Abstract:Chinese solar greenhouse (hereafter referred to as solar greenhouse) has been widely applied for growing vegetable during winter with little or without additional heating. The traditional back wall could store heat in the daytime and release heat in the solar greenhouse in the night. It plays an important role in maintaining high indoor air temperature in the solar greenhouse. However, this kind of wall has the disadvantages of high cost and uncontrollable exothermic process. The solar greenhouse with the traditional back wall was easy to show low air temperature in the late night. To solve the problems, it was proposed to replace the traditional back wall by employing the heat insulation back wall and the active heat system, which could collect heat in the daytime and release heat actively in night. The active heat system developed with capillary tube mats (AHSCTM) was developed. The heat collecting and releasing performances of AHSCTM was investigated and compared with the composite wall, which was constructed with 370mm clay brick and 100mm polystyrene board, aiming to test the above proposal. AHSCTM was composed of capillary tube mats installed on the back wall or hanged on the south roof of the solar greenhouse, water tank, water pump and pipes. By circulating water, AHSCTM could collect the heat from the solar radiation intercepted by the capillary tube mats in the daytime and stored in the water tank. And in the night when the air temperature was low, those heat could be recovered to heat the solar greenhouse by circulating water again. According to the test, the heat collected in the daytime and released in the nighttime by AHSCTM were 84.4%~111.3% and 74.8%~100.7% of those collected and released by the composite wall, respectively. The coefficient of performance（COP）of AHSCTM was 1.1~2.4. Nevertheless, during operation of AHSCTM in the nights of solar day, cloudy day and overcast day, the heat released by AHSCTM was 98.2%~172.5% of the composite wall. in the other hands, a dynamical model was developed to simulate the water temperature of the water tank. The results showed that the simulated water temperature agreed well with the measured water temperature. This model can be used to improve the heat collecting and releasing performances of AHSCTM. Based on this model, ASHCTM can be improved by lengthening the capillary tube and increasing the number of capillary tubes in each mat. Then, the heat collected in the daytime and released in the nighttime by the improved AHSCTM were 67.6%~112.1% and 69.0%~128.3% of the composite wall respectively. COP of the improved AHSCTM was 2.8~7.0. During operation of AHSCTM in the nights of solar day, cloudy day and overcast day, the heat released by AHSCTM was 2.5~5.1 times of that of the composite wall. Thus, it was feasible to replace the composite wall in the solar greenhouse by employing the improved AHSCTM and the insulation back wall.
