Development of an Occupant-centric Control Algorithm for Mixed-Mode Ventilation Buildings to Regulate Window Operations

Abstract

Mixed-mode ventilation is a design feature to improve building energy efficiency and indoor air quality by combining natural ventilation and mechanical ventilation. Mixed-mode ventilation commercial buildings are often equipped with variable air volume (VAV) terminal device and air handling unit (AHU) as the mechanical ventilation system and operable windows to deliver natural ventilation. However, in practice, mixed-mode ventilation buildings do not always achieve better performance than mechanically ventilated buildings, largely due to inappropriate window operations. Therefore, the sequences of operation for terminal devices serving zones with operable windows should be designed in recognition of these risks, which in turn should be informed by research investigating occupants' window and thermostat use behaviour. This research examines window and thermostat use data collected from two mixed-mode ventilation buildings in Ottawa, Canada.Discrete-time Markov logistic regression models and decision tree models were established to predict the likelihood of thermostat keypress and window opening/closing instances and identify the indoor conditions that trigger these actions. Based on this analysis, a set of control algorithms are developed to improve terminal device sequencing in mixed-mode ventilation buildings in cold climates such that the comfort and energy savings potential of operable windows can be fully realized. The control algorithm applies a thermostat setpoint setback to encourage occupants to open windows when conditions are advantageous for saving energy, and discourage occupants from opening windows when energy penalties may be caused. The control algorithms are tested by using building performance simulation (BPS), and 3-16% of energy reductions could be achieved when control sequences encouraged occupants to undertake energy-efficient window use behaviours compared to an ii identical buildings with unregulated window operations. It is also found that the unregulated window operations could increase the heating load up to 21% and cooling load by 22% relative to identical buildings with fixed windows in a cold climate. These findings suggest that control algorithms should be designed properly in mixed-mode ventilation buildings to realize its full energy-saving potential and avoid adverse energy impacts caused by unregulated window operations.iii PrefaceThis integrated thesis consists of two journal papers, either published or under review.Should readers wish to refer to materials from this thesis, the current thesis is required to be cited. The articles included in this thesis are as follow:• Article 1 : W. Liu, H. B. Gunay, M. M. Ouf. Modelling window and thermostat use behaviour to inform sequences of operation in mixed-mode ventilation buildings.