Joseph C. Lam

A study of Weibull parameters using long-term wind observations

The two parameters of a Weibull density distribution function were calculated for three different locations; a city area, an extremely exposed area in a city centre and an open sea area in Hong Kong. A long-term data source, consisting of thirty years (1968–1997) of hourly mean wind data, was adopted and analysed. Based on these data, it was found that the numerical values of the shape and scale parameters for these weather stations varied over a wide range. The shape parameter varied from 1.63 to 2.03 and the scale parameter ranged from 2.76 to 8.92. The yearly Weibull probability density function distribution for the city area indicated that the wind data could be grouped into two distinct periods, 1968–1981 and 1982–1997. Seasonal Weibull distribution for the three locations were compared and wider distributions were observed in the more open areas.

Sensitivity analysis of energy performance of office buildings

Abstract The sensitivity of energy performance of office buildings in Hong Kong is examined. Basic principles of sensitivity methods for the study of building energy performance are explained. The DOE-2 building energy simulation program is used on a generic model of an office building to generate data for the study. Important input design parameters are identified and analysed from points of view of annual building energy consumption, peak design loads and building load profiles. It is believed that sensitivity techniques are useful for assessing thermal responses of buildings and data variability in building energy simulation. However, the results should be interpreted in context with clear understanding of the implications and limitations.

Evaluation of lighting performance in office buildings with daylighting controls

Lighting control integrated with daylighting is recognised as an important and useful strategy in energy-efficient building designs and operations. It is believed that proper daylighting schemes can help reduce the electrical demand and contribute to achieving environmentally sustainable building development. This paper presents field measurements on daylighting for a fully air-conditioned office building in Hong Kong. Electricity consumption by the fluorescent luminaires, indoor illuminance levels and the room parameters affecting daylighting designs were recorded and analysed. The measurements covered several cellular offices facing opposite orientations with and without daylighting controls. The findings suggest that daylighting schemes can result in substantial energy savings in air-conditioned office buildings in Hong Kong. Results are presented and the design implications are discussed.

Energy analysis of commercial buildings in subtropical climates

The overall thermal transfer value (OTTV) concept has been extended to correlate the OTTV of building envelope designs with other key building design parameters through DOE-2 computer simulations. A survey of 146 commercial buildings completed between 1975 and 1995 provides the information on the prevailing architectural designs and construction practices in Hong Kong. This information forms a basis for the development of a generic office building used in the computer analysis. Four major design aspects have been considered, namely the building envelope, indoor design conditions, internal loads and heating, ventilation and air-conditioning (HVAC). Implications for energy efficiency in the commercial sector energy use are discussed.

Climatic and economic influences on residential electricity consumption

We have performed regression and correlation analyses to investigate the relationships between residential electricity consumption and economic variables and climatic factors for Hong Kong. Economic and energy data for the 23-year period from 1971 to 1993 have been gathered and analysed. It has been found that both the seasonal and the yearly electricity use in the residential sector can be estimated based on the household income, household size, electricity price and cooling degree-days.

CORRELATION BETWEEN GLOBAL SOLAR RADIATION AND ITS DIRECT AND DIFFUSE COMPONENTS

Abstract Work on typical correlations between global solar radiation and its direct and diffuse components is reviewed. Data for diffuse, global horizontal radiation measured at the City University of Hong Kong for the period 1991–1994 are analysed. Three correlations are considered — the diffuse coefficient (K d ) and the clearness index (K t ), the diffuse fraction (K) and K t , and the direct normal (I dn ) and K t . A hybrid correlation model based on hourly measured data is proposed for the prediction of hourly direct and diffuse components from the global solar radiation for Hong Kong.

An analysis of daylighting and solar heat for cooling-dominated office buildings

Computer simulation techniques were used to assess the energy performance of a generic commercial office building in Hong Kong. The simulation tool was DOE-2.1E. The thermal and energy performance of daylighting schemes were analysed in terms of the reduction in electric lighting requirement and the cooling penalty due to solar heat. Regression analysis was conducted to correlate the peak electricity demand and annual incremental electricity use with two fenestration variables, namely the solar aperture and the daylighting aperture. Contours of equal annual incremental electricity use were shown to be a function of the solar and daylighting apertures. It is envisaged that these simple charts can be a useful design tool for architects and engineers to assess the relative energy performance of different fenestration designs, particularly during the initial design stage when different building design schemes and concepts are being considered and developed.

An analysis of climatic parameters and sky condition classification

Abstract In modelling solar radiation, of the required data daylight illuminance, luminous efficacy, radiance and luminance sky distributions, are always analysed under various sky types. Sky conditions are frequently categorised into overcast, partly cloudy and clear using some common climatic data including cloud cover ( CLD ), sunshine hour ( SH ) and solar radiation. This paper presents the study of these climatic parameters and their applications in the classification of sky condition. Frequency of occurrence and cumulative frequency distribution of each sky indicator have been established to interpret the prevailing sky conditions in Hong Kong. Special features on defining the sky clearness are highlighted and the implications for energy-efficient building designs are discussed.

Solar heat gain factors and the implications to building designs in subtropical regions

In subtropical Hong Kong, solar heat through fenestration, particularly on vertical surfaces, plays a major role in determining the thermal performance of a building. For sizing air-conditioning equipment, maximum solar heat gain factors (SHGFs) are used for estimating the design peak load. Recently, the SHGF data representing the prevailing weather conditions have become important and more practical for evaluating daylighting designs and the determination overall thermal transfer value (OTTV). This paper describes a procedure for calculating hourly SHGFs for horizontal and vertical surfaces based on the 8-year (1991 to 1998) horizontal global and diffuse radiation and the 3-year (1996 to 1998) vertical global solar radiation data measured at the City University of Hong Kong. A simple approach for estimation of solar heat gain is developed. Average and peak SHGFs and sky factors for OTTV are computed and compared. An analysis of the SHGF data has shown that except for the north-facing surface, the ASHRAE clear sky approach tends to overestimate the solar heat gains, particularly at large significant levels. The findings provide information for the determination of the total air-conditioning plant capacity at peak load operation and multiple equipment sizing under part load condition.

Residential sector air conditioning loads and electricity use in Hong Kong

Abstract We present the household electricity use for air conditioning in the residential sector in Hong Kong during the 26 year period from 1971 to 1996. Air conditioning accounts for about one third of the total electricity use in the residential sector. A survey of the existing residential buildings has been conducted to establish typical design features. Based on these typical design variables, we use computer simulation techniques to estimate the likely energy savings from two energy efficient measures — the use of tinted glass to reduce solar heat and the application of thermal insulation to the external walls to lower heat conduction. The building energy computer program DOE-2 was used to predict the electricity savings for the 11 year period from 1997 to 2007. It has been found that the electricity savings are small during the initial years, about 0.2% of the total electricity use in the residential sector in 1997. However, as older buildings are replaced by newer ones with more energy efficient design features, the energy savings in subsequent years will have a bigger impact on the overall electricity use situation in the residential sector.