Improving the energy efficiency of a control cabinet air conditioner through the use of variable refrigerant flow capacity control

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Control cabinet air conditioners are used to regulate the temperature of an enclosure containing electrical equipment. Normally, these air conditioners are selected for worst-case conditions, and work on an on/off control. This paper describes the work carried out to analyse the performance of an air conditioner (AC) with variable refrigerant flow (VRF) for a masters degree dissertation [1]. The performance of a standard on/off air conditioner was first measured. The implementation of VRF in a control cabinet was carried out successfully by installing a variable-speed compressor within a standard AC unit. Experiments performed showed that the energy savings are 14% at full load and between 8 and 32% at part load. For most conditions, the enclosure temperature could be controlled to a stable value with a flat enclosure temperature profile. Maintaining a stable enclosure temperature reduces electronic component failure. A computer model was created using Microsoft Visual Basic for Applications, which could be used within Microsoft EXCEL. For a given set of ambient temperatures and enclosure loads, the model estimates the power consumption of a standard AC and a VRF AC and calculates the potential savings. When applied to various scenarios, savings of 18-25% were achieved. The system efficiency can be improved further by other changes to the AC design. A mathematical software model of the AC was built using Visual Basic Express 2005, to evaluate these potential improvements. It was shown that the COP could be improved by increasing the air-flows and by controlling evaporator superheat. By using an electronic expansion valve, the degree of superheat could be accurately controlled. Changes in refrigerant charge were found to have more effect at high ambient temperatures, with the cooling capacity being maximised with only small changes in power consumption.dc201

Analysis of the operation and performance of a solar cooling system

In recent years, renewable sources of energy have been increasingly sought after to shift the consumption of energy from conventional sources to clean energy sources. A myriad of applications exist to exploit solar, wind, geothermal and any other means to provide the required process. Solar energy systems can either produce electricity or hot water. Solar cooling systems are being installed to provide space cooling or process cooling in locations where sufficient thermal energy is present to operate the vapour absorption chiller to replace vapour compression systems. Thus since sufficient solar energy was incident on the building of the Oenology and Viticulture Research Centre at Buskett, it was used to generate hot water to operate a solar cooling system to supply chilled water to control the temperature of fermenting wine. Prior to the installation, process cooling was provided through a vapour compression system. Initially a control system was designed to operate the solar cooling system. The system could not operate during high solar radiation scenarios and thus significant number of experimentats were carried out to improve the operation and performance of the solar cooling system.peer-reviewe

Experimental investigation of the effects of hydrogen enhanced combustion in Si and Ci engines on performance and emissions

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Hydrogen enhanced combustion (HEC) is promoted as an end-user add-on that has the capability of reducing both engine tailpipe emissions and fuel consumption. An experimental investigation was carried out to measure the effects of HEC in typical engines through laboratory dynamometer testing. Three engines – (1) a carburetted petrol engine, (2) a fuel injected petrol engine and (3) a diesel engine – were tested to investigate the effects of adding hydrogen to the air intake of the engines and measure the effects on performance and emissions (HC, CO and CO2). The engines were tested at different engine speeds and loads to simulate a wide range of operating conditions. The hydrogen was produced from the electrolysis of a solution of distilled water and sodium hydroxide using two different electrolyser designs. The electrolyser constructions were suitable for automotive applications, that is, small in size and consuming current within the capability of a typical car alternator. Both the hydrogen and oxygen that were produced by electrolysis were added to the engine‘s intake during the tests. Results showed that the addition of HHO is most effective in stabilizing and enhancing the combustion of lean air-fuel mixtures inside the petrol injected engine, allowing for lower HC, CO and CO2 emissions. Thus hydrogen enhanced combustion could play a role in stabilizing lean burn petrol engines.dc201

Computer modelling of high temperature air combustion

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.High Temperature Air Combustion, HiTAC, is an innovative combustion technology which offers improved heat transfer and a reduction in fuel consumption and NOx emissions. This paper describes a project in which a computational fluid dynamic model of a furnace working on high temperature air combustion technology was developed using FLUENT® CFD software. The model was validated against experimental data obtained from KTH in Sweden. The predicted results compared very well with this experimental data, and were also closer than the predictions from the model built by KTH. The model was applied to a steam boiler of Malta’s Delimara Power Station. Two scenarios were considered: the boiler with conventional combustion and the boiler converted to HITAC. To reduce computational time, a 400:1 scaled down version of the boiler was modelled based on NOx scaling. Further reductions were made by taking advantage of the symmetry of the boiler and by obtaining the solution for a single burner, and then prescribing the parameter profiles for the single burner to the full boiler model as boundary conditions. The computer model results showed much lower NOx emission levels when firing the boiler with methane compared to heavy fuel oil. Further reductions in NOx emissions were obtained with HITAC technology and using methane as a fuel.dc201

Solar cooling at the oenology and viticulture research centre, Buskett, Rabat

This paper describes the design, installation and testing of two solar cooling systems at the Oenology and Viticulture Research Centre, Buskett, Rabat, Malta. One system consisted of a bank of photovoltaic panels converting solar energy into electricity which was fed into the national grid and a conventional vapour compression chiller powered by electricity from the grid. The second system was based on an ammonia-water vapour absorption chiller which was driven by hot water from a bank of vacuum-tube solar collectors. Dry re-cooling was chosen as the method of heat rejection.peer-reviewe

Molecular Architecture and Functional Model of the Complete Yeast ESCRT-I Heterotetramer

SummaryThe endosomal sorting complex required for transport-I (ESCRT-I) complex, which is conserved from yeast to humans, directs the lysosomal degradation of ubiquitinated transmembrane proteins and the budding of the HIV virus. Yeast ESCRT-I contains four subunits, Vps23, Vps28, Vps37, and Mvb12. The crystal structure of the heterotetrameric ESCRT-I complex reveals a highly asymmetric complex of 1:1:1:1 subunit stoichiometry. The core complex is nearly 18 nm long and consists of a headpiece attached to a 13 nm stalk. The stalk is important for cargo sorting by ESCRT-I and is proposed to serve as a spacer regulating the correct disposition of cargo and other ESCRT components. Hydrodynamic constraints and crystallographic structures were used to generate a model of intact ESCRT-I in solution. The results show how ESCRT-I uses a combination of a rigid stalk and flexible tethers to interact with lipids, cargo, and other ESCRT complexes over a span of ∼25 nm

The dynamin-like GTPase Sey1p mediates homotypic ER fusion in S. cerevisiae

The endoplasmic reticulum (ER) forms a network of tubules and sheets that requires homotypic membrane fusion to be maintained. In metazoans, this process is mediated by dynamin-like guanosine triphosphatases (GTPases) called atlastins (ATLs), which are also required to maintain ER morphology. Previous work suggested that the dynamin-like GTPase Sey1p was needed to maintain ER morphology in Saccharomyces cerevisiae. In this paper, we demonstrate that Sey1p, like ATLs, mediates homotypic ER fusion. The absence of Sey1p resulted in the ER undergoing delayed fusion in vivo and proteoliposomes containing purified Sey1p fused in a GTP-dependent manner in vitro. Sey1p could be partially replaced by ATL1 in vivo. Like ATL1, Sey1p underwent GTP-dependent dimerization. We found that the residual ER–ER fusion that occurred in cells lacking Sey1p required the ER SNARE Ufe1p. Collectively, our results show that Sey1p and its homologues function analogously to ATLs in mediating ER fusion. They also indicate that S. cerevisiae has an alternative fusion mechanism that requires ER SNAREs