Polygeneration systems in buildings

This chapter examines polygeneration systems in buildings with a primary focus on emerging approaches that address the growing Net Zero and Positive Energy building agendas. The built environment must rapidly move toward improved energy efficiency, increased penetration of renewable energy technologies, and elimination of fossil fuel use to address the climate crisis and ensure sustainable use of global natural resources. Despite technical and market advances in renewable energy systems and legislative efforts around the world to decarbonize, we remain heavily reliant on fossil fuels to meet the heating, cooling, and electricity needs of our buildings. Throughout history, polygeneration concepts have been used (in one form or another) to serve the energy needs of buildings and their occupants. A hearth fire in a Neolithic hut can be considered a very basic fuel combustion polygeneration device given that it produces thermal energy, light, and induced ventilation airflows. Likewise, a south-facing glazed window in a medieval European castle can be considered a very basic solar polygeneration device that provides daylighting and space heating. Modern polygeneration systems such as combined heat and power (CHP) plants, combined cooling, heating, and power (CCHP) systems, and building-integrated photovoltaic-thermal (BIPV/T) devices serve the additional energy demands of modern buildings, including motive power, electricity, and cooling, but are correspondingly more complex and costly. Fuel-based polygeneration requires a solid, liquid, or gaseous fuel input, whereas solar-based polygeneration is driven entirely by sunlight. Most fuel-based and solar-based approaches produce heat that can be used for space heating, for domestic hot water production, to induce ventilation via thermosiphonic airflows, or to produce cooling via sorption processes. In addition to the heat output, fuel combustion polygeneration produces motive power which can, in turn, drive electricity generators or vapor compression chillers. Solar photovoltaic and fuel cell polygeneration produces electricity as the primary output, in tandem with either heat or light (or both) as a secondary output.