HVAC for Navy Submarines

The subject here is the HVAC system, but some preliminary considerations are important to understand the process, especially about the renewal of air and the autonomy of some submarines to remain underwater for long periods.

When you look at a submarine, at least two questions come to mind:

How can we breathe inside when it is submerged?

How is air renewed or purified in submarines?

Back to the past!

Working in a claustrophobic environment like a military submarine is task for few people, who need to be very well trained to withstand long periods submerged into the sea.

Indoor air quality is necessary on surface ships, but the quality and volume of breathable air available on submarines is critical for the crew survival.

The air conditioning system is needed to control and maintain ambient temperature and relative humidity, ensuring good working conditions in confined space.

There are different classes of submarines currently in service with navies worlwide, but let's keep our attention mainly in the extremes, the conventional diesel-electric submarine and the modern nuclear-powered submarine.

"Conventional Submarines"

The conventional navy submarines with diesel-electric propulsion, need to emerge periodically or even navigate in a shallow depth (~15 meters from surface), also known as periscope depth, using the snorkel to take the atmospheric air, allowing the diesel engines to operate and also to guarantee the renewal of air inside the ship.

The figure above shows a typical engine room of a conventional submarine.

The conventional submarine is equipped with electric motors that receive energy from batteries, which are recharged by electric generators powered by diesel engines, which needs air to mix with the fuel to run.

Above type of battery used in Oberon class submarines.

"The main function of the batteries is to provide energy for propulsion and other equipment while the ship operates under conditions in which the main combustion engines cannot be used to provide that energy as while submerged.

The Oberon class submarine has 448 batteries connected in series, 224 of them are locared in the compartiment under the seamen's quarters, and the rest of them are located under the floor of maneuvering compartmemt.

Each battery weighs 500 kg when totally filled with acid and lead".

Propulsion:

2 x 16-cylinder Admiralty Standard Range 16 VVS-ASR-1 diesel engines

2 x 1280 kW generators (1720 hp)

2 x AEI electric motors generating 6000 hp (4470 kW)

2 x axes with three-blade propellers

The main problem is when totaly exposed in the surface or even only exposing the periscope , the conventional submarine become vulnerable and can be easily detected by aircrafts or ships radars. To limit such exposure, that should save energy as much as possible, which limits the mobility and type of mission.

When the submarine is standing on the quay or sailing at calm sea, the sail's hatch and emergency hatches at the top of the hull can be opened for fresh air intake and / or general inspections by crew members.

View of S Riachuelo S22 sail.

My reference of a conventional navy submarine is the Oberon class (length 89.9 m), where three of these were built for the Brazilian Navy, named (S Humaitá / S20, S Tonelero / S21 and S Riachuelo / S22) by former Vickers-Armstrong in Cumbria - England, nowadys BAE Systems Submarine Solutions.

A view of the Riachuelo submarine at the quay.

In 1992, I was asked by a company contracted by the Brazilian Navy to design, build and assist in the installation of a complementary air conditioning equipment for the three Brazilian Oberon class submarines.

Last week, after many years I went to visit S22 again.

The S-22 was launched in 1975, commissioned in 1977 and decommissioned in 1997. The submarine usually sailed with seventy-four men in the crew during fifty-six days of autonomy on mission.

Today the Riachuelo S-22 submarine is a museum, open to the public for visiting in Rio de Janeiro city.

Sub's Profile and General Arrangement

The air conditioning system for Oberon-class submarines was the old DX system (direct expansion). The necessary heat was added to the air by passing it over electrical heating elements, the load being adjusted as required.

Air cooling effected by passing the air over coils which from the evaporator circuit of a conventional vapour-compression system in which gas is compressed and liquefied after being expanded and evaporated while extracting heat from the air.

(*) Believe me, the refrigerant used was R-12!

Originally, the total cooling capacity of the Air Conditioning Plant for the whole ship was only 200,000 BTU's (~ 16.7 TR).

In submarines, generally the cooling capacity is not so high, since the ship practically spends most of the time submerged and recirculating the internal air. In conventional submarines, the renewal of the air occurs with the use of the snorkel or when it is in the sea surface.

The cooling machinery consists of two identical plants, one either side of the ship's center line, working in conjunction with the direct-expansion coolers in the diverse air conditioning units.

Each set of machinery comprises a driving motor and compressor mounted on a common baseplate, a delivery-oil separator, condenser, drier and liquid-to-suction gas heat exchanger. The compressor driven by five endless V-belts and cooling water for the condenser supplied from the Forward Services System.

Oberon Class Subs - The Original Diagram of the Air Conditioning / Refrigeration System.

Currently we could considered the cooling plant as a "Multy-Split Air-Conditioner".

Short ventilation ductwork and some booster fans assist in the circulation of air through out the ship.

Under PROSUB - Submarine Development Program , the Brazilian Government / Navy chose the French company Naval Group (former DCNS) to build four conventional submarines Scorpéne class (S-BR) and one nuclear-powered submarine (SN-BR).

The first of the series, S-BR1 also named Riachuelo (S-40) is due to be launched to the sea in December 2018.

For the construction of the Brazilian submarines, a new company was created, ICN, which is a partnership between the French company Naval Group that owns the technology and the Brazilian company Construtora Norberto Odebrecht - CNO.

AIP - Upgrade on "Conventional Submarines"

Just a quick reference for an intermediate technical evolution in between the extremes.

The most limiting factor for a conventional submarine is the time it can remain submerged, until the need to recharge the batteries and renew the circulating air.

Some countries are developing new classes of conventional submarines with technological improvements, which allows to increase "the diving time".

Air-independent propulsion (AIP) is any marine propulsion  technology that allows a conventional or non-nuclear submarine to operate without access to atmospheric oxygen by surfacing or using a snorkel . The AIP can replace the diesel-electric propulsion system of non-nuclear ships.

AIP increased significantly the submersion time of submarines. This system uses fuel cells, which produce energy and oxygen through electrolysis.

Hermetic environments, such as the interior of submarines, also require the use of artificial air purification. Without this purification, the crew would die suffocated by the carbon dioxide produced. The exhaled gases in respiration are removed and oxygen can be regenerated through a variety of acid-base and oxy-reduction chemical reactions.

CO2 Absorbers

Air Purifiers or CO2 Absorbers were used in conventional Oberon class submarines. known as "canister", these reduced the rate of CO2 inside the ship, making the air circulate through drums containing consumable / Soda-Lime element.

Even today there are several manufacturers of soda-lime cartridge absorption systems like Dr?gersorb?, manufactured by the well-known worldwide company Dr?ger from Lubeck in Germany.

The submarines also have oxygen tanks for emergencies, such as a fire on board. There is a tubing in which the crew can quickly connect masks for breathing.

"Nuclear-Powered Submarine"

In modern warships including nuclear-powered submarines, the preference for the air conditioning system comes to the chilled water plant, using navy magnetic bearing chillers, fan coils and special air treatment / filtration units.

There are several excellent manufacturers of these HVAC equipment for Navy, and the Van Halteren Group from Netherlands is one of them.

Van Halteren Special Products BV, formally known as Bronswerk the Netherlands.

As said by the business manager, they developed an state of the art oil free, magnetic bearing chilled water unit, in compliance to the MIL-Standard, EMC requirements with a low magnetic signature.

They have designed, built, installed and commissioned these units on the Dutch Navy Walrus class Submarines, Singapore Navy Littoral Mission Vessels, Norwegian Navy Logistic Support vessel and some more.

The oil free chilled water units are becoming the new standard for Navy vessels.

They also are the OEM (Original Equipment Manufacturer) for the NBC / CBRN modular filter units.

All right! If you're going to choose an HVAC system for a submarine, whether it's the conventional diesel-electric or nuclear-powered submarine, choose preferably a chilled water system with a low magnetic signature.

Presently low magnetic or nonmagnetic electric motors are used on board of navy vessels and some submarines. 

Electric motors generate internal magnetic stray fields and can be detected. To avoid that is necessary to reduce these signatures as much as possible, to be able to operate in stealth mode.

Now, let's talk about oxygen!

Each crew man needs at least12 cubic meter of air every day, just to stay alive and more if they are working hard!

Q: If nuclear submarines don't emerge to "breathe" the atmospheric air, where do they get the air from?

A: From sea water.

By passing electricity through the water, it is possible to separate the substance into two parts, hydrogen and oxygen.

Yes, oxygen from water but on a very large scale.

For this is used the oxygen generator system, usually two, one on-duty and another stand-by, and Treadwell Corporation from USA is a renowned and well-known manufacturer.

Let's dive?

Hatch saved!

"Dive! Dive! ...

You can't see her, she can dive to over 250 meters and stay down for six months.

You can't hear her, she can run for twenty years without refueling.

She is the most lethal weapon ever designed".

She is the largest submarine in the U.S Navy, the USS Pennsylvania, an Ohio-class ballistic missile submarine, which has been in commission since 1989.

One hundred sixty-five men on board during patrol for seventy-two continuous days.

Nowadays the limiting factor for nuclear submarines is the crew morale, or perhaps more specifically, the amount of food the ship can hold.

Worth watching the movie below about USS Pennsylvania, which was published on the Web in September 2013 by Largest Dams.

The evolution of technology is a show, but there are cool things to know as the history of Turtle, the first submarine to be put on military use as told by Encyclopaedia Britannica.

"Turtle, one-man submarine, was the first to be put to military use, built and designed by the American inventor David Bushnell in 1775 for use against British warships. The pear-shaped vessel, made of oak reinforced with iron bands, measured about 2.3 m (7.5 feet) long by 1.8 m (6 feet) wide.

It was equipped with a mine that was to be attached to the hull of an enemy ship. In 1776, in New York harbour, the Turtle tried to sink the British warship HMS Eagle but failed and none of its succeeding missions was successful".

Watch the short video below, published on the Web by Science Channel in May 2016.

In this article, the focus was on military submarines, although there are submarines for oceanographic research and also for leisure / short sightseeing tours.

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I have worked many years with marine & offshore HVAC-R and part of the time dedicated to the HVAC for Navy vessels.

It's time to pass on the knowledge to trainees, fresh graduated engineers and young apprentices.

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