Abstract: This paper discusses the principle of heat measurement, designs a high-reliability heat meter using advanced sensors, and presents the hardware and software design methods. Because the system adopts single-bus technology, analog signals are converted into digital signals at the measurement site, enabling long-distance measurement with high accuracy and application value. Keywords: Heat meter; DS2450; DS18B20; Single-bus 0 Introduction In recent years, due to energy shortages, various energy billing systems have emerged. Air conditioning is a major energy consumption item for users. Traditional air conditioning billing systems often only consider electricity costs or calculate based on area, which is obviously unreasonable. This system, based on single-bus technology and using advanced sensors, realizes network-based individual household billing functionality. 1 Measurement Principle and System Composition 1.1 Measurement Principle Hot water supplied by the heat source flows into the exchange system (radiator, etc.) at a higher temperature and flows out at a lower temperature; in this process, heat is provided to users through heat exchange. According to the thermal measurement formula, the heat obtained by the user can be calculated by the following equation: E=∫ K×（T[sub]S[/sub]-T[sub]d[/sub]）×dv Where: E— heat output of the heat exchange system; T[sub]S[/sub]— inlet water temperature (T); T[sub]d[/sub]— outlet water temperature (T); V— hot water flow rate (liters) through the heating system within a certain time. K—correction coefficient for specific gravity and specific heat. The K value is used to correct for specific gravity. The flow meter measures volumetric flow rate, which needs to be converted into mass flow rate suitable for heat calculation. The specific gravity of water changes with temperature, so specific gravity correction is required. The K value is also used to correct for specific heat. The heat value corresponding to water temperature is not absolutely linear. Therefore, even if the supply and return water temperature difference is the same under two operating conditions, if the supply or return water temperature is different, the corresponding heat value will also be different. The K value is a variable that depends on both the supply and return water temperature values. The introduction of the correction coefficient K is very important in heat calculation. Without this correction factor, the resulting calculation error would be significant. 1.2 System Composition As shown in Figure 1, the system consists of a host unit and user units. Each user installs only one user unit, which comprises a flow sensor, a supply water temperature sensor, a return water temperature sensor, an indoor temperature sensor, a button module, and an LCD display module. To ensure that the temperature sensors match the temperature of the water being measured and to reduce errors, two temperature sensors are mounted on heat-conducting rings and fixed to the air conditioner's supply water pipe (cold end) and return water pipe (hot end), respectively, and covered with heat-insulating material to reduce heat loss. A solenoid valve is installed on the inlet pipe, and a flow meter measures the flow rate of hot water. The indoor temperature sensor senses the indoor temperature in real time and compares it with the set temperature. The microprocessor determines the opening and closing of the solenoid valve based on the comparison result. The microprocessor calculates the heat supplied to the user based on the temperature difference between the inlet and outlet pipes and the flow meter value. It reads the heat value from the previous time period from the non-volatile memory AT24C01 and adds it to the current value. The accumulated value is sent to the display module for display and stored in the AT24C01. When the host computer requests data, it is transmitted to the host computer. When the flow meter reading is 0, the calculated heat value is 0, and the microprocessor is in sleep mode. [align=center] Figure 1 System Schematic Diagram[/align] 3 Component Selection 3.1 Flow Sensor The flow sensor adopts a rotor structure. Its principle is: the impeller is placed in the fluid being measured. The liquid impacts the impeller along the tangential direction, causing the impeller to rotate. Its rotational speed is related to the flow rate as follows: Q=Kn K=4×3.1415RA/cosα Where: Q-flow rate of liquid; n-rotor rotational speed; R-rotor radius; A-area of ​​inlet; α-angle between impeller blade and inlet. When R, A, and α are constants, K is also constant. Ideally, the flow rate is linearly related to the rotational speed. The sensor has a total of 7 blades on its impeller. Each blade is inlaid with a magnet. A sealed PTFE plate is installed above the impeller. There is a blind hole at the same diameter position on the plate and the magnet to house the Hall switch detector. When the impeller rotates with the fluid flow, the 7 magnets sequentially excite the Hall switch, causing it to emit an electrical pulse signal. The pulse frequency is proportional to the rotational speed. The frequency signal is converted from F/V to output the required voltage signal. After calibration, the flow rate can be measured. 3.2 Temperature Sensor The temperature sensor selected is the DS18B20, a networkable single-bus digital temperature sensor, which features simple structure, small size, low power consumption, and strong anti-interference ability. 3.3 Single-bus A/D chip DS2450 DS2450 is a single-bus 4-channel successive approximation A/D converter, namely A, B, C and D analog voltage input channels. Its input voltage range, conversion accuracy bits and alarm threshold voltage are programmable; each channel has its own memory to store voltage range settings, conversion results, threshold voltage and other parameters (for detailed information, please refer to reference [1]). DS2450 converts the voltage signal output by the flow sensor into a digital signal and transmits it to the microprocessor. 3.4 LCD display module LCM12864ZK LCM12864ZK is an LCD display module with Chinese character library graphics. It has strong functions and simple control. Since it has its own Chinese character library, it greatly reduces the workload of programming. This module is mainly used to display the current time, room temperature value and heat value. 3.5 Button module The system is set with three buttons. Button 1 is used to set the room temperature, and buttons 2 and 3 are the increase and decrease buttons, respectively. 4. Working Process After the system is powered on, it initializes the DS2450, DS18B20, and LCM12864ZK, sequentially sending the addresses of each sensor group (i.e., the serial numbers of DS2450 and DS18B20), initiating conversion, reading the temperature sensor values, comparing the room temperature value with the set temperature value. If they are equal, the hot water pipe valve is closed; if they are not equal, the temperature difference between the inlet and outlet pipes is calculated, the A/D value (i.e., the flow sensor value) is read, the heat is calculated, and the data is displayed on the LCD module and stored in the non-volatile memory AT24C256. Simultaneously, the lower-level machine can also upload data to the upper-level machine via RS-485, and the upper-level machine can also send commands to the lower-level machine. 5. Software Design Figure 2 shows the system's software flowchart. Since the system uses a single-bus protocol, the timing of the single-bus protocol must be strictly followed. [align=center]Figure 2 Software Flowchart[/align] 6. Conclusion The temperature, flow rate, and heat power of the heat exchanger were tested using standard instruments. The temperature difference error was less than 0.115℃, the actual flow rate totalization error was less than 5%, and the heat totalization error was less than 2%.