Design of Low Exergy Buildings. Method and a Pre-Design Tool

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 (ECBCS 2002). 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 thermodynamics. A more holistic view in these calculations is gained by estimating the primary energy demand for all processes. As shown in this paper, through analyses and examples, the energy conservation concept alone is not adequate in gaining 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 laws of thermodynamics, is presented here for a better understanding and design of energy flows in buildings. This concept of exergy is described in detail and a summary of work conducted earlier has been included. Although the basic principles had already been stated in the nineteenth century, it wasn't until the mid nineteen fifties that the term exergy was introduced. A pre-design tool for buildings has been programmed utilising this concept and its functionalities are shown in this paper. Using a typical case, the advantages of the analyses and the difference between energy and exergy analyses are demonstrated. In conclusion, an analysis of a real and existing building is presented and some design guidelines deriving from all of the analyses are given. In order to achieve an exergy optimised building design, loads on the building service 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 the next priority, will be much more efficient.