Free Cooling: Air Economizers
December • 2014
Free Cooling With Air Economizers
Even in cool climates, buildings often need air conditioning systems that can reduce internal temperatures. That's because machines and bodies can create heat that makes the building's internal temperature uncomfortable. Air economizers bring cool air into the building, essentially offering free cooling that requires little, if any, conditioning.
On a simple level, air economizers pull cool exterior air into a building. Depending on the building's internal and external temperatures, the economizer might provide a stable, comfortable interior temperature that balances out heat created by machines and bodies.
Even in circumstances when the outside temperature is not cool enough to maintain a comfortable interior temperature, an air economizer could significantly reduce the amount of power needed to lower the building's temperature. That's because cool air outside of the building doesn't need as much processing as warm interior air. Starting with cool air helps HVAC systems use less energy.
Pulling air in from the outside can also improve a building's air quality since recycling conditioned air often means pollutants and allergens get trapped in the building.
Air economizers work best under certain conditions. Buildings in cooler climates like Orange County, can improve HVAC efficiency by using air economizers year round. However, buildings in hot climates like Palm Springs primarily benefit from air economizers during the cooler months when the exterior air temperature is lower than interior temperatures.
In some instances, buildings will only rely on air economizers during certain seasons. Outside air might be too hot during summer, but it might fit a building's needs perfectly during spring, fall, and winter.
The most efficient air economizers know how to determine whether they should bring air in from the outside. Many experts use a 55 degree cutoff point. They just set the air economizers to bring air into the building whenever the outside temperature reaches 55 or lower. At 55 degrees, most buildings can get all of the cooling that they need from air economizers.
The air economizers might still pull in air above 55 degrees, but only when the outside temperature is lower than the building's interior temperature. At a certain point, the air economizer should turn itself off completely. Otherwise, the HVAC system will expend even more energy trying to lower the temperature of hot air than trying to cool recycled air.
55 degrees is a handy reference point, but getting the most free cooling from air economizers requires a closer look at several factors, including relative humidity and dew point. Most professionals keep it simple when talking to their clients. For the most part, it's effective and accurate for them to tell clients about thermal break-even temperatures.
In reality, though, an experienced HVAC and air economizer professional will consider many factors when installing products. This makes it important for building owners to hire reliable professionals who look at much more than the 55 degree reference point. Doing so often means that businesses save money by making their HVAC systems much more efficient in a variety of climate conditions.