9.8.1. Radiant heating – unsatisfactory heat calculation results<br>

### 9.8.1. Radiant heating – unsatisfactory heat calculation results

When unsatisfactory results of heat calculations are obtained for a defined HZ, i.e. when there is shortage of or excess output (surplus Q/F not equal to zero), a number of changes may be introduced to data to improve the results.

First check whether the current pipe spacing has been specified by the user. The spacing might have been specified during previous calculations.

¨ The following changes in data cause increase of output from HZ:

- decreasing the thermal resistance of floor covering,

- introducing a peripheral zone or extending existing peripheral zone. Remember that uPZ is a more effective type of peripheral zone, while cPZ allows only relatively small increase of output per unit of surface area,

- increasing the effective surface area of HZ, e.g. by leaving out the spacing between HZ and walls (if applied), decreasing the occupied area, etc.,

- decreasing the area taken up by passing pipe feeds, e.g. by specifying small pipe spacing for them, even if accompanied by insulating them. The effect will be particularly large, when pipe feeds have not more than 50% of its output (default value) accounted for. Decrease in area taken up by pipe feeds will increase the effective area available to the proper heating circuit,

- increasing the supply temperature,

- allowing lower minimum temperature difference.

To decrease the output of HZ, adjustments opposite to the above should be made.

! Some changes that in theory should increase the output of floor heating, in effect reduce it. This is because some pipe spacing options are rejected due to non-compliance with the standard with regard to tfs/qfs_max.

For example, increase of the supply temperature may cause that the pipe spacing of the least value is rejected, and in effect the best available option provides lower output than before ts/qs increase. The same effect may cause that ts/qs reduction allows increased output of HZ achieved by specifying lower pipe spacing, which was not available at higher ts/qs .

Similar effects, contradictory to intuition, may occur after selecting a floor covering of higher thermal resistance. Usually increase of thermal resistance of floor covering leads to decrease of floor heating output. However, often it is not the thermal resistance of floor covering that is the limiting factor, but the need to meet the standard with regard to maximum point temperature of floor. In this situation the increased thermal resistance of floor covering ensures better dissipation of heat in the floor resulting in increased average temperature of floor without exceeding the maximum point temperature of floor. In effect, for instance, a carpet lining may allow higher heat output of floor heating than ceramic tiles.

An interesting solution to situations when some pipe spacing options are rejected because of the need to comply with the standard, is the application of an integrated peripheral zone at the beginning of the circuit (uPZ). The permissible tfs/qfs max in the peripheral zone is higher. The structure of uPZ causes that the heating medium with a high temperature first flows through the PZ, where permissible tfs/qfs_max is higher, cools down and enters the occupied zone at a lower temperature, so that the standard is not exceeded.

If all possible ways of changing data and construction have been exhausted without attaining the required output, Qrh/Frh has to be lowered in the room data by reducing the contribution of floor heating to total heating output in the room.