Field studies were carried out to investigate the thermal performance of ceiling-based HVAC systems, which typically consist of package air-conditioners and an energy recovery ventilator (ERV), and to test the energy-saving efficiency of CO2-demand controlled ventilation systems with integrated ERV systems. Measurements from sensors placed in both the occupied zone (0-1.8 m) and the upper ventilation zone (at ceiling height) were taken in an environmentally controlled, open-type office, configured with workstation furniture and partitions. The distributions of temperature, relative humidity (RH), and CO2 concentration were assessed throughout the test site for four scenarios. Tests were conducted to investigate the effects of the ERV, heat loss from the ducts, CO2 demand control strategies, and contaminant patterns generated in a real office. Measurements showed that, with the application of an ERV system, the energy consumption of the air conditioning system could be reduced by 20-30% and that of the ventilation system, i.e. outdoor air load, likewise reduced by 60-70%. (C) 2013 Elsevier B.V. All rights reserved.