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Comment by EVa5I7bHFq9mnYK | Hacker News Reader

I have such system running 24/7 for 5 years now in my apartment. It costs $20/month in the winter because it needs to heat the freezing air coming in. There is also noticable noise if I am doing physical activity and it needs to blow the CO2 out more quickly.

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$20/month is quite good for 7x24 heating of winter air. Could you share some details about the heating mechanism for incoming air, e.g. wattage, airflow, physical size? e.g. this combo fan+heater has a 1300W heating element, which would add up quickly in power consumption, https://www.deltabreez.com/RAD80.php

How often do you need to change the inbound air filters?

max wattage = 1400wt, av airflow = 40 m3/hr, size 20 x 20 x 7 inch, there are 3 filters, I just wash the coarse filter every 2 months, and replace the hepa filter once a year. I don't replace the coal filter as I don't have odors problem.

It's interesting how an anecdote like this:

"There is also noticable noise if I am doing physical activity and it needs to blow the CO2 out more quickly"

significantly increases my sense of the strength of the evidence base that a device like this is actually doing its intended job. The idea of a repeatable (and repeated) experiment based on principles that we know a priori must be correct (that our lungs exhale more CO2 than they inhale, and at a greater scale during vigorous exercise)

Somehow it's more convincing than if poster had even said, 'I set a CO2 generator up and looked at the ventilation device's activity indicator and saw it increase whenever the CO2 generator's output setting was increased".

Rather, one hears the device working harder, when doing an activity that's familiar to all of us, in a repeatable way.

Also, the poster didn't have to tell us that lungs exhale more CO2 than they inhale, rather leaving that to our internal models of how that works. If they described that overtly, it would somehow already make me slightly more skeptical of the overall assertion of the device's efficacy.

I think the statement is made more powerfully convincing precisely because it leaves it to us to infer the implications of the obvious bits. When it's our own subconscious reminding us of the priors (1. lungs expel more CO2 during vigorous exercise than normal, and 2. many machines are noisier when they have to work harder to accomplish the task they are designed for), we intuitively trust that our own model of the situation is accurately informing us more than if someone else had to tell us that those underlying assumptions were correct.

I wonder how other demonstrations of innovations of less-apparent efficacy can be directed towards presenting their evidence in this more intuitively convincing framework. (Note I'm not saying I have particular reason to accept the poster's description without further diligence, merely that it 'feels' more convincing in a powerfully intuitive way, which is what I'm after here).

Like 'dependent variable X should be something familiar to everyone, drawing on principles that most people would have already ascertained a priori, and, 'dependent variable Y should manifest as an un-instrumented artifact of the device in question, one that can be intuitively perceived with as few opportunities for technical obfuscation (which could otherwise give rise to either intentional misinterpretation or simply misapprehension) as possible.' (in the example, this is the device making more noise).

Anyway, I found it very satisfying to read that sentence from the poster.

And the decisions you can make with such knowledge: do less indoor sports to save money and to have less noise

What are CO2 levels in a typical gym?

Lower than in a typical office conference room during a meeting.

I still can't understand why the allied trades didn't press for building refits while everyone else was home and the "do something" sentiment among CEOs anxious to bring people "back to work"* was high.

* Please don't say "back to work"; it's propaganda that presumes remote or home can't work. Try "back to office" for something neutral, or consider "butts in seats" to throw shade on contentless managerialists who can't evaluate if someone's productive.

the trades were dealing with bigger problems, generally

construction was an essential industry, they didn't stop working during the pandemic. that being said, a lot of construction involves people in close quarters with each other, which was a major risk factor for COVID, and so there was a bit of work trying to figure out how best to get construction going and also not get all the workers sick. And there has been a worker shortfall in the trades for a while now, so it's not like refits could've significantly ramped up with nobody to work on them.

grrrr. the origin of this was joking about sex

Maybe you could add a heat exchanger to the system to recover some of the heat?

There are commercially produced systems to do this. They're called ERV or HRV:

ERV: Energy Recovery Ventilation eg: https://ephoca.com/aio-wall-mounted-pro/

An example of a less expensive module sized for a whole home: Panasonic intellibalance https://na.panasonic.com/us/home-and-building-solutions/vent...

I did the calculation, at that rate that investment will never pay off. Besides, I find it hard to believe compact heat exchangers can exchange meaningful amount of heat at 40 m3/hr flow rate.

They can't, but you don't run them constantly at a low rate. They cycle on and off to hit your targeted air exchange rate. That would be about a 50% duty cycle on low, so like 15 minutes on, 15 minutes off, constantly.

They're definitely not "free", but they do return a lot of the heat you're using. 90% or so is pretty standard.

I have one-direction air flow in the apartment, where inbound clean air enters at one side of apartment, and exhaust exists the other side. The scheme that you mentioned would take clean air and throw it back outside, doesn't make sense for me.

Clean air exits your apartment anyways otherwise you couldn't pump in the fresh one.

But pairing heat exchanger or pair of heat exchangers with your setup is probably not easy.

Why not just get plants? They thrive on the stuff, and give you Oxygen.

When they say a lot of them, they mean, a LOT: "Realistically, you would need hundreds of plants in any one room in your home to compensate the CO2 emissions from just one person."

https://www.realhomes.com/news/do-house-plants-remove-carbon...

Because that would require a lot of plants. A human exhales about 2.3kg CO2 per day. So that's 12/(12+216)2.3kg or 630g of carbon. A plant maybe absorbs 1g a day? Lets say a bit more... You probably need somewhere in the range of 500 indoor plants.

And I am to remember that they only absorb CO2 when photosythesising. When it is dark they are still respiring and producing CO2 with the humans

a number I found quickly says a greenhouse full of crops consumes 0.12-0.24 kg CO2 per hour per 100m²

I don't think those numbers are applicable to house plants. Crops grown in a greenhouse are specifically grown to increase their mass in as short a time period as possible. Regular house plants usually don't increase their mass that much (you don't really want them to), they don't get nearly as much energy and nutrient input as greenhouse crops.

I thought "you'd need a large apartment worth of plants per person" was bad enough already, without caveating it on plant type

only during daytime. At night they also dump out CO2.

Plus you need a lot.

you’ll probably need a lot of them. or actual trees.

Algeae. Bubble your exhaust through some water, gain back some of your heat too. Maybe produce Hydrogen on the side. You could feed animals with the excess algaea.

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