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Economizer Systems and HVAC Control - Direct Digital Controls Systems in HVAC control have taken leaps and bounds in the last few years. Especially so in being user-friendly, ease of designing systems, troubleshooting system problems, and increasing efficiency over the older energy management systems. When discussing the increasing efficiency of systems the idea of economizing always comes up.
Economizer Systems and HVAC Control
Economizers can be found in many different forms. Such as using outside air when conditions are right to cool inside spaces. Recovering heat loss from the relief air leaving the building. Additionally, making full use of the heat a boiler produces by recovering heat from the flue gases. There other ways to capture and conserve energy. However, for the sake of brevity, we’ll cover the basic way many buildings make use of economizers. That is using the outside air to cool the inside spaces instead of using mechanical cooling.
Building and Energy Codes
Air Changes per Hour
First of all, we have to understand that the mechanical codebook along with guidelines released by ASHRAE (ASHRAE 62.1 and 62.2 guidelines) requires so many changes of air per hour in commercial and public buildings. Many building owners rely on a manual fixed damper system to meet these requirements. Other systems have stand-alone dampers that will actuate to the open position based on certain rudimentary input devices. There is a specific calculation for fresh air requirements or air changes per hour that are based on occupancy and square foot of the building/space being conditioned.
The accuracy of these devices and the function they serve are rarely set up properly. Additionally, they are hardly ever calibrated to ensure they function as designed. Typically, within a year of installation, they are disabled and the damper is closed off permanently in some way. The second realization we must look at is the fact that, depending on geographical location, a building owner can save lots of money with a properly designed and calibrated energy management and control system that will allow the economizer to work through the HVAC systems direct digital control system.
| Building Type | Air Changes per Hour |
|---|---|
| Residential | .35 to 1 |
| Hotel Rooms (not including convention halls or meeting rooms) | 1 to 2 |
| Office Spaces | 2 to 3 |
| Retails Spaces | 2 to 3 |
| Schools (not including auditoriums) | 5 to 6 |
| Restaraunts | 6 to 8 |
| Sports Facilities Including Gymnasiums | 4 to 8 |
Economizer Systems and HVAC Control | Remote Monitoring
That a good energy management HVAC Controls system has the ability to be monitored from a remote location over the internet. That it collects trend data and proves energy savings using charts and graphs. Furthermore, without mentioning the fact that the final proof will be the lower utility bill. Those devices that are out of calibration or broken can be observed from a remote location. Furthermore, action can be taken to repair such devices if they fail. A good HVAC Control energy management system will do all this and more.
CO2 Monitoring – Economizer Systems and HVAC Control
To properly set up an economizer so that it works as efficiently as possible we must have at least three input variables to control it. CO2 monitoring inside the space, an outside air temperature reading, and an outside relative humidity reading. The CO2 will override everything else if it reaches a specified set point in the DDC program. By monitoring CO2 inside the spaces we eliminate the need to have a minimum outside air damper position to meet the code requirements.
That means that as long as the CO2 inside the spaces is below a specified amount the unit can operate and condition the inside air without any influence from the outside air because of minimum positions on the outside air damper. That saves energy costs and safely monitors the building spaces for CO2 levels. The next thing we need to make the economizer effective is an enthalpy calculation on the outside air.
Economizer Systems and HVAC Control | Conclusion
To get an enthalpy reading we must know what the temperature and relative humidity are outside. The HVAC Control program will crunch the numbers and determine the enthalpy value of the outside air. Based on a predetermined set point the HVAC Controls program will lock out mechanical cooling and open the outside air damper to bring in cool air for the purpose of cooling the space. This feature alone has the ability to save lots of money on energy costs.
Economizer Systems and HVAC Control
