By Thomas Renner
Most people in the United States have a vision of Tahiti that includes year-round summertime temperatures, majestic ocean scenery, and extended vacations with days of de-stressing.
While all that is accurate, facilities managers might take an interest in the island for other reasons. Last year, workers from Geocean installed a climate-friendly sea water air conditioning system at the General Hospital of French Polynesia.
The system is the longest of its kind in the world and includes two underwater pipelines spanning 4,000 meters – nearly 2.5 miles – with a unique monitoring system that protects the structural integrity of the pipelines. The system provides multiple benefits, including cost savings for the hospital and significant reduction of greenhouse gases.
Sea water air conditioning (SWAC) systems started in the 1960s and gained traction in the 1990s. The systems use cold ocean water from depths of below 700 meters. The cold water is pumped to the building, where it can be used in cooling systems. The warmer water returns to the ocean. While the start-up costs are higher than traditional systems, SWAC systems operate at about 15% of the power consumption of standard systems.
While sea water systems would only be available to a fraction of the U.S. – don’t expect to see them in Omaha, Des Moines, or St. Louis – lake source cooling is an alternative and operates similarly to sea water systems. The system in French Polynesia is used at a hospital, but any large commercial space, such as airports, hotels, data centers, and manufacturing facilities could be candidates for air conditioning systems powered by water from a sea or lake.
Traditional cooling systems require extreme amounts of electricity and bring about undesired environmental consequences. Amid the worldwide focus on climate change, many scientists and engineers are collaborating to identify technologies that reduce greenhouse emissions while still providing necessities such as air conditioning.
Climate control is essential at the hospital. The average temperature of Tahiti is between 75- and 90-degrees year-round. While perfect for tourists, the 400-bed hospital requires year-round air conditioning to keep patients and staff comfortable throughout the day.
The government of French Polynesia commissioned the SWAC system for the hospital with the objective of helping phase out fossil fuels and taking advantage of the reduced costs and lower energy consumption.
SWAC systems reduce greenhouse gas emissions and eliminate chemicals needed for chiller machinery and cooling towers. They also reduce noise and the need for on-site machinery space.
Dual Piping Systems
The system designed by Geocean includes two piping systems: A 3,800-meter intake pipe reaches a maximum depth of 900 meters in the South Pacific while a 200-meter discharge pipe returns the water to the ocean. The pipelines are formed of several NPS 710 mm HPDE pipes welded together through polyfusion. The first pipe sends sea water at 41°F into the hospital air conditioning system while water is discharged back into the ocean at temperature of around 53°F.
Geocean, based in France, specializes in marine and offshore works. It is part of VINCI Construction Grands Projets, which develops projects worldwide including marine intake and outfall systems, offshore floating, and pipeline and offshore oil terminals. The $32.6 million project was completed in less than a year. It includes three pumps and has an expected lifespan of 30 years.
“The SWAC makes it possible, with very low energy consumption, to put cold sea water and fresh water from the air conditioning network in thermal contact through a layer of titanium plates,’’ David Wary, an engineer at Airaro, told Le Monde. “This exchange does not require [the waters to mix]: the sea water, after having transmitted its negative calories, is discharged into the ocean without having been altered.”
Piping system integrity is crucial for owners and operators of water, gas, and chemical plants. SWAC systems also rely on the strength of the piping systems.
The hospital’s system was installed using ultrasonic non-destructive testing for pipes developed by GF Piping Systems. The technology can be applied to a wide variety of materials, including the HDPE used at the General Hospital. Using ultrasonic waves, the system detects possible defects in a material and a weld assessment algorithm, identifying any indications of weakness in the weld. It also analyzes the information to evaluate the weld’s strength over the long term.
Weld issues are significant in many piping systems. Nearly 1 in 300 welds deteriorate annually due to poor installation. The breakdowns result in a loss of more than $1 million to repair a leak in gas pipeline. Just one failure can jeopardize an entire system. Leaks in new systems can have a serious detrimental impact on the economic benefits of the project and the image of the business.
Ultrasonic Non-Destructive Testing
In ultrasonic non-destructive testing (NDT), inspectors visit the site and use advanced, patented equipment and ultrasonic testing methods, such as time of flight diffraction (TOFD) and phased array ultrasonic testing (PAUT).
If inspectors see indications of weakness, they identify and measure them before recording the information. Data is fed into an assessment algorithm, which assigns a pass/fail grade. A full report is available within 24 hours.
If the welds are approved, trenches can be resealed and no further action is required, ensuring complete peace of mind to the owner. For the Tahitian project, this level of confidence in the SWAC’s roughly 400 welds were critical since they would be completely impossible to repair once the pipe was installed in the ocean’s depths.
Ultrasonic NDT testing warrants the same level of efficiency in welds as in the rest of the pipes throughout the system’s lifespan. It can also be used prior to installation and operation without sending random welds to a laboratory.
While costly and elaborate, the combination of sea water air conditioning with sophisticated weld testing is an important achievement as the world wrestles with converting to green energy sources.
Renner writes on building, construction, engineering, and other trade industry topics for publications throughout the United States.