I would love to find a portable air exchanger too—opening windows helps with CO2 levels but it’s inefficient for most of the year in much of the United States. Built-in air exchangers with heat recovery are available but are a non-starter for anyone in a rented place. Unfortunately, no good solution exists so far
Typically the solution to high CO2 in indoor air is to exchange it with outdoor air.
Most users will open a window. The energy cost of that is relatively huge, when room air is heated or cooled.
In modern eco buildings, there might be counterflow heat exchangers - those can recover 80+% of the heat - but still, the energy loss through air exchange can quickly add up to be a major component of the buildings energy bill.
I believe we should work towards buildings that don't exhaust dirty air to the environment. Throwing away contaminated stuff and letting nature deal with it is 1900's thinking. We should instead break that CO2 back into oxygen, filter the dust, and remove VOC's. We should fix the air, not replace it.
So far, to my knowledge, nobody does this except on submarines.
Not being snarky, but a window is one of the best options. Air conditioners can often be your worst option, as the air is recirculated more aggressively. We use a window fan that has multiple settings: circulate, ingress, egress. I find that no matter what setting you use, air is recirculated significantly well. On hot days, the fan is set on egress. This seems to do a really great job of removing excess CO2 while not bringing that much hot air into the house. We have a window fan running in the kitchen for the bulk of the year. We also find that simply cracking the windows in the winter makes a large and measurable difference in CO2, but not with heat.
I wish there was such a thing as an in-window heat exchanging ventilator. Yes, I can just run the heater, but I shouldn’t have to. And punching a whole in my wall to install something permanent is so… permanent. And expensive!
You can get air exchangers with filters. They use the hot/cold air from inside to heat/cool the air from outside as they filter it. It reduces co2 by venting it outside.
I’ve seen ads for medical “oxygen concentrators” which involves a face mask. No idea how they work, or what they do.
In modern houses the solution to this is a “whole house air exchanger” which acts to cycle on low power the airflow in/out of house. You can also get these for single rooms and equipped with a heat recovery component.
Where I live, it can get very cold. Not always very efficient to open windows for 5 months out of the year.
A great option for keeping CO2 levels down in a house is with an HRV (or ERV) [1] that will heat the fresh air coming in to cycle it throughout the house.
By far the simplest solution is to just crack a window. Even a modest amount of fresh air exchange is enough to offset most of the CO2 generated by the people inside.
I use a relatively small 10x11ft spare bedroom as my home office. If I close the door and window, it'll quickly climb above 1200ppm after 15-30 minutes (and set off an alarm on my sensor). It'll cross 1500ppm easily if left unchecked. HVAC helps but gets outpaced quickly if my apartment windows are all closed.
That said, keeping doors open, running HVAC normally, and cracking a small window open, even 1-2 inches and on the opposite side of my apartment, is enough to keep CO2 levels around 550ppm while sleeping and 700ppm (in occupied rooms) while awake.
Heat recovery ventilators using heat exchangers have proven to be very successful too. Something like over 90% efficient. Couple that with triple glazing and you almost need no heating.
What I do wonder why there aren’t more in-window air conditioners coupled with heat recovery ventilators?
What kind of options do apartment dwellers have in this space? I've been thinking of DIY-ing something like this (suck in air from the window, heat it resistively in the rare event it's too cold inside, pass it through a HEPA filter, pass it through a humidifier, enjoy), but that is clunky and I'm wondering if products actually exist that I could just buy instead.
(I own my apartment, but no HVAC system. Through-the-wall AC, steam radiator heating.)
Air exchange is the most economical solution. You can’t stuff enough plants in a typical home to make a measurable difference and there are other pollutants such as VOCs that air exchange will address. Here are the two least expensive options I know of:
1) Get a CO2 monitor and partially open a couple windows whenever the level is above 800 ppm. Cost: $60.
2) Get a good air filter such as an IQAir HealthPro+ and pair it with a ducting adapter such as https://www2.iqair.com/sites/default/files/documents/InFlowW.... This will allow you to constantly exchange your indoor air with filtered fresh air. If you don’t want to install a wall intake for the duct, you can connect it to a window adapter like what is used for portable A/C units. Cost: $1,500.
They are usually triggered by a timer or humidity, but it would be also possible to trigger them based on VOC or CO2 levels.
Single-room heat recovery ventilation units are relatively affordable (about $400). There are also some which can be integrated into the window frame if drilling a 6" hole into a wall isn't an option.
Houseplants do not exchange anything near significant amounts of CO2 for this purpose.
The long term answer is to improve the HVAC: reconfigure for more external air mixing (commercial), or find a way to install an HRV or ERV, or open a window, but that can be expensive or impossible depending on the situation.
What you really want is a heat exchange / heat recovery ventilation system. Brings in fresh, filtered air from outside, and warms it up by swapping heat with the stale, warm air that it removes.
The beauty of a real ventilation system is the heat exchanger. I’m still waiting for someone to make one that I can run by feeding a tube out my window, but until then, you need to spend a bit of cash on a permanent installation.
When I bought a good CO2 monitor I have discovered how difficult it is to keep CO2 levels down in an apartment that does not have two permanently open windows on two sides of the building.
For example, the most surprising thing I have discovered is that just keeping the window open IS NOT ENOUGH.
In my location, it is common for the outside temperature to be lower than room temperature at night but higher than room temperature during the day.
There obviously is some time in the morning / evening where the temperature inside and outside is exactly the same. At this time, the air stops flowing in and out of the apartment, even if you have the windows wide open. The CO2 starts accumulating at a very high rate pretty much as if the windows were closed.
I was very surprised by the graph showing large spikes up to 1500ppm in the morning while I was asleep. I was suspecting it is causing me to feel poorly in the morning and I started to feel much better when I started to sleep in a room with also the door open so that the air can freely flow through entire apartment.
Energy recovery ventilator. It will exchange indoor air with outdoor air while maintaining indoor heat and humidity. Unfortunately small window mounted models are hard to come by. Most are whole-home systems.
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