Increased global competition and growing environmental concerns around the world are two major trends affecting companies today. Tougher competition has led companies to focus primarily on their core business activities, which may lead to a shortage of resources for support activities, such as energy management. This development takes place while environmental concerns step up requirements regarding companies' environmental performance, with global warming at the forefront. Together these issues have increased the management complexity and thus the need for relevant decision support. The purpose of this thesis is to study ways to reach a more comprehensive view of industrial energy systems than is the case today, and thereby achieve more efficient systems.

One theme in this thesis is to investigate analysis approaches, mainly based on optimisation, that can help to produce a comprehensive view of industrial energy systems. The subject of the studies was an integrated steel plant in Sweden which has a connected CHP plant that uses the excess process gases from the steel plant as fuel. The studies included analyses of the operation planning during both internal process variations and changed external conditions. They also included analyses of relations between objectives such as cost, energy use, and environmental performance by applying a multi-objective approach. The analyses proved to provide a comprehensive view of how the system reacts to various changes, which factors are the essential ones for different objectives, and what trade-offs can be made between the objectives.

In addition to this, two studies were conducted of energy-related co-operations between companies. The first looked at co-operation where energy service companies bring competence and other resources related to energy efficiency to the pulp and paper industry. The main aspects of concern were: the managers' views on the opportunities and risks with energy-related co-operation; and its implications for industrial energy management. The second study investigated co-operation between process industries and municipal energy companies with regard to indus trial waste heat deliveries and jointly owned combined heat and power plants. The study emphasised incentives for and barriers to this kind of co-operation. In both studies it was found that trust between the parties is important, that the form of the contract is also important especially to bring the focus to bear on common benefits rather than just one's own, and to reduce the risks involved in co-operation.

Based on the performed studies possible implications of decision support based on optimisation and co-operation between companies are discussed.