Experimental investigation of building envelope integrated ventilative cooling design for high-performance buildings

Description

We are in this new exciting stage of building design and construction stage where we strive to realize net-zero buildings. To get to net zero, the building must produce locally as much energy as it utilizes. Hence, lower energy consumption is required. However, high performance buildings with highly insulated walls usually face an overheating problem in the summertime and end up using more energy for cooling. Literature indicates that natural ventilation for cooling or ventilative cooling method to be an ideal system for energy saving. In this study, naturally ventilating the air gap behind the cladding by the indoor and outdoor air is experimentally investigated for optimization considering energy performance in the summer time and shoulder seasons. The proposed design allows outside air to be pulled into the interior space and the warm indoor air to be exhausted to the outside through the cavity behind the cladding; thereby creating ventilative airflow to cool the building thus named exhaust ventilated (EV) wall design. The major driving force of interest is thermal buoyancy. The experimental study also includes optimizing ventilated cladding (VC) wall setup, a variation of the rainscreen wall system. The performance of the different variations of the two wall design is compared based on their potential to reduce the cooling load or overheating of a building. From the experimental data analysis, A VC wall of 6" (15 cm) cavity depth and opaque cladding showed a 40% reduction in heat gain compared to a commonly used ventilated rainscreen wall indicating a wider cavity perfo1ms better. Similarly, the opaque cladding is also shown to be better than the transparent cladding in cooling seasons. The sheathing membrane colour (emissivity) has an insignificant effect if it is behind the opaque cladding but may produce a major difference if used in combination with transparent cladding. The exhaust ventilative design is indicated to have an improved cooling potential by generating bulk air movement. interestingly, the airflow for the EV wall is shown to produce a peak for the day as well as night-time. Daytime flow is promoted by solar radiation and night-time flow is generated by indoor and outdoor temperature differences. The experimental result indicated that, in transparent cladding, the effect of cavity width on the EV wall thermal performance is very little. An EV wall with transparent cladding attains a higher cavity temperature, but more air moves in the opaque EV wall. Similarly, walls with bigger wall openings allow more airflow. And finally, as cavity temperature is crucial in accurately estimating the cavity airflow rate, from the monitored data, a regression model to predict the cavity temperature, as well as airflow, are developed.