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The Truth About Airside Economizers

The airside economizer is a mechanical device that draws in fresh outside air when temperatures are cool enough, enabling building owners to take advantage of free cooling and improve indoor air quality. Economizers are extremely effective in reducing energy costs, often to the tune of hundreds or even thousands of dollars a month, and are required by code in most commercial buildings.

The problem is, however, that most economizers don’t function properly, and many simply don’t work at all. Furthermore, when economizers aren’t working right, most building operators don’t even know it.


Before we go into the reasons why this is often the case, it’s important to first understand what these devices are and the basics of how they work. The airside economizer is an automatically-monitored and -controlled system of outdoor and return air dampers that’s integrated into a building’s air handling system. These dampers deliver measured amounts of outside air based on outdoor temperature and humidity to help meet the building’s cooling load. When conditions are right, economizers eliminate the need for mechanical cooling altogether.


Some of the biggest reasons why things go wrong with economizers are poor design and/or installation. Common design problems include improper sensor type, poor sensor placement, return damper oversizing, and inadequate pressure relief, just to name a few, and these issues are especially prevalent in systems that were never properly commissioned. Compounding this is the fact that many of the mechanics who install economizers have little idea of how they actually work, which is why proper commissioning is so very crucial. Some mechanics don’t even bother to connect the economizer at all, and it sits idle for years. MSC has run across so many non-functional units in our travels that it rarely even comes as a surprise.


So how is a building owner to know whether their airside economizer is functioning properly, if at all? Through preventive maintenance – which brings us to the other main reason why these devices often don’t work. Even in buildings that have a maintenance program in place for their air handling system, economizers are frequently overlooked, misunderstood, or both. Without proper PM, sensors drift out of calibration, dampers get stuck, linkages break, seals fail, and actuators stop working properly. On the controls side, there may be problems with sequences and settings that can seriously reduce system efficiency. Still another common problem is that facilities personnel will frequently disable economizers to remedy unrelated HVAC problems because they don’t understand what they are and how they work, and building owners oftentimes are none the wiser.


MSC is expert in economizer system design, service, diagnostics, commissioning, and retro-commissioning, and detailed airside economizer maintenance is included in all of our PM programs. For more information, please contact us at (973) 884-5000.