1,720,959 research outputs found
Dynamic simulation of Ground-Coupled Heat Pumps (GCHPs): insights on the economic convenience and on the environmental benefits
No full textGround-Coupled Heat Pumps (GCHPs) allow to achieve noticeable reduction of primary energy consumption, of CO2 emissions, and operational costs of Heating, Ventilation and Air Cooling (HVAC) systems. The large installation expense is a strong barrier to their diffusion; however, GCHPs can be economically convenient in a number of contexts. We present a study which identifies such cases, based on integrated building-HVAC-GCHP dynamic simulations carried out with the software TRNSYS. Three building types were simulated, with very different schedules - a detached house, a hotel, and an office building – considering, for each of them, the case of a highly-insulated and a lowly-insulated envelope by adopting, respectively, the transmittance values typical of brand-new and Sixties’ buildings. To take into account climate conditions, 6 locations were chosen ranging from warm Mediterranean (Seville) to cold Scandinavian climate (Stockholm). The results of simulation allow to identify key parameters which influence the economic viability of GCHP systems, such as peak power demand and full-load equivalent operating hours. As shown in the results, geothermal heat pumps covering the whole heating demand are almost unfeasible without public subsidies, since the reduction of operational cost is not sufficient to cover the difference in the initial expense compared to a gas boiler. An exception is represented by hotels, due to their intense use of the heating system. To reduce the initial investment, hybrid heat pump-gas boiler configurations can be adopted, where the HP is installed to cover the base demand and a backup gas boiler is used to cover peaks. In this way, a cheaper heat pump can be installed, although covering a large share of the heating demand with renewable heat from the ground. The ratio between electricity price and fuel price is another driving parameter, since it influences the saving margin and hence the payback time of installing a heat pump. Payback times can dramatically be decreased acting on the electricity price, e.g. reducing taxes.
Finally, we analysed the effectiveness of incentives granted for different energy refurbishment interventions to avoid CO2 emissions, finding that GCHP (and, in particular, hybrid GCHP) are much more effective than interventions on the building envelope, such as window replacement
Thermal impact assessment of Groundwater Heat Pumps (GWHPs): modelling assumptions and key parameters
No full textThe increasing diffusion of Groundwater Heat Pumps (GWHPs), especially for large buildings in urban areas, needs to be managed in order to avoid reciprocal impacts between neighbouring installations and on other water uses. For this reason, a thorough hydrogeological characterisation and a rigorous modelling of the subsurface thermal impact of GWHPs is required; however, this subject has been addressed by a few studies only, among which those reported in Refs. [1-4].
We present a comprehensive sensitivity analysis, based on numerical flow and heat transfer simulations carried out with the software FEFLOW, in order to assess how the thermal plume size is affected by the aquifer’s hydrodynamic parameters, the subsurface thermal properties, the thickness of the vadose and saturated zones, and by the thermal load exchanged [5]. In particular, we addressed the plume length, width and their temporal evolution in the long term. The results of this analysis identify which parameters most affect the propagation of the thermal plume, and hence can most contribute to possible simulation errors if not properly assigned. In addition, we addressed a number of different ssumptions in the modelling of GWHPs. The heat exchange between the aquifer and the atmosphere strongly impacts on the plume length, and hence GWHPs should be modelled in 3D rather than 2D. Using the yearly average of a thermal load dramatically reduces calculation times, but may lead to a severe underestimation of the plume width. An acceptable estimation of the plume width can be performed with analytical formula by Banks [1], while this is not possible for the plume length. This work, carried out in the framework of the GRETA project [6], provides a methodological basis for the assessment of the thermal footprint of GWHPs, and hence on their sustainability in densely inhabited areas
Assessment of Energetic, Economic and Environmental Performance of Ground-Coupled Heat Pumps
Full text linkGround-coupled heat pumps (GCHPs) have a great potential for reducing the cost and climate change impact of building heating, cooling, and domestic hot water (DHW). The high installation cost is a major barrier to their diffusion but, under certain conditions (climate, building use, alternative fuels, etc.), the investment can be profitable in the long term. We present a comprehensive modeling study on GCHPs, performed with the dynamic energy simulation software TRNSYS, reproducing the operating conditions of three building types (residential, office, and hotel), with two insulation levels of the building envelope (poor/good), with the climate conditions of six European cities. Simulation results highlight the driving variables for heating/cooling peak loads and yearly demand, which are the input to assess economic performance and environmental benefits of GCHPs. We found that, in Italy, GCHPs are able to reduce CO2 emissions up to 216 g CO2/year per euro spent. However, payback times are still quite high, i.e., from 8 to 20 years. This performance can be improved by changing taxation on gas and electricity and using hybrid systems, adding a fossil-fuel boiler to cover peak heating loads, thus reducing the overall installation cost compared to full-load sized GCHP systems
Heat Pumps, Wood Biomass and Fossil Fuel Solutions in the Renovation of Buildings: A Techno-Economic Analysis Applied to Piedmont Region (NW Italy)
Full text linkThe levelized cost of heat (LCOH) and the technical feasibility in the specific context of building construction or renovation are the major drivers of users’ choices for space heating and cooling solutions. In this work, the LCOH was assessed for the most diffused heating technologies in Piedmont (NW Italy): that is, fossil fuels (methane, heating oil and liquefied petroleum gas—LPG), wood biomass (wood logs and pellet) and heat pumps (air-source and ground-source), both in heating-only and in a heating and cooling configuration. A sensitivity analysis of the main LCOH drivers was performed to assess whether and how each technology is vulnerable to energy price and upfront cost changes. The results show that heat pumps are competitive against gas boilers, but they are heavily dependent on refurbishment incentives and penalized by the high electricity prices in Italy; on the other hand, wood biomasses are competitive even in the absence of incentives. The analysis confirmed that LPG and heating oil are no more competitive with renewable heating. Acting on the taxation of natural gas and electricity is key to making heat pumps the most economically convenient solution to cover the heating and cooling needs of buildings
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Thermal Impact Assessment of Groundwater Heat Pumps (GWHPs): Rigorous vs. Simplified Models
Full text linkGroundwater Heat Pumps (GWHPs) are increasingly adopted for air conditioning in urban areas, thus reducing CO2 emissions, and this growth needs to be managed to ensure the sustainability of the thermal alteration of aquifers. However, few studies have addressed the propagation of thermal plumes from open-loop geothermal systems from a long-term perspective. We provide a comprehensive sensitivity analysis, performed with numerical finite-element simulations, to assess how the size of the thermally affected zone is driven by hydrodynamic and thermal subsurface properties, the vadose zone and aquifer thickness, and plant setup. In particular, we focus the analysis on the length and width of thermal plumes, and on their time evolution. Numerical simulations are compared with two simplified methods, namely (i) replacing the time-varying thermal load with its yearly average and (ii) analytical formulae for advective heat transport in the aquifer. The former proves acceptable for the assessment of plume length, while the latter can be used to estimate the width of the thermally affected zone. The results highlight the strong influence of groundwater velocity on the plume size and, especially for its long-term evolution, of ground thermal properties and of subsurface geometrical parameter
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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