4) Do You Have Zone Heating and Cooling Paired with Controls?
Depending on how deep your building is, keep in mind that operable windows will only benefit spaces close to the perimeter as fresh air can’t easily reach the core without mechanical help, notes Brinton. Open plans are also helpful as there are fewer barriers that could block air flow, adds Frank, though you can always add ceiling fans to help carry a breeze.
If you don’t want occupants guessing when it’s a good day to ventilate naturally, there are several ways to add automation.
- Full Automation: In addition to a remote panel or switch, “windows can be integrated with the HVAC system using sensors. This configuration balances the use of air conditioning with natural ventilation whenever it is feasible or desirable,” Jackson says. “An integrated HVAC system is best when approached during the design phase.”
- Notification System: You can install outdoor weather stations that measure air conditions. These sensors connect to your BAS and will trigger your perimeter HVAC to shut off when presets are met, Frank explains. This ensures your air conditioning isn’t running full blast when the windows are open.
- This ventilation sequence also includes a reset for the interior supply air or room setpoint temperature to ensure those units aren’t maxed out, he adds. If your HVAC isn’t connected to your BAS, note that this option will necessitate a controls upgrade.
- Interlocking Controls: Another possibility is to add interlocking controls to the windows. These use a binary contact that is broken when a window is opened, which in turn sends a message to the HVAC system to shut off.
In addition to these controls, you may elect to add a ventilator, notes Jackson: “These are typically small horizontal devices constructed within the framing system that allows air to flow into occupied spaces. When windows are in the open position, the ventilators provide a steady amount of outdoor air. They are usually equipped with screens to keep out insects and weather.”
5) Will Your Occupants Be On Board?
It goes without saying that for operable windows to be effective, they need to be easily accessed by occupants. That means they’re within reach, don’t require much force to open, and aren’t blocked by any objects, says Jackson.
If you don’t have full automation, you have to rely on occupants to open windows, and more importantly, close them, she adds. Without good habits, employees may neglect to shut windows at the end of the day or over the weekend. This can present energy, moisture, and security concerns if left unaddressed.
A little occupant training can go a long way, so take the time to educate users about the benefits of open windows and what they can do to be good environmental stewards. If that falls short, you can always task your cleaning crew to shut open windows just as they might already be doing with lights that are left on, advises Frank.
When hitting the sweet spot for the trifecta of temperate weather, acceptable outdoor air quality, and smart HVAC controls, operable windows can be a sustainable and energy-efficient way to supply natural ventilation to occupants.
Jennie Morton firstname.lastname@example.org is senior editor of BUILDINGS.