Bigger can be better 
St Paul goes horizontal

where: Trenton, ON
what: secondary school, 7,500 m² (80,000 ft²)
when: 1988

Like many of its academic counterparts throughout Ontario, St Paul Catholic High School is a single story building with conventional insulation (R-12 in the brick and block cavity wall, R-20 in the roof, 15% fenestration). 

But the Hastings - Prince Edward County Roman Catholic Separate School Board decided to do something a bit unconventional a decade ago, when it decided that it wanted to incorporate an earth energy system that would provide heating, cooling, and air conditioning for the facility. 

St Paul is one of Canada's largest horizontal ground-loop installations; heat comes from 17,000 metres (50,800 ft) of 3-cm piping that is buried throughout the sports field in a horizontal configuration. All pipe is at least 1.5 to 2 metres below grade, where the earth's solar heat can be transferred easily into the building and sent to individual classrooms which have their own heat pump unit and controls. 

The main mechanical room is only 13 m², and each classroom has its own heat pump unit and control. The earth energy units, with combined capacity of 113 tons, are decentralized throughout the building to provide local comfort to each classroom, and allow each teacher to control his or her own environment to reflect occupancy and use. 

System costs were below many conventional space conditioning systems: 

- HVAC components cost $10.80 per square foot;
- electrical cost $6.50/ft²;
- plumbing cost $5.60/ft²

Annual energy consumption is also quite impressive. The school consumes 485,000 kWh (or about 6 kWh/ft²) for its HVAC system, and another 275,000 kWh (about 3.5 kWh/ft²) for lighting and power. The total of 9.5 kWh/ft² (equivalent) translates into an electric peak load of 3 W//ft²

Although the ground loop array is extensive, it is buried and protected from accidents or vandalism, and the circulating pumps and earth energy units are also located inside the school envelope for greater protection from humans and the elements. Inside the mechanical room, the largest pipe is 8 cm diameter, and most components are smaller than the parts of a conventional combustion heating system. 

Indoor air quality is an increasingly important issue for school boards, and the ventilation rate at this school is 7.5 cfm per student. Heat recovery ventilators provide an efficient and economic method to pre-heat and pre-cool make-up air, thereby increasing the environmental benefits of the school and its students. 

 "These sheets are made possible through a contribution from Natural Resources Canada."