Borehole Cooling

Why is traditional air-conditioning a problem?

Traditional air conditioning used in the majority of modern offices uses highly energy-intensive refrigeration plant. These can consume up to half of a building's energy consumption and cause air pollution as well. Such heavy energy consumption has environmental as well as financial costs, contributing to air pollution and climate change.

Beaufort Court

Ideally, a sustainably-designed building is cooled by encouraging air to flow through the building from the ground floor windows to vents in the roof. This is what architects call 'natural ventilation'. At Beaufort Court we have adapted this principle to suit the environment and pump naturally cool water from the ground using a 75m deep borehole. Deep down below the thick layer of impermeable clay that the London Basin sits on is a layer of chalk that is saturated in water (the 'aquifer'). The water here sits at a constant temperature of about 12ºC. This is water can extracted using borehole and a pump and then circulated around the building using underground pipes to cool the office buildings.

Construction

The 200mm wide borehole was 'percussion drilled' to a depth of 75 metres through several different layers of rock. By this method, a hollow metal tube is repeatedly dropped from a rig. The weight of the tube falling pushes some soil/chalk into the tube. Every few drops, the soil/chalk is rinsed out of the tube. The only force is gravity - there is no mechanical drilling.

Operation

The water is pumped out at 5 litres per second. While the water is surprisingly clear when it comes out of the aquifer, it is filtered before it enters the building to remove grit. The water level in the aquifer is hardly affected by the extraction. First it is used in the Air Handling Units to cool and dehumidify the incoming air, which then travels via floor vents to cool the building. Then the water itself is circulated at around 15ºC (just above dew point, to avoid condensation) through 'chilled beams' around the upper floor, cooling the air inside. Finally, the water is pumped out, along with the run-off from the car park, to irrigate the energy crop growing in the fields nearby before returning to the ground. The temperature in each office is controlled centrally by a computerized Building Management System, which automatically adjusts it as required.