Efficient design

The mechanisms of exchange between the water in the tube and the surface of the room

Hydronic radiant systems are systems that work with a low temperature difference between the water and the room and, as such, are commonly defined as low-temperature difference systems. The thermal power supplied by the water during the heating phase is able to be released into the room thanks to a heat exchange mechanism between the hot water and the internal surface of the radiant surface, such as the floor for example. The same principle applies to cooling, but in this case thermal power is removed by the cold water circulating in the tubes.

Since the area of the surface next to the tube is most affected by the temperature of the water, it is evident that the closer the tubes (and therefore the narrower the spacing), the greater the efficiency of the heat exchange.

So the thermal power can be easily transferred to the room, it is essential that the tube is in thorough contact with the conductive layer into which it is inserted, keeping air pockets, in the case of dry systems, or contact with insulating systems, to a minimum. In floor systems, the conductive layer also has to perform the function of supporting any loads placed on the floor. Therefore a traditional or self-levelling screed, or a fibre-plaster board of suitable size is used.

In certain cases, it is possible to insert a sheet of highly conductive material, such as aluminium, in the area separating the material above the tubes (as can be screed) and the insulating layer below. This is usually done if the tube is fitted underneath the supporting layer.

Another important parameter for determining the efficiency of the radiant system is the coating material. If a wood covering is chosen - wood being an insulator - rather than a conductive material such as ceramic, higher water flow temperatures will be required to achieve the same degree of thermal comfort, which will involve supplying more power to the water. Similarly, a wooden floor in summer would require lower flow temperatures.

Finally, it is important not to underestimate the conductivity of the tube as a factor. More and more often, plastic tubes are being used in radiant systems. They guarantee long-term reliability, are low cost, are not subject to corrosion and allow versatility in installation. Compared to the copper or steel tubes traditionally used in the home heating industry, plastic tubes have a lower coefficient of thermal conductivity, around 0.3 -0.4 W/(m K) for polyethylene tubes.