At least one condo building in the GTA won’t face the perennial dilemma of when to switch over its HVAC system from heating to cooling this spring. Its heating and cooling are available all year round, with one minor exception: cooling is disabled when the temperature outside dips below minus 10.
The 300-unit condo building runs on cogeneration or combined heat and power (CHP), which is basically like an on-site power plant. CHP installations feature natural gas-burning engines, which generate electricity efficiently, capturing and using the waste heat created in the process.
The process of generating electricity on site costs less than what building owners pay to obtain it through the grid from local utilities. And if the electricity generated on site exceeds the needs of the building, the building owners can export the excess electricity to the grid, where they can sell it to local utilities.
The 300-unit condo building is doing just that. Its 350-kilowatt CHP installation is able to satisfy demand for heat and domestic hot water for the whole building, which does not have a boiler. Deep geothermal wells work with ground-source heat pumps to create chilled water for the fan coils, which produce the building’s cooling. The building can also operate in “island mode,” whereby the cogeneration installation sustains the entire building on electricity when the grid goes down and power gets knocked out, recovering heat from the generator, as long as natural gas is available.
As shown in this case, CHP can be used to efficiently supply domestic hot water to a building, offset some of its electrical load and power emergency systems during power outages. These installations may even have extra capacity to power non-emergency systems during power outages thanks to energy-saving technologies such as LED.
CHP can be part of the original design of the building, as was the case here. Projects like this may be eligible for incentives for high-performance new construction — high performance meaning that the building is more energy efficient than its base design.
CHP can also be a retrofit solution for an existing building. Buildings that have old back-up generators due for major retrofits or replacement are good candidates for cogeneration.
These opportunities can be identified in a comprehensive energy audit or a preliminary or detailed engineering study. There are incentives available to implement a CHP system that has at least a 70-per-cent overall system efficiency in converting natural gas into hydro and using recovered waste heat. Efficiency can be far greater, depending on the amount of recovered heat being used to offset the building’s heating load.
In either case, proper engineering is required to make sure the system will work as designed and captures the expected benefits in the shortest possible payback period.
Costs can range from $500,000 for a small micro-turbine system that generates hydro and domestic hot water to multi-millions of dollars for a system that can run in island mode. Most projects pay for themselves within five years.
Not having to replace an aging back-up generator can greatly reduce the payback time. What’s more, a CHP installation is a long-term investment as it generates revenue when excess electricity can be exported to the electric grid and sold to local utilities.
Building automation systems (BAS) are used to control when the CHP will run, factoring in the price of electricity and the building’s heating and domestic hot water demands. The more waste heat that the CHP can put to use in the building, the more efficient the installation. The less waste heat the CHP can put to use in the building, the less efficient the installation. Excess heat must be vented outside to protect the CHP plant and heat pumps from overheating. The BAS ensures this occurs as needed and facilitates occupant comfort.
Once a CHP installation is set up, ongoing monitoring and optimization is advised to ensure all building systems continue running smoothly so energy savings and other benefits don’t disappear. It took a lot of commissioning work to keep the CHP installation at the 300-unit condo building functioning properly.
With a passion for energy conservation, Per Polderman, CEIT, serves as a senior account manager at Mann Engineering. For close to 30 years the leading energy management company has specialized in comprehensive energy audits, reserve fund studies, engineering reviews, BAS, incentives, HVAC design/build and energy retrofit needs. He can be reached at 416-550-3275 or [email protected]