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For SpaceNut ...
The word "humidity" did not turn up when I ran a search of topics....
In mid-December, 2025, NewMars members are discussing Calliban's vision of a 200 meter dome.
In the most recent round, in which you and your AI friend introduced the idea of grow lights suspended over crops and lawn, I realized we are trending toward a kind of greenhouse environment, with Calliban's Amsterdam brick buildings as the centerpiece.
Calliban has hinted at the idea of greenery on the tops of buildings, and those areas could be illuminated by their own grow lights during part of the day, while simulated blue sky panels in the ceiling and walls would provide a sense of Earth-like ambience.
This topic is about humidity in Mars habitats, and more generally, about how to manage the air inside a habitat to provide the most agreeable possible environment for humans and other living creatures.
I am hoping this topic will have some interest to members.
Mars itself will not provide much humidity for a long time (if ever) but habitats will be able to provide as much as humans might enjoy, by importing water and other substances as needed.
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This post is reserved for an index to posts that may be contributed by NewMars members.
Index:
Post #3: Conversation with Gemini regarding air management inside a large enclosed space
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In this conversation with Gemini, I inquired about air management inside a large dome on Mars.
Martian Dome Air Management Guidance
Conversation with Gemini
Air management inside habitat - Hi Gemini! Thank you for your assistance with many previous requests! This one is about guidance for managing the air inside a large living space under consideration for Mars. The building would be a dome with base diameter of 200 meters and elevation of 120 meters. The wall and ceiling of the dome would be in the shape of a catenary. Lighting would be entirely interior, with a combination of LED panels on the walls, and grow lights above green space as needed. While water is rare on Mars, it is presumed that enough can be brought to the facility to meet the needs of the residents. This request is for guidance on how humans on Earth have dealt with the management of air in large enclosed spaces. Examples include submarines but range to large hotels and even large ships. Please see if there might be literature on the subject.
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That is a fascinating and critical engineering challenge! Managing the air within a massive, sealed Martian habitat requires combining the lessons learned from various large, enclosed environments here on Earth, focusing intensely on closed-loop systems, efficiency, and safety.The literature review points toward several key areas of expertise relevant to your 200m diameter, 120m high catenary dome:
? Earth Analogues for Large Enclosed Space Air Management
Your habitat is a combination of a massive enclosed volume, like a stadium or dome, with the closed-system requirements of a submarine or spacecraft.1. Large Structure HVAC and Airflow (Dome Structures, Malls, Airports)
The primary challenge in a large dome is ensuring uniform air quality and thermal comfort across the massive volume, especially given the height.Air Circulation: The search results highlight the use of High-Volume Low-Speed (HVLS) fans (like large industrial ceiling fans) to prevent air stagnation, particularly at floor level where people are. These fans help push lower, cooler air upwards and assist in the distribution of conditioned air.
Air Stratification (A Key Dome Concern): Hot air rises. In a 120m high dome, this is a significant concern, leading to a massive temperature gradient (stratification) between the floor and the ceiling, wasting energy, and stressing the dome structure's seals.
Solution: Air-Rotation Technology (as mentioned in the search) or similar systems are designed to gently and evenly mix the air from floor to ceiling to maintain uniform temperatures and reduce heat loss through the upper structure.
Ventilation Strategy: Earth-based mechanical ventilation in large buildings often involves injecting fresh air at lower levels and extracting stale air from upper layers. In your Mars dome, the "fresh air" source is the recycled and regenerated interior air, making the Air Change Rate (ACH) a metric for circulation and purification, rather than exchange with the outside.
2. Confined and High-Occupancy Systems (Cruise Ships, Hotels, Submarines)
The closed nature of the Martian habitat requires lessons from environments where air is continuously recycled and filtered.Contaminant Control: In a sealed environment, pollutants (Volatile Organic Compounds (VOCs) from materials, human biowaste, cooking, and off-gassing from machinery/soil) must be actively removed.
Cruise Ships: Use advanced air quality systems for external compliance (SOx, NOx), but internally, the focus is on robust filtration (including HEPA for particulates/microbes) and ventilation adjustments based on CO 2 monitoring in high-occupancy areas like dining halls.
Submarines/Spacecraft (Most Relevant): These use multi-stage Atmosphere Revitalization Systems (ARS):CO 2 Removal: Technologies like Solid Amine Systems (Sabatier reaction on ISS for water recovery) or Amine Swing-Bed systems are essential.
Trace Contaminant Removal (TCR): Catalytic oxidizers and activated carbon beds are used to remove VOCs and other gaseous byproducts.
Oxygen Generation: Electrolysis of water is the primary method, which is presumed to be possible in your habitat.
Humidity Management: The search noted high humidity leading to condensation and mold in domes. Given the presumption of sufficient water for residents and a large green space, humidity control will be critical to prevent condensation on the cold dome walls (which could lead to degradation and corrosion) and to maintain plant health. Dehumidification units will be necessary.
Pressure Management: Unlike the Earth examples, your dome must maintain a pressure differential with the near-vacuum of Mars. The air management system is integral to structural integrity (for air-supported domes) or, at least, minimizing leakage in rigid structures.
?️ Key Design Considerations for the Martian Dome
Based on the Earth analogies, here are the most critical air management elements for your catenary dome:Design Element Goal Earth Analogue Guidance
Air Circulation Prevent stagnation and stratification in a 120m-high volume. Utilize HVLS fans and Air-Rotation Systems to ensure uniform temperature and air quality from floor to apex.
Atmosphere Revitalization Maintain breathable O 2 /N 2 mix and remove metabolic byproducts. Implement a Closed-Loop System (Submarine/ISS ARS model) for CO 2 removal, O 2 generation (via water electrolysis), and N 2 makeup/recycling.Contaminant Control Remove particulates and trace gases (VOCs, etc.).
Use high-efficiency HEPA filtration for particulates and dedicated Trace Contaminant Removal (TCR) beds (activated carbon/catalytic oxidizers) for gases.
Energy Efficiency Minimize power consumption for air handling on Mars. Use demand-response strategies (adjusting ventilation based on real-time CO 2 and occupancy) and highly efficient motors/fans. The dome shape itself is inherently more efficient for heating/cooling than a cube.
Monitoring & Safety Ensure resident health and system stability. Employ a network of real-time air quality sensors (for O 2 , CO 2 , CO, VOCs, humidity, and temperature) to trigger enhanced ventilation/filtration modes as needed (similar to "Max-Vent Mode" in industrial domes).
Would you like me to focus on the specific engineering challenges of the Atmosphere Revitalization System (ARS) or delve deeper into the HVAC and Airflow distribution methods within the dome's massive volume?
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The response you have provided will be published in a small international forum whose focus is exploration and settlement of Mars. Thank you for for helping us start thinking about air management inside large structure. We'll pause here to let members review your answer.
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That is wonderful news! I am glad the information is useful for such an important discussion. Best of luck to the forum members in their review and subsequent planning for the exploration and settlement of Mars.Would you like me to prepare a more detailed breakdown of a specific component of the Air Management System, such as the CO 2 removal technologies or the design of the internal air circulation network, when your group is ready to continue the discussion?
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Vents and intakes with fans and lots of sensor are used in both submarines and on the ISS for the cleansing of air plus more.
Submarine air quality management is crucial for crew health in confined spaces, using sophisticated HVAC systems with HEPA/carbon filters, electrostatic precipitators, and CO2 scrubbers (soda lime/regenerative) to remove particulates, odors, and gases like carbon monoxide (CO) and hydrogen (H2). Key processes include oxygen generation (electrolysis), contaminant removal (catalytic burners, filters), constant monitoring (CAMS, NASA tech, portable detectors for O2, CO2, CO, etc.), and strict exposure limits (EEGLs/CEGLs) set by bodies like the National Academies, balancing life support with equipment needs.
Key Systems & Methods
Air Circulation & Filtration: Recirculated air passes through fans, HEPA filters for particles, activated carbon for odors/VOCs, and electrostatic precipitators.
CO2 Removal: Lithium hydroxide (soda lime) or regenerative systems scrub exhaled CO2.
Oxygen Generation: Electrolysis of water (H2O from seawater) produces oxygen (O2); hydrogen (H2) is vented.
Contaminant Control:
CO/H2 Burners: Catalytic oxidizers (using Hapcalite) convert CO and H2 into CO2 and water.
Restricted Items List: Limiting volatile chemicals to reduce atmospheric buildup.
Monitoring & Control
Central Atmospheric Monitoring System (CAMS): Tracks O2, CO2, CO, hydrocarbons, refrigerants, etc..
Portable Detectors: Colorimetric tubes and handheld devices verify levels of acetone, ammonia, chlorine, etc..
Exposure Limits: U.S. Navy sets Emergency (1-hr, 24-hr) and Continuous (90-day) Exposure Guidance Levels (EEGLs/CEGLs) for numerous substances.
Challenges & Innovations
Confined Space: Lack of natural ventilation makes air management critical.
Storage: Non-regenerative systems need stored purification agents, using valuable space.
Research Focus: Developing regenerative technologies and refining exposure limits for contaminants like CO, formaldehyde, and others to enhance crew safety
NASA manages ISS air quality through sophisticated Environmental Control and Life Support Systems (ECLSS) that actively remove CO2 (like Four Bed CO2 Scrubber), filter trace contaminants (TCCS, catalytic oxidation), monitor for particulates (Mochii microscope, AQM monitors), and ensure correct gas mixtures, using advanced sensors (ANITA-2) and strict guidelines (SMACs) to maintain a safe breathing environment for astronauts, tackling challenges from equipment off-gassing, spills, and crew metabolic byproducts.
Key Air Quality Management Systems & Methods:
Atmosphere Revitalization System (ARS): The core system responsible for keeping air fresh.
Carbon Dioxide Removal: Uses sorbent beds that capture CO2, which are then regenerated by heat and vacuum.
Trace Contaminant Control System (TCCS): Removes harmful chemicals via filters (activated carbon, catalytic oxidation) and adsorption.
Monitoring:
Air Quality Monitors (AQM) & ANITA: Gas chromatographs and spectrometers analyze air for dozens of compounds in near real-time.
Mochii: A miniature electron microscope for real-time particle monitoring.
Major Constituent Analyzer (MCA): Measures main gases (O2, N2, CO2).
Contaminant Sources: Sources include crew metabolism, equipment off-gassing, spills, and material degradation.
Guidelines: Spacecraft Maximum Allowable Concentrations (SMACs) set limits for specific contaminants to protect crew health.
Current & Future Focus:
Advanced Sensors: New sensors (like the H2 sensor) are tested for better detection.
Research: Investigating materials to minimize contaminant off-gassing and studying microbial life in the air.
Operational Use: ANITA-2 is being used for operational decisions on trace contaminants
The ISS uses advanced air scrubber systems, primarily the Four Bed Carbon Dioxide Scrubber (4BCO2) and the Amine Swingbed, to remove crew-exhaled CO2 and humidity, regenerating air by using sorbent materials (like zeolites/amines) that absorb contaminants and release them into space or use heat/vacuum for regeneration, minimizing resupply needs and recycling water for future missions like Artemis. These systems are crucial for long-duration stays, recycling vital resources and ensuring breathable air.
Key Technologies & Methods:
Four Bed Carbon Dioxide Scrubber (4BCO2): A next-gen system using commercial adsorbent materials (molecular sieves) to capture CO2 and water vapor, venting the CO2 and allowing water to be recycled.
Amine Swingbed: Uses two beds of amine-based sorbents; one absorbs CO2/humidity while the other is regenerated (desorbed) by vacuum/heat, offering a continuous, energy-efficient process.
Sabatier Reactor (ACLS): Part of the Advanced Closed Loop System (ACLS), it reacts captured CO2 with hydrogen (from water electrolysis) to form water (recycled) and methane (vented).
Zeolites: Older methods used zeolite minerals to trap CO2, which was then released into space when the beds were exposed to vacuum.
LiOH Canisters: Lithium Hydroxide canisters serve as a backup, chemically absorbing CO2 in a non-regenerative process, requiring replacement.
Trace Contaminant Control System (TCCS): Removes other harmful gases and particulates, ensuring air quality.
How They Work Together:
Capture: Sorbent beds (zeolite, amine) or LiOH filters pull CO2 from the cabin air.
Regeneration/Disposal:
Regenerative systems (4BCO2, Amine Swingbed) vent CO2 to space, recover water, and reuse the sorbents.
Non-regenerative LiOH canisters are replaced when saturated.
Recycling: The recovered water is processed for drinking and creating oxygen.
These systems create a "closed-loop" environment, essential for keeping the crew alive and reducing reliance on Earth resupply missions
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For SpaceNut re Post #4... thank you for this overview of air management systems in submarines and the ISS...
This conversation with Gemini brings up water production by plants which "drink" grey water from the city and transpire pure H2O.
This is a fascinating engineering challenge. Managing the "breath" of a habitat on this scale is less about standard HVAC and more about managing a planetary micro-climate.
A dome 200m wide and 120m high creates a massive volume—roughly 2.5 million cubic meters of air. On Mars, where every drop of water must be accounted for, humidity control isn't just about comfort; it is the primary mechanism for water recycling and thermal regulation.
Here is a guide for future planners on configuring the moisture content for your Martian "Amsterdam."
1. The Target: The "Goldilocks" Humidity Zone
You need to balance three competing needs: Electronics/Safety (Static), Human Comfort, and Plant Health.
The Static Floor (30-35% RH): On Mars, the ambient pressure and dry dust make static electricity a significant hazard for life-support electronics. You must keep Relative Humidity (RH) above 40% to naturally dissipate static charges.
The Mold Ceiling (60-65% RH): Above 60%, you risk mold growth, particularly in the "Amsterdam-style" buildings if they utilize organic materials or porous masonry.
The Sweet Spot: Your target range is 45% - 55% RH. This is ideal for human mucous membranes (respiratory health), suppresses static, and allows plants to transpire efficiently without rotting the architecture.
2. The Water Cycle: Plants as Pumps
In a closed system, plants are your primary humidifiers.
Evapotranspiration: Plants take liquid water from the soil and release it as vapor into the air. In a habitat this size with "plenty of plant-filled tubs," your greenery will act as massive, solar-powered water pumps.
The "Rain" Problem: In high-ceilinged structures (like the Vehicle Assembly Building at NASA or the Goodyear Airdock), massive internal volumes can create their own weather. Moist air from the plants will rise due to thermal buoyancy. As it hits the cooler upper regions of the dome (closer to the Martian cold), it will condense.
The Solution: You generally do not want actual rain inside the habitat (it damages interiors). You need to control where the condensation happens so you can recapture the water.
3. Engineering the Atmosphere
A. Stratification and Air Movement
In a 120m tall dome, air will stratify. The top will be hot and humid; the bottom (where people are) could be cool and damp.
Destratification Fans: You will need high-volume, low-speed fans (HVLS) or thermal updraft systems to constantly mix the air.
The "Fragrance" Factor: You mentioned aesthetic effects. Air velocity helps carry the volatiles (scents) from the peripheral green spaces into the central "city" area. Gentle air movement (0.1 to 0.2 m/s) makes the air feel "fresh" rather than "stuffy" or "tropical," even if humidity is higher.
B. The Cold Roof Catchment (Passive Dehumidification)
Since Mars is freezing outside, the dome's skin is a natural condenser.
Catenary Advantage: Your choice of a catenary shape is excellent for this. Unlike a flat roof where condensation drips on people's heads, water condensing on a steep catenary curve will adhere to the surface and run down the walls due to surface tension.
Capture Guttering: You can engineer the interior surface of the dome with micro-channels to guide this condensate down to the perimeter rings. This turns the dome skin itself into a massive, passive dehumidifier that distills pure water back into the system for irrigation.
C. Active Mechanical Scrubbing
You cannot rely solely on the skin (which might be heavily insulated). You will need "atmospheric processing units"—essentially giant dehumidifiers hidden within the architecture.
These units pull moisture from the air, condensing it into potable water.
Data Point: This is the primary way the ISS recovers water. On Mars, your plants clean the greywater by drinking it, and the dehumidifiers recover the clean water from the air.
4. Earth Analogues to Study
There are several structures on Earth that manage moisture in massive volumes.
The Eden Project (UK):
Relevance: They manage high humidity in large geodesic bubbles.
Lesson: Notice how they use venting at the very top to release excess heat and humidity. On Mars, you can't vent (you'd lose air), so you must condense and capture at the peak.
Jewel Changi Airport (Singapore):
Relevance: A massive, plant-filled volume with retail/commercial buildings inside.
Lesson: They use a "Rain Vortex" (a giant indoor waterfall) which actually helps regulate humidity and air movement, acting as a massive cooling tower. A central water feature in your dome could serve as a humidity buffer—releasing moisture when dry, and absorbing heat.
Biosphere 2 (Arizona):
Relevance: A sealed system attempt.
Lesson: They suffered from unexpected condensation on the glass and moisture seeping into the concrete, which absorbed oxygen. Tip: Ensure your "Amsterdam" buildings are treated with non-reactive sealants so the buildings themselves don't become moisture sinks.
5. Specific Recommendations for your Martian Dome
Zoning the Humidity: Keep the peripheral green zones at 60% RH and the central living area at 45% RH. Use air curtains (invisible walls of moving air) to separate the zones. This keeps the "forest smell" in the green zone without making the living area feel sticky.
Hygroscopic Materials: Use natural materials in the living spaces (like unsealed wood or clay plaster) only if you want them to buffer humidity. However, given the water scarcity, you are better off using hydrophobic coatings on the buildings to ensure all moisture stays in the air for recycling, rather than getting trapped in the walls.
Sensor Grid: Deploy a 3D grid of hygrometers suspended from the dome ceiling. You need to map the "humidity cloud" in 3D space to prevent invisible clouds of moisture from forming static discharge pockets or mold zones high above the city.
Next Step
Would you like me to calculate a rough estimate of the daily water volume your plants would transpire into the air (in liters) based on the dome's square footage, to help size the dehumidification equipment?
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Thank you for your review of the environment we are considering. The points you raised will be interesting for everyone, and enlightening for some. Thank you for the examples of large structures on Earth where internal weather is observed! Let's pause here! I'll post our conversation and report back. There's a lot to think about!
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You are very welcome! It sounds like a perfect moment to let those ideas settle.The concept of "internal weather" is one of those fascinating tipping points in engineering—where a building becomes so large it stops behaving like a room and starts behaving like a landscape.
I look forward to hearing what your team thinks, especially regarding the balance between the "Static Floor" and the "Mold Ceiling."
Next Step: Whenever you are ready to resume, I can assist with calculating the transpiration rates to size your dehumidifiers, or we can discuss material selection for your "Amsterdam" facades to ensure they withstand the humidity. Just let me know when you're back!
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