Proposal for a modified cost-optimal approach by introducing benefits evaluation

The recast of the Energy Performance of Buildings Directive introduced the concept of nearly-zero energy building and encouraged setting the nearly-zero energy target with a view to cost-optimal level - the energy performance that leads to the lowest cost during the building estimated economic lifecycle. To searching this regard, the cost-optimal methodology based on the global cost was defined providing a tool to assess different nearly-zero energy scenarios. Nowadays, the cost-optimal analysis is used as a decision-making tool between different energy design alternatives mostly on a theoretical level; but it has spread little among the professional field. The aim of this paper is to give a more holistic and all-comprehensive approach to the cost-optimal methodology. This paper proposes and applies a modified approach of the cost-optimal evaluation, which will lead to the achievement of more interesting results for all the actors involved, including investors and final users. This study highlights the usefulness of including not only costs but also benefits that can derive from each energy design scenario. Choosing different energy efficiency solutions, the related benefits evaluation could turn the tables. Different kinds of benefits could be considered as the increase of the real estate market value, the enhancement of the indoor comfort, the reduction of CO2 emissions and others. Thus, a proposal of how quantifying these qualitative benefits in monetary terms is shown to introduce them in the global cost formula. Actually, benefits conversion into monetary values is the most challenging issue. Precisely, this paper shows a list of benefits that can affect the choice of different envelope and HVAC system solutions, pointing out their influence on the global cost evaluation. Certainly, introducing benefits in the global cost formula means using a more holistic and complete approach, while the already complex degree of the cost-optimal methodology – due to the numerous input data –increases. To validate the reviewed global cost formula, it will be necessary to apply it to various case studies.