High Performance HVAC Air Conditioning & Heating: High Performance Air Conditioning and Heating Economizer Systems

High Performance HVAC Air Conditioning & Heating: High Performance Air Conditioning and Heating Economizer Systems
There are rudimentary economizer systems which are used for commercial HVAC systems to comply with code requirements but in my experience these systems do not work very well and are simply on the units to meet minimum code requirements for commercial fresh air code. Depending on the type of building and space in the building and its use depends on the code requirements for so many changes of air per hour. For example: A movie theater with a maximum occupancy of 150 people will require 15 CFM's per person of outside air to satisfy the mechanical code. In the old days before solid state sensors and controls an adjustable panel or damper on the air handling unit would be opened a certain percent to the outside air depending on the required amount of fresh outside air needed to meet the fresh outside air requirement in the code.
The better electro-mechanical controls were introduced which were economical and reliable and could automatically open the outside air damper based on time or some other method of control and this was better than leaving the panel or damper open 100% of the time to the outside air but it was still not that efficient because other factors like outside air temperatures and humidity were not always ideal to open this damper based on a time variable or a thermostat call for heat or cooling.
Enter the digital age and high performance HVAC controls which were economical and reliable 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. The older economizers were not as economical as the modern day economizers which are solid state and computer controlled. So, with a solid state HVAC control system one can go beyond the code requirements for the 15 CFM's per person in the movie theater and instead measure the CO2 in the theater 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) which is the reason why the code requires 15 CFM's per person in a movie theater with a 1,000 person occupancy.
Taking the economizer a step further HVAC control engineers figured out that with the newer modern 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. I suppose it all started when someone asked the question "What if?” What if we used the outside air when the temperature and humidity outside were ideal for cooling instead of using mechanical cooling? They had all the necessary controls in place to facilitate this request. 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.
For residential applications, a whole house fan is very applicable.