W. K. Chow

Solar radiation model

Solar radiation models for predicting the average daily and hourly global radiation, beam radiation and diffuse radiation are reviewed in this paper. Seven models using the Angstrom-Prescott equation to predict the average daily global radiation with hours of sunshine are considered. The average daily global radiation for Hong Kong (22.3°N latitude, 114.3°E longitude) is predicted. Estimations of monthly average hourly global radiation are discussed. Two parametric models are reviewed and used to predict the hourly irradiance of Hong Kong. Comparisons among model predictions with measured data are made.

Numerical studies on performance evaluation of tunnel ventilation safety systems

The performance of tunnel safety systems for fire protection and ventilation provision is evaluated using Computational Fluid Dynamics (CFD). Ventilation safety systems commonly used in tunnels are reviewed first. The safety aspects related to tunnel fire and ventilation are then discussed. Air flow induced by an accidental vehicular fire in a tunnel is simulated using CFD. Based on the results, performances of different safety systems are evaluated and compared. Systems considered are longitudinal, semi-transverse, transverse, partial transverse, and combined longitudinal and semi-transverse ventilation systems. Furthermore, sensitivity analyses on the effects of the grid size, and number of iterations on the required computing time and accuracy of the results are carried out.

Application of Computational Fluid Dynamics in building services engineering

Abstract Application of Computational Fluid Dynamics to building services design is illustrated and reviewed. Principal areas of application are designs requiring an understanding of the air flow pattern, such as design of smoke control systems and air distribution in a heating, ventilation and air-conditioning system. In such an approach, the indoor air motion is described by a set of partial differential equations describing conservation of mass, momentum, enthalpy and chemical species concentration, if any. The air flow pattern, temperature contour, and chemical species concentration distribution induced by thermal sources are predicted by solving that system of equations using the finite difference method. Assessment of the longitudinal ventilation in a tunnel, smoke filling in an atrium, and the interaction between the airflow induced by a fire and a sprinkler water spray are illustrated in the area of fire engineering. Simulation of the combustion process is briefly reviewed. Calculation of the macroscopic flow parameters in an air-conditioned gymnasium and an office is demonstrated.

Review on chemical reactions of burning poly(methyl methacrylate) PMMA

Chemical reactions of burning Poly(methyl methacrylate) (PMMA) are reviewed in this paper although kinetics of thermal decomposition are believed to be fairly simple. Basically, there are three stages in the combustion of PMMA. Firstly, PMMA decomposes to produce monomer methyl methacrylate (MMA). Secondly, monomer MMA decomposes to generate small gaseous molecules that are usually combustible. Finally, these small molecules undergo combustion. Recent studies on the thermal decomposition kinetics and thermal stability of PMMA are also introduced. Results are useful for understanding the heat released of burning PMMA per unit mass of oxygen. Finally, the effects of additives on thermal decomposition are also discussed.

Building Fire Safety in the Far East

Building fire safety activities in the Far East will be briefly reviewed in this paper. Fire safety concerns in some buildings with new architectural features will be discussed. Glass constructions need special attention. Key points on building fire safety provisions, including both passive building construction and active fire protection systems will be pointed out. Whether the current fire codes are applicable for new architectural features, the use of new materials, new style of living and capability of solving the new fire safety problems will be discussed. The total fire safety concept of implementing software fire safety management to control hardware provisions is recommended. Application of fire models is reviewed. Performance-based design is then discussed. New problems to consider such as fire spread over buildings, crowd movement and control, and fire impact to structures are outlined.

Studies on the thermal behavior of polyurethanes

The number of fires appear to be increasing all over the world with some big fires started from burning sofa polyurethane foam (PUF). The general public is quite concerned about the risk of fire due to the extensive use of polyurethane-based materials. Better understanding of the fire behavior of the materials would provide guidelines on fire safety provision. The first step is to review the thermal decomposition mechanisms of polyurethane under different environmental conditions, which will be reported in this paper. Recent studies on the thermal decomposition kinetics and thermal stability of polyurethane are described. Thermal decomposition and combustion reactions of polyether-polyurethane and polyester-polyurethane in air and nitrogen atmospheres investigated by using thermogravimetry analysis will then be outlined. The kinetic processes of polyurethane decomposition studied by the model fitting method are discussed. Polyester-polyurethane was found to be thermally more stable than polyether-polyurethane. The presence of oxygen would significantly affect the breaking down of the polymeric chains. Fire retardants for polyurethane are also briefly reviewed. Results are useful for developing fire retardants for polyurethane-based materials with better fire behavior.

Use of Computational Fluid Dynamics for Simulating Enclosure Fires

This paper reports on comparing results on the fire environment predicted by using the technique of computational fluid dynamics (CFD) (or field modelling) on simulating an enclosure fire at the preflashover stage with those results reported experimentally in the literature. The theory behind this is to solve a system of partial differential equations describing conservation of mass, momentum and heat with the k-ε turbulence model. The computer pro gram PHOENICS is used as the simulation tool. By specifying the geometrical configurations of the enclosure and the location, size and thermal power of the fire source, it is possible to predict the fire-induced flow and temperature fields. The package can be executed in an IBM personal computer at or above 486 level. Experiments reported by Steckler et al. at the National Bureau of Stan dards, U.S.A. on a single fire chamber; Nakaya et al. at the Building Research Institute, Japan on a double room fire chamber; the corner fire plume by Tran and Janssens; the two-room fire experiment reported by Hagglund at the Na tional Defence Research Establishment (abbreviation: FOA), Sweden; and in the full-scale burning hall by Ingason and Olsson at the Swedish National Test ing and Research Institute (abbreviation: SP), Sweden are considered. Some of the results on the temperature and interface height of the smoke layer are com pared with the popular fire zone model CFAST.

Preliminary studies on burning behavior of polymethylmethacrylate (PMMA)

The burning behavior and combustion mechanism of polymethylmethacrylate (PMMA) were studied by using cone calorimeter, mass spectrograph and gas chromatograph. Main combustion mechanisms of PMMA were reviewed. Results indicated that PMMA would burn steadily under low radiative heat flux; or with thicker samples. The yields of carbon dioxide and carbon monoxide would not be changed. Under high heating rate, there are three broad stages. Firstly, upon heating by external sources, PMMA would decompose to generate monomer MMA and a small amount of other products. Secondly, monomer MMA would decompose to produce small molecule products. Finally, these small gaseous molecules would undergo oxidation, i.e., burning. The main oxygen consumption reaction, i.e., the heat release reaction, is the burning of small molecule products. Main combustion products are found to be carbon dioxide and water, with a small amount of carbon monoxide. At high temperature, the monomer MMA would react with oxygen directly to produce methyl pyruvate, formaldehyde and acetone. However, these reactions are not important in the combustion process of PMMA.

Energy use in commercial buildings in Hong Kong

The energy performances of 20 commercial buildings, covering the common types found in Hong Kong, have been studied. The monthly electricity billing data as well as the results from computer modeling were analyzed. Energy signatures for the commercial buildings were found by a method similar to PRISM. Correlation equations of energy use with building envelope parameters, such as OTTV, building size, envelope heat gain, and the annual chiller-load were derived. The results are useful for building envelope design, energy audit, and legislative control of energy use in commercial buildings.

Fire Safety in Green or Sustainable Buildings: Application of the Fire Engineering Approach in Hong Kong

‘Green’ or ‘sustainable’ buildings might give new architectural features where prescriptive fire codes are difficult to follow. Examples include the internal voids, double-skin facades and others. As a result, ‘fire engineering approach’ which is similar to applying fire safety engineering to passive construction design through engineering performance-based fire codes used in overseas has been accepted by the local government since 1998. In this paper, the historical background of local fire codes will be briefly discussed first. The fire engineering approach will then be introduced. How fire engineering approach was applied to safety provisions in ‘green or sustainable buildings’ since 1998 will be described. Basically, three levels of studies had been adopted for over 30 new projects or renovations of the existing buildings related to ‘green or sustainable’ buildings.