2011Presented at Geothermal Tunnel Lining WorkshopTRANSCRIPT
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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
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Tunnel Geothermal Linings- Principles, Benefits, and Potential Issues
Duncan Nicholson 15/02/2011 Presented at Geothermal Tunnel Lining Workshop
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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
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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)
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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)
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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
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Geothermal Tunnel Concept
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Access points at 500m centres for each tunnel
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Position of pipes inside tunnel segment
Thermal Loops Inside Segment
Box out section for the pipe connections.
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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
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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
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Cold Tunnel Example Janbech Tunnel
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Details to be given by Dr Franzius from Zblin
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Linking Header pipes to surface
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Existing access points
Shafts, stations, entrances,
Dedicated access points
Boreholes
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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
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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
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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
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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.
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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).
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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
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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
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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.
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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
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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
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Benefits of Tunnel Geothermal
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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.
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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
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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
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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
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Added Benefit Cooling the Tube
Extracted significant heat from tunnel Reduce cost on cooling/ventilation system
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Potential Issues and Risks
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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
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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
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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
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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
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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
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Thank you for your attention
Any Questions?
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Any Questions?
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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