The “extended building energy hub”: A new method for the simultaneous optimization of energy demand and energy supply in buildings

Abstract

This article deals with simultaneous optimization of building energy performance from both the building and system design points of view. Most research conducted on building energy demand reduction and energy supply optimization treats the demand and supply aspects separately. First, the demand side parameters are analyzed for a demand reduction and then the most suitable configuration for the primary energy conversion is investigated. The relationship between the building energy demand and supply may not be clearly understood when they are analyzed sequentially instead of simultaneously. This article investigates the potentiality of an integrated building demand-supply energy optimization method that could provide a solution to the building energy efficiency problem. The method is based on the Extended Building Energy Hub (EBEH) concept, which is an evolution of the Building Energy Hub (BEH) method. In the BEH approach, the vector of energy inputs—the energy supply—is related to the vector of energy outputs—the energy demand—by means of a coupling matrix. The coefficients of this matrix are functions of the efficiency of the various energy conversion systems and of the distribution of energy fluxes in the energy converters. In the EBEH method, the demand side building design parameters are also included in a coupling matrix and are evaluated together with primary energy options. In this way, for example, the demand side parameters (U values, window-to-wall ratio, etc.) can be contrasted with the opportunity of using solar energy for the production of electricity, and the optimum configuration can be calculated by maximizing the primary energy savings. The article introduces the basic principles of this approach. A preliminary practical demonstration is also developed through the application of a simplified procedure to a case study of an existing building.

Acknowledgments

Meltem Bayraktar is PhD student. Enrico Fabrizio, PhD, is Assistant Professor. Marco Perino, PhD, Associate Member ASHRAE, is Full Professor.

Notes

The hub is “hybrid” since it manages different types of energy from different sources (electric energy, heat, biomass, fossil fuels, solar, wind, etc.).

This is a situation for which optimization techniques are particularly useful.

In reality, these two quantities are not completely independent of each other. In a future developmnent of the method, current features of commercially available glazing need to be implemented. At all events, in this work, the values of g and T_vis supplied by the optimization procedure have been, subsequently, checked for coherence with commercially available glazings.

This method was tested during the early stages of development of this research.

In this paper, for the sake of brevity, only the results related to the use of the electric energy equivalent demand optimization function, f ^e.el _d , are presented. In the frame of the research, the primary energy equivalent demand optimization function, f^pe _d , was also used, and substantially analogous results were obtained.

In this case, the electric energy equivalent demand function, f ^e.el _d , was only assessed for comparison purposes, but it was not used for the optimization.

In this case, the economic objective function, f^ec _d+s was only assessed for comparison purposes. The two economic optimization functions, f^ec _d and f^ec _s , were used sequentially for the optimization procedure.