• Floor radiant system
  • Floor radiant system

Floor radiant system

HVAC applications and controls

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The floor radiant system is a widespread hydronic system for heating and cooling rooms.

The heat transfer fluid circulates inside circuits made up of plastic pipes placed under the surface covering of the floor; in the most common version, the pipes are laid on an insulating layer and embedded in the cement base. The system is invisible and uses the whole surface of the floor as a large terminal for the heat exchange prevailing at radiation. In both seasons the system works with a very limited temperature difference between the heat transfer fluid and the room air; for this reason it is also defined as a“low-temperature difference” heating and cooling system.

The system shown in the example is intended for a residential building. It is a combined system, i.e. it combines the radiant floor panels with one or more fan-coil units, mainly for the integration of sensible loads in cooling conduction mode.

Ekinex devices Other system components
A) Time / astronomical digital switch EK-TM1-TP 1) Window contact
B) GPS module EK-GPS-1 2) Fan-coil unit
C) Actuator-controller for fan-coils EK-HC1-TP 3) Valve with ON / OFF servomotor
D) NTC temperature sensor (contact) EK-STC-NTC-3435 4) Access point LAN Wi-Fi
E) Room thermostat EK-EQ2-TP 5) Switch
F) NTC temperature sensor (air) EK-STL-NTC-3435 6) Smartphone with App delégo (Apple iOS or Android)
G) Server Delégo EK-DEL-SRV-... 7) Circolating pump for unmixed circuit
H) Mixing group controller EK-HH1-TP 8) Mixing group
I) NTC temperature sensor (external) EK-STE-NTC-3435 9) Mixing valve with servomotor
L) TC temperature sensor (immersion, flow) EK-STI-NTC-3435 10) Circolating pump for mixed circuit (floor radiant system)
M) NTC temperature sensor (immersion, return) EK-STI-NTC-3435 11) Distribution manifold for low-temperature circuits
N) Actuator-controller for electrothermal drives EK-HE1-TP 12) ON / OFF electrothermal actuators
O) Touch-panel Delégo EK-DEL-xPAN... 13) Condensation sensor
  14) Thermal generator (warm and cold fluids)
  15) Boiler room manifold (flow)
  16) Boiler room manifold (return)
Control with Ekinex

The EK-TM1-TP time / astronomical digital switch (A) ensures that the system is allowed to operate according to predefined time scheduling and is constantly synchronised with date and time by the (optional) GPS module EK-GPS-1 (B).

The need to produce heat transfer fluid at two different temperatures for the combined system (consisting in floor radiant panels / fan-coil units) is solved by controlling a mixing group with the EK-HH1-TP controller (I). The device controls a mixing valve and a circulating pump; by means of the EK-STI-NTC-3435 sensors (M, N) it can measure the flow and return temperatures of the heat transfer fluid.

On the unmixed circuit it can also control, as required, a circulating pump (7) or a zone valve. The room air temperature is controlled by room thermostats EK-EQ2-TP (E), measuring temperature and relative humidity, in combination with actuators-controllers for electrothermal drives EK-HE1-TP (N) and actuators-controllers for fan-coils EK-HC1- TP (C). The thermostats are able to calculate and send to the bus the dew temperature; if the thermo-hygrometric conditions of the room are close to those critical for the formation of condensation on the cooled surfaces, it is possible to implement one of the several protection strategies provided by the ekinex® thermoregulation system (see table on the right); for example, recalibration of the flow temperature of the heat transfer fluid through the EK-HH1-TP controller (H).

The optional delégo (E) supervision allows the monitoring and control of the home automation system through an App for smartphones (6) and/or a Delégo touch-panel (F).

Two-stage system (main / auxiliary)

In the system configuration of the example, the room thermostat EK-EQ2-TP (E) allows you to easily realise a two-stage heating / cooling system. When the main stage consists of a radiant panel system, the high inertia (especially typical of the version with cement base), makes it rather slow in the start-up phase to achieve comfort conditions. In this case, it is possible to configure the fan-coils as an auxiliary stage; thanks to their much lower inertia, they contribute in the initial phase to quickly heat or cool the room and then stop their action when the difference between the measured and setpoint temperatures can be satisfactorily addressed by the main stage alone. The auxiliary stage works in automatic mode with a configurable offset with respect to the temperature setpoint set for the radiant floor (main stage).

 
 
Prevention of condensation in cooling conduction mode
 
In summer cooling operation, the latent loads (due to the increase in the humidity level in the room) are taken care of by the air handling integration. If this is not done satisfactorily, or in the event of a sudden change in thermohygrometric conditions (e.g. due to accidental stopping of the machines or opening of windows), additional safety measures must be taken to prevent or limit the formation of condensation on cold surfaces. The EK-EQ2-TP (E) room thermostats provide various active and passive protection strategies depending on the system configuration and the presence of home automation devices.
 
 
Type Mode Action
Passive
With condensation sensor (13) connected to an input of the room thermostat (E)
Closing of the circuit serving the involved room by means of the actuator (N)
With condensation sensor communicating with the thermostat (E) via KNX bus
Closing of the circuit serving the involved room by means of the actuator (N)
Active
Comparison between fl ow temperature (fixed design value, ETS parameter) and dew temperature calculated by the room thermostat (E)
Closing of the circuit serving the involved room by means of the actuator (N) when the flow temperature is lower than the dew temperature
Comparison between fl ow temperature (measured value received from the KNX bus) and dew temperature calculated by the room thermostat (E)
Closing of the circuit serving the involved room by means of the actuator (N) when the flow temperature is lower than the dew temperature
The dew temperature from the thermostat (E) is sent via KNX bus to the mixing group controller (H)
Calibration of the cold fl uid fl ow temperature by the controller (H) and maintenance of the opening of the circuit serving the involved room by the actuator (N)

 

Active protection is always preferable, as the intervention tends to prevent the conditions of formation of condensation, while passive protection intervenes when the formation of condensation has already begun.
 
Surface temperature limitation
In some cases it is advisable to limit the surface temperature when the radiant floor system is used as an auxiliary stage for heating; the dispersions to the outside of the building are handled by the main heating system, while the auxiliary stage works only to maintain the temperature of the floor at a pleasant level in the bathrooms of residential buildings or in the rooms of sports centers, spas, etc. This limitation is also included in the EN 1264 standard (Underfloor heating, Part 3) which defines the maximum allowed temperature (TSmax) for the surface of the floor from a physiological point of view as follows:
 
  • TSmax ≤ 29°C for areas of normal occupancy of the rooms;
  • TSmax ≤ 35°C for the peripheral areas of the rooms.