Signalling systems that tell building occupants when to open and close windows have become a popular strategy for balancing the comfort benefits of manual windows with the efficiency benefits of automation in mixed-mode buildings. Data from surveys, interviews and site observations in 16 US buildings reveal a diversity of design objectives, control sequences and circumstances to anticipate when designing buildings with window signalling systems. The signals had the strongest influence on occupants’ use of windows when they were visible, the logic behind the controls algorithms was clearly understood, and they were seen as an informational device linked to an explicit internal policy that has to do with efficient and comfortable building operation. Lower levels of participation occurred when occupants tend not to pay attention to their windows, or the signals, unless they are uncomfortable, at which point it matters little what the signals indicate. However, occupants who do discover value in the signals are more likely to be more satisfied with their personal control. Occupants’ reasons for opening windows may include the desire for fresh air or air movement, which is as important to them as temperature adjustment, but admittedly difficult to program into the controls’ algorithms. 

Signaling systems that tell building occupants when to open and close windows have become a popular strategy for balancing the comfort benefits of manual windows with the efficiency benefits of automation in mixed-mode buildings. Data from surveys, interviews and site observations in 16 U.S. buildings reveal a diversity of design objectives, control sequences and circumstances to anticipate when designing buildings with window signaling systems.Signals influence window use patterns for a minority of occupants, although greater participation is possible if the signals are linked to an internal policy with clear, tangible comfort benefits. Low levels of participation likely occur because most occupants (though not all) tend not to pay attention to their windows, or the signals, unless they're uncomfortable, at which point it matters little what the signals say.However, occupants who do discover value in the signals are more likely to be more satisfied with their personal control.

Designs for low-energy buildings increasingly incorporate operable windows for the benefits of personal control, environmental quality, and architectural value. In practice, however,there are unresolved debates about whether operable windows can be integrated with mechanical systems to optimize both comfort and energy efficiency. Signals that inform occupants about when to open and close their windows (usually red/green lights) have become a popular solution. These systems essentially propose a compromise between manual and automatic control philosophies, asserting that information from the building can influence behavior while retaining the fundamental benefit of personal control. Results from interviews, site visits and surveys of 16 U.S. case studiesshow mixed results. Signals play a role in window use behavior for only a minority of occupants under normative management/education practices. However, greater participation is possible given efforts to communicate the tangible benefits of the devices. Office type (shared or private), visibility of the signals from workstations, reliability of the signal modes, and a range of personal circumstances (noise, wind, window hardware) also influence participation.If conceived as reinforcement to an internal policy rather than as an element of the building controls, this technology holds promise for a wide range of building and user types, and the programming can be flexible and adaptable as circumstances change in our rapidly changing built environment. 

Designs for low-energy office buildings increasingly incorporate operable windows for the benefits of personal control, environmental quality, and architectural value. However, integrating operable windows with mechanical systems to achieve their full benefits is an unresolved energy challenge. If operable windows are left up to the control of the occupants, designers run the risk of putting unpredictable or unnecessary loads on the HVAC system, causing air pressure balancing issues, or causing unreliable or unwanted air change rates. However, if windows are automated for natural ventilation, the building design loses the comfort benefits, amenity, appeal and robustness of manually-controlled windows.

New buildings with operable windows situate themselves in an ongoing debate about the efficiency benefits of manual versus automatic building control. The decision to use manually-operated windows rests on assumptions about their value and a faith in the idea that occupants will actively participate in maintaining indoor environmental quality (compared to a conventional, sealed office environment). Concurrent with this debate, there has been growing interest in occupant behavior as the new low- hanging fruit for improving a building’s energy performance and closing the gap between predicted and actual performance. Emerging research that is relevant to these topics includes studies that better characterize and model behavior, as well as those that look at the impact of information systems and feedback on energy-using behaviors. However, these research questions are seldom considered together. This literature review draws together a number of topics that contribute to our understanding of building-occupant control interactions in mixed-mode buildings, beginning with the known (and as- yet unresolved) benefits and limits of operable windows when combined with mechanical cooling. 

Our study uses EnergyPlus simulations to examine whole-building demand and energy end-use profiles for different design options and then uses these outputs to evaluate cost and carbon impacts of each scenario in Xendee, a modeling platform designed to “right size” and balance investments in distributed energy resources (DER).

Our results show that efficiency measures are key to meet the ambitious performance metrics for this project; however, most of the technology potential occurs for heating, ventilation and air conditioning (HVAC) or domestic hot water (DHW) loads which are a relatively small portion of a mid-rise multifamily building’s overall energy use. The most meaningful strategies to reduce or shift loads for this building include DHW load shifting, energy recovery ventilation, dynamic ventilation, and ceiling fans. Envelope strategies improve overall annual building performance but become an issue when lower heat loss increases cooling during the critical afternoon peak.

Compared to efficient, packaged air source heat pumps, a hydronic heating and cooling system (also serving DHW loads) with thermal energy storage has the best energy performance, highest load shifting capability, and best thermal resilience during outages. But because heating and cooling demands are small and hydronic systems are expensive, the net benefits of thermal energy storage are not substantial.

Sizing on-site generation and storage systems to cover the “worst case” outage conditions significantly drives up system size and cost. Even small deviations from 100% coverage (95%, or 99%) can dramatically reduce size and cost without a very meaningful change in resilience.