It is a general belief among householders that there air conditioners bring fresh air from outside the house.
Which is absolutely wrong.
And in this article, we will debunk this belief.
Do AC bring air from outside?
The short answer to this question is “NO” for residential spaces and “YES” for commercial spaces.
Home ACs merely recirculate the room air, this means the blow of air you feel is actually the same air that was present in the room and is being recirculated via the AC fan.
Residential ACs does not require to bring fresh air from outside, it can be achieved with small opening via doors and window but for commercial spaces it is a must to bring fresh air from outisde. This is needed to maintain oxygen level, remove odor, etc.
Let’s talk about different types of air conditioning systems.
Ductless Mini-Split Air Conditoner
In split air conditioning system the ac is divided into two units.
One is the indoor unit and other is the outdoor unit.
Here only the gas is circulated between both the units. There is no option for air to travel from outdoor to indoor unit or vice versa.
That is why split AC cannot bring air from outside.
Then what can split AC bring from outside?
Actually the heat from inside the house is transferred to the outside unit which is ultimately expelled in the environment.
AC cooling work on the refrigeration mechanism, if you study the system you will know there is no option for outdoor air to come inside.
To further know how split ac works and cools your room check this article.
Does Fan mode bring fresh air from outiside?
Many people ask do the fan mode bring air from outside.
The answer is No there is no option for outside air to come inside.
In Fan mode, AC only recirculates the room air without producing any cooling. Using fan mode is same as using ceiling fan.
Window Air Conditioner
In window AC, the entire air conditoning system is packed inside a single unit.
Evaporator, condensor, expansion valve, etc everything is stuffed inside the same space.
Window AC too cannot bring air from outside.
Though older window AC units had a small opening to bring outside air. In old days outside air was fresh and healthy but that’s not the case today.
The outdoor environment is getting more and more polluted.
With time manufactures ditched this functionality and today window ACs cannot bring outside air.
Till Now we can see home ACs like window, split and portable units cannot bring air from outside.
Then how to bring air from outside?
This is somewhat important as oxygen levels will gradually drop in a airtight room.
But actually our rooms are not 100% airtight and cannot be completly airtight.
Outside air can come inside through small openings and space via doors and windows.
To increase the input of outside air you can open a window or door slightly.
But do not open too much as it will also bring the outside heat and will increase load on the AC.
Central Air Conditoner
Central Air conditioners are meant for big house and apartments, they are expensive too.
To answer the question whether or not central air conditoner bring outside air or not depends on the HVAC company you got your central AC designed and installed.
Central AC can have many components other than cooling like a furnace or heat pump, AHU, etc.
An HVAC company can design your central AC such that the possibility of bringing outside air becomes true.
So ask your HVAC company.
Commercial HVAC systems must bring outside air
Commercial spaces like malls, hotels, industrial space, etc needs outside air to maintain oxygen levels, remove odor and so the HVAC systems designed for such areas will have the functionality to bring outside air.
For such spaces, the HVAC system needs to provide outside air based on occupancy type, occupancy load, and amount of floor area.
Here the outside air is mixed with the circulating air, which get cooled via coming in touch with evaporator coils.
Infact it is code in United States to have commercial HVAC systems to provide atleast 10% air from outside.
From July 2021 in Washington, even new residential constructions require HVAC system to have minimum 10% outside air introduced.
Do Car AC bring air from outside
There are two modes in car – fresh air mode and air recirculation mode. Both are used while running the AC.
If your car has fresh air mode than its AC can bring outside air thorugh vents and further remove inside air.
This fresh air is made to pass through the cold evaporator of the car and thus dissipate cold air inside.
On the other hand the same vent which bring air from outside is closed during the recirculation mode. Here the inside air only recirculates.
One should use “fresh air mode” for few minutes only as pollutants from other vehicles too come inside clogging the AC filters. This will increase your visit to the car servicing.
For maitaining the oxygen levels inside, opening the car window occasionally for few minutes is a better option.