EHT System Control by Thermostat on Site
What is a simple way to control the EHT system to maintain temperature?
When I need to propose an EHT system, clients often ask me to design it based on my experience. For me, the control system has always been the aspect that requires more attention than other topics.
What is a control system with thermostat?
Simply put, in winter, we turn on the boiler to warm the house. But when it reaches a certain temperature, we want it to automatically turn off to prevent overheating and save energy. When it gets cold again (below the desired temperature), it should turn back on. The thermostat is responsible for this automatic on/off function.
Similarly, a good electrical heat tracing (EHT) system should have a control system to maintain the desired temperature and conserve energy.
In this article, I’d like to explain a simple method to control an EHT system—using a thermostat on site.
In an industrial EHT system, the thermostat is typically housed within a box, which looks like this:
Thermostat housed in aluminum / GRP box
The thermostat allows us to set a desired temperature. We want our pipe (or tank) to maintain this set temperature. To compare the pipe’s (or tank’s) temperature with the set temperature, we need to measure it using a sensor.
Sensor connected to the thermostat
If the measured temperature is lower than the set temperature, the heating cable stays on. When the measured temperature reaches the set temperature, the heating cable turns off. When the temperature drops again, the heating cable turns on once more. This way, the temperature of the pipe (or tank) is maintained at the set temperature.
Wiring Method of Thermostat
So, how does the heating cable turn on and off in sync with the thermostat? It requires proper wiring. Are you curious about how to do this? First, let’s look at the diagram of an electrical heat tracing system.
Above is a general diagram of an EHT system. The control panel supplies power to the junction box through the power cable, energizing the heating cable connected to the junction box. To control the heating cable and maintain the set temperature, we use a thermostat beside the power junction box, and the connection is made as shown below.
Inside the junction box, there is a terminal block. We connect one wire of the power cable and one wire of the heating cable to the same block, while the other wire is connected to a different block. When the two wires of the thermostat connect these two blocks, the wiring is complete!
When the measured temperature is lower than the set temperature, the circuit closes—energizing the heating cable. When the measured temperature exceeds the set temperature, the circuit opens—de-energizing the heating cable.
The picture below shows a simple way of connecting the power junction box and the thermostat.
Controlling the EHT system with a thermostat is a simple method. It only requires placing a thermostat next to the power junction box, making it a relatively inexpensive temperature control method. Since the system is simple, it is easy to install and maintain on site.