By Steve Wiggins, The NEBB Professional — Q3 2023 Edition
What is Retrocommissioning (RCx) and why should owners invest in it? Performed correctly, there is no process in the marketplace that can have a greater impact on our carbon footprint than RCx – and more importantly, have a greater impact on the proper operation of our facilities.
As a process, RCx has been around for many decades. I worked for Headquarters Air Force Civil Engineering Support Agency (HQ AFCESA) in the late 1980s and, as an owner organization, they had been retrocommissioning existing facilities and acceptance testing their new facilities for a number of decades.
The leaders of that organization were truly ahead of their time, as they also combined training the local operation staff with their RCx efforts. They recognized the importance of educating the local hands-on staff on how to maintain the optimized systems that were retrocommissioned to ensure persistence in their proper operation.
So why did this owner perform RCx? The number one driver was not energy reduction, but to improve facilities operations and resiliency. Many of the facilities that we were called to work on were in a failed state, and the expectation was that implementation of the RCx process would result in a facility that worked to its best possible state without capital improvement.
Their Civil Engineering Maintenance Inspection and Repair Teams (CEMIRT) originally utilized emergency response teams for any critical facility in the world. These teams responded and repaired facilities to get them operational as quickly as possible. When they noticed that a number of these facilities were repeat “failures,” the teams then combined training the local operations staff with the RCx to produce persistence in the facility systems.
As an added benefit, their efforts greatly reduced the energy consumption in these facilities, too. The driving force, however, was proper performance and occupant satisfaction.
Traditionally, there have been two driving forces in owners choosing to utilize RCx on existing facilities: energy reduction and lack of proper performance. I have been involved in performing RCx in hundreds of facilities in my career, and most of those projects have produced a significant reduction in energy consumption. Only two facilities found a need to consume more energy for proper operation.
Both of those facilities had their outside air intakes completely blocked and a number of pieces of equipment inoperable at the beginning of the projects. However, all of the RCx projects we have performed have been primarily driven by the need for proper performance.
We performed RCx on 118 facilities for a client located across the country in all of the major climate zones in the continental United States. The performance in these facilities improved to the point that the client reported receiving letters of appreciation from the occupants of all 118 facilities.
The client also monitored the energy consumption in these facilities and saw a reduction in electrical consumption by 18 percent and a reduction in natural gas by 40 percent. These projects easily paid for themselves in less than 18 months.
The process that we utilize when we perform RCx is delineated in ANSI/NEBB Standard 120-2019, Third Edition, Technical Retro-Commissioning.
The US Energy Information Administration states, “In 2021, the combined end-use energy consumption by the residential and commercial sectors was about 21 quadrillion British thermal units (BTUs). This was equal to about 28 percent of total U.S. end-use energy consumption in 2021. End-use energy consumption includes primary energy consumption and retail electricity sales but excludes electrical system energy losses. Total energy consumption by the residential and commercial sectors includes end-use consumption and electrical system energy losses associated with retail electricity sales to the sectors.
When electrical system energy losses are included, the residential and commercial sectors accounted for about 21 percent and 18 percent, respectively—39 percent combined—of total U.S. energy consumption in 2021″.
Taking that into consideration, why should owners perform RCx on their facilities? First, to provide facilities that meet their Current Facilities Requirements (CFR). The majority of existing buildings do not meet their original Owner’s Project Requirements (OPR) aspects, and they surely do not meet their CFR requirements! In my experience, very few owners have an original OPR, and even fewer have developed a CFR for their facilities.
We typically develop a CFR as part of the RCx process. Meetings are scheduled with key stakeholders in the facility to determine what they need the facility to provide so they can efficiently and effectively perform their tasks to achieve the company’s goals. A series of questions is presented to determine if there are any existing issues with facilities systems included in the scope of the project. These questions also include inquiries related to the RCx project timeline, hours of operations, manpower in all spaces, and other pertinent elements of the process.
Once the CFR is developed, the RCx plan and data logging plan are created by the RCx team. It is highly recommended that the maintenance team for the facility participate as a part of the RCx team. There is no better training available than the RCx process to provide the facility’s operations team with the knowledge needed to keep a facility operating at peak levels.
Performing RCx as presented in ANSI/NEBB Standard 120-2019, Technical Retro-Commissioning of Existing Buildings requires trained staff with the ability to perform numerous in-depth tasks throughout the entire process. Standard 120 presents the RCx process as if it is linear in nature due to the constraints that are part of the ANSI standard process.
However, the process is actually circular, repeating itself at many different points during assessment and discovery. As issues that are contributing to the less-than-optimal performance of systems are uncovered and corrected, the discovery portion of the process is executed repeatedly, as needed. Any issues that can be corrected utilizing a “quick fix” approach are corrected by the RCx team on the spot. This results in a better operating facility early on during the process. Each system and sequence are evaluated for optimal operation, and new optimized sequences are programmed and downloaded to increase system performance.
As the process continues, each of the systems is investigated and optimized as needed, any issue requiring either capital investment, remedial design, and/or additional resources to correct discovered issues are dealt with by the owner and the RCx team.
The following are examples of issues that have been discovered and corrected during actual RCx projects:
RCx Example 1
The variable air volume (VAV) controllers for the terminal units in the facility were not set up and operating properly. Judging by the percentage of devices that were found not set up correctly, it would appear that they had never been set up. All of these devices were calibrated and set up by the team, taking approximately six weeks of the team’s time. The specific details for each controller are included in Appendix A, Diffuser and Grille Test Data Forms.
The air-handling units (AHUs) were tested after the terminal unit testing was complete. The inlet vanes for the variable air volume AHUs were found to be in very poor condition. The leakage of the vanes in the fully closed position was so great that the static pressure in ductwork was over 4” on a couple of units. All of the inlet vanes were replaced with variable speed drives.
The control programs for the AHUs in the facility were found to be incorrect in every unit. The team wrote, installed, and debugged new control programming for every AHU in the facility.
The laboratory areas of the facility were tested for proper pressurization. All of the laboratories were found to be operating out of proper parameters. The supply and exhaust terminal were balanced to provide proper pressures in all rooms that had pressure regime requirements. The corridors on the third and fourth floor were not designed to have make-up air terminal units. The corridors are the reference point for the laboratories; constant pressure in the corridors is critical for efficient pressure control. The team recommended that make-up terminal units be added in the corridors on both the third and fourth floors, and a cost estimate was provided.
The central energy plant was being operated manually when the team arrived on site. There were several factors contributing to the need for manual operation of the chillers and boilers. These included no programmed sequence of operation, incorrect piping of the chilled water loop, including two decoupler lines with neither one installed in the correct location, and less than optimum piping of the hot water boilers and the steam heat exchanger.
The waterside economizer for the chilled water loop was also disabled. Since the owner had a full-time piping shop, the team re-piped the central energy plant’s chilled water and hot water loops and wrote programs for both systems. These programs were installed and debugged.
These efforts not only resulted in a properly functioning facility but also reduced energy consumption by $72,000 per year.
RCx Example 2
On another project, the owner had installed pressure-independent energy valves as a means of trying to correct perceived issues with their two central energy plants. They reported that they had contracted with the manufacturer to set up the valves on four different occasions with poor results all four times. The RCx team checked the setup and found no consistency in the setup of the valves.
Through discussions with the owner operations staff, the best setup for their application was determined. After setup, the delta T at the plants was found to increase from 4-5°F to 13-14°F, resulting in better performance of the plants.
During the discovery of the laboratory systems, the AHU was found to be providing 16,131 CFM while it was designed to supply 23,682 CFM or 68 percent of design. One branch duct serving room 107 was analyzed to determine the cause of the low airflow.
Inlet static pressure was found to be 2.2”w.c. at the inlet of the terminal unit and at the inlet of the reheat coil downstream from the supply balancing valve. Static pressure on the discharge side of the coil was found to be .145”w.c., an extremely high static pressure drop indicating that the coil was blocked with dirt and trash. The access door for the coil was removed, and Figure 1, Coil Face shows the condition of the coil.
The exhaust fan (EF) that serves the same area as the AHU flow volumes were tested. All three of the fume hoods served by this exhaust fan were found to be within acceptable values. However, the overall exhaust volume for the fan for this floor was extremely low. The total flow volume needed for this system was 22,234 CFM, while the actual flow for this fan on this floor was found to be 11,630 CFM or 52 percent.
We tested the branch duct serving one of the student workbenches. The static pressure before the balancing valve was found to be -5.25”w.c. and the static pressure after the cross-flow in the terminal unit was found to be -.24”w.c., making for a total drop across the terminal unit of -5.01”w.c. This drop normally should have been around -.6”w.c. A hole was drilled in the duct before the cross-flow, and a fiber-optic probe was inserted to inspect the terminal unit, allowing us to discover that the cross-flow was completely blocked with paper.
Another AHU was tested next. It was designed to supply 29,008 CFM, but testing revealed an actual supply volume of 21,417 CFM or 74 percent of design. One of the branch ducts serving a portion of the area was analyzed to determine the cause of the low airflow.
Inlet static pressure was found to be 4.97”w.c. at the inlet of the terminal unit and 4.81”w.c. at the inlet of the reheat coil downstream from the supply balancing valve. Static pressure on the discharge side of the coil was found to be .023”w.c., an extremely high static pressure drop indicating that the coil was blocked with dirt and trash. The access door for the coil was removed, and Figure 2, Coil Face shows the condition of the coil.
The EF serving the same area as the AHU was tested. All of the fume hoods served by this EF were found to be within acceptable values. However, the overall exhaust volume for the fan for this floor was extremely low. The total flow volume needed for this fan was 28,145 CFM, while the actual flow for this fan was found to be 16,177 CFM or 57 percent.
We tested the branch duct serving one of the student workbenches. The static pressure before the balancing valve was found to be -4.397”w.c., and the static pressure after the cross-flow in the terminal unit was found to be -.1125”w.c. for a total drop across the terminal unit of -4.285”w.c. This drop normally should be around -.6”w.c. A hole was drilled in the duct before the crossflow, and a fiber-optic probe was inserted to inspect the terminal unit. We discovered that the cross-flow was completely blocked with paper.
The RCx project was temporarily halted while the owner marshalled a quick-fix team to clean all of the reheat coils, clean all crossflows, and install wire mesh at the workbench opens to prohibit papers from being sucked into the system.
After this effort was executed, the RCx process continued, and the systems were optimized. Additional issues were discovered and corrected during the process, allowing the facility to perform at a high level upon completion of the project.
RCx Example 3
One more example I can give of an RCx project is a five-story building that had four AHUs serving the facility in vertical stacks. This meant that the RCx team had to treat the mechanical system as if it were one system with five supply fans and cooling coils.
The system airflows were tested for correct volumes. These tests were performed at the VAV terminal units first, and then each air handling unit was tested. Each terminal unit and associated room temperature sensor was checked for proper calibration and operation.
Upon arrival at this facility, the commissioning team carried out a test on the building pressure and found the facility to be in an extreme negative pressure condition. The facility had four constant volume relief fans (RF-1, RF-2, RF-3, and RF-4) installed on the fifth floor for the purpose of maintaining proper building pressurization, approximately +.05”w.c. These fans were designed to relieve 17,075 CFM of air.
The team proceeded to experiment with the relief fans and ended up with all relief fans turned off, and the facility still measuring -.026”w.c. The team investigated further to determine the cause of this negative pressure condition. Such a condition in a facility can very easily lead to health and environmental impacts, such as high humidity and eventually mold growth.
The design airflows for each AHU are shown in Table-1: AHU Air Volumes. As the airflow for each AHU varies between the minimum and maximum air volume, the outside air volume must remain constant. The units designed to control the outside air volume to accomplish this task, however, were non-existent. Further assessment of the four AHUs revealed that the outside air ductwork in the units had failed due to high velocity and oil canning.
Recommendations from the commissioning team to increase the dimension of the outside air intake duct to reduce the airflow velocity and to install static pressure transducers in the mixing chambers of the AHUs were discussed. The owner carried out the replacement of the outside air ductwork on all four units and installed the static pressure transducers. When the outside air ductwork project was completed, the team set the outside air to the required values on all four AHUs. Pressure tests revealed that once the systems were set up, the facility maintained its proper relationship to the outside.
The decisions regarding budget and what to correct when executing an RCx project must be a collaborative effort between the RCx team and the owner’s staff. RCx varies from new building Cx in that any owner will tell you that their expectation for their new building is to achieve as close to 100 percent perfect as possible. I like to call the desire on an RCx project a sliding scale of economics. In other words, we want to get an existing building as close to 100 percent perfection of the CFR as the owner’s budget will allow.
It has been our experience that if you can take a building from below 60 percent performance to a percentage in the high 80s for the cost of RCx, the vast majority of owners will be satisfied with that. Some facilities and CFR will require capital investment due to the nature of issues found within the systems. In those cases, the RCx team works with the owner’s team to determine what must be done at a minimum to satisfy safe and proper operation for a facility.
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