59 research outputs found
Replacement of gas boilers with air source heat pumps: An economic analysis based on a trnsys evaluation and on the actual energy prices in Italy
In this work, we investigate the replacement of a gas boiler with an electric air-to-water heat pump (AWHP) as a heating generation system for a detached single-family house. Attention is paid to the recent increase in energy prices in Italy. The evaluation of the energy consumption is done via a dynamic analysis performed by employing Trnsys. The investment results are economically advantageous only if the thermal energy demand is quite high, and the recent energy price increase (for both natural gas and electricity) leads to disadvantages in replacing the heat generation system in all the considered cases
A concentrated-parameter model for the validation of a tractor heating system during artificial winter conditions
In the present paper, a concentrated-parameter model is presented, in order to simulate the behavior of a climatic chamber suitably designed for testing tracked and wheeled tractors. Reference is made to standard-severe winter conditions (–18°C), i.e., the tractor dissipates thermal power in a climatic chamber that reproduces winter temperature and humidity conditions. The software package Matlab-Simulink is utilized and the system under investigation consists of 5 blocks. The dynamic modeling first covers a 10 hours period to reach the prescribed conditions for the climatic test chamber. Then, after this preparation period, the tractor’s engine is supposed to work. The simulations show that higher values of the adduction coefficient are preferable since they allow obtaining quickly, and with a lower heating power, the desired comfort conditions for the machine’s cabin
Effect of a magnetic field on the couette forced convection of a buongiorno’s nanofluid over an embedded cavity
The paper investigates the effect of a magnetic field on the forced convection of a nanofluid in a channel with an embedded cavity. The nanofluid is described by the Buongiorno’s model, and a fixed temperature boundary condition is prescribed. The governing equations are written in a dimensionless form and solved numerically by employing COMSOL Multiphysics. The obtained velocity, temperature and concentration fields are presented as function of the governing parameters, and the Nusselt number on the upper boundary is evaluated as well. Particular attention is paid to the effect of the inclination angle of the magnetic field, showing that variations up to 40% may affect the Nusselt number
The scop of an air source heat pump: Comparison between on-off and inverter heat pump
The paper investigates the seasonal performance of electric air-to-water heat pump comparing an on-off heat pump with an inverter-driven variable speed compressor. Reference is made to a heat pump for domestic space heating installed in Bologna, and the bin-method proposed by UNI/TS 11300-4 is employed in order to investigate the effect of external temperature. The analysis shows that the inverter heat pump performs better than the on-off one, displaying higher values of SCOP about at least 10%
Hourly data for evaluating the carbon dioxide emission factor of heat pumps or other devices connected to the Italian grid
This data article includes an elaboration of carbon dioxide data available from three different online sources in the years from 2016 to 2019. The data article refers to the paper “Interpolating functions for CO2 emission factors in dynamic simulations: the special case of a heat pump” by the same authors. The data are provided on an hourly basis and are useful to determine the carbon dioxide emission of an electric heat pump or other devices connected to the Italian grid. The importance of the provided data is related to the possibility of having an accurate estimation of the CO2 emission when the device works for only a limited period of time during the year or day. Moreover, since the given data are provided in electronic format (.txt file or .xlsx spreadsheet) they are very useful to perform dynamic simulation using self-made or commercial software such as Trnsys, Energy Plus etc
Influence of Nanoparticles and Magnetic Field on the Laminar Forced Convection in a Duct Containing an Elastic Fin
In the present paper, an investigation of the effect of a magnetic field and nanoparticles suspended in pure water on the forced flow in a duct containing an elastic rectangular fin is performed. The nanofluid, i.e., CuO nanoparticles suspended in water, flow in the duct with an inlet fully developed velocity profile and a cold temperature. The lower boundary of the duct is kept at a hot temperature, while the upper boundary is adiabatic. According to the ALE formulation, numerical simulations of the laminar flow are carried out, by employing the software package Comsol Multiphysics, to solve the governing equation system: mass, momentum, energy, and deformation. The behavior of the Nusselt number, of the temperature and velocity fields as well as of the stress profiles are presented and interpreted. As a result, the addition of CuO nanoparticles to pure water improves the local and global heat transfer rate by up to 21.33% compared to pure water. On the other hand, it causes an additional deformation of the elastic fin as well as the increase of the stress due to the presence of the nanoparticles, leading to an increase of its maximum displacement of 34.58% compared to the case of pure water flow. Moreover, the enhancement of the flexibility of the fin (and thus its deformation) leads to a relative reduction in terms of convective heat transfer rate, especially downstream of the fin
A Long-Term Dynamic Analysis of Heat Pumps Coupled to Ground Heated by Solar Collectors
In agreement with the decarbonization of the building sector to meet the 2050 climate neutrality targets, borehole thermal storage for solar energy represents a potential solution to increase the energy efficiency of renewable energy plants. As is well known, electricity is not the optimum solution to integrate large inflows of fluctuating renewable energy. In the present paper, we investigate the possibility to use the solar collector to give energy to the borehole field. In detail, a solar-assisted geothermal heat pump is applied to a school located in Milan, Italy. In winter, both the energy from the solar collector and the heat pump are collected into a storage tank connected to the emission terminals, whereas, in summer, as there is no energy demand, the hot water from the solar collector flows into the geothermal probes. By means of this seasonal thermal energy storage technology, the intermittent solar energy collected and stored during the summer months can be utilized during the winter months when the heating demand is high. A long-term dynamic analysis is performed by employing Trnsys. The results show that solar collectors coupled with ground-source heat pumps can give an important contribution to the soil temperature drift, and this also applies in cases of un-balanced loads during the heating season. Moreover, the employment of solar collectors increases the seasonal coefficient of performance of the heat pumps and may rise to reductions to the probes field
Performance evaluation of transcritical CO2 desiccant heat pumps for electric vehicles
Transcritical CO2 heat pump systems are eco-friendly and have excellent heating performance, which makes them suitable for electric vehicles. The recirculation mode can save energy but requires a dehumidification function to ensure driving safety. Therefore, this paper proposes a transcritical CO2 desiccant heat pump, which differs from the typical transcritical CO2 heat pump system by incorporating an indoor evaporator and a full-pass throttle valve. The flow area of the full-pass throttle valve can be adjusted to obtain the appropriate dehumidification rate. In addition, this study suggested using the desiccant heat pump coefficient of performance (DHCOP) to evaluate the overall energy efficiency of the heat pump system. We have investigated the dehumidification rate and optimal discharge pressure under different operating conditions. The results show that even under the harsh operating conditions at -10 °C, the HDCOP of the transcritical CO2 desiccant heat pump can still exceed 2.1, and reach 3.12 at a moderate condition of Ta=5 °C. The transcritical CO2 heat pump desiccant system demonstrates significant energy-saving potential
Energy and Environmental Performance Comparison of Heat Pump Systems Working with Alternative Refrigerants
Featured Application: An energy and environmental performance analysis of air-source and ground-source heat pump systems able to operate with traditional (R-410A) and alternative low-GWP (R-454B) refrigerants is conducted. The case study is composed of an existing residential single-family house, and the coupled HVAC system is modeled by means of the commercial software TRNSYS. The TEWI index is considered to evaluate the environmental impact of the heat pump systems. The results of the numerical simulations show a significant reduction in the overall greenhouse emissions of those systems in which R-454B is employed as a refrigerant. The European Parliament has imposed to reduce by 2030 whole HFC emissions by at least two-thirds with respect to 2014 levels. With the aim of contributing to determine the energy and environmental advantages of refrigerants alternative to R-410A, this paper reports the results of a numerical study focused on an HVAC system coupled to a residential building and based on a reversible electric heat pump. In particular, two heat pump typologies are considered: an air-source and a ground-source heat pump, both operating with the two refrigerants R-410A and R-454B. The environmental performance of the studied system is assessed by means of the TEWI (total equivalent warming impact) index. The adoption of R-454B involves a slight decrease (2–3%) in the overall annual energy performance of the system with respect to the use of R-410A. On the other hand, the working fluid R-454B guarantees a marked decrease in the TEWI indicator. Indeed, considering the current Italian emission factor of electricity taken from the grid, the total emissions over the entire heat pump operating life drop by about 25% and can decrease by up to 89% in perspective, following the current reduction trend of the emission factor
Influence of different heating systems on thermal comfort perception: a dynamic and CFD analysis
In this paper, we investigate the influence of different heating systems on the thermal comfort indexes, Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD), for a residential apartment located in Bologna (Italy). The apartment has an area of 40 m2 and is located on the ground floor of 4 floors building. The envelop consists in horizontal perforated bricks with internal thermal insulation material and two windows. The analyses are performed employing Trnsys, a commercial dynamic simulation software and Simcenter STAR-CCM+, a multiphysics computational fluid dynamics (CFD) software. The CFD analysis regards a steady condition of a typical winter day in Bologna. Thermal comfort indexes and thermal energy demand are studied comparing two different heating generation systems existing in the considered apartment: a condensing gas boiler coupled with radiators as terminal emitters and an air-to-air heat pump. By crossing the results obtained by the dynamical approach and by the CFD simulations, a two-objective methodology where energy consumption is minimised while thermal comfort is obtained, is presented
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