Hot Mode Research Articles

Applicability performance evaluation of cascade heat pump for building electrification in winter

This study aimed to evaluate the performance of indoor air heating and domestic hot water supply using a cascade heat pump system. The focus was on using existing heat pump equipment to satisfy system requirements in the context of building retrofitting. The experimental setup was located in nearly net-zero experimental building of the South Korea. The system was configured to heat air in the low-cycle heat pump and supply hot domestic water in the high-cycle heat pump. The study compared three operational modes: a low-cycle-only mode; a hot water-only mode; and a combined mode. While low-cycle-only mode and hot-water-only mode fulfilled the required condition with 3.94–5.38 COP and 60 °C hot water temperature with a flow rate of 15.8 LPM separately, the combined mode failed to reach the target air temperature fulfilling only hot water temperature. In conclusion, the system demonstrated satisfactory performance when heating indoor air and providing hot water separately. However, the indoor heating performance declined when both functions were operated simultaneously. To address this issue, possible solutions could include revising the system operation logic to better align with heating and domestic hot water usage schedules or altering the refrigerant flow path.

Effect of hot rolling on microstructure and mechanical properties of hot isostatically pressed 30CrMnSiNi2A ultrahigh strength steel

The prior particle boundaries (PPBs) are a typical powder metallurgy (PM) defect, which usually leads to the deterioration of mechanical properties in PM materials. In this study, two different hot rolling modes (unidirectional rolling and cross rolling) are designed to improve PPBs in hot isostatic pressed (HIPed) 30CrMnSiNi2A ultrahigh strength steel. The microstructure, mechanical properties and fracture features of the HIPed compact, the hot unidirectional rolled (HURed) and hot cross rolled (HCRed) sheets are systematically compared. The results manifests that hot rolling has a significant influence on size and distribution of PPBs. PPBs in HIPed compact are comprised of Al-rich oxides which is distributed along particle boundaries. After hot rolling, large PPBs inclusions are crushed and the size of PPBs are mostly concentrated in 0–0.20 μm. Unidirectional rolling makes continuous PPBs structure broken into short-chain fragments and dispersed oxides completely, while cross rolling makes most of continuous PPBs structure maintained and only a few oxides are dispersed. Excellent mechanical properties are obtained by hot rolling, reflecting on an ultimate tensile strength (UTS) of about 2.0 GPa, a total elongation (TE) of 17.9 %, a Charpy impact energy of 28.6J along rolling direction and a UTS of over 2.1 GPa, a TE of 16.1 %, a Charpy impact energy of 18.1J along transverse direction, respectively. High performances can be attributed to formation of martensite, grain refinement, improvement of PPBs and work hardening. Furthermore, hot-rolled samples manifests an obvious anisotropy in mechanical properties. The HCRed sample reveals a lower anisotropy compared to the HURed sample, mainly owing to differences of PPBs distribution and rolling textures.

Analysis of the performance and operation of a photovoltaic-battery heat pump system based on field measurement data

Photovoltaic-heat pump (PV-HP) combinations with battery and energy management systems are becoming increasingly popular due to their ability to increase the autarchy and utilization of self-generated PV electricity. This trend is driven by the ongoing electrification of the heating sector and the growing disparity between growing electricity costs and reducing feed-in tariffs in Germany. Smart control strategies can be employed to control and optimize the heat pump operation to achieve higher self-consumption of PV electricity. This work presents the evaluation results of a smart-grid ready controlled PV-HP-battery system in a single-family household in Germany, using 1-minute-high-resolution field measurement data. Within 12 months evaluation period, a self-consumption of 43 % was determined. The solar fraction of the HP amounts to 36 %, enabled also due to higher set temperatures for space heating and domestic hot water production. Accordingly, the SPF decreases by 4.0 % the space heating and by 5.7 % in the domestic hot water mode. The combined seasonal performance factor for the heat pump system increases from 4.2 to 6.7, when only considering the electricity taken from the grid and disregarding the locally generated electricity supplied from photovoltaic and battery units.

Reliability analysis and redundancy optimization of k-out-of-n systems with random variable k using continuous time Markov chain and Monte Carlo simulation

This article discusses the problems associated with the redundancy of structures k-out-of-n as a method of increasing system availability. A parallel k-out-of-n system was considered, with k repairable and homogeneous components. The other (n – k) objects are in hot redundancy mode. Failures and repairs are independent processes, and each repaired object is treated as full-fledged in terms of operation. The system operates under dynamically changing conditions, so the minimum number of operable components essential for its proper operation is a random variable with a specific distribution. Component damages and repairs are independent stochastic processes. A probabilistic and simulation approach based on Continuous Time Markov Chain and Monte Carlo simulation is proposed. This study aims to optimize the number of components in the k-out-of-n structure, which will ensure the system operation with a certain availability and performance. The proposed methods were applied to real transport systems, for which models were developed with parameters estimated on the basis of empirical data. The convergence of the results obtained, using two methods, testifies to the correctness of the methodology used and the reliability of the models developed. The risk to system performance associated with changing input parameters was assessed using model sensitivity analysis. As indicated, the model is not susceptible to changes in the damage and repair intensity. It has also been shown that optimization of the k-out-of-n structure brings a significant reduction in the costs incurred for system development and operation.

Relationship between hot workability and texture evolution in an Al–Zn–Mg–Cu alloy under hot compressive stress mode

Relationship between hot workability and texture evolution in an Al–Zn–Mg–Cu alloy under hot compressive stress mode

Highly sensitive SERS platform on isotropic ionic liquid-based liposome

An ionic liquid (IL)-based liposome, consisting of an imidazolyl head and two undecene tails (N, Ń-bis(10-undecenyl)-2-methylimidazolium bromide, [MimV11, V11]Br), was prepared through self-assembly and used as a carrier to create an isotropic surface-enhanced Raman scattering (SERS) platform. The bridging of IL terminals was employed to enable the co-assembly in both hotspot formation and the induced localization of analytes. Specifically, gold nanoparticles (Au NPs) were grown and stabilized on the surface using the anion exchangeability and coordination effect of IL. Besides, the confinement effect of the isotropic surface spatially arranges the Au NPs in an array-like pattern, which not only facilitates the formation of hotspot-rich planes but also provides a uniform electrostatic driving force for molecular loading. This contributes to the improvements in detection sensitivity and reproducibility of the SERS signal. On this basis, the co-assembled platform presented an ideal enhancement factor (3.04 × 107) and a low detection limit (10-12 M) for methyl orange (MO). Additionally, the detection performance, adsorption orientation, and their influencing factors were investigated. The results showed that the adsorption of MO on the liposome exhibited two typical orientations, lying-type, and standing-type. It was mainly regulated by the resonance structures of MO and the steric effect of the SERS substrate. The isotropic co-assembly strategy achieves ultrasensitive trace detection and draws a fascinating application prospect for this hotspot-motivated and hot region-located SERS detection mode.

Thermal performance of a novel water blind-Trombe wall system: A comparative experimental investigation

A traditional Trombe wall suffers from undesired heat gains, single service function, and poor aesthetic appearance, and these drawbacks act as a barrier to its widespread application. This study introduced a newly designed Trombe wall, which neatly incorporated a water-flowing channel and venetian blind (named WBTW). The WBTW can efficiently provide space heating, domestic hot water, and simultaneously act as a shade for reducing cooling load in hot summer. To examine the operating performance of the WBTW under different modes, long-term comparative experiments between a room with the WBTW and that with a flat plate solar water collector (SCCW) and one with a conventional south wall were conducted under realistic climate conditions. Through the test under hot water mode, it was observed that the average thermal efficiency of the WBTW reached 52.8% throughout different seasons, which was 8.2% higher than that of the SCCW. Furthermore, in summer the combined use of external circulation ventilation and water circulation for the WBTW was suggested to avoid overheating phenomenon although that was at the sacrifice of hot water temperature. Space heating experiments showed that the coefficient of thermal comfort enhancement was 0.744 for the room with WBTW under linked air–water heating mode, while that was only 0.155 under stand-alone air heating mode. Finally, based on the validated theoretical model of the WBTW system, a sensitivity analysis of operating and structural parameters was conducted. As to the influence on the annual heat gains of the WBTW system, the order was blinds angle (a) > the ratio of blind spacing to width (r) > air inlet velocity (v) > water mass flow rate (w) > air channel depth (d). The optimum level combination was a = 30°, r = 1, v = 0.4 m/s, w = 0.08 kg/s and d = 0.3 m.

On the dominant role of wind in the quasar feedback mode in the late-stage evolution of massive elliptical galaxies

ABSTRACT In this paper, we investigate the role of active galactic nucleus (AGN) feedback on the late-stage evolution of elliptical galaxies by performing high-resolution hydrodynamical simulation in the MACER framework. By comparing models that take into account different feedback mechanisms, namely AGN and stellar feedback, we find that AGN feedback is crucial in keeping the black hole in a low accretion state and suppressing the star formation. We then compare the energy from AGN radiation and wind deposited in the galaxy and find that only wind can compensate for the radiative cooling of the gas in the galaxy. Further, we investigate which plays the dominant role, the wind from the cold (quasar) or hot (radio) feedback modes, by examining the cumulative energy output and impact area to which the wind can heat the interstellar medium and suppress star formation. Our results indicate that first, although AGN spends most of its time in hot (radio) mode, the cumulative energy output is dominated by the outburst of the cold (quasar) mode. Second, only the impact area of the cold-mode wind is large enough to heat the gas in the halo, while the hot-mode wind is not. Additionally, the cold-mode wind is capable of sweeping up the material from stellar mass-loss. These results indicate the dominant role of cold-mode wind. The limitations of our model, including the absence of jet feedback, are discussed.

Isotope dependence of transport in ST40 hot ion mode plasmas

The ST40 compact, high-field spherical tokamak, operating at 2.1 T and with 1.8 MW of neutral beam heating, achieved central carbon impurity ion temperatures in excess of 10 keV, surpassing their business milestone of 100 M ∘C (8.6 keV). The high temperature discharges were in the hot ion mode, with , and they were achieved in both hydrogen and deuterium plasmas with deuterium neutral beam injection. In order to achieve the high temperature scenarios, careful wall conditioning and scenario optimization was carried out in , , and finally in plasmas. The TRANSP transport code was employed to study the dependence of confinement and transport on isotopic mass, and the conditions that led to the high measured central ion temperatures in the and plasmas. The kinetic profiles input into TRANSP were inferred from line-of-sight and limited radial measurements as well as consistency with a number of other experimental constraints. The TRANSP results first showed that the main species central ion temperature was only 0.5–1 keV lower than the measured carbon impurity temperature, and thus in the high performance plasmas also surpassed the 100 M ∘C level. TRANSP also showed that while the electron thermal conduction loss was dominant, reductions in central ion transport, and an effective decoupling of the ions from the electrons, led to an increase in central ion temperatures with increasing plasma mass. In fact, the associated confinement times exhibited a strong dependence on the isotopic mass of the thermal plasma. These preliminary results are foundations for dedicated experiments with full kinetic profile measurements on ST40 in the next run campaign.

Optimization of inlet conditions of hot steam injection into the non-equilibrium condensing steam

Injecting hot steam into the cascade flow is one of the procedures for resisting losses and damages caused by condensation. In the current study, utilizing a 3D (three-dimensional) geometry for steam turbine blades, the hot steam has been injected into the steam cascade via the embedded channel. In the power plant industry, the hot steam injection process is done in two ways: constant pressure with a reservoir or constant mass flow rate utilizing a control valve. Therefore, considering these two methods and the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) optimization method, the best temperature for injecting hot steam into non-equilibrium steam in a constant steam turbine blade has been gained. At the optimal temperature of 540 K at the constant pressure mode, Er (erosion rate ratio) and Lr (condensation loss ratio) were obtained as 66.6% and 30.7%, respectively, and Kr (kinetic energy ratio) showed a 0.6% growth in the hot steam injection mode, in comparison with the original mode. In addition, the economic cost of hot steam injection was calculated as 0.457 ($/hour). By the TOPSIS optimization method, the optimal temperature of hot steam injection, utilizing the constant mass flow rate method, has been obtained as 460 K, and the Er, Lr, and Kr values were 31.2%, 66.1%, and 88.48%, respectively at the optimal temperature. Moreover, the economic cost was 0.43 ($/hour). It is easier to control the steam injection by the constant mass flow rate method utilizing a control valve; therefore, the 460 K temperature and constant mass flow rate method are introduced as the optimal method.

Photocatalytic water splitting in the gap between plasmonic gold nanoclusters

Plasmon-mediated photocatalytic water splitting holds promise for efficient solar energy harvesting. Experimental studies have shown that “hot spots” in an assembly of plasmonic nanoclusters, which is the real case for practical applications, are beneficial for photocatalysis, but the interactions between different nanoclusters are difficult to observe by experimental techniques. Theoretical studies, however, have employed the model with a water molecule adsorbed on a single plasmonic metal nanocluster. Here, we employed the representative model of a water molecule placed in the gap between two gold nanoclusters and computationally investigated the effects of the configurations of plasmonic nanoclusters on plasmon-mediated water splitting. Results show that the hot electron transfer mode can be tuned by the plasmonic configurations. Compared to the configuration with only one gold nanocluster, more significant contribution of direct charge transfer was observed for the configuration with two gold nanoclusters, which is attributed to a stronger field enhancement; as a result, the water splitting rate was also enhanced. Results also demonstrate a charge transfer chain from one gold nanocluster to the water molecule and then to the other gold nanocluster, which is tunable by the distances between the water molecule and the gold nanoclusters. This charge transfer chain significantly affected the amount of hot electrons accumulated on the water molecule. Caused by this, the configuration where the water molecule was placed right at the center of the two gold nanoclusters, i.e., the configuration corresponding to the strongest field enhancement, was surprisingly not the most favorable one for the reaction.

A novel dual condensers heat pipe photovoltaic/thermal (PV/T) system under different climate conditions: Electrical and thermal assessment

The PV/T hybrid system has irreplaceable advantages in the comprehensive utilization of energy because of its capability to simultaneously generate heat and power. A heat pipe PV/T system is often used in cold area duo to its high energy efficiency and anti-frost properties. While most of existing systems only focus on the hot water supply, rarely involving in the function of space heating. In this paper, a novel dual-condensers heat pipe system is proposed to extend its energy supply functions and application areas. This study aims to establish a mathematical model of the proposed system, and analyze the performance of the system in different climatic region cities. Three cities in different climate zones were selected as boundary conditions for the analysis. The numerical result shows that in the hot water mode the system's electrical efficiency is 13.6%, 13.3% and 13.5%, and the total efficiency is 56.1%, 59.7% and 60.6%, respectively. In space heating mode, the system's electrical efficiency is 14.7%, 14.8% and 14.8%, and the total efficiency is 55.4%, 55.4% and 51.1%, respectively. The results confirm that the performance of the novel PV/T is steady and suitable for the cities with different environmental conditions.

Fuel Consumption and Emission Reduction for Non-Road Diesel Engines with Electrically Heated Catalysts

In this study, an exhaust system compliant with future regulations was developed for a non-road 110PS engine with a Tier-4f aftertreatment system, and the emission characteristics of the engine were investigated in the non-road transient mode (NRTC). For the system to comply with future exhaust regulations, a DPF was installed, and an electrical heated catalyst (EHC) device was installed to manage exhaust gas temperature. The emission characteristics of exhaust gas were examined according to the power and applied duration of EHC, and the effects of catalyst coating and the urea water solution (UWS) injection map on NOx reduction, NH3 slip, and N2O emissions in NRTC mode were investigated. The application of a 4 kW class EHC system enables the lowering of the injection starting temperature of the UWS, as reliable gas heating (heating duration control) is guaranteed. When the injection starting temperature (based on the SCR inlet temperature) was set to 150 °C, NSR map, (III) in conjunction with the operation of the EHC, effectively achieved significant NOx reduction in NRTC mode without deposit and wetting occurring in the mixer and exhaust pipe. Regarding changes in EHC power from 3 kW to 4 kW, it was observed that a NOx reduction of 0.05 g/kWh occurs in the cold NRTC mode, but in the hot NRTC mode, it was found that the relative decrease in the UWS is due to the increased NO2 conversion efficiency as a result of the oxidation catalyst, making 3 kW more advantageous. Furthermore, due to the increase in NO2 concentration caused by the oxidation catalyst and the increase in the low-temperature injected UWS, NH4NO3 was formed, which resulted in an increase in PM emissions and a significant increase in N2O emissions around an exhaust temperature of 250 °C. When the EHC power was set to 3 kW and the volume of oxidation catalyst and the amount of UWS injection were adjusted, applying EHC in the NRTC mode resulted in an additional NOx reduction of 58.6% and 88.4% in cold and hot modes, respectively, compared with not using EHC, with a fuel penalty of approximately 1.67%, while limiting the peak concentrations of N2O and NH3.

Hot Ion Mode in the Globus-M2 Spherical Tokamak

NBI-assisted plasma heating with one or two injectors of fast neutral atoms was studied at the Globus-M2 spherical tokamak at the toroidal magnetic fields of 0.8–0.9 T and plasma currents of 0.35–0.4 MA. Measurements of the spatial temperature and electron density distributions, performed using the Thomson scattering diagnostics, showed a twofold increase in heating of plasma electrons during the injection of neutral particles with energies of up to 45 keV at the beam power of 0.75 MW, as compared to the ohmic heating regime. Switching on the second additional beam with the particle energy of up to 30 keV and power of up to 0.5 MW resulted in obtaining the hot ion mode in the range of mean plasma densities of (1.6–10) × 1019 m−3. According to the data of active spectroscopy and neutral particle analyzer diagnostics, in the hot zone, the ion temperature reached 4 keV at the plasma density of 8 × 1019 m−3, which is more than 2.5 times higher than the electron temperature.

Study on hot air heating characteristics of greenhouse in cold region

Agriculture is the main industry in northeast China. As an important part of facility agriculture, agricultural greenhouses are playing a more and more important role. Due to geographical location, Northeast China is cold in winter, and the solar radiation energy is less, therefore, the large-span greenhouses commonly used in northeast China are prone to uneven temperature and insufficient heating. In this paper, in order to solve the phenomenon of uneven air flow field, humidity field and temperature field in greenhouse, based on AIRPAK simulation, four kinds of hot air heating return air modes, such as upper air supply and lower air return mode, lower air supply and upper air return mode, two-side air supply mode and left air supply and right air return mode, we explored the influence of temperature field, humidity field and air flow field in greenhouse. The results showed that the heat load of the greenhouse in winter is 161.51 kW, using two-side air supply mode is the best way. The air supply wind speed is 1.6 m/s, and the return wind speed is 3.1 m/s. The environment of the greenhouse can be maintained at about 15°C day and night, and the relative humidity is relatively uniform. In the crop growing area, the wind speed is between 0 m/s and 0.25 m/s. According to this research, suitable crops can be selected for reasonable planting and distribution in the greenhouse to maximize productivity.

Numerical study on the thermal and electrical performance of a novel MCHP PV-Trombe wall system

Most of existing photovoltaic (PV)-Trombe wall systems use a single coolant which has the drawbacks of low utilization efficiency and unreasonable heat distribution of space heating. In order to address these problems, a novel micro-channel heat pipe PV-Trombe wall system is proposed in this paper. The system uses heat pipe and Trombe wall to cool the PV collector decreasing its operating temperature and thus improving the overall efficiency. Moreover, an air-cooled condenser is used to control the thermal energy transfer in the room to improve the thermal comfort. The mathematical model of the system under different operation modes is verified to investigate the performance of the system in Lhasa, Beijing and Nanjing. The results show that: (ⅰ) during the space heating mode, the average room temperature of 20.36 °C, 19.80 °C and 20.18 °C can be reached while the daily total power generation of 0.86 kWh, 0.81 kWh, 0.72 kWh can be achieved in Lhasa, Beijing and Nanjing, respectively; (ⅱ) during the hot water mode, the water temperature in the tanks increases only by 8.08°C–12.76 °C and the total power generation is around 0.20 kWh-0.23 kWh in the three cities while the indoor temperature increases by less than 0.1 °C due to the lowest facade solar radiation in summer.

A dual-mode novel Parabolic Trough Collector for process heating applications in small scale industries—Thermo-hydraulic and performance investigation

Only a few industries worldwide use solar heat for industrial processes, despite the fact that it is a proven and cleaner solution. More over, Small-scale industries need hot water and low-enthalpy steam, but such systems receive scant attention due to the active nature of Parabolic Trough Collectors as well as the use of less efficient flat plate technology in this temperature range. This delineate the opportunity for research focus in efficient passive technologies especially in low temperature range. In this regard a novel dual mode Parabolic Trough Collector based on an Open Natural Circulation Loop (PTC-ONCL) is proposed here. Focus of this work is to assess the proposed system’s suitability for process heating applications requiring hot water/low enthalpy steam, especially in rural areas. Experiments are conducted on an in-house prototype. A novel methodology for correlating actual solar data to the input heat load for the in-house test facility is developed. Five representative solar days are considered for individual tests. Startup, transient, and efficiency parameters are evaluated. Productivity, industrial viability, and environmental impact are also accessed. Throughout the test, the loop maintained a stable flow, where the start-up oscillations, thermal oscillations and type-I instabilities are observed. The system operates at an unprecedented efficiency of 72 ± 4% in hot water mode and 70 ± 5% in Steam generation over a 7 h period. The economic analysis shows an ambitious Levelized Cost of Heat of 2.8 cents/kWh, with a payback period of 3.21 years. Moreover environmental study shows its huge potential in reducing the CO 2 emissions. A dimensionless index is proposed to represent the solar day and is correlated to predict the average water temperature and steam generated with RMSE values of 0.98 °C and 0.125 kg respectively. The solar day index comprehends the total irradiation, wind velocity and the ambient temperature. The proposed PTC-ONCL system is capable of producing an annual average of 8.67 kgday −1 and/or 150 L of hot water at an average temperature of 89.07 °C. The results, and the system’s low cost and near-maintenance-free nature demonstrates its capability in the desired application, both technologically and economically. • A passive Parabolic Trough Collector based on an Open Natural Circulation Loop for process heat at low temperature. • New methodology correlates actual solar data to input for an in-house test facility. • Generates 8.67 kg of steam/ hot water at 89 °C on a yearly average with 65% efficiency. • Levelized Cost of Heat of 2.8 cent/kWh & 3.2 years of payback period found promising. • Dimensionless solar day index includes combines irradiation and ambient condition.

Assessment of factors affecting the performance of a novel double condenser heat pipe Photovoltaic-thermal (PV/T) system in hot water mode: An experimental study in the lab

Assessment of factors affecting the performance of a novel double condenser heat pipe Photovoltaic-thermal (PV/T) system in hot water mode: An experimental study in the lab

MATHEMATICAL MODEL OF COMPUTER SYSTEM RELIABILITY IN RESIDUAL CLASSES

The subject of the article is the construction of a mathematical model of the reliability of a computer system (CS) that operates in a system of residual classes (RNS). This mathematical model is based on the use of structural sliding reservation. The purpose of the article is to increase the reliability of the CS, which operates in the system of residual classes, as well as to calculate and compare the reliability, in terms of the probability of failure-free operation, of the CS in the RNS and the ternary computing system, which operates in the positional binary number system (PBNS). Tasks: to analyze the influence of the number system used on the reliability of the CS; to investigate the properties of the RNS and determine their influence on the structure of the CS in the RNS; build a mathematical model of reliability and, on its basis, perform the calculation and comparative analysis of the reliability of the CS in the RNS and the tripled CS in the PBNS. Research methods: methods of analysis and synthesis of computer systems, number theory, coding theory in RNS, reliability theory. The following results are obtained. The paper shows that the provision of a given level of reliability in the design of the CS using the RNS is due to the presence of various types of redundancy at the same time: structural, informational, temporal, functional and load. In RNS, these types of redundancy can be effectively used to improve the reliability of the CS. The CS in the RNS represents a computational structure that is identical in structure and principle of operation to the sliding structural redundancy model in the PBNS in the case of a loaded (hot) mode of operation of the redundant elements. Proceeding from this, the paper presents a mathematical model of the reliability of the CS in the RNS. In this paper, the calculation and comparative analysis of the reliability of a tripled computing structure in a PBNS with an ideal majority element and a CS in an RNS with an ideal reliability automaton are carried out. Conclusions. As shown by the results of calculations and comparative analysis in some time intervals of operation, the probability of non-failure operation of the CS in the RNS is higher than the probability of non-failure operation of the aircraft in the PBNS with a tripled majority structure. This implies the effective use of the RNS to improve the reliability of the CS.

HALOGAS: Strong constraints on the neutral gas reservoir and accretion rate in nearby spiral galaxies

Context. Galaxies in the local Universe are thought to require ongoing replenishment of their gas reservoir in order to maintain the observed star formation rates. Cosmological simulations predict that this accretion can occur in both a dynamically hot and cold mode, depending on the redshift, halo mass, and the details of the included feedback processes. However, until now, observational evidence of the accretion required to match the observed star formation histories is lacking. Aims. Within the framework of the Hydrogen Accretion in LOcal GalaxieS (HALOGAS) survey, this paper attempts to determine whether galaxies in the local Universe possess a significant reservoir of cold neutral gas and the possible accretion rates these reservoirs could provide. Additionally, with this moderately sized sample, we can start to investigate whether the observed accretion is connected to intrinsic properties of the galaxies such as Hubble type, star formation rate, or environment. Methods. We searched the vicinity of 22 nearby galaxies in a systematic and automated manner for isolated H I clouds or distinct streams that are not yet connected to the galaxy disk. The HALOGAS observations were carried out with the Westerbork Synthesis Radio Telescope and represent one of the most sensitive and detailed H I surveys to date. These observations typically reach column density sensitivities of ∼1019 cm−2 over a 20 km s−1 line width. Results. We find 14 secure H I cloud candidates without an observed optical counterpart in the entire HALOGAS sample. These cloud candidates appear to be analogs to the most massive clouds detected in the extensive cloud distributions around the Milky Way and M 31. However, their numbers seem significantly reduced on average compared to the numbers in these galaxies. Within the framework of cold accretion, we constrain upper limits for H I accretion in the local Universe. The average H I mass currently observed in a state suggestive of accretion onto the galaxies amounts to a rate of 0.05 M⊙ yr−1 with a stringent upper limit of 0.22 M⊙ yr−1, confirming previous estimates. This is much lower than the average star formation rate in this sample. Our best estimate, based on the Green Bank Telescope detection limits of several galaxies in the sample, suggests that another 0.04 M⊙ yr−1 of neutral hydrogen at most could be accreted from clouds and streams that remain undetected. Conclusions. These results show that in nearby galaxies, neutral hydrogen is not being accreted at the same rate as stars are currently being formed. Our study cannot exclude that other forms of gas accretion are at work, such as those provided by direct infall of ionized intergalactic gas or the condensation of coronal gas, triggered by galactic fountain activities. However, these observations do not reveal extended neutral gas reservoirs around most nearby spiral galaxies either.