Introduction: Fan Coil Unit

This tutorial will teach you how to build your own fan coil unit at home. It will be controlled by a Raspberry Pi. Two temperature sensors will provide the necessary data for the Raspberry Pi to switch on and off the circulation pump. If you follow our instructions below, you will never be cold again !

This project has been carried on for our Applied Electronics course, as part of our 2nd Master in Industrial Engineering at HELHa, Mons (Belgium).

Step 1: Materials

To carry out this project, we tried to use as many recycled materials as we could. We only bought a few items : the electronic components.

Here is what you would need to recreate this project :

  • 1 water tank
  • 1 heating resistance
  • 1 circulating pump
  • 1 heat exchanger
  • 1 fan
  • 1 Raspberry Pi
  • 2 heat sensors
  • Relays compatible with the Raspberry Pi
  • Electrical cables
  • Water hoses
  • Water

Step 2: Hydraulic Part

To begin the construction of this model, you will need a tank as big as possible to contain both water and an electrical resistance. For our project, we chose recycled elements such as an old big metallic pot (first picture) and an old water heater resistance (second picture).

To ensure the efficiency of the heating cycle, the assembly of the tank and the heating resistance is probably the most important part.
In order to realize it , you will need a circular hacksaw to cut through the steel of the tank. Make a hole big enough to allow the resistance to fit in the tank but small enough so that the two bases can be one against the other. To avoid water losses, you will need to make the construction insulated from water leaks. That is why you will have to put a rubber band between the two elements. We carved ours from an old rubber piece and fixed it to the tank, as you can see on the third picture.

You can now drill through the element to prepare the hole for the bolt that will maintain the tank and the electrical resistance together.
When this step is done, connection valves have to be added to the model. You need to drill two holes at the top and at the bottom of the tank for the water outlet and inlet. Just as for the previous hole, you can use a circular piece of rubber cut with a cutter to make the assembly more insulated. For example, these valves are commonly used in family houses to have a water outlet for the garden. Therefore, they are easy to find.

Now the tank is fully ready (fourth picture). You can connect the water pump to the inlet valve which is the upper one. Just as the entire project, the pump is also from recycling. It is an old circulation pump of a domestic installation. It is equipped with the same diameter as the tank tip fast join. It allows own-makers to connect each hydraulic element easily with garden flexible hydraulic pipes. You will only need a female tip fast join for the tank side. For the pump side, you will need a clamp around the flexible pipe. These elements are on the last three pictures.

Now, you can assemble the pump with the inlet tank valve and check the next part to know how to connect the pump to the heat exchanger part.

Step 3: Aeraulic Part

This part will describe the way that the air is heated and blown in order to warm up your room.

First you will need the two main parts of the aeraulic system: the air fan blower (first picture) and the heat exchanger (second picture). These two items are recycled parts, the fan was used in a boiler and the heat exchanger comes from a car. The purpose of our project was to reduce as much as possible its price by using old but still useful components.

Then the building step is to assemble these two parts. You need to build a conduit for the air which will be flowing through the heat exchanger. For that, you can use simple pieces of wood board to connect both parts. The construction needs to be as insulated as possible to avoid air loss. For this, duct tape can be used to insulate the box (third and fourth pictures).

When this step is done, the water pump (fifth picture) can be added to the set up after the heat exchanger. To do so, you can use a piece of hydraulic hose that can be found in everyone’s garden. This way, the tank can be connected to the exchanger then to the pump and finally water can come back to the tank thanks to the last coupling between the pump and the top of the tank.

Step 4: Software

The computer code is divided into 3 main parts:

The first one is the declaration of the library and GPIO (General Purpose Input/Output). In this brief part, you have to import the time and GPIO library. After that you can set up 3 GPIO which are the 3 electrical parts of the project controlled by relays.

You can see the different Pins on the Raspberry Pi on the picture.

We selected 3 GPIO out of them: pin 11 for the resistance, pin 13 for the pump and pin 15 for the fan.
The second part is the introduction of functions: there are two functions. The first one will allow you to open, read and close the temperature file. The second one will allow you to collect the temperature of the sensor on a variable called temperature. The name of the sensor 1 (28-01142fbcd608) is used for the temperature of the water tank and the sensor 2 (28-02131a437caa) is used for the temperature of the room. They are obtained before running the computer code.

The third part is the while loop and the conditions. This loop will allow you to obtain the temperature of the sensor every two seconds. It takes the number of the variable temperature and displays the temperature on the screen every two seconds. There are four conditions for the project to work properly. The first one is the initial condition : if the temperature of the water tank is under 50 degrees Celsius the resistance must be activated. The second condition is active all the time : when the water temperature is higher or equal to 45 degrees Celsius, the resistance must be deactivated, as well as the pump and the fan to warm up the room. After that, for the third condition, when the temperature of the room reaches 25°C, the fan must be deactivated. The last condition is about the room too, when the temperature of the room reaches 22°C, the fan must be activated again to keep a good temperature into the room.

You can find our code here :