Keywords: buildings, ambient anergy sources, built environment, exergy utilisation ratio, reference environment, heat pumps, efficiency, low exergy systems, performance optimisation, exergy analysis, ambient environmental conditions
The reference environment: utilising exergy and anergy for buildings
The utilisation of exergy and anergy concepts for low exergy system design extends the potential of performance optimisation of buildings. We propose a new perspective for buildings and their external environment. It recognises exergy as the utilisable potential that maintains comfort inside relative to outside ambient conditions. It considers environmental heat sources as a form of transiting exergy that is utilised internally to increase second law efficiencies and then returned to the environment. These sources are not chosen to optimise energy inputs, but rather temperature inputs. They are optimised as anergy sources coming from a dispersed state, which are transited through the building system and deposited back in an anergy sink, which defines the reference environment. A major obstacle in the application of exergy analysis to buildings is the lack of an accepted definition of the reference environment. The absence of this factor leads to ambiguity in analysis and hinders comparisons between studies. Choosing the reference environment influences the amount of exergy contained in buildings and with the low quality levels often dealt with in buildings, the influence can be significant. The perspective we present clarifies the use of the ambient environmental conditions as the reference environment for exergy analysis of whole buildings. It also validates the unencumbered use of free ambient anergy sources from the ground, water, air and the sun to increase exergetic performance.