Calculating the heat output of radiant panels

What factors affect the calculation of the heat output of radiant panels? Find out more on the Giacomini S.p.A. Blog

Systems that use radiant floor panels are among the most energy-efficient air conditioning systems, ensuring a high level of comfort in the home by producing even temperatures in the rooms in which they are installed.

Characteristics such as quietness, invisibility and the absence of convection currents make them the ideal choice not only for domestic buildings but also for professional and industrial contexts, when designing new buildings and upgrading existing spaces from a structural and energy perspective.

But what is the right way to plan the installation of a radiant system? We look at how to calculate the heat output required for radiant floor panels and which factors should be taken intoconsideration when embarking on this kind of project.

Radiant floor systems: preliminary studies

If you have decided to equip a building with radiant floor panels, you must perform some preliminary studies to allow you to size the system correctly, analysing the unique features of the spaces in which they will be installed and determining key elements such as the heat loads, the pipe spacing and the overall configuration of the system.

Heat loads of the spaces

In order to calculate the heat output required from a heating system, it is important to firstly examine the heat loads of the spaces that are being analysed, in other words, the amount of thermal energy that is dispersed into the external environment during winter. This is actually the total of the heat loads of the spaces served by the system, which will help to define the output of the system and the energy that will be supplied to each room.

Standard UNI EN 12831 specifies how to calculate heat loss and encourages you to calculate heat loads by determining three main factors:

• Transmission load, affected by the type of structure of the building in which the system will be installed, by solar radiation and by the conductivity of the materials used in the building;
• Ventilation load, linked to the power dispersed for the renewal of air in the spaces that will be heated, for infiltration or for the occasional opening of doors and windows;
• Recovery power, which is the power required by the system to return to the required temperature.

Surface temperature

According to standard UNI EN 1264, which regulates wall, floor and ceiling radiant systems for heating and cooling, the type of room that will be heated and the heat loads are essential to determine the maximum surface temperatures that an air-conditioned floor can reach through radiant systems.

The suggested limits are:

A maximum of 29°C for habitable areas;

A maximum of 33°C for bathrooms;

A maximum of 35°C for perimeter areas.

Installation depth, flow temperature and temperature difference

To calculate the heat output of radiant floor panels, you then use the heat loads to define the system's flow temperature, a parameter that influences the thermal performance of the panels and that, along with the pipe spacing, is also linked to the surface temperature that can be achieved.

Analysing the stratigraphy of the floor that will house the radiant panels and establishing the thickness of the insulating layer are essential steps when determining the final output of the radiant system, both upwards and downwards.
It is also important to study the influence that the temperature difference could have on the temperature of the surface on which the panels are installed: this is the temperature difference between the system's flow water and return water. Generally, for spaces that are normally occupied, a temperature difference of around 6°C is expected.

Spacing and dimensions of the radiant panels

Once you have finished the essential evaluations mentioned above, you can determine the spacing and layout of the radiant floor panels, making sure that you establish each parameter in line with the data already determined. For spaces that are usually inhabited, generally a spacing of 10-15cm is adopted, which can be increased at the perimeter bands and rooms with specific uses.
The length of the pipes used will correspond to the area of the panel that will used divided by the selected spacing: a longer panel means bigger losses, so this must be considered extremely carefully in the final panel design, to make sure that it is the most efficient solution.

Of course, each space included in the design will then have to be studied individually based on its distinctive characteristics, its layout and its intended use, with the aim of designing functional and energy efficient systems.