Green Energy Services - Commercial - Economizer Tune Up
Studies have shown that over 70% of all installed economizers are either not working or not working efficiently. The primary reason for this is the HVAC Technician not fully understanding the proper integration of an economizer with the system thermostat or building automation system.
Another common problem is the use of a standard temperature control to control the economizer instead of an enthalpy control for maximum system operation when conditions are acceptable. A standard thermostat senses only temperature. When this type of control allows the economizer to operate for free cooling it is very common for occupants to complain about a lack of cooling or muggy feeling. An enthalpy control sense the total heat content of the air, this means it looks at both the temperature of the air and the humidity content. This allows for maximum energy efficiency for the economizer.
Free Cooling or Free Air Conditioning
Enter the digital age and high performance HVAC controls which were economical and reliable economizer and if programmed properly would actually take the system beyond the code requirements and pay for itself in a matter of a few years by saving money. Older economizers are not as economical as modern day economizers which are solid state and computer controlled. So, with a solid state HVAC control system one can go beyond the common code requirements for the 20 CFM per person for an office building and instead measure the CO2 (carbon dioxide) in the office building and open the economizer damper only when the CO2 levels reach a set point safety limit as determined by ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers). This can also be referred to as free cooling or free air conditioning because it mostly relies on outside for air conditioning when the outside air is ideal for such purpose. When outside air conditions are ideal the HVAC controls lock-out the mechanical cooling and begin the free cooling or free air conditioning mode.
Taking the economizer a step further HVAC control engineers figured out that with the newer modern HVAC controls they can also squeeze more efficiency out of the HVAC system by adding more control to the economizer and utilizing it more often under ideal conditions. All the technology is economically available and easily retrofitted to the existing set up. And finally the economizer evolved from this manual damper which was highly inefficient to a system of HVAC controls and a damper which actually saved money on HVAC operating costs plus it has the required CO2 set point limits to open as necessary for CO2 control. Based on outside air temperature and humidity the economizer will open and allow fresh cool air into the building and lock out mechanical cooling which will save energy. It is called free cooling or free air conditioning and while it is in wide use in commercial HVAC control it still has not found its way into residential HVAC control.
HOW DOES ECONOMIZER COOLING WORK?
Figure 1: The components of an economizer
An economizer is simply a collection of dampers, sensors, actuators, and logic devices that together decide how much outside air to bring into a building.