Second law analysis of building systems

Abstract Available energy is based on the Second Law and goes back to Maxwell and Gibbs. Unfortunately, it has not yet caught on in engineering practice, or in managerial decision-making. It is the available energy content of a substance, not its energy content, that truly represents the potential of the substance to cause change. Available energy is the only rational basis for evaluating (1) fuels and resources, (2) process, device, and system efficiencies, (3) dissipations and their costs, and (4) the value and cost of system outputs. This paper presents a brief overview of Thermodynamics and a description of the methodology of Second Law analysis. Some results from two case studies are given, which illustrate the efficiency analysis of a dual-duct HVAC system in Milwaukee and of a total energy power plant in Jersey City. While exposing many misconceptions resulting from energy analyses, the results of the efficiency analyses pinpoint the opportunities for improving energy systems, showing great potential for alleviating ‘the energy problem’ via conservation. This potential for conservation lies not in the usual, negative concept of austerity (‘belt-tightening’), but in a positive approach: the reduction of very large dissipations in the process that convert the resource to the desired form of ‘energy’. In turn, the analyses show how economic-analysis decisions regarding ‘energy’ systems can be greatly facilitated, while avoiding the The efficiency analysis evaluates the inefficiencies in and the effluent losses from the various components misappropriations (often gross) that result from energy analyses. making up the systems: For the dual-duct system, (i) at summer design operating conditions, and (ii) at winter designs. For th e total-energy plant, (iii) during the winter (heating season) and (iv) during the summer (cooling season).