S.L. Wong

Daylighting and its implications to overall thermal transfer value (OTTV) determinations

The overall thermal transfer value (OTTV) and daylighting are two approaches controlling building energy use. In Hong Kong, although OTTV calculations are mandatory in the submission of building plans for approval, daylighting credits are not included in building envelope designs. To promote energy-efficient building designs we use the computer simulation tool, DOE-2, to illustrate the energy performance of a generic commercial building due to various daylighting schemes and OTTV designs. The year-round energy expenditures and loads are determined from the simulation results. Analysis is carried out in terms of the reduction in electric lighting requirement and the cooling penalty due to solar heat. Regression techniques are conducted to correlate the annual incremental electricity use with OTTV and daylighting aperture (DA) (product of window-to-wall ratio (WWR) and light transmittance (LT)). Contours of equal annual incremental electricity use for different building envelope parameters are developed. Important features for daylighting schemes are highlighted and implications for OTTV designs are discussed.

Climatic effects on cooling load determination in subtropical regions

The prevailing local climatic conditions affect the building loads and the heating, ventilating and air conditioning equipment sizing and performance. This paper presents work on the determination of outdoor design conditions for cooling load calculation. The computer package DOE-2.1E was used to simulate the hourly cooling load of a generic commercial office building in Hong Kong. Totally, 22 weather data sets, from 1979 to 2000, were used for the analysis. The findings indicate that the outdoor climatic conditions developed for cooling load estimation via the simulations are less stringent than the current outdoor design data and approaches adopted by local architectural and engineering practices. Building designers should select and evaluate critically the outdoor design conditions in order to achieve optimum air conditioning equipment sizing.

Experimental measurements and large eddy simulation of expiratory droplet dispersion in a mechanically ventilated enclosure with thermal effects

Abstract Understanding of droplet transport in indoor environments with thermal effects is very important to comprehend the airborne pathogen infection through expiratory droplets. In this work, a well-resolved Large Eddy Simulation (LES) was performed to compute the concentration profiles of monodisperse aerosols in non-isothermal low-Reynolds turbulent flow taking place in an enclosed environment. Good care was taken to ensure that the main dynamical features of the continuous phase were captured by the present LES. The particle phase was studied in both Lagrangian and Eulerian frameworks. Steady temperature and velocity were measured prior to droplet emission. Evolution of aerosol concentration was measured by a particle counter. Results of the present LES were to compare reasonably well with the experimental findings for both phases.