Humidity control in offices in the Belgian climate

In the survey study ‘Kantoor 2000’ the HVAC-system of several large office buildings in Flanders was monitored. Some of these buildings use air humidity control, most of them not. This triggered the question : why? In this paper the humidity control strategy is studied for some of these offices. A humidity transport model is developed by using simplified assumptions for the building envelope. This model is validated on a test case, using measured humidity inside a real office building and weather-data logged by the building control system. The model is proven to be sufficiently accurate. The possibility to insert a recovery heat exchanger in the ventilation system was added to the model. Not only recovery of heat was calculated, but also the recovery of moisture. Two buildings are then evaluated : a smaller size office building and a large office building. In both cases it is shown that the relative humidity drops below 30% for an unacceptable period in time. Adding a recovery heat exchanger is only productive when active humidification is used. These heat exchangers can save about 20 to 25 % of the operation costs of the humidification system.