Commissioning: Trend Log or Ongoing Monitoring and Optimization
This month, I would like to extrapolate the topic of my last two columns (trend log analysis, June and July, 2009) into ongoing O&M. In the spirit of new construction commissioning being just the beginning of systems optimization (see my December 2008 “Commissioning” column), I recommend that the facilities manager incorporate trend log analysis into the PM program for the new systems.
It is important to maintain individual pieces of equipment for continued reliable performance, and this is what most PM programs address. However, it is equally important to preserve the integrated operation of all of those components as a system. This is the operations side of the O&M program. As demonstrated in the examples from my June and July columns, the fact that space conditions and IAQ are fine does not necessarily mean that those conditions are being achieved as efficiently as practical.
TrendsettersAs a starting point, for systems that are commissioned as part of the design and construction project, the O&M staff should continue running the trend logs used during commissioning. This will allow them to use the commissioning trend logs as a baseline against which to evaluate performance of the systems after occupancy. If the building was not originally commissioned or if commissioning did not include trend log analysis, the first step of the O&M trend analysis program will be to define and set up the trends that will be most beneficial to monitor long term. In most cases, it will not be cost-effective to monitor every point in the BAS; that is usually too overwhelming an undertaking, and some points have minimal impact on major systems operations.
I recommend evaluating each system - and this should be considered on a system-by-system basis instead of on a point-by-point basis - for its relative impact on two things: maintaining critical building parameters (temperature, IAQ, pressurization, etc.) and energy consumption.
Based on the above two criteria, create a prioritized list of systems that would benefit from ongoing trend log analysis. Then, based on resources available to implement and maintain the trend monitoring plan, set up trend logs for the highest-priority systems first. It is always possible to add more trends in the future, but if you bite off more than you can chew at the beginning, the program will go nowhere.
Each trend log should consist of points such as temperatures, valve positions, damper positions, setpoints, motor speeds, etc., that can illustrate the reaction of inter-related control parameters all on one graph. I recommend keeping the number of points on each graph to no more than six to eight, if possible. That may mean splitting a system into separate “temperature control,” “humidity control,” “pressure control,” etc., trends.
Monitoring The TrendsFor the O&M monitoring program, each trend should have an instruction sheet directing the reviewer as to what to look for when evaluating that specific trend graph. This should include a baseline “expected” graph for different modes and/or seasons of operation. If there are no baseline trend logs from initial commissioning, the first year of operations may need to focus on collecting and documenting the baseline trends. The instruction sheet can also recommend specific actions for the O&M staff to take if the trend logs do not match expectations.
The end-of-construction or first year performance baselines should not be seen as the target for future measurement and verification efforts, but should be seen as the minimum performance standard against which future enhancements and fine tuning can be measured. The O&M trend analysis process should continually look at ways to match system integration, setpoints, schedules, and control sequences to the dynamic needs of building occupants and processes.
The goals of the trend analysis program are to provide a means and method to:
- Identify operational problems before they become performance problems;
- Identify inefficiencies before energy use and costs escalate; and
- Track energy consumption and measure the impact of conservation measures implemented by the O&M staff.
This process is something which could - and has been - automated through computer programs which continuously analyze the collected data and report on its deviations from expectations. These computer programs need to be customized for each individual building system; i.e., off-the-shelf analysis programs will only be meaningful when there are off-the shelf systems to be analyzed. In addition, the O&M department still needs operations specialists to understand and respond to the deviations reported by the computer program.
Ongoing trend analysis is one more step towards putting optimization into the “O” in O&M. ES