Impianti intelligenti per un pianeta mig
Radiant systems in heating
Floor, wall or ceiling? What is the best performing system in heating?
When I compare myself with my professional colleagues, both plumbers and designers, we all agree on what is considered the maximum power of an underfloor heating system: about 100 watts per square meter (actually, as we will discover in the article, would be 97 watts/sqm).
What does it mean?
It means, for example, that in a bedroom, with dimensions of 5 meters by 4 meters, the floor has an area of 20 square meters and the heating system can deliver a maximum power of 100x20 = 2000 watts.
But where does this maximum output value come from? And what is the corresponding value for a radiant wall or a radiant ceiling? Which system has the highest heating efficiency?
Let's try to answer each of these questions.
How is the maximum output of a radiant surface calculated?
Currently the UNI EN 1264 standard is used for the design and installation of radiant systems. Among all the requirements introduced by this standard, there are 2 fundamental ones to answer our question:
- Power emitted by a radiant surface
- Average surface temperature of the radiant surface
Here is what the UNI EN 1264 standard says:
The image shows the three formulas for calculating the heat exchange power of a radiant surface. It is not surprising that the first coefficient is different in the three hypotheses (floor, wall or ceiling): the effects of radiation are in fact different depending on the position of the surface with respect to our body.
This image, on the other hand, shows the maximum allowable values for the average surface temperature of a radiant surface.
Nowtoday we finally understood that, in order to be able to talk about well-being and comfort, a floor heating system must have a maximum surface temperature of 29° C. The underfloor systems of the early years (1960s) were unsuccessful precisely because this temperature was often exceeded! What many don’t know is that there is a limit temperature, to fall within the parameters of comfort and well-being, even for a radiant wall (40° C) or for a radiant ceiling (33° C)!
A separate discussion must be made for the "bathroom" and "swimming pool" rooms, where comfort is in any case guaranteed by having a radiant floor that reaches an average surface temperature of 33° C.
To understand the difference between "living areas" and "perimeter areas" of a radiant floor, the following images may be useful:
The perimeter areas are the floor surfaces close to the perimeter walls that face outwards, for a width of 1 meter. In these areas the standard allows to reach a slightly higher average surface temperature (35° C) as these are portions of the floor where normally a person does not stay for a long time. As a result, it is possible to lay the heating pipes with a shorter installation distance (as seen in the picture).
In any case, if in the formulas introduced by the UNI EN 1264 standard we replace the average maximum surface temperature values and the ambient temperature values normally used in our homes, we can obtain the following results:
As you can see, leaving out the "bathrooms" and the perimeter areas of the floor and wanting to consider only the areas of the house where you normally stay, we have the following classification of the radiant surfaces in terms of heat output:
Final classification in heating:
- 1st place = wall system with 160 watts/mq
- 2nd place = floor system with 97 watts/mq
- 3rd place = ceiling system with 85 watts/mq
Conclusions
- The wall system is the one that wins the comparison with other radiant systems, but we must take into consideration the fact that inside a house there are very few portions of the wall that can actually be used: many walls are partially occupied by doors, windows, cabinets and other furnishing accessories. This system is often used as a supplement, when the floor or ceiling system is unable to cover the energy requirement in watts.
- The floor system, with its 97 watts/mq for the living areas and 162 watts for the perimeter areas, is certainly more performing than the ceiling system and is better suited to guaranteeing the coverage of thermal needs. But let's not forget that in new buildings, where particular attention is paid to the insulation of the entire building envelope, the heat requirement is reduced to a minimum and therefore in most cases it is also possible to resort to the radiant ceiling system alone.
- The radiant ceiling system has very specific limits: a maximum power of 85 watts/mq. We must necessarily take these limits into account. For example, returning to the initial hypothesis of a 5 m by 4 m room that needs 1900 watts for heating, this requirement could easily be covered with a floor system; on the contrary, a ceiling system would not be able to guarantee the heating of the room!
Below is a summary card that lists all the topics covered in this article. This card can be useful in the design phase of our radiant system, when perhaps we have the possibility to choose between several solutions, even integrated with each other:
For those wishing to download the card in PDF format, you can use the following link:
Please note. Source of some images: web