Retro-commissioning is a process that involves an assessment of building systems to ensure they operate correctly, taking into account the original design and specifications, but also addressing any changes in occupancy since construction. Retro-commissioning can be a very cost-effective way to improve building energy efficiency: according to the ENERGY STAR Building Manual by the US Environmental Protection Agency, a retro-commissioning project has an average cost of $0.27 per square foot, while achieving energy savings of 15% and a payback period of just 0.7 years.
Retro-commissioning is characterized by being a knowledge- and labor-intensive process, where material costs are minimal or zero. However, a retro-commissioning project can also help identify opportunities for building improvements that require more capital, such as retrofits and equipment upgrades. The following examples illustrate the difference between the three types of projects:
- Adjusting HVAC controls to optimize performance is a retro-commissioning project.
- Upgrading the lamps in a lighting system to LED while preserving the fixtures and ballasts is a retrofit project, where parts of the existing installation are still used.
- Replacing window-type air conditioners with ductless mini-split units is a.
In New York City, retro-commissioning is legally required every 10 years for all individual buildings with at least 50,000 ft2 of floor spaces, groups of buildings under the same tax lot adding up at least 100,000 ft2, and groups of buildings under condominium ownership adding up at least 100,000 ft2. Local Law 87 of 2009 establishes the minimum requirements for the retro-commissioning process and the report that must be submitted.
How is Retro-Commissioning Carried Out?
Each building is unique, and the same applies for retro-commissioning projects. However, the most significant energy-saving opportunities are normally found in lighting and HVAC systems. The following are some of the main requirements established by LL87 for NYC buildings:
1) Operating protocols, sensor calibration and sequences
- Adequate HVAC temperature and humidity set points.
2) Cleaning / reparations
- Cleaning HVAC system components, especially those more susceptible to dust accumulation, such as air dampers, ducts and coils.
3) Documentation and training requirements
- Correct and up-to-date permits for all HVAC, plumbing and electrical equipment.
There is no single retro-commissioning procedure that applies in every case, but activities can be summarized as: calibration, adjustment, testing, low-cost modifications, training and documentation.
Retro-commissioning and recommissioning are basically the same procedure. The main difference is that the term recommissioning is used when the building has already been commissioned before, and the process tends to be faster and simpler as a result.
Benefits of Retro-Commissioning
As previously stated, the main benefit of retro-commissioning is energy efficiency. However, the procedure brings many other benefits:
- Visual and Thermal Comfort: Occupant complaints are reduced after a retro-commissioning project, thanks to the improvement in lighting levels, temperature and humidity.
- Equipment service life: When equipment operates optimally, its service life is extended. This allows building owners to delay capital expenditures that are due to equipment replacements.
- Indoor air quality (IAQ): Poor HVAC operation can lead to the accumulation of air pollutants or excessive humidity. In turn, humidity stimulates the reproduction of mold and dust mites, both of which can cause allergic reactions or trigger asthma attacks.
- Improved productivity: Retro-commissioning can help eliminate issues such as noise or lamp flicker, which may distract occupants and reduce productivity in office environments.
- Improved safety: This applies to lighting improvements in particular, where improved visibility and uniform lighting reduce the chance of an accident.
- Maintenance savings: Equipment issues are addressed and solved permanently during retro-commissioning, which results in long term maintenance savings.
Even if major upgrades are planned for a building, retro-commissioning or recommissioning is recommended as a first step. It helps identify the most promising opportunities for building upgrades, and also provides energy savings that can be used to help cover the cost of future projects. In addition, after optimizing performance of building systems, it may be possible to reduce the capacity of new HVAC equipment. For instance, a significant improvement in the building envelope reduces both heating and cooling loads.
Retro-commissioning can also be a powerful tool when a building owner is striving for ENERGY STAR certification, where a minimum score of 75 is required. The program has documented cases where buildings earn 10 points or more towards the certification with retro-commissioning alone. For example, the federal Hartfield Courthouse in Portland, Oregon, had an ENERGY STAR score of 65, which was increased to 75 after retro-commissioning alone. In other words, the building was certified without major building system upgrades.
When is Retro-Commissioning Recommended?
In general, a retro-commissioning project can yield a higher return on investment in older buildings, or buildings that have never been commissioned before. However, there are many situations that indicate building systems must be checked and tuned:
- Recent occupancy change: HVAC and lighting needs vary significantly according to the type of occupancy. For instance, if space previously used for a store is converted to an office area, increased ventilation rates will be needed due to the higher occupancy.
- Increasing energy consumption: If the electricity and gas bills of a building have been constantly increasing with no evident explanation, retro-commissioning can be an effective way to identify and address the cause.
- Increasing occupant complaints: These are typically the result of poor lighting, noisy HVAC systems, poor water pressure, excessive temperature or moisture extreme, just to name some possibilities.
Hiring a commissioning consultant is highly recommended to achieve the best possible, especially if the retro-commissioning project is being carried out to meet the requirements of Local Law 87. Even in properties where the procedure is not mandatory, the return on investment can be significant, freeing up capital for business operations or for other building upgrades.