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WHITEPAPER:Understanding Retro-Commissioning Ali Mahmood, PE, Stanley Consultants Inc., Chicago, Illinois

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Understanding Retro-Commissioning Ali Mahmood, PE, Stanley Consultants Inc., Chicago, Illinois

Buildings consume 45 percent of the energy used in the United States. Mandated by Executive Order 13462, federal agencies are required to reduce energy intensity by 3 percent each year, leading to 30 percent 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 never have been realized, i.e. 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, indoor air quality 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, retro-commissioning 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 throughout the process it identifies operational and maintenance improvements. One of the goals of RCx is to bring the buildings up to the original design intent or usage. The RCx may or may not bring the building back to its original intended design, and the original design documentation may no longer exist or be relevant.

PROCESSThe 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 to focus on energy usage of the energy-consuming 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. RCx process results 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 retro commissioning 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 RCx team will vary based on the overall scope of work. Our firm’s RCx team usually includes, but is not limited to, 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 remonitored to fine-tune improvements. This process

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.

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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 detailed multi-step 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.

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 and many or all of the following items are executed:

• Check for equipment calibration and set up for trending of temperature, humidity, equipment status, air flow, 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.

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, which 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 VS. RETRO-COMMISSIONING Majority of the owners, federal agencies, and private and public entities are looking to reduce their utility consumption by improving energy efficiency practices. An energy audit or retro-commissioning project is the perfect starting point for the existing buildings and sometimes for new buildings. However, it can be

Figure 1 - Overall Retro-Commissioning Process

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difficult or confusing for the owners and users to differentiate between the two processes, and to determine the best option for their facility.The single most important objective of an energy audit is to inform the building owner or user about how well the facility is performing from an energy consumption standpoint. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) defines Preliminary Energy Use Analysis, Level I – Walk-Through Analysis, Level II – Energy Survey and Engineering Analysis, and Level III – Detailed Analysis of Capital-Intensive Modifications. 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 or 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, and this baseline will be used to compare with similar buildings and operations in the area. At our engineering firm, the 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 (i.e. lighting, heating/cooling, outlet plug loads, etc). Some clients may require that the energy audit scope should 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 retro-commissioning 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 retro-commissioning. The precise goals of a retro-commissioning 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 indoor air quality; improving the effectiveness of operation and maintenance procedures; reducing utility bills; reducing energy consumption; and reducing the number of complaints from building occupants.

The outcome of retro-commissioning is a more comfortable and efficient building and well trained facilities staff. Candidates for retro-commissioning 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 retro-commissioning 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 they hope to achieve in order to choose the best course of action for building improvement.

RETRO-COMMISSIONING AS AN INVESTMENT As a building owner should I invest in RCx? Simple payback for an RCx project is typically less than two years and sometimes less than one year. In addition, the RCx process produces better and longer performance out 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 found average cost savings in the following ranges:

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Value of Energy Savings: $0.11 - $0.72/ft²

Value of Non-Energy Savings: $0.10 - $0.45/ft²

Significant cost savings from an RCx process are often a result of reduced energy use. A 2004 study conducted by Lawrence Berkeley National Laboratory (LBNL) aggregated RCx results from 100 buildings and found whole-building electricity savings ranging from 5 percent to 15 percent and gas savings ranging from 1 percent to 23 percent. 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 educating the building owners. The lack of effort could be a direct result of lack of understanding of RCx, lack of properly trained personnel, and 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 Building Commissioning Association (BCA) and University of Wisconsin at Madison. Personnel with TAB backgrounds, Building Control Systems were added to the Commissioning and Retro-

Commissioning Group. The formal training is important but the most valuable skill is the 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 STUDYA building owned by the US Fish and Wildlife Service had a history of problems from the beginning. The contractor was changed halfway through construction, the head of maintenance retired, and heating and ventilation systems never worked right.

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, but what it actually did was preserved the artifacts, which are priceless and represent the core mission of the facility.

The retro-commissioning effort by this engineering firm focused on the full systems assessment including calibration of instrumentation and controls, Test, Adjust, and Balance (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, Operation and Maintenance 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 return air duct, outside air duct, supply air duct, filter section, heating and cooling coils and fan section. The outside air is drawn through an area way louver. The outside air duct damper and return air duct damper modulates to maintain the space pressure and temperature. The

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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 MODEThe 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 70F. 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 percent 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 active control valve is less than 25 percent open, then the fan is switched to low speed. A differential pressure sensor across the pre-filter and final filter generate a maintenance alarm when the pre-filter pressure drop is a minimum of 0.10” wc greater than its pressure drop when clean, or when final filter pressure drop is a minimum of 0.50” wc greater than its pressure drop when clean.

UNOCCUPIED MODEThe supply fan cycles on/off at high speed to maintain a heating setback temperature of 65F with the heating valve open, outside air dampers closed

and return air dampers open. If the space temperature exceeds the cooling setup temperature of 81F, 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 45F 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.

Figure 3

Figure 2 - Fan Coil 1

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FINDINGSFCU-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; the filter was removed and cleaned. The fan coil unit filter was replaced with a clean filter. Upon installation of the new belt, filters the fan were tested and the design airflow was achieved.

The field inspection revealed that the unit was missing the pre-filter, 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 Building Automation System.

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 according to as-built drawings.

The purpose of the data loggers were to record the temperature and the humidity of the area served by the fan coil units. It is clear that the temperature remains steady, modulating between 69º-73ºF, however the relative humidity shows a peak of 55 percent on Day One around 11:00 a.m. and a drop on Day Two to 38 percent around midnight. The control

sequence specified to maintain 70 deg. F with a maximum of 50 percent relative humidity in the space.

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

The control system and its communication links were repaired along with re-calibration of the gauges and meters. The overall system start operating as designed and retest of the system showed significant indoor air

quality (drop in CO2 levels) and overall space temperature improvements.

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

CHILLED WATER SYSTEMThe chilled water system consists of a Carrier air-cooled chiller and two base mounted pumps. The chiller contain three reciprocating compressors and a Comfort Link electronic control system that controls and monitors all operations of the chiller. The overall chiller load is modulated via multiple compressors and based on the return chilled water temperature from the building.

Figure 4

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According to the sequence of operations, the chilled water pumps are at a constant volume and are to operate in a lead/lag sequence, with lead and lag designation switched weekly. The lead pump operates when there is a demand for chilled water, as indicated by at least one fan coil unit chilled water valve being open at least 10 percent. The pumps are to supply 42ºF water to the fan coils. A run time log is recorded for each chilled water pump. When the outside air temperature is less than 50ºF, the chilled water pumps are 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 pressure drop across the strainers for the chillers and pumps was much higher than the design condition 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 re-installed, and the pressure drop across the strainers was reduced significantly.

Both pumps were operating once the outside temperature was above 90ºF and caused excessive flow through the chiller. These pumps did not operate according to the lead/lag sequence. The pumps were tested for the flow and pressure drop and it was noticed that Chilled Water Pump No. 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 were repaired and operating as designed, the overall building condition improved tremendously. According to the users, “This building never was this comfortable.”

Ali Mahmood, a senior mechanical engineer at Stanley Consultants, has 19 years of technical experience. His 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. He can be reached at 773-714-2031 or mahmoodali@stanleygroup.com.

Figure 5 - Air-Cooled Chiller Figure 6 - Chilled Water Schematic

Figure 7 - Chilled Water Pumps 1 and 2