How Dual Energy Can Make a Difference in Commercial, Institutional and Multi-unit Rental Buildings

How does dual energy work?

Dual energy involves electrifying a building’s heating system while maintaining natural gas heating. So long as the outside temperature remains above -12°C (or -15°C for customers in Abitibi and the Saguenay), the electrical system provides the heat. When the temperature falls below the threshold, the gas-powered equipment takes over to take pressure off the power grid. Depending on the type and capacity of the electrical equipment used, natural gas (and therefore GHG) savings can be as high as 70% to 80%.

Fictitious decarbonization scenario in a school

To help you understand how this solution works in practice and compare the benefits under the different scenarios, let’s look at a fictitious example of decarbonizing a school.

Dual energy makes a difference

As the results above show, significant reductions in GHG emissions are achieved with all of the scenarios. Since we’re fortunate to have clean electricity in Quebec, complete electrification eliminates virtually all the building’s emissions. But full electrification of the building requires more than double the electrical power of the efficient dual-energy scenario.

How can we reduce GHGs to the same level as with full electrification without monopolizing too much power during peak winter periods? That’s where renewable natural gas (RNG) comes in. By combining the new dual-energy program with RNG, we achieve a carbon footprint similar to Scenario B (100% electric) without using all the electricity, availability of which may be limited depending on the region. What’s more, there are major differences in annual energy costs between Option B and Option C and Option E. In today’s energy environment, power savings could help finance more projects, ultimately reducing GHG emissions even more.

In order to meet demand from small and large consumers who want to use dual energy to decarbonize their building heating systems, the Government of Quebec, Hydro-Québec and Énergir have created two grant application streams (simplified and custom). The amounts available under the two options are described below:

 
In our example, the grant for switching to dual energy would be $390,500 under the custom option.

Cooling and ventilating our schools with dual energy

The case presented above is relatively straightforward, but for aging and heterogeneous building stock, it’s obvious that we'll need to look at other approaches to dual-energy conversion can be analysed. For example, funding could be requested to upgrade a school’s ventilation and air conditioning system – a scenario that could be applied on a broad scale given the significant ventilation and air conditioning needs of Quebec schools.

Starting from the same initial situation, it would be possible to add mechanical ventilation at the school by installing new air units. Preheating and conditioning of outdoor air could be ensured through heat recovery and aerothermal heat pumps. To minimize ductwork space requirements, a variable refrigerant system called a “VRF" could be considered. Fan coils installed in classrooms could heat and cool the thermal envelope via the new heat pumps. The building’s existing hot water loop would be more useful than ever, as it would be possible to switch to natural gas to provide heat when temperatures fall below -12°C (or -15°C for Abitibi and Saguenay) or to keep occupants comfortable. In addition, heat pump sizing could be based solely on the air conditioning load. However, low temperature limits for heating with the units would still need to be calculated in order to accurately assess the GHG savings.

This configuration would not only provide heating and cooling according to the season, in addition to providing classrooms with mechanical ventilation. Given that adding air conditioning would allow the deployment of dual energy, the additional installation costs would be subsidized at a rate of $250/tonne of GHGs or up to 80% of the investment, a major incentive to boost students and teachers’ well-being, improve indoor air quality, and reduce the building’s carbon footprint.

Martin Brière-Provencher.
Senior Advisor, Energy expertise
DATECH Group – Development and technical assistance