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ver since open vessels were enclosed into com- partments, ventilation has been a paramount concern, for passengers, crew and the existence of the ship itself.

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In 2021, and for the next few years, HVAC experts cite three top priority issues: the COVID-19 pandemic; en- ergy ef? ciency; and ? nding safe, new refrigerants with low global warming potentials (GWP).

In some ways these challenges are linked. In other ways they are evolving separately. But each presents naval archi- tects and ship owners with a myriad of questions.

I. COVID-19.

The cruise industry is at the eye of the coronavirus storm. Ventilation and air quality are central to the indus- try’s return to sail plans.

In July 2020, to tackle the pandemic crisis, the Royal

Caribbean Group and Norwegian Cruise Line Holdings established a team of public health and medical experts, referred to as the Healthy Sail Panel. HVAC and ventila- tion were in the crosshairs. In September, in an extensive report, the panel recommended a number of HVAC and air management strategies. Examples include: • Enhanced ? ltration – Upgrade HVAC ? lters to the highest level possible given the constraints of ship age and ventilation type.

• Optimize air? ow patterns – Don’t recirculate air. If that’s unavoidable then use high-grade ? lters.

• Think strategically – establish preventative practices where the virus might be hardest to control or where crowding is common.

The report emphasizes that “HVAC upgrades can drasti- cally improve ? ltration of pathogens” and that “cruise opera- tors should make every possible effort to upgrade the HVAC ? lters throughout their ships to MERV 13 ? lters” (MERV =

Minimum Ef? ciency Reporting Value, a 1 – 20 rating sys- tem in which 1 is the lowest level of ? ltration, 20 is highest).

The cruise industry, at least as represented by the Cruise

Lines International Association (CLIA), supported the panel’s recommendations. “The CLIA Global Board unani- mously voted to adopt all of the listed core elements for an initial restart of limited operations in the Americas,” CLIA wrote in a September 2020 press release. HVAC was among the listed core elements slated for change: “Ventilation. Air