A Ship's Environmental system can be thought of as consisting of several parts. There is typically a central location where the majority of the large environmental control devices are located. These are things like air and water tanks, treatment beds and pumping stations. On a small ship these units are usually located near each other in engineering. On larger ships they may be located in several environmental system bays distributed throughout the ship. Each system also usually has component parts located in each compartment that is served.
A typical stateroom will have supply and return vents, a water delivery unit, temperature and humidity control units. If there is a fresher present sanitation and cleaning units will also be present. All will be connected to water and fluid supply and collection piping. The locally installed parts of the system will usually be controlled by an LCP.
Most species in known space require very similar atmospheres to survive. Imperial norm, as set by the Imperial Interstellar Scout Service and recognized by the Office of Calendar Compliance is 78% percent nitrogen, 21% oxygen, with 1% made up of other inert gases. In a spacecraft these inert products can increase to dangerous levels, as oxygen is consumed by the respiratory activities of the sophont aboard, who will also exhaust waste products into the ship's air. Not just gases, but other products, such as water vapor, are also the result of respiration in most species and must be dealt with by a ship's environmental control system.
Atmospheric Environmental Systems can be divided into gas mixture/recycling and temperature control systems.
Gas Mixture/ Recycling Systems
The Gas Mixture/Recycling System consists of a number of subsystems, each of which is controlled by its own LCP (Local Control Processor.) Each system communicates with the ship's computer to ensure an even environmental transition between different systems. Environmental Systems are also typically designated either Limited or Full Life Support systems.
Limited life Support systems are almost never used as the primary system on modern spacecraft, though limited life support is usually installed in specific areas to act as a backup in case of failure of the Full Life Support system. The system consists of bottled oxygen and rebreathing equipment which allow limited extension of the duration of system operation. Since the rebreathing equipment requires power most installations include rechargeable power cells to ensure operation even in a power outage, the time the emergency life support system is most likely to be needed. A standard sized male of Solomani or Vilani lineage requires about 4.2 lbs of compressed air an hour to survive. Staterooms, control stations, and even passageways will typically have a tank containing at least one hour of air for every sophont expected to be in that space. The rebreathing equipment will allow the bottle air mixture to last 10 times as long. The duration of a Limited Life Support system is measured in man-days.
Full Life Support
Full Life Support systems are the standard. They consist of holding tanks, humidity control units, recycling beds, filtration, and forced ventilation.
Holding Tanks provide a surge volume to ensure that there is always enough gas aboard to fully fill the internal volume of the ship. It is from this volume that air exhausted from the ship in an emergency is replaced. The holding tanks also provide sufficient volume to raise the internal pressure of the ship above standard when required.
Humidity Control is provided to ensure that the air in the ship remains comfortable. If the air is too dry it will be uncomportable for the crew to breath, their eyes will hurt, their sinuses burn. If the crew consists of dolphins it is even more vital that the air be kept moist enough. Conversely air that is too humid can be equally uncomfortable, as well as bad for equipment. Most ships have independent humidity control for each stateroom. This allows passengers (and Crew) from especially dry or humid environments to comfortably reside there.
Recycle Beds are used to convert waste gases, like carbon dioxide into oxygen. The beds may be either chemical or biological constructs and are essentially self renewing. Advanced biological recycle beds can even produce protein as a byproduct, allowing for a Total Life Support system, which does not even require that food be kept on board. Though nourishing if properly prepared, such food is only marginally palatable and is not typically used as the only provoder for a ship's crew or passengers.
Filtration is used to remove particulate and chemical waste matter from the system. Most systems have a central filtration bank that removes the majority of waste products and local filters which remove vent dust and other paticulate. Most filters are installed in systems that are self cleaning, though local filter racks must sometimes be removed by hand for delivery to a cleaning shop. The Type S Scout/Courier Sulieman-Class is known to suffer from poor design of this filter self renewal system, which can result in the failure of the filtration system to control odors. The only solution is a costly refitting of the system or periodic replacement of the filters combined with atmospheric purging of the ship.
Forced Ventilation provides for the recycling of air through a system of supply and return vents from centrally located life support systems. Mechanical or inline gravity fans are used to provide circulation. On most ships ventilation ducting is fairly small and runs in the spaces between decks. Larger ships will have proportionally larger vent ducts, though only the very largest ships will have ducting large enough for a full grown adult to fit into, (vid plots notwithstanding.) Each compartment must have at least one supply vent and one return vent. Each vent must be of a size that will allow enough air to circulate to the compartment to prevent the build up of waste gases and allow temperature and humidity control. Where ever a vent passes through a bulkhead or deck there will be an isolation valve, which will operate like an iris valve should either section of vent ducting become exposed to vacuum. This prevents cascading depressurization across bulkhead or deck boundaries.
Supply Vents contain the humidity and temperature control units, as well as racks for local filtration. The cover of the vent may be either a grill, or at higher tech levels, a permeable membrane. Most compartments will further distribute air throughout the compartment through a number of discharge ports.
Return Vents typically contain a local filter to prevent getting excessive dust into the system. On some ships this part of the system is also part of the ship's self-cleaning system and air can be further filtered to remove even more dust through the use of a vacuum impeller or inline gravity pump. In that case the return vent will almost always be installed just above the deck and be much wider than it is tall to maximize dust intake. Part of the humidity control system is also installed in the return vent and is also associated with the temperature control system.
Modern spacecraft almost always use air temperature systems to control the environmental temperature in each individual compartment. This method is seen as superior to the direct radiant heat and heat absorption technologies that are available. Each space typically has an independent temperature control system. Air is heated or cooled prior to being pumped into the compartment. Sensors in each compartment are fed into the environmental LCP in each space to provide for constant temperature control.
Purging and Reclamation System
Most craft equipped to land onworld are equipped with an atmosphere purging system. This system will allow the entirety of the ship's atmosphere, including any air in holding tanks to be expelled overboard, while collecting air from the exterior environment to replace the discharged air. The planetary air can be run through a filtration and bio-decontamination system prior to being distributed through the system, though this is not common when collected air is from a known safe environment. Close cycle purging can take many hours for a ship of any substantial size and the loss in time is not considered worthwhile except when there exists the possibility of harmful pathogens or excessive toxins.
The system consists of supply and return vents external to the ship. These vents are normally covered and sealed with double isolation valves to prevent the accidental purging of ship's air. As for airlocks, most purging systems have some kind of encrypted key code to prevent unauthorized use.
Standard fittings allow small amounts of replacement gas and water to be acccepted by the system to allow "topping up" retention tanks, to replace air and water lost in normal use. This is typically done from store supplies available at most starport berths.
Most ships will have a cross connect between the atmospheric environmental system and the airlock or hanger/cargo gas control system. This allows gas reclaimed from the airlocks or hanger/cargo areas to be retained onboard, rather than vented off. Air from the atmosphere holding tanks is used to repressurize airlocks and hangers. Volume monitoring devices will prevent venting the entire ship's atmosphere through a faulty airlock.
Water is a vital commodity on a starship. A member of Humaniti can spend the entire duration of jump without food, but will almost certainly die within days without water. Safe, drinkable water is the result of careful recycling of resources. Most of the water used by the majority of sophont species is returned to the environment as either water vapor from perspiration or respiration or is expelled as bodily waste products.
The potable water system must take water from the holding tanks and the recycling system and deliver it to where it is needed. Most water used on board is used for cooking. Drinking water makes up the balance of water usage. Small amounts are often needed for the atmospheric filtration system and for any plants kept aboard. Unlike in earlier ages, cleaning, even of living beings, is almost entirely done using recyclable cleaning compounds separate from the potable water system.
The potable water system must have holding tanks sufficient to hold an adequate volume of water to see to the ship's need. Most ship's carry enough water to allow survival for the duration of jump should something happen to the recycling system. This amount is sufficient for drinking water needs, but not for other uses.
Pumps, Pipes, and Valves
Mechanical or inline grav pumps provide pressure to deliver water throughout the potable water system. Automatic valves are installed where ever a pipe penetrates a bulkhead or deck to prevent a compartment depressurization from compromising the system. Most modern ships use a single loop system, which provides cold water to all sections of the ship. Hot water is provided at each location that requires it by the water delivery unit.
Water Delivery Unit
The water delivery unit provides water at a controlled temperature to what ever container is placed under it. It can produce water at any temperature from ice cold to boiling hot at the direction of the operator. There is a water delivery unit installed in each fresher. Passenger staterooms will often also include one. It is also common for there to be WDU located at places where people work, as on the bridge or in engineering. Galleys will usually include several, some with attachments to make filling cooking pots and pitchers easier.
Every form of biological life produces waste products. These products can be generally divided into gaseous/vapor, liquid and solid wastes. Gaseous/vapor wastes are collected by the Atmospheric Environmental system. Liquid and solid wastes are collected by the Sewage system, which transports that waste to the Recycling system. This system is most commonly called the Black Water system, even though the amount of water that is processed is limited to that contained in the liquid and solid wastes.
The system consists of transport pipes, mechanical or inline grav pumps, and bulkhead/deck isolation valves. A transport fluid entrains the waste, making it more transportable.
The Recycling and Disposal system is primarily concerned with the recycling and retention for disposal of potable water, cleaning, sewage transport, and atmospheric byproducts.
Water from the Atmospheric Environmental humidity and temperature control systems is sent to the recycling system to be purified and made into potable water. Water from the sewage system can also be separated out from the sewage transport fluid and sufficiently purified to provide potable water, though this is not generally done on commercial vessels. Water is also reclaimed from the Gray Water system. This system receives excess water from the water delivery unit drains. Like the sewage system it consists of pipes, pumps and isolation valves.
Commercial starships visit ports often and will typically retain liquid and solid wastes rather than recycling them. The wastes are always separated from the transport fluid, which is recycled.
The cleaning fluid system delivers cleaning foam, which is used for personal hygiene, to each fresher and recovers the fluid. The recovered fluid is purified. The entrained dirt, germs and wastes are separated out and the cleaning fluid reused. Though basically harmless to most sophont species passengers are reminded to minimize the amount of fluid ingested.
Decontamination showers, which are located in airlocks, egress stations, and chemical cargo spaces, use cleaning fluid from the hygiene system, but do not recycle their waste products. Decon shower drains lead to holding tanks which can be either vented overboard, while in space, or off loaded to hazardous waste systems when in port.
Each compartment that is normally occupied will include an independent power system for life support and gravitational control. Larger ships often have emergency power distribution systems to provide for gravity and air in case of failure of the primary power distribution system. Every area that is independently controlled will have an LCP for gravity control and a separate LCP for other environmental systems. Emergency gravity systems are described under grav plates. Emegency life support is described under limited life support.