online maps of wind forecasting. Look for data from the National Wind Technology Center, the National Center for Atmospheric Research, or the National Climatic Data Center.
2) Is Your Outdoor Air Safe?
In addition to a mild climate, outside air quality is a major
concern. It’s an unfortunate reality that many locations suffer
from high levels of pollutants. You cannot open a window at
the cost of exposing occupants to harmful toxins.
“Keep in mind that in a mechanical ventilation system, all of
the air goes through a common filtration point. With operable
windows, however, you don’t have a way to remove contaminants,” Frank cautions.
Not sure about your site’s air safety? Consult the National
Ambient Air Quality Standards, a function of the Clean Air Act.
The measurements establish harmful levels of lead, carbon
monoxide, nitrogen dioxide, ozone, particulate matter, and
sulfur dioxide. These standards are then used to determine
nonattainment areas where air pollution is routinely high.
“If you’re in one of these EPA nonattainment areas and
you’re bringing in untreated outdoor air, you are actually pol-
luting your building,” Brinton stresses. “It would only increase
your operating costs to filter properly.”
Even if your location has safe levels of particulate matter,
there are additional sources of airborne contamination. Flying
dust and plant debris may be of concern, as could vehicle
exhaust if your windows are near street level on a busy thor-
oughfare, explains Frank. Even outdoor noise could drift in and
become a distraction, adds Brinton.
To ensure you aren’t below the requirements for ANSI/
ASHRAE Standard 62.1-2013 – Ventilation for Acceptable Indoor
Air Quality, you can add IAQ sensors throughout your building
to keep an eye on pollutant and thermal comfort factors.
3) Are You Ready to Upgrade Your Existing Windows?
Beyond air quality considerations, it makes the most financial sense to add operable windows during a facade renovation. Particularly if your current windows need better sealing
www.buildings.com BUILDINGS 17
What would your occupants give to open their win- dows and let in a nice breeze? More than the desire to enjoy pleasant weather,
natural ventilation supports productivity, learning, and health
for employees and students alike. It will also flush the space of
potential VOCs and CO2 concentrations, which helps to reduce
the likelihood of sick building syndrome. If you are pursuing a
green certification, LEED, Green Globes, Living Building Chal-
lenge, and the WELL Building Standard all reward designs that
improve ventilation and IAQ.
Passive ventilation is out of reach for most existing buildings
without a costly remodel, so your best retrofit option is oper-
able windows. The trick with using this type of mixed-mode
ventilation, however, is to ensure that the fresh air doesn’t
bring in outdoor pollutants or overwork your HVAC system.
Ask yourself these five questions to ensure that this solution
won’t undermine air quality or energy costs.
1) Are You in the Right Climate?
Operable windows are best suited to regions that have temperate climates; otherwise cold, humidity, precipitation, and
extreme heat limit the number of days you might be able to
let in untreated air. If your building is in a region with unpredictable weather, you may want to keep the status quo with
“Everywhere in the country experiences those 68- to 72-de-
gree days, but for many areas, they’re rare or only occasional,”
says Marty Brinton, senior applications engineer with LG
Electronics. “You need to look at the first costs of an operable
window compared to a fixed one and calculate how many days
of the year you can actually use the operable one.”
Wind resource – an assessment that measures how gusty
your location is – also plays a role.
“While operable windows are a simple device, you are
dependent on wind or temperature differences to create buoyancy for air movement to flow through your building,” notes
Michael Frank, director of engineering with the firm McKinstry.
You can consult anemometers from your local airport or
Operable Windows Deliver a Breath of Fresh Air
Use controls to balance mechanical and natural ventilation