<p>Room air quality and air contamination are key arguments for the use of a ventilation system. Bad air results in loss of concentration and fatigue in case of CO2, and it may become even dangerous if other potentially hazardous gases are involved [1]. The ventilation efficiency and the efficiency of a complete ventilation system is described in the REHVA guide book [7]. A high air change does not only remove contamination but also wastes thermal energy and subsequently effects the room temperature. To address this issue the incoming air must be conditioned. An energy-efficient way to do this is to use a centralized-decentralized cooling concept [4]. </p>

<p>In this article a study of a system of a trench cooling unit (TCU) with a combined fresh air supply is presented. Transient computational fluid dynamic (CFD) calculations for a standard office room are shown with a look on the CO2 concentration. The analysis focusses on the room air contamination as well as on the efficiency of the ventilation system. The TCU recirculates room air for cooling instead of using fresh air in contrast to also known Under Floor Air Distribution (UFAD) systems, and therefore only needs to reduce the circulating room air temperature. A deeper insight into the working principles of such a TCU is given schematically. The interaction of the TCU unit with a fresh air outlet is discussed. </p>