HVAC systems are milestones of building mechanical systems that provide thermal comfort for occupants accompanied with indoor air quality.

HVAC systems can be classified into central and local systems according to multiple zones, location, and distribution. Primary HVAC equipment includes heating equipment, ventilation equipment, and cooling or air-conditioning equipment. Central HVAC systems locate away from buildings in a central equipment room and deliver the conditioned air by a delivery ductwork system. Central HVAC systems contain all-air, air-water, all-water systems.

Two systems should be considered as central such as heating and cooling panels and water-source heat pumps. Local HVAC systems can be located inside a conditioned zone or adjacent to it and no requirement for ductwork. Local systems include local heating, local air-conditioning, local ventilation, and split systems.

Buses are an easy and convenient way to get around whether traveling long distances or just commuting around the city.

Air conditioners on buses operate similar to those on trains, but there are additional conditions. HVAC units on buses are commonly housed on the top or rear of the bus with the compressor being run by the engine as in cars. In recent years, roof mounted units have grown in popularity due to their improved energy efficiency. Constant exposure to the elements and rough road conditions can take their toll on the compressor of a bus HVAC system, so protecting the compressor is crucial to the longevity of the HVAC system.

While train and subway HVAC systems are less standardized, they operate under similar basic principles and surely get the job done.

HVAC systems in trains are often composed of multi unit inverter condenser and evaporator sections mounted on top of the train or beneath the floor in the undercarriage, although they can also be mounted on the side of the train as well. The systems can also be split so that cooling is distributed from the ceiling within the cabin and heat is distributed from the floor. HVAC systems must be particularly efficient at ventilation on subway cars not only to provide quality air to passengers but also for safety reasons in case of a fire or other emergencies.

Let’s also take a journey under the sea to have a look at how cooling is managed in submarines.

There is only a small amount of space for occupancy in a submarine, but within the inner hull, heat is constantly being produced by elements such as engines, storage batteries, stoves, electric lights and even people. With this heat, moisture is also continuously being produced. Only a few cubic feet of space is available for housing air conditioning equipment, but air conditioning is crucial not only for the comfort of the occupants but to control this level of moisture. The temperature at which the air becomes saturated with moisture is called the ‘dew point’ and this dew point must be managed to limit the amount of moisture on board the submarine. To achieve this, air from inside the submarine is drawn by fans into an evaporator that removes moisture from the air and that water is drained away and stored in a tank away from the internal environment of the submarine. The drier, cooler air is returned to the interior of the submarine for a drier and cooler environment.