In recent years, most municipalities have adopted building codes for energy conservation for new construction and major renovations. This mandated building code known as commissioning is an intensive quality assurance process, with a goal of operating a building efficiently while providing uniform comfort for all occupants. After years of operation most buildings operate less efficiently and use more energy. At which point, retro-commissioning may provide a path to occupant comfort and improved energy efficiency for buildings that are underperforming.
The 2015 and 2018 International Energy Conservation Codes (IECC) for new building construction and major renovations is the basis for many current design standards for energy conservation. The IECC mandates that an independent third party consultant employed by the building owner provide commissioning services during the design and construction or renovations. Commissioning is typically required for facilities above 30 tons of cooling and 650-MBTU of heating.
Buildings tend to use more energy with age. After about 10 years of operation, this process may accelerate. Much of the building inventory in the United States is at the point where evaluating performance and energy usage is required or highly recommended, particularly for office buildings, schools, medical professional buildings, and other health care facilities.
Retro-commissioning is applied to existing buildings with a goal of identifying how to improve the operation and efficiency of energy consuming systems and equipment. Retro-commissioning is usually a multi-step process that begins with an analysis of an existing building through a study of energy efficiency and benchmarking with peer buildings. Retro-commissioning may address latent design or construction deficiencies after a building is occupied. It also develops a process to implement energy efficiency and operational improvements. Potential capital improvements are categorized from lowest to highest. At the conclusion of retro-commissioning, documentation of the process including findings and improvements is provided and is carried into operator training.
To determine if a building is a good candidate for retro-commissioning, a team of specialists will first start with identifying high energy use, equipment or systems with persistent failures and repairs to equipment or systems, and frequent complaints from occupants on temperature, relative humidity, and indoor air quality. Building size and equipment age are confirmed and building documentation is located. Next, the owner’s operating requirements are considered and factored into a plan for potential improvements. An initial site walk-through is performed. Identification of the type of HVAC and lighting controls is performed. The capabilities of in-house staff are assessed.
Once the planning phase has been completed, the investigation phase begins. The team will review facility documentation such as drawings and control sequences of operation, perform functional diagnostic tests, and perform quick, low cost repairs during the investigation and testing. During this phase, they will perform diagnostic monitoring of operating characteristics such as utility meters, temperature and relative humidity levels, operating hours, building indoor air pressures, and CO2 levels. A master list of findings will be developed for use as a tool for decision-making. Additionally, it’s time to prioritize and select energy saving and operational improvements using cost-to-benefit analysis.
The next phase is focused on the development of an implementation plan and scope of work from the master list of findings. At this point, the team will select operational or capital improvements using outside contractors and owner led or in-house staff. The team will test improvements implemented for anticipated results. A summary report with further actions is developed.
The final phase of the retro-commissioning process is the verification phase. The team installs recorders and monitoring equipment as utility meters, temperature and relative humidity recording tests, operating conditions, and other diagnostics. A final report of retro-commissioning activities and measures implemented is created, and includes: a master list of findings, updated estimates of energy cost savings, results of performance improvements, test results, recommended frequency of re-commissioning, complete documentation, and a list of further capital improvements warranting investigation. Next, the team will compile a systems manual including re-commissioning documentation, and operation and maintenance recommendations. They will also develop a re-commissioning plan with intervals to keep systems at peak performance. Training will be provided for in-house staff, and a hand-over meeting will be held to close the project.
Work performed by Terracon for The Children’s Hospital of San Antonio serves as a good example of how retro-commissioning can result in long-term benefits to the owner and occupants. Terracon’s retro-commissioning team was initially engaged to address the issue of elevated room temperatures and relative humidity levels in operating and patient rooms varying from requirements of owner and state health statutes. Lack of building indoor pressurization by the HVAC system had led to environmental control problems.
Investigation showed that air handling systems were not reliably supplying conditioned air temperature and relative humidity to many areas. Systems were also not delivering stable indoor pressure in all areas. The solution involved retrofit of the HVAC system with direct digital controls an repair and re-calibration of the air handling systems. The building was re-balanced to the design amounts of conditioned air and outside air ventilation in all areas.
Next, new sequences of operation were developed for more accurate temperature and relative humidity control savings, and to maintain net positive indoor air pressures on all floors. Testing was completed after retrofit to verify requirements of the redesign. The retro-commissioning project resulted in improved HVAC performance, reduced occupant complaints and substantial energy savings.
Retro-commissioning of a building to improve performance is not a process that only needs to be performed once. Owners should monitor assets to validate their performance versus the design intent for optimal operation.
Re-commissioning is enacted when a building has previously undergone commissioning or retro-commissioning. This process is usually triggered by a change in occupancy, increasing energy use, operational problems, or other comfort complaints by occupants. Re-commissioning is usually recommended at routine intervals to preserve the operational benefits and energy efficiency realized in previous commissioning or retro-commissioning of a commercial building.
Retro-commissioning goes beyond day-to-day building maintenance and resolving operational problems by conducting a thorough diagnostic assessment of mechanical HVAC systems, lighting, and controls. Operational and occupancy changes may require reconfiguration of the mechanical HVAC and lighting systems and controls. Retro-commissioning helps the building owner identify and meet targeted energy efficiency and performance requirements through benchmarking. It reduces the potential for unexpected repairs and replacements. It also verifies that maintenance personnel are adequately trained and have documentation to operate the building efficiently and achieve optimum performance. Retro-commissioning takes a holistic view by observing, testing, monitoring, and trending energy consumption of building systems. It identifies and addresses potential HVAC operational concerns such as indoor air quality and building humidity and temperature control.
Jeffrey A. Miller, P.E., is a Senior Engineer and Principal in Terracon’s Houston office. Jeff has more than 40 years of experience specializing in mechanical, electrical, and plumbing diagnostics, design, engineering, commissioning, and retro-commissioning.