The heat source tower (HST), as a cleaner energy production, which can absorb the low-grade energy from ambient air to drive the heat pump unit without emissions has attracted more and more interest. In addition, HST has excellent economic applicability by using cooling tower equipment, which was idle in winter. However, there are few studies on comparative analysis of thermal behavior between counter-flow and cross-flow HST. A mathematical model suitable for both HST types was developed to identify the performance discrepancies between them. Then a parametric study was carried out in order to investigate the impact of solution and air as well as packing material properties on energy transfer of HSTs. Finally, the characteristics of solution dilution and dehumidification were investigated. As the inlet solution temperature increases, increases first, then decreases gradually, but a transition point occurs in the solution at −5 °C. Moreover, the transition section of moisture transfer direction for counter-flow HST was located in the 0.78 m and 0.26–1.56 m of packing material height, under the condition that the air relative humidity was 50%. In summary, this work intuitively indicates the thermal performance difference between counter-flow and cross-flow HST, also could assist the selection of proper operating conditions in HSTs.

Against the backdrop of the global energy transition and carbon reduction in the building sector, this study proposes a photovoltaic solar chimney coupled with an earth–air heat exchanger (PVSC-EAHE) system to integrate passive ventilation, thermal pre-treatment, and photovoltaic power generation in cold and arid regions. A coupled numerical model is presented using MATLAB 7.2 and TRNSYS 16.0, with user-defined models for the earth–air heat exchanger, solar chimney, and photovoltaic system implemented as TRNSYS-callable modules. The novelty of the study lies in the systematic year-round investigation of five inclination angles of photovoltaic (PV) panel (20°, 30°, 40°, 50°, and 60°) and their effects on the coupled thermal, ventilation, and electricity-generation performance of the system under different seasonal conditions. An 8760 h annual dynamic simulation was conducted using typical meteorological data for Hami, Xinjiang, China, to evaluate system performance and the effect of PV inclination angles ranging from 20° to 60°. The results show that, compared with a conventional building without the coupled system, the PVSC-EAHE system reduces the average indoor summer temperature by approximately 4 °C, maintaining temperatures below 28 °C, while increasing winter indoor temperatures by up to 8 °C. The system also provides an average fresh-air supply of 132 m³/h and generates 2180.1 kWh of electricity annually. The inclination analysis reveals a season-dependent trade-off: higher inclination angles are more favorable for solar radiation capture and ventilation during winter, whereas lower angles are comparatively more favorable during summer. The inclination angle has a relatively limited effect on indoor thermal conditions, while increasing it from 20° to 60° raises the maximum instantaneous PV output from 198 to 220 W/m². Overall, the results demonstrate the potential of the PVSC–EAHE system to improve indoor thermal conditions, enhance natural ventilation, and generate renewable electricity in cold and arid climates. As annual heating and cooling consumption was not explicitly calculated, the observed performance improvements indicate the potential to reduce building energy demand rather than quantitatively demonstrating specific annual energy savings.