Radiant cooling

The final component of the radiant system: dehumidification

The final component of the radiant system: dehumidification. To maximise the air-conditioning potential of a radiant system it‘s essential to install an air dehumidification system. Humidity inside the home can be significant during the summer months. This is in part due to unfavourable weather conditions and the presence of people whose indoor activity contributes to an increase in water vapour. Conditions such as these can lead to condensation forming on the cold surface, but this should be avoided so as not to damage the structure. Another aspect is the perceived comfort of occupants. In accordance with that advised by UNI EN 7730, to ensure a sensation of comfort and keep indoor air healthy, relative humidity should not exceed 60-65%. Several studies have shown that fitting a radiant system in a Mediterranean climate without installing an air dehumidification system will likely result in the relative humidity exceeding permitted limits causing personal discomfort. In conditions such as these it is preferable to close the passage of cold water to the cold floor or ceiling in order to prevent condensation. A room can be dehumidified using a special machine called an isothermal dehumidifier, which is capable of lowering the relative humidity of the air removed from the room. A refrigerant (or compressor) dehumidifier works by dehumidifying the air using an internal chiller and a cold water flow. Alternatively, in a non-compressor unit, the air flows over a system of air-to-air heat exchangers and a cold water coil and exits dehumidified and slightly cooled. The water can be further cooled using an additional water coil inside the machine described above. In this case it is called a dehumidifying air conditioner. A room can also be dehumidified using a fan convector. However, a fan convector‘s capacity for dehumidification is significantly less than a dehumidifier at the same flow of treated air. This means that the number of fan convectors in a home must be appropriate to the actual dehumidification requirements of the environment. In addition, it should be remembered that the main function of a fan convector is to heat. Therefore, the control system for any radiant system combined with such a machine must be carefully evaluated at the design stage. Finally, there is the option of installing a mechanical ventilation (MV) system with dehumidification, which injects clean, dehumidified air, drawn from the outside, into each room while at the same time removing pollutant-rich air, after heat recovery if it is energetically efficient to do so.