April 24, 2008

NATURAL RESOURCES CANADA

The Drake Landing Solar Community in Okotoks Alberta features 52 homes equipped with two solar collectors on each house to provide domestic hot water. The panels on the garages collect the sun's energy for space heating and send heated glycol back to the central collection and distribution building located in the subdivision.

Point-Counterpoint

Still lots of life left in mechanical systems

PETER KENTER

correspondent

While the idea of eliminating mechanical systems from buildings has appeal, increasingly efficient systems have a bright future, says Skip Hayden, a Senior Research Scientist with Natural Resources Canada (NRCan).

“I agree with the goals of creating net zero buildings, but if you use efficient mechanical systems you’re already doing awfully well regarding energy consumption,” says Hayden. “If you can generate some electricity to sell, you’re essentially using no energy.”

Hayden argues that existing buildings can be “tightened up” and outfitted with more efficient systems in the near term to reduce energy consumption dramatically.

“With current building envelopes, a whole lot less energy is lost, but because of that we have to change the air supply at an increasing rate,” he says.

“You can’t just bring in air at -20 degrees Celsius during the winter, so you have to heat it up, but the energy required to do all of this is about the same as it was to heat the building in the first place.”

By recovering heat from the flue gases emitted by a condensing boiler and using that to pre-heat air entering the building, a boiler can achieve efficiencies approaching 96 per cent. “There’s so much available heat that’s lost,” says Hayden. Removing summer humidity—the major factor in occupant discomfort—using mechanical systems can also reduce air conditioning usage.

Integrated gas lighting systems can take light generated by burning natural gas and distribute it throughout a building using light pipes. Heat generated by the burning gas is captured for space heating, while the relatively cool light reduces summer air conditioning requirements.

If a building is fitted with extremely efficient mechanical systems, it doesn’t take much to push it over the top into producing more energy than it consumes, says Hayden.

“A lot of the work we’re doing at NRCan involves micro-co-generation systems. If we use a condensing boiler and pick up all the heat we can from solar radiation, we may be able to generate some electricity with the energy the building doesn’t use and sell it.”

Drake Landing, a 52-home sub-division near Calgary, is heated by a Solar District Energy System. While the project is residential, the principles in operation could easily apply to a commercial building, says Hayden.

The homes each feature two rooftop solar panels to provide domestic hot water, while a total of 800 panels on the development’s garages collect the sun’s energy and transmit it by using glycol as a medium.

The development uses hot water storage tanks to retain short-term energy. Long-term energy is stored in a borehole thermal energy storage system that employs 144 holes which stretch 37 metres below the ground.

Unused solar energy is transferred to the surrounding soil which reaches a temperature of 80 degrees Celsius by the end of summer. Heat is drawn back from the soil during the winter.

An energy centre building provides mechanical system support and in each dwelling, a high-efficiency motor fan coil, developed by NRCan’s High Efficiency Combustion Laboratory, provides customized heat. A high-efficiency gas-fired boiler provides back-up support in case passive sources of energy prove inadequate.

“There are plenty of opportunities in new construction, but it will also take a long time to replace the buildings we’ve got,” says Hayden.

“Sophisticated mechanical systems can take us a long way to where we want to be regarding energy consumption.”

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