Greenhouse cultivation in cold climates is highly energy-intensive due to substantial heating demands driven by large transparent envelopes, strong climatic coupling to the outdoor environment, and the challenge of maintaining a uniform indoor thermal environment. This study investigated the thermal performance of wall confluent jets (WCJ) heating and cooling systems for year-round greenhouse climate control, with a focus on harnessing low-temperature heat sources. It aimed to develop practical knowledge and predictive tools for designing WCJ systems that maintain stable greenhouse thermal environments under variable climatic conditions while minimizing primary energy use. This study adopted a multi-method approach, including experimental, statistical, and numerical methods, to assess the flow behavior, thermal performance, and techno-economic performance of the WCJ system. Constant-current anemometers measured WCJ air velocity and temperature, thermocouples measured air and surface temperatures, and pyranometers measured solar radiation. Statistical analysis using Response Surface Methodology aided experimental design and produced predictive response surface (RS) models. Building energy simulation using IDA ICE evaluated the techno-economic and energy performance of the WCJ heating system.

The results showed that the WCJ preserved its fundamental flow behavior under both isothermal and non-isothermal conditions and maintained recommended near-floor air velocities of 0.3–0.9 m/s in the greenhouse. The study developed second-order RS models to predict velocity decay, surface temperature, and inlet and indoor air temperatures. The WCJ heating system maintained spatially uniform indoor temperatures under varying climatic conditions. WCJ supplied at temperatures of 27–40°C during the winter demonstrated potential for use with low-temperature heat sources (<50°C), thereby reducing primary energy demand. During summer and autumn experiments, WCJ inlet temperatures of 14–25 °C maintained indoor temperatures within ±1.5 °C of the prescribed setpoint. Increasing the indoor temperature setpoint by 4 °C reduced cooling demand by 25%. External wall shading decreased indoor air temperature by 35%. The study identified airflow rate, shading, and indoor temperature setpoint as key parameters governing WCJ thermal performance. The effective thermal transmittance attributable to WCJ heat transfer characteristics was estimated at 2.69 W/m2·K, based on field measurements taken during the wintertime. Techno-economic analysis demonstrated the potential of using low-exergy heat sources in the WCJ heating system, with heating demand ranging from 204.5 to 571.6 kWh/m2, driven by outdoor climate and indoor temperature setpoints. Coupling WCJ with ground-source heat pumps reduces final energy use by approximately 50% compared with district heating, lowering costs from 198-534.2 SEK/m² to 35.7-89.9 SEK/m². Overall, the study presents WCJ technology as a key primary energy-saving and climate-resilient solution for sustainable, year-round greenhouse climate control and low-carbon agriculture.