Search Results (940)

This paper proposes a novel solar-assisted inter-cooling air source heat pump (SCAS–HP) system that integrates a solar collector/evaporator into the intermediate injection branch to utilize solar energy for increasing the refrigerant flow rate at intermediate pressure. A numerical model of the system was developed and validated against the literature data, and then employed to investigate performance under varying operating conditions. Three configurations were examined—two-stage throttling (T–SCAS–HP), single-stage throttling (S–SCAS–HP), and parallel evaporators (P–SCAS–HP)—and their performance was compared with a conventional vapor injection air source heat pump (VI–ASHP) across solar radiation intensities of 10–1000 W/m², outdoor air temperatures of −20 °C to 10 °C, and outlet water temperatures of 35 °C and 55 °C. Hourly performance, economics, and CO₂ reduction were further assessed for Lhasa, Beijing, and Harbin. The results show that the COP_h improvement of SCAS–HP over VI–ASHP rises with increasing solar radiation intensity. Furthermore, the solar radiation threshold at which the COP_h of SCAS–HP begins to exceed that of VI–ASHP lies within the range of 100–200 W/m². Moreover, the COP_h increase rate of SCAS–HP rises with larger solar collector area and higher outdoor air temperature, but declines as the outlet water temperature rises. Among the three configurations, T–SCAS–HP outperformed S–SCAS–HP and P–SCAS–HP by 0.37 and 0.42 in COP_h at outlet water temperatures of 35 °C and 55 °C, respectively. In typical-day simulations, the COP_h showed a relative increase of 50.9% compared to that of the VI-ASHP system, corresponding to an absolute rise from 3.73 to 5.62 with a 130 m² collector at 35 °C outlet water temperature. The energy saving rate ranked highest in Lhasa, followed by Beijing and Harbin. The shortest payback period (5.6 years) was achieved in Harbin with a 130 m² collector area at the outlet water temperature of 55 °C. The proposed system is particularly suitable for large heating demand and long heating seasons in cold climates with abundant solar resources. Full article

Public buildings play a critical role in national decarbonization strategies and green energy transitions due to their high energy consumption densities, large occupant capacities, and potential to drive public awareness. Optimizing energy efficiency in these structures not only alleviates the financial burden on public budgets but also serves as a benchmark for sustainable urban development. To investigate the energy-saving potentials, thermal comfort dynamics, and financial feasibilities within this sector, this study selects two university buildings from two different countries with distinct climatic, structural, and operational profiles as comparative case studies: university buildings in Türkiye (TR) and Italy (IT), respectively. A total of seven tailored retrofitting scenarios were developed based on country-specific legislative frameworks and subsidy mechanisms: the Minimum Environmental Criteria (CAM) and Conto Termico 3.0 for Italy, and the Public Buildings Energy Efficiency Project (KABEV), Energy Performance Contracting (EPC), and Nearly Zero Energy Buildings (NSEB) mandates for Türkiye. The scenarios evaluate deep building envelope insulation, high-efficiency window replacements, lighting automation (LED with daylighting controls), mechanical ventilation with heat recovery units (HRV), air-to-water heat pump integrations, and rooftop photovoltaic (PV) installations using calibrated DesignBuilder simulation models. The quantitative results demonstrate that country-specific green building incentives drastically enhance both the energy performance and financial viability of deep retrofits. For the Turkish case study, the comprehensive near-zero energy building (nZEB) retrofitting package (TR-4) successfully reduced annual primary energy consumption by 75% (from 284 to 71 kWh/m²·year) and cut annual thermal comfort discomfort hours by 72% (from 3147 to 880 h), yielding a Subsidized Net Present Value (NPV) of +310,600 €. Similarly, for the Italian case study, the holistic retrofit combined with rooftop photovoltaic integration (IT-4) achieved an 80% energy reduction (dropping from 128 to 25.6 kWh/m²·year), minimized annual discomfort hours to 45 h, and generated a Subsidized NPV of +425,500 €. Furthermore, national incentive mechanisms shortened simple payback periods by more than half, establishing that targeted public policy is vital to accelerate public sector building decarbonization while ensuring long-term fiscal profitability. Full article

The solar–air source heat pump (S-ASHP) system is used to prepare domestic hot water and is an important form of hot water preparation in many colleges and universities in China. However, the traditional design specifications and operation control strategies can cause excessive design capacity for the hot water system and energy waste. To address these issues, in this study, we integrate the S-ASHP hot water system with predictive modeling of user demand, proposing two distinct control strategies for the hot water supply system. Scheme I: The traditional hot water demand specification is used for design, and the feedback control strategy of the end hot water demand is set according to a fixed mode. Scheme II: A feedforward–feedback combined control strategy based on the ANN-LSTM-STA model is used to predict water consumption and set the end hot water demand. Compared with Scheme I, Scheme II shows significant advantages in heat supply, total energy consumption, and coefficient of performance (COP). The heat supply of the solar collector (SC) supply system is increased by 9.47%, the heat supply of the ASHP supply system is significantly reduced by 57.52%, the running time is reduced by 33.45%, the pump’s energy usage decreases by 16.65%, and the overall system energy consumption drops by 43.85%. Additionally, the coefficient of performance (COP) improves by 6.42%, and the coefficient of performance of the system (COPsys) sees a significant increase of 18.39%. Full article

Green hydrogen production through water electrolysis is a key pathway to the decarbonization of future energy systems. However, part of the electrical input is transformed into waste heat. In this study, alkaline, proton-exchange membrane, anion-exchange membrane, and solid oxide electrolysis systems are compared in terms of operating temperature, heat generation, heat transfer medium, and integration constraints. Reported COP values for commercial high-temperature vapour-compression heat pumps range from 2.4 to 5.8, depending on operating conditions. The heat-pump technologies reviewed include vapour-compression systems with single-stage, multistage, cascade, and transcritical configurations, together with absorption and adsorption systems, with a focus on suitable working fluids and practical limitations. The review distinguishes between direct heat recovery and heat recovery assisted by heat pumps, and it identifies two main areas of application: external supply for district heating, industrial consumers, and energy communities; and internal support for feedwater preheating, water cycle integration, and steam generation. A selection framework is proposed in which source- and sink-temperature compatibility determines thermodynamic feasibility, COP characterizes heat-pump performance, and LCoH supports techno-economic comparison. Direct heat recovery should be preferred when temperatures are compatible, while heat pumps can operate as enabling technologies when temperature upgrading is required and system-level economic and environmental performance remains advantageous. Full article

This study investigated a high-temperature heat pump for industrial steam production at 200 °C. Considering refrigerant thermal degradation at elevated temperatures, R1336mzz(Z) was selected because of its thermal stability. Two systems were analyzed: a flash tank (FT) cycle producing steam using a water valve and flash tank, and a steam generator (SG) cycle directly generating steam in the gas cooler. Unlike previous studies focusing primarily on cycle-level thermodynamic performance, this study systematically compares two steam production configurations for a 3 MW-class HTHP by considering heat pump–steam loop interactions and further evaluates their economic and environmental feasibility through LCC and LCCP analyses. Applying an internal heat exchanger reduced the operating pressure and increased the heat pump coefficient of performance (COP) by up to 13%, depending on the pressurized water temperature. In the FT cycle, lowering the valve outlet temperature from 180 °C to 150 °C increased the heat pump COP to a maximum of 3.06. However, the additional mechanical vapor recompression (MVR) power limited the overall system COP to 2.29–2.44. In the SG cycle, the system COP ranged from 1.94 to 2.54 according to the saturated water temperature at the gas cooler inlet, although operation at lower water temperatures approached the critical region, resulting in a narrower operating margin. LCC and LCCP analyses showed that replacing conventional boilers with heat pumps reduced operating costs by 26–59%, depending on regional energy prices, with payback periods of 2.27–8.76 years. Heat pump adoption also reduced life cycle climate impacts by 13–72%. These results demonstrate that high-temperature heat pumps can provide an economically and environmentally viable alternative for industrial steam production at 200 °C. Full article

This study investigates the atmospheric and upper-ocean responses associated with Super Typhoon (TY) Lekima (2019) during 4–12 August, including its landfall over Zhejiang Province, China. Variations in sea surface temperature (SST), latent heat flux (LHF), water vapor flux (WVF), total column water vapor (TCWV), vertical integral moisture divergence (VIMD), mean sea level pressure (MSLP), wind circulation, precipitation, subsurface temperature and salinity, and Ekman pumping velocity (W_E) were analyzed throughout the typhoon life cycle. Before intensification, SSTs of 29.5–31.0 °C indicated favorable ocean-surface conditions. During and after the storm passage, SST decreased to approximately 26.0–27.5 °C along portions of the track and below 25.0 °C near the Zhejiang coast, with stronger cooling on the right-hand side of the track. Surface salinity decreased by approximately 0.3–0.8 PSU during 8–10 August, with freshening extending through the upper 30–40 m. The Ekman pumping field identified regions where wind-stress curl favored upwelling and downwelling, with stronger positive signals occurring on the right side of the track. During the active maritime stage, LHF values of approximately −300 to −200 W m⁻² indicated enhanced upward latent heat transfer. WVF reached 1800–2200 kg m⁻¹ s⁻¹, TCWV exceeded 70 kg m⁻², and VIMD decreased below approximately −100 × 10⁻⁵ kg m⁻² s⁻¹, indicating enhanced moisture transport and convergence. These conditions coincided with daily precipitation exceeding 120 mm and locally reaching approximately 160 mm over northern and northwestern coastal Zhejiang. The minimum daily mean MSLP decreased from 1000 to 972–976 hPa during peak intensity and subsequently increased as Lekima approached landfall and weakened inland. While these responses are qualitatively consistent with previous TY case studies, our study provides new quantitative benchmarks and process attribution through heat budget analysis. This integrated, stage-based analysis provides a comprehensive quantitative reference for model validation and future comparative studies of landfalling typhoons in the western North Pacific. Full article

Ground source heat pump (GSHP) systems contribute to sustainable building decarbonization while confronting two intertwined challenges: long-term ground thermal imbalance in shallow borefields and the requirement for coordinated operation between thermal systems and electrical grid dynamics. Hybrid shallow–deep borefield configurations have been proposed to mitigate thermal imbalance for sustainable geothermal resource exploitation, yet their grid-interactive demand–response potential remains unexplored. Here, we develop a coupled thermal–electrical model for a shallow–deep mixed GSHP (SDBHE) system equipped with water-tank thermal storage, validated against scaled sand-tank experiments (3.5–8.3% error), and assess its year-round performance under time-of-use electricity tariffs for a 200,000 m² residential district in cold-climate conditions. The SDBHE system reduces the required shallow borehole count by 28% and total drilling length by 22% compared with a shallow-only baseline, saving 11% on operational electricity costs over 10 years. Integrating water-tank thermal storage with a 50% load-shifting strategy yields an additional 10.9–11% cost reduction without degrading the system’s coefficient of performance. Under higher load-shifting ratios, the combined capital and operational savings reach 19–29%, with the optimal allocation assigning the incremental high-price-period load preferentially to deep boreholes (COP 6.29 versus 5.25 for shallow). These results demonstrate that integrating shallow and deep geothermal tiers with thermal storage enables both capital-efficient borefield design and economically viable demand-side grid participation. The findings are bound by the cold-climate residential context and the rule-based control scheme; field-scale validation and lifecycle cost analysis are needed to generalize the conclusions. Full article

This article presents a technical and economic analysis of a photovoltaic system operating in conjunction with a heat pump in a single-family home. The aim of this study was to compare the cost-effectiveness of two prosumer billing systems currently in use in Poland, net metering and net billing, implemented in accordance with the provisions of the Renewable Energy Sources (RES) Act and the Energy Law and to assess the effectiveness of a proprietary algorithm for managing surplus electricity produced by the photovoltaic system. The energy performance of the facility was determined using ArCADia Termo 11.1 software, while energy and economic calculations were performed using Microsoft Excel 365 and a developed heat pump control algorithm. The algorithm is based on an analysis of the building’s energy balance with a 15 min resolution and utilizes data on outdoor temperature, energy production from the PV system, building heat loss, heat pump operating parameters, and energy self-consumption. Its goal was to maximize the use of energy produced for the building’s own needs by appropriately controlling the heat pump and storing surplus energy as heat stored in domestic hot-water tanks. The annual electricity consumption of the analyzed building was 6902.18 kWh, of which 3724.13 kWh was for heating and domestic hot water provided by the heat pump. The algorithm reduced grid energy consumption by approximately 900 kWh per year and achieved a self-consumption level of 12.73 (%). Full article

To address the limited cooling range of ventilation in deep, high-temperature development headings and the lack of coordinated design between coil-based cooling and the ventilation system, this study proposes a coupled “twin-forcing–coil” cooling scheme. Building on conventional overlap (forcing–exhausting) ventilation, a rear-mounted second forcing duct is added to the conventional overlap (force–exhaust combined) auxiliary ventilation system, forming a dual-duct forcing, single-exhausting configuration—hereafter termed the “twin-forcing–single-exhausting” (TFSE) system—that provides a booster (relay) air supply to mitigate the along-path attenuation of cooling capacity and the short-circuiting of cold air; an in situ heat-exchange coil wall further provides supplementary cooling where ventilation-based temperature control weakens. Using a development heading at the 790 m level of a metal mine in Yunnan as the engineering background, a three-dimensional numerical model coupling the roadway, ventilation system, and coil wall was established and validated against nine field monitoring points, showing average relative errors of approximately 1% for temperature and 2–3% for humidity, comparable to the measurement uncertainty of the field instrumentation. Because the numerical model does not account for evaporative and condensation phase-change processes, two supplementary development headings with standing water at the face were used for validation; results showed that model error increases with water accumulation and heading length, indicating the model’s applicability is limited to conditions with intact surrounding rock and minimal seepage. Six operating cases were designed with duct placement and coil spacing as variables. Results show that single-duct ventilation cooling decays markedly beyond 30 m from the face, whereas twin-forcing booster (relay) air supply effectively extends the cooling range, reducing the 30–70 m section temperature by 2.7–2.9 K; the second duct should be positioned where the first duct’s cooling capacity begins to attenuate but is not yet depleted. Based on only two spacing configurations tested (10 m and 15 m), coil-staggered spacing showed limited effect on cooling performance under the field conditions examined; this preliminary finding requires validation across a broader range of spacings. Among the chilled-water conditions tested, an inlet temperature of 280.65 K and a flow velocity of 0.5 m/s offered a reasonable trade-off between cooling uniformity and economic efficiency. Under the boundary conditions and equipment parameters of this case, energy consumption estimates further indicate that the cooling effect per unit electricity consumption of twin-forcing ventilation is roughly 6–8 times that of coil-based cooling, primarily due to pumping losses over the ~240 m chilled-water delivery distance. This energy penalty indicates that coil-based cooling is better suited as a localized, short-distance supplementary measure rather than as a means of extending the cooling range over long distances. Full article

Photovoltaic–thermal (PVT) collectors coupled to thermochemical energy storage (TCES) can turn intermittent low-grade solar heat into a dispatchable service, but solar intermittency poses a closed-loop control problem. A companion study established the feedback-only lower bound: a 937 kJ accumulated exergy-delivery-deficit benchmark under optimally tuned proportional–integral–derivative (PID) flow control. The corresponding upper bound is quantified here by means of a deliberately idealised search-based predictive controller that, at each 10 s step, enumerates 51 candidate pump rates, predicts the reactor-inlet temperature by a single forward-Euler step, and is granted perfect future irradiance. On the experimentally validated shared plant (matched to the companion baseline), against an optimally tuned PID, the perfect-foresight advantage is marginal: +0.96% daily exergy on synthetic days and +0.07–0.24% on two measured Walailak University monsoon days, all controllers tracking within 6–13 K on the measured days. Under tropical-monsoon irradiance, the 95 °C desorption setpoint is rarely sustained, so the delivered exergy is nearly controller-independent: the perfect-foresight upper bound lies just above the feedback-only lower bound, and together the two results bracket the exergy envelope available to any flow-rate controller of this system. A horizon sweep localises the bottleneck to internal-model fidelity, not anticipation depth. The eight-node plant is validated against measured module temperature (root-mean-square error 3.5 °C, coefficient of determination R² = 0.89) and a copper-tube PVT prototype (1.5 °C; peak hot water up to 79 °C). The central contribution is therefore a rigorously defined, experimentally grounded upper bound showing that, at this scale and latitude, deployability rather than anticipation is the effective design lever. Full article

Metal foams and nanofluids are recognized as attractive and effective heat transfer enhancement methods. This study numerically investigates forced convection heat transfer and second-law thermodynamic behavior of water and a 0.02% Cu–MXene/water hybrid nanofluid flowing through a tube partially filled with metal foam. Three configurations are examined: a clear tube as the reference case; Case A (three discrete foam blocks occupying 3/16 of the tube length); and Case B (a single block occupying 9/16), using four metal-foam types (aluminum 30/45 PPI, copper 40 PPI, and nickel 60 PPI). The governing equations are solved using the finite-volume method with the SIMPLER algorithm and validated against published experimental and numerical data. Results show that Case B provides higher heat-transfer rates and performance evaluation criterion (PEC) values than Case A, although at the expense of larger pressure-drop and pumping-power penalties. The highest heat-transfer enhancement is obtained with Cu-40 PPI foam and the hybrid nanofluid in Case B, where the average Nusselt number increases by a factor of 3.33 at a Reynolds number of Re = 200 relative to water in the clear tube. Higher-thermal-conductivity foams, combined with the hybrid nanofluid, provide greater thermohydraulic benefits than lower-conductivity foams with water. The second-law analysis reveals that increasing Re reduces thermal irreversibility but increases frictional irreversibility, highlighting the competing effects of heat-transfer enhancement and hydraulic resistance. Overall, the Cu-40 PPI/hybrid nanofluid combination in Case B at low Re provides the most favorable performance among the investigated conditions. Full article

PV/T collectors and Air Source Heat Pump (ASHP) are widely studied for building heating, but solar intermittency and ASHP low-temperature frosting limit their large-scale deployment. A novel PV/T-ASHP coupled heating system is proposed to cut building carbon emissions and relieve ASHP performance degradation in cold zones. Circulating water cools PV/T panels to boost power generation, and the warmed water preheats ASHP evaporator inlet air to reduce frosting and defrosting frequency. With a Xi’an office building as the research object, validated TRNSYS 18.0 models are established for comparative analysis with conventional systems and cross-climate evaluation in Xi’an, Beijing, Shanghai and Chengdu. Results show the new system lifts PV/T combined efficiency by 17.56%, reduces energy consumption by 19.9%, and achieves an average COP of 3.2. Across climate zones, its COP rises 11.5–24.6% and 50-year carbon emissions fall 16.4–26.2%, supporting low-carbon heating promotion for office buildings. Full article

The use of hydrogen for heating is one of the pathways toward zero-emission buildings. Two possibilities for using hydrogen in combination with heat-pump systems were analyzed: an electrically driven heat pump powered by a fuel cell and a mechanically driven heat pump powered by a hydrogen internal combustion engine (ICE). Heat-pump operation was adapted to local climatic conditions using typical meteorological year datasets for 30 representative locations across Bulgaria. The seasonal coefficient of performance (SCOP) values were further adjusted toward actual operating conditions using a field-performance correction factor. The results reveal a thermodynamic transition between the two pathways, defined by a critical seasonal coefficient of performance, SCOP_crit. For the reference ICE heat-recovery fraction of 0.45 and without direct fuel-cell heat recovery, SCOP_crit is 2.53. Above this threshold, the fuel-cell-driven pathway requires less hydrogen, whereas below it, the mechanically driven pathway requires less hydrogen. A strong correlation was identified between pathway dominance and the mean outdoor temperature during the heating period, with a transition temperature of about 2.4 °C. The sensitivity analysis shows that SCOP_crit ranges between 1.40 and 3.52. Overall system efficiencies ranged from approximately 1.2 to 1.8 on a lower heating value (LHV) basis, exceeding typical direct hydrogen-combustion efficiencies. Full article

Hybrid nanofluids raise the thermal output of evacuated-tube solar collectors, but the heat-transfer gain comes at the cost of friction and pumping power, so the working fluid must be chosen in line with a constrained thermo-hydraulic criterion. Its design is posed here as a constrained single-objective optimisation over the hybrid pair, base fluid, weight fraction, component share and flow rate. A variance-based screening of a 54,432-run full-factorial dataset reduces the design space from eight variables to five, justified by the invariance of the optimal hybrid pair across thirty-six operating points. Gradient-boosted surrogates for the four state and constraint responses (efficiency, pumping power, Reynolds number and outlet temperature) reproduce the simulator to held-out coefficients of determination of 0.9998–1.0000; the performance-criterion surrogate has a lower global coefficient of determination (0.46) and is assessed by top-region ranking accuracy. The reduced problem is solved with a selection hyper-heuristic over twelve operators, pairing an upper-confidence-bound selector with late-acceptance hill-climbing. Under Friedman-, Nemenyi- and Holm-corrected Wilcoxon testing, it ranks within the leading statistically indistinguishable group, but is not separable from a random-selection ablation, locating its value in robustness rather than adaptivity; furthermore, it attains the grid-reference optimum within 0.40 percent. The criterion optimum is an Al₂O₃-Cu suspension in ethylene-glycol and water at three percent loading; the constrained-efficiency optimum reaches a surrogate thermal efficiency of 0.760, cross-checked against a grid-reference value of 0.762 and a reconstructed-model value of 0.760, conditional on the supplied reduced-order model and its single-tube dataset convention. The constrained-efficiency objective is treated as the primary design objective, while the performance criterion is reported as a secondary screening index that characterises the additive rather than selecting the operating fluid. Full article

Heat pumps are core equipment for efficient low-grade thermal energy utilization and low-carbon transformation of the energy structure, offering significant energy-saving potential in building heating and industrial waste heat recovery. This paper reviews the research progress and technical challenges of compression, absorption, and adsorption heat pumps as well as nanofluid-enhanced heat transfer technology and elastocaloric heat pump systems. Air source heat pumps can delay frosting through variable frequency, heat storage, and waste heat recovery. However, accurate prediction models for performance degradation under extreme cold conditions are lacking. Although ground source and water source heat pumps exhibit significant energy efficiency advantages, ground source systems may suffer from performance degradation due to underground thermal imbalance. The application of water source systems is strictly constrained by water resource conditions. Driven by low-grade waste heat, absorption heat pumps employing traditional working pairs suffer from crystallization, corrosion, or high rectification energy consumption. The COP of a single-effect cycle under 80~100 °C waste heat is only 1.2~1.9, while hybrid cycles can reach approximately 3.2 at 120~150 °C. Although adsorption heat pumps achieve significantly improved performance under continuous heat recovery cycles, the full-scale power density of novel adsorbents such as metal–organic frameworks is inferior to the power density of traditional silica gel. Moreover, under off-design conditions, the performance drops by 23~48% compared to theoretical values. Nanofluids can enhance heat transfer, but the long-term effects of particle agglomeration at high temperatures on pump power consumption and system compatibility remain to be systematically evaluated. Elastocaloric heat pump systems can achieve refrigerant-free cooling, but current prototypes still cannot compete with traditional vapor compression systems in long-cycle fatigue reliability and power density. Current heat pump technologies generally face challenges such as insufficient adaptability to extreme conditions, bottlenecks in working fluids and materials, and a lack of long-term validation. Future research must construct a multi-source coupling optimization system, address common problems in working fluids and materials, promote long-term validation and kilowatt-level prototype demonstrations, and drive the large-scale deployment and engineering application of heat pump technology toward high efficiency, intelligence, and high reliability. Full article