Summer Mode Research Articles

Heat pump combined with single-stage or two-stage desiccant wheel system? A comparative study on different humidity requirement buildings

Heat pump desiccant wheel hybrid systems can control indoor temperature and humidity for industrial and civil buildings. To clarify the boundary of heat pump combined single-stage desiccant wheel system and two-stage desiccant wheel system for judging the optimal system under different conditions, the performance of the two systems is analyzed with experiment and simulation method. Firstly, the fresh air process is compared for different humidity set points under typical operation conditions. Secondly, the energy moisture ratio (EMR) of desiccant wheels is analyzed. At last, based on system energy consumption and economy, the humidity boundary of the single-stage and the two-stage dehumidification system is proposed, under different conditions. It is found that the energy performance of desiccant wheel increases with the reducing of humidity set point for both systems, and higher EMR can be obtained by the desiccant wheel of the single-stage dehumidification system for all operation modes. The two-stage dehumidification system is more energy efficient when humidity for the controlled space is lower than 49%, 55% and 40% for high temperature mode, typical summer mode and typical dehumidification mode, separately. With the proposed operation boundary, the optimal system can be quickly judged according to the humidity control requirement and outdoor environment.

Performance analysis on parallel condensing air-source heat pump water heater system

Based on the technology of heat pumps, a parallel condensing air-source heat pumps water heater systems providing domestic hot water is proposed to improve the energy efficiency of common ASHPWH system. Considering the climate in southern China, two operating modes of system are designed to adapt to the different water temperature conditions. the simulation model was built to analyzed the factors affecting system performance. Taking Changsha, China as an example, the COP and the energy consumption of system in each month are analyzed. We can find that the parallel condensing air-sources heat pumps water heater system can effectively disperse the total heating quantity by steps heating; the average COP in summer mode increases from 5.42 to 6.44, approaching 19.00%; the average COP in winter mode increases from 4.05 to 5.45, approaching 34.68%. The system has excellent energy-saving effect especially in winter.

Inactivation of airborne microbial contaminants by a heat-pump-driven liquid-desiccant air-conditioning system

The COVID-19 pandemic has led to increasing interest in controlling airborne virus transmission during the operation of air-conditioning systems. Therefore, beyond an examination of the ability of liquid-desiccant material itself to inactivate microbes, a heat-pump-driven liquid-desiccant air-conditioning system was proposed and constructed to experimentally investigate the effect of liquid-desiccant solution on the inactivation of airborne bacteria and fungi in various air-conditioning processes. The proposed system comprises a liquid-desiccant unit to dehumidify or humidify process air using a desiccant-solution and heat-pump unit to cool or heat it and accommodate solution thermal loads. The decrease in the concentration of airborne bacteria and fungi before and after passing through the system (i.e., inactivation efficiency) were compared for the base, summer, and winter operating modes. The results indicated that airborne fungi were less inactivated than bacteria because they possess more stress-resistant cellular structures that resist inactivation. During the air-conditioning processes in both the summer and winter operating modes, the bacterial and fungal inactivation efficiencies improved compared to the base mode owing to the contact with desiccant solution. The higher solution flow rate and solution temperature improved the bacterial inactivation efficiency by 27% for the winter compared to the summer mode. Conversely, because of possible growth of fungi in the heated and humidified supply air in the winter, the fungal inactivation efficiency improved by only 1.5% for the winter compared to the summer mode. In conclusion, the proposed system can contribute to control the airborne transmission of microbial contaminants while operating air-conditioning systems.

Reactive power compensation method in modern power system facing energy conversion

The equivalent model of modern power system is more and more difficult to describe its complex stability characteristics, with the continuous promotion of power conversion. This paper proposes an improved equivalent method to consider the voltage deviation between the system side and the load side. On this basis, the voltage stability margin index is derived. Therefore, the relationship between voltage stability margin and reactive power compensation can be analyzed. Finally, the correctness and effectiveness of the method are verified by IEEE39 node system and actual provincial grid. The proposed method can obviously improve the voltage stability margin when applied to the small summer mode of the actual system. (The stability margin of the weakest node increased by 12.8%, and the average stability margin of the whole network increased by 1.5%.)

Experimental of natural ventilation in a semi-transparent photovoltaic double skin façade in summer

Semi-transparent photovoltaic double skin façade (STPV-DSF) is a novel structure which integrates photoelectric, photothermal, ventilation and energy-saving features, which proves to be extremely attractive and promising. In this study, a full-scale experimental system was built, airflow and heat transfer in a rectangular cavity with different transmittance (τ) and different ventilation modes in summer that studies a STPV-DSF and includes natural ventilation were examined experimentally. The Rayleigh number and Nusselt number of STPV-DSF is significantly higher than that of traditional DSF. This also means stronger intense flow. And the maximum temperature difference at night between mode 1 and mode 2 can reach 7.3°C. When the external air circulation mode is switched to the external and internal mode, the indoor temperature drops by 2.88°C in ten minutes. Therefore, making fully use of natural ventilation can effectively reduce the cooling load of air conditioning in summer. The solar radiation intensity is proved to have the greatest influence on the cavity temperature, followed by the transmittance, and the the ventilation mode least influence. Applying naturally ventilated STPV-DSF would be a new efficient way for the curtain wall buildings to meet the task of sustainable building design.

Low‐carbon economic operation for integrated energy system considering carbon trading mechanism

AbstractCarbon trading mechanism is an effective means to control greenhouse gas emissions. This paper focuses on the low‐carbon economic operation of the integrated energy system under carbon trading mechanism in China. The integrated energy system includes the energy storage, ground source heat pump, and other equipment. The objective of this paper was to minimize the annual total cost of the system considering the carbon trading cost and study the operation modes under different carbon trading prices by commercial optimization software. The simulation results show the operation modes in summer are changed obviously with the increase of the carbon trading prices, while the operation modes in winter basically are not changed with the fluctuation of the carbon trading prices; under the carbon trading mechanism, the integrated energy system can not only reduce the carbon emissions, but also reduce the annual total cost through carbon trading, which shows its advantages and good development prospect. In addition, the setting of the carbon emission quota has a direct impact on the economy of the enterprises. Furthermore, the ground source heat pump and the electric refrigeration units can stabilize the fluctuation of the equipment output caused by the change of natural gas prices in this integrated energy system.

How does the onset time of El Niño events affect tropical cyclone genesis and intensity over the western North Pacific?

AbstractPrevious studies have shown that the equatorial Pacific Ocean warming can be separated into spring (April~June; SP) and summer (July~October; SU) modes based on the onset time of El Niño events. Different onset times are caused by different atmospheric and oceanic conditions, which, in turn, should influence tropical cyclone (TC) activity. While the location of TC formation in the western North Pacific (WNP) shifts significantly eastward and equatorward in the SP type relative to climatology (1951–2017), only an eastward shift occurs in the SU type. Only intense TCs (category 1 + 2 + 3 and 4 + 5) have an obvious eastward and equatorward shift in the SP type, with no such shift in any TC category in the SU type. The number of category 4 + 5 TCs in the SP type increases significantly, but fewer category 1 + 2 + 3 TCs in the SU type. In the SP type, TCs are generally stronger, with more in category 4 + 5, and longer life spans occurring across all categories. However, no obvious change in TC intensity can be identified except for category 1 + 2 + 3 in the SU type. The eastward and equatorward shift of the mean genesis position in the developing phases of SP can be attributed to a southeastward shift of favourable atmospheric and oceanic conditions, which include weaker zonal vertical wind shear, stronger relative vorticity, higher mid‐level relative humidity, and enhanced upper‐ocean temperature (5–100 m). All these conditions are mainly related to the onset time of the westerly anomalies near the central equatorial Pacific. These results suggest that the onset time of El Niño events could serve as a good forecasting indicator for TC genesis position and intensity over the WNP.

Laboratory study on the thermo-mechanical behaviour of a phase change concrete energy pile in summer mode

Phase change concrete energy pile (PCCEP) is a kind of underground energy structure with economy and efficiency. A set of model experimental system of PCCEP was built in the laboratory to assess the effects of phase change process, inlet water temperatures, intermittent modes, mechanical loads and thermal cycles on its thermo- mechanical behaviour in summer mode. The results indicate that compared with traditional energy pile, the PCCEP can improve heat transfer performance, reduce the thermal deformation, thermal stress and pile tip soil pressure. The total heat exchange amount are found to be 2900.5 and 3162.7 kJ for traditional energy pile and PCCEP, respectively, and the corresponding pile top displacement, peak stress and pile tip soil pressure are respectively 0.12 mm, -196 kPa, 9.2 kPa and 0.109 mm, -179 kPa, 8.4 kPa. Increasing inlet temperature can enhance thermal performance of PCCEP, but it also leads to the increase of pile top displacement, pile thermal stress and pile tip soil pressure. For different intermittent operation modes, the longer the operation time, the greater the total heat storage capacity, but the lower the hourly average heat storage capacity, and the greater the pile top residual displacement, pile thermal stress and pile tip soil pressure. The total heat exchange amount are found to be 3688, 4090, 4527 and 4925 kJ for intermittent modes of 8 h:16 h, 10 h:14 h, 12 h:12 h, 14 h:10 h, respectively, and the corresponding pile top residual displacement, pile tip soil pressure and peak pile stress are respectively 0.015 mm, 0 kPa and -157 kPa, 0.021 mm, 1 kPa and -179 kPa, 0.029 mm, 1.7 kPa and -199 kPa, 0.045 mm, 2.3 kPa and -207 kPa. The settlement accumulation can be incurred when the PCCEP subjected to pile top mechanical load, and the larger the pile top mechanical load, the more obvious the settlement accumulation, and the greater the pile stress and pile tip soil pressure.Thermal cycles will result in the increase of temperature rise degree of pile and soil, and cause the accumulation of pile temperature rise, pile stress and pile top displacement.

Mathematical and experimental evaluation of a mini-channel PV/T and thermal panel in summer mode

In this paper, a mini-channel PV/T and mini-channel thermal panel hot water system is presented. The thermal panels in this system use mini-channel tube as the heat exchanger, which has a small hydraulic diameter and large heat exchanger area, and this special structure can improve the heat transfer coefficient at the same flow rate than the conventional type. The performance of this system for generating hot water and electricity in summer has been tested, and a simulation model of this operating mode has been developed. Based on a typical day’s weather data, the simulation model is verified, and the experimental and simulated results agree with each other very well. The results reveal that the experimental and simulated electrical efficiencies of PV/T panels are 11.5% and 12.6%, respectively. The experimental and simulated thermal efficiencies of thermal collectors are 46.8% and 48.0%, respectively. The experimental and simulated final water temperatures in the tank are 59.3 °C and 60.9 °C, respectively. Based on these results, an error analysis is carried out. The experimental and simulation results of the system in summer provide a fundamental data and method for predicting the annual performance of the system in the future.

A vapor compression-adsorption thermal management system for electric vehicle: Concept and working fluid pairs

Thermal management system that usually based on vapor compression refrigeration system plays a significance role in electric vehicles. The system can be also based on the adsorption refrigeration, which can work for battery waste heat recovery. However, the adsorption refrigeration can hardly operate continuously. To combine the advantage of vapor compression and adsorption technology, a vapor compression-adsorption thermal management system (VCATMS) is proposed to provide battery waste heat recovery for cooling in summer and preheating in winter. Therefore, the cooling/preheating load reduces and electricity is saved. Schematic and detailed working modes are presented. The performance prediction method of the system is established, and the performances of different working fluid pairs are investigated. The results show that the activated carbon (AC)-R410A working fluid pair has the best performance because of its good equilibrium adsorption characteristic. Electricity saving can reach 31.3 kJ on recovery mode in summer and 67 kJ on preheating mode in winter, respectively. As for temperature control, battery can be preheated at around 30 °C under −30 °C to 10 °C ambient temperature without any electricity consumption. Besides, heat transfer performance of battery heat exchanger has an adverse effected on AC, which can be weaken by impregnating high thermal conductivity material.

Development of Methodological Bases of the Processes of Steam Formation in Coil Type Boilers Using Solar Concentrators

A mathematical model of the vaporization process in the coil is developed, taking into account the experimental data. To investigate and visualize the evaporation procedure in the coil, a mathematical pattern of the vapor-liquid mixture motion is compiled and reproduced. In the methodology of the study of the movement of the steam-water mixture, correction coefficients are proposed for calculating the velocities of the coolant in non-standard coaxial coils. The parameters were calculated using data sensitivity analysis and data validation was performed by repeated tests; uncertainty was detected when using the instruments, as well as the total extended uncertainty, the upper and lower limit of uncertainty for each measured parameter. In addition, as part of the steam generator set, solar collectors operate in the summer mode. Using the example of the studied steam generator operating in the conditions of an oil and gas field in the subarctic climate, it is shown that it is possible to use air-type solar collectors for the ventilation system of the production room, as well as water-heating solar collectors for technical systems of hot water supply and chemical water treatment.

The performance analysis of a double-skin ventilated window integrated with CdTe cells in typical climate regions

In this work, a double-skin ventilated window integrated with CdTe cells was proposed, which can adapt to various climate conditions by switching the work modes. Firstly, the experiment of testing the thermal and electrical behaviors of this window was conducted on an actual building. Secondly, the simulation model coupling this window with the building was developed and validated against the experimental data. Thirdly, the annual performance of the proposed window (including heat, daylight, PV output) in typical climate regions of high, middle, low latitudes was predicted. Finally, the impact of change in parameters on the energy performance was analyzed. The experimental results showed that the proposed window could provide the hot air to the room under winter mode, and effectively reduced solar heat gain under summer mode. The PV efficiency was greatly affected by solar incident angle. The simulated results indicated that the electricity loss due to the extinction and reflection of glass was about 25%-30%. For Hefei and Harbin, the most energy-efficient orientation of the proposed window was south, and it was west for Haikou. As the PV coverage ratio increased, the net energy consumption decreased firstly and then increased. The optimal values for Harbin, Hefei, and Haikou were 50%, 60%, and 70%, respectively. Increasing the window-wall ratio and the cavity depth was always beneficial to reduce NEC.

Comparative analysis of the energy efficiency of different types co-generators at large scales CHPs

The comparative engineering analysis for the following cogenerator types have been performed: eleven Jenbacher piston engines J920 (Jenbacher, 11xJ920) with an installed power capacity per engine of 9.52 MW; 2 S Gas Turbines SGT-800 (Siemens 2 x SGT-800) with an installed power capacity of each turbine of 56.35 MW; one General Electric Gas Turbine 6F.03 (GE 1 × 6F.03) with the installed power capacity of 83.05 MW. Considered variants of co-generators should replace ineffectively operating existing unit in summer mode in a large scale CHP, which includes steam boiler TGMP-344A and steam turbine T-250/300-240-2. A multi-parameter analysis was performed to select a cogeneration plant and for the first time is one of the largest district heating plants of Central and Eastern Europe, incorporating several different technologies (gas turbine installation, gas-piston engine). Comprehensive analysis of significant components (technical, economic, environmental, noise, etc. specific) allows making the right investment decision.

The influence of baroclinity on tidal ranges in the North Sea

On short time scales, the tidal range has a significant influence on coastal inundations. Therefore, it is very important to investigate the dynamics of tidal range variations over different time scales. The baroclinity has the potential to modulate surface tides through ocean stratification on seasonal and secular scales. In order to better understand the influence of ocean stratification on tidal ranges in the North Sea, numerical simulations were carried out in the baroclinic and the barotropic modes covering the period from 1948 to 2014, using the regional 3D hydrodynamic prognostic Hamburg Shelf Ocean Model (HAMSOM). The tidal range difference between the baroclinic and the barotropic modes in winter and summer are compared at 22 tide-gauge stations, where the simulated sea surface elevations agree well with observations from 1950 to 2014. The statistical analysis shows that generally the difference in summer is much larger than in winter, with a maximum magnitude of approximately 11 cm. The spatial distribution of the tidal range difference indicates a westward shift in the amphidromic system of the North Sea due to baroclinity, which originates from an altered vertically averaged tidal current velocity in stratified regions, as an effect of decoupling induced by stratification. This implies subsequent alterations of tidal ranges in coastal well-mixed regions. Finally, it is demonstrated that, on the secular scale, an enhanced stratification and ocean warming may lead to positive trends in the tidal range and the mean sea level, respectively. Both can have a significant impact on future coastal inundation.

Numerical investigations of the effects of different factors on the displacement of energy pile under the thermo-mechanical loads

The displacement characteristics of energy pile are very important for its safe and sustainable operation. In order to obtain the influences of various factors on the displacement of energy pile, a thermo-mechanical coupled numerical model of energy pile with groundwater advection was established based on COMSOL Multiphysics software. The effects of thermal load, thermo-mechanical coupling load, groundwater advection, soil type, soil stratification and cooling and heating cycle operation on the displacement variation of energy pile operated in summer and winter modes were studied. The results indicate that for thermal load alone, the pile displacement in summer mode can almost be restored to its initial state, and an irrecoverable pile head displacement will occur in winter mode. The lower the inlet temperature, the larger the displacement variation degree. For the thermo-mechanical coupling load, the change ratio of pile head displacement increases with the decrease of mechanical load and increases with the increase of inlet temperature in summer. For winter mode, it increases with the decrease of mechanical load and inlet temperature. In addition, the larger the advection velocity of groundwater, the more heat (cold) can be taken away from the pile, and thus the smaller the displacement changes. For the soil types and stratification, the pile head displacement in soft clay is the largest, followed by silty clay and hard clay, and the rock soil is the smallest. Moreover, the soil stratification and cooling and heating cycle operation has a significant effect on the displacement changes of energy piles and should be considered in the design of energy piles.

Long-term thermo-mechanical behaviour of energy piles in clay

In engineering practice, energy pile foundations are often designed for the lifetime of the building. Thermal exchange between a pile and the surrounding soil depends on the annual energy needs of the building, as heating mode in winter and cooling mode in summer. Thus, energy pile foundations will undergo a heating–cooling cycle per year. In the present work, an experimental method based on a small-scale pile model installed in saturated clay was used to study the thermo-mechanical behaviour of energy piles under thermal cycles. Thirty cycles were applied (to represent a 30-year period if the daily cycles are neglected) while a constant pile head load was maintained. Four tests were performed corresponding to pile head loads equal to 0, 20, 40 and 60% of pile resistance. The results obtained show an increase in irreversible pile head settlement with the thermal cycles. In order to interpret the experimental results better, the finite-element method is used to simulate the experiments numerically. This allows the important role of pile thermal contraction/expansion in the pile–soil interaction under thermo-mechanical loading to be highlighted.

Tropical Cyclone in the North of the South China Sea as a Factor Affecting the Structure of the Vietnamese Current

Tropical cyclones play a significant role in the formation of the hydrodynamic regime of the South China Sea, including its western part, which is bordered by the coast of Vietnam. In this region, the main hydrodynamic structure is the Vietnamese (western boundary) Current. Its structure depends on both seasonal monsoons and tropical cyclones. Therefore, the study of this dependence is an important task for Vietnamese scientists. The results of these studies are not only of scientific, but also of great practical importance, because the social and economic development of Vietnam largely depends on the activity and variability of synoptic and hydrodynamic processes in this region. This paper presents the results of joint Russian–Vietnamese studies on the dependence of the vertical structure of the Vietnamese current on tropical Pacific cyclones in the north of the South China Sea during the interseasonal winter–summer period. This study is based on numerical modeling. The calculations were performed for April–June 1999, for which the necessary initial field data are available. The simulation results indicated that the Vietnamese Current during this time period is not a uniform stream of water masses. Instead, the structure of water masses in this region is governed by a strong anticyclonic circulation and a deep cyclonic circulation, which are responsible for the complex pattern of the Vietnamese Current. The Vietnamese Current transfers coastal water masses in the summer mode (from south to north) within the anticyclonic circulation and in the winter mode (from north to south) within the cyclonic circulation.

Interannual variability of summer surface mass balance and surface melting in the Amundsen sector, West Antarctica

Abstract. Understanding the interannual variability of surface mass balance (SMB) and surface melting in Antarctica is key to quantify the signal-to-noise ratio in climate trends, identify opportunities for multi-year climate predictions and assess the ability of climate models to respond to climate variability. Here we simulate summer SMB and surface melting from 1979 to 2017 using the Regional Atmosphere Model (MAR) at 10 km resolution over the drainage basins of the Amundsen Sea glaciers in West Antarctica. Our simulations reproduce the mean present-day climate in terms of near-surface temperature (mean overestimation of 0.10 ∘C), near-surface wind speed (mean underestimation of 0.42 m s−1), and SMB (relative bias <20 % over Thwaites glacier). The simulated interannual variability of SMB and melting is also close to observation-based estimates. For all the Amundsen glacial drainage basins, the interannual variability of summer SMB and surface melting is driven by two distinct mechanisms: high summer SMB tends to occur when the Amundsen Sea Low (ASL) is shifted southward and westward, while high summer melt rates tend to occur when ASL is shallower (i.e. anticyclonic anomaly). Both mechanisms create a northerly flow anomaly that increases moisture convergence and cloud cover over the Amundsen Sea and therefore favors snowfall and downward longwave radiation over the ice sheet. The part of interannual summer SMB variance explained by the ASL longitudinal migrations increases westward and reaches 40 % for Getz. Interannual variation in the ASL relative central pressure is the largest driver of melt rate variability, with 11 % to 21 % of explained variance (increasing westward). While high summer SMB and melt rates are both favored by positive phases of El Niño–Southern Oscillation (ENSO), the Southern Oscillation Index (SOI) only explains 5 % to 16 % of SMB or melt rate interannual variance in our simulations, with moderate statistical significance. However, the part explained by SOI in the previous austral winter is greater, suggesting that at least a part of the ENSO–SMB and ENSO–melt relationships in summer is inherited from the previous austral winter. Possible mechanisms involve sea ice advection from the Ross Sea and intrusions of circumpolar deep water combined with melt-induced ocean overturning circulation in ice shelf cavities. Finally, we do not find any correlation with the Southern Annular Mode (SAM) in summer.

Seasonal experimental study of a hybrid photovoltaic-water/air solar wall system

Traditional BIPVT systems are faced with the seasonal use issues that they run efficiently only during certain parts of the year, and perform poorly or even out of service for the rest of the time. To overcome the problems, this paper performs several tasks as follows. (1) A hybrid photovoltaic-water/air solar wall (HPSW) system is presented, which combines the air cooling channel and water cooling channel together in one single BIPVT system. (2) The HPSW system can run three modes according to different seasonal needs of the building: ① PV/Air mode in winter, ② PV/Water mode in summer, ③ PV-water/air mixing mode in transition season, which means that the new system is able to satisfy annual demands of the buildings. (3) The HPSW system were experimentally tested in different seasons under different modes during a whole year. (4) The results showed that the all-day average electrical efficiency can reach 15.3% by PV/Air mode in winter, 7.8% in summer and 11.6% in transition season by PV/Water mode. The average daily power generation of the system in summer, transition season and winter was 973.0 kJ, 3226.4 kJ and 4460.5 kJ, respectively. As for thermal performance, the PV/Water mode performed well both summer and transition seasons, with the average thermal efficiency of 55.1% and 51.5% respectively. The temperature rise of experimental room reached 8.1℃ compared to the reference room in winter. The results proves that the HPSW system can operate efficiently as expected throughout the year and has great value in different seasons and different regions.

Performance analysis of a purified Trombe wall with ventilation blinds based on photo-thermal driven purification

This article proposes a year-round purified Trombe wall with ventilation blinds based on solar photo-thermal driven purification that realizes formaldehyde degradation in whole year, space heating in winter and space cooling in summer. The purification blinds are installed in the air channel in traditional Trombe wall, with a photocatalytic layer and thermal catalytic layer on both surfaces, respectively. Firstly, the purification blinds were designed and manufactured. Secondly, based on the verified models, a numerical model of Trombe wall with ventilation blinds considering heat and mass transfer processes was established. Thirdly, the effect of blinds angle on the energy performance was investigated. Finally, the annual optimal operation strategy on blinds angle was investigated. Main results are: (1) The purification performance in summer mode is better than that of in winter mode because of the combination effect of photocatalytic and thermal catalytic purification. (2) The optimal operation angles on purification blinds from January to December are 45°, 45°, 45°, 15°, 30°, 15°, 15°, 15°, 15°, 15°, 0° and 15°, respectively. (3) Applying the annual optimal operation strategy on blinds angle, the total volume of annual generated clean air is 7.12 * 104 m3/m2. The total reduced heating loads for Trombe wall with ventilation blinds in winter seasons are 986 MJ/m2, which is 1.75 times larger than that of in Trombe wall. While based on Trombe wall, Trombe wall with ventilation blinds could save the total reduced cooling loads of 141 and 59.2 MJ/m2 in summer and transition seasons, respectively.