Air conditioning is now seen as a new and major contributor to CO2 emissions in the UK. This is partly due to global warming and partly to the increased use of IT systems. A novel system for reducing or eliminating the need for air conditioning was developed to the proof-of-concept stage under an earlier project at the University of Nottingham. The present paper describes field tests on the system that have recently been completed and which demonstrate the effectiveness of the system under real operating conditions. Systems were installed in two offices and detailed monitoring of their performance was carried out during the summer months. On the basis of the results obtained it is concluded that the system functions very well and is practically and technically the most attractive of the available alternatives to air conditioning. The fact that it is suited to retrofitting in existing buildings means that both the potential market and the CO2 reductions are large.