Development Of Soil Temperature Field Measurement System In Ground Source Heat Pump System

With the rapid growth of the world's population and the rapid development of the economy,problems such as environmental pollution caused by human development and the scarcity of available energy are becoming increasingly prominent.As a highly efficient,energy-saving and environment-friendly air conditioning technology that can use underground shallow geothermal resources to complete functions such as heating,cooling,and domestic hot water,ground-source heat pump technology is developed in this context.The law of the change of soil temperature field is an important basis for the design of ground source heat pump system.The cooling tower-type ground source heat pump system designed in combination with the conditions in the hot summer season also needs to detect the soil temperature field in order to achieve better energy-saving effect and higher cycle efficiency.The ground temperature field measurement method used in most of today's projects is to place a temperature sensor in a sealed well and put it into a temperature measuring well.The temperature sensor is connected to the surface temperature measuring device through a wire.Each temperature sensor needs a separate set of wires.The temperature measuring device is connected.A large number of measuring lines will not only increase the cost of measurement,but also result in the inability to install enough temperature sensors in the same test well.Generally,only three to five temperature measurement points can be installed because of the number of temperature measurement points.Less,the reliability of the research on ground temperature field changes will be greatly reduced.The soil temperature field measurement method used in most of today's projects is to put a sealed and packaged temperature sensor into a temperature measuring well.The temperature sensor is connected to the ground temperature measuring device through a wire.Moreover,each temperature sensor requires a separate set of wires to connect with the temperature measuring device.A large number of measuring lines will not only increase the cost of measurement,but also greatly reduce the number of temperature measurement points,and the reliability of the research on ground temperature field changes will be substantially reduced.In this paper,we design a set of soil temperature field measurement system applied to ground source heat pump system.The system is composed of three parts:underground temperature measuring line,data collector and upper computer.The underground temperature measuring line adopts the RS-485 bus for temperature acquisition,which overcomes the problem of too many harnesses caused by traditional measurement methods.A temperature measurement circuit is placed at each temperature measurement point to measure the temperature.Using the PT1000 temperature sensor as a temperature measuring element,the method of nearest measurement and the method of measuring the resistance by capacitive charging and discharging greatly increase the accuracy of the temperature measurement.By simplifying the circuit design and rationally arranging components,the temperature measuring circuit board is designed to be slender and attached to the RS-485 bus,and stainless steel bushings with built-in threads,stainless steel connectors,and epoxy resin are used for sealing,which ensure the structural strength of the temperature measuring line and the tightness of the temperature measuring node;the data collector is placed on the ground and its function is Power supply to the bus,collect data of each temperature measurement point,and send the collected temperature data to a remote host computer through a wireless method.A data collector can collect up to 8 temperature measurement lines.Comparing various wireless transmission methods and integrating field conditions,the SX1278 wireless data transmission chip based on LoRa wireless communication technology was selected for wireless data transmission;the upper computer was programmed using LabVIEW software,and its function was to receive,store and process temperature data.The unique human-computer interaction interface enables managers more easily to process data and maintain the system.