An RC-network model in the frequency domain for radiant floor heating coupled with envelopes

This paper proposes a comprehensive thermal resistance and heat capacity (RC) network model in the frequency domain for lightweight radiant floor heating (RFH) coupled with envelopes under intermittent operation. The model transforms the calculation in the time domain into that in the frequency domain and applies the epsilon - NTU method and the concept of the core temperature layer. The accuracy of this model is validated by average relative errors of data from the experiment, where the air temperature, the floor surface temperature and operative temperature are less than 3.54%, 3.95% and 4.41% in four test conditions respectively, and heat flux at the supply water side shows high consistency with experiment results. 118 cases are studied by using the proposed model. A concept of the Ratio of radiant floor to unheated surfaces (RRF) is proposed. The RRF have a noticeable impact on the thermal performance of lightweight RFH. Based on the results of the case study, it is recommended that the influence of room size should be considered in the design phase. Furthermore, the thermal performance of the RFH during intermittent operation is inferior to that of continuous operation, implying that employing heat flux per unit area (HFPUA) as the only design index is insufficient. The model for lightweight RFH can be applied to estimate the influences of various factors on the dynamic thermal performance of lightweight RFH under the interaction of different envelopes, and further provide a theoretical basis for lightweight RFH operation design and energy consumption management.