# Design and Analysis of a Floor Radiant Heating System Based on Energy Substitution Technology
## 2 Heating System Design  
The design idea of this system is the formation of a dual-system coordinated operation that combines a photothermal floor radiant heating system and a photovoltaic floor radiant heating system. In the photothermal floor radiant heating system, a solar thermal collector converts solar energy into heat energy and then heats the ground through hot water pipes that are laid in the floor. In the photovoltaic floor radiant heating system, the AC heating cables that are laid in the floor are heated by a photovoltaic power system to supply heat energy to the room. The overall design of the system is shown in Figure 1. The solid line in bold and black is the photothermal floor radiant heating system, and the single solid line is the photovoltaic floor radiant heating system (Figure 1). AC heating cables and water pipes are intertwined and laid evenly in the floor of the room, which has a temperature and humidity sensor. The room temperature can be set and controlled. In the photothermal floor radiant heating system, a solar thermal collector heats the water, which is circulated by the heat collection pump in the water tank. Another circuit of the water tank is the indoor hot water, which is circulated by the heat supply pump. The controller collects the indoor temperature signal and adjusts the opening of the electric control valve on the heating circuit by the fuzzy PID algorithm according to the temperature setting value. The heat collection circuit and the heat supply circuit are equipped with temperature sensors and flow transmitters, respectively, for collecting and monitoring the temperature, flow and energy data. The level transmitter, which helps the controller to determine whether to start the water supplement electromagnetic valve, is installed in the water tank. The top of the water tank is equipped with an exhaust pipe to maintain the normal pressure of the water tank. The bottom of the water tank is equipped with a blowdown valve for drainage, which can ensure long-term stability. In the photovoltaic floor radiant heating system, solar cells convert solar energy into electricity, which is delivered to the inverter through a DC stabilizer. The inverter converts the DC 48 V to AC 220 V to supply the AC heating cables. Solar cells also provide DC 48 V and DC 24 V for the control system and the battery. Diodes that prevent battery reverse charging of the solar cells are installed in the DC stabilizer. The supply mains AC 220 V can supply the heating cables directly and charge the battery through the battery charger to ensure battery life in the case of a shortage of battery power. Using night valley electricity to charge the battery and run the heating system in the daytime is another method of energy saving. The current sensors (A1-A3) and voltage sensors (V1-V3) in the power supply circuit are used for the monitoring of current and voltage. The monitor data are used to judge whether the system is operating normally. The entire photovoltaic power supply circuit is equipped with various circuit breakers (K1-K5), contactors (KM1-KM5) and fuses (FU1-FU2) for remote, automatic and manual control. A fuzzy PID controller that can monitor and control the entire heating system is designed in this system. The controller contains DO, AI, and AO ports, a power supply port and an RS485 communication port as shown in Figure 2. DO ports output digital instructions to control the on-off operation of the corresponding contacts. Each indicator light that corresponds to the contactor shows the on-off state. The power supply of some contactor coils mainly originates from the battery (DC 48 V) and inverter (AC 220 V).