Demand controlled ventilation in a bathroom

In residential buildings moisture is a dominant pollution source removed by the ventilation system. The Danish building code requires a minimum air change rate of 0.5h-1 in residential buildings to avoid moisture related problems. However a constant ventilation rate results in unnecessary energy consumption during periods where the demand for ventilation is low and poor indoor climate during periods where the demand for ventilation is high. Controlling the ventilation rate by demand can improve the energy performance of the ventilation system and the indoor climate. This paper compares the indoor climate and energy consumption of a Constant Air Volume (CAV) system and a Demand Controlled Ventilation (DCV) system for two different bathroom designs. The air change rate of the CAV system corresponded to 0.5h-1. The ventilation rate of the DCV system was controlled by occupancy and by the relative humidity in the bathroom. The two designs differed by the construction of the shower cubicle which in one case was sealed and in the other case unsealed. The construction influenced the relative humidity within the bathroom during a shower, i.e. the pollution source the ventilation rate was controlled by. The indoor climate and the energy consumption were estimated based on a simplified calculation of the variation of the water content within the bathroom during a day. The results showed that the DCV system controlled by occupancy and relative humidity had an improved energy performance and an improved indoor climate compared to the ventilation system with a constant air change rate of 0.5h-1. Moreover it was found that the bathroom with a sealed shower cubicle reduced the period where the relative humidity exceeded 70% by approximately half and in both the CAV and DCV system. Moreover the energy performance of the DCV system was slightly improved in the case with the sealed shower cubicle compared to the unsealed cubicle. The study indicated that indoor climate and energy optimizations of DCV systems should not be limited to considerations of the control system, but should also include considerations of the design of the ventilated rooms.