Sustainability at Sea:
Efficiency Analysis Backs Plastic Piping for Marine HVAC Systems
by Roberto Chiesa

he international shipping trade is under intense pressure to reduce its greenhouse gas emissions (GHG). With current levels of CO2 production at about 1 billion metric tons per year, the maritime industry has a larger carbon footprint than the entire Federal Republic of Germany. In response, the International Maritime Organization (IMO) has set an ambitious goal: a 50 percent reduction in total marine industry GHG contributions by the year 2050.

Within that overall framework, shipbuilders and their suppliers are free to experiment with a wide variety of strategies for reducing fossil fuel consumption. Energy efficiency is the order of the day, as engineers and technicians strive to lower costs and meet industry targets. In this light, the HVAC systems of passenger vessels have come under increased scrutiny.

Climate control is of obvious importance to the passenger experience. However, heating and cooling systems are energy-intensive to operate, driving higher fuel costs. These systems have also historically required extensive networks of post-insulated steel pipe, which is energy-intensive to produce, heavy to transport and vulnerable to corrosion, adding maintenance costs to fuel expenses. It thus seems well worth investigating the alternative of using plastic piping solutions, which are corrosion-free and far lighter.

In 2021, a plastic piping manufacturer combined forces with a shipbuilding firm to test the theory that the choice of polyethylene for shipboard HVAC piping could improve energy efficiency for passenger vessels. Results indicated that as one element in an overall optimization strategy, polyethylene can make a meaningful contribution to sustainability at sea.

Cruise ship in water between lush green mountains
In 2021, GF Piping Systems and the marine engineering firm Foreship measured the efficiency benefits of pre-insulated polyethylene piping for marine HVAC systems.
Cruise ship at sea during sunset
In a head-to-head comparison with post-insulated steel, a marine HVAC system using GF Piping Systems’ COOL-FIT 2.0 and 4.0 would be expected to save up to US$3.8 million in annual operating costs for a single cruise ship.
Head-to-head comparison
To understand the impact of the piping alternatives on energy efficiency, researchers designed a complex simulation. Calculations were based on the typical dimensions of a 150,000 gross-ton cruise ship, which would include approximately 600 meters of HVAC piping. The study design assumed the use of a chilled water air conditioning system with four chiller units and four centrifugal supply pumps.

A baseline system of post-insulated steel was compared to a specific alternative product made of pre-insulated polyethylene. The expected electrical power draw of the two systems was then calculated under various operating conditions.

Results showed reduced energy use in the polyethylene scenario, whether the pump was assumed to be operating at full speed (constant flow) or whether it was assumed to be running at variable speeds in response to demand (variable flow). For example, under the variable flow assumption, total power draw would be 60 kilowatts less for the system made of polyethylene. The polyethylene system also operated at a lower pressure and caused less temperature rise.

Impact measured by the ton
The study then calculated the environmental and financial impact of this difference in performance. For a 150,000 GT cruise ship, the lower power requirements of polyethylene would result in a savings of 82.1 tons of fuel per year, assuming a liquid natural gas (LNG) powered ship with variable flow pumps. For a ship powered by marine gas oil (MGO) with constant flow pumps, savings could reach 112.5 tons of fuel per year.

The use of pre-insulated plastic piping would thus be expected to reduce greenhouse gas emissions for the same ship by up to 373.7 tons per year. This figure was calculated using a “well-to-wake” analysis that considers the entire lifecycle of LNG and MGO fuels. The GHG total includes not only carbon dioxide but also nitrogen oxide, sulphur oxide and particulate matter. To put the amount in perspective, this tonnage is equivalent in size to two full-grown blue whales or 94 Asian elephants.

Overall, this degree of reduction in GHG emissions would also create small but measurable changes in key indicators of climate impact used by the IMO, the Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator (CII).

View of ocean from balcony of cruise ship during sunset
The use of GF Piping Systems’ COOL-FIT 2.0 and 4.0 pre-insulated polyethylene piping in a cruise ship’s HVAC system could reduce the vessel’s greenhouse gas emissions as much as 373 metric tons per year.
Welcome financial benefits
And how does all this affect the bottom line? To calculate the cost savings resulting from the use of polyethylene, researchers used average prices for LMG and MGO as recorded between April and September 2021 at the port of Rotterdam, The Netherlands. Based on those price figures and an estimated inflation rate of 2.5 percent, the greater efficiency of polyethylene piping would result in a savings of US$2.3 million over the next 25 years — for just one ship.

Meanwhile, steel piping also carries higher maintenance costs. Corrosion is a perennial concern, and steel piping systems are commonly post-insulated with rubber-based foam. Human error can damage the foam in the insulation process and gaps can allow condensation or even ice to form between the pipe and the insulation.

By contrast, pre-insulated plastic piping is corrosion-free and maintenance-free. When this differential in maintenance costs is also considered, polyethylene would save that same cruise ship closer to US$4 million over the same time span.

Crosscut of clean and dirty plastic and steel pipes
For passenger vessel operators, pre-insulated polyethylene (such as GF Piping Systems’ COOL-FIT 2.0 and 4.0) is both lighter in weight and lower in maintenance costs than post-insulated steel.
One piece of a strategy
The scale of the challenge faced by maritime operators is imposing. With sustainability widely accepted as an important collective goal, and tougher standards on the way all around the world, the industry is confronted with a critical need to reduce both its consumption of fossil fuels and its impact on the environment. Developments in the economy since this study was conducted have only raised the financial stakes, as fuel costs and inflationary pressures have increased.

In this context, it may be tempting to focus on seeking the next paradigm shift, some not-yet-envisioned form of green technology that will drastically reduce emissions in one single, straightforward step. But while efforts in that direction go forward, the need to make progress is pressing now. In this regard, materials specialists have much to contribute, if changing the composition of even one system in a complex vessel can have the impact demonstrated here. The scale of the current problem means that even an improvement of many tons in GHG emissions will sound paltry when expressed as a percentage. But combined with many other such meaningful changes, the potential of lighter, maintenance-free and recyclable materials such as polyethylene to make shipping more sustainable is impressive indeed.

Roberto Chiesa is head of marine business development for Georg Fischer Piping Systems. He is based in Milan, Italy. For more information, see www.gfps.com/marine or contact roberto.chiesa@georgfischer.com, phone +(39) 335-7432422.