Abstract

Zero Energy Buildings (ZEBs) are considered as one of the key elements to meet the Energy Strategy of the European Union. This paper investigates cost-optimal solutions for the energy system design in a ZEB and the subsequent grid impact. We use a Mixed Integer Linear (MILP) optimisation model that simultaneously optimises the building’s energy system design and the hourly operation. As a ZEB have onsite energy generation to compensate for the energy consumption, it is both importing and exporting electricity. The hourly time resolution identifies the factors that influence this import/export situation, also known as the building’s grid impact. An extensive case study of a multi-family house in Germany is performed. The findings show that the energy system design and the grid impact greatly depend on the ZEB definition, the existing policy instruments and on the current energy market conditions. The results indicate that due to the feed-in-tariff for PV, the cost-optimal energy design is fossil fuelled CHP combined with a large PV capacity, which causes large grid impacts. Further, we find that heat pumps are not a cost-optimal choice, even with lower electricity prices or with increased renewables in the electric power system.

Abstract

Detailed knowledge of electricity demand is essential for power system planning and operation. EUs 20-20-20 targets will increase the development of more energy efficient buildings as all new buildings shall be “nearly zero energy buildings” by 2020. The result from this ambition is that so-called passive buildings and nearly-net-zero-energy-buildings (nZEB), with lower energy demand, or even onsite power generation, will significantly change the way buildings are integrated in the power system. System operators must consequently prepare for changes in load profiles. However, the knowledge on the aggregated impact of nZEBs is so far limited because the actual number of such buildings is still very small. This paper contributes to this knowledge gap by estimating the aggregated effect on electricity demand profiles.

The load modelling is based on a statistical approach deriving hourly electricity load profiles of non-residential buildings based on measurements of 100 buildings. The profiles will be used as basis in further work to study the impact of a
large rollout of ZEBs on the power system.

Index Terms-- zero energy buildings (ZEB), load modelling, load
profiles, regression, non-residential buildings, and statistics.

Abstract

The main objective of this paper is to contribute to the discussion on the role of Net Zero Energy Buildings (Net ZEBs) on future energy systems by the interplay between on-site generation and the building loads, often called load matching, and the resulting import/export interaction with the surrounding electricity grid, commonly named grid interaction. This investigation analyzes five case studies with high resolution data, three of which are based on real monitored buildings. The research aims at selecting and suggesting a limited set of quantitative indicators that: (a) can provide practical information for building as well as grid designers and operators, and (b) are understandable for a wider audience and do not require complex simulation tools or additional resources. This paper also presents novel graphical representations describing the yearly or daily variation of the indexes in an understandable manner.

It has been found that the hourly values of the cover factors (namely, the load cover factor and the supply cover factor) provide quite a good picture of the correlation between on-site demand and supply of energy. These factors illustrate both the daily and seasonal effect, the production pattern of different renewable energy technologies, and applied operation/control strategies. The loss-of load probability factor shows how often the on-site supply does not cover the on-site demand but it provides limited information. Several grid interaction indicators are presented in a normalized form based on the connection capacity between the building and the grid. The generation multiple is an index that compares peak values of exported/imported energy; it may also be used with generation/load values. The dimensioning rate and the connection capacity credit relate the building with the electrical grid. These indexes can be used to analyze individual buildings and extend their use in the case of cluster of buildings. Although some general trends have been identified in the results and the usefulness of these indicators is demonstrated, it should be noted that further studies are needed in order to define reference values for particular building topologies, clusters of buildings and climates, which could be used as a rule-of-thumb for grid/building designers.

The aim of the Norwegian research centre on Zero Emission Buildings(ZEB) is to develop competetive products and solutions of buildings with zero emission of greenhouse gases related to their production, operation and demolition.

However, to develope solutions and concepts for zero emission buildings it is first necessarry to develop a sound definition of ZEB (for single buildings, and also cluster of buildings). During the first 3 years of the centres running, significant work have been done to adress different issues related to the ZEB-definition, among them defining CO2 factors for various energy wares. Work done in the International Energy Agency (IEA), and European organisations in light of the revised Energy Perfomance Buidling Directive (EPBD) have been an important basis for the ZEB-defintion work. Experience from the design process of 7- 8 ZEB pilot building projects comprising approximately 100 000 m2 floor area has also been an important background for the agreed ZEB-definiton. The ZEB-definition consist of nine points