10.2190/4RB4-PXJ7-U7CY-M41W 4RB4PXJ7U7CYM41W 6 Use of Macroscopic Flow Number For Assessing Spaces With Mechanical Ventilation 425 434 20020509 20020509 20020509 20020509 4RB4PXJ7U7CYM41W.pdf http://baywood.metapress.com/link.asp?target=contribution&id=4RB4PXJ7U7CYM41W 4 W. K. Chow The Hong Kong Polytechnic University The performance of the mechanical ventilation system in large spaces is proposed to be evaluated by macroscopic numbers describing the air flow. This includes the air changes rate per hour, the air change rate per hour per floor area, the momentum jet number, and the nominal time constants. To determine which number is the best choice, experimental studies in nine big waiting halls were performed. the indoor environment in the mechanical ventilated spaces can be assessed by the measured local mean air velocity, carbon dioxide level, and local age of air. Correlations of the measured mean values of local air velocity, carbon dioxide level, and local age of air with those macroscopic flow number are investigated. It is found that the relationships of the air change rate per hour, the air change rate per hour per floor area and the nominal time constants with the mean air speed, the mean carbon dioxide concentration, and the mean local age of air were not clear. A revised momentum jet number taking the height of the diffuser into account is proposed and linear relations can be fitted empirically to correlate it with the mean air speed, carbon dioxide concentration, and the local age of air for these nine sites. It seems that this flow number can be used for evaluating the performance of the ventilation systems. European Concerted Action, <i>Indoor Air Quality and Its Impact on Man</i>, Report No. 11: Guidelines for Ventilation Requirements in Buildings, Office for Publications of the European Communities, Lexembourg, 1992. ASHRAE Standard 62-1989, <i>Ventilation for Acceptable Indoor Air Quality</i>, ASHRAE, Atlanta, U. S. A., 1989. ASHRAE Standard 55-1992, <i>Thermal Environmental Conditions for Human Occupancy</i>, ASHRAE, Atlanta, U. S. A., 1992. ISO Standard 7730, <i>Moderate Thermal Environments—Determination of the PMV and PPD Indices and Specification of the Conditions for Thermal Comfort</i>, International Standards Organization, Geneva, 1985. ISO Standard 7726, <i>Thermal Environments—Instrument and Methods for Measuring Physical Quantities</i>, International Standards Organization, Geneva, 1985. W. K. Chow and W. Y. Fung, <i>Experimental Studies on the Air Flow Characteristics of Spaces with Mechanical Ventilation, ASHRAE Transactions, 103</i>:1, pp. 31-41, 1997. P. O. Fanger, A. K. Melikov, H. Hanzawa, and J. Ring, Air Turbulence and Sensation of Draught, <i>Energy and Building, 12</i>, pp. 21-39, 1988. J. R. Ogilive and E. M. Barber, Jet Momentum Number: An Index of Air Velocity at Floor Level, in <i>Building Systems: Room Air and Air Contaminant Distribution</i>, L. L. Christianson (ed.), ASHRAE, pp. 211-214, 1988. W. M. Barber, S. Sokgansanj, W. P. Lampman, and J. R. Ogilive, <i>Stability of Air Flow Patterns on Ventilated Space</i>, ASAE Paper 82-4551, 1982. M. Sandberg and M. Sjoberg, the Use of Moments for Assessing Air Quality in Ventilated Rooms, <i>Building and Environment, 18</i>:4, pp. 181-197, 1982. W. K. Chow, <i>On Ventilation Design for Underground Car Parks, Tunnelling and Underground Space Technology, 10</i>:2, pp. 225-246, 1998.