AC/DC Office Buildings - Implementation of Electricity Networks with Alternating and Direct Current in Office Buildings - Feasibility and Energy Efficiency Potentials
In recent years, the number of appliances that can be supplied by direct current (DC) such as computers, printers, routers, consumer electronics and mobile phones rapidly increased. With the further development of LED technology already used in practice, another user of DC appeared on the market. However, up to now only alternating current (AC) supply systems are in use.
The development and application of intelligent DC-supply-storage-distribution-end user systems could have numerous advantages:
- reduction of transformation losses
- easy integration of decentralized energy supply systems
- control of feeding in stored energy in the power grid
- minimization of appliances
- cost reduction due to abdication of transformers
- reduction of transformation losses by centralizing transformation
- safe energy supply
Contents and Objectives
The goal of this project is to show what technologies and concepts for the supply and use of DC-systems already exist or are discussed internationally and what the potential for energy efficiency gains are. This will be analyzed using the example of a concrete office building.
The work was carried out in 4 steps:
- In a first step existing or discussed technologies and concepts for buildings are documented.
- In a next step technological options for supply (e.g. photovoltaic), distribution, storage and use (e.g. IT, lighting, white goods, HVAC) of DC in office buildings were documented and analysed.
- For a concrete virtual office building scenarios for the use of DC-systems were developed resulting in an estimation of energy efficiency potentials. Finally, important future questions were discussed and the need for further research was defined.
Internationally, several concepts for the use of DC in buildings are discussed. In most cases these are hybrid systems where low power appliances are supplied with 24 or 48 V DC while for big loads 380/400 V DC is used. However, small voltages lead to significantly higher losses in the wiring than high voltages where - on the other hand - arcing is a serious problem. For the investigation here 120 V DC was used. All apliances can be supplied by one single voltage and losses are on a reasonable level even when using standard wiring. Arcing problem exists as well but to a smaller extent.
The major result of the screening of technologies could show that in practice all appliances used in office building can be supplied by DC. This is obvious for electronic devices but also for HVAC or white goods up-to-date technology uses DC as an intermediate voltage.
In a detailled simulation of a realistic office building it could be shown that DC has some efficiency gains compared to AC. However, the size is in a magnitude that savings are most likely to be smaller than extra cost for investment for a DC system. From an economic point of view DC systems might not be feasible.
Even though the disput on AC or DC exists for more than 150 years, there are still a lot of research questions to be solved. Topics are the general concept of DC-grids, grid-typology, arcing, switching of DC, safety questions, energy efficiency and finally, the standardisation of components.
In the near future it is unlikely that DC supply of buildings will be a standard solution. There are some international examples and activities but the future direction of the general development is not clear yet.
One aspect could gain more importance in the future. If the prices for energy storage systems will decrease to a level that batteries will be standard elements of decentralized energy supply systems a broad implementation of DC in building should be discussed again.
The project results show clearly that the focus should be on the complete configuration of a building under realistic framework conditions and not on single components.
DI Christof Amann
e7 Energie Markt Analyse GmbH