1,721,110 research outputs found
Passive systems in traditional houses in Middle East areas: Solutions and effects of natural ventilation
No full textThe Middle East area, has a specific culture and habits, enhanced by adaptation to the environment and local climate through the traditional building constructions where typical design, structures and materials represent the basis for passive strategies. In these hot-dry regions, many traditional houses consist of compact design structures with internal courtyard where the effects of thermal inertia and natural ventilation can be well exploited. This paper focuses on the analysis of passive techniques used in some houses located in Damascus old city, which are renowned for their distinctive adaptability. These traditional houses have a unique structure consisting of two levels: the first floor built with heavy mass stones, while the second has light mass (timber and mud). The presence of an internal courtyard on which several rooms of different size overlook, give rise to an appreciable natural ventilation (single side or cross ventilation) through a proper opening of windows. Based on experimental data (air temperature, air velocity) acquired during a summer period in a traditional house, dynamic simulation for different type of structures and opening are performed in order to investigate the influence of natural ventilation on reducing internal temperature and evaluate comfort conditions using ASHRAE standard. Results also suggest strategies to optimize passive techniques to reduce energy needs
Analysis of the impact of convector heaters operating at low supply temperature on the possibility of deterioration of thermal conditions
Full text linkThe increasing use of renewable energy sources reduces the operating parameters of district heating networks. As a consequence, it is necessary to reduce the supply temperature of already existing building central heating systems. Therefore, there is a doubt whether such operations will not cause deterioration of the thermal conditions of rooms, in particular with a large glazing area. A balance of jet momentum fluxes was developed between the cold down draught and warm stream generated by the heater. A mathematical correlation was formulated based on this comparison. It allows to determine the minimum average velocity of convective currents of warm air generated by the heater, which protects the occupants from the undesired local cooling. The article also includes computer code to perform this calculation in a simple and quick way. A number of experimental studies and CFD modelling were performed to determine the characteristics of the convective currents rising above the typical convector heater with widths of 96 mm, 146 mm, 186 mm, and 236 mm. The type and area of the glazing, air temperature conditions, as well as the supply temperature and the size of the convector were analysed. The results of these experiments and computer simulations were presented in the form of graphs showing the impact of the most important parameters on the minimum warm air velocity value
Energetic Optimisation of the Domestic Hot Water System in a Residential Building by Means of Dynamic Simulations
No full textThe present study deals with the energetic optimisation of Domestic Hot Water (DHW) system in a residential building located in Catania, Italy. Each dwelling is equipped with a specific decentralised tank with an internal heat exchanger which is connected to a 2-pipe hot water network system for tank charging. The technical water is produced by an Electrical Heat Pump (EHP) coupled to a central storage tank. The energy performance analysis of the DHW model is evaluated by means of dynamic simulations under three different scenarios of charging the decentralised storage tanks by circulating pump unit: Pump activated during daytime, activated twice a day, and activated three times per day. The results obtained allow an evaluation of the DHW consumption profile, temperature variation in central storage and decentralised tanks, and the annual electrical/thermal energy analysis. The results indicate that the activation of the circulating pump during the day leads to an achievement of the highest amount of thermal energy, as well as having minimum temperature oscillation in both central storage and decentralised tanks. However, these advantages are at the cost of consuming much more electrical energy by the heat pump and up to 29 % higher emissions of CO2. The best scenario in terms of energy-saving and CO2 emission is the case in which the circulating pump works twice a day, consuming annually 5,832 kWh less electrical energy, compared to the case of an activated pump during the day
Nanofluid suspensions as heat carrier fluids in single U-tube borehole heat exchangers
Full text linkThe borehole heat exchanger (BHE) is a critical component to improve energy efficiency and decreasing environmental impact of ground-source heat pump systems. The lower thermal resistance of the BHE results in the better thermal performance and/or in the lower required borehole length. In the present study, effects of employing a nanofluid suspension as a heat carrier fluid on the borehole thermal resistance are examined. A 3D transient finite element code is adopted to evaluate thermal comportment of nanofluids with various concentrations in single U-tube borehole heat exchangers and to compare their performance with the conventional circuit fluid. The results show, in presence of nanoparticles, the borehole thermal resistance is reduced to some extent and the BHE renders a better thermal performance. It is also revealed that employing nanoparticle fractions between 0.5% and 2 % are advantageous in order to have an optimal decrement percentage of the thermal resistance
Energetic Optimisation of the Domestic Hot Water System in a Residential Building by Means of Dynamic Simulations
No full textThe present study deals with the energetic optimisation of Domestic Hot Water (DHW) system in a residential building located in Catania, Italy. Each dwelling is equipped with a specific decentralised tank with an internal heat exchanger which is connected to a 2-pipe hot water network system for tank charging. The technical water is produced by an Electrical Heat Pump (EHP) coupled to a central storage tank. The energy performance analysis of the DHW model is evaluated by means of dynamic simulations under three different scenarios of charging the decentralised storage tanks by circulating pump unit: Pump activated during daytime, activated twice a day, and activated three times per day. The results obtained allow an evaluation of the DHW consumption profile, temperature variation in central storage and decentralised tanks, and the annual electrical/thermal energy analysis. The results indicate that the activation of the circulating pump during the day leads to an achievement of the highest amount of thermal energy, as well as having minimum temperature oscillation in both central storage and decentralised tanks. However, these advantages are at the cost of consuming much more electrical energy by the heat pump and up to 29 % higher emissions of CO2. The best scenario in terms of energy-saving and CO2 emission is the case in which the circulating pump works twice a day, consuming annually 5,832 kWh less electrical energy, compared to the case of an activated pump during the day
Techno-economic analysis of a novel retrofit solution for the domestic hot water system: A comparative study
Full text linkThe retrofit solution for domestic hot water (DHW) system in existing buildings requires to ensure the long-term energy security and efficiency as well as to minimise occupants’ disturbance, construction works and installation costs. In this regard, the present study performs a techno-economic evaluation on a novel retrofit solution for DHW production in a pilot building. The proposed solution appoints a substantial role to the thermal energy storage through a 2-pipe hot water network utilisable for both DHW and heating purposes. The first storage level is provided by a centralised buffer storage supplied by a PV-BESS-driven heat pump while the second level consists of decentralised modular tanks installed in each dwelling for the production and storage of hot water. Firstly, experimental thermal performance of the proposed decentralised storages is investigated. By developing a dynamic simulation code, the energy efficiency of the proposed solution is compared to that of the existing system in the pilot building as well to that of a typical centralised system as a benchmark solution. Finally, economic analysis of the retrofit solution is performed to address capital expenditures of the system, including purchasing and installation costs, as well as its life cycle cost (LCC). The obtained results indicate that the proposed system reduces the annual energy consumption for DHW production more than 7,200 kWh, with respect to the existing DHW system. Furthermore, it is shown that, in the proposed system, the fraction of thermal loss from piping network decreases by 31.5%, compared to a typical DHW centralised system. Economic assessment of the proposed solution implies that this system, in terms of both mechanical and electrical components, requires 13.7% lower initial investment than a typical centralised system. However, the cost of control systems in this system is higher since it is inherently a control-based system
Numerical study on indoor environmental quality in a room equipped with a combined hrv and radiator system
Full text linkHeat recovery ventilation (HRV) systems can be integrated with an additional air heater in buildings with low energy demand in order to cover space heating demand. The employment of coupled HRV-heater systems is, therefore, gaining increasing interest for the improvement of the indoor environmental quality (IEQ), as well as the reduction of ventilation energy loss. The present paper analyses the efficacy of a HRV system, coupled with a low-temperature radiator, in satisfying the IEQ indices inside a retrofitted dormitory room. A computational fluid dynamic (CFD) model based on the finite volume method is established to investigate IEQ characteristics including indoor air quality and thermal comfort condition. The presented CFD code provides a practical tool for a comprehensive investigation of the IEQ indices in spaces employing a coupled HVAC system. In an analysis of indoor air quality, parameters such as age of the air, air change efficiency, and ventilation efficiency in removal of gaseous contaminants, namely VOCs and CO2, are evaluated. The results obtained by the numerical model allow addressing the interaction between HRV and radiator systems and its effects on airflow field. The results show the decrease of the indoor operative temperature with increment of the supply air flow rate, which is mainly due to the decreased thermal efficiency of the HRV system. The obtained results indicate that, while higher ventilation rates can significantly decrease the age of the air and gaseous contaminants level, at the same time, it would cause a local discomfort in some parts of the room
Experimental evaluation of noise propagation through rectangular ducts in HVAC system
No full textSound propagation through a rectangular duct of an HVAC system has been investigated in an experimental set-up, in order to evaluate the sound attenuation through different components and the self-noise generated by the airflow. Acoustic and vibration measurements inside the duct were carried out in order to correlate different aspects of noise reduction. The attenuation effects of rectangular straight ducts and of bend ducts with different flow velocities have been evaluated and compared with theoretical formulations
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
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