Updated at 6.56pm: Some 174 schools in Hong Kong switched off their school air conditioning systems during Wednesday?s hot weather as part of a community energy-saving campaign, a student environmental group said on Thursday. The group, Footprint, said on their website that the exercise, carried out when temperatures reached 30 degrees Celsius, was done to emphasise just how much energy air conditioners use. It said that as much as 173,000 kilowatts of electricity ? worth $138,000 ? was saved on Wednesday. Some 109 tonnes of carbon dioxide emissions were also avoided ? a volume that takes a forest 2.7 times the size of a football pitch one year to absorb, the Footprint website claimed. Footprint was established by a group of university students in 2002. It said 174 primary and secondary schools participated in Wednesday?s ?No Air Con Day?. It is part of a three-month-long campaign which urged families and schools to shut down unnecessary electronic appliances and keep air conditioners above 25 degrees Celsius. Some 262,000 people from 174 schools and 300,000 have signed up to participate in the three-month campaign. The organisers hope 593,000kw of electricity will be saved. Footprint said it held the ?No Air Con Day? last year and it had attracted 250,000 people from 162 schools and 300,000 families. It said around 400,000kw of electricity was saved on Wednesday. ?Electricity consumed in school is very little compared with [energy consumed by] companies,? Footprint programme officer Leung Wing-kin said. ?But schools are the cradle of future leaders. They [the students] will be more environmentally conscious when they grow up,? ventured Mr Leung. According to Footprint, air conditioners account for 70 per cent of schools? electricity bills. They also account for 60 per cent of electricity consumed during the summer in Hong Kong.