WATER-BASED RADIANT HEATING Warm water-based radiant heating displays different variants as a function of the hand-over conditions of the structural substrate, which is usually a concrete floor or deck, with regard to the following needs: ► ►

Incorporation of a levelling layer to provide flatness and level for the installation of the radiant heating system Inclusion of a specific layer for housing particular installations beneath the radiant heating

In addition to these variants, European standard EN 1264 establishes two types of construction solution, depending on whether a floating floor screed is to be laid on the heating system: Type A: Thermal insulation and a protection layer are laid on the flat and levelled substrate. Serpentine systems are installed for water circulation with supporting fasteners or using panels with studs, which serve as insulation while securing the pipes on the protection layer. Finally, a screed is installed that will receive the flooring. Type C: This incorporates a decoupling layer on a first layer that houses the pipes, and a floating floor screed that receives the flooring. There is a third type (B), in which the pipes are flush with the thermal insulation protection layer, and are embedded in the insulation. Conductive plates (thermal diffusers), the protection and decoupling layer, and the floating floor screed are installed on the pipes.

Type A underfloor heating system with water pipes, according to EN 1264

A variant of the Type A heating system according to EN 1264, in which the pipes are embedded in the floating floor screed

Type C heating system according to EN 1264 with floating floor screed on the radiant floor. The separating layer prevents contact of the thermal insulation with the mortar that could filter through the joints of the studded panels

Electric radiant floor heating system

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The fundamental components of a radiant heating system are the pipes and their fastenings, the insulations, the radiant floor and, where appropriate, the floating floor screed installed on the radiant floor, and the type of installed flooring. System complements include: perimeter bands, separating/protection layers, load distribution and/or anti-crack lath, and intermediate movement joints. The system is rounded off by the cold- and/or heat-generating equipment and the collectors/distributors.

Cross-section illustrating the components of the radiant floor heating system and the juncture with an abutting construction element

Pipes Although the first radiant heating installations were made with copper and galvanised steel pipes (the latter with corrosion problems), current demand has tended to thermoplastics since their performance is assured in the middle term, and they are competitive in price and easy to install. These principally involve cross-linked polyethylene [PE-X], polypropylene copolymer [PP-c], and polybutylene [PB]. They are all flexible, resistant to temperatures above 100 ºC and also to the pressures at which they work. Some are treated in order to mitigate their permeability to oxygen. Their low resistance to ultraviolet radiation is not a drawback, since they are completely embedded in the radiant floor. Cross-linked polyethylene displays the greatest thermal conductivity [0.38 W/m•K, compared to 0.22 W/m•K of the other two], and has an intermediate flexibility [750 N/mm2 elastic modulus] between polypropylene (more rigid) and polybutylene (more flexible). It is currently the most widely demanded thermoplastic material because of its value for money. The pipe cross-section is a feature to be decided in the design phase. Pipes are usually marketed with cross-sections ranging from 12/16 mm to 16/20 mm or larger, in rolls of 50, 120, and 200 metres (the diameter notations refer to the inner diameter/outer diameter, thus also indicating pipe thickness).

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The three types of pipes are cross-referenced to standards that specify the characteristics they must conform to. The following are common requirements: Type of pipe Cross-linked polyethylene Polybutylene Polypropylene

Reference standard

►

EN ISO 15875 EN ISO 15876 EN ISO 15874

► ► ► ►

Minimum pipe wall thickness according to the standard (in mm) Thickness Diameter D 1.1 ≤ 12 1.5 12 < D ≤ 16 1.9 > 16

Class 4, according to article 4 of the standard Minimum durability of 50 years Minimum service pressure of 4 bar Minimum pipe wall thickness according to the table shown Outer diameters between 12 and 25 mm

Twelve mm pipes are used in domestic housing and small building areas. In large building areas, pipes of at least 16/20 mm are used to avoid excessive load losses.

It is key rule that the circuit embedded in the radiant floor shall contain no threaded joins, to prevent leaks by those weak elements. Although guides and clips were formerly used to secure pipes in certain design arrangements, nowadays panels with profiles (studs and projections) are used that allow serpentine pipes to be secured (exceptionally with the aid of harpoon clips in sharp bends) and to elevate them slightly so that mortar can penetrate into the part under the tubes, completely enveloping them. With a view to preventing condensations and not penalising the energy efficiency of the system, it is further a key rule that empty spaces and air entrapment are to be avoided, by all means, in the radiant floor. This objective justifies the use of fluidised (cement or calcium sulphate) mortars, as opposed to conventional mortars (industrial mortars or mortars prepared in situ) and semi-dry mortars for industrial use.

Arrangement of tube-bearing panels on the thermal insulation protection layer. SOURCE: [1] Saunier Duval®

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Installation of the pipes, pressed between the panel studs SOURCE: [1] Saunier Duval®

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Installation of clips with sharp bends to assure pipe securing. SOURCE: [1] Saunier Duval®

View of the installed serpentine system according to the design layout without any joint or threaded join. SOURCE: [1] Saunier Duval®

The thermal insulation layer Since radiant floor surface heating needs to heat the building area uniformly by radiation and convection from the radiant floor, a thermal insulation layer is required that mitigates heat propagation downwards through the deck, concrete floor, or first layer housing fittings and pipes. This insulation layer is resolved with sheets or mats of different materials in one or more layers. For the sake of installation simplicity, a single high-density rigid layer is used that not only addresses the thermal insulation requirement but also the direct installation of the pipes. However, in certain project designs with particular thermal insulation, soundproofing, and load resistance requirements, it is necessary to use different materials. In general, expanded high-density polystyrene sheets (Porexpan) are used (exceeding 20 kg/m3), with a view to assuring top layer stability. Rigid polyvinyl chloride (PVC) or polyethylene panels of very high density are kept for floors subject to important live and dead loads. The first important magnitude to be taken into account is the thermal conductivity of the material [W/m•K], as a function of the thermal conditions of the building area or space beneath the radiant system. The following table provides certain characteristics of the different types of expanded polystyrene. CHARACTERISTICS OF DIFFERENT TYPES OF EXPANDED POLYSTYRENE Characteristic Nominal density [kg/m3] Minimum density [kg/m3] Thermal conductivity at 0 ºC [W/m•K] Thermal conductivity at 20 ºC [W/m•K] Compressive strength [kg/m2]

I 10 9 0.044 0.047 4000

II 12 11 0.042 0.045 4000

III 15 13.5 0.037 0.040 5000

IV 20 18 0.034 0.037 9000

V 25 22 0.033 0.035 12000

SOURCE: [1] ATECYR

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According to standards EN 1264-3:1997 and EN 15377-2:2008(E), the thermal resistance required for the insulation layer is calculated from the following equation: S Rλ ,ins = ins , where:

λins

Rλ,ins is the thermal resistance of the insulation [m2•K/W] Sins is the thickness of the insulation [m] λins is the thermal conductivity of the insulation [W/m•K] For radiant floor systems that use flat insulation panels [Figure A], Sins is equal to panel thickness. For formed insulation panels (with pipes embedded in the surface of the insulation and conducting layer) [Figure B], effective thickness Sins is calculated from the expression:

Sins =

Sh • (T − D) + Sl • D T

this being the weighted measurement as a function of the relative surface areas of the different thicknesses.

Figure A

Figure B

Standard EN 1264-4:2001 establishes a minimum thermal resistance for the thermal insulation according to the underlying building area, which is summarised in the following table. MINIMUM THERMAL RESISTANCE OF THERMAL INSULATION ACCORDING TO EN 1264-4:2001

Thermal resistance [m2•K/W] [1]

Underlyin g heated building area

Non-heated or intermittently heated building area. Floor in contact with the ground[1]

0.75

1.25

Air temperature of the underlying building area Nominal design temperature Td ≥ 0ºC 0ºC >Td ≥ -5ºC -5ºC > Td ≥ -15ºC 1.25

1.50

2.00

When the water table is 5m or less deep, the value of the thermal resistance shall be increased

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The simplest and fastest installation on flat and levelled floors is achieved with panels that already incorporate pipe-securing elements, have tongue-and-groove joints and, by their density and thickness, conform to thermal resistance requirements. Under these premises, and if the insulating material needs no protection, the Type A radiant flooring system will only require installation of the radiant floor screed on the insulation, with fully embedded pipes. When the thermal resistance required with pipe-bearing formed panels is not achieved, or a certain degree of sound-dampening is required, the following layers are arranged on the flat and levelled floor. ► ► ►

Soundproofing, where appropriate The necessary layer(s) of thermal insulation for the required thermal resistance A protection layer against the penetration of mortar, when the pipe-bearing panels have no tongue-and-groove joints, using a polyethylene film at least 0.15 mm thick

When the Type C radiant flooring system is adopted, the following are installed on the pipe-bearing panels: ► ► ►

A first radiant floor screed to embed the pipes A decoupling layer, consisting of two 0.15-mm polyethylene films A floating floor screed, with a compressive strength of 20 N/mm2 after 28 days

French standard NF DTU 65.14 (September 2006), based on EN 1264, is explicit in the selection and characterisation of the materials involved. For the thermal insulations it requires: ► ►

For Type A radiant systems, insulations of class SC1 a, SC1 b, or SC2 a. If these are arranged in a single layer, they shall also be class Ch. For Type C systems, the insulations shall be class SC1 a Ch or SC1 b Ch

Other system elements Radiant floor heating systems include other complementary elements: perimeter insulation and deformation bands, laths arranged in the radiant floor screed as load distribution or anti-crack features, and intermediate movement or dividing joints. Perimeter insulation bands, resolved with thermal insulation material, are installed at all system junctures with abutting construction elements (building envelopes, columns, partitions, etc.). They not only prevent thermal and acoustic bridges, but also allow free horizontal movement of the radiant floor and, where appropriate, of the floating floor screed. The standard requires 5-mm minimum thickness for these perimeter bands, though it is recommended that they should be 10 mm thick in building areas with surface areas larger than 25 m2.

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In relation to reinforcing lath, in some national standards (like the already cited NF DTU 65.14, Part 1), this features more as an anti-crack than as a load distribution element. For Type A radiant floor systems, lath of 50x50 mm and a minimum mass of 650 g/m2, or 100x100 mm grid and a minimum mass of 1000 g/m2 are specified. For Type C radiant floors, lath of 100x100 mm and a minimum mass of 325 g/m2 are specified. This anti-crack lath is located either beneath the tubes, in Type A systems with flat thermal insulation (without studs), at a distance of at least 15 mm from the tubes, or above the tubes, in the middle of the radiant floor, which shall have a thickness of at least 40 mm from the top of the tubes. Standard EN 1264-4:2001 establishes the arrangement of intermediate movement or dividing joints, which generate independent stretches with a maximum surface area of 40 m2 and largest side of 8 m, when it is intended to cover the radiant floor with modular rigid flooring. In Type A radiant floors, these joints penetrate down to the anti-crack lath arranged on the pipes or to 1/3 of the layer thickness when lath is not installed. In Type C radiant floors, the division joints reach the decoupling layer. The serpentine system layout shall observe the stretches divided by the movement joints. The tubes can only cross these joints when the tubes are connecting tubes, in which case they shall be protected with a flexible insulation at least 30 cm long. On substrates with structural movement joints, these joints shall be observed in their entire length and width, the pipes being arranged such that only the connecting pipes, with the appropriate protection, cross these joints.

Dimensioning of a radiant heating system Standard EN 1264-3 (August 1997) already established an approach to the basic principles, boundary and limit conditions, and design [thermal flux density, output temperature, and flow rate] for radiant floors; however, it is standard EN 15377 that establishes, in its different parts, the design conditions of the different hot/cold radiant floor surface systems using embedded pipes with circulating water: ► ► ►

EN 15377-1 (June 2008), for the determination of the nominal design heating and cooling capacity EN 15377-2 (June 2008), devoted to design, dimensioning and installation EN 15377-3 (October 2007) [published in Spain as UNE-EN 15377-3 (October 2008)], to promote the use of renewable energy sources in these embedded heating/cooling systems, and to provide a calculation method for the use of thermo-active building systems (TABS)

In turn, standard EN 13577 is complemented with a series of standards that have been published in recent years on energy efficiency in buildings [EN 15251, EN 15255, EN 15265, EN ISO 13370,…].

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Given their effect on comfort and on the energy efficiency of buildings and building areas, radiant surface heating/cooling systems deserve greater attention from Architects and Designers, there being a specialised commercial offer in these systems. The Atecyr publication on the ‘Radiant floor system DTIE 9.04’[1] is a good introductory reference document on the method of dimensioning (chap. III) and laying out radiant systems (chap. IV). It also provides a calculation example of a radiant heating/cooling system (chap. V). [Access to the book library card] The following pictures illustrate two pipe layouts, based on the need or not to establish a thermal output difference corresponding to areas with a greater or smaller thermal load.

Double serpentine layout to achieve greater temperature uniformity in the floor. SOURCE:[1] ATECYR

Differential thermal load distribution, with pipe concentration under the large window SOURCE:[1] ATECYR

A schematic illustration follows of radiant floor cooling/heating.

Elements of a radiant heating and cooling installation. SOURCE: [1] ATECYR. SAUNIER DUVAL® system

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Radiant floor and floating or levelling floor screed In view of the general nature of the references to the characteristics of these radiant floor system layers in standard EN 1264, one needs to resort to national standards to obtain more precise references. This part focuses on radiant floor screeds, since floating or levelling floor screeds shall conform to all the requirements already described in another section of this documentation [floating floor screeds]. French standard NF DTU 65.14 (Part 1) [September 2006] establishes the following requirements for floors that house pipes: ►

►

►

Use of industrial mortars of class C20/25 [EN 206-1], with appropriate consistency for full coverage of the tubes, with the use of plasticisers or superplasticisers [EN 934-2] compatible with the nature of the tubes Use of mortars prepared in situ, with cements CEM I-V [EN 197-1] of resistance class 32.5 N or 32.5 R, 42.5 N or 42.5 R, with cement/aggregate proportioning of 350 kg/m3 and use of plasticisers compatible with the nature of the tubes [EN 934-2] Installation of the floor screed with fluidised cement or calcium sulphate mortars, with the characteristics laid down in standard EN 13813, with a minimum spreadability of 220 mm. The use of anhydrite floor screeds is limited to dry building areas with low damp levels.

The French standard establishes a minimum thickness for this floor of 45 mm, while also fixing certain minimum thicknesses as a function of the type of thermal insulation beneath the pipes: ► ►

Type A radiant floors: 35 mm with insulations SC1 a or SC1 b and 40 mm with insulations SC2 a [SC2 b insulations are not allowed] Type C radiant floors: 20 mm with insulations SC1 a or SC1 b [SC2 insulations are not allowed]

It is generally recommended that the radiant floor thickness above the flush level of the tubes should be at least 30–35 mm in Type A. In the Type C system, the thickness of the floating floor screed on the decoupling layer depends on the type of mortar used and the compressive and bending strength characteristics that the floor demands. A minimum compressive strength is laid down of 20 N/mm2 after 28 days. Both the radiant floor and the floating or levelling floor screed require a thermal conductivity of 1.2 W/m•K or higher.

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Installation of the floor screeds Before the installation of the floor screed, once the circuits have been completed, these are subject to general cleaning with mains water, this taking place prior to the pressure trial, under stricter conditions than those of the trial run, with a view to assuring watertightness of the system. The indications of the Regulations on Thermal Installations in Buildings [RITE] are applied for this purpose. The watertightness trial includes previous purging of the circuit. When there is frost risk, antifreeze shall be added to the circuit water, in a variable quantity depending on the temperature that can be reached by the environment, and outer pipe diameter. After this operation, the radiant floor can be installed in its different modes, according to the layers involved. A first layer can be laid, embedding the pipes, this then being completed in a second step by the thick-bed installation of the modular rigid flooring with cement mortar. The floating floor screed is also laid in two steps when anti-crack lath needs to be installed 15 mm above the pipe plane. The conventional or semi-dry mortars pumped up to the storey are spread longitudinally to the pipes in order not to leave any voids at the pipe sides or under the pipes. The floor screed is then mechanically smoothed/floated to achieve flatness and final level for the modular rigid flooring or other finish material. The compaction produced by mechanical floating also avoids the formation of voids and air entrapment. In the Type C radiant floor, screed layer thickness above the pipe plane is at least 20 mm. The decoupling layer and floating floor screed are then installed on top of the radiant floor. After mortar application, the maturing times must be observed: 3 days before treading on the layer, three weeks before subjecting it to loads, and four weeks or more (depending on environmental conditions) before the flooring is installed. Radiant floor hand-over conditions, in regard to flatness, are specified in certain national standards, and depend on the tile installation mode (thick bed or thin bed) and whether a floating floor screed is to be laid. The handed-over gross substrate, on which the radiant floor system is to be installed, shall display flatness with deviations that do not exceed 7 mm in 2 m, in all directions. The current use of fast-maturing, anti-crack fluidised mortars notably simplifies the installation of these layers, assuring system quality and durability. The following pictures illustrate the industrial installation process of a radiant floor with calcium sulphate mortar (anhydrite).

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Setting the radiant floor height

Verification of mortar flowability. Minimum spread of 200 mm

Detail of the complete embedding of the tubes and studs that secure them

Spreading the mortar pumped on to the storey

being

Rodding of the fluidised mortar to Carbide hygrometer for the reach optimum levelling and verification of floor residual flatness moisture content

In anhydrite floor screeds in particular, but also in cement mortar floors, it is advisable to verify moisture content with a carbide hygrometer, in order to assure adequate screed maturity and stability before heating start-up and the installation of modular rigid flooring. In anhydrite floor screeds, a residual moisture content shall be reached of 1% at most before those operations, and 2% maximum residual moisture content in the cement mortar floors. The newly installed radiant floor must be protected with polyethylene film against adverse climate conditions, particularly when anhydrite floor screeds are involved [direct exposure to sunlight, air currents, and extreme conditions of environmental dryness and/or high temperature]. The film also protects the floor screed from dust and the disaggregated materials of other trades, avoiding preliminary cleaning before the adhered floor tile installation. For the first heating start-up, after due observation of the minimum maturing times of 7 days for anhydrite floor screeds and 21 days for cement mortar floors after installation, the following procedure is followed: ► ► ►

Fill the circuit with cold water up to working pressure [1-2 kg/cm2], verifying that the circuit is complete purged Start up the heating until the water reaches 25 ºC and hold that temperature for 3 days, adjusting the circuit flow rate After that first phase, raise the water temperature by 5 ºC/day, up to the peak temperature foreseen in the design [45–50 ºC].

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► ►

Hold the circuit at that peak temperature for at least 4 days Progressively cool the radiant system to ambient temperature during a further 3 days before initiating the flooring installation

Tile installation The thermal resistance of a radiant heating system finish shall not exceed 0.15 m2•K/W. However, the optimum thermal conductivities of ceramic and natural stone floorings make these materials optimum heat diffusers while they also contribute to the thermal inertia of the system as heat accumulators. The construction of radiant floors and floating floor screeds with fluidised mortars leads to the option of adhered thin-bed tile installation with deformable cementitious adhesives [of the C2 S1 type according to EN 12004] as the safest solution when faced with an intermediate layer that has a slightly unstable condition as a result of expansion and shrinkage phenomena caused by heating and/or cooling. Radiant heating also allows thick-bed fixing with mortar, in the ‘on-decoupledscreed’ mode, though it increases the system thickness. The installation of modular rigid flooring on a radiant floor heating/or cooling system requires tile installation with minimum open joints of 5 mm, thorough setting out as a function of the intermediate movement joints (should they be necessary), and the selection of medium-sized tiles. It is also recommended to use CG 2 grouts [EN 13888], with deformable properties.

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