Model analysis on thermal efficiency of suspended Kang of rural households in Zhuanglang county, Gansu province

Abstract: As the weather is cold in the winter in the loess hilly region of western China, space heating becomes a necessary demand for rural households. Kang is the main method of heating in rural households of this region. A new type of kang (suspended kang) was constructed in six rural houses and traditional kang (a heatable brick bed) constructed in four rural houses in two villages in Zhuanglang County. The suspended kang was raised above the floor on columns, which is different from traditional kang on the ground. Indoor and outdoor temperatures were monitored hourly by intelligent digital temperature recorders in these houses. The daily amount of fuel used was also recorded. A mathematical model, the trend surface model, was designed to utilize the monitored time series data of temperature change to estimate indoor and outdoor cumulative temperature. It is supposed that the house is an enclosed system which is heated only by kangs and stoves, and the influence of other random factors was not considered. Based on the above and according to the heat transfer theory, a new model of the heat loss of the house was designed. The law of conservation of energy dictates that the heat gain indoors equals the heat lost in a given period, which also equals the effective heat releases by burning fuel. Using Matlab 7.0 software, the thermal effectiveness of the two types of kang during heating periods was modeled according to typical daily life scenarios of rural households. The results show that annual average energy consumption for heating accounted for one-half of the total energy required by that lifestyle. Actual fuel consumption of suspended kang and traditional kang are 868.43 and 1338.51kgce in Gaoyahan village respectively, and are 956.36 and 1583.5kgce in Xiawan village respectively. The heat loss of a house is a function of the interaction between outdoor temperature change and fuel use. The heat loss obviously increases when the outdoor temperature falls, and vice versa. The hourly change of heat loss is illustrated, as a U-shaped curve over the period of one day, and the daily change as an inverted U-shaped curve over the whole period of the study. The thermal efficiency of the suspended kang is between 27% and 37%, and is higher than that of the traditional kang's. Therefore, it is suggested that the suspended kang should be promoted as much as biogas digesters as a way of improving the indoor thermal comfort of rural residents in the winter.