1,721,014 research outputs found
Energy performance assessment of the heating system refurbishment on a school building in Modena, Italy
No full textThe aim of this paper is the energy performance assessment of the school building Istituto Comprensivo “G. Marconi”, located in
Modena, Italy. This work describes the dynamic modeling of the building envelope and its heating system, carried out by means
of the simulation software TRNSYS 17. According to the developed model, the school space heating loads, as well as the
seasonal energy requirements, are evaluated by considering the actual heating system, which consists of gas-fired condensing
boilers coupled to high temperature radiators. Then, the school heating system refurbishment is simulated: the paper evaluates
the energy savings obtained by replacing boilers and radiators with an air-to-water multi-compressor heat pump, coupled to low
temperature aluminum radiators, and by improving the system control strategy. Finally, the impact of the discussed energy
saving measures on building energy performance and students thermal comfort is reported
Dynamic Simulation of Solar Thermal Collectors for Domestic Hot Water Production
No full textAbstractIn this paper a system for the Domestic Hot Water (DHW) production based on solar collectors is analyzed by means of a dynamic approach based on a Simulink model and by using the F-chart method, able to evaluate system performances on a monthly basis. Following the dynamic approach, it is possible to evaluate hour by hour the energy collected by the solar panels and the temperature of the hot water produced by the system, by taking into account the impact of different daily DHW consumption profiles on the percentage of thermal energy produced by the solar collector (Solar Coverage Factor, SCF). The comparison between the prediction made both by using the Simulink model and the F-Chart method in terms of SCF is shown by taking into account the effect on SCF of the typology of solar collector (unglazed, glazed and evacuated collectors), of the storage tank volume connected to the solar panels and of the hourly DHW consumption profile. The results point out that SCF is strongly dependent on the daily DHW consumption profile, which cannot be taken into account in a quasi-static approach like the F-chart method
Sizing effects on the energy performance of reversible air-source heat pumps for office buildings
No full textThis paper deals with the numerical analysis of the energy performance of HVAC systems for heating and cooling, based on a reversible electrical air-source heat pump. The aim of this study is to highlight in which way the energy consumption of these systems is influenced by the heat pump modulating capability, the heat pump sizing and the climate. A numerical model based on the bin method and the energy signature procedure, able to take into account the performance of the heat pump at partial load, has been followed in order to calculate the seasonal and annual performance of the HVAC system coupled to a typical office building, located in three different European locations (Frankfurt, Istanbul, Lisbon). Different kinds of heat pumps (mono-compressor on-off, multi-compressor and inverter-driven heat pumps) have been considered. The numerical results presented in this paper point out that the heat pump sizing strongly affects seasonal and annual HVAC energy consumption: the ratio between the full thermal capacity of the heat pump and the building peak load strongly influences the energy performance of the system. It has been demonstrated that, depending on the season, the seasonal performance of the above-mentioned kinds of heat pumps are influenced in a different way by their sizing
Summer Performances of Reversible Air-to-water Heat Pumps with Heat Recovery for Domestic Hot Water Production
No full textAbstractA numerical model for the seasonal performance evaluation of electric air-to-water reversible heat pumps during summer is presented. The model employs the bin-method, as indicated by the standards EN 14825 and UNI/TS 11300-4, but also considers domestic hot water (DHW) production through condensation heat recovery. The model evaluates the heat pump Seasonal Energy Efficiency Ratio (SEER) as function of the heat pump typology (multi-compressor, inverter-driven). The energy saving potential of DHW production integrated with the heat pump cooling function with respect to traditional separate cooling and DHW devices is analyzed as function of the building demand and of the heat pump typology
Effetto del clima sull’efficienza stagionale di sistemi di riscaldamento basati su pompe di calore aria-acqua
No full textIn questo lavoro è utilizzato un modello matematico per analizzare l’effetto di diverse condizioni climatiche italiane sulle prestazioni stagionali di sistemi di riscaldamento a pompa di calore elettrica aria-acqua. Attraverso il modello impiegato, viene evidenziata l’importanza del dimensionamento della pompa di calore in funzione della tipologia di macchina (on-off, multi-compressore o con inverter), della firma energetica dell’edificio e del clima della località in cui si trova.This work employs a mathematical model to evaluate the effect of different typical Italian climates on the seasonal performances of heating plants based on electric air-to-water heat pumps. The importance of the right heat pump sizing is highlighted as a function of the machine typology (on-off, multi-compressor, inverter-driven), of the building energy signature and of the climate
Influence of sizing strategy and control rules on the energy saving potential of heat pump hybrid systems in a residential building
Full text linkHybrid heat pump systems are a suitable solution to mitigate the well-known disadvantages of air-source heat pumps, such as energy losses linked to defrost cycles and a significant reduction of their heating capacity during the most severe part of the season. In hybrid systems the heat pump is sized to satisfy only a fraction of the building peak load and is coupled to a second heater (back-up device), which helps the heat pump during the coldest part of the winter. In this paper, a series of dynamic simulations has been performed to calculate the seasonal performance of hybrid systems based on an air-to-water heat pump and to assess the optimal configuration of the system. Results point out that the energy performance of these systems strongly depends on the heat pump sizing, the back-up device typology and the control algorithm used for the activation of the heat generators. It is demonstrated that the adoption of hybrid systems in which the heat pump is coupled to a gas boiler allows to obtain relevant primary energy savings. The overall seasonal efficiency can be increased up to 6% and 22%, if compared to monovalent systems respectively based on a heat pump or a gas boiler, only if the heaters are activated following an alternative operating mode, with a cut-off temperature selected between the design and the bivalent temperature. On the contrary, if the back-up device of the hybrid system is an electric resistance, the heaters have to work in parallel during the whole heating season and the only achievable advantage is that the heat pump can be slightly under-sized with respect to the nominal building load
Climate Influence on Seasonal Performances of Air-to-water Heat Pumps for Heating
No full textAbstractA mathematical model for the evaluation of the seasonal performances of electric air-to-water heat pumps for heating is used to analyze the efficiency of on-off heat pumps, multi-compressor heat pumps and heat pumps with inverter compressor, integrated by electric heaters as back-up system, in the service of several buildings located in different Italian climates.The paper points out the importance of a good dimensioning of the heat pump as a function of the building energy signature and of the climate of the city where the building is placed, in order to enhance the system seasonal efficiency
Annual Performances of Reversible Air Source Heat Pumps for Space Conditioning
No full textAbstractThe paper presents the results obtained by a numerical simulation of a heating and cooling system based on a reversible air-to-water electric heat pump and electric resistances as back-up. According to the procedure suggested by the current standards EN 14825 and UNI/TS 11300-4, by using the bin method the influence of outdoor conditions and of the typology of heat pump installed has been investigated by determining the value assumed by the seasonal coefficient of performance (SCOPon), the seasonal efficiency ratio (SEER) and the annual performance factor (APF). The numerical results allow discussing the rules for an optimal heat pump sizing in a fixed site
Effect of real temperature data on the seasonal coefficient of performance of air source heat pumps
Full text linkIn this paper, a transient analysis is performed in order to evaluate how effective climate data affect the determination of the seasonal coefficient of performance of ASHPs. Three Italian cities, characterized by different climates, are considered as reference case studies and the influence of real meteorological data, collected from different years, on the heat pump SCOP is performed. The analysis is carried out by employing the dynamic software TRNSYS. Numerical results show small variations in SCOP, while a significant influence on annual thermal energy demand can be observed. The analysis also underlines the absence of a general correlation between annual thermal energy supplied by the heat pump and SCOP and between HDD and SCOP
Numerical Modeling of Pure and Metal-Foam Loaded PCMs
No full textDespite many desirable properties, most phase change materials (PCMs) undergo timing issues during the phase change process due to a low thermal conductivity, which limits their application in heat storages. Thus, many techniques have been pointed out to overcome these disadvantages and improve heat transfer, such as coupling PCMs with metal inserts, like high porosity open-cell metal foams. Indeed, the presence of a metal foam increases the effective thermal conductivity of the composite medium and speeds up the charging and discharging phases. In the present paper, a numerical model developed in COMSOL ambient has been calibrated by comparison with experimental results on the melting of pure and metal-foam loaded PCMs, placed in a small case and heated from the top by an electric resistance. The numerical model considers the metal foam as a static solid, filled with a phase changing fluid and employs a literature correlation to evaluate the effective thermal conductivity of the composite medium. The performance of two different paraffinic PCMs (RT35 and RT35HC by Rubitherm GmbH, D), loaded either with a copper foam (20 PPI, 95% porosity, by Porometal, China) or with an aluminum one (10 PPI, 96% porosity, by Recemat, NL) has been investigated in terms of speed rate of the phase change front, time required to complete the melting process, temperature distribution and effect of foam porosity. The obtained results clearly evidence the significant heat transfer improvement yielded by metal foams, whose presence increases the effective thermal conductivity of the composite medium (from 0.2 to 7.03 W/mK for copper foam and to 3.52 W/mK for aluminum one), leading to a significant decrease of the charging time and to a lower temperature gradient within the PCM (from about 16 to 3 K)
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