Polygeneration systems are integrated energy supply systems that simultaneously generate two or more energy carriers (e.g. electricity and heat); where the output or byproduct of one process can be the input for another energy supply process). Hospitals are considered good candidates for polygeneration systems due to their sustained and relatively high energy requirements (heat, steam, coolth, and electricity), and their need for high power quality and reliability. The complex energy requirements of a hospital are similar to the energy requirements in the metal mining industry, and other industries, making the stand-alone hospital an ideal test site. Using a hospital in Northern Ontario with energy pricing and tariff arrangements that are specific to Ontario, MIRARCO was able to test their optimization methodology. The work aimed to identify the lowest annual cost of meeting site demand through determination of optimum polygeneration technologies, and the optimum manner for operating that set of technologies. CO2 emissions could be simultaneously minimized in the procedure, if required.
In order to identify the optimal configuration, annual energy demands were estimated by the team and then validated against actual data for the hospital. A polygeneration superstructure for optimization (using MILP—Mixed Integer Linear Programming technique) of the energy supply system was created so that the energy demands of the hospital could be met and different scenarios of constraints could be investigated. Energy prices were determined and conditions arising from the regulatory framework were introduced.
Surprisingly, the optimal economic solution indicated that generating electrical power using an onsite energy supply technology from gas is more economical than connecting to the electricity grid – even when an electricity grid connection point is available close by. The methodology and findings have far-reaching implications, particularly for energy-intensive industries. This is of particular significance to mining operations relying on multiple energy utility sources. Similar to the hospital, mines too, must find ways to reduce production costs through improvements in the efficiency with which they consume energy resources.
- Damien Duff, CEMI
- Benoit Valley, CEMI
- Mark Diederichs, Queen’s University