Solar Assisted Heat Pump Dryer Research Articles

Experimental and simulation study on the performance of a solar assisted multi-source heat pump drying system in Zhengzhou area

Zhengzhou of Henan province is an important agricultural production base. To improve the performance of the combined drying system and promote the development of agricultural products in Zhengzhou area, a solar assisted multi-source heat pump (SMSHP) drying system was proposed based on a traditional solar assisted air source heat pump (SASHP) drying system. The simulation models were developed for the air source heat pump (ASHP), SASHP, and SMSHP drying system respectively. The coefficient of performance, energy consumption and specific moisture extraction rate of the drying systems under different seasons were analyzed. Moreover, to validate the simulation models, an experimental platform of the combined drying system was designed and set up, and the experimental tests were carried out on the ASHP, SASHP, and SMSHP drying system. The simulation results revealed that the SMSHP drying system had lower energy consumption, higher coefficient of performance and specific moisture extraction rate than that of the SASHP drying system. The most significant performance enhancement was observed in spring, where the SMSHP system demonstrated a 22.69 % increase in coefficient of performance, a 19.2 % increase in specific moisture extraction rate, and a 16.11 % decrease in energy consumption compared to the SASHP drying system. Comparing with the experimental data, the simulation model errors of the energy consumption, coefficient of performance, and specific moisture extraction rate of the SMSHP drying system were 3.19 %, 0.28 %, and 2.27 %, respectively. Therefore, the accuracy of the simulation results was confirmed. To better calculate the heat provided by the solar collection system, the concept of the tank heating guarantee rate was first introduced, and it was found to be more scientific than the solar energy guarantee rate. At last, The economic and environmental benefit of the drying systems were analyzed during the life cycle, and the SMSHP drying system exhibited better comprehensive performance than the SASHP drying system. This paper provides valuable insights into the comprehensive utilization of solar energy and the control logic of solar assisted air source heat pump combined drying system under different seasons.

Recent trends on energy-efficient solar dryers for food and agricultural products drying: a review

AbstractThe energy efficiency enhancement of solar dryers has attracted the attention of researchers worldwide because of the need for energy storage in solar drying applications, which arises primarily from the irregular nature of solar energy that leads to improper drying which will reduce the quality of the products being dried. This work comprehensively reviews the state-of-the-art research carried out on solar dryers for energy efficiency enhancement using various alternative strategies, including hybrid solar dryers that use auxiliary heating sources, such as electric heaters or biomass heaters, solar-assisted heat pump dryer, use of desiccant materials, and heat storage systems that use both sensible and latent heat storage. The advent of phase change materials (PCM), such as thermally and chemically stable PCMs, for long-term storage, bio-degradable and bio-compatible PCM materials to alleviate the negative environmental impact of conventional PCMs is also presented. The performance parameters considered for evaluating dryers include the maximum temperature attained inside the drying chamber, drying time and efficiency, specific moisture extraction rate (SMER), energy and exergy efficiency and CO2 mitigation effect. The factors considered to analyze the PCMs application in solar dryers include cost and sustainability of PCMs, and both energy and exergy analyses of dryers using PCMs. The gaps in current knowledge and future scope for further improvement of solar dryers are also elucidated. Graphical abstract

Thermal Performance and Technoeconomic Analysis of Solar-Assisted Heat Pump Dryer Integrated with Energy Storage Materials for Drying Cavendish Banana (Musa acuminata)

This study examines a novel solar-assisted heat pump dryer integrated with a thermal energy storage system using soapstone as storage material. The dryer is investigated through experimental analysis across three operating modes: mode 1 with thermal energy storage during daytime, mode 2 without thermal energy storage during nighttime, and mode 3 without thermal energy storage during daytime. Experiments were carried out to investigate the drying of 500 g of Cavendish banana. Thermal performance, as well as economic, and nutritional content were examined. Three replicates of the experiment yielded consistent results, showing a significant reduction in the moisture content of the initial sample from 74.4% to 9.6% after undergoing distinct drying durations. Mode 1 achieved this reduction in 270 minutes, mode 2 in 390 minutes, and mode 3 in 360 minutes. The average specific moisture extraction rates for modes 1, 2, and 3 were 0.13, 0.11, and 0.12 kg/kWh, respectively. Simultaneously, the drying rate ranged from 0.16 to 0.24% per minute. The drying efficiency varied among the tested modes, with mode 1 achieving the highest efficiency at 23.23%. In terms of coefficient of performance, mode 1, mode 2, and mode 3 exhibited values of 3.69, 2.57, and 2.54, respectively. The economic analysis conducted specifically for mode 1 revealed a payback period of 1.5 years, indicating the time required to recover the initial investment. Additionally, the results indicated that the dried Cavendish banana had significantly higher concentrations of proximate parameters and minerals compared to the fresh Cavendish banana, as evidenced by a p value less than 0.05.

Experimental and techno-economic analysis of solar-assisted heat pump drying of biomass

Drying enhances the attributes of biomass, such as storability and heating value. In regions with low solar radiation, solar drying has demonstrated limited economic viability. Hybrid systems, combining solar drying with a stable heat source such as a heat pump, present an opportunity to improve drying performance and achieve cost savings, especially with time-variable electricity pricing. To quantify this potential, we constructed an experimental drying system in Finland, incorporating an air-source heat pump and solar thermal collectors for drying woody biomass. Experimental work, consisting of 316 h of operation in varied conditions, evaluated the performance of the hybrid drying system. Subsequently, we developed data-driven models to estimate drying rates and power consumption in both hybrid and solar operation modes. Finally, these models were integrated into a techno-economic optimization model to assess the economic feasibility of the concept through hourly simulations. Hybrid drying experiments resulted in a significantly improved average drying rate (33.0 kg/h ± 5.4 kg/h) compared to solar drying (9.0 kg/h ± 3.2 kg/h) with a 45% increase in specific electricity consumption. The experimental work also revealed limited operating flexibility in colder temperatures due to an exponentially increasing preheating time (up to 4.2 h at 0 °C). With techno-economic modelling, the simulations yielded a simple payback time of 7.5 years for a commercial-scale drying system without investment subsidies. Applying an optimized operating strategy, system operation shifted on average from hybrid mode (96–33%) to solar mode (3–36%) and inactive state (1–31%) with an increased electricity price level, highlighting the need for advanced operation planning. Commercial deployment should prioritize use cases with high value increase through drying or obtaining compensation from avoided biogenic CO2 emissions through drying, as these two parameters were shown to have the greatest impact on the investment payback time.

Techno-economic analysis of a solar-assisted heat pump dryer for drying agricultural products.

Postharvest losses (PHLs) of biomaterials, such as vegetables and fruits, significantly impact food security and economic stability in developing nations. In Tanzania, PHLs are estimated to range between 30% and 40% for cereal crops and even higher for perishable crops such as fruits and vegetables. Open-sun drying (OSD) is the most extensively employed method because of its affordability and simplicity. However, OSD has several drawbacks, including difficulties in managing drying parameters, long drying times owing to adverse weather, and product contamination. The solar-assisted heat pump dryer (SAHPD) is a technology designed as an alternative solution for drying biomaterials and reducing PHL. A limited number of SAHPDs have been constructed in developing nations. Most of the works have concentrated on the performance analysis of the systems. This neglects the techno-economic assessment, which is important to provide both a quantitative and qualitative understanding of the financial viability of the technology. The present study therefore investigates the techno-economic analysis of a novel SAHPD for drying agricultural products, particularly vegetables and fruits. To determine whether the SAHPD technology is technically and economically viable, tomatoes and carrots were dried and analyzed to determine their thermal and economic performance. The results show that the initial moisture contents of tomatoes (Lycopersicum esculentum) and carrots (Daucus carota) were reduced from 93% and 88% to 10% in 11 and 12 h, respectively. The coefficient of performance (COP), drying time (DT), specific moisture extraction ration (SMER) and thermal efficiency () were found to be 3.4, 2.3 kg/h, 1.33 kg/kWh and 54.0%, respectively. The economic analysis was assessed using the annualized cost, lifecycle savings, and payback period for the dryer's life span of 15 years. The initial investment of the SAHPD was $5221.8 and the annualized cost was $1076.5. The cumulative present worth for 15 years was found to be $23,828.8 and $27,553.1 for tomatoes and carrots, respectively. The payback period for tomatoes was found to be 3 years, whereas for carrots it was 2.6 years. Based on thermal and economic performance assessment results, the developed SAHPD is technically and economically viable to be considered for further investments.

Influence of Duct Configurations on the Performance of Solar-Assisted Heat Pump Dryer for Drying Tobacco Leaves

In the present study, a solar-assisted heat pump dryer (SAHPD) has been designed, fabricated, and tested its performance on drying tobacco leaves. The hot air generated from the solar collector and condenser unit of the heat pump was used as a source of heat in the drying chamber. In this study, we investigated the influence of three duct configurations (open, partially closed, and completely closed) on the thermal performance of SAHPD to establish the best configuration for drying tobacco leaves. The average drying temperature was found to be 66, 64, and 60°C; the coefficient of performance of the heat pump was 3.4, 3.2, and 3.0; the heat energy contribution from the solar collector was 6.6%, 5.0%, and 5.1% while for the condenser was 93.4%, 95.0%, and 94.9%, and electrical energy consumption was 2.3, 2.8, and 2.6 kWh, for the open, partially closed, and completely closed duct system, respectively. Based on these results, the open system demonstrated the best performance. According to the study’s findings, SAHPD has been shown to be an energy-efficient method of drying tobacco leaves and is environmentally friendly as opposed to the conventional use of wood fuel, which results in environmental pollution, desertification, and deforestation.

Performance evaluation of solar-assisted heat pump dryer integrated with thermal energy storage for drying Moringa Oleifera leaves

Performance evaluation of solar-assisted heat pump dryer integrated with thermal energy storage for drying Moringa Oleifera leaves

Development of hybrid solar-assisted heat pump dryer for drying paddy

This recent study evaluated a hybrid solar-assisted heat pump dryer (HS-AHPD) for drying paddy and its product quality. R22 is used as a working fluid in the heat pump system during the drying experiment. The HS-AHPD decreased the paddy's weight from 420 kg (31.67% db) to 370.60 kg (16.18% db) in 5.5 h with an average air temperature of 62.9 °C and an average relative humidity of 16.1% at a mass flow rate of 0.195 kg/s. The average drying rate, specific moisture extraction rate (SMER), and specific energy consumption (SEC) were 8.34 kg/s, 0.44 kg/kWh, and 4.69 kWh/kg, respectively. The HS-AHPD's average thermal efficiency and the exergy efficiency of the drying section were found up to 29.1% and 18.4%, respectively. The furnace and the solar collector contributed 19.7% and 12.9% of energy to the HS-AHPD, respectively. The improvement potential (IP) was in the range of 628.8–824.4W. The drying resulted in higher-quality products due to higher head rice yield (93.10 ± 1.044%), lower broken rice (4.41 ± 0.737%), and lower rice grouts (1.11 ± 0.271%).

Analysis on characteristics and operation mode of direct solar collector coupled heat pump drying system

To solve the intermittent problem of solar drying systems, this study proposes a solar vacuum tube collector coupled heat pump drying (HPD) system that can adopt three operating modes as different climatic conditions. The performance of the system under different working modes and drying characteristics was analyzed; moreover, the system was also based on the relationship between energy supply and consumption. The results show that under load conditions, the system runs in the solar drying (SD) mode and the drying chamber temperature can reach >50 °C. In the HPD mode, the average heating power of the system is 11.88 kW, the heating coefficient is 2.26 and the average thermal efficiency of the heat exchanger is 39.3%. In the solar-assisted heat pump drying (SAHPD) mode, the average coefficient of performance of the system is 3.26, compared to HPD model, a 44.2% increase. The heating ratios of the SD, HPD and SAHPD modes were 37.9%, 58.5% and 3.6%, respectively. Furthermore, the Two-term models with R2 value of 0.9986 and RMSE value of 0.01038 was considered the best drying kinetics model for the vacuum tube collector coupled heat pump drying grapes. This study guides the application of SAHPD systems in agricultural products drying.

Design of a Greenhouse Solar-Assisted Heat Pump Dryer for Kelp (Laminaria japonica): System Performance and Drying Kinetics

In order to solve a series of problems with kelp drying including long drying time, high energy consumption, low drying efficiency, and poor quality of dried kelp, this work proposes the design of a novel greenhouse double-evaporator solar-assisted heat pump drying system. Experiments on kelp solar-assisted heat pump drying (S-HP) and heat pump drying (HP) under the condition of irradiance of 100-700 W/m2 and a temperature of 30, 40, or 50 °C were conducted and their results were compared in terms of system performance, drying kinetics, and quality impact. The drying time was reduced with increasing irradiance or temperature. The coefficient of performance (COP) and specific moisture extraction rate (SMER) of S-HP were 3.590-6.810, and 1.660-3.725 kg/kW·h, respectively, roughly double those of HP when the temperatures are identical. The Deff of S-HP and HP were 5.431 × 10-11~11.316 × 10-11 m2/s, and 1.037 × 10-11~1.432 × 10-11 m2/s, respectively; additionally, solar radiation greatly improves Deff. The Page model almost perfectly described the changes in the moisture ratio of kelp by S-HP and HP with an inaccuracy of less than 5%. When the temperature was 40 °C and the irradiance was above 400 W/m2, the drying time of S-HP was only 3 h, and the dried kelp maintained the green color with a strong flavor and richness in mannitol. Meanwhile, the coefficient of performance was 6.810, the specific moisture extraction rate was 3.725 kg/kWh, and the energy consumption was 45.2%, lower than that of HP. It can be concluded that S-HP is highly efficient and energy-saving for macroalgae drying and can serve as an alternate technique for the drying of other aquatic products.

Performance Analysis of Solar Assisted Heat Pump Drying System with Dual Condensers

The main components of the dual condenser solar-assisted heat pump (SAHP)drying include the solar collector, evaporator, compressor, fan coil, twin condensers, expansion valve, and drying chamber. The solar drying process was assisted by a heat pump, and the optimal efficiency was determined by heating and dehumidifying the air, and recirculating the air that has been heated. The efficiency of the heat pump system was assessed by its coefficient of performance (COP), which is the percentage of the actual heat delivered by the heat pump to the total electrical power necessary to operate the heat pump. The average temperature of the drying chamber reached a temperature of 60 °C with a relative humidity of around 70%, and the system's COP was 5.546 with no contribution from solar energy or at no solar fraction (SF = 0). The same conditions in the drying chamber can be achieved at solar faction or SF = 0.83, with COP increased to 12.7.

Economic Operation Optimization of Solar Assisted Heat Pump Drying System Considering Heat Storage Characteristics of Drying Chamber

Economic Operation Optimization of Solar Assisted Heat Pump Drying System Considering Heat Storage Characteristics of Drying Chamber

Economic Operation Optimization of Solar Assisted Heat Pump Drying System Considering Heat Storage Characteristics of Drying Chamber

Economic Operation Optimization of Solar Assisted Heat Pump Drying System Considering Heat Storage Characteristics of Drying Chamber

Experimentation and Performance Analysis of Solar-Assisted Heat Pump Dryer for Intermittent Drying of Food Chips

Abstract A solar-assisted heat pump (HP) dryer is fabricated for intermittent drying. The experiment is performed for different intermittency ratios for radish drying using future refrigerant, R1234yf. The effect of total drying time (on-period + off-period) on various energetic, exergetic, and economic performances is investigated. Radish chips were dried to extract moisture from 92.4% to 11.9%. Energy efficiency and drying efficiency (DE) are estimated higher for a lower intermittency ratio. The moisture extraction rate (MER) and the specific moisture extraction rate (SMER) are higher for intermittent drying as compared with continuous drying and increase with a decrease in intermittency ratio. The economic analysis concludes that the payback period is lower for a lower intermittency ratio. The payback period for intermittency ratio of 1, 0.66, 0.33, and 0.2 are estimated as 1.617 years, 1.459 years, 1.384 years, and 1.347 years, respectively. Present experimental thermoeconomic analysis reveals that intermittent drying is much better (maximum enhancement of specific moisture extraction rate is 60.6%, that of energy efficiency is 56.4% and maximum reduction of drying cost is 37.9% with studied conditions) than continuous drying.

Study on heating performance of solar-assisted heat pump drying system under large temperature difference

In this study, a heat pump drying (HPD) system platform complemented by solar hot water was designed and established. The objective was to address the declines in the heating performance of air source HPD at high altitudes (more than 3000 m), cold conditions (annual average temperature at 5 °C), and with large temperature differences between day and night (more than 20 °C), i.e. under harsh conditions. A theoretical model was derived to determine the system parameters and to support the experimental analysis. Under no-load conditions, four cases with ambient temperature were tested and compared to explore the relationships between the system parameters and performance, as well as the effectiveness of the supplementary solar hot water. The heating performances under HPD and solar-assisted HPD (SHPD) modes were compared and analysed under load conditions (930 kg Mu Xiang). The results indicate that a decrease in the ambient temperature and increase in the temperature in the drying room causes attenuations of the compressor mass flow rate, evaporator cooling power, condenser heating power, and system coefficient of performance (COP). In addition, solar water heating can significantly improve the heating performance of the HPD system. Under no-load conditions, the average heating power of the HPD-mode system is 19.27 kW, and the average COP is 2.76. The average heating power of the SHPD mode system is 23.34 kW, and the average COP of the system reaches 3.24, an increase of 17.4%. Under load conditions, the average heating capacity power of the HPD mode is 9.64 kW; the COP is only 1.34, and fluctuates significantly with the decrease in ambient temperature. The average heating capacity power of the SHPD mode is 17.62 kW and the COP is 2.42, i.e. 1.8 times of that of the HPD mode. By raising the drying room temperature to the same set temperature, the SHPD mode time is shortened by 70%.

Numerical Analysis and Optimization of Solar-Assited Heat Pump Drying System with Waste Heat Recovery Based on TRNSYS

In this paper, a new solar-assisted heat pump drying system with waste heat recovery and double water tanks (SCAHP) was established and the system optimized by TRNSYS and variable air volume experiment. The annual cumulative efficiency of the SCAHP (COPac), buffer tank heating efficiency (ηBT) and hot water storage tank heating efficiency (ηST) are all considered as optimization objectives, and this paper discusses the relationship between the three optimization objectives and studies the influence of hot air volume (qDR), area of solar collector (ASC), inclination angle of solar collector (ISC) and volume of heat storage water tank (VST) on system efficiency in the drying process. In order to explore the general rule of system optimization, numerical analysis and optimization were carried out in five typical cities in five climatic regions of China. The results show that the mixed variable air volume mode can increase the drying rate with less energy loss, and shorten the drying period by 28.6–33.3%. When the system surface body ratio (SBR) in Nanjing is between 3.1 and 4.1, the COPac, ηBT, and ηST can reach the maximum value simultaneously. It is estimated that the cost can be recovered in 5 years when the system configuration parameters are optimized.

Modeling and optimization of solar-assisted heat pump drying of pumpkin slice

PurposeTo reduce energy consumption, the time needed of drying, and the loss of ß-carotene content, and ascorbic acid content, response surface methodology (RSM) was employed for optimization.Design/methodology/approachTo reduce energy consumption, the time needed of drying, and the loss of ß-carotene content, and ascorbic acid content, response surface methodology (RSM) was employed for optimization.FindingsThe results show that the optimum solar-assisted heat pump drying (SAHPD) conditions for drying pumpkin slice were: drying temperature of 67.40 °C, loading density of 1.05 kg/m3, and material thickness of 4 mm. Under these conditions, slice of pumpkin were dried in 440.637 min, where the unit energy consumption, ascorbic acid content, and ß-carotene content were 16.737 kJ/g, 25.682 mg/ (100–g dried sample), and 10.202 mg/g, respectively. The structure of the samples dried using the optimized SAHPD method exhibited a more complete cell morphology than those dried using heat pump drying when examined using scanning electronic microscopy.Originality/valueThis suggests that the optimized SAHPD conditions used in this study are important for production and processing.

Drying and dynamic performance of well-adapted solar assisted heat pump drying system

A new type of well-adapted solar assisted heat pump drying system (SAHPDS) was put forward to choose and switch more efficient and energy-saving drying mode according to outdoor environment. The drying characteristics of shiitake mushroom, energy consumption level and running characteristics of system under five drying modes were investigated systematically. The drying modes were independent solar drying system (ISDS), independent closed heat pump drying system (ICHPDS), and SAHPDS of closed, open and semi-open modes. The results concluded drying system performed well in each mode. In ISDS, inlet air temperature of drying chamber can reach above 50 °C, heat collection efficiency of solar air collector (SAC) is 0.562 and SMER is 3.56 kg/kWh. In ICHPDS, the average COP is negatively correlated with air temperature and loading capacity, while positively correlated with air speed. In SAHPDS (assisted only by SAC), the average air temperature is 59.17, 62.38 and 60.83 °C in open, closed and semi-open modes at air speed of 3.5 m/s. With the corresponding modes, the heat collection efficiency of SAC was 0.526, 0.223 and 0.434 respectively. The average COP is 3.08, 2.68 and 3.20, which is significantly more energy-saving than ICHPDS mode in order to obtain same air temperature. In the later drying period, it switched to the closed drying mode of SAHPDS (only assisted by solar collector (SC)). In addition, the energy saving rate can reach 37.96% compared with ICHPDS under the same condition. The study provides a guidance and reference for the operation mode switch of SAHPDS with higher energy saving and efficiency.

Comparative performance of a solar assisted heat pump dryer with a heat pump dryer for Curcuma

<p>This study evaluated the performances of solar assisted heat pump dryer (SAHPD) and heat pump dryer (HPD) for drying of <em>Curcuma xanthorrhiza Roxb</em>. The HPD and SAHPD reduced mass of <em>Curcuma</em> from 30.70 kg to 7.85 kg needed 10.5 hours and 8 hours with average temperature and relative humidity 49.2oC and 26.5%, and 57.7oC and 19.8%, for SD and SAHPD respectively. The moisture of Curcuma dried from 3.167 db to 0.065 db with an air mass flow rate of 0.121 kg/s. The SAHPD reduced the drying time about 24% compared to HPD. The drying rate and the specific energy consumption were calculated in an average 1.05 kg/h and 1.36kg/h, and 1.17kWh/kg and 2.07kWh/kg for HPD and SAHPD, respectively. The specific moisture extraction rate and the dryer thermal efficiency were calculated in an average 0.931 kg/kWh and 0.521 kg/kWh, and 61.0% and 34.3% for HPD and SAHPD, respectively. Whereas, the pickup efficiency and the coefficient of performance of the heat pump were calculated in an average 57.5% and 59.2%, and 4.03and 4.35 for HPD and SAHPD, respectively. The SAHPD is capable of drying <em>Curcuma</em> quickly because of the high pickup efficiency and high drying rate.</p>

Numerical Analysis and Preliminary Experiment of a Solar Assisted Heat Pump Drying System for Chinese Wolfberry

The present work investigated a solar assisted heat pump system for drying Chinese wolfberry. The kinetic characteristic was firstly analyzed through a series of lab experiments. It was concluded that the Page model was the most suitable for predicting the heat and mass transfer of the wolfberry. Based on the wolfberry kinetic model, solar collector model and chamber air model, the coupled drying system model was developed. The accuracy of the mathematic model was determined through comparing with the preliminary experimental results. The influence of operating conditions on the thermal and energy performance of the dryer for the different operating mode was discussed. The drying weight of no more than 75 kg may be preferable in the stand-alone solar drying mode, and less than 15 h was needed to be dried. The electric energy consumption in the solar assisted the heat pump drying mode was lower than that in the stand-alone heat pump mode, and it was recommended that about 50 kg of wolfberry to be dried in the solar assisted heat pump system. Compared to the autumn drying, the reduction in the electric energy consumption was around 9.1 kWh during the 11 h summer drying process. The obtained results demonstrated the feasibility of the combined system for drying wolfberry, and also can provide the basic theoretical and experimental data support for the following research.