Often, many of us (including the authors of this column) lament on the sad state of affairs of controls. Why is designing controls so hard? Why don’t systems work the way they should without continued commissioning? How come the industry isn’t delivering better projects?
And yet, it is sometimes valuable to step back and look at the incredible progress we have made as an industry over the last 20 years. To go back in time, you don’t need a time machine, or even a good recollection for history. You can see readily observe the “state of the art” from the 1970s and 1980s in many existing buildings, which are continuing to operate, stopped in time, in the same method that they were installed so many years ago. Here are a few key areas where we have made significant progress over the last 20 years.
VAV BOX CONTROLThe accurate control of a VAV terminal requires proper measurement of both zone temperature and the ability to use it to reset airflow. Early VAV box controls often did not provide the ability to measure airflow and provided pressure-dependent control. These systems result in variations in airflow as the system static pressure varies and rarely result in either good comfort or consistent ventilation. A step up from pressure-dependent control was the mechanical volume regulator, followed closely by the pneumatic and analog electronic volume regulator. Both concepts can work if rigorously maintained, but in reality, they rarely operate properly, providing improper airflow.
These early devices also do not provide the ability to have multiple flow minimums or to provide any feedback to the operator. The end result of these old solutions: ongoing challenges with comfort, ventilation, and energy efficiency. DDC systems are able to solve all of these problems and to readily support optimization concepts including zone based scheduling and static pressure reset, which is not possible with other technologies.
FAN CONTROLAttempting to control air handler capacity with the use of inlet guide vanes, cones, or discharge dampers is an effective way to reduce duct static pressure. However, it has little impact on reducing fan energy usage, and we are finding cases where this fan energy is causing significant heating during low airflow. Today, the use of VFDs provides a cost-effective solution for fan (and pump) modulation, which is both more effective and also results in significant energy savings. Drives provide added benefits including the ability to meter energy usage of key equipment for just the cost of integration.
ECONOMIZER CONTROLOn older buildings, we frequently find that economizers are not utilized. When they are used, it is at best a drybulb changeover. While this is a good strategy, it tends to run the economizer for fewer hours than may be applicable, resulting in wasted energy. Deploying and enthalpy or wetbulb economizer is available for little cost with most DDC systems, resulting in improved efficiency and performance.
These three examples are just a few of the many improvements that are available for control systems. The good news is that all of these can be attractive upgrade opportunities and are readily achievable today, using the current generation of BAS. Moving to more efficient control provides benefits, both in terms of more energy-efficient operation and with regard to improved ventilation, comfort, and operational efficiency. ES