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Hidden luxury: Knightsbridge's ground source heat pumps

A luxury hotel development in Knightsbridge is pioneering an innovative method of placing pipework in a basement diaphragm wall. Gemma Goldfingle reports.

Knightsbridge’s latest hotel will have all the accessories one would expect to find in one London’s most expensive neighbourhoods: penthouse apartments, grand ballroom, luxurious spa and, of course, ground source heat pumps.

It is testament to the growth of this technology that Prime Developments, the client behind the five-star development, approached piling contractor Cementation Skanska with geothermal already in mind.

“Geothermal energy was always in the client’s specification,” says Cementation project manager Neil Abbott. “Originally they wanted to place pipework in both the diaphragm wall and the basement slab.”

Cementation is a pioneer in geothermal engineering in the UK. The firm developed its innovative energy pile technology, which draws heat and cooling from the ground surrounding the structural pile, in 2001 on Keble College in Oxford.

“The beauty of using foundations to generate heat is that it’s relatively simple. No specially trained people are needed.”

Neil Abbott

As piles are constructed, flexible plastic pipes are incorporated within the pile reinforcement cages. Upon completion of the foundation works, the sections of pipework embedded in the pile are plumbed into the building’s heating and cooling system.

The concrete forming the piles provides an ideal energy transfer medium, allowing the energy derived from the ground to be used to heat and cool the structure. The 10-storey Prime Knightsbridge development has a six-level basement requiring a 30m-deep perimeter wall.

Despite Cementation being a geothermal pioneer, it had never before inserted pipework into a diaphragm wall. “This is a first in the UK,” says Cementation Skanska geothermal manager Peter Smith. “It has been done overseas, which is why the client had heard about it, but never in the UK.”

Harnessing heating and cooling from diaphragm walls will open up a wealth of opportunities for ground source energy.

Plastic loops are attached to the pile reinforcement cage

Plastic loops are attached to the pile reinforcement cage

For example, ground source heat pumps could be incorporated into civils works as well as building projects. In fact, representatives from Crossrail and London Underground have visited the site to see the installation.

“I believe Crossrail is considering installing heat pumps into some of the station boxes. The Tottenham Court Road tender documents express an interest in geothermal,” says Smith.

At Knightsbridge Cementation has adopted techniques used at the NEO Bankside development on London’s South Bank to install the geothermal elements in the diaphragm wall.

At Bankside, a project both Smith and Abbott worked on, 52m energy piles - the UK’s deepest - were installed on the outside of the reinforcement cage, under bentonite.

“The system does require more capital. In times of recession clients can’t justify any extra up-front costs.”

Neil Abbott

“The beauty of using foundations to generate heat is that it is a relatively simple operation, no specially trained people are needed,” says Abbott. Once building work begins the pipework is plumbed into heat pumps in the building’s plant room.

This then converts the low-grade heat or cooling from the ground and upgrades it to a higher, more useful temperature.

With Smith insisting he cannot think of any foundation element that geothermal pipework could not be inserted into, and delays to construction minimal, is there any reason why a client would not adopt the technology on their scheme?

“Money,” says Abbott. “The system does require more capital. Although there is only five to seven years’ pay back, in times of recession clients can’t justify any extra up-front costs.”

Cementation Skanska began working on the £4M contract last September, and piling was due to finish last month.

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