ISO 11855-6:2012 pdf download – Building environment design — Design, dimensioning, installation andcontrol of embedded radiant heating and cooling systems — Part 6: Control
ISO 11855-6:2012 pdf download – Building environment design — Design, dimensioning, installation andcontrol of embedded radiant heating and cooling systems — Part 6: Control.
In conditioned spaces. the coollng power of radiant heat exchange may be limited to avoid condensation on the surface and in the building structure. The risk o indoor surface condensation is avoided in practice by limiting the supply water temperature according to the dew point temperature in the space, by maintaining the floor surface temperature above the space dew point temperature. Simultaneously dehumidifying the ventilation air to a certain level will result in lower dew point and higher cooling capacity, as the cooler temperature of the radiant surface increases radiation asymmetry and decreases operative temperature: precautions must be taken In such a case so as to not exceed the comfort limits in the space. In particular, the temperature of the cooling surface should not be reduced below the limit of 17 C and 19 C for wall or ceiling and floor, respectively, and the indoor operative temperature should be controlled according to the standard required temperature
A central control is also essential when using floor cooling. Due to the limitation of the cooling capacity a floor system will not always be able to control the room temperature at a fixed level. Basically the control should provide the maximum cooling power taking into account comfort (floor temperature, room temperature) and the risk for condensation (dew point temperature). The central control for floor cooling must then take into account the dew point In the bulldingJspace when controlling the supply water temperature. This is done by adding a humidity sensor in the building/space connected to the central control unit.
A.2 Example of control system components
Figure A.1 shows the control system components which comprise a closed circuit complete with circulating pumps. This circuit Is connected to the supply and return header. The circuit Is also provided with all the necessary isolatingand balancing valves. There are two mixing pipes installed in the circuit. One is for heating and the other is for cooling. The heating mixing pipe is connected to a heating supply which can have a variable temperature together with a return. The cooling mixing pipe is connected to a cooling supply which can have a variable temperature together with a return.
The performance of a radiant floor subjected to different solar radiation intensities will depend on the controllability of the radiant cooled floor to maintain certain conditions such as space temperatures and floor surface temperatures. Embedded systems with and without coverings must be analysed to assess the influence of floor coverings.
A.3 Dew point
The floor surface temperature of the radiant floor cooling system Is lower than the air temperature In the space. Therefore, if the surface temperature of the floor falls down below the space air dew point at any area, water falls out and the floor gets wet. The floor surface temperature is dependent on the water temperature at the specific area, the cooling load of this area and the distance between the tubes within the floor construction. Because of the distance between the tubes, the floor surface temperature is nut uniform. It is recommended to select a minimal supply water temperature equal to the supposed maximal dew point temperature to avoid condensation on the Iloor surface and to guarantee the selected cooling capacity of the radiant system. Additionaly, the supply water temperature should be controlled by a humidity control sensor.
If for any reason a water supply temperature below the supposed dew point is selected, the minimal possible surface temperature of the Floor In areas with reduced loads must be calculated carefully.
For example, when the indoor air is controlled at a dry bulb temperature of 24°C and a relative humidity of 50%, the suggested dew point Is approximately 13 C.Therefore, a minimal supply water temperature of 13 °C may be selected.
The combination of the radiant floor cooling system with a natural ventilation concept requires an accurate calculation of the maximal suggested dew points within the space, considering the outdoor air conditions as well as the latent loads of the space.