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AIM: To evaluate three types of ventilation systems for operating rooms with respect to air cleanliness (in colony forming units, CFU/m(3)), energy consumption, and working environment comfort (noise and draught) as reported by surgical team members.METHODS: Two commonly used ventilation systems, vertical laminar airflow (LAF) and turbulent mixed airflow (TMA), were compared with a newly developed ventilation technique: temperature controlled airflow (TcAF). CFU concentrations were measured at three locations in an operating room during 45 orthopaedic surgeries: close to the wound (FINDINGS: We showed that LAF and TcAF, but not TMA, resulted in less than 10 CFU/m(3) at all measurement locations in the room during ongoing surgery. Median values of CFU/m(3) close to the wound (250 samples) were 0 for LAF, 1 for TcAF and 10 for TMA. Peripherally in the room, the CFU concentrations were lowest for TcAF. The CFU concentrations did not scale proportionally with airflow rates. Compared to LAF, TcAF's power consumption was 28% lower and there was significantly less disturbance from noise and draught.CONCLUSION: TcAF and LAF remove bacteria more efficiently from the air than TMA, especially close to the wound and instrument table. Like LAF, the new TcAF ventilation system maintained very low levels of CFU in the air, but TcAF used substantially less energy and provided a more comfortable working environment than LAF. This enables energy savings with preserved air quality.