I have been talking about recommissioning/continuous commissioning of chilled water plants for over a decade now in Dubai and in the GCC region. However, it’s apparent that very few plants have gone through the process or incorporated the concept at all.
First, I think it’s important to understand what the commissioning process is, how it has sometimes fallen short when it comes to chilled water plants and why I feel it’s so important to recommission/continuous commission as well as what the recommissioning process is. It’s also important for the plant owner or management to fully understand that recommissioning is not part of an Annual Maintenance Agreement – it is well beyond that and a cost is associated with this type of in-depth service, but without question the savings achieved will far outweigh the additional cost. One other important point: It is my strong opinion that a specialist chiller company, a qualified one with a proven track record of performing recommissioning of chilled water plants be utilised to carry out this service.
The concept of commissioning comes from the Naval lexicon, meaning “put a warship on duty”. This is likely the origin of the concept of commissioning, as popularly used today. A ship that has been commissioned has been through a thorough process of quality assurance on the installation of the equipment, performance of the system and training of the crew. Only once all the materials, systems and staff have been thoroughly vetted is the ship commissioned into active duty.
For a chilled water plant, commissioning can be thought of as the process that ensures that a plant operates as the consultants, design engineers and owners intended it to and that the O&M staff are trained and organised to operate and maintain the plant’s systems and equipment. This is done by verifying and documenting that the plant systems, equipment and components are planned, designed, installed, tested, put into beneficial service, and operated and maintained to meet the owner’s requirements and as designed by the engineers and consultants. Commissioning is performed to keep the chilled water plant in optimal condition through the life of the plant from the viewpoints of environment, energy and facility usage. These viewpoints should include energy conservation, environment, and preventive maintenance of the plant equipment and systems.
Unfortunately, many of the chilled water plants that have been labelled as ‘commissioned’ have not been through the thorough process that the term encompasses. Energy efficiencies of the equipment are rarely, if ever, verified on individual equipment basis or as a system. Chillers, pumps and towers are not started and put into beneficial services with enough precision and with an emphasis on energy and design performance, not only at full- load but part-load design. This reason, along with some others, is why I have been calling for recommissioning or continuous commissioning, which are basically the same type of commissioning, to be implemented at chilled water plants.
The goal of a continuous or ongoing commissioning is the same as an ongoing programme of re-commissioning. The key difference is that monitoring equipment, and trending and analysis software are left connected to the plant systems to enable continuous tracking and reporting. “Continuous commissioning” is a term that was trademarked by the Energy Systems Laboratory of Texas, a division of the Texas Engineering Experiment Station, and a member of the Texas A&M University System. They define it as “an ongoing process to resolve operating problems, improve comfort, and optimise energy use”.
A new class of software products, referred to as Fault Detection, Continuous Energy Oversite, Remote Monitoring and Equipment Diagnostics, has emerged over recent years to support continuous commissioning. These products are generally cloud based and remote operated, enabling the plant performance to be monitored against its optimal operating conditions in a near to real-time format. The software tools provide visibility into plant performance and help identify anomalies that result in excess energy consumption and pose risks to system health.
Why I recommend recommissioning/continuous commissioning
Water-cooled electric centrifugal chillers in the GCC region are generally selected and designed to operate in the range of 0.687-0.760 kW per tonne. USCS, from 2003 to 2012, looked at data from operating chillers and plants in the region, from the newly constructed and commissioned plants to five-year-old plants, as well as chillers up to five years old. All were electric-driven centrifugal plants. What we determined was that the operating range of these chillers before recommissioning, continuous commissioning, Corrective Service Procedures and Chiller Optimisation Strategies were applied was between 0.98 and 1.8 kW per tonne. Of the chillers these services and strategies were applied to the kW per tonne ranges were between 0.513 and 0.759.
Further, the results of a survey by San Diego State University’s Energy Engineering Institute on 31 chiller plant sites across the United States found:
- Chillers that should be operating in a range of from 0.65 to 1.00 kW/tonne, according to the OEM specifications, were often actually operating at 1.5-3.0 kW/tonne and that most chiller plant operators had no idea how well their chiller plants were performing
- A report on 14 chiller plants by the Northwest Energy Efficiency Alliance found a substantial variation in plant energy efficiency ranging from 0.55 to 1.80 Kw per/tonne
- A report by the California Energy Commission addresses the problem that buildings and chilled water central plants do not perform as well in practice as is anticipated during design
The reasons for the above are…
- Improper equipment selection and installation
- Lack of rigorous commissioning and proper maintenance
- Poor feedback on operational performance and energy performance
The re-commissioning process is fully documented with before equipment and plant energy benchmarks as well as post recommissioning energy results as well as all NDT inspections and analyses and complete equipment performance reports. It should also include recommendations to optimise the plant’s operation and further recommendations on equipment reliability and energy savings. Many technologies and advancements have been made in chiller design with improved energy efficiencies being realised; however, these efficiencies may not be realised unless proper commissioning is performed and continuous commissioning and recommissioning programmes are in place.
I strongly recommend that any chilled water plant from 400 tonnes of refrigeration to 50,000+ tonnes of refrigeration should consider implementing recommissioning services. It is sure to save you energy and money.
Dan Mizesko is Managing Partner, U.S. Chiller Services Int, HVAC & Energy Services International. He can be contacted at firstname.lastname@example.org.
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