Experimental study on the operating characteristic of a combined radiant floor and fan coil heating system: A case study in a cold climate zone

The development of the combined radiant floor and fan coil heating (RF-FCH) systems have improved the energy efficiency. In this study, the heating capacity and system operation state of the combined heating system were analyzed by experiments. The heating influencing factors of the combined heating system were investigated by two-way analysis of variance (ANOVA) and the Pearson correlation coefficient. Based on the technique for order preference by similarity to ideal solution (TOPSIS) the optimal operation scheme was determined. The results show that during the operation of the combined heating system, the fan coil bears significant heating capacity. The fan coil heating capacity accounts for about 62.2%-70.4% of the total heating capacity. The radiant floor plays an increasingly important role in the combined heating system with the decreasing outdoor temperature. The radiant floor response time varies from 1.5 h to 5.4 h. The fan coil responds faster to outdoor temperature changes compared to the radiant floor. The control of the fan coil can be considered as the dominant factor for dealing with outdoor temperature changes. The operation status of the RF-FCH system is mainly affected by the outdoor temperature. The energy conversion efficiency of the RF-FCH system increases with the increase of outdoor temperature. The energy efficiency ratio (EER) of the RF-FCH system varies from 2.2 to 3.2. The Pearson correlation coefficient analysis results are consistent with two-way ANOVA. Compared with the radiant floor, the indoor temperature and system energy consumption were more influenced by fan coil supply water temperature. When the evaluation indexes of the TOPSIS method have the same weight, the scheme with the fan coil supply water temperature of 32 °C exhibits a better performance. The innovation of this paper is that the best water supply scheme of the combined system is determined by TOPSIS method, which provides guidance for engineering projects.