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

Control with Ekinex

The need to produce heat transfer fluid at two different temperatures for the combined system (radiant floor/ fan coil) is solved by controlling a mixing unit by means of the EK-HH1-TP controller (D). The device controls the mixing valve (9) and the circulator (10); by means of the two EK-STI-NTC-3435 probes (L, I) it can acquire the flow and return temperatures of the heat transfer fluid.

On the unmixed circuit it can also control either a circulator (7) or a zone valve as required. Room temperature is controlled by means of EK-EQ2-TP (C) thermostats, which can measure temperature and relative humidity, in combination with EK-HE1-TP (N) actuator-controllers for electrothermal drives and EK-HC1- TP (A) actuator-controllers for fan coil units. The thermostats are capable of calculating and sending to the bus the dew temperature; in case the thermo-hygrometric conditions of the environment approach those critical for the formation of condensation on the cooled surfaces, it is possible to implement one of the protection strategies provided by the Ekinex thermoregulation platform (see side table); for example, recalibration of the flow temperature of the thermovector fluid by means of the EK-HH1-TP controller (D).

Optional supervision using the Delégo Server (G) enables monitoring and control of the home automation system through an App for smartphones (6) and/or a Delégo touch-panel (M).

Two-stage system (main / auxiliary)

In the system configuration of the example, the room thermostat EK-EQ2-TP (C) 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 (C) 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)
Passive	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.