If industry outsiders were to add up all the promotional claims related to the energy performance of building systems and their associated energy savings, they could reasonably assume our industry has achieved maximum energy savings and there are no building systems left to improve upon.
In regard to building automation systems (BASs), there is no shortage of various controls solutions, whole building and/or plant optimization packages, and fixes utilizing artificial intelligence (AI) algorithms in this industry. Similarly, there is no shortage of claims of energy savings on behalf of the providers of these solutions. Some of these claims are quite unrealistic, while others are absolute greenwashing. What is the value to the environment when a solution claims a 10% reduction in the source energy use intensity (EUI) if the net source EUI is 200? Is our message to the environment that “it could have been worse,” and the building should still get an award for decreasing the EUI by 20? If industry outsiders were to add up all the promotional claims related to the energy performance of building systems and their associated energy savings, they could reasonably assume our industry has achieved maximum energy savings and there are no building systems left to improve upon. Most new BAS and optimization solutions are far from achieving their promised energy savings.
Further, in order for an industry professional to be able to discern the "noise" from the "real" and valid solutions, one needs to have a good understanding of BAS basics. This article is the first of a two-part series intended to provide industry professionals with a few tools that could help them see beyond the smoke and mirrors.
In general, at the core of each typical BAS controller, there is a library of proportional integral derivative (PID) loops used to control and/or monitor the various control points, aka variables, connected to the controller. Figure 1 shows a sample controls diagram and control logic for a single-duct variable air volume (VAV) box with hot water reheat coil.
A controls sequence loop for the control valve that directs the flow of hot water may be similar to 1) when the space temperature falls below set point, the heating loop shall be enabled; 2) from 0%-100%, the heating loop shall increase the discharge air temperature from the air-handling unit (AHU) supply air temperature to the maximum discharge air temperature set point, and 3) The VAV damper shall be modulated to maintain the measured airflow at the active airflow set point. The active airflow set point shall be the minimum airflow set point. It’s important to note a similar sequence and diagram is presented in ASHRAE Guideline 36, “Advanced Control Sequences for HVAC Systems.”