Hotel Verde near Cape Town airport claims to be the greenest in Africa. Among the environmentally-friendly systems used to build and run the hotel are 100 underground boreholes that regulate the building's temperature, saving on energy costs. Other smart technology includes intelligent control that switches off air conditioning in unoccupied areas and ground-source heat pumps that use underground water to help respond to the building's heating and cooling needs. The hotel's sustainability engineer explained how it works. "We can circulate water through these pipes, and basically access the temperature of the ground. In summer what that means is when we've got lots of cooling demand, we've got excess hot water. So just imagine it's a 30 degree day outside, which is quite common here in Cape Town, and the ground is at an undisturbed 19 degrees, so we circulate hot water through the ground. It cools down by getting rid of some of that energy to the ground and comes back up cooler," said Andre Harms. As well as geothermal water temperature control, environmentally-friendly techniques were used to reduce the amount of building material used. Hollow recycled plastic balls were mixed in with the cement. While maintaining the building's structural integrity, this method reduces the amount of concrete used - up to one third according to engineers. A considerable saving considering how much energy it takes to produce cement . The recycling of grey water, the relatively clean waste water from baths, sinks, washing machines, and other kitchen appliances, for use in toilet flushing for instance, also helps bring down the hotel's consumption. And finally, rainwater and subsoil water is also put to good use. "The water table is somewhere in the region of my waist and that needs to be drained out of here. And basically what we do as opposed to dumping that into storm water, we're actually moving it into the tank from where we can use it for car washing, irrigating and other outside activities," says Andre Harms. Solar panels located on the northern face of the building not only provide power but also shade for the windows that get the most sun. While keeping fit, hotel guests also contribute to the power supply when using the gym. And the elevators partly run on regenerative power, which makes use of excess elevator energy, saving up to one third of electricity usage. As for the hotel garden, it is irrigated with rainwater and subsoil water that has been filtered using aquaponics, a system of aquaculture in which fish waste supplies the nutrients for underwater plants, which in turn purify the water. The garden provides the hotel's chefs with fresh vegetables and herbs for their dishes. It is estimated that all these water-saving measures help reduce the amount of drinking water used by up to one-third. The aim is to keep the hotel's carbon footprint as low as possible: "We grow our own lettuce and herbs in our aquaponics and we are also in the process of starting our own vegetables. And we're sourcing our vegetables from small companies within a 160-kilometre radius," says sous-chef Yolande Burger. euronews knowledge brings you a fresh mix of the world's most interesting know-hows, directly from space and sci-tech experts. Subscribe for your dose of space (Mondays) and sci-tech (Wednesdays): eurone.ws/Y9QTy3 Made by euronews, the most watched news channel in Europe.

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