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A presentation by Iain Howley MD of Ground Source Consult Ltd to the member of The Chartered Institute of Builders (CIOB) on Ground Source Energy System Design.
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GROUND SOURCE ENERGY SYSTEM DESIGN FOR
Chartered Institute of Building
Iain Howley ( Director ) Ground Source Consult Ltd
19th March 2014
Presentation AgendaIntroduction to GSC LtdGround Source Systems – The DriversBrief Introduction to Ground Coupling Techniques
Closed Loop: • The Differing techniques & what suits what • Getting it wrong & the consequences
Open Loop: • How it works – variations in design• Design risks – The need for a skilled approach• Thermal modelling – How & Why
Case Studies: Open and Closed Loop
• Directors are from a drilling background and therefore have a very strong understanding of designing & installing ground heat exchangers
• Professional team headed by an IGSHPA Accredited GeoExchange Designer, Own Hydrogeologist / Groundwater & Thermal Modeller and own Drilling & Pipe Fusion Engineers etc
• Specialise in the design and consultancy of commercial open and closed loop systems – consider Design & Build roles for certain clients
• Completed schemes to date ranging from 5 kW to 2,200 kW
Ground Source Consult Ltd
• Originally, Part L Planning & The Merton Rule
• The growing desire to be green – Corporate Responsibility and desire to build, own or operate BREEAM high standard facilities
• New legislation regarding code for sustainable homes leading to increasingly ultra-efficient housing development
• The Renewable Heat Incentive ( RHI ) – 9.4p/kWh paid for upto 1500 full load hours of heating – Designed to accelerate ROI terms
• As de-carbonisation of the grid is introduced, ground source systems become increasingly desirable
Ground Source Systems – The Drivers
• Pre-design / planning advice
• Full feasibility investigation
• Transparent design by Certified GeoExchange Designer (CGD®)
• Demonstration of sustainability, efficiency and CO2 savings
• Full design responsibility
• Installation management ( supervision ) by experienced engineers
• Thermal groundwater modelling for open loop schemes
• All Environment Agency Regulatory Engagement
• Design & Build through Uponor Ltd
GSC - Services
Ground Source Heat Pumps - How It Works
http://www.kensaengineering.com/
When Should Ground Source Design be Considered?
But please not here
Feasibility Investigation and Preliminary Design
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HORIZONTAL CLOSED LOOP – OFTEN KNOWN AS ‘SLINKY’S
Used typically for domestic sites or can be used to serve larger projects such as schools where large area’s of land are available.
A 50m slinky row typically services around 3-4kW of heating load
FOUNDATION PILES Piles only offer limited heat exchange capacity because they are usually shallow & in London generally drilled into low TC clay
In our opinion, not enough research has been initiated into how heating and cooling via piles affects the pile itself
Free Drilling ? Cheap as Chips ? No its not ! There are wider reaching implications for a piled system verses other ground coupled techniques such as impact on build programme
POND, LAKE, RIVER or OCEAN CLOSED LOOP
Coiled pipe or SS plates are submerged in the water and using an existing lake or river can be a very cost effective heat exchanger system
Any development considering a water feature should perhaps keep in mind the potential to use it as a source for heat exchange
Used anywhere where a body of water is available. Can service both small and large systems depending on size of lake and through-flow of water
VERTICAL CLOSED LOOP( BOREHOLES )
Used on small or large schemes
Closed Loop Systems – The Rights & Wrongs
If you need more energy, you just need a bigger pipe or a larger cable
The Ground Source Energy Concept – Why is this important?
Why is ground source heat different from traditional resources?
• The ground is not an infinite resource• You are replacing or reducing dependency on these
with a Ground Heat Exchanger
Why is this not an infinite resource?Imagine the ground heat exchanger as a Battery on Trickle Charge
The Ground Source Energy Concept
Can the battery go flat?
When we hook a building up to a ground heat exchanger, if the “battery” isn’t man enough for the job, the battery could go flat.
To ensure this “battery” is sized correctly, the ground loop needs be properly designed by somebody who knows what they are doing.
What if you get it wrong? You don’t want to over-stress the ground.
The Ground Source Energy Concept
Who’s Designing your system ?
Certified GeoExchange Designer ?? Or Somebody who has downloaded the software ?
The Ground Source “Lottery” – Poor Approach
• 50 watts per metre gives a 7,000 m loop field;• Divide 7,000 m by 100 (a nice round number) to give 70
boreholes;• Arrange the boreholes 5 m apart because it says so on the
internet;• Arrange the boreholes in a square because it looks tidy on the
drawings;
Office Building: • 350 kW peak Cooling• 150 kW peak Heating
• Assess actual peak loads and annual loads;• Investigate the feasibility and “drillability” in outline
design work;• Undertake thermal analysis with in-situ thermal testing;• Determine a detailed load profile and specify heat pump;• Develop detailed design and establish system
optimisation;• Produce a transparent and detailed specification; and• Experienced drilling engineers supervise the installation
throughout.
Ground Source Design – The Right Approach !
To avoid playing the ground source lottery altogether, you need the following to be building and site specific:
Office Building: • 350 kW peak Cooling• 150 kW peak Heating
Getting it wrong !!
Drilling the borefield to the previous spec would have worked. But it would have needlessly cost an extra £175k.CGD reduced borefield by 3,000m !!
Over 10,000m of drilling in this proposal !!
150 kW peak heating and 80 MWh annually
350 kW peak cooling and 200 MWh annually
Our office
Borehole Depth
Borehole Spacing
Boreholes Required
Borehole Capacity (per borehole)
Effective Design 100 m 8 m 60 5.8 kW
Poor Design 100 m 5 m 9260 3.8 kW
150 kW peak heating and 80 MWh annually
350 kW peak cooling and 350 MWh annually
Our office
Borehole Depth
Borehole Spacing
Boreholes Required
Borehole Capacity (per borehole)
Effective Design 100 m 8 m 60 5.8 kW
Poor Design 100 m 5 m 92 3.8 kW
Poor Design 100 m 5 m 152 2.3 kW
Effective Design 100 m 12 m 92 3.8 kW
Poor borehole spacing results in more boreholes being required due to interference effects. At £3,000 - £4,000 per borehole, this increases the costs significantly.
350 kW peak cooling and 200 MWh annually
Greater Load Imbalance: increase annual cooling load to 350 MWh
Example Two: poor design on our office – when will this system fail?Using the original “rule of thumb” example: 60 boreholes, 5 m spacing, 100 m deep arranged in a square
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After 5 years, it would still just about be working at 35°C but efficiency would be unacceptably low
But after 7 years the system is close to total failure.
Correct Design:our typical single home would require a 53.4 m deep borehole.
Social housing
Interference effects:However, with 6 terraces in a row we have 6 m spacing between boreholes (one in each front garden). Interference effects increases the required borehole length to 66.2 m per household if correctly designed.
Poor design, resulting in reduced spacing between boreholes will increase the interference effect.
Furthermore, without thermally enhanced grout and having used incorrect pipe diameter the required effective length increases again to 85.3 m.
Open Loop System
Subject to Lengthy & Complex Environment AgencyRegulatory Process
Borehole Yield Likely ?
Sufficient and sustainable groundwater flow (and thermal store) in the aquifer?
Types of Open Loop SystemUnidirectional Reversible
cooling period
heating period
Borehole Construction – Critical Process
Borehole Construction: How important is experience in this?
Down-hole view from 83.0 mBGL
Down-hole view from 84.1 mBGL
Understanding Thermal Interference
Other Issues and Licensing
Environment Agency:• Protect existing users;• Abstraction licence; and Risk Assessment• Discharge consent.
Other issues:• Biofouling; and• Sand ingress.
From initial feasibility report to handover of working systemtypically takes at least 15 months
System Design and Risk Assessment using FEFLOW
•Finite-element simulation software;•2D and 3D Simulations;•Dynamic modelling of groundwater flow and
heat transport
Used to simulate the groundwater flow regime and heat transport resulting from the operation of open loop ground source heat pump systems.
Building & Calibrating the Model for Your Open Loop System
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Modelling ‘Fine-tuned with a Thorough Site Investigation
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Site Investigation and Conceptual Model
Numerical Model
Open Loop Design
Risk Assessment Modelling• Derogation of the environment or other protected rights:
Open Loop Design Modelling One:• How Efficiency/Sustainability is affected by horizontal
separation of the boreholes:Large Borehole Separation Small Borehole Separation
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Abstraction Borehole
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Investigate How Efficiency and Sustainability are affected by plant (e.g. dry air cooler):
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Open Loop Design Modelling Two:
Open Loop Design Modelling Three:
Groundwater Gradient:
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Mean Gradient Abstraction BH
Maximum Gradient Recharge BH
Maximum Gradient Abstraction BH
Modelled Scenarios: Flow Mechanism – Long Term
FM: Fracture modelEPM: Equivalent Porous Medium model
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Abstraction temperature is
critical for direct
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CASE STUDY 1: LARGE CLOSED LOOP SYSTEMLMB CAMBRIDGE – Background to New Build
The birthplaces of molecular biology, notably the sequencing of DNA.
LMB has attracted 9 Nobel prizes shared amongst 13 LMB scientists.
Designed by RMJM architects Main contractor BAM Construction
Start date: Summer 2008Main contract: April 2009Completion date: due in 2012
Whole project value of £200 million
The total area will be 27,000m2 of fully air-conditioned space.
All heavy plant servicing the building is housed in the four stainless steel-clad towers linked to the building. This removes weight and sources of vibration from the laboratory itself, allowing a more lightweight construction.
CASE STUDY 1: LARGE CLOSED LOOP SYSTEMLMB CAMBRIDGE – GSHP Details
• 1,600 Kw Peak Cooling• 170 Boreholes• 152 Metres Deep• Approximate borefield size 150 m x 45 m
CASE STUDY 2: LARGE OPEN LOOPRIVER ISLAND Headquarters – Background to Refurbishment
Driver: Corporate Social Responsibility Policy for the Environment
M&E Engineers: CJ Design Partnership Limited
Office and design studio Refurbishment with a total project value of £2 million
Start date: May 2007Completion date: December 2009
CASE STUDY 2: LARGE OPEN LOOPRIVER ISLAND Headquarters – GSHP Details
1,400 Kw Peak Cooling
Serviced by: 6 Boreholes • 3 Abstraction • 3 Recharge
Each 130 Metres Deep
Collectively abstractingand continually recharging 60 l/s to and from the Chalk Aquifer approximately 70 m below ground level
Thanks for listening
Iain Howley
Design, Installation Management and Consultancy Services for Commercial Ground Source Heating & Cooling Projects
Unit 5, Hope & Aldridge Business Park · Weddington Road Nuneaton · Warwickshire · CV10 0HFTel: 024 76 629762 l Email: [email protected] l Web: www.gscltd.co.uk
