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Heat distribution

Heat distribution in the maxit Comfort Floor.

The aluminium plates mainly distribute the heat generated within the maxit Comfort Floor in the system. The quality of heat distribution depends on how even the temperature is spread on the top surface, especially comparing the areas directly on top of the heating pipes and the areas in between.

The heat distribution in the aluminium layer serves several purposes:

  1. Comfort: The bare human foot will recognise a temperature difference of more than 2°C. 3°C is considered to be uncomfortable.
  2. Less piping. As the heat is efficiently spread sideways in the aluminium, we can use double spacing compared to systems where the heating pipes are embedded in the screed. Thanks to this, we can also reduce the amount of heating circuits, as one circuit can supply a bigger area without the pipe being too long for the pump to circulate efficiently. This usually allows the use of one circuit for each room in normal apartments.
  3. Heating capacity: The heating emission from the floor (Watt/m² floor) is almost proportional to the temperature difference DT between the Air (TAir) and the Floor (TFloor).
  4. Possible damages to wooden floor covering can be reduced by the more even heat distribution.

The heat distribution of a 'traditional system' floor heating system.


The following picture shows isotherms in a traditional floor heating system with the pipes embedded in the screed.
D = 15mm parquetry
C = 35mm screed
B = 25mm insulation
A = 200mm concrete slab.

The isotherms are calculated as an FEM-analysis.
Conclusions

  • Big variations between the temperature of the pipes and between the pipes can be seen.

  • In this traditional floor heating system, c/c 200mm is too wide. In order to achieve comfort, the spacing should be c/c 75mm at windows and perimeter walls and c/c 150mm elsewhere.

  • The average floor temperature in the case above is 25.5°C. The heat emission q = 55.3 W/m² in the above case (TAir = 20.5° C). With a uniform 27°C floor temperature, the emission capacity would have grown by 17 W/m².

  • The heat under the parquet (35.5°) will darken the wood, as the oil in the wood becomes rancid, resulting in darker stripes in all areas of the floor.

Heat distribution in the maxit Comfort Floor system

With heating pipes in every rail
(c/c 150mm).

With heating pipes in every
second rail (c/c 300mm).


Click on the picture to enlarge it!
Click on the picture to enlarge it!

A = Aluminium rail without pipe.
B = 35mm system insulation.
C = Running water at 28°C.
D = The double railed aluminium, l = 237 W/mK.
 

E = 25mm maxit's pumpable screed.
F = 8mm tiles + tile fix, in total 14mm.
G = Indoor air.

We can see that with c/c 150mm pipe spacing, the temperature difference is 0.2° C. Even when having a pipe spacing of c/c 300mm, the temperature difference does not exceed 0.6°C. The above pictures were of a floor with a tile top covering. This represents the 'worst' case when it comes to a uniform heat distribution. Parquetry or carpets insulate much better, thus letting the heat spread out horizontally and more constantly.

The simulations are based on CFD-analysis (Computational Fluid Dynamics) for a room with 6000mm width, 2800mm height and a perimeter wall to the left with a 2400mm high window, a partition to the right and an outdoor roof and floor. The outdoor temperature in this case was 0°C. More info.
 
Example:

Rules and assumptions:

  • A rule of thumb* is that every degree ÄT means approximately q = 11 W/m² heat emission.*)  More info.

  • As we want to limit the maximum temperature on for example, wooden floors to TFloor, max. =  28°C, we can have this temperature above the pipe as the maximum.

  • We want to have an inner temperature of TAir = 22°C.

Case 1
In 'traditional systems', the temperature at the pipe would be 28°C and between the pipes maybe only 26°C. Our average floor temperature, TFloor, would then be at a maximum of 27°C and DT = 5°T.

Case 2
If however we have 28°C uniformly spread over the whole floor area, our average floor temperature TFloor is now 28°C.

Case 1 will give us a floor at a maximum of q = 5 x 11 W/m² = 55 W/m².
Case 2 The floor will give us a maximum of q = 6 x 11 W/m² = 66 W/m², i.e 20% more.


Dependent on how cold and windy it is outside, and how good or bad the quality of windows, walls, roof and base floor are, the extra 20% might be needed to keep the inner temperature at the thermostat regulated 22°C.