Evaluating the Tradeoffs of Occupant Comfort and Energy Savings: A Study of Window Control Sensitivity

This paper investigates the tradeoffs between occupant comfort and energy savings for a wide range of control scenarios in several variations of mixed mode buildings. A series of EnergyPlus simulations were conducted for a future university campus building located in Boulder, Colorado. These simulations show that occupant comfort, as defined by ASHRAE, does not correspond to the modeled design with the highest energy savings. A variety of building shell, HVAC and mixed-mode operation schemes were tested to measure energy savings over a baseline building with the energy results juxtaposed against the predicted mean vote as well as the number of hours the cooling setpoint is not met. This paper also highlights some areas where existing standards are not clear in regards to application of adaptive comfort models and the number of hours when a cooling setpoint is not met. EnergyPlus simulations show 5-8% savings for mixed mode design over a sealed building for four types of shell and HVAC configurations. However, when a typical window opening behavior is modeled much of that savings is eroded. This results in concurrent mixed mode design buildings (buildings where HVAC systems are running while windows are open) being less prone to changes in energy use as a consequence of human interaction.