Designing low-"exergy" buildings

There is an obvious and indisputable need for an increase in the efficiency of energy utilisation in buildings. Heating, cooling and lighting appliances in buildings account for more than one third of the world's primary energy demand. In turn, building stock is a major contributor to energy-related environmental problems. There are great potentials, which can be obtained through a more efficient use of energy in buildings. Calculations in energy simulations and analyses of energy flows in buildings have commonly been based on the energy conservation principle, the first law of thermodynarnics. A more holistic view of these calculations is attained by estimating the primary energy demand for all processes. As shown in the paper by way of analyses and examples, the energy conservation concept alone is not adequate to gain a full understanding of all the important aspects of energy utilisation processes. Thus, a method for exergy analyses based on a combination of the first and second law of thermodynamics is presented for a better understanding and design of energy flows in buildings. This concept of exergy is described. Although the basic principles had been stated as early as in the nineteenth century, it wasn't until the mid nineteen fifties that the term exergy was introduced. A number of analyses have been performed using a pre-design tool for buildings. Using a typical case, the advantages of the analyses and the difference between energy and exergy analyses are demonstrated. In conclusion, some design guidelines deriving from all of the analyses are given. A number of so-called low-exergy demonstration buildings, both new constructions and retrofitted buildings, are presented. In order to achieve an exergy-optimised building design, loads on the building services system have to be reduced as much as possible. Generally, in the retrofit or new design of buildings, first priority should be given to creating an energy-efficient building shell. Then, improvements to the building service system, which should be next in priority, will be much more efficient. The presented research work is related to the international cooperation work lately concluded under IEA ECBCS Annex 37 "Low-Exergy Systems for Heating and Cooling of Bulildings" and to the established Network for "Low-Exergy Systems in Buildings - LowExNet". Further, an overview of ongoing German activities in the exergy collaboration project, involving industry partners and research institutions, is presented.