Living in an Area with High Air Pollution? Consider Positive Pressure Systems.

A positive pressure system (PPS) in your house is probably the best solution if you live in a highly polluted area. Standalone air purifiers work but they quickly lead to high CO2 concentrations inside rooms that can significantly impact cognitive performance and well being.

How does a positive pressure system work?

You take outside fresh air, filter it through a HEPA filter and then pump the air into your house or room.

What are the advantages of a PPS?

1. Due to the higher pressure inside the room, you will have less dirty air coming into your room. Through the higher pressure, air will push outwards your air leaks and thus prevents polluted outside air from entering.
2. You can also keep your CO2 levels inside the room at low levels as you are constantly taking fresh air in. This will make you feel much better and productive.

In the end, a PPS is like an air purifier that would take outside air, filter it and push it into the room.

What are the disadvantages of a PPS?

A PPS also has a few disadvantages

1. Energy Costs. If you live in very hot or cold climates, you will put more stress on your A/C or heating system because it needs to adjust the outside air to your room temperature. This might lead to increased energy costs. There are PPS with heat and humidity exchangers that could mitigate that effect to some extend.
2. Installation. Unlike an air purifier that you just plug-in, a positive pressure system needs to be installed. This means you need to break a 4 or 6-inch hole into your wall for the air intake and install an air outlet in your wall or ceiling.
3. Costs. PPS pressure systems tend to be more expensive than air purifiers.
4. Closing Air Gaps. In order for a PPS to work well, a room should be as airtight as possible. So you need to seal your room as much as possible. Depending on the room this might be significant additional work.

How does a PPS perform?

Here at AirGradient we make extensive use of positive pressure systems and measure the results with our own monitoring solution.

Here are our main observations:

1. Zero AQI no matter what! With traditional in-room purifiers, your in-room AQI normally correlates with the outside AQI. So if the outside air quality is really bad, sometimes air purifiers struggle and it will be difficult to maintain good air quality inside because dirty air is constantly coming into the room. Here at AirGradient, we have rooms with PPS that stay at Zero AQI no matter what the outside AQI is. The reason is that these rooms have good airtightness and the positive pressure inside the room prevents any dirty air from getting inside. See some charts below demonstrating that effect.
2. Permanent Operation. A PPS tends to take more time to bring the air quality down inside a room as it takes time for the dirty air to escape but once the room is down, they need less power to keep the room clean. Therefore it is recommended to keep the PPS running at least half a day and not constantly switching it on and off.
3. Noise. PPS tends to be much more silent than air purifier because the fan that makes the noise is either outside the house or in a noise isolated box under the ceiling. Often PPS also use larger fans that are less noisy.

Here some CO2 charts from our AirGradient monitoring system:

Closed Bedroom, No PPS, two persons

This is what we see in most bedrooms if your bedroom does not have a ventilation system and you keep the windows closed.

You can see that CO2 levels increase quite substantially throughout the night and hover around 1200ppm.

PPS in one Bedroom, two persons

Now if we run a small positive pressure system in the same bedroom with two people sleeping, we can observe considerably lower CO2 levels below 900ppm.

PPS in one bedroom, one person

The below chart is from a kid’s bedroom with a PPS. As you can see, the CO2 levels are excellent due to a child producing less CO2 and also only one person being in the room.

The PPS system keeps the CO2 levels in the bedroom consistently below 600ppm.

Let’s have a quick look at the PM 2.5 levels in the same room. As you can see, the particles inside the room stay at extremely low levels as the positive pressure system prevents polluted air from entering.

Effect of sealing of Rooms

In the above PM 2.5 chart, you can still detect a very small amount of pollution in a room. If you ensure that your bedroom is additionally sealed, you can actually achieve a flat-line. Below shows another very well sealed bedroom.

The spike at around 5 pm was the result of having a window open. Other than that you can see that the pollution in the room was most of the time Zero.

Conclusion. PPS or Air Purifier or?

We believe that PPS has a better performance than purifiers but needs more effort to install. You also need to make sure that your room is relatively airtight which might pose additional challenges and costs.

In the end, the optimum solution might be to use both. A PPS to create a positive pressure to prevent dirty air coming into the room and an additional air purifier to accelerate air cleaning inside the room.