A project in the US has helped save $840 million (£529m) in energy costs since 2011.

Businesses that took part in the Better Buildings Challenge programme cut 94 TBTUs of energy waste since it was first launched four years ago.

It also saved six million tons of carbon emissions – equivalent to one million cars.

The project involves more than 250 partners from 50 cities and states and challenges them to reduce their energy use by 20% in the next 10 years.

It is also setting a new water saving goal, the Energy Department states.

Ernest Moniz, Energy Secretary said: “As the Better Buildings Initiative enters its fourth year, leaders continue to showcase how saving energy saves money, creates jobs and most importantly accelerates the nation’s competitiveness in the clean energy economy while preserving our environment for generations to come.”