Photovoltaic-thermal (PVT) technology refers to the integration of a photovoltaic (PV) and a conventional solar thermal collector, representing the deep exploitation and utilization of solar energy. In this paper, we evaluate the performance of a solar PVT cogeneration system based on specific building energy demand using theoretical modeling and experimental study. Through calculation and simulation, the dynamic heating load and electricity load is obtained as the basis of the system design. An analytical expression for the connection of PVT collector array is derived by using basic energy balance equations and thermal models. Based on analytical results, an optimized design method was carried out for the system. In addition, the fuzzy control method of frequency conversion circulating water pumps and pipeline switching by electromagnetic valves is introduced in this paper to maintain the system at an optimal working point. Meanwhile, an experimental setup is established, which includes 36 PVT collectors with every 6 PVT collectors connected in series. The thermal energy generation, thermal efficiency, power generation and photovoltaic efficiency have been given in this paper. The results demonstrate that the demonstration solar PVT cogeneration system can meet the building energy demand in the daytime in the heating season.

The existing control systems for the parallel pumps in HVAC systems are mostly based on a centralized structure in which all the data from sensors and control instructions are processed by a master controller. This structure has somehow limited the stability, expandability, and the universality of the control system. The strategies are always case by case, ones which cannot be easily transplanted to other systems and when some devices are out-of-order the entire control system will be influenced. In the current article, a distributed control structure has been proposed for the parallel pumps in which the master controller is replaced by several independent distributed controllers cooperating together to handle the global task. An evolutionary algorithm artificial fish swarm algorithm has been transplanted to the proposed structure to optimize the pumps working in parallel mode. Simulation studies have been conducted based on the models of a physical pump system and the performance of the proposed algorithm is compared with other common heuristic algorithms in both effect and stability. The results show that distributed artificial fish swarm algorithm has inherited the characters of artificial fish swarm algorithm and it is more efficient in the calculation.

In this paper, two sets of experimental devices have been established for studying the falling film evaporation outside a horizontal tube and condensation inside a horizontal tube, with three different tube arrangements and seawater as the experimental fluid. The rules of the overall heat transfer coefficient (K) are determined by changing saturation temperature (T), Reynolds number (Re), total temperature difference (ΔT), inlet steam velocity (v_s), and vapor quality (x). Experimental results indicate that the overall heat transfer coefficient of the rotated square arrangement (K_rs) is higher than that of the triangular arrangement (K_t), and the square one (K_s) is the lowest with less impact on Re, T, ΔT, v_s, or x changing. With Re increasing, the K increases first and then declines, especially when Re > Re_cr, K_rs and K_t are almost the same. The increment of T and ΔT leads to the decreasing of the K, while v_s has little effect on the K. The growth of x contributes a lot to the increment of the K. In the evaporator, the vapor quality contributes a lot in the horizontal direction, while Re is more influential in the vertical direction.

The efficient utilization of solar energy significantly contributes to energy efficiency in buildings. Solar photovoltaic thermal (PVT) heat pumps, a hybrid of photovoltaic and solar-assisted heat pumps, have demonstrated a significant development trend due to their multi-generational capacity for heating, power, and cooling with reliable operational performance. This research work presents and investigates a single-stage compression PVT heat pump system, along with the operation principle of the system’s heating and power co-generation throughout the winter and transitional season. The construction of the testing facility, data reduction, error analysis, and performance evaluation indices of the system are all explained theoretically. A continuous experiment research project focusing on system heating and power performance was carried out in Dalian during the transition season (November in this study) and winter season (December in this study) as part of our investigation into the potential uses for space heating, residential hot water, and power supply in northern China. The findings of the experimental research demonstrate that the proposed system can generate electricity and heat at high efficiency during the winter and transitional seasons, with long-term stable performance. The system’s average heating COP_t is 5 during the transitional season and 4.4 during the winter season. Meanwhile, the average photovoltaic power efficiency under both weather conditions is 11.9% and 10.2%, with a peak value of 15.7% and 12.0%, respectively. Additionally, the system compression ratio’s variation range is 2 to 3.88, which is lower than the standard heat pump system. As a result, the entire system heating operating process remains constant.