Daylighting and energy implications due to shading effects from nearby buildings

Daylighting has long been recognized as a potential energy-efficient design strategy for buildings. Natural light can help reduce the electrical demand and the associated sensible cooling load due to artificial lighting. In Hong Kong, however, many buildings are constructed close to each other and hence the external environment plays a significant role in daylighting designs. This paper investigates the shading effects due to nearby obstructions when daylighting schemes are being employed. We used the computer simulation tool, EnergyPlus, to illustrate the energy performance of a generic commercial building with daylighting controls obstructed by neighbouring buildings of various heights. Analysis of electricity savings was carried out for the perimeter zones of the whole building and individual floors. Regression techniques were conducted to correlate the building energy savings and the angles of obstructions. It was found that the shading effects due to nearby obstructions strongly affect the building energy budget when daylighting designs are used. Building designers should critically consider the external environment in order to achieve energy-efficient building designs.     

Carbon emission offsets for aviation-generated emissions due to international travel to and from New Zealand

International air transport emissions are not subject to liability under the Kyoto Protocol. However, pressure is mounting globally for international aviation to be included in post-Kyoto arrangements. In the absence of international collective action, a number of so-called carbon offsetting schemes have emerged that allow individual travellers and companies to compensate for their international air travel emissions. These schemes offer technological solutions, such as planting sink forests to sequester emissions. To consider the implications of future collective action, this paper presents a case study assessment of the physical feasibility of five schemes for all short duration journeys to and from New Zealand. This is the first comprehensive national-level case study assessment of competing offsetting options for international aviation emissions in the peer-reviewed literature. The CO₂-e emissions produced by the air travel of international visitors to New Zealand, and for New Zealand residents travelling overseas, is calculated in this paper to be 7893 and 3948 Gg, respectively, in 2005. It is then shown that no single offsetting scheme targeted inside the country appears physically and/or politically realistic. This indicates the sheer size of these emissions, and the challenge that the international community faces for collective action on this matter.     

Characterization of transport properties in gas diffusion layers for proton exchange membrane fuel cells: 1. Wettability (internal contact angle to water and surface energy of GDL fibers)

This is the first in a series of papers in which we present state-of-the-art methods demonstrated at Case for the estimation of transport properties in gas diffusion layers (GDLs) for proton exchange membrane fuel cells (PEMFCs). Most of the methods used today for measuring wettability properties of GDLs are related to the external contact angle to water. The external contact angle however does not describe adequately capillary forces acting on the water inside the GDL pores. We show as well that the direct method of estimation of the internal contact angle using goniometry on micrographs is impractical. We propose and describe in this paper a method for estimating the internal contact angle to water and the surface energy of hydrophobic and hydrophilic gas diffusion media. The method was applied to GDLs having different contents of hydrophobic agent and carbon types. The method can be applied separately to different components of the GDL including macro-porous substrates and micro-porous layers. The uncertainty estimates using this method are usually within 3% of the measured value.