• Fan-coil systems
  • Fan-coil systems

Fan-coil systems

HVAC controls and applications

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Fan-coils are terminal units that are widely used in offices, shopping centres, hotels and hospitals and, in general, in medium-large buildings.

Fan-coils are used in hydronic systems for room heating and cooling, using small terminals for convection heat exchange (with prevailing forced effect). One or two batteries for water-air heat exchange, a fan unit and the actuating devices (2 or 3-way valves with electrothermal actuators or servomotors) to regulate the flow rate of the heat transfer fluid to the exchange battery provide for this.

Some versions can be equipped with an auxiliary heating battery powered by electricity. In addition to the units with the traditional 3-speed fans, there are also versions with brushless motor and inverter board that allow a continuous control of the fan speed by means of a 0-10V control voltage. From a construction point of view, the fan-coil units can have different shapes, such as cabinets for ceiling or wall mounting; the ceiling versions can be stand-alone or connected to air ducts installed in the plenum.

The application examples show two different and very common system configurations.

2-pipe distribution
Ekinex devices Other system components
A) Time / astronomical digital switch EK-TM1-TP 1) Fan-coils units
B) GPS module EK-GPS-1 2) Valve with ON / OFF servomotor
C) Room thermostat EK-EP2-TP 3) Heat exchange battery
D) Actuator-controller for fan-coils EK-HA1-TP 4) Fan group
E) NTC temperature sensor (contact) EK-STC-10K-3435 5) Contact for condensate drip tray
F) NTC temperature sensor (immersion) EK-STI-10K-3435 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 3-speed fan unit and connected to a 2-pipe heat transfer fluid distribution system.

In the heat exchange battery (3), warm or cold fluid circulates alternately and the flow is controlled by the valve (2). The room air temperature is controlled by room thermostats EK-EP2-TP (C) and actuator-controllers for fan-coils EK-HA1-TP (D). The room thermostats (C) are connected to the window contacts (6) and contact temperature sensor EK-STC- 10K-3435 (E), while the actuators (D) are connected to condensate drip tray contacts (5) and immersion temperature sensors EK-STI-10K-3435 (F) installed on the inflow pipe of the heat transfer fluid.

In this application, the switchover between heating and cooling can be carried out automatically, by measuring the temperature of the fluid arriving from the distribution by means of an immersion temperature sensor (F) connected to an actuator input (D). Alternatively, ekinex® devices can receive the switching control via bus (centralised manual switching mode).

4-pipe distribution
Ekinex devices Other system components
A) Time / astronomical digital switch EK-TM1-TP 1) Fan-coil unit
B) GPS module EK-GPS-1 2) Valve with ON / OFF servomotor (warm fluid)
C) Room thermostat EK-EQ2-TP 3) Heat exchange battery (warm fluid)
D) Actuator-controller for fan-coils EK-HC1-TP 4) Valve with ON / OFF servomotor (cold fluid)
E) NTC temperature sensor (air) EK-STL-10K-3435 5) Heat exchange battery (cold fluid)
F) Presence sensor EK-Dx2-TP 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 batteries (3, 5) and a fan unit with brushless motor controlled by an inverter board. The units are connected to a 4-pipe heat transfer fluid distribution system.

With this kind of distribution, if both fluids are available from the boiler room, there can be heated and cooled rooms simultaneously in the same building; the flow is controlled by two valves with ON / OFF servomotor (2, 4).

The room air temperature is controlled by room thermostats EK-EQ2-TP (C) and actuator-controller for fan-coils EK-HC1-TP (D) which have an output with the 0-10V voltage required for a continuous control of the fan speed, obtaining all the advantages of these terminals: more precise response to the variation of heat loads, better temperature stability, reduced noise and high efficiency even at partial load with a consequent reduction in electricity consumption. Temperature attenuations can be called up automatically in the absence of people, thanks to the presence sensor EKDF2- TP (F).

In this application, an automatic switchover between heating and cooling, based on measured temperature and setpoint values, can be advantageous. Alternatively, and with both transfer fluids available, the switchover can also be performed locally on the room thermostat in manual mode.

In both cases, several utility functions for comfort, energy efficiency and system maintenance can be added according to the needs of customers and end-users: a few examples are given below.

Comfort

The contact temperature sensor (E) installed 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 the users (warm-start function). If the sensor (E) is missing, the function can also be performed by setting a simple start-up delay. In rooms with big height and volume (atriums, gyms, commercial rooms), air stratification can occur, with energy waste and discomfort for the end-users. To limit this effect, a temperature sensor (E) is connected to the thermostat (C) and a maximum temperature gradient is configured that must not be exceeded.

Energy saving

The window contact (6) connected to an input of room thermostat (C) automatically switches the operating mode from comfort to building protection, avoiding the loss of heating and cooling energy to the outside.

Maintenance

The actuator-controller (D) is provided with an operating hours counter which increases the count when the fan unit (4) is set at least at first speed. When the set time interval is reached, a signal is activated to replace the filter of the fan-coil unit.

 

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