A House Divided

With its red brick exterior, Edwardian entryway and small tower rising above the second storey, 31 Sussex Avenue looks run down, but still possessed of its 19th-century stateliness.

This university-owned house, though, has become part of a research project that makes its future much more interesting than its past. Kim Pressnail, a professor of civil engineering, and one of his former students, Russell Richman, a professor at Ryerson University, are stripping the house to its bones, and rebuilding it with “nested thermal zones” that should make it up to 80 per cent more energy-efficient.

“Normally within a single family dwelling, there is one zone – everything is heated to the same temperature,” Pressnail says. “Our concept is to create two thermal zones within that building – a core zone and a perimeter zone – and insulate them both. Occupants then have the option of heating only the core.” He adds that the perimeter zone can be heated in a matter of hours, meaning the occupants don’t have to say goodbye to their guest bedroom for the entire winter.

Building thermal zones into new homes is easier, but this project is meant to test how well houses can be retrofitted. “This house is probably the toughest assignment we could have. It was built in 1879,” says Pressnail. “It’s a listed historic property, so we can’t change the facade. There are also internal architectural features we don’t want to change.”

If thermal zones prove viable at 31 Sussex, it will demonstrate that the concept is viable for almost any home, he says. Pressnail and his research team plan to augment energy savings through the use of a heat pump. Unlike conventional heating methods, heat pumps don’t actually generate heat. Instead, they move existing heat from one place to another – extracting heat from one area and releasing it in another.

Refrigerators and air conditioners use heat pumps to remove energy from a contained space and expel it into the environment. But that process can be reversed: a heat pump can draw energy from cooler air and pump it into the core of the house to warm it.

Heat pumps run on electricity, but it takes less energy to move heat than to generate it. In fact, the closer the inside and outside temperatures are, the more efficient a heat pump becomes. In a conventional house, a heat pump would draw energy directly from the outside, meaning that on a cold day, it would not be much more efficient than other heating methods. But in a zoned house, the pump can draw heat efficiently from the perimeter zone, which is warmer than the outside.

In these circumstances, a heat pump can be up to three times as efficient as other methods. (And during hot summer months, heat pumps can work in the opposite direction, creating energy-efficient cooling.)

Pressnail’s team plans to complete the retrofit by June. For the following year, a designated occupant will live in and operate the house as efficiently as possible – providing a best-case scenario. Subsequently, the property will become a home for visiting faculty with less stringent operating instructions – allowing the researchers to assess how people actually make use of the options available to them.

At current electricity rates, Pressnail says, it would take about 15 years to recoup the additional costs of building thermal zones in a new house, and longer for a retrofit. But he believes energy costs will rise faster than inflation, meaning the savings become more significant over time. He also points out some side benefits. “The walls are warmer, the house is less drafty and it’s quieter,” he says. “A low-energy home is more comfortable.”