Cooled ceilings/displacement ventilation hybrid air conditioning system : Design criteria design criteria

For realizing comfort and ventilation efficiency simultaneously using a cooled ceiling (CC)/ displacement ventilation (DV) hybrid air conditioning system (CC/DV), Vertical distribution of temperature, local ventilation efficiency, and thermal comfort were studied by conducting a series of experiments to determine the design conditions. The characteristics of the thermal environment were measured in a laboratory, which was set up to simulate an office room in summer. The local air change efficiency was measured by tracer gases method and a subjective experiment was also carried out. The interaction between the major system parameters of room cooling load (P), CC cooling output ratio (η), ventilation airflow rate (Q), temperature gradient (dt) and the relevant constraints were studied. The results of these experiments showed the temperature gradient in the occupied zone, an important factor of DV, adversely affects thermal comfort. As a result, the temperature gradient in the occupied zone should be in a range of 2-2.5 deg. C to realize comfort and ventilation efficiency simultaneously. A diagram for the system design was developed using the relationship among the above factors, which provides a useful and practical design tool.