894 research outputs found
The role of emitters, heat pump size, and building massive envelope elements on the seasonal energy performance of heat pump-based heating systems
The influence of emitters, heat pump size and building envelope thermal inertia was investigated on the energy consumption of a heat pump-based heating system with a numerical study performed with the dynamic software TRNSYS. An algorithm based on a Thermal Inertia Control Logic (TICL), which can exploit the capability of the building envelope to store thermal energy, has been applied. When the proposed algorithm is employed, the indoor air temperature set-point is increased when the outdoor temperature is larger than the bivalent temperature of the building-heat pump system. Different configurations of the heating system were simulated considering either convective (fan-coil) or radiant (radiant floor) emitters coupled to a variable-speed air-to-water heat pump. Simulations have been carried out considering a reference building derived from the IEA SHC Task 44 and evaluating the influence of the proposed control logic on both the heat pump seasonal energy performance and the internal comfort conditions perceived by the building users. The obtained results highlight how the introduced TICL can guarantee the use of downsized heat pumps, coupled to radiant emitters, with a significant enhancement of the seasonal performance factor up to 10% and a slight improvement of comfort conditions. On the other hand, when convective terminal units are considered the proposed logic is not effective and the overall energy consumption of the system increases up to 15%
Experimental measurements of thermal-hydraulic performance of aluminum-foam water-to-air heat exchangers for a HVAC application
In this paper, thermal and hydraulic performance of in-house made prototypes of water-to-air heat exchangers are experimentally investigated and compared to those of a compact heat exchanger, used in a commercial fan coil. The prototypes are built replacing the fins with aluminum foam surfaces characterized by a large porosity, higher than 96%. In order to evaluate the performance of the foam-based heat exchangers in a real-scale application, the geometry of the prototypes was based on that of the reference model and, moreover, experimental tests were performed placing the heat exchangers within the commercial cabinet, under the same fan power. Different bonding techniques were also tested to couple metal foams to copper tubes. Results show that similar hydraulic performance can be obtained with the foam-based heat exchangers, if compared to the commercial device. However, the large foam porosity accounts for a lower value of the surface-to-volume ratio of the aluminum foam media, thus yielding a strong penalty, up to 60%, of the heat transfer rate with respect to that of the conventional finned surface. Moreover, experimental results highlight how the bonding technique and the foam packaging have a strong influence on the contact thermal resistance and, consequently, on the overall heat transfer coefficient. Epoxy bonding allows to increase the thermal performance of the heat exchanger, if compared to press fitting, between 15% and 110%. In conclusion, results presented in this paper suggest that metal foams can be considered as a potential alternative to fins in water-to-air heat exchangers only if the foam tube bonding is obtained by welding or brazing
A new electric streamer for the characterization of river embankments
River embankments are linear earth structures, worldwide diffused, commonly used for flood protection. Their integrity and stability are fundamental prerequisites for the protection efficiency they can offer to the increasing frequency and magnitude of extreme flood events associated to changes in climate. Proper characterization and monitoring are essential to verify the construction requirements of newly built structures and to evaluate the durability of aged ones. Considering their linear extent, the characterization requires not only local geotechnical investigations but also the application of efficient and economically affordable methods. This is even more essential when the investigations are performed after, or in foresee of, significant flood events, when these structures get stressed and timing of the surveys is crucial. In these conditions, new survey methodologies, with the use of mobile systems, are a main research topic. In this paper the application of a new electric streamer, specifically designed for these aims, is presented. The technical solutions adopted for its construction are described and its application to the characterization of three different river embankments is presented. These case studies were chosen in accordance with the Po River Interregional Agency (AIPO), which is the authority deputed to the safety of flood protection structures in North-West Italy, along the hydrographic network of the Po River. The selected embankments are all earth structures, constructed above the natural alluvial soils, but are characterized by different conditions and challenges. The results obtained with the new system were comparable to standard Electric Resistivity Tomography (ERT) methods. The new system has significant advantages in terms of reducing the survey time, improving the efficiency of the surveys and increasing the data coverage. This resulted in a better definition of potentially dangerous anomalies
Experimental Investigation on Latent Thermal Energy Storages (LTESs) Based on Pure and Copper-Foam-Loaded PCMs
In this work, a commercial paraffin PCM (RT35) characterized by a change range of the solid-liquid phase transition temperature Tsâl=29â36 °C and the low thermal conductivity ÎťSL=0.2 W/m K is experimentally tested by submitting it to thermal charging/discharging cycles. The paraffin is contained in a case with a rectangular base and heated from the top due to electrical resistance. The aim of this research is to show the benefits that a 95% porous copper metal foam (pore density PD=20PPI) can bring to a PCM-based thermal storage system by simply loading it, due to the consequent increase in the effective thermal conductivity of the medium (ÎťLOAD=7.03 W/m K). The experimental results highlight the positive effects of the copper foam presence, such as the heat conduction improvement throughout the system, and a significant reduction in time for the complete melting of the PCM. In addition, the experimental data highlight that in the copper-foam-loaded PCM the maximum temperature reached during the heating process is lower than 20K with respect to the test with pure PCM, imposing the same heat flux on the top (P=3.5 W/m2)
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
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 (2â3%) 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
From combinations to single-molecule polypharmacologyâcromolyn-ibuprofen conjugates for alzheimerâs disease
Despite Alzheimerâs disease (AD) incidence being projected to increase worldwide, the drugs currently on the market can only mitigate symptoms. Considering the failures of the classical paradigm âone target-one drug-one diseaseâ in delivering effective medications for AD, polypharmacology appears to be a most viable therapeutic strategy. Polypharmacology can involve combinations of multiple drugs and/or single chemical entities modulating multiple targets. Taking inspiration from an ongoing clinical trial, this work aims to convert a promising cromolynâibuprofen drug combination into single-molecule âcodrugs.â Such codrugs should be able to similarly modulate neuroinflammatory and amyloid pathways, while showing peculiar pros and cons. By exploiting a linking strategy, we designed and synthesized a small set of cromolynâibuprofen conjugates (4â6). Preliminary plasma stability and neurotoxicity assays allowed us to select diamide 5 and ethanolamide 6 as promising compounds for further studies. We investigated their immunomodulatory profile in immortalized microglia cells, in vitro anti-aggregating activity towards Aβ42-amyloid self-aggregation, and their cellular neuroprotective effect against Aβ42-induced neurotoxicity. The fact that 6 effectively reduced Aβ-induced neuronal death, prompted its investigation into an in vivo model. Notably, 6 was demonstrated to significantly increase the longevity of Aβ42-expressing Drosophila and to improve fly locomotor performance
Impact of the built environment and the neighborhood in promoting the physical activity and the healthy aging in older people: An umbrella review
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