| ▲ | coder543 4 days ago |
| Outside air isn’t a panacea. There is often plenty of pollution right outside your window unless you live on an idyllic beachfront property. The humidity level outside is also rarely what you want in your home, whether it is too high or too low. Much better than cracking a window is the use of ERVs (energy recovery ventilators) and air filters on the incoming air. An ERV is a fairly simple device that exchanges air with the outside while mitigating the loss of energy and humidity. Any modern home build likely has an ERV as part of the design, but it’s not like they can’t be retrofitted, and I’ve even seen some DIY-friendly window unit ERVs (but I’ve never heard if those are any good). |
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| ▲ | azornathogron 4 days ago | parent | next [-] |
| > Any modern home build likely has an ERV as part of the design Sounds very country dependent. I really doubt it's true here in the UK. But then, UK housing is just garbage all around unless you build something custom and put a lot of money and attention into it. |
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| ▲ | coder543 4 days ago | parent [-] | | > Sounds very country dependent. Yes, I meant in the US. Apologies for not making that clearer. I don't think ERVs are uncommon in new construction outside the US, but I don't know as much about that. | | |
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| ▲ | elric 3 days ago | parent | prev | next [-] |
| I installed an ERV system in my very small and very old home. It was quite a bit of work, but nothing terribly difficult. Finding a suitable spot for the ERV unit was the biggest challenge: it is quite bulky and not silent, and you need to be able to route ducting to it from all over the house. It's easily the favourite thing in my home. It filters the outdoor air, reducing pollen and mosquitoes. It keeps out excess moisture in summer. I don't have to open a window when it's cold. It automatically goes into overdrive after a particularly steamy shower. It's great. |
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| ▲ | musha68k 3 days ago | parent [-] | | Could you share which one you installed and under which circumstances? I'm running two mobile HEPA air filters; not very efficient nor very effective I'd assume. | | |
| ▲ | elric 3 days ago | parent [-] | | I have a Zehnder ComfoAir Q350. Overall I'm very happy with it. My only regret is not having installed the optional additional filter box. Due to the limited space and the place I've installde it, it's not feasible to retrofit it. |
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| ▲ | Hnrobert42 4 days ago | parent | prev | next [-] |
| I live in an apartment in Washington DC. Opening a window reduces CO2 and VOCs. An ERV is great if you can afford it, but cracking the window is still quite reasonable. |
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| ▲ | coder543 4 days ago | parent [-] | | CO2 and VOCs, but what about PM2.5 and PM10? What about pollen? What about humidity control? Cracking a window is also costly, since it directly raises your heating and cooling bills. It's just an "invisible" cost that's easy for some people to ignore since it's hard to directly measure. An ERV pays for itself over time, so it's more a question of whether you can afford to just crack a window? Living in an apartment makes this difficult because your landlord may not let you improve this situation, but just ignoring the cost of opening a window doesn't make the cost go away. | | |
| ▲ | zephyrthenoble 4 days ago | parent | next [-] | | I live in the DC area and whenever I hear people say "just crack a window" I think, that brings in all of the pollen I'm allergic to in all seasons except winter, plus humidity and 95 f degree heat if it's the summer... I' be been looking into getting an ERV for a while. | | |
| ▲ | Hnrobert42 3 days ago | parent [-] | | The humidity and temperature are rough. Some months I can't open the window at all. This month has been pretty good though, huh? At least for the temperature and humidity. I feel you about the pollen. I use a Blueair filter, and that keeps PM 2.5 and PM 10 in check. |
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| ▲ | encom 4 days ago | parent | prev [-] | | Don't leave your windows open all the time. Open them for 5-10 minutes at least once a day. Heating air is cheap, it's heating all the other mass in your home that's hard, so don't let it cool down. If you live somewhere uninhabitable like Texas, change heating for cooling. | | |
| ▲ | coder543 4 days ago | parent [-] | | > Heating air is cheap, it's heating all the other mass in your home that's hard Is the air cheap to heat? Even if it were, that still wouldn't solve the other issues that were mentioned. | | |
| ▲ | owenversteeg 3 days ago | parent [-] | | The GP comment is technically correct, if somewhat incomplete. A 40 m3 room (about 14’x14’x8’) has about 50kg of air in it; that’s only ~300 Wh to heat every molecule of it by an entire 20C. The thermal mass of the other things is orders of magnitude larger. The reason that I consider that explanation somewhat incomplete is the behavior of the air and the embodied energy. Imagine it’s winter, the exterior air is quite dry, and you open a window. You will easily lose a large amount of moisture, making the air uncomfortably dry. So you turn on a humidifier, but that will cool the room further with the evaporation of water. You also have to consider convective heat transfer. The fast-moving air is quite good at transferring heat to the outdoors. So, even if you don’t care about humidity, you will lose a lot of heat through convection. But yes, strictly speaking, the thermal mass of the air is very low in most structures and situations. | | |
| ▲ | fuzzfactor 3 days ago | parent [-] | | I've got one laptop case where it is quite spongy with panels like neoprene and some stretch fabric. When I ride about half an hour with a driver who is not smoking but had smoked in the vehicle (supposed to be always with the windows open out of courtesy to the other drivers), the next morning when I pick up the laptop it smells like tobacco and it takes a few days to go away. This doesn't happen with the backpack which is not built like that. You can also take the domestic calculations further. If you have 50 kilos of dead weight for instance, whether it's a set of workout weights or a piece of furniture, and it's all a stable 10 degrees C through and through, it's going to take 50 kilos of 30 C warm air constantly coming into intimate contact with the dead weight however long it takes before your dead weight gets to 20 C and the air does too. That can be a whole lot longer without forced air. But it still takes 50 kilos of air no matter what. >the thermal mass of the air is very low This is exactly it, along with heat exchange capacity. If you pull out the water hose you could spray it down with 50 kilos of water in no time, but not everybody's living room can withstand that :) Now if you had 500 kilos of 20 C furniture along with everything else, and you opened your windows and let out the full 50 kilos of air which was fully replaced by 0 C air, then shut the window to achieve a closed system once again, you'd still be sitting on 20C furniture for some time and only breathing 0C air for a short period before the overwhelming mass of the furniture itself warmed the much lesser mass of air right back up a few degrees, and to about 18 C eventually. Which none of the other heated mass will drop below. With no additional heat added, assuming insulation was perfect, but that's the number of degrees lost from one single full air exchange alone under those conditions. While the windows are open is the time to vacuum the carpets, drapes and furniture so you can get some forced air through them and let absorbed irritants out instead of just stir it up and move it around. The high-surface-area porous materials can soak up more than you think. Air exchange matters again because some of the irritants are not the kind that evaporate or "dissolve in air" very fast, and they might have had all kinds of continuous time to accumulate. You've got to figure that curtains can hold grams of unwanted stuff in their pores from previous bad air days, furniture ounces & carpets pounds plus a lot of the latter is solids which may give off odors or stir up allergens for quite some time once it has gotten into the pores and other tortuous passages. That's a lot of air exchange when you do the math. Change your air filter after stirring things up and breathe easier after that :) |
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| ▲ | sfilmeyer 3 days ago | parent | prev | next [-] |
| Can you link an example of a window unit ERV? I tried searching briefly, and came across some folks hacking together units to make them work with windows or adding their own ducting, but nothing analogous to a simple window air conditioning unit. As a renter of an apartment in a very much not modern home, I don't really see anything that seems like it would work. |
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| ▲ | physarum_salad 3 days ago | parent | prev | next [-] |
| Yes, consider spores from harmful microorganisms that are released during building work or harmful airborne particles from transport vehicles. Its not as simple as: open the window! |
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| ▲ | crazygringo 3 days ago | parent | prev [-] |
| If you have ERVs and filters then amazing. That's still outdoor air. Yes you have to take into account running an air filter for PM2.5, closing the window while a truck is idling outside, running your humidifier or dehumidifier if you want. But you need fresh air coming in somehow, at a certain rate. There's no way around it. Pollution in terms of VOC's, and CO2, is always higher indoors than outdoors, because things indoor generate it and don't remove it. |
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| ▲ | coder543 3 days ago | parent [-] | | > Most people don't, and cracking a window is the only option. It's not usually the only option. Installing an ERV is an option for the more than half of the population that owns their own property in the US, and an ERV will save money and pay for itself compared to opening your windows, in addition to the other benefits. For renters, that's where the window units I mentioned come in, but there aren't as many options there as I would hope yet. If people don't ask for ERVs en masse, then apartments won't offer ERVs as a benefit to attract tenants unless they are legally required. Helping people understand that options exist seems like the first step to changing things. Ideally, even window-unit ERVs wouldn't be the only option for renters. Nearly 90% of households in the US have air conditioning now (which I believe includes rentals), because people asked for air conditioning and were willing to pay for it. ERVs have the added benefit that they don't just make things better, but they should pay for themselves in energy savings too. Maybe I'm too optimistic. I believe the 2024 IECC building codes make ERVs mandatory in new construction in climate zones 6 through 8, as one example of a change that is coming. |
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