The study of a installing heated floor is based on a number of intangibles rules:
The insulation should consist in foamed plastics exclusively;
The exposed pipes and related equipment (pumps, control valves...) must be insulated;
The thermal resistance over the tube is limited to 0.13 m² K/W.
Slab coating: 0.04 m² K/W.
Flooring: 0.09 m² K/W.
+ coating mass per unit area of floor - 160 kg/m² max - to minimize the thermal inertia. The insulation should be about 7 cm thick;
Ventilation of the premises;
The average difference in temperature imposed during the construction or major renovation and every day to reduce the heat input to a minimum.
The device limits the flow temperature at the entrance of cooling system in the summer. The flow temperature is defined according to the geographical location.
The device is independent of the regulations that automatically cut the production of cold water when the fluid temperature reaches 12 ° C.
Thermostats are programmed not to go below 24 ° C.
Calculations in cooling mode
The coefficient of heat transfer through the floor is calculated so as not to exceed 7 m² K/W.
The transmission power:
An ambient temperature of 24 ° C; Delta T = 31 ° C; 18/21 W/m².
An ambient temperature of 27 ° C; Delta T = 49 ° C; 18/22 W/m².
An ambient temperature of 28 ° C; Delta T = 54 ° C; 18/22 W/m².
Note: Condensation is the return of water vapor in liquid form. The temperature descends below the dew point when the air comes into contact with a cold wall and the water vapor it contains condenses.
Floor heating: The pitch of the tubes
The heating network is called loop or ground.
There is a loop that adapts the heating system to the desired temperature.
The pitch (or spacing) of tubes ranges between 5 and 35 cm (statutory limits).
It is determined based on preliminary calculations of the heat necessary to cover the area.
The tube diameter should also be taken into account:
Common diameters: 10 × 12 mm, 13 × 16 mm, 16 × 20 mm, 20 × 25 mm.
Common sizes: 13 × 16 (120 m max L.) and 16 × 20 mm (160 m max L.).
Number of tubes: What is the right density?
The density (or charge) of tubes depends on the area to be heated.
In principle, the density is higher near the exterior walls and windows to offset the decrease in heat radiation of the cold walls (discomfort).
The density is lower in the rest of the loop so as to obtain an initial temperature as low as possible without reducing the level of comfort.
Sample reports:
20 cm in the middle surface: 10 cm edge.
30 cm in the middle surface: 15 cm edge.
A line must be arranged:
5 cm along the vertical structures (walls, fixed equipment...);
20 cm around chimneys, flues and stair cavities.
Note: In theory, the cooling mode requires a density greater than the heating mode because the tubes have to absorb the maximum amount of ambient heat. In fact, the simple solution often leads designers to base their calculations on the initial temperature of the heating fluid. They act on the flow and speed to optimize the refreshing capacity.
The types of installation of underfloor heating systems
There are two principles:
Coil loops;
Snail loops.
In the past, snail loops guaranteed a better distribution of heat (limited losses) in little or poorly insulated buildings. However, today coil loops are more popular because of the softer thermal requirements and the simplicity of implementation.
Note: An edge of 5 cm is the maximum conceivable with a snail loop, which raises the tubes in a quarter-round bow (90 °). The half-round bending (180 °) of the coils is virtually impossible to achieve with the current tube diameters.
Underfloor heating: The layout plan
The layout plan embodies the thorough study of the heating system. It is reproduced to scale for each floor and piece. To this end, the sheets are numbered in chronological order and contain the special features:
The type of installation
The red, blue return lines
The size of the step edge and surface
The passages between rooms
The location of the generator (boiler or heat pump) is also indicated, as well as the collectors and the temperature sensors (internal and external).
The nomenclature of each loop is indicated next to the plane:
The number
The diameter and tube length
The fluid flow
The surface emission capacity...
The main characteristics of collectors are:
The brand
The total thermal power
The thermal reference
The overall throughput
The reference speed
Note: The layout plan is provided to the installer, who must comply with the nomenclature.
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