TRNSYS Simulation Research Articles

Theoretical Analysis of a Novel Rock Wall to Limit Heating Demands in Historical Buildings

In the near future, the building sector will continue to absorb the greatest share of primary energy worldwide. It is necessary to find innovative solutions that promote energy efficiency through renovation measures, especially in historical buildings, for which refurbishment is constrained by several issues. In this study, we propose a novel Trombe Wall configuration that is easily integrable and based on a rock wall made of caged stone to use as a thermal accumulator. The system was investigated preliminarily using a transient Finite Difference Method (FDM) code to analyse the temperature field inside the rock wall. Successively, FDM results were employed as input data in TRNSYS simulations to determine the savings achievable in thermal heating requirements. The results demonstrated that the proposed solution, in the considered climate and on a reference historic building, can produce monthly heating savings varying between 26% and 85%. So, the rock wall results in a reliable solution for buildings in which refurbishment is difficult, allowing for preserving aesthetic features and improving energy efficiency by rationally using solar radiation.

Evaluating the energy and economic performance of hybrid photovoltaic thermal system integrated with multiwalled carbon nanotubes enhanced phase change material

Photovoltaic thermal (PVT) systems represent an advanced evolution of traditional photovoltaic (PV) modules designed to generate electrical and thermal energy simultaneously. However, achieving optimal and commercially viable performance from these systems remains challenging. To overcome this issue, in this research, multiwalled carbon nanotube (MWCNT) enhanced phase change materials (PCMs) integrated with PVT system to enhance electrical and thermal performance has been studied. An experimental investigation with three different configurations, PVT, PCM integrated PVT (PVTPCM), and MWCNT enhanced PCM integrated PVT (PVTNePCM) systems, was carried out under varying solar radiations and a water flow rate of 0.013–0.016 kg/s compared to conventional PV system. A two-step technique was employed to formulate the nanocomposites, and the energy performance of both PV and PVT systems assessed experimentally. The performance of PVTPCM and PVTNePCM systems was evaluated using the TRNSYS simulation technique. The formulated nanocomposite exhibited a 71.43% enhancement in thermal conductivity, a significant reduction in transmittance up to 92% and remained chemically and thermally stable. Integration of NePCM in the PVT system resulted in a notable decrease in panel temperature and a 25.03% increase in electrical efficiency compared to the conventional PV system. The highest performance ratio and overall efficiency for PVTNePCM were 0.55 and 81.62%, respectively, at a flow rate of 0.013 kg/s. The energy payback periods of PVTNePCM, PVTPCM, and PVT setup were 4.7, 4.8 and 5.6 years, respectively. Additionally, a significant improvement in thermal efficiency were observed for PVTPCM and PVTNePCM systems compared to water-based PVT systems, due to the energy stored in the thermal energy storage material.

Research on performance and potential of distributed heating system for peak shaving with multi-energy resource

Climate change and its negative effects are driving the global shift from fossil fuels to renewable energy sources. To tackle the dependency on traditional energy sources in harsh winter regions and improve heating quality during periods of thermal demand fluctuations, this paper proposes a new distributed heating peak shaving system (DHPS). The system combines municipal heat and clean energy within the secondary network while reducing the return water temperature in the primary network. It comprises solar collectors, electric thermal storage tanks (ETST), and absorption heat pump (AHP) units, integrated into conventional heat exchange stations. The system operates in two modes to manage peak and off-peak loads respectively, with TRNSYS simulation used to evaluate performance across a range of peak-shaving gradients. A multidimensional comprehensive assessment is conducted between the DHPS under optimal peak shaving coefficient (θ) conditions and conventional peak clipping boiler (PCB). Results indicate that DHPS achieves a high primary energy ratio (PER) of 1.251 at θ = 0.5, reducing combustion emissions by nearly 40%. The static payback period (PBP) of the system is 3.5 years. When the electricity price drops to 0.275 CNY, its operational costs are comparable to PCB. DHPS caters to the energy characteristics of cold regions where electricity supply exceeds demand. It enables flexible peak shaving while ensuring the complete utilization of clean energy and effectively utilizing waste heat from power plants.

Design and performance evaluation of a solar-assisted biogas and air-source heat pump hybrid system for radiant heating applications

Energy and environmental crises have become critical challenges, making the efficient use of clean energy a focus of public attention. Although emerging clean energies have high economic and environmental values, these single energy sources are not well-developed. In colder climates, maintaining a stable fermentation temperature can be difficult, leading to the idling of many biogas digesters. Furthermore, despite extensive research on solar-assisted air-source heat pumps, these systems perform poorly in cold climates with low solar irradiance. To address these issues, this study investigates the integration of a solar-assisted biogas and air-source heat pump hybrid heating system (SBHP-HHS) for capillary radiant heating in rural North China, specifically adapted to local conditions. The system aims to utilize the combined benefits of various clean energy sources to improve system reliability in harsh climates. By combining experimental analysis with TRNSYS simulation, the system performance during the heating season in rural northern China was evaluated. Experimental results show that the hybrid system, utilizing the radiant capillary terminal, is capable of maintaining room temperatures above 20 °C, demonstrating its effectiveness. Simulation results show that the air-source heat pump achieves a coefficient of performance (COP) of 4.6. This efficiency level is generally favorable, ensuring stable operation. Additionally, the system achieves a solar-biogas hybrid utilization rate exceeding 75 % and a primary energy-saving rate of 78 %. Economically, the system offers an 8.23-year dynamic payback period and annual cost savings of 3055 CNY. Environmentally, it reduces CO2 emissions by 4263.6 kg annually. This study provides a solid experimental foundation for further research, offering empirical evidence to optimize system performance.

Long-term operational characteristics of subway source heat pump system under various tunnel internal heat source intensities

In recent years, subway systems have effectively alleviated urban traffic congestions. However, thermal pollution of underground spaces is a prevailing problem, which poses a serious threat to the safe and efficient operation of subways. The subway source heat pump system (SSHPS), equipped with a front-end tunnel lining heat exchanger, is an effective solution to tackle the aforementioned problem. However, the design methodology and operational strategy of the system is not yet established, which necessitates an analysis of its long-term operational characteristics. In this study, an SSHPS simulation model was developed using the TRNSYS simulation tool based on a demonstration project and the model was subsequently validated against measured data. The validated model was used to evaluate the long-term performance and operational characteristics of the subway system under various internal heat source intensities ranging from 0 W/m to 240 W/m. The simulation results showed that the tunnel air temperature steadily increased as the internal heat source intensity increased. When the internal heat source was 0 W/m, the average annual decrease in tunnel air temperature was 0.11 °C. However, the average annual tunnel air temperature did not fall below the minimum subway design specification temperature of 5 °C at any point in time. When the internal heat source was 120, 180, and 240 W/m, the tunnel air temperature exceeded the maximum temperature of 40 °C stipulated in subway design guidelines on multiple occasions. As the internal heat source intensity increased, the performance of both the heat pump unit and SSHPS progressively decreased during the cooling season and gradually increased during the heating season. The runtime of the heat pump unit gradually decreased from 92.72 % to 77.57 % during the cooling season, whereas it increased from 46.92 % to 89.41 % during the heating season. The heat pump unit exhibited an average energy efficiency ratio (EER) of 5.07, 4.95, 4.87, 4.80 and 4.76 whereas the SSHPS demonstrated an average EER of 3.04, 3.01, 3.00, 2.99 and 2.98. Throughout its operational years, the SSHPS consistently maintained stable and cyclically high performance. However, the system did not fully meet the specified cooling and heating loads under all operational conditions, indicating that there was a source–load mismatch issue within the system. Hence, it is recommended to incorporate auxiliary cold and heat sources, thereby establishing a composite heating and cooling system based on subway source heat pump technology, with the aim of enhancing the reliability of energy supply for the system. This study can serve as a valuable reference for formulating high-efficiency and energy-saving operational strategies for SSHPSs.

Optimization for the temperature range of radiator for preventing draught risk of cold window

High surface temperature of radiator can provide thermal plume with enough momentum intensity and thus counteracts the downdraft caused by window. Meanwhile, it is necessary to avoid causing indoor temperature to exceed upper limit of thermal comfort zone. In this paper, influence of heat transfer coefficients of window and exterior wall, outdoor temperature, and average surface temperature of radiator on operative temperature (Top) and temperature difference between indoor air and window (Td) was investigated. Based on response surface method, single factor and interaction effects for the four influencing factors on Top and Td were analyzed. A framework optimizing average surface temperature of radiator for preventing draught risk of window was established. When the heat transfer coefficient of window was around 1.4 W/m2·°C and satisfied related energy-conservation standard, cold draught could be eliminated without causing indoor environment overheating. Based on the optimized temperature range, the supply water temperature was controlled, and seasonal performance using the variable temperature strategy was investigated based on TRNSYS simulation. With the variable water temperature control strategy, the output hourly indoor air temperature was within the comfortable range. In the whole heating season, hours that did not meet cold draught requirement occupied 77.22 %, as the heat transfer coefficients of window dis-satisfied the energy-saving design standard. As meeting the design standard, the proportion decreased to 12.97 %. Utilizing the optimized temperature interval can prevent discomfort caused by cold draught to the greatest extent. This study is conducive to improving thermal environment with the convective–heating system and may lead to the reduction of energy consumption for heating.

Experimental and numerical study on the integration of solar-driven desiccant and thermoelectric Systems for Sustainable Thermal Comfort

Global reliance on traditional cooling systems is a pressing concern, especially given their substantial energy demands and refrigerant-related greenhouse gas emissions. The need for sustainable cooling solutions is especially urgent in hot and humid regions. This study presents an innovative solution by introducing a compact, solar-driven cooling system that integrates a Desiccant Wheel (DW) and a Thermoelectric Cooler (TEC). This novel combination leverages solar energy to enhance cooling efficiency while reducing environmental impact. The system's performance was tested through experimental methods and non-dimensional analysis, which served to validate the TRNSYS simulation. The simulation included custom components representing the DW and TEC's physical characteristics. Results demonstrated that the system effectively reduces air temperature and humidity to maintain thermal comfort, achieving Coefficients of Performance (COP) of 0.94 and 1.13in Toronto and Vancouver, respectively. A key feature of the system is the heat recovery design, which uses waste heat from the TEC to regenerate the desiccant material, enhancing COP by 68%. Further analysis through TRNSYS simulation explored the system's adaptability to various climate conditions by testing a range of temperatures (26–43°C) and relative humidity levels (30–100%). This analysis identified three operational regions, optimizing the system's application based on environmental conditions. A life cycle assessment determined a Global Warming Potential (GWP) of 0.0172 kg CO2 per kW of cooling capacity and an Energy Payback Time (EPBT) of 3.34 years. The economic analysis indicated a total system cost of $2719, predominantly due to the DW and TEC components. In conclusion, this research offers a sustainable and efficient cooling system that provides thermal comfort in hot and humid climates, marking a significant advancement in climate control technology.

TRNSYS modelling and feasibility study of natural gas absorption heat pump (GAHP) for Canadian homes

An investigation was conducted to explore the potential use of a Natural Gas Absorption Heat Pump (GAHP) for heating and cooling. This investigation involved experiments and simulations using TRNSYS software. In the experimental and modelling study, a working fluid comprising a solution of 50% Propylene Glycol (PG) and water was utilized to prevent freezing in the system’s primary loop, which is exposed to extreme cold weather conditions. The data from the experimental study was utilized to develop performance curves used in the system simulations. TRNSYS simulations were conducted to predict the performance behaviour of the system under different operating and climatic conditions. The results of the analysis indicate that the GAHP can be a substitute in areas where natural gas is the primary heating fuel. However, it was noted that the GAHP’s capacity, Gas Utilization Efficiency (GUE), and Coefficient of Performance (COP) were significantly lower during the heating and cooling seasons. It was observed that the heating GUE values ranged from 0.53 to 0.64, and cooling GUEs ranged from 0.32 to 0.38. These GUE values are significantly lower than anticipated for this technology per system specifications. Furthermore, the lower performance of the GAHP operation in Canada is attributed to extremely cold conditions, excessive cycling, and part-load performance. It was concluded that optimizing the control system is necessary to improve the practicality of GAHP in Canada.

A case study on optimizing industrial air conditioning with thermal solar energy in Egypt

This study investigates the feasibility of implementing a solar-assisted adsorption chiller in an industrial building at the Oriental Weavers International factory located in 10th of Ramadan City, Cairo, Egypt. The objective is to replace an inefficient split air conditioning system currently used to cool the Jacquard units during carpet manufacturing. The research begins by analyzing the performance of the existing cooling system to establish a baseline. It then explores the potential energy savings achievable by replacing the current system with a solar-assisted adsorption chiller. The existing oversized boiler will serve as an auxiliary heater for the new system. TRNSYS simulation tools are employed to model the building, simulate its thermal performance, and develop a solar-assisted cooling system. A parametric analysis investigates the impact of varying collector area and hot/cold-water storage tank volumes on key energy performance indicators. This analysis aims to determine the optimal component sizes needed for efficient system operation. Results indicate that a collector area of 90 m2 offers the optimal balance between performance and cost. There are minimal benefits to increasing the collector area beyond 100 m2. Larger hot water storage tanks demonstrate reduced outlet temperatures, reaching a maximum solar fraction at a capacity of 4 m³. The impact of cold-water storage tank volume on the system is minimal. The economic assessment reveals a payback period of 7.6 years, an Internal Rate of Return (IRR) of 14.3 %, and a Return on Investment (ROI) of 34.5 % over a 10-year period, indicating the financial viability of the proposed system. Furthermore, the solar-assisted adsorption chiller system has the potential for substantial environmental benefits. The system has the capacity to reduce CO2 emissions by up to 7200 metric tons. This highlights not only the technical feasibility of the system but also its economic and environmental advantages.

Energy optimization algorithms for multi-residential buildings: A model predictive control application

This study presents an optimization algorithm for Model Predictive Control (MPC) of the HVAC systems in multi-family residential buildings assessing the performance of four objective functions. Implemented in C++, using the free OR-Tools optimization library, the model is formulated a Mixed Integer-Linear Programming (MILP) problem. The study analyses the results of tests conducted on a 20-dwelling block in Switzerland across various weather and occupancy conditions, resulting in a parametric study of 64 cases.The models developed for the MPC are Grey-box type for the interconnected energy systems: the building, thermal storage tanks, a heat pump, the ventilation system and PV collectors, highlighting a radiant wall heating system integrated into the building facade. The tanks and the heat pump models were informed with manufacturer data, while for the building a R3C3 thermal-electrical equivalent model was developed, calibrated using TRNSYS simulations with a root mean square error of 1.7%.Findings demonstrate how the algorithm optimizes the operation according to the desired criteria, while ensuring indoor comfort with a 15-minute time resolution. The time execution of the majority of cases is under 3 min in a low-specs computer, affirming its practical viability for real-world implementation.

TRNSYS Simulation of a Bi-Functional Solar-Thermal-Energy-Storage-Assisted Heat Pump System

The escalating energy demands in buildings, particularly for heating and cooling demands met by heat pumps, have placed a growing stress on energy resources. The bi-functional thermal diode tank (BTDT) is proposed as thermal energy storage to improve the heating and cooling performances of heat pumps in both summer and winter. The BTDT is an insulated water tank with a gravity heat pipe (GHP), which can harvest and store heat passively from sun radiation and the external environment during the daytime. In summer, it harvests and stores cold energy from the air and night sky during the daytime. The performance of the BTDT-assisted heat pump (BTDT-HP) system in Adelaide, Australia, during the 2021–2022 summer and winter seasons was evaluated by conducting a TRNSYS simulation. This study revealed that the BTDT-HP system outperformed the reference ASHP system, where up to 8% energy in heating and 39.75% energy in cooling could be saved. An overall reduction in the energy consumption of 18.89% was achieved. Increasing the BTDT volume and GHP panel area enabled the tank to store more thermal and cold energy across the winter and summer seasons, thereby improving the system’s performance. The maximum ESPs were found to be 31.6% and 41.2% for heating and cooling for the study case under optimal conditions. When the GHP panel area was fixed at 15 m2, the BTDT volume should be at least 28 m3 for the BTDT-HP system, boasting cooling and heating capacities of 40 kW and 43.2 kW, to achieve positive energy savings.

Study on indoor temperature optimal control of air-conditioning based on Twin Delayed Deep Deterministic policy gradient algorithm

The optimization of HVAC system control affects the thermal comfort of building environment and air-conditioning energy consumption. However, most existing studies concentrate on human thermal comfort and neglects to incorporate air-conditioning energy consumption required to establish a controlled indoor thermal environment within the policy, which results in air-conditioning system high energy consumption. This paper suggests an indoor temperature intelligent control method based on thermal comfort and energy consumption of air-conditioning, and the TD3 algorithm is employed as an intelligent control algorithm to obtain the optimal setpoint that maximizes the joint benefit of the occupant’s thermal comfort and the energy saving rate of air-conditioning system. The air-conditioning indoor temperature intelligent control model based on TD3 algorithm is trained by using the experimental data, and the method is simulated in TRNSYS simulation software to corroborate the efficacy and energy saving rate of the method. The results indicate that the indoor temperature intelligent control model based on thermal comfort and energy consumption of air-conditioning has less optimal adjustment of indoor temperature setpoints, which is more stable for the air-conditioning system and can satisfy the thermal comfort demand at the initial control stage to prevent significant fluctuations in human thermal sensation compared to the linear control method based on thermal sensation and the fuzzy control method based on thermal sensation. Besides, the average daily energy consumption can be reduced by 6.54% and 3.37% respectively, when compared to the linear control method based on thermal sensation and the fuzzy control method based on thermal sensation.

Artificial neural networks for predicting the performance of heat pumps with horizontal ground heat exchangers

A Ground Coupled Heat Pump (GCHP) is a highly energy efficient heating, ventilation, and air conditioning (HVAC) system that utilises the ground as the heat source when heating and as the heat sink when cooling. This paper investigates GCHP systems with horizontal Ground Heat Exchangers (GHEs) in the rural industry, exemplifying the technology for poultry (chicken) sheds in Australia. This investigation aims to provide an Artificial Neural Network (ANN) model that can be used for GCHP design at various locations with different climates. To this extent, a Transient System Simulation Tool (TRNSYS) model for a typical horizontal GHE applied in a rural farm was first verified. Using this model, over 700,000 hourly performance data items were obtained, covering over 80 different yearly loading patterns under three different climate conditions. The simulated performance data was then used to train the ANN. As a result, the trained ANN can predict the performance of GCHP systems with identical (multiple) GHEs even under climatic conditions (and locations) that have not been specifically trained for. Unlike other works, the newly introduced ANN model is accurate even with limited types of input data, with high accuracy (less than 5% error in most cases tested). This ANN model is 100 times computationally faster than TRNSYS simulations and 10,000 times faster than finite element models.

Hybrid silver-graphene nanoparticles enhanced Lauric Acid phase change material for photovoltaic and thermoelectric generator applications: Experimental and simulation analysis

The global initiatives for renewable energy promote sustainable energy technologies such as photovoltaic thermal (PVT) systems and thermoelectric generators (TEGs). Latent heat energy storage is an effective method for conserving excess thermal energy and can be applied to PVT and TEG technologies. The fatty acid phase change materials (PCMs) are appealing, but their low thermal conductivity limits their practical usage. In this study, silver (Ag) and graphene (Gr) hybrid nanoparticles (NPs) are considered as additives to augment thermo-physical properties of lauric acid (LA) PCM for implementation in PVT and TEG applications. The nanocomposites are prepared by two-step technique. Additionally, implementation of composites in PVT has been evaluated experimentally and through TRNSYS simulation. Besides, composites impact on TEG application was assessed experimentally. As per results, photo-absorption analysis; nanocomposite LAG-3.5 (LA with 3.5 % hybrid Ag and Gr NPs) displayed the highest 76 % decrease in transmissibility. In addition, LAG-3.5 nanocomposite augmented thermal conductivity of LA by 57 % due to integration of high thermally conductive hybrid NPs. Further, LAG-3.5 composite reported an 8 % increment in latent heat enthalpy. As per reliability, after 500 thermal cycles, nanocomposite LAG-3.5 showed chemical stability and thermal durability. Moreover, optimal composite LAG-3.5 exhibited enhanced electrical characteristics while implementing in photovoltaic and thermoelectric generator application. Therefore, the nano-enhanced composite can be significant application prospects in the 45 °C to 50 °C melting temperature range.

Experimental and simulated evaluation of inverse model for shallow underground thermal storage

This study employs an inverse grey-box (IGB) modeling approach, which combines measured data and the physics of systems to predict the performance of shallow underground thermal energy storage (UTES) with top and side insulation. A simplified IGB model of the shallow UTES was developed using thermal network analysis. Experimental studies were conducted for shallow vertical and horizontal UTES configurations. Detailed models representing the field experiments were developed using the TRNSYS simulation tool and calibrated with the measured data from the experimental setup. The 4 Resistance 2 Capacitance (4R2C) IGB model was trained and tested in MATLAB using field experimental data and the data from the calibrated TRNSYS model. In comparing experimental data with the TRNSYS model for UTES, the prediction of outlet water temperature showed good agreement, with root mean square error (RMSE) and coefficient of variation of RMSE (CVRMSE) values of 0.94 °C and 3.16 % for vertical, and 0.99 °C and 2.97 % for horizontal configurations. The IGB model also aligned well with the experimental data, showing CVRMSE of 7.91 % and 3.17 % for vertical and horizontal systems, respectively. Sensitivity analysis revealed that model performance improves with longer training durations and closer testing times to training periods. However, a convergence point of 20 weeks of training data was achieved for making long-term performance predictions.

Electric vehicle-based distant energy sharing between zero-emission coastal office and hotel buildings

With the rapid growth of distributed renewable energy systems, energy sharing brings a practical solution to mitigate mismatching between intermittent electricity generation and building demand. In past research, energy sharing was designed mostly for onshore energy integrated systems and is commonly realised with the assistance of microgrids, distributed battery storage, or peer-to-peer energy trading. This research innovatively proposed a distant energy sharing between the ocean energy-supported coastal office building and hotel building by ten electric vehicles, enabling the circulation of ocean renewable energy between two buildings. This project aims to accomplish maximum technical, environmental and economic benefits for the stakeholder. Using bidirectional vehicle-building interaction, advanced control algorithms, including shifting vehicle batches, sizing renewable capacity, and involving stationary batteries, are implemented successively in the TRNSYS simulation as analysis groups to enhance the current system's performance. According to the results, the vehicle-based bidirectional energy sharing between these two buildings can attain a relative net present value of 49.18 million HKD and a weighted matching index of 0.63. After implementing advanced controls with stationary batteries, the system achieved a relative net present value of 62.15 million HKD with an improved matching index of 0.70. Both batteries contributed to increase the matching performance of the system, but the increase in battery capacity reduces the benefit due to their replacement cost. This research developed an energy management system for effectively utilising electric vehicles and coastal renewable energy for distant energy sharing. It elucidated the technological, environmental, and economic benefits to the stakeholders for effective decision-making.

Techno-economic evaluation of a seawater source heat pump system with auxiliary heat source in cold region of China

The utilizing of renewable seawater energy through seawater source heat pumps (SWHPs) in coastal areas is considered as a sustainable technology with minimal environment impact. Promotion of this technology needs clear understanding of its techno-economic performance but there are limited relevant studies. An empirical study was conducted in Qingdao, China, based on a practical installation comprising SWHPs supplemented by electric boilers. On-site measurements revealed considerable COP of 3.81 for SWHP and COPs of 2.87 for the whole system, implying SWHP as a viable and efficient solution for space heating in mild winter in this region. Results from TRNSYS simulations showed SWHP with auxiliary gas boilers (SWHP-GB) achieved the lowest annual primary energy demand and best economic and environmental benefits compared with other three schemes, namely SWHP with electric boilers (SWHP-EB), chillers with gas boilers (Chiller-GB) and air source heat pumps with gas boilers (ASHP-GB). SWHP played important roles in energy efficiency of the whole system with a considerable seasonal COP of 3.72 and 3.22 respectively for heating and cooling. Annual primary energy demand of SWHP-GB accounted for 55 %, 78 % and 56 % of SWHP-EB, Chiller-GB and ASHP-GB, respectively. SWHP-GB achieved the lowest life cycle costs and a rapid payback period of 10.9 years. Moreover, using direct or indirect heat exchange with seawater was found with limited impact on techno-economic performance of the system. To conclude, SWHP-GB could be used as an efficient solution for building heating and cooling in northern coastal cities in China.

Design and Economic Analysis of a Solar Thermal Pre-Cooling System for Agro-Cold Chain in Lesotho

The agricultural sector in Lesotho grapples with significant challenges regarding post-harvest losses. Given that 40% of all agricultural products require cold storage, food quality is compromised due to lack of cold storage to extract the heat from exposure to high field temperatures after harvest. This research proposes a solar thermal cooling system tailored to the specific needs of preserving fresh agricultural produce, leveraging Lesotho’s abundant solar energy resources. Through TRNSYS simulation and MATLAB economic analysis, optimal system parameters are determined, ensuring both technical efficiency and financial viability. The outcomes indicate that the proposed absorption solar thermal cooling system, incorporating evacuated tube collectors and an auxiliary boiler, effectively manages a cooling load of 7.318 kW, preserving fresh vegetables at 6.1°C. The optimized design features a chiller with a Coefficient of Performance of 0.8, a collector area of 12 m², and a hot storage volume of 0.2 m³, maximizing solar energy utilization. Importantly, economic metrics such as Levelized Cost of Energy ($0.085/kWh), Net Present Value ($9,200), Discounted Payback Period (12 years), and Savings to Investment Ratio (achieving 1 in year 13) demonstrate the financial feasibility and profitability of the system. These findings underscore the potential of solar thermal cooling as a promising investment option for addressing refrigeration needs in Lesotho, offering a sustainable solution to mitigate post-harvest losses and enhance economic performance in the agricultural sector.

The variable water temperature control strategy of the air-source heat pump compatible with floor heating system for an apartment

The adjustment of operating parameters and control strategies of an air-source heat pump (ASHP) heating system is of great significance for achieving system energy-saving. Ordinary constant supply water temperature setting could lead to higher energy consumption without concerning the changing of outdoor ambient temperature. In order to save the operational cost, we proposed a variable water temperature control strategy based on the hourly outdoor temperatures. In combination of TRNSYS simulation and experimental study, the system performance under variable supply water temperature control strategy were investigated and compared with four-period-adjusted supply water strategy and constant supply water strategy. The results showed that compared to operating at a constant supply water temperature of 35 °C, the daily power consumption of the system decreased by 56.7 % and 29.5 %, respectively under the typical high and low ambient temperature circumstances. Relative to operation with four-period-adjusted supply water temperature, the power consumption of the system decreased by 53.6 % and 24.6 %, respectively. Moreover, the variable water temperature control strategy could improve the coefficient of performance (COP) of the heating system. The control method proposed in this study would provide design reference for equipment manufacturers and help users to efficiently operate the ASHP unit.

Thermoeconomic Analysis of a Solar-Assisted Industrial Process Heating System

Thermal energy in the industrial sector for process heating applications in the range of 50 to 250°C consumes about 35% of the global fossil fuel. Cascaded solar thermal systems are promising solutions to meet clean and uninterrupted thermal energy supply for industrial process heating. Well-engineered cascaded arrangement of solar thermal collector (STC) and photovoltaic thermal (PVT) collector can attain an average solar fraction of more than 50%. In the present research, a solar-assisted process heating system, wherein a STC integrated in series with PVT, has been designed to produce low- to medium-temperature heat at higher solar fractions. Herein, thermal performance and economic viability of this novel system have been investigated and analyzed methodically. In the present research, a comprehensive TRNSYS simulation model is developed and validated experimentally. Results show that PVT integrated with heat pipe evacuated tube collector (PVT-HPETC) and PVT integrated with flat plate collector (PVT-FPC) system can generate thermal energy as high as 1625 and 1420 W with a thermal efficiency of 81 and 77% and exergy efficiency of 13.22 and 12.72%. Levelized cost of heat (LCOH) for PVT-HPETC at process heat temperatures of 60, 70, and 80°C is 0.214, 0.208, and 0.201 MYR/kWh, respectively. It is worth to note that LCOH is less than the existing cost of heat generation which proves that these systems are economically feasible.