Design and performance test of biomass briquette heating system for solar greenhouse

Traditional solar greenhouses use sunlight and cotton blankets to increase indoor temperatures during winter, which lead to low internal temperatures. Existing active heating methods suffer from severe coal pollution, high costs of gas and electricity, and uneven temperature distribution. In this study, a novel low cost biomass briquette heating system coupled with buried pipes and steel radiators was designed. The results indicated that the heating system could ensure both soil and air temperature for plant growth. Located 0.1m, 0.7m, 1.3m and 1.9m in solar greenhouse, the air average temperatures were 16.0 °C, 18.2 °C, 18.6 °C and 17.8 °C, and the average humidity were 83.8%, 79.6%, 77.9% and 79.2%, respectively. What is more, the average soil temperature was 24.8 °C, 27.1 °C, 22.4 °C and 24.0 °C at depths of 0.1, 0.2, 0.3 and 0.4 m, respectively, and the average humidity was 27.4%, 27.8%, 26.8% and 25.5% at the same depths. The cost of heating system operating was 9 yuan/m2, which was less than electric heating or gas heating. The emissions were lower than NB/T 34006-2020, which was environmentally friendly. The recommended location for steel radiators was in the middle of solar greenhouses, and the optimal distance and depth for buried pipes were 0.3 m and 0.4 m, respectively. Furthermore, the recommended heat load of the solar greenhouse was 34.78W/m2. The biomass briquette heating system achieved low-cost and clean heating for solar greenhouse. The research provided a theoretical basis for heating systems design in solar greenhouses.