Deep heat

As you walk across the Millennium Bridge in London, you can’t miss the new luxury residential development rising on the south bank adjacent to Tate Modern. Heating for these new buildings will be provided partially by geothermal energy piles® drilled 52 m deep into the ground to harness the natural energy of the earth. A total of 130 energy piles® with more than 22,000 metres of geothermal pipes imbedded into them, are linked to heat pumps, which will provide 760 kW of heating and 650 kW of cooling energy to the residences, accounting for 10 per cent of total energy consumption.

With fossil fuel depleting and energy bills on the rise, urgent action is needed to explore alternative and cheaper means of energy supply and reduce our reliance on gas and oil.  Looking upwards to the sky to harness wind and solar energy is not the only way to meet the world’s huge appetite for energy. Deep within the earth is an untapped source of energy: geothermal energy. Although it’s just a small part of a bigger picture, this fast developing technology is able to make a significant contribution to the built environment.

The basic concept behind geothermal energy is simple. As every child learns at school, the soil gets warmer and warmer as you go deeper and deeper underground. At about 4,000 miles below the ground surface, the temperature is extremely hot, in fact hotter than the sun’s surface. Geothermal energy is essentially the heat energy generated and stored within the earth. However, geothermal energy can also refer to heat transfer caused by the application of sunlight on the soil during the day and release during the night, and heat transfer from man-made structures such as tunnels buried in the soil.  At shallow depth soil largely maintains a constant temperature below 15 to 20 metres from the ground level. By drilling down into the earth, it is possible to exchange and store heat with this reservoir.

Large scale geothermal exploration is undertaken in a number of countries for the purpose of electricity generation utilising heat transported through very deep boreholes.  However, shallow geothermal capture for heating buildings has seen slow progress in the UK. This may be because the British planning system and the construction industry tend to be conservative and, in some cases, over-cautious in embracing new technologies. The pioneers in geothermal technology for residential buildings are the Swedes, who have shown how it can work through ground source heat pump systems.  As the UK government is increasingly eager to promote Carbon Footprint reduction across all business streams, tapping into the geothermal heat is surely one of the most efficient ways of achieving this goal.

Take energy piles® for example: a high strength PVC pipe is installed inside the pile during the pile construction process. The top end of the PVC pipe running along the pile is connected to a heat pump unit. The heat pump functions as an air conditioner by ‘moving’ heat from one source to another. By circulating the refrigerant along the PVC pipe in the ground, geothermal energy can be continuously converted for the normal domestic heating and cooling.

The new buildings at Bankside were planned right from the onset to incorporate energy piles.  During the construction a high strength PVC pipe was attached to the reinforcement cage along the piles along with a novel sensor to monitor fibre optic strain and temperature. This sensor is a vital component of a monitoring programme which will provide a thorough understanding of the long-term behaviour of pile foundations in response to mechanical and thermal changes.

In practice, engineers are concerned about stability.  Pile foundations must be able to accommodate structure loads, as well as the thermal loads. The slow uptake of geo thermal piles stems from concerns about how the continuous changing in temperature might affect the structural capacity of pile foundations. This is where my PhD research comes in. My work, which is sponsored by Cementation Skanska (who is the pioneer in promoting energy piles® industry), looks at the geotechnical behaviour of energy piles, with the view to understanding how temperature modifies the soil-bearing capacity and provide certain design guidelines for the industry. Working with engineers from different disciplines, including structural, geotechnical and geothermal engineers on the Bankside project, has provided me with a great insight, particularly in measuring and interpreting field measurements from the behaviour of real structures.

In parallel, it is important to appreciate the potential disadvantages of the general application of this new technology, which is resource-sharing. If one building taps into the geothermal energy, then adjacent buildings may encounter problems if they want to share the same geothermal resource and they may have to settle for the expensive solution of drilling deeper.

I first became interested in engineering when I was at school where I was the kind of student who would take things apart to find out how they worked. I studied Civil Engineering at the China University of Geosciences and then moved to South Korea to take a Masters in Geotechnical Engineering.  After working for SK Engineering & Construction, I made a change in direction and studied environmental science in Switzerland. It was life changing to observe how a glacier had progressively receded in the space of just ten years.  When I saw with my own eyes the evidence of how climate was affecting our planet, I decided to look for a practical engineering technology which would provide environmentally friendly solutions. I was fortunate enough to be able to come to Cambridge where I am based at the Schofield Centre, part of the Engineering Department.

Working on a technology that is still in its infancy is hugely exciting – but also very challenging.  There are so many barriers to overcome in order to take an idea from conception to reality. The Bankside building will be a showcase for the long term monitoring of operational energy piles® in the UK. This study will be used to demonstrate the validity of this technology and encourage awareness of its potential. In a few years’ time perhaps residential buildings will make use of energy piles or energy boreholes for domestic heating or cooling. The cost of installing and running these geothermal systems is expected to reduce with time.  The planning regulations and design guidelines will be updated to facilitate the wider applications of the geothermal energy and I would be more than happy to be part of this bigger picture.