K.T. Chan

Applying condensing-temperature control in air-cooled reciprocating water chillers for energy efficiency

This paper reports on the modelling and findings of the energy performance of an air-cooled reciprocating multiple-chiller plant under the conventional head pressure control and the new condensing-temperature control in a subtropical climate. The simulation model was validated using the operating data of an existing chiller plant. As noted from this existing air-cooled reciprocating chiller plant, there was a substantial efficiency drop at part-load resulting from the head pressure control. If operating at variable lower condensing-temperatures based on the established operating mode of the condenser fans and compressors, it is shown that the chiller consumption can be maintained below 2 kW/refrigeration ton throughout the entire range of outdoor temperature and part-load conditions, giving an average efficiency of 1.08 kW/refrigeration ton. The energy imposition due to cycling on more condenser fans can be compensated by the reduced compressor consumption. Potential energy savings of 18.2 and 29% in the annual chiller consumption are achievable by applying the condensing-temperature control to two existing chiller plants studied. This supports the need to develop the condensing-temperature control as an improvement to the conventional head pressure control.

Energy impact of commercial-building envelopes in the sub-tropical climate

Existing commercial buildings are surveyed and categorized based on the construction characteristics of their envelope. The envelope heat gain and the resulting cooling load demand are analysed with the aid of energy simulation tool DOE-2.1D. The concept of the overall thermal transfer value (OTTV) is applied to study the association of the envelope designs with the cooling requirement, and a modified approach in assessing the effective envelope heat gains under a sub-tropical climate is proposed. The predicted OTTV gives a good indication of the thermal performance of the envelope under a sub-tropical climate. The energy impact and possible range of cooling-load demands, for various envelope designs, under similar internal characteristics and cooling system, are identified.

Parameterization study of the overall thermal-transfer value equation for buildings

Modern buildings in Hong Kong are characterized by high window-to-wall ratios. This leads to large energy consumption due to the solar radiative heat gain. The problem is now of great concern to the industry not just because of the energy usage, but also due to the environmental problem that arises from overusage of energy. The government is considering implementing some regulations for controlling the cooling load in centrally air-conditioned buildings. The concept of overall thermal-transfer value (OTTV) is proposed to be used as a guideline for designing the building envelopes. However, those equations for calculating the OTTV recommended by the draft design guide are rather unclear. Many parameters that influence the OTTV equation have not been studied thoroughly yet. This paper aims at carrying out a parameterization study on the OTTV equation. The window-to-wall ratio, shading coefficient, wall absorptance and wall heat capacity are found to be important parameters. Modification of the equivalent temperature that appears in the OTTV equation is recommended. Finally, the effect of overhang on the solar load value is also investigated.

Fire safety engineering: comparison of a new degree programme with the model curriculum

Abstract The curriculum design of a new degree programme in Building Services Engineering with Fire Engineering Specialism for the local fire engineering professionals in the Hong Kong Special Administrative Region is reported. The programme was approved by The Hong Kong Polytechnic University and offered in September 1997 with an intake of 25 students per year. The aims are to train fire engineers who can handle not only ‘traditional’ fire engineering systems, but also perform the ‘new’ procedure of fire safety engineering hooked up with the development of ‘performance-based fire codes’ in an ‘engineering approach’. Subject contents to be included in a fire safety engineering degree programme are proposed. A comparison of this new scheme with the model curriculum in Fire Safety Engineering is made. Coverage of topic areas on fire engineering and teaching hours are compared. Differences in the curricula have been identified and discussed.

Building energy analysis simulation: Experience of three programs in use

This paper reports an experience of using three building energy analysis programs- BLAST-3.0, DOE-2.1D and ESP version 7 release 2b. The programs are validated and their results compared for the subtropical climate of Hong Kong. Two occupied buildings have been studied to evaluate the programs; a ten-storey office building and a Polytechnic lecturers office. The indoor conditions and the energy consumptions of the two buildings were measured. The predicted energy performance is compared with the measured energy consumption for the two buildings. Discrepancies between the simulated results and the measured performance, and likely problems in the application of these programs by practicing engineers, are discussed. The applicability of the three programs is further demonstrated by simulating the energy performance of a hypothetical test building, where the programs predictions of building load imposed on the air conditioning plant are compared.