Energies2015, 8(10), 11139-11152; doi:10.3390/en81011139 - published 7 October 2015 Show/Hide Abstract
Abstract: Temporary housing must be developed to support the long-term residence needs of disaster victims. The present study assesses a temporary housing unit, the so-called Mobile Energy Shelter House (MeSH), incorporating the “Korean Dwelling Insulation Standard” in order to reduce energy usage for cooling and heating. To assess energy performance, the characteristics of the indoor thermal environment were measured during the winter and summer seasons. In summer, at maximum insolation, the outdoor temperature was 37.6 °C and the indoor temperature of the MeSH ranged from 18 to 24 °C when the cooling system was not used. Conversely, during winter, the average outdoor temperature was −11.3 °C and the indoor temperature ranged from 16.09 to 20.63 °C when a temperature-controlled floor-heating was installed. Furthermore, the Predicted Mean Vote (PMV) was adopted to determine whether the ISO 7730 comfort criterion (i.e., PMV range from −0.5 to +0.5) was achieved. Based on the calculations presented here, PMV in summer ranged from −1.21 to +1.07 and that in winter ranged from −0.08 to −0.85, suggesting that the thermal environment is not always comfortable for occupants in either summer or winter. Nevertheless, the ISO comfort criterion can be achieved through varying air velocity in summer and changing clothing characteristics in winter. A comparison between yearly energy demand of existing characteristic temporary housing (Shelter House) and the MeSH modules used in this study was performed. The simulation results show a 60% difference in energy demand between MeSH and existing temporary housing shelter houses.
Energies2015, 8(10), 11120-11138; doi:10.3390/en81011120 - published 7 October 2015 Show/Hide Abstract
Abstract: This paper investigates the energy performance of off-grid residential hybrid renewable electric power systems, particularly the effect of electric load profiles on the ability to harvest available solar energy and avoid the consumption of auxiliary energy in the form of propane. The concepts are illustrated by an analysis of the energy performance of electric and propane-fired refrigerators. Off-grid electric power systems frequently incorporate a renewable source, such as wind or solar photovoltaic (PV), with a back-up power provided by a propane fueled motor/generator. Among other design decisions, residential consumers face the choice of employing an electric refrigerator with a conventional vapor compression refrigeration system, or a fuel-fired refrigerator operating as an absorption refrigeration system. One interesting question is whether it is more advantageous from an energy perspective to use electricity to run the refrigerator, which might be provided by some combination of the PV and propane motor/generator, thereby taking advantage of the relatively higher electric refrigerator Coefficient of Performance (COP) and free solar energy but having to accept a low electrical conversion efficiency of the motor/generator, or use thermal energy from the combustion of propane to produce the refrigeration effect via an absorption system, albeit with a much lower COP. The analysis is complicated by the fact that most off-grid renewable electrical power systems utilize a battery bank to provide electrical power when it is not available from the wind turbine or PV system, so the state of charge of the battery bank will have a noticeable impact on what energy source is available at any moment in time. Daily electric load profiles combined with variable solar energy input determine the state of charge of the battery bank, with the degree of synchronization between the two being a critical factor in determining performance. The annual energy usage and fuel input depend strongly on the ability to make use of the renewable sources in real time to avoid battery bank conversion losses and dumping of excess electrical power, as well as to have sufficient battery storage capacity to minimize the need for operation of the motor/generator to meet electric loads which occur during periods when the renewable energy is not available.
Energies2015, 8(10), 11095-11119; doi:10.3390/en81011095 - published 7 October 2015 Show/Hide Abstract
Abstract: The scheduling of both absorption cycle and vapour compression cycle chillers in trigeneration plants is investigated in this work. Many trigeneration plants use absorption cycle chillers only but there are potential performance advantages to be gained by using a combination of absorption and compression chillers especially in situations where the building electrical demand to be met by the combined heat and power (CHP) plant is variable. Simulation models of both types of chillers are developed together with a simple model of a variable-capacity CHP engine developed by curve-fitting to supplier’s data. The models are linked to form an optimisation problem in which the contribution of both chiller types is determined at a maximum value of operating cost (or carbon emission) saving. Results show that an optimum operating condition arises at moderately high air conditioning demands and moderately low power demand when the air conditioning demand is shared between both chillers, all recovered heat is utilised, and the contribution arising from the compression chiller results in an increase in CHP power generation and, hence, engine efficiency.
Energies2015, 8(10), 11076-11094; doi:10.3390/en81011076 - published 6 October 2015 Show/Hide Abstract
Abstract: A simplified version of the ecological footprint method is proposed for assessing the environmental performances of urban transportation systems. The method, starting from the knowledge of the composition of the running vehicular fleet, is here applied to a southern Italian province. It represents a synthetic indicator of the environmental pressure exerted by the system also matching the pollutant emissions with the carrying capacity of the site. Particularly, the forested area needed to absorb the CO2 emissions of the system is compared with the total forested area of the province. The results of the case-study indicates the yearly maximum distance that each vehicle of the fleet can cover in order for their emissions to be absorbed by the surrounding forested area. Specifically, if all cars of the fleet would travel for 10,000 km/year, 97% of the forested area would be involved. Thanks to its features, this indicator can be usefully adopted for ranking different transportation options. Therefore, it could allow local administrations to environmentally hierarchize alternative plans concerning urban transportation choices.
Energies2015, 8(10), 11047-11075; doi:10.3390/en81011047 - published 2 October 2015 Show/Hide Abstract
Abstract: The contribution of embodied energy (EE) and greenhouse gas emissions to building materials and structures has been recognized as significant, especially for nearly-zero energy-efficient buildings. The aim of this paper is to evaluate the composition of non-transparent structures of building envelopes from energy and environmental perspectives using the life-cycle assessment method. The study assesses environmental indicators such as EE from non-renewable resources and CO2eq and SO2eq emissions from proposed assemblies of building structures for nearly-zero energy wooden houses. Material compositions are also calculated in terms of selected thermal-physical aspects (U-value, phase shift of thermal oscillation, relaxation time) to ensure the reduction of energy consumption during building operation. All results are compared using a multi-dimensional evaluation approach through mathematical methods. The multi-criteria decision analysis demonstrates that material optimization of building structures is possible to ensure a marked reduction of the energy consumption and carbon footprint of buildings.
Energies2015, 8(10), 11030-11046; doi:10.3390/en81011030 - published 1 October 2015 Show/Hide Abstract
Abstract: The accurate information of the initial rotor position is very critical for successful starting of the Surface-mounted Permanent Magnet Synchronous Motor (SPMSM). In order to solve the problems of low accuracy and unreliability in the conventional estimation strategy, in this paper, an improved initial rotor position estimation strategy without any position sensor for SPMSM at standstill is proposed based on rectangular pulse voltage injection. In the work, when the second series of pulse voltages were applied. By the ways of strengthening the effect of weakening or strengthening magnetic fields and increasing the difference between each current of the vector. The improved strategy enhanced reliability and raised the initial position estimation accuracy from 7.5° to 1.875°. The improved strategy does not need any additional hardware. Experimental results demonstrate the validity and usefulness of the improved strategy.