The Giessen Free-Air Carbon Dioxide Enrichment technique was developed during 1994-1996 by S.W. Schmidt at the Department of Plant Ecology based on the classical FACE technique in order to adapt it to local site requirements.

Each ring (8 m inner diameter) consists of 24 identical segments. The main features of the Giessen system are:

• a circular active plenum which consists of a modular structure with individually controlled exhausting and sucking vent pipes
• the symmetric layout without any external blower provinding wind-direction independent CO₂ enrichment control
• the regulation of the CO₂ target concentration with an electronic controller, which leads to CO₂ concentrations of 22 % above ambient in a height of 40 cm above ground
• low maintenance requirements
• a reduction of the CO₂ usage by approximately 5 %

detailed description of the enrichment technique:

Jäger, H.-J., Schmidt, S.W., Kammann, C., Grünhage, L., Müller, C. & Hanewald, K. (2003): The University of Giessen free-air carbon dioxide enrichment study: description of the experimental site and of a new enrichment system. Journal of Applied Botany 77, 117-127.

Schmidt, S.W. (2003): Ein modulares System zur Untersuchung der Auswirkungen von erhöhtem atmosphärischen Kohlendioxid auf Grünland-Ökosysteme. Dissertation, JLU Gießen.
Quelle: http://geb.uni-giessen.de/geb/volltexte/2003/1125/