💧 Fan coil unit and fan radiator powered by the energy of flowing water
Let’s start with a simple radiator (heater) with a fan driven by the energy of the heating medium flow. A fan coil unit is an extension of this system with additional functions.
The centerpiece is that the heating medium itself sets the fan in motion. Our radiator therefore works without an external electrical supply. We assume the heating medium is water. The fan shaft is coupled to a turbine installed inside the medium circuit, so it is the flow of the heating medium that drives the fan.
To limit, or rather eliminate, the risk of water leaks, I recommend coupling the fan to the water turbine through a magnetic coupling. The fan is then completely separated from the turbine: the turbine shaft and the fan shaft do not touch, no moving shaft has to be sealed, and so there is no risk of leakage. What remains is the effect of the rotating magnets on the housing, i.e. eddy currents. This can of course be solved, for example by using aluminum or composite parts near the moving magnets, but that is not the point here.
This raises the heating output with a smaller radiator, and the fan is powered from the heating medium circuit. Room temperature can be controlled with a thermostatic head or with actuators connected to a control system, as we often see in systems with radiators and chilled beams, or in underfloor heating. The solution with a thermostatic head is the most simplified one.
🔌 When is power needed?
A thermostatic head needs no power, so an ordinary radiator with such a fan can work completely analog. Power is only needed by a control head (actuator):
- in a fan coil unit, which has heating and potentially also cooling, i.e. two independent valves,
- in a radiator connected to an energy management system.
The source of electricity can be a small generator on the turbine or, independently, a battery. Best of all would be a combination of both: a battery recharged from the flow of the medium.
👍 Advantages of a “wireless” fan radiator
- Smaller radiators with the same output.
- Ability to work at a lower medium temperature, which is extremely important with a heat pump, especially in older buildings.
- New aesthetic and design possibilities thanks to the smaller size and forced air circulation, e.g. small radiators under a windowsill or high on a wall, with the air blown downwards.
- Faster air heating thanks to forced circulation.
- Forced circulation of warm air quickly gives the feeling of a heated room.
- Ordinary mechanical thermostatic heads (no power) or simple wireless control heads can be used.
⚠️ Disadvantages of a wirelessly powered fan radiator
- The fan is an additional source of noise, especially after long use without cleaning and maintenance.
- Increased flow resistance in the hydronic system.
- Maintaining the rotor is fairly simple, but the fan has to be cleaned periodically.
- The water in the circuit has to be kept clean. In plastic piping systems that is easier, and a local strainer can be installed before the unit.
🌡️ Additional functions
Extension: a motion sensor powered by the generator or the battery detects presence and raises the heating parameters. After a longer period without movement, e.g. when we leave for work or sleep, the radiator maintains a standby temperature.
🌀 Wireless fan coil unit powered by the energy of the medium flow
Thanks to the water drive, fan coil units will be quick and simple to install and configure, and at the same time they will solve many operating problems, such as fan failures and noise.
- The fan is driven by the energy of the water flow. The fan shaft is coupled to a turbine installed inside the heating/cooling water circuit, and the drive reaches the fan through a magnetic coupling, which limits the risk of leaks.
- Wireless communication of the fan coil units simplifies installation. A fan coil unit has separate heating and cooling valves, so its control head needs power. You can either bring in a power supply, or power the control from the energy of the water: the battery charges while the fan coil unit is idle and water flows through the circuit.
- If the flow from the building circuit is insufficient, an additional circulation pump can be installed on the connection. A local mixing loop (its own heat exchanger, its own circuit and pump) is recommended here. A dedicated circuit will always ensure proper supply for every fan coil unit or fan radiator.
🔋 Advantages of a “wireless” fan coil unit
- Quick and cheap installation thanks to completely eliminating electrical connections in the variant with wireless controllers.
- Faster installation thanks to fewer electrical wires in the variant with wired controllers.
- Safe voltage generated inside the fan coil unit itself, with no supply cables, which allows operation e.g. in high humidity.
- Sparking can be completely eliminated, which allows use in explosion hazard zones.
🔧 Disadvantages of a “wireless” fan coil unit
- Greater flow resistance in the system, which has to be taken into account in hydraulic calculations.
- Higher costs and fairly high complexity in the wirelessly powered version.
- Condensate must be drained by gravity. Powering a condensate pump is possible, but it requires a higher generator output and battery capacity, which is why a gravity drain is recommended.
- The fans are sensitive to contamination and have limited output because of the magnetic coupling, so they need periodic cleaning.
Watch the full explanation on video: Fan coil without electricity? A fan driven by the flow of water (synthetic voice-over).
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