50,885 research outputs found
Il Raffrescamento per Ventilazione: uno Strumento per il Controllo Passivo del Carico Termico negli Edifici
No full textLa ventilazione naturale, meccanica o ibrida è un meccanismo ben noto ed utilizzato da tempo per il controllo della qualità dell'aria indoor. Tuttavia, in tempi recenti, sotto la spinta dei requisiti sempre più stringenti posti dalla normativa Europea in relazione all'efficienza energetica degli edifici, si è iniziato a rivolgere un crescente interesse verso la ventilazione, specie naturale, quale strumento per il raffrescamento passivo degli edifici. Le recenti evoluzioni del quadro normativo e legislativo, infatti, hanno portato nel cor-so del tempo a costruire edifici sempre più isolati termicamente e sempre più a tenuta d'aria. Tali misure hanno consentito indubbiamente di ridurre la domanda energetica per il riscaldamento invernale, ma hanno determinato delle crescenti problematiche di surriscaldamento dell'ambiente interno. Molti degli edifici ad alta efficienza energeti-ca di nuova costruzione presentano la necessità di essere raffrescati non solo nel periodo estivo e/o primaverile, ma anche in alcuni momenti della stagione invernale. Uno dei rimedi per ovviare a questo inconveniente, in modo energeticamente efficien-te, è quello di utilizzare la ventilazione. Quando la portata d'aria di ventilazione è ge-nerata primariamente per il controllo dei carichi termici di raffrescamento si parla di "Ventilative cooling" o "Raffrescamento per ventilazione". L'effetto benefico di questo provvedimento è duplice. Da un lato agisce sul bilancio termico dell'edificio, sfruttando la portata d'aria per rimuovere i carichi ambiente e, dall'altro, incrementa lo scambio termico sul corpo umano, poiché aumenta la velocità locale dell'aria sulla pelle, modificando quindi e le sensazioni termiche. Permette, inoltre, di abbinare la funzione di controllo dell'IAQ con quella del controllo termico. Una corretta progettazione ed utilizzo di questa tecnica deve tuttavia considerare con attenzione una serie di elementi critici e di potenziali inconvenienti. In primis, l'efficacia del ventilative cooling è legata ad una progettazione attenta dell'involucro edilizio e del sistema edificio/impianto. La misura è infatti efficace solo in quei casi dove gli apporti solari ed endogeni siano stati opportunamente e preventivamente ri-dotti. Secondariamente, l'utilizzo di aria esterna non termodinamicamente modificata può determinare problematiche di umidità relativa interne. Infine, specie nel caso di ventilazione naturale, l'impossibilità di filtrare l'aria immessa e la necessità di realizzare portate volumetriche significative comporta rischi connessi al deterioramento del-la qualità dell'aria indoor e la nascita di situazioni di rischio per ciò che concerne il discomfort locale da correnti d'aria. Nel presente articolo verranno illustrati i principi fisico tecnici alla base del ventilative cooling, si fornirà una panoramica delle strategie mediante cui questa tecnica può essere implementata negli edifici e si analizzeranno criticamente vantaggi e svantaggi. Infine, saranno presentati alcuni esempi realizzativ
Application of high-resolution domestic electricity load profiles in network modelling:A case study of low voltage grid in Denmark
Full text linkThe ongoing development towards electrification of the energy consumption together with large deployment of renewable energy sources creates new challenges of variability and fluctuation of the electricity supply and increases complexity of the network operation. In order to capture all the particularities of electricity demand and on-site generation, e.g. the short-term spikes due use of high electricity consumption appliances such like electric kettle, and get a full picture of network performance, a high-resolution input data are needed. This paper compares the business-as-usual network modeling with modeling when 1-minute domestic electricity demand and generation profiles are used as inputs. The analysis is done with a case study of low-voltage network located in Northern Denmark.The analysis includes two parts. The first part focuses on modeling the domestic demands and on-site generation in 1-minute resolution. The load profiles of the household appliances are created using a bottom-up model, which uses the 1-minute cycle power use characteristics of a single appliance as the main building block. The profiles of heavy electric appliances, such as heat pump, are not included in the above-mentioned model, as they are closely related to the thermal properties of a building. Therefore, two type of single family houses equipped with heat pump are simulated in EnergyPlus with 1-minute time step. The PV generation profile is obtained from a model developed in Matlab environment. In the second part the generated profiles are inputted in a low-voltage network model created in DIgSILENT PowerFactory.By means of employing 1 hour based demand and generation profiles in during dynamic studies, the representation of the local power system performance might sometimes not be as accurate as needed. In the test system employed in this case the simulation indicates that no stress is created in the grid. The loading of the transformer and power lines is 65% and 41%, respectively, which is below the limit of 80% of available capacity. The maximum voltage drop is 5.1% thus with the maximum allowed deviation of ± 10% and ± 6% according to standards and common practice, respectively. The same investigation, but with 1-minute input data, shows that the transformer is overloaded by 2% and the minimum voltage level is 0.922 % [p.u], which is below limits of common practice grid operation. When adding on-site PV on 50% of buildings, the loading of the transformer and power lines is reduced in the summer time to 58% and 51%, respectively. However, the power lines are stress with bi-directional power flow.The results indicate that the business-as-usual approach to network modeling is not sufficient to capture the characteristic spikiness of the domestic load profiles and on-site generation. Hence the network overloading and high voltage deviations are not visible and the control strategies may be wrong
Control Strategies for Ventilative Cooling of Overheated Houses
No full textBuildings constructed before 1979 in Denmark are responsible for 75% of the total energy consumption of the sector. However, many post-occupancy comfort studies of energy renovated dwellings have documented elevated temperatures not only during the summer period but also during the transition months. Ventilative cooling can be an energy-efficient solution to avoid overheating in energy renovated residences. The aim of the research is to investigate the ability of a representative manual window use and different automated window control strategies in order to eliminate overheating under different opening positions, wind conditions and discharge coefficients. The study will also include examination of the ability of mechanical ventilation and shading systems regarding the overheating occurrence. The objectives are fulfilled through the simulation and analysis of a real representative single-family house from the 1970s. The case study is renovated deeply and high- efficient (nZEB) creating two different scenarios. Mechanical ventilation system and manual control of the openings for both renovation scenarios cannot sufficiently eliminate the overheating risk indoors. The discharge coefficient of the windows, the presence of the wind and the opening position of the windows are critical parameters of the effectiveness of the ventilative cooling strategies. The fully all-day automated control strategy presents the best performance among the three strategies of the automated control (parallel use, automated during the occupied period and fully automated). In most of the cases of the parametric analysis the high-efficient renovation scenario presents lower values of overheating risk compared to the deep renovation scenario.</p
Experimental Assessment of Mechanical Night Ventilation on Inner Wall Surfaces
No full textThe cooling potential of night ventilation largely depends on the heat exchange at the internal room surfaces. During night time, increased heat transfer on a vertical wall is expected due to cool supply air that flows along the internal wall surface from the top of the wall. This paper presents an experimental study of the cooling of wall surfaces in a test room by mechanical night-time ventilation. Significant improvement of indoor thermal environment is presented resulting from the enhanced internal convection heat transfer
Experimental Assessment of Mechanical Night Ventilation on Inner Wall Surfaces
Full text linkThe cooling potential of night ventilation largely depends on the heat exchange at the internal room surfaces. During night time, increased heat transfer on a vertical wall is expected due to cool supply air that flows along the internal wall surface from the top of the wall. This paper presents an experimental study of the cooling of wall surfaces in a test room by mechanical night-time ventilation. Significant improvement of indoor thermal environment is presented resulting from the enhanced internal convection heat transfer
Control Strategies for Ventilative Cooling of Overheated Houses
Full text linkBuildings constructed before 1979 in Denmark are responsible for 75% of the total energy consumption of the sector. However, many post-occupancy comfort studies of energy renovated dwellings have documented elevated temperatures not only during the summer period but also during the transition months. Ventilative cooling can be an energy-efficient solution to avoid overheating in energy renovated residences. The aim of the research is to investigate the ability of a representative manual window use and different automated window control strategies in order to eliminate overheating under different opening positions, wind conditions and discharge coefficients. The study will also include examination of the ability of mechanical ventilation and shading systems regarding the overheating occurrence. The objectives are fulfilled through the simulation and analysis of a real representative single-family house from the 1970s. The case study is renovated deeply and high- efficient (nZEB) creating two different scenarios. Mechanical ventilation system and manual control of the openings for both renovation scenarios cannot sufficiently eliminate the overheating risk indoors. The discharge coefficient of the windows, the presence of the wind and the opening position of the windows are critical parameters of the effectiveness of the ventilative cooling strategies. The fully all-day automated control strategy presents the best performance among the three strategies of the automated control (parallel use, automated during the occupied period and fully automated). In most of the cases of the parametric analysis the high-efficient renovation scenario presents lower values of overheating risk compared to the deep renovation scenario.</p
Application of high-resolution domestic electricity load profiles in network modelling:A case study of low voltage grid in Denmark
No full textThe ongoing development towards electrification of the energy consumption together with large deployment of renewable energy sources creates new challenges of variability and fluctuation of the electricity supply and increases complexity of the network operation. In order to capture all the particularities of electricity demand and on-site generation, e.g. the short-term spikes due use of high electricity consumption appliances such like electric kettle, and get a full picture of network performance, a high-resolution input data are needed. This paper compares the business-as-usual network modeling with modeling when 1-minute domestic electricity demand and generation profiles are used as inputs. The analysis is done with a case study of low-voltage network located in Northern Denmark.The analysis includes two parts. The first part focuses on modeling the domestic demands and on-site generation in 1-minute resolution. The load profiles of the household appliances are created using a bottom-up model, which uses the 1-minute cycle power use characteristics of a single appliance as the main building block. The profiles of heavy electric appliances, such as heat pump, are not included in the above-mentioned model, as they are closely related to the thermal properties of a building. Therefore, two type of single family houses equipped with heat pump are simulated in EnergyPlus with 1-minute time step. The PV generation profile is obtained from a model developed in Matlab environment. In the second part the generated profiles are inputted in a low-voltage network model created in DIgSILENT PowerFactory.By means of employing 1 hour based demand and generation profiles in during dynamic studies, the representation of the local power system performance might sometimes not be as accurate as needed. In the test system employed in this case the simulation indicates that no stress is created in the grid. The loading of the transformer and power lines is 65% and 41%, respectively, which is below the limit of 80% of available capacity. The maximum voltage drop is 5.1% thus with the maximum allowed deviation of ± 10% and ± 6% according to standards and common practice, respectively. The same investigation, but with 1-minute input data, shows that the transformer is overloaded by 2% and the minimum voltage level is 0.922 % [p.u], which is below limits of common practice grid operation. When adding on-site PV on 50% of buildings, the loading of the transformer and power lines is reduced in the summer time to 58% and 51%, respectively. However, the power lines are stress with bi-directional power flow.The results indicate that the business-as-usual approach to network modeling is not sufficient to capture the characteristic spikiness of the domestic load profiles and on-site generation. Hence the network overloading and high voltage deviations are not visible and the control strategies may be wrong
Short-term airing by natural ventilation - modeling and control strategies
No full textThe need to improve the energy efficiency of buildings requires new and more efficient ventilation systems. It has been demonstrated that innovative operating concepts that make use of natural ventilation seem to be more appreciated by occupants. This kind of system frequently integrates traditional mechanical ventilation components with natural ventilation devices, such as motorized windows and louvers. Among the various ventilation strategies that are currently available, buoyancy driven single-sided natural ventilation has proved to be very effective and can provide high air change rates for temperature and IAQ control. However, in order to promote a wider applications of these systems, an improvement in the knowledge of their working principles and the availability of new design and simulation tools is necessary. In this context, the paper analyses and presents the results of a research that was aimed at developing and validating numerical models for the analysis of buoyancy driven single-sided natural ventilation systems. Once validated, these models can be used to optimize control strategies in order to achieve satisfactory indoor comfort conditions and IA
- …
