The Broader Environmental Impacts of Combined Heat and Power (CHP) Systems using an Infrastructure Ecology Approach

Cities are growing at a rapid pace, and as such they arethe main stakeholders through which global sustainability can be reached. To this end, cities have to improve the sustainability and resilience of the infrastructure systems on which they rely. The infrastructure systems are akin to ecological systems in that they are interconnected and transfer resources between each other, as well as with the environment. The concept of infrastructure ecology can be used to examine how infrastructure systems within a city interact. In this study we analyzed the impact that a combined heat and power system, which consists of an air-cooled microturbine and an air-cooled absorption chiller, can have on the energy and water for energy requirements of a medium-sized office building. The microturbine and absorption chiller are used to supply the thermal load, which consists of heating, hot water, and cooling loads of the building with the boiler and the absorption chiller meeting any loads not met. We looked at the partial loads of five microturbine systems that ranged in capacity from 30 to 150kW, and varied their outputs from 10 to 100%. We found that running the largest CHP system at 100% will not meet the entire electrical load of the building but will produce 10 times the thermal output required by the small office building. The "water for energy" savings can be reduced to almost zero by the 150kW turbine running at 100%. The 150kW turbine at 100% mitigates the "water for energy" of a building with similar characteristics, if allowed to sell excess electricity produced to the grid. Further analysis is being done to look at the emissions and economic impacts of these CHP systems.