An Ontario university has cut its greenhouse gas emissions -- not to mention its air conditioning bill -- using a relatively simple technology.

The University of Guelph built a 30-metre-high tank that cools 22 million litres of water each night. The water is piped around campus during the day, cooling classrooms, offices and labs.

The thermal energy system cost about $15 million to build but the university says it already has saved about $2.5 million on its electricity bills since the system went online earlier this summer.

John Kuri, who works for the energy consultancy MCW, said the savings come partly from the fact that it takes less energy to cool things at night, and partly from the fact that Ontario electricity is cheaper from 7 p.m. to 7 a.m.

It’s cheaper during those so-called “off-peak hours†because Ontario is forced to supplement its nuclear and hydroelectric sources during the day by burning natural gas, which creates climate-changing carbon emissions.

At night, the energy is basically “emissions-neutral†Kuri said. That means the university’s new system is also helping to slow climate change.

Ontario Minister of Energy Glenn Thibeault, who toured the facility Monday, told reporters that innovations like these allow the province to avoid spending “billions of dollars†to build new nuclear plants.

It’s one of the reasons the Ontario government chipped in $5.8 million toward the cost. Students also contributed, through a special fund that’s collected alongside tuition fees.

According to Kuri, thermal cooling systems are relatively common in the southern U.S., but Guelph’s is the first of large-scale system of its kind in Ontario.

With a report from CTV Kitchener