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Fan coil units are terminal units that find wide application in tertiary, commercial, hotel and hospital environments and, in general, in medium to large buildings.
By means of fan coil units, a hydronic system for space heating and cooling is realized using small-sized terminals for forced convection heat exchange. This is provided by one or two coils for water-to-air heat exchange, a fan unit and the actuating devices (2- or 3-way valves with electrothermal or servomotor actuation) to regulate the flow rate of heat transfer fluid to the exchange coil. Some versions can be equipped with an electrically powered auxiliary heating coil.
Machines with traditional 3-speed discrete fan units have been joined by versions with brushless motor and inverter board that allow continuous control of fan speed by means of 0-10V control voltage. In terms of construction, fan coil units can take different forms: cabinet or for recessed mounting in the ceiling or wall; ceiling versions can be stand-alone or connected to air ducts arranged in the plenum.
The application examples show two different and very common system configurations.
2-pipe distribution
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| Ekinex devices | Other system components |
| A) Room thermostat EK-EP2-TP | 1) Fan-coils units |
| B) Actuator-controller for fan-coils EK-HA1-TP | 2) Valve with ON / OFF servomotor |
| C) NTC temperature sensor (contact) EK-STC-10K-3435 | 3) Heat exchange battery |
| D) NTC temperature sensor (immersion) EK-STI-10K-3435 | 4) Fan group |
| 5) Contact for condensate drip tray | |
| 6) Window contact | |
| 7) Thermal generator (warm fluid) | |
| 8) Thermal generator (cold fluid) | |
| 9) Boiler room manifold (flow) | |
| 10) Boiler room manifold (return) |
Control with Ekinex
In the first case (example I), the fan coils (1) are equipped with a fan unit with 3 discrete speeds and connected to a 2-pipe heat transfer fluid distribution system.
In the heat exchange coil (3) either hot fluid or cold fluid circulates alternately and the inflow is controlled by the valve (2). The room temperature is controlled by means of EK-EP2-TP room thermostats (A) and EK-HA1-TP fan coil actuators (B). To the room thermostats (A) are connected window-opening contacts (6) and EK-STC- 10K-3435 contact temperature probes (C), while to the actuators (B) are connected condensate drip tray contacts (5) and EK-STI-10K-3435 immersion temperature probes (D) arranged on the flow pipe of the heat transfer fluid.
In this application, the switchover between heating and cooling can take place automatically by measuring the temperature of the heat transfer fluid arriving from the heating unit via the immersion temperature probe (E) connected to an actuator inlet (B). Alternatively, Ekinex devices can receive the switching from the bus (centralised manual switching mode).
4-pipe distribution
.svg)
| Ekinex devices | Other system components |
| A) Room thermostat EK-EQ2-TP | 1) Fan-coil unit |
| B) Actuator-controller for fan-coils EK-HC1-TP | 2) Valve with ON / OFF servomotor (warm fluid) |
| C) NTC temperature sensor (air) EK-STL-10K-3435 | 3) Heat exchange battery (warm fluid) |
| D) Presence sensor EK-Dx2-TP | 4) Valve with ON / OFF servomotor (cold fluid) |
| 5) Heat exchange battery (cold fluid) | |
| 6) Contact for condensate drip tray | |
| 7) Window contact | |
| 8) Thermal generator (warm fluid) | |
| 9) Thermal generator (cold fluid) |
Control with Ekinex
In the second case (Example II), the fan coils (1) are equipped with two heat exchange coils (3, 5) and a fan unit with a brushless motor controlled by an inverter board. The units are connected to a 4-pipe heat transfer fluid distribution system.
With this type of distribution, if both fluids are available from the thermal power plant, there can be heated and cooled rooms in the same building at the same time; the inflow is controlled by two valves with ON / OFF servomotor (2, 4).
Room temperature control is by means of EK-EQ2-TP room thermostats (A) and EK-HC1-TP fan coil actuator-controllers (B), which have the required 0-10V voltage output to continuously control the fan speed, achieving all the advantages of these terminals: more precise response to changing heat loads, greater temperature stability, reduced noise and high efficiency even at part load with consequent reduction in power consumption. Temperature attenuations can be recalled automatically in the absence of people, thanks to the EK-SG2-TP-P (D) real presence sensor.
Automatic switching between heating and cooling, based on measured temperature and setpoint values, can prove advantageous in this application. Alternatively, and with fluids both available, switching can also be done locally on the room thermostat in manual mode.
In both cases numerous utility functions for comfort, energy efficiency, and system maintenance can be added depending on the needs of principals and end users: a few examples are given below.
Comfort
The contact temperature probe arranged on the heat exchange coil allows the fan unit (4) to be started only when the temperature of the heat transfer fluid is comfortable for users (warm-start). If the probe is missing, the function can also be carried out by setting a simple start-up delay. (Ex. Application I) In rooms with great height and volume (lobbies, gyms, commercial rooms), air stratification can occur, wasting energy and discomforting occupants. To limit this effect, a temperature probe (C) is connected to the thermostat (A) and a maximum temperature gradient not to be exceeded is configured. (Ex. Application II)
Energy saving
The window-opening contact (6) detected by a thermostat input (A) automatically determines the switching of the operating mode from comfort to building protection, avoiding dissipation of heating and cooling energy outside the building.
Maintenance
The actuator-controller (B) has an operating hours counter that increments the count when the fan unit (4) is at least in first speed. When the set time interval is reached, a signal for replacement of the fan coil filter is activated.