Exergy: Game Changer or Game Maker

Birol Kilkis,S.I Tanabe,P Wargocki,C Inard,M.C Gameiro Da Silva,H Zhang,J Kurnitski,I Nastase,G Cao,L Mazzarela

doi:10.1051/e3sconf/201911106024

Abstract

Many standard practices of today in the High Performance and Sustainably Green Buildings simply rely on the First-Law of Thermodynamics and economic feasibility in their evaluation and ratings. Although these practices seem to be quite `efficient` and green, new metrics, which are based on the Second-Law, namely exergy rationality metrics show that these practices are not feasible and environmentally advantageous, unless they are redesigned accordingly. For example, a simple ORC system using low-enthalpy geothermal source is not feasible, which means that such a system may save money and apparently energy but definitely destroys exergy compared to direct use of the thermal power from the geothermal well. This poster emphasizes the urgency of switching to exergy-based designs and practices.

Highlights

In order to electrify the HVAC sector by heat pumps especially in the EU countries the use of ORC technology is a relatively new trend where low-enthalpy geothermal energy resources and waste heat prevail. This is a viable approach within the scope of the First-Law of Thermodynamics but this condition usually does not hold true if a careful and optimum allocation of low-enthalpy energy sources and balancing with demand with different quality and quantity is not characterized by the Second-Law of Thermodynamics along with the First-Law
Carbon dioxide has been widely investigated for use as a working fluid in refrigeration cycles, because it has no ozone- depleting potential (ODP) and low global warming potential (GWP)
ORC systems seem to be a good company for low-enthalpy geothermal energy sources but they need a complete analysis and planning [3, 4]

Summary

Introduction

In many cases-depending on the geothermal source temperature- it is more exergy-rational to keep the heat for thermal consumption. The following exergy-based equations, which are necessary to optimize the split ratio, X describe the system performance. The total exergy of the system is the exergy sum of electrical output and the thermal output minus the sum of exergy demand related to the electrical power demand of circulation pumps and the dry-cooling fan.Figure 1 shows the general arrangement of a geothermal energy driven ORC.

Application

Game Changers

Conclusions