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Photovoltaic thermal systems have gained tremendous popularity in the production of electric and thermal energy. In this paper, the photovoltaic thermal modules for the building façade assisted by heat pump system is proposed which combines the photovoltaic modules with an evaporator part of the heat pump system to produce hot water and electrical energy. Also, the photovoltaic thermal panels are used to preheat the cold ambient fresh air without heat pump operation. The proposed system was constructed at the Institute of Building Energy, Dalian University of Technology, China to study the ambient fresh air heating characteristic, electrical power generation, and hot water generation through performance evaluation indices under natural weather conditions. It was found that the average electrical, thermal, and overall efficiencies are 8.8%, 26%, and 50%, respectively during the pre-heating of fresh air. While the average air temperature is 15.2°C inside an air gap. The average COP for water heating is 3.91 during the water heating mode. This study could be used as a guide for photovoltaic thermal solar-assisted heat pump systems on building envelopes in a multi-energy generation under different weather conditions. Practical application: The study considers the photovoltaic thermal modules for building façade not only to generate the electrical energy and pre-heated fresh air but also to generate the hot water when assisted with the heat pump system. This research could assist researchers and engineers in the field of photovoltaic thermal façade systems in multi-energy generation such as for the production of electricity, heated/cooled fresh air, and hot water generation.

Purpose This paper aims to present a numerical study on the natural convection, which operates either as an evaporator or condenser unit of the heat pump system to pre-cool and pre-heat the ambient fresh air. Design/methodology/approach This study focuses on natural air cooling or heating within the air channel considering the double skin configuration. Particular focus is given to the analysis of airflow and the heat transfer processes in an air channel to cool or heat the ambient fresh air. In this study, the physical model consists of one wall, either heated uniformly or cooled uniformly, whereas the other wall is adiabatic. Findings The results show that the variation of both velocity and temperature is observed as the flow transition occurs at the evaporator or condenser wall. In either case, the temperature rises in the range of 6.3–8.4°C with an increase in mass flow rate from 0.07–0.08 kg/s in the photovoltaic thermal condenser part, while in the photovoltaic thermal evaporator part, the change in mass flow rate from 0.048–0.061 kg/s causes a decrease in temperature from 7.1–4.5°C. Practical implications The solar-assisted photovoltaic thermal heat pump system, in building façade having an air layer application, is feasible for pre-heating and pre-cooling the ambient fresh air and also reduces the energy needed to treat the fresh air. Originality/value The influence of condensing and evaporating temperature under natural convection mode in double skin conformation is considered for pre-heating and pre-cooling of ambient fresh air.

Systematic and random errors for working sensors in building systems can seriously affect the operation performance and have a significant negative impact on energy efficiency and indoor comfort. H...

This paper presents a radiative/convective hybrid heat dissipation photovoltaic-thermal heat pump (HHD-PVT-HP) refrigeration system based on the traditional PVT solar heat pump, which can be used to meet the cooling demand of buildings. PVT modules are used for the system condenser. The PVT modules emit heat to the ambient surroundings (hybrid heat dissipation) mainly by two ways: radiation to the night sky and convection with the surrounding air. An experimental study and parametric analysis of the HHD-PVT-HP system is conducted. The experimental results indicate that the HHD-PVT-HP system is able to stably refrigerate on summer night, with an average COPref value ranging from 1.8 to 2.1. Moreover, the heat dissipation performance of the PVT modules is good, with an average hybrid heat dissipation flux of ∼420 W/m2. To predict the operation characteristics of the HHD-PVT-HP under various ambient conditions, a system simulation model is established and validated with experimental data. The simulation results show that changes in the ambient air temperature and wind velocity have obvious effects on the heat dissipation characteristics of the PVT modules and system refrigeration performance. However, when the outdoor wind velocity is greater than 1 m/s, its influence is obviously lessened. Additionally, the relative humidity of the ambient air has little effect on the refrigeration capacity and COPref of the HHD-PVT-HP system.

Photovoltaic thermal heat pump technology stands for the combination of solar heat pump technology and a photovoltaic system, which has the characteristics of tri-generation (heating, cooling, and electricity) to meet the building's energy requirement. In this paper, the dual-use photovoltaic thermal heat pump system was used and investigated experimentally with an emphasis on the refrigeration mode, which with the feature of the novel roll-bond photovoltaic thermal unit working as condenser directly. Moreover, renewable energy such as solar radiation and long-wave radiation are the main energy source of this system. The experimental investigation of the system comprising; 4 roll-bond photovoltaic thermal units, 1 horsepower heat pump unit and 600 L ice storage tank was carried out. The performance evaluation method and uncertainty analysis of the system was proposed and implemented along with the examination on the refrigeration performance and operating characteristics of the system. The results indicate that the proposed photovoltaic thermal heat pump system can achieve the refrigeration for building space cooling demand in summer with high performance and long-term stable operation. This study could provide a valuable reference for the photovoltaic thermal heat pump multi-generation system design and large-scale practical application in northern China.

Direct-expansion solar assisted heat pump (DX-SAHP) is a promising technology for saving energy. In this paper, vapor injection (VI) cycle system to DX-SAHP system is studied. Thermodynamic comparative analyses of ideal VI cycle and ideal conventional vapor compression cycle was carried out for verifying the advantages by applying VI cycle into DX-SAHP. Additionally, photovoltaic/thermal (PVT) modules were used in the system to harvest thermal energy and electric power. A PVT based solar heat pump system employing VI cycle (PVT-VISHP) was proposed, fabricated and investigated experimentally. Performance of the experimental prototype was subsequently evaluated for seven days in winter. The system’s performance was evaluated based on the average ambient temperature of −1.13 °C and solar irradiation of 164.03 W/m2. Results showed that the total generated electricity, heat, and consumed power of the system were 0.51 kWh, 23.68 kWh, and 7.24 kWh, respectively. Moreover, average heating coefficient of performance (COPth) and advanced coefficient of performance (COPPVT) of the PVT-VISHP system were 3.27 and 3.45, respectively. In the study, the ambient-evaporating temperature difference ranged from 9.2 °C to 17.1 °C. Furthermore, variations of injected vapor’s pressure, mass flow rate, mass flow rate ratio, and subcooling effects were analyzed in detail. Performance of the PVT modules during a sunny day was tested. It was found that the PVT modules’ average thermal collecting and PV efficiencies were 49.9% and 7.51%, respectively.

The hybrid photovoltaic-thermal system has shown great progress. Electrical energy is produced from PV panels while thermal energy is produced via a working fluid carried through the panels. In this paper, the vertical PV/T is introduced using working fluids such as air and liquid, which serve to control the excess temperature of the PV panels as well as to collect heat to be made available as thermal energy. Installations of PV/T systems on building façades, as well as integration with other technologies such as heat pipe and heat pump are also discussed. Current studies of such building integration technologies are also explored, including the scale of application. This study aims to provide constructive information which can be used in future development of building facades for large-scale applications, to contribute to future sustainable development. Practical application: This study helps researchers and engineers who are considering photovoltaic thermal systems for building façades to have better understanding of its effect on electrical and thermal energy – for space heating, fresh air supply and hot water supply – using an active building envelope.

Photovoltaic thermal heat pump system has gained much popularity in the recent research field, which generally refers to the integration of photovoltaic and solar assisted heat pump to meet the various building energy demand. In this paper, dual-use roll-bond photovoltaic thermal heat pump system employing new roll-bond photovoltaic thermal unit has been proposed and investigated experimentally. The system operation principles and the design method of the main components are introduced in more details. A mathematical model of each component of the system is developed according to distributed and lumped parameter models. The tri-generation performance evaluation method of the unit and system is also proposed. The experimental investigation on the tri-generation performance of the system is carried out simultaneously, in terms of the heating, cooling and power supply capacity. Through analysis, it is evident that the proposed system has the potential to provide space cooling, hot water, and electricity for buildings with high efficiency and long-term stable working condition. Furthermore, the detailed performance parameters analysis has been carried out. The results demonstrate that the roll-bond photovoltaic thermal heat pump system is practically feasible and has a large potential for building energy conservation.

The BECMP (building energy consumption monitoring platform) is a valuable tool that can bring about a remarkable improvement in terms of energy conservation. With the growth in scale and use BECMP, data packet loss is becoming an ever-increasing and more serious problem. Large-scale BECMPs are typically configured using a hierarchical structure, making it susceptible to problems such as congestion and packet loss due to malfunctions in the link layer. These problems lead to a loss in efficiency of maintenance, thus eroding the gains realized by BECMP. In this paper, a decentralized and self-organized network structure is proposed. Rather than a hierarchical structure, a flat topology is implemented to improve robustness and the efficiency of data transmission. A corresponding routing strategy based on the minimum spanning tree algorithm has been developed and validated. Simulation results have shown that the proposed network is able to adapt to interference within the network and achieve a better overall performance.

Photovoltaic thermal (PVT) heat pump technology refers to the integration of photovoltaic and solar heat pump, representing the deep exploitation and utilization of solar energy. In this paper, roll-bond-PVT heat pump (RB-PVTHP) system with single stage compression is proposed and investigated experimentally. The roll-bond-PVT (RB-PVT) unit is introduced in detail which is combined with the photovoltaic module and single-sided roll-bond evaporation heat exchanger laminating together. The designed experimental system consists of 4 pieces of RB-PVT units, 1 HP heat pump unit and 150 L heat storage tank, which is also equipped with various monitoring sensors to explore the system operating characteristics. Then the performance evaluation method of the unit and system is proposed. The experimental investigation on the cogeneration performance of the system in northern China during summer is carried out simultaneously, in terms of the thermal efficiency, electrical efficiency, thermal-based overall efficiency of the unit and heating COP of the system. The operating characteristics monitoring results show that the system works in a long-term stable condition during the daytime with considerable cogeneration performance. The detailed performance parameters have been given in this paper. This study demonstrates that the RB-PVTHP system has the large-scale practically feasible application value in northern China.

Current thermal sensation estimation models mostly are suitable for the sedentary condition, failing to consider the difference of human thermal sensation in different activity states. This has caused critical limitations in accurately predicting thermal sensation. Moreover, the development method of current models primarily relied on regression analysis, which ignored the non-linear characteristics between the skin temperature and thermal sensation. This paper aimed to identify the significant parameters that can accurately estimate human thermal sensation in different activity states by experimenting and developing the estimation model based on the Takagi–Sugeno (T–S) fuzzy model. A series of human subject experiments were carried out in an environment chamber. The results indicated the feasibility of using wrist skin temperature and its time differential and heart rate as variables for developing thermal sensation estimation model. After that, the T–S fuzzy model was used to develop the thermal sensation estimation models, taking into account the influence of gender. To analyze the applicability of the estimation models in an unstable condition, several experiments were further carried out in the actual built environment. The study revealed that the thermal sensation estimation model based on skin temperature and its time differential and heart rate showed a high degree of accuracy, while the estimation model based only on skin temperature and heart rate also indicated good prediction effect. In addition, the verification results illustrated that the proposed models can predict the human thermal sensation in the unstable environmental condition.

The Internet of things presents tremendous opportunities for the energy management and occupant comfort improvement in smart buildings by making data of environmental and equipment parameters more readily and continuously available. Long-range (LoRa) technology provides a comprehensive wireless solution for data acquisition and communication in smart buildings through its superior performance, such as the long-range transmission, low power consumption and strong penetration. Starting with two vital indicators (network transmission delay and packet loss rate), this study explored the coverage and transmission performances of LoRa in buildings in detail. We deployed three LoRa receiver nodes on the same floor and eight LoRa receiver nodes on different floors in a 16-story building, respectively, where data acquisition terminal was located in the center of the whole building. The communication performance of LoRa was evaluated by changing the send power, communication rate, payload length and position of the wireless module. In the current research, the metrics of LoRa were quantified to facilitate its practical application in smart buildings. To the best of our knowledge, this may be the first academic research evaluating RTT performance of LoRa via practical experiments.

This paper is aimed at improving the performance of a building-integrated photovoltaic thermal (BIPV/T) system driven by a refrigerant pump. The research is aimed at optimizing and upgrading the BIPV/T system to address the shortcomings of the original system by replacing roll-bond PV/T units with improved heat transfer features. The system’s connecting form was redesigned using a liquid separator to solve the uneven distribution of the refrigerant on the PV/T façade. We proposed the variable frequency refrigerant pump that can be adjusted to suit the working condition. An experimental study was performed to analyze the electrical and thermal efficiency of the proposed system. The results show that the electrical efficiency of the BIPV/T system was 8% which is 14.3% higher than the traditional BIPV system, while in the test period, the BIPV/T system average COP was 3.4. The thermal and comprehensive efficiencies were 20% and 42%, respectively. Besides, the proposed system’s average COP was 3.7 times greater than the original BIPV/T system.

Solar energy technology applied to the building has shown a progressive trend in the architecture sector. Building integrated with the photovoltaic thermal system is called BIPV/T system, thus electrical energy is generated by photovoltaic modules and thermal energy is collected through working fluid. This paper presents an opaque ventilated PV/T facade system, which utilized the specific PV/T module as the external skin. A forced circulation with a refrigerant pump was adopted to cool the PV/T module and the coolant was R134a. The experimental research is carried out to evaluate the performance of the cogeneration system under outdoor climatic conditions of Dalian, including useful heat gain, the heating coefficient of performance, photovoltaic efficiency. In addition, thermal impacts on cavity air and solid wall are also analyzed. The results show that such system can reduce the heat flux of building envelope, and the system heating coefficient of performance can reach 3.1, the water temperature in thermal storage tank maximizes to 43.9 °C. The average photovoltaic efficiency is about 9% during the test period. Besides, the study shows that it is feasible to mount PV/T cogeneration system on the building facade. Furthermore, the system driven by a refrigerant pump operates stably and safely.

Existing automatic control of building thermal environments do not consider the individual's real-time thermal sensation, which could reduce the occupants’ thermal comfort. Therefore, it is very important to accurately obtain an individual's thermal sensation and real-time reflect on the control logic of air-conditioning systems. Current thermal sensation estimation models mostly apply to sedentary condition without considering human sensation in different activity states, which caused these models have critical limitations in accurately predicting human thermal sensation. In this paper, an intelligent wristband device is used for online monitoring of human thermal characteristics in different active states. The wrist skin temperature and its time differential as well as the heart rate are used for the evaluation index of human thermal sensation, and a series of environmental chamber experiments are carried out to obtain the relationship between the wrist skin temperature and thermal sensation in different activity states in summer. The correlation models of human thermal sensation, wrist skin temperature and its time differential, and heart rate has been formulated by statistical analysis and correlation analysis. In order to verify the feasibility of correlation models in the unstable environmental condition, several tests were conducted in the actual built environment. This study indicates that the wrist skin temperature and its time differential and heart rate can be used for estimating human thermal sensation with a high degree of accuracy in the different activity states. In addition, results of this study also demonstrate the promising applicability of obtained correlation models in the unstable environmental condition.

PV/T facade system is a novel style for solar renewable energy applications, which the system can improve the efficiency of the comprehensive utilization of solar energy. In order to research the performance of PV/T facade system, a modular remote monitoring system based on the Internet of Things and cloud platform technology is proposed, built, deployed as experimental prototype in this paper. The system collects temperature, pressure and wind speed through two RS485 RTU modules, and transmits data to database on the cloud platform via 4G network. The monitoring system allows authorized users to access real-time data or alarm information in a remote way via a website or mobile application. Besides the PV/T System operating parameters, meteorological data are also monitored to ensure a more complete analysis of performance. The proposed modular architecture can be built easily and rapidly, and onsite experimental test shows the stability of the monitoring system, which makes the system flexible enough for potential future modifications.

The current paper added several kinds and amounts of nanoparticles into traditional engine oil to form a new type of cooling medium (nanofluids). Two interface-tracking methods (CLSVOF and Eulerian) were employed to discuss the transient flow and heat transfer of engine oil and nanofluids with different nanoparticles (copper and diamond) and volume concentrations (1%, 2% and 3%). The distributions of oil filling ratio and heat transfer coefficient were investigated at various crank angles. The advantages of nanofluids on cooling down the piston gallery were illustrated by comparing the statues of flow and heat transfer in local surfaces at the same moment.

This paper presents an active solar building facade system, which can generate domestic hot water and electric power. The design system utilizes the specific photovoltaic/thermal modules as an external skin to form an opaque ventilated facade, and the additional active layer can reduce the heat flux transferred into the building envelope and has the potential to preheat fresh air. To investigate the thermal impact of this solar facade on the building’s envelope, a number of heat transfer analysis work is done from the aspect of theoretical analysis and an experimental platform consisting of the opaque photovoltaic/thermal ventilated facade and a hot water system is set up to evaluate the net heat gain combined from the experimental research aspect. The specific photovoltaic/thermal facade in experimental system is a hybrid module composed of glass lamination, photovoltaic cells, single-sided inflatable plate collector, and ethylene-vinyl acetate. The results indicated that the coefficient of performance of designed system can reach 3.1 and average photovoltaic conversion efficiency is about 9%. The opaque ventilated PV/T facade is superior to conventional wall, which can reduce heat flux through the external envelope by 40%.

In this paper, the transmission performance of multi-modal orbital angular momentum (OAM) antenna array based on vortex electromagnetic wave (VEMW) are investigated by simulation and measurement. An eight-element circular array antenna with feed network is designed to excite and receive multi-modal vortex wave. Radiation patterns of several modes are simulated and mode isolation at different distances and radii of the array are obtained and compared by methods of adding receiving array and concentric rings. Furthermore, insertion losses are measured for different distance, which show the transmission characteristics of VEMW.

In this study, a novel structure, which is applied to different metal layers of ultra-wideband frequency selective surfaces (FSS), is proposed. It has been found that by adjusting the size of the circular coupling metal pieces in the novel structure, a narrow stopband can be generated at different locations within the passband, which can be used to shield narrowband electromagnetic interference (EMI). In addition, the equivalent circuit model of the novel FSS is also given in this paper, and it provides references for more comprehensive understanding of the FSS’ s filtering mechanism and the improvement of subsequent performance.

In this paper, we design a stepped miniaturized 4 × 4 Butler matrix using the principle of impedance transformation. Compared with the traditional Butler matrix, the miniaturized Butler matrix has a reduced area of 78.6%, and the output amplitude is stable, the output phase gradient meets the design requirements.

Development of different curvatures of cylindrical and spherical Frequency Selective Surface (FSS) has been demonstrated in this paper. The wideband metallic FSS has a passband between 9–11 GHz with a performance that is independent of the direction of the incoming wave between 0°~40°. HFSS is used for simulating and optimizing in search of the optimum dimension of the FSS unit cell. Current and dielectric distribution are analyzed and the existence of fringe effect is validated. For potential instructions in designing conformal FSS in the future, a bandwidth fitting curve with respect to conformal radius is created.