HVAC In Space – Air Comfort on the International Space Station

 Have you ever wondered what it would be like to live on Mars? With the newest rover exploring the red planet’s surface, it’s interesting to think about making a home on our neighboring planet. Chances are you probably haven’t considered HVAC in space. Would your galactic home be cozy like it is on Earth?

A Home in Space

Space, for all its beauty and wonder, is not a comfortable place to be. The empty millions of miles between planets, stars, and other celestial bodies ranges in temperature from super hot to beyond freezing cold depending on if you are near a star or in the shadow of a planet. On top of that, the vacuum of space offers nothing to breathe and nothing to protect against the sun’s radiation as it travels through the solar system. 

And yet, humanity has established a home base in near space–the International Space Station (ISS). This interstellar home away from home has kept astronauts from all over the world not only safe, but comfortable as they work and study in a zero-gravity environment. The International Space Station is a triumph of technology and science. The ISS allows astronauts to study the effects of space on plants and microscopic creatures. It also has a way to keep astronauts on board safe and protected from the harsh conditions of the surrounding intergalactic atmosphere. 

The Importance of Insulation

Here on Earth, insulation is a key factor in keeping a home or building comfortable. It’s also true on the International Space Station. However, the materials for an HVAC in space look a little different compared to what you’ll find in your home. A home’s walls, attic, and basements or crawl spaces are usually filled with insulation. The material used can vary widely to include fiberglass, cellulose, foam, and even recycled denim. Some types of insulation material can be mixed with pest-resistant chemicals. This prevents rodents, bugs, and other nuisances from entering and nesting in the interior spaces of a house. 

Insulation’s main job is to regulate the temperature inside the home, keeping it warm in the winter and cool in the summer. You know when you step into a room without insulation. Without proper insulation, temperature is much harder to regulate. A well-insulated house also saves the homeowner money as they don’t need as much air conditioning to stay comfortable. 

In the harsh environment of space, the International Space Station needs to use different materials to help regulate interior temperature. The Refrigeration School explains that Multi-Layer Insulation is used to protect astronauts from the harsh temperatures outside of the ISS. Aluminum coated with Mylar and dacron (a type of fabric that is good for insulation) make up these layers. With many layers of these fabrics working together, the ISS is wrapped in protection from constant extreme heat and cold.

Keeping Cool in Orbit

If insulation protects the ISS against the harshness of space, how is it kept comfortable on the inside? NASA’s Science webpage explains that the astronauts and their scientific equipment, not to mention the life support systems that keep them safe and healthy, all create heat that must be removed to maintain a comfortable environment. This means the well-insulated interior doesn’t allow built-up heat escape. Scientists created a new solution to solve this problem: the Active Thermal Control System. 

What is the Active Thermal Control System?

The Active Thermal Control System is a heat exchange that transfers heat away from the ISS by using fluid-filled tubes. First, “cold plates” within the ISS draw heat away from the hot equipment and interior space of the station. Then, that heat is transferred to a second liquid-based system that draws the heat out to the radiators of the ISS so that it can be cooled. The liquid within this second system is ammonia, because it can withstand the cold temperatures of space without freezing and stopping the heat-exchange process. The radiators of the International Space Station are the long, wing-like rectangles that can be seen underneath the solar power panel structures. This gives the liquid cooling system enough distance to travel so that the heat can be removed. 

Home air conditioner units also work to transfer heat in the same way as HVAC in space. An air conditioner has a condenser and an evaporator to move refrigerant to first gather heat, and then remove it from the system and provide cool air to a home. The evaporator allows low-pressure, liquid refrigerant and to absorb heat, removing it from the air. As the refrigerant heats up, it becomes a high-pressure gas. It moves through the air conditioning system to the condenser where it cools and returns to a liquid state. This process happens again and again to make the air in a home comfortable. The reverse process is used to heat a home. 

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No Space Like Home

Whether you are on your couch watching TV or an astronaut prepping for a space walk, we can all agree that air comfort is an important aspect of any home, no matter where it is in the solar system. Keeping the International Space Station comfortable is an amazing feat of science and construction. Scientists developed these strategies just so mankind can survive and work together to learn more about the universe beyond our planet. Next time you reach to adjust the thermostat or hear your air conditioning unit automatically turn on, look up to the sky and think about the astronauts that are also keeping cool during their day.

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