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Abstract Two office layouts with high and low levels of thermal control were compared, respectively traditional cellular and contemporary open plan offices. The traditional Norwegian practice provided every user with control over a window, blinds, door, and the ability to adjust heating and cooling. Occupants were expected to control their thermal environment to find their own comfort, while air conditioning was operating in the background to ensure the indoor air quality. In contrast, in the British open plan office, limited thermal control was provided through openable windows and blinds only for occupants seated around the perimeter of the building. Centrally operated displacement ventilation was the main thermal control system. Users’ perception of thermal environment was recorded through survey questionnaires, empirical building performance through environmental measurements and thermal control through semi-structured interviews. The Norwegian office had 35% higher user satisfaction and 20% higher user comfort compared to the British open plan office. However, the energy consumption in the British practice was within the benchmark and much lower than the Norwegian office. Overall, a balance between thermal comfort and energy efficiency is required, as either extreme poses difficulties for the other.

In this paper, a hybrid modeling approach is proposed to model two-phase flow evaporators. The main procedures for hybrid modeling includes: (1) Based on the energy and material balance, and thermodynamic principles to formulate the process fundamental governing equations; (2) Select input/output (I/O) variables responsible to the system performance which can be measured and controlled; (3) Represent those variables existing in the original equations but are not measurable as simple functions of selected I/Os or constants; (4) Obtaining a single equation which can correlate system inputs and outputs; and (5) Identify unknown parameters by linear or nonlinear least-squares methods. The method takes advantages of both physical and empirical modeling approaches and can accurately predict performance in wide operating range and in real-time, which can significantly reduce the computational burden and increase the prediction accuracy. The model is verified with the experimental data taken from a testing system. The testing results show that the proposed model can predict accurately the performance of the real-time operating evaporator with the maximum error of ±8%. The developed models will have wide applications in operational optimization, performance assessment, fault detection and diagnosis.

Abstract Specification by central government of the heating levels which are to be maintained in British school buildings has recently been altered. This paper is concerned with examining the nature of changes that have been made by comparing present requirements with their counterparts during the preceding one hundred years. Attention is focused on the apparently contradictory implications of these changes for those charged with responsibility for maintaining heating levels in school buildings while, at the same time, conserving fuel. It is suggested that the new statutory requirements present those who are responsible with a duty which may, in practical terms, prove difficult or costly to discharge. Although discussion is specifically restricted to British school buildings, issues are raised which are pertinent to attempts to integrate regulation of heating with control of fuel consumption in other types of non-domestic buildings both in Britain and abroad.

It is conventionally believed that there are no self-sustained thermoacoustic oscillations in the absence of acoustic modes in combustors. However, such oscillations (also known as intrinsic thermoacoustic instability) are recently found to occur in a premixed combustor with a mean flow present but no acoustic eigenmodes involved. Practical combustors are associated with entropy waves, pressure jump and mean flow, which are ignored in previous studies without justification. In this work, an entropy-involved energy measure is defined and used to study the stability behaviors of intrinsic thermoacoustic modes. The concepts and methods are exemplified with the classical time-delay n–τ unsteady heat release model. The intrinsic thermoacoustic eigenmodes are found to be related to not only a flame transfer/describing function but also the acoustic impedance at the flame, which is boundary-dependent. It is shown that the predicted frequency ωfr of the intrinsic modes and the critical gain nc depend on the ratio T¯2/T¯1 between the after- and before-combustion temperatures and the inlet mean flow Mach number M¯1. Comparison is then made between the present results and those available in literature. Good agreement is obtained for ωfr. Furthermore, the predicted stability of intrinsic modes based on calculated nc is found to agree well with direct numerical simulations (DNS). It is also interesting to show that as T¯2/T¯1→1, the critical gain as predicted from the previous models is nc→+∞, which means that all intrinsic eigenmodes are stable. However, the present works shows that nc→1.0. Further illustration is then performed by conducting case studies of measured flame transfer and describing functions in premixed combustors. The present work opens up an alternative but more applicable way to study intrinsic thermoacoustic oscillations via the entropy-involved energy measure.

Metal-based fuel-borne catalysts (FBCs) have been used with diesel fuels to effectively reduce soot and diesel particulate matter (DPM) emissions from both on-road and off-road applications. However, there is a lack of detailed investigations on the potential changes in the properties of particulates, when FBCs-doped fuels are combusted in diesel engines. This study fully evaluates the potential impacts of ferrocene-doped ultralow sulfur diesel (ULSD) fuels on physical, chemical and toxicological characteristics of the particulates emitted by a single cylinder, direct-injection diesel engine working at a constant speed and at three engine loads. The results indicated that ferrocene-doped fuels could effectively reduce the particulate mass and elemental carbon (EC) emissions, while increasing the proportion of both organic carbon (OC) and water-soluble organic carbon (WSOC) in particles. Particle-phase PAHs and n-alkanes emissions increased with an increase of Fe in the fuels. Ferrocene addition also led to lower soot ignition temperature and activation energy. However, the total number emissions of particles from ferrocene-doped fuels dramatically increased due to the formation of Fe-rich nuclei mode particles. Compared to pure ULSD, the particles emitted from ferrocene-doped fuels showed a slight decline in cell viability. The Fe in the particles and the changes in chemical composition of particulates are thought to be responsible for the variation of cell viability.

Abstract Steady-state free and forced convective cooling of vertical, rectangular, 3 mm thick, 250 mm long fins, uniformly separated and protruding vertically upwards from a 250 mm × 190 mm isothermal horizontal base was investigated. For each combination of specified fin protrusion, horizontal forced air flow-rate in the direction along the fins and fin base temperature, the optimal fin spacing—corresponding to the maximum rate of heat loss—has been deduced. As the fin protrusion of the heat exchanger increases, this optimal value rises significantly in forced convection conditions, but declines slightly in the presence of free convection alone. The temperature distributions over the fins' surfaces were also studied, when the fin base was maintained at constant temperatures of either 40°C, 60°C or 80°C above that of the ambient environment. Large temperature depressions occurred near the leading edges and tips of the fins in forced convection, whereas much nearer isothermal temperature distributions were present under free convection conditions.

Abstract With the increasing demand for an environmentally-friendly fluid medium in the fluid-power industries, recent advances in water hydraulics technology have sparked renewed interest in the application of water, instead of oil, as the energy-transmission medium. This paper introduces the history of water hydraulics and its present research. The advantages and disadvantages of water as an energy-transmission medium are discussed. A water-hydraulic system in Nanyang Technological University is introduced.

Abstract The field of energy harvesting holds the promise of making our buildings “smart” if effective energy sources can be developed for use in ambient indoor conditions. Photovoltaics (PV), especially in its thin flexible form for easy integration, become a prime candidate for the aim, if tailored for low-density artificial light. We designed a test system which enabled us to measure the performance of PV devices under compact fluorescent lamp (CFL) and light-emitting diode (LED) illumination at different illuminance levels and compared polycrystalline and amorphous silicon cells with our own flexible dye solar cells (DSCs). Whereas poly-Si cells, with 15% outdoor efficiency, delivered at 200 lux under CFL only 2.8 μW/cm2 power density (and an efficiency of 4.4%), a-Si specifically designed for indoors, gave 5.9 μW/cm2 and 9.2% efficiency under the same CFL conditions (and 7.5% efficiency under LED). However, we show that the customization of flexible DSCs, by simply formulating ad-hoc less-concentrated, more transparent electrolytes, enabled these devices to outperform all others, providing average power densities of 8.0 μW/cm2 and 12.4% efficiencies under 200 lux CFL (more than quadruple compared to those measured at 1 sun), and 6.6 μW/cm2 and 10% efficiency under 200 lux LED illumination.

Abstract Algae have been considered as a promising biodiesel feedstock. One of the major factors affecting large-scale algae technology application is poor wintering cultivation performance. In this study, an integrated approach is investigated combining freshwater microalgae Chlorella zofingiensis wintering cultivation in pilot-scale photobioreactors with artificial wastewater treatment. Mixotrophic culture with the addition of acetic acid (pH-regulation group) and autotrophic culture (control group) were designed, and the characteristics of algal growth, lipid and biodiesel production, and nitrogen and phosphate removal were examined. The results showed that, by using acetic acid three times per day to regulate pH at between 6.8 and 7.2, the total nitrogen (TN) and total phosphate (TP) removal could be increased from 45.2% to 73.5% and from 92.2% to 100%, respectively. Higher biomass productivity of 66.94 mg L−1 day−1 with specific growth rate of 0.260 day−1 was achieved in the pH-regulation group. The lipid content was much higher when using acetic acid to regulate pH, and the relative lipid productivity reached 37.48 mg L−1 day−1. The biodiesel yield in the pH-regulated group was 19.44% of dry weight, with 16–18 carbons as the most abundant composition for fatty acid methyl esters. The findings of the study prove that pH adjustment using acetic acid is efficient in cultivating C. zofingiensis in wastewater in winter for biodiesel production and nutrient reduction.