A design team tasked with creating a carbon neutral building in central Wisconsin needed to assess techniques for minimizing the energy use associated with the building’s HVAC systems, especially its ventilation system. Nonventilation building thermal loads are met with radiant slabs while carbon dioxide sensors allow adjustment of ventilation flow rates within the space. The ventilation system includes both mechanical and natural operational modes, as well as ancillary pretreatement devices such as earth ducts and energy recovery ventilators. An existing connection between an integrated building energy simulation tool and a multizone bulk airflow modeling tool was enhanced to allow the airflow tool to dynamically respond to control signals (such as changes in window opening area) sent by the building energy tool during the course of annual simulations. Building on experimental validation of the bulk flow model’s ability to reasonably predict the performance of natural ventilation systems and relying on the use of transparent and flexible simulation tools, the integrated model allowed the design team to explore the impacts of natural ventilation control strategies (purely mechanical, purely occupant-controlled, and occupant control with humidity lockout controls) as well as the interaction of those strategies with the performance of the mechanical ventilation systems and to develop control recommendations that allow the building to operate in its natural ventilation mode during 20% of the building’s annual occupied hours.

Units: Dual