More and larger data centres are being built around the world. The rated electrical power of a single large data centre campus is often in the three-digit megawatt range nowadays. Such a data centre has the power consumption of a large city. But what is the total power consumption of all data centres worldwide? How high is the demand for other resources such as water and materials? And what future developments can be expected? A powerful and promising approach to answering these questions is the use of bottom-up models, which determine the energy and resource requirements based on the inventory figures of the devices and systems present in the data centres. Unfortunately, there is little available and reliable data on such inventory figures. This paper aims to make a contribution to reducing this lack of information. To this end, it focuses on the server equipment category, which clearly accounts for the highest proportion of the energy and resource requirements of data centres. Based on available information in scientific publications and data from market analysts, we estimate the total number of existing servers. We come to the conclusion that around 80 million servers will probably be in operation worldwide in 2024.

Innovations and efficiencies in digital technology have lately been depicted as paramount in the green transition to enable the reduction of greenhouse gas emissions, both in the information and communication technology (ICT) sector and the wider economy. This, however, fails to adequately account for rebound effects that can offset emission savings and, in the worst case, increase emissions. In this perspective, we draw on a transdisciplinary workshop with 19 experts from carbon accounting, digital sustainability research, ethics, sociology, public policy, and sustainable business to expose the challenges of addressing rebound effects in digital innovation processes and associated policy. We utilize a responsible innovation approach to uncover potential ways forward for incorporating rebound effects in these domains, concluding that addressing ICT-related rebound effects ultimately requires a shift from an ICT efficiency-centered perspective to a "systems thinking" model, which aims to understand efficiency as one solution among others that requires constraints on emissions for ICT environmental savings to be realized.

Energy consumption for heating, cooling, and warm water production in the building sector is a major source of CO 2 emissions in Europe. Building automation and control systems (BACS), using ICT-based monitoring and management applications to reduce energy consumption, have long been considered a key technology to improve efficiency in the building sector but CO 2 abatement potential is unclear. Most studies on the technology either use a vague definition of BACS or calculate on the basis of insufficiently evaluated applications and efficiency potential. This paper builds on a study previously conducted by the authors that analyzed CO 2 reduction potential (Mt CO 2 emissions saved) from clearly defined application scenarios of BACS in the residential and non-residential building sectors in Germany. Effects were calculated using secured efficiency factors derived from standards (EN ISO 15232, etc.). The methodological approach and the results of this study were subsequently used to apply the ETSI/ITU framework, in particular to evaluate application scenarios of building automation. Through application of the ETSI/ITU framework, the authors also draw preliminary conclusions for CO 2 mitigation strategies in the building sectors of other European member states by discussing possible use of the framework for other housing and heating structures.

Der steigende Energiebedarf der Rechenzentren stellt eine Herausforderung bei der Erreichung der Klimaschutzziele sowie der Realisierung der Energiewende dar. Auch die sogenannte graue Energie – also die Energie, die für Herstellung, Transport, Lagerung und Entsorgung der Komponenten benötigt wird – kann ganz erhebliche Anteile am Gesamtenergiebedarf ausmachen. Dieser Artikel stellt eine selbstentwickelte Modellstruktur vor, welche die graue Energie in Rechenzentren erstmalig berechnet.

Renewable electricity from wind and solar is on the rise and, consequently, flexible energy consumption and the conversion of electricity into heat or mobility are becoming valid options for integrating fluctuating energy production into the grid. This is a particular challenge for the building sector since it has a high energy demand but often steady and predictable consumption patterns. The authors present results from a case study in Germany in which flexible consumption of energy and the conversion of renewable electricity into heat were tested and evaluated in a smart residential neighborhood. A prerequisite for the study is an interoperable ICT infrastructure that connects smart buildings to flexible energy markets. The case study allows conclusions to be drawn about the technical applicability and economic viability of these solutions as well as about the CO2 emissions saved as a result of flexible energy consumption. Finally, a brief analysis of a large-scale application of flexibility in the building sector is included.

Data centers are responsible for a constantly growing demand for energy and resources. Numerous studies show that there is still considerable potential for improving the energy and resource efficiency of data centers. Against this background, it is of great importance that existing efficiency technologies be applied to a greater extent and new technologies put into practice. One instrument to support this development is a technology radar for energy efficiency technologies in data centers. A technology radar is an instrument for monitoring technology that supports the identification, evaluation and observation of relevant technologies in specific areas. This paper describes how such technology radars are developed in a transdisciplinary process and presents current and future efficiency technologies for data centers. Keywordsdata center, energy efficiency, technology radar, transdisciplinary approach, energy, cooling, power supply, IT management)

Digitalization is driving the increasing energy and resource needs of ICT. In Ger- many, ICT accounts for eight percent of electricity consumption. Data centers alone cur- rently consume 2.3% of the electricity in Germany, with an upwardtrend.Although the ICT sector is generally considered to be very innovative and new solu- tions are often implemented very quickly, deployment of energy- and resource-efficient innovations is frequently confronted with considerable obstacles and barriers.Innovation alliances of companies are a promising instrument of governmental sup- port for new environmental technologies in the fast-paced ICT sector. In the past ten years, several initiatives of this kind have been launched, e.g., the consortium GreenIT Amsterdam, the Innovationsallianz Rechenzentren (Innovation Alliance Data Centers) in Hesse, Germany, and the Netzwerk energieeffiziente Rechenzentren (Network Energy- Efficient Data Centers). Some of these initiatives have achieved remarkable successes.The present paper analyzes such innovation alliances using the example of energy efficiency in data centers as the field of application. Three good-practice examples from Germany are presented. The paper shows what these innovation alliances can achieve and analyzes the factors contributing to their successful implementation. It concludes with concrete recommendations for practical implementation of such initiatives.