MANIFOLDS, PANELS AND INSULATION: THE COMPONENTS OF THE RADIANT SYSTEM

A guide to choice

Radiant floor, ceiling, and wall systems are one of the most viable solutions for heating and cooling residential and nonresidential buildings, including large industrial spaces. The use of radiant systems ensures high performance in heating and cooling with reduced energy consumption, uniform temperature without temperature changes or air movement, and a healthy and pleasant climate all year round. Technically, these systems consist of many components: insulating slab, manifold, piping and regulation are the main ones.

INSULANTION

The insulating slab for radiant systems must meet industry-specific standards (UNI EN 1264, UNI EN ISO 11855), e.g. it must be characterized by a certain thermal resistance according to the condition under consideration and it must have superior protection in the case of floors.

However, the insulating slab, in order to be CE certified, must also meet the harmonized standard for it.
CE marking requires initial tests to be carried out by a notified laboratory and factory production checks to be carried out during panel production.

The main standards involved are as follows:

• UNI EN 13163 for EPS expanded polystyrene insulation.
• UNI EN 13164 for XPS extruded expanded polystyrene insulation - UNI EN 13165 for PUR expanded polyurethane insulation
• UNI EN 13171 for wood fiber insulation.

MANIFOLD

The manifold is a very important element in the radiant system. There is no product standard related to the manifold, but if one wanted to provide a higher degree of assurance, general standards for hot and cold water pipes and fittings should be applied. For example, in the calculation of thermoplastic manifolds there is UNI EN 12293:2001, which describes the test method for evaluating resistance to temperature cycling.
For example, Eurotherm's SL collector was subjected to more than 5,000 temperature cycles by passage of pressurized water lasting 30 minutes as follows:

• 15 minutes at (20°C ±5°C)
• 15 minutes at (95°C ±2°C)

without reporting any visible leakage.

Another type of test involving manifolds involves pressure resistance, to check tightness at nominal pressure, which can be at 4 or 6 bar. For example, Eurotherm's Command Duo temperature control with Black line manifold was subjected to a pressure of 9 Bar without reporting any damage. The failure value was much higher than the rated pressure (around 36 Bar).

PIPE

Piping is perhaps the most important element of radiant systems, as it is the one that physically allows heat exchange between the fluid (water) and the environment through heating/cooling the material in which it is inserted.

POLYETHYLENE PIPING

Plastic piping is widely used for heating and domestic hot water systems because it offers a number of advantages, such as:

• long-term reliability (they are not subject to corrosion)
• light weight
• flexibility (especially appreciated in radiant systems)
• the low cost.

Polyethylene is material obtained from the polymerization of simple organic substances that have a double bond between carbon atoms. There are two types of polyethylene piping: cross-linked polyethylene PE-X and polyethylene PE-RT, which is characterized by greater resistance to high temperatures.

Butene is inserted into PE-X piping through a process called “cross-linking,” which aims to ensure that cross-links are established between the polymer chains.

Through cross-linking, a thermoplastic polyethylene becomes a thermosetting material, so it cannot be melted without undergoing chemical degradation. Depending on the type of regulation, one can distinguish:
 

• PE-X a, peroxide-crosslinked polyethylene (Engel method, Point à Mousson method, Daoplast method)
• PE-X b, silane-crosslinked polyethylene (Sioplas, Hydro-Cure, Monosil and Spherisil method)
• PE-X c, radiation-crosslinked polyethylene (by electron beam)
• PE-X d, polyethylene cross-linked by azo compounds.
   

All PE-X pipes must comply with EN ISO 15875.

In contrast, in PE-RT pipe, a cross-linking process is not necessary because the material has a unique molecular and microcrystalline structure that provides high elasticity and mechanical strengths at high and low temperatures similar to those of cross-linked pipe.

There are two types of PE-RT, Type I and Type II. Both suitable for radiant installation, Type II provides higher mechanical strength at high temperatures.

To be suitable for radiant installations, polyethylene pipe must be protected from the passage of oxygen as stipulated in UNI EN 1264-4 and UNI EN ISO 11855-5. The barrier may consist of a layer of aluminum or EVOH, which is a layer of ethylene-polyvinyl alcohol that prevents the permeability of the pipe to oxygen diffusion and the consequent oxidation and corrosion of the metal components that make up the system.

The oxygen barrier can be put on the outside or on the inside. In the former case, it could be subjected to abrasion during site operations, resulting in high oxygen runoff in some places. In addition, the oxygen barrier on the outer layer could compromise the typical malleability of polyethylene, making it difficult to make the tightest bends.

The fact that the oxygen barrier (in EVOH) is within the thickness of the pipe ensures:
 

• greater strength of the pipe's properties, as risks of abrasion of the EVOH barrier at the construction site are reduced
• increased flexibility of the pipe

greater resistance to oxygen passage (because the barrier is in a protected position).
Eurotherm's Midix Plus pipe is a pipe consisting of a double layer of type II PE-RT and an EVOH barrier inside, made by extrusion using the most advanced technology on the market. It is manufactured in Germany under the strictest quality criteria.

STANDARDS AND CERTIFICATION FOR PE-RT POLYETHYLENE PIPE

UNI EN 1264 and UNI EN ISO 11855 standards allow the use of plastic pipe, provided that the regulations specific to each material are met, that adequate measures are taken against corrosion, and that it has an appropriate oxygen barrier.

Plastic pipe must fall within Class 4 according to ISO 10508:2006 with an operating pressure greater than or equal to 4 bar and a life of more than 50 years.

ISO 10508 CLASS I, II, III, IV, V. Application radiant systems and low temperature radiators.

Note: According to the standard, if a pipe falls into one of the classes in the table, it is suitable for transporting water at 20°C for a period of do 50 years and at the pressure of 10 bar.

For PE-RT pipe, the technical standard that must be met is ISO 22391: it gives the characteristics of the pipe (such as dimensions, internal pressure resistance, thermal stability), but also the procedures for performing tests.

ISO/TS 22391-7:2011 reports how to draw up a product conformity assessment based on the other parts of the standard, providing for true production control.

To date, there is no harmonized standard for radiant system pipe. The harmonized standard is a standard that, if met, allows a CE certificate to be made in accordance with Reg. (EU) 305/2011 on construction products.

However, there is the possibility of certifying pipe according to voluntary quality protocols administered by independent associations such as the internationally recognized KIWA. For each type of product analyzed, there are procedures for quality assessment named by the abbreviation BRL followed by a number.

With regard to PE-RT pipe for installation in radiant systems or for connection to radiators, there are BRL 5602 and BRL 5607 protocols, respectively; within these, reference is made to the individual standards for pipe (e.g., EN ISO 22391-2) or connections in metal or plastic material.

Similarly, the German DIN-CERTCO certification allows the pipe quality of connections to radiators to be certified according to the German DIN standard in addition to the European and international standard. With regard to PE-RT pipe, for example, reference is made to DIN 4726 (concerning plastic pipes for underfloor heating) and DIN EN ISO 22391.

Finally, in the absence of a harmonized standard, there is the possibility of requesting for a product a European Technical Assessment from a suitable technical assessment body.