Make sense of retro-commissioning

Retro-commissioning, or RCx, is the practical application of the commissioning process to existing buildings. The goals and objectives for applying the process, as well as the level of effort, will vary depending on the needs of the owner, budget, and condition of the equipment.

10/14/2011


Buildings consume 45% of the energy used in the United States. Mandated by Executive Order 13462, federal agencies are required to reduce energy intensity by 3% each year, leading to 30% by the end of fiscal year (FY) 2015 compared to a FY 2003 baseline. A majority of the buildings in operation today were not commissioned during construction and start-up. As the buildings aged and their usage changed over the years, the overall system performances degraded, and in some instances the original design intent may have never been realized, that is, the performance was degraded from the start. Common problems in the existing buildings include but are not limited to excessive equipment maintenance and repair costs, IAQ issues, and high utility costs. The facilities industry, building owners, and federal agencies are looking to reduce their operating costs and high utility costs through a process called retro-commissioning (RCx).

RCx is the practical application of the commissioning process to existing buildings. This process looks into improving the building equipment condition along with the system operations. Depending on the age of the building, RCx can often resolve problems that occurred during design or construction, or address problems that have developed throughout the building's life.

This is a systematic, documented process and that identifies operational and maintenance improvements throughout.

Process

The goals and objectives for applying the process, as well as the level of effort, will vary depending on the needs of the owner, budget, and condition of the equipment.

The overall process focuses on energy usage, building envelopes, and plumbing systems. Some owners prefer focusing on energy usage of equipment such as mechanical equipment, lighting, and related controls with the goal of reducing energy waste, obtaining energy cost savings, and identifying and correcting existing problems. The RCx process can result in optimized system performance, improved air quality, comfort, controls, and energy efficiency. It’s also important to realize that the non-energy benefits of the RCx process can bring significant financial gain to the owners.

The RCx process usually involves a joint effort on the part of building owners who seek improvements in the performance and efficiency of their facilities and commissioning providers who are typically field-savvy building service professionals capable of providing the service. The composition of the RCx team will vary based on the overall scope of work. Our firm’s RCx team usually includes personnel specializing in HVAC; controls, testing, adjusting, and balancing (TAB); electrical; fire alarm; life safety; and communications. RCx typically includes an audit of the entire building, including a study of past utility bills and interviews with facility personnel. The process can focus on a specific item if the overall budget is limited, and expand later based on the initial findings. Then diagnostic monitoring and functional tests of building systems are executed and analyzed. Building systems are retested and monitored to fine-tune improvements. This process helps find and repair operational problems. The identification of more complex problems is presented to the owner as well.

A detailed RCx process is a multistep process and a team effort. The RCx process begins with development of the RCx plan. Team members are selected based on their skill sets and scope of work. A typical team includes engineers (mechanical, electrical, and controls), a test and balance technician, and an RCx agent/project manager. Detailed roles and responsibilities of each team members are typically defined in the RCx plan.

Figure 1: Fan Coil Unit 1: Outside air is drawn through an area way louver, while the outside air duct damper and return air duct damper modulate to maintain the space pressure and temperature. Courtesy: Stanley Consultants Inc.Upon completion of the RCx plan, the design review plan phase starts. At this phase, the team reviews the existing construction drawings, and modification drawings that may have taken place during the life of the building. The RCx team identifies the original intent, type of systems, and system capabilities. In many instances, the original documents for the facilities are not available; when this occurs, the RCx team determines the system capabilities and flexibility from the nameplate and other auxiliary information.

At the completion of the review phase, the RCx team initiates an interview process with the facilities staff and the users. Prior to the interview process, the RCx team will review the maintenance record or work orders, if available. The interview process is extremely important to the overall RCx process in understanding the issues and shortcomings of the system. This process helps the team in gathering information regarding “modifications” made to keep the occupants satisfied. Another major benefit is to identify the “areas of training” for the facilities staff. The site visit phase starts after the interview phase. This phase is time-consuming and tedious, because many or all of the following items are executed:

  • Check for equipment calibration and set up for trending of temperature, humidity, equipment status, airflow, water flow rate, electrical, gas, etc.
  • Survey physical condition of the equipment, and systems as per the scope of work 
  • Record light levels and space air quality of the space
  • Perform a point-to-point controls systems test and simulate for different scenarios. 

Typically, the final phase of the process starts with preparation of the RCx report and its presentation. A master discrepancy list or findings list is normally part of the report; it identifies the system discrepancies and recommended repairs. Some of the items or “quick fixes,” such as minor maintenance items, TAB adjustments, and control systems reprogramming, are executed during the process by the maintenance staff and/or RCx team members. Depending on the scope of services, multiple training sessions are conducted for the facilities maintenance staff on operations and maintenance procedures.

Energy audit versus RCx

A majority of owners, federal agencies, and private and public entities are looking to reduce their utility consumption by improving energy-efficiency practices. An energy audit or RCx project is the perfect starting point for existing buildings and sometimes for new buildings. However, it can be difficult or confusing for the owners and users to differentiate between the two processes, and to determine the best option for their facility.

Figure 2: The chilled water system consists of a Carrier air-cooled chiller and two base-mounted pumps. Courtesy: Stanley Consultants Inc.The most important objective of energy audit is to inform the building owner or user about how well the facility is performing from an energy consumption standpoint. ASHRAE defines Preliminary Energy Use Analysis, Level I; Walk-Through Analysis, Level II; Energy Survey and Engineering Analysis; and Detailed Analysis of Capital-Intensive Modifications, Level III. All levels of effort are led by a vendor-neutral licensed professional engineer (PE) with extensive experience in the energy-efficiency industry, and not by a vendor hoping to sell a product. The audit report includes a list of energy-saving measures one may choose to implement, including the payback and annual energy savings associated with each measure. While performing the energy audit, engineers will examine at least one year—and possibly multiple years—of energy bills to understand how the building consumes energy throughout the various seasons. Then the energy data will be used to create a baseline of energy usage, which will be used to compare with similar buildings and operations in the area. At our engineering firm, the Trane TRACE program is used to model the energy consumption of the building.

The energy audit team will study all of the building systems in place and their operating schedules, breaking down the building’s total energy consumption by use (lighting, heating/cooling, etc.). Some clients may require that the energy audit scope include the review of water usage.

The final product of an energy audit is a report explaining how the building is currently performing and providing a list of no-cost, low-cost, and capital-cost energy conservation opportunities. The report also calculates the rate of return or payback duration based on the savings and capital cost for modification.

The RCx process systematically analyzes and fine-tunes an existing building’s individual systems as well as all operation and maintenance (O&M) procedures. Unlike an energy audit, energy reduction is not the sole goal of RCx. The precise goals of a RCx project can vary between projects but can include any combination of the following: extending the life of equipment, improving comfort of a building for its occupants, improving IAQ, improving the effectiveness of O&M procedures, reducing utility bills, reducing energy consumption, and reducing the number of complaints from building occupants.

The outcome of RCx is a more comfortable and efficient building and well-trained facilities staff. Candidates for RCx include: buildings where the occupancy and use has changed since the building was constructed, buildings that have occupant comfort issues, and buildings that need to reduce energy consumption.

Both an energy audit and RCx will lower a building’s operating cost. Before taking on any building performance improvement project, it is vital for the owner or operator to outline the goals he or she hopes to achieve in order to choose the best course of action for building improvement.

RCx as an investment

As a building owner, should I invest in RCx? Simple payback for a RCx project is typically less than two years and sometimes less than one year. In addition, the RCx process produces better and longer performance of existing equipment, and the benefits reach far beyond energy savings.

Cost savings from RCx can be significant; however, they can also vary significantly depending on building type and location, and the scope of the RCx process. A comprehensive study by the Lawrence Berkeley National Laboratory (LBNL) found average cost savings in the following ranges:

Value of energy savings: $0.11 to $0.72/sq ft

Value of non-energy savings: $0.10 to $0.45/sq ft

Significant cost savings from the RCx process are often a result of reduced energy use. The 2004 study aggregated RCx results from 100 buildings and found whole-building electricity savings ranging from 5% to 15% and gas savings ranging from 1% to 23%. Corresponding payback times ranged from 0.2 to 2.1 years.

If RCx can produce these results, the majority of building owners should want to invest in RCx, but that is not the case yet. As consulting engineers, we have not done an effective job in marketing or in educating the building owners. The lack of effort could be a direct result of lack of understanding of RCx, lack of properly trained personnel, or unwillingness to venture out of the “comfort zone.” Some clients have the perception that the RCx process is too expensive and may not have the payback.

Prior to offering the RCx services to the client base, our engineering firm invested in the personnel to properly train them through the Building Commissioning Assn. (BCA) and University of Wisconsin at Madison. Personnel with TAB backgrounds and building control systems were added to the commissioning and RCx group. Formal training is important, but the most valuable skills are hands-on training and understanding of the overall system. The RCx agent or team members should be able to identify and maneuver the equipment and systems.

Case study

A building owned by U.S. Fish and Wildlife Service, containing a museum, had a history of problems from the beginning. The contractor was changed halfway through construction, the head of maintenance retired, and the HVAC systems never worked right.

Figure 3: Chilled Water Schematic: The pressure drop across the strainers for the chillers and pumps was much higher than the design condition in the as-built drawings. Courtesy: Stanley Consultants Inc.

Track lighting in the museum generated considerable heat and the humidifiers were not working. This wasted energy in conjunction with occupant discomfort was assessed for remediation. The non-energy benefit here was repair of the humidifier, which made the space slightly more comfortable while simultaneously preserving the artifacts, which are priceless and represent the core mission of the facility.

The RCx effort by this engineering firm focused on the full systems assessment including calibration of instrumentation and controls; TAB of air and hydronic systems; and overall observation of current systems’ conditions, operating strategies, and practices for the purpose of finding and implementing cost-effective improvements. The investigation included testing individual systems and verifying calibration of damper and valve actuators, instrumentation, and BAS control points. Proper balancing of air and hydronic flows were tested and compared to current design parameters. In addition, O&M documentation was enhanced and agency staff trained in the proper operation of their systems. In the course of the investigation, any energy efficiency capital improvements that are thought to be effective were offered as recommendations to the owner.

Based on field investigation, functional testing of the systems and equipment, and interview of the occupants, a list of discrepancies was prepared. This list identified the discrepancies for each piece of equipment, location, corrective action implemented, and recommendation of any future action (if required). The list was followed by recommendations for comfort and energy savings.

The following paragraphs will discuss a few selected major findings and remediation.

Fan coil unit 1 (FCU-1): The unit is equipped with a return air duct, outside air duct, supply air duct, filter section, heating and cooling coils, and fan section. The chilled water used for the cooling coil and hot water is used for the heating coil. The FCU-1 is to operate based on the following:

Occupied mode: The fans operate continuously. Fans are initially started on low speed, and the hot water valve, economizer damper, and chilled water valve are modulated in sequence to maintain a room heating temperature setpoint of 70 F. The outside air damper is opened to minimum position. If outside air temperature is greater than return air temperature, the economizer dampers are closed to minimum position. If the unit is unable to maintain setpoint after 15 minutes at low speed with the heating or cooling valve 100% open, the fan is switched to high speed. If the unit is able to maintain setpoint after 15 minutes of operation at high speed, and the active control valve is less than 25% open, then the fan is switched to low speed. A differential pressure sensor across the prefilter and final filter generate a maintenance alarm when the prefilter pressure drop is a minimum of 0.10 in. wc greater than its pressure drop when clean, or when final filter pressure drop is a minimum of 0.50 in. wc greater than its pressure drop when clean.

Figure 4:Chilled Water Pumps 1 and 2: Both pumps were operating once the outside temperature was above 90 F, and they caused excessive flow through the chiller. These pumps did not operate according to the lead/lag sequence. Courtesy: Stanley ConsultantsUnoccupied mode: The supply fan cycles on/off at high speed to maintain a heating setback temperature of 65 F with the heating valve open, outside air dampers closed, and return air dampers open. If the space temperature exceeds the cooling setup temperature of 81 F, and the outside air temperature is less than the space temperature, the fan operates at high speed with outside air dampers open and return air dampers closed. When the supply fan is off, the hot water valve modulates to maintain 45 F in supply air plenum. If the smoke detector trips, the fan coil units shut down. If the freeze-stat trips, the unit shuts down, the outside air damper closes, the heating valve opens, and an alarm is generated. UV lights operate continuously to prevent microbial growth on coils and drain pan.

Findings

FCU-1 was found with an inoperable drive belt. The drive belt was replaced and adjusted for proper torque and tension. The outside air louver filter was clogged with debris, so it was removed and cleaned. The fan coil unit filter was replaced with a clean filter. Upon installation of the new belt and filters, the fan was tested and the design airflow was achieved.

The field inspection revealed that the unit was missing the prefilter, and the dirty filter pressure sensor tube was in the incorrect location. This was causing a lack of communication between the controls system and the unit sensors. As noticed from the physical inspection, the unit filter was heavily loaded and experiencing excessive pressure drop, but no alarm was generated through the BAS.

Data loggers were installed after the test and balance of the systems were conducted, and all fan coil units were set at the operating conditions specified by the as-built drawings.

It is clear that the temperature remains steady, modulating at 69 F to 73 F; however, the relative humidity shows a peak of 55% on day one around 9 a.m. and a drop on day two to 38% around midnight. The control sequence specified to maintain 70 F with a maximum of 50% relative humidity in the space.

Figure 5: Temperature-Relative Humidity Graph: The purpose of the data loggers was to record the temperature and the humidity of the area served by the fan coil units. Courtesy: Stanley Consultants Inc.

The building controls system was tested to manually exercise the outside air damper, return air damper, chilled water coils, and hot water coils for 100%, 50%, 25%, and 0%. The test revealed that dampers and valves were not properly calibrated and did not perform according to the control’s command. The outside damper was found to be set at 0%, and no ventilation air was provided in the space. The hot water control valve did not close and remained at 25%.

The control system and its communication links were repaired the gauges and meters were recalibrated. The overall system start operating as designed and retest of the system showed significant IAQ (drop in carbon dioxide level) and overall space temperature improvements.

Approximately 11 fan coil units in the building had similar issues as FCU-1. After the RCx process was completed, a 9-month follow-up revealed that the overall energy usage had decreased by 15%, based on electric usage, and user complaints had decreased by 90%.

Chilled water system

The chiller contains three reciprocating compressors and a Comfort Link electronic control system that controls and monitors all operations of the chiller. The overall chiller load was modulated via multiple compressors and based on the return chilled water temperature from the building.

According to the sequence of operations, the chilled water pumps were constant volume and operate in a lead/lag sequence, with lead and lag designation switched weekly. The lead pump operates when there was a demand for chilled water, as indicated by at least one fan coil unit chilled water valve being open at least 10%. The pumps were to supply 42 F water to the fan coils. A run time log was recorded for each chilled water pump. When the outside air temperature was less than 50 F, the chilled water pumps were shut down.

Findings

To begin the testing process the chiller and the pumps were put in operation. Overall system pressure and flow was field measured and compared to the design intent. Initial observation revealed that the pumps were not operating according to the sequence of operations identified in the as-built drawings.

The strainers were removed and inspected, and an excessive amount of foreign material was noticed. The strainers were cleaned and reinstalled, and the pressure drop across them significantly reduced.

The pumps were tested for the flow and pressure drop, and it was noticed that chilled water pump 2 (CHP-2) was not operating properly. Attempts were made to correct the deficiencies but did not work according to the design parameters. Chilled water pump 1 (CHP-1) tested successfully after the strainers were cleaned and replaced. All the coils for the fan coil units were tested for flow and found to be adequate with CHP-1 operating. The CHP-2 was taken out of operation manually and was left in place for repair or replacement.

Once the controls system was repaired and started operating as designed, the overall building condition improved tremendously. According to the users, “This building never was this comfortable.”

Mahmood, a senior mechanical engineer at Stanley Consultants, has 19 years of technical experience. Mahmood's project experience includes quality control and quality assurance of bid documents, including analysis, engineering, and designing mechanical systems encompassing HVAC, plumbing, and fire protection. He is a member of the Consulting-Specifying Engineer editorial advisory board.


References

New York State Energy Research and Development Authority (NYSERDA). Guideline to the Building Commissioning Process for Existing Buildings, or “Retrocommissioning” (2003). Prepared by Portland Energy Conservation, Inc. (PECI).

Oregon Department of Energy. Retrocommissioning Handbook for Facility Managers (2001). Prepared by Portland Energy Conservation, Inc. (PECI).

U.S. Department of Energy, Rebuild America Program. Building Commissioning: The Key to Quality Assurance (1998). Prepared by Portland Energy Conservation, Inc. (PECI).

U.S. Department of Energy/PIER. Strategies for Improving Persistence of Commissioning Benefits (2003).

U.S. Environmental Protection Agency. 2003-2008 EPA Strategic Plan: Direction for the Future (September 30, 2004).

U.S. Environmental Protection Agency. Operations and Maintenance Assessments: A Best Practice for Energy-Efficient Building Operation (1999). Prepared by Portland Energy Conservation, Inc. (PECI).

Williams, Scott D. “Owner’s Strategies for In-House Commissioning,” Proceedings of National Conference on Building Commissioning (New York, NY, May 4–6, 2003).



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