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Electric Energy Efficiency in Power Production & Delivery
Published in Clark W. Gellings, The Smart Grid: Enabling Energy Efficiency and Demand Response, 2020
The efficiency of water heaters is measured with a quantity called the energy factor (EF). Higher EF values equate to more efficient water heaters. Typical EF values range from about 0.7 to 9.5 for electric resistance heaters, 0.5 to 0.8 for natural gas units, 0.7 to 0.85 for oil units, and 1.5 to 2.0 for heat pump water heaters (Smith, et al., 2008). Since there are no flame or stack losses in electric units, the major factor affecting the efficiency of electric water heaters is the standby loss incurred through the tank walls and from piping. The heat loss is proportional to the temperature difference between the tank and its surroundings. Newer systems produce hot water on demand, eliminating the storage tank and its associated losses.
Toward comprehensive zero energy building definitions: a literature review and recommendations
Published in International Journal of Sustainable Energy, 2021
Javad Taherahmadi, Younes Noorollahi, Mostafa Panahi
Net-zero emissions: A net-zero emissions building produces at least as much emissions-free renewable energy as it uses from emissions-producing energy sources. Maybe it can be said, the two most common definitions in articles are ‘net-zero site energy’ and ‘net-zero source energy’. The meaning of Net-zero site energy is that annual energy production in the site and annual energy demand are similar, and these values are independent of energy production or utilisation. In the definition of ‘net-zero energy source,’ calculation for energy export and import is done by a primary energy conversion factor, which can be useful to create flexibility in the heating fuel usage. For instance, if the primary electricity factor is higher than other heating fuels factor and a building sells electricity to the utility companies, the allowed amount of heating fuel will be more significant because of its smaller primary energy factor.
Experimental study of paper drying with direct-contact ultrasound mechanism
Published in Drying Technology, 2023
Zahra Noori O’Connor, Jamal S. Yagoobi, Burt S. Tilley
Hardwood and softwood hand-sheet samples are dried using direct-contact ultrasound mechanism. The results confirm that ultrasonic drying mechanism is more efficient at higher moisture content levels. IR camera images for the temperature on the surface of the transducer revealed that by applying ultrasound, first the temperature in the center increases and then by propagating the oscillations through the surface of the transducer, the temperature increases through the surface. Comparing the drying curve of ultrasound mechanism with the drying curve from thermal drying at 80 °C showed a significant decrease in drying time. ANOVA is done for both hardwood and softwood. The independent factors in the analysis are including initial moisture content, thickness, and refining condition of the pulp and two high and low levels are considered for each factor. The results showed that for the total time of ultrasonic drying, the thickness has the maximum effect and after that initial moisture content is important. These findings for ultrasonic drying behavior of paper samples are related to the structural characteristics of the samples. Therefore, microstructure of the samples is investigated and the surface profilometers are measured. The results showed that softwood fibers are coarser than hardwood fibers. Therefore, the pores in softwood are larger and the porosity is higher compared to hardwood. In addition, unrefined samples have larger pores compared to refined samples and hence, unrefined dries faster. Therefore, as it is expected, the structure of the sample (refined, unrefined, or a mixture) has a significant impact on drying curve. The quality of the ultrasonically dried samples is measured using colorimeter analysis for whiteness index. Using regression analysis two equations for both hardwood and softwood are provided. These equations describe the total time of drying and whiteness index. To analyze the energy efficiency of the ultrasonically dried samples, energy factor (EF) is defined as the ratio of the energy required for evaporation to the energy that generates the ultrasonic vibrations. The higher energy factor means the process is more energy efficient. The results showed that the energy factor for direct-contact ultrasonic drying for the current setup is 0.2-0.6. This implies that better design of transducers is required to increase the efficiency of the process. Furthermore, increasing the initial moisture content to 700% results in higher energy efficiency for ultrasonic drying compared to thermal drying. The energy factor for unrefined samples is higher than refined samples, which agrees with the fact that unrefined samples dry faster than refined samples. The refined samples show higher tensile strength comped to that of unrefined samples. This study provides the foundation for the next studies of fundamental understanding of ultrasound mechanism for hand-sheet drying.