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Air Purifier vs. Positive Pressure Fresh Air System – An Unfair Battle?
- turtlebits 3y agoWhy not both? I have an ERV setup for positive pressure and constant air purifier running on low.
- micro_cam 3y agoDoes anyone make a quality standalone pps with a heat recovery ventilator? I’d buy one I could retrofit in without existing ducting in a second.
- amluto 3y agoHeat recovery and positive pressure are a bit at odds. Zehnder and Lunos both make cut-a-hole-in-a-wall ventilation systems.
- andai 3y agoDo I understand that with a PPS, it's healthier to be inside than outside? (At least along the "fresh air" dimension.) Obviously there's sunlight, exercise, and health benefits to socializing, but I always thought fresh air was one of the main reasons to go outside.
- dsab 3y agoIt might be not so trivious, here in Poland life expectancy is the highest in Kraków, where there is also the highest air pollution due to location.
- prvc 3y agoAny strategies for maintaining positive pressure in a dwelling in which installation/ deployment must be reversible (i.e. must not destroy any part of the dwelling)?
- btbuildem 3y agoYou could look at how window AC units are installed -- "temporary" (ie, reversible, but long-term) installations, using various kits that generally boil down to foam strips and extensible accordion partitions to close off space not filled by the unit.
- taeric 3y agoI thought the general view was that outside air was what you wanted for a lot of reasons? I know the general advice was "open windows and hasten air exchange." Is that out the window if you can keep the place pressurized?
- kshahkshah 3y ago"It depends" If you're in an older building (leaky) with a recirculating range hood (not actually vented) then opening a window is going to improve your air. Many prewar buildings in NYC were constructed with 'overpowered' radiators by the windows with the idea that people would in winter have the windows slightly ajar to bring in clean air. In a more modern building with a tight thermal envelope (not leaky) you're not passively through cracks, etc. exchanging w/the outside world. So everything builds up. One solution is a fresh air system like an ERV or HRV which exchanges air, filters, and exchanges heat and humidity too (so an improve version of keeping the window open). My 1985 run of the mill center hall colonial is moderately leaky. If I run the bathroom fans a negative pressure environment is created and air is pulled from under the slab (which creates a radon concern, for me). I suspect this approach, slightly pressurizing every room, would work for me. But I think this is very similar to what an HRV/ERV might do anyway...
- pivo 3y ago> Many prewar buildings in NYC were constructed with 'overpowered' radiators by the windows with the idea that people would in winter have the windows slightly ajar to bring in clean air. Wow, thank you! I've always wondered why the heat seemed so unnecessarily overwhelming in radiator buildings I grew up in. We'd keep the windows open because there was no way to control the heat and I'd always thought it was such a waste of energy. Not sure how clean the outside air was at the time, but I did really miss the mix of cold and warm air in the winter when I moved to a more modern building.
- blamazon 3y agoOne explanation for this phenomenon is that the initial rapid proliferation of 'modern' radiators in NYC happened around the same time as the 1918 influenza pandemic. It was understood that fresh air was something of an antidote. Tangentially, people wore masks as well during that global pandemic [1] and there were even anti-mask groups. [2] It makes me wonder what a pandemic a hundred years from now would be like and what physical manifestations of 2020 will remain. [1]: https://twitter.com/georgiatech/status/1307410628470956032 https://twitter.com/georgiatech/status/1307410628470956032 [2]: https://en.wikipedia.org/wiki/Anti-Mask_League_of_San_Francisco https://en.wikipedia.org/wiki/Anti-Mask_League_of_San_Franci...
- ahaucnx 3y agoAuthor of the article, happy to answer any questions. A bit of background, my house is in Northern Thailand that has similar levels of air pollution every year than what we see currently in North America and Canada and it took me a few years to get my house to zero PM even when having the worst wildfires around. So before installing a positive pressure system and making my house air tight in the process, I experienced with all types of air purifiers but did not find anything that works consistently at very high pollution levels. The experience with these wildfires let me actually found AirGradient and we are proud of open sourcing many of our air quality monitors.
- sampo 3y agoI have a pet peeve about graphs with bad / non-existent labeling. Here is how to read the graph: The black line is the outside air PM2.5. The green-yellow-orange-red bars are the indoors air PM2.5.
- stephen_g 3y agoWhat kind of NOx and SOx readings do you get? (I assume the AirGradient sensors can measure that?). Do you think an activated charcoal filter is a worthwhile addition?
- domoritz 3y agoIt’s great that PPS can reduce PM2.5 and CO2 to extremely low levels. I live in an area with industrial pollution (coal etc) and am concerned about VOCs, NOXs, SO2s etc as well. Wouldn’t I bring in more of those if I constantly bring in outside air even when the pollution is high outside? Unfortunately I haven’t been able to exactly identify the chemical that’s causing issues for me yet. I’d love to hear your thoughts on this situation.
- WhatIsDukkha 3y agoWhat do you need for a 700sqft space built tight? So its going to make the minisplit work harder but to what extent at 30 and 40 degree air outside?
- ahaucnx 3y ago
- sbirch 3y agoYou might conclude that the only real option is to buy a positive pressure fresh air system, but this comparison doesn't match my experience. I have no trouble driving the PM2.5 very close to 0 with a few standalone purifiers in my house (verified with a couple air quality monitors) even during bad wildfire smoke events. I'll grant I live in a modern house which is pretty well sealed, but it's also a question of sizing the purifier to the room's size and drafts. There are some orthogonal advantages and disadvantages though. On the upside, you'll reduce CO2 and other pollutants from inside your house -- it can get quite stuffy when you can't ventilate due to poor outdoor air quality. A downside is that it may also bring in air at a different temperature or humidity than you'd like (though that can also be controlled to some extent with a HRV/ERV.)
- ahaucnx 3y agoI agree, if you have a modern house you could bring down the levels with air purifiers but having no fresh air exchange really makes the house feeling very stuffy and you could get into very high CO2 levels which have its own set of health impacts.
- stinos 3y agobut having no fresh air exchange That 'but' isn't a given, modern houses which are properly sealed should have ventilation as well specifically to address that issue. Proper ventilation comes with inlet filters but those usually don't keep out PM<x> so still the purifier will have to do sme more work because of the constant sucking in of polluted air. However, I honestly do not know how common venitlation is already on other continents than mine where it's been made pretty clear by now that sealing a house equals need for ventilation.
- coda_ 3y agoThat's impressive... What are you using for purifiers?
- ahaucnx 3y agoThe positive pressure system is from a local supplier in Thailand and only available in Thailand and China. PM me if you need more information.
- jdavis703 3y agoMy experience from west coast wildfires and taking indoor air pollution measurements is if I put 3 air purifiers in one master bedroom and keep the windows and doors closed I can go from code purple air outside to code orange air inside… So it’s not perfect, but it does kind of work if you’re in a situation where you can’t integrate a positive air pressure system.
- ninacomputer 3y agoThis is too real and relatable. We take clean air so for granted huh.
- crazygringo 3y agoSomething would seem to be wrong in your situation then, just one should be enough to get it to green if windows and doors are closed. Not sure if your filters need to be replaced, if you need to wipe dust off their exteriors, or something is just wrong with their airflow that they're not filtering. A $100 Levoit purifier (the longtime Amazon bestseller) has been keeping my bedroom in the green (measured by an Awair) while it's been maroon (400+) AQI outside today here in NYC.
- 29athrowaway 3y agoWith those you have to vacuum it every 2 weeks and change the filter every 6 months.
- bagacrap 3y agoChanging a filter every 6 months sounds more than reasonable to me
- 29athrowaway 3y agoYes. Just saying that the filter is not simply an appliance that runs forever.
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- mhb 3y agoIt would be helpful if you labeled the top curve (outside air) and the lower bars (inside air).
- infoseek12 3y agoOne day I’d love to build a house with positive pressure and a glass topped courtyard. Designed correctly I think you could achieve very low pollution and CO2 levels even if the air outside is awful. The details get complicated though.
- zo1 3y agoI'd love to do that as well - my idea would also involve a large body of water to stabilize the temperature variations. It can double-up as a swimming pool and as a source of drinking water for the "coming apocalypse". Likewise, the water can be used to grow some plants in that glass-topped courtyard, that can act as a greenhouse.
- ninacomputer 3y agoPicked up a filter purifier here and it's in good use now with the fires. Wish I could get the more fancier and more functional options, but they are so expensive with demand.
- Shank 3y ago> 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. [0] Hmm, my apartment has a 4-6 inch hole for air exchange in the living room, but is otherwise a tight air envelope due to being a relatively modern building. Is there...something I can buy for this? This seems reasonably doable, unless I'm missing something obvious. [0]: https://www.airgradient.com/open-airgradient/blog/positive-pressure-systems-for-clean-air/ https://www.airgradient.com/open-airgradient/blog/positive-p...
- Too 3y agoYou surely have air egress in your bathroom and kitchen fan? Modern apartments usually have these on low speed all the time, creating a flow from the rest of the intakes in other rooms.
- amluto 3y agoThis is a nice balanced system. I don’t know whether it can run in a positive pressure mode: https://products.zehnder-systems.com/en/product/zehnder-comfoair-70 https://products.zehnder-systems.com/en/product/zehnder-comf... Its big sibling, the Q series, can run balanced or at a configurable amount of imbalance. These are really neat, but they’re intended for a pair of holes in different rooms. Maybe you can get one and get it to run in supply only mode: https://www.lunos.de/heat-recovery https://www.lunos.de/heat-recovery
- drakenot 3y agoWhat air quality monitors are y’all using?
- LTL_FTC 3y agoPurple air has some nice monitors and I think IQair also has one.
- geerlingguy 3y agoIf you're talking about the author of OP, I'm guessing he uses the AirGradient sensors, since he made them :) I like them enough I'm now up to four in my home. They did send two for evaluation initially (I did a video on them last year) but I liked them and bought more. I reflash them to ESPHome so I can easily pop them into Home Assistant.
- bb88 3y agoThere's a bunch but a lot of them are going to have something like this plantower sensor: https://www.aliexpress.us/item/3256801607354554.html https://www.aliexpress.us/item/3256801607354554.html It's a off the shelf part easily manufactured and possibly also easily calibrated. As a bonus you can hook it up to a Raspberry Pi or ESP32 board if you want.
- c_o_n_v_e_x 3y agoFormer HVAC and controls guy here. If you are going to the trouble of putting in a PPS, why not measure and control the fan speed based off of static pressure inside the space? You could measure your static pressure at a point furthest from the fan or you have multiple static sensors and select/control based off the lowest reading. The pressure only needs to be just slightly above ambient to keep the dirty ambient air out of the home. Providing unnecessary extra flow/pressure is doubly bad - one because your are spending extra energy to over-pressurize the space, two because your exchanging more outside air and thus the delta T between inside and outside. Another consideration is that if your flow/pressure is too high, you'll have trouble trying to open/close exterior doors.
- usbinsider 3y agoWhat’s a good sensor to do that with over the long term?
- c_o_n_v_e_x 3y agoYou need a differential air pressure sensor. I couldn't tell you any brands that would fall in the DIY price range. Dwyer is a big name in the commercial space.
- rocqua 3y agoMight it be possible to DIY a differential sensor by taking two callibrated air pressure sensors, and subtracting their difference in software? Would solve needing holes in walls, etc.
- bb88 3y agoIn my office I have a Costco MERV 13 furnace filter tied to a box fan. I am down to 0 PM2.5 after a couple of hours. In my case it's just a 20" box fan with a 20" square filter bungee corded together. The filters last 3-4 months, but are commodities at this point.
- 29athrowaway 3y agoThat's a clever trick. Creating the air pressure with a box fan and then filtering using a MERV filter. I guess if you can find a 20x20 box fan and attach a 20x20x1 filter to it you can do this easily. But how much the filters last depend on a variety of factors. If you have pets (with fur) your filters will last much less.
- bb88 3y agoWhat's interesting is that if you look on amazon, MERV 13 filters + Bungee Cords + 20" box fans are commonly ordered together. Further you can do a 20x20x4" MERV 13 to increase the lifespan of the filters. It also beats the price of buying specialized HEPA filters for a particular brand of air filter.
- lamontcg 3y agoMake a cube out of 4 MERV 13 filters and a box fan on top and the cardboard the box fan came in on the bottom and secure it with duct tape. That'll help reduce the load on the box fan and push more air through more filters.
- bredren 3y agoIt is called a Cosri-Rosenthal box [1]. I've built three variations on these using different kinds and sizes of Filtrete filters they are very cheap and effective. The downsides are that they take up a lot of space, are a big eye sore and awkward to carry and move. They also can make a lot of (white) noise on high, which can mask sounds you want to hear. They're great for special situations like wildfires or out of the way areas like basements where looks don't matter. For common living spaces we use Coway Airmega AP1512's which are relatively compact, auto cycle up and down fan speed and are much more attractive than DIY stuff. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box
- chuckledog 3y agoWe created a cheap effective DIY positive pressure system and it’s been working well for about a year now. Intake: old Winix filter, HEPA ish, broken fan removed, nice filter changability. Fits in joist bay, faces down drawing air from a protected exterior part of the house. $50/yr … connected with a steel hvac boot to… Duct Fan: AC Infinity 6” leave it on 1/10 … connected with 10’ of 4” duct to another hvac boot which blows air into a floor register in the bedroom. We have 3 of these, always on, ready for the next round of purple air Edit: house is in mild climate California
- ttul 3y agoThe magic that everyone needs is a combination of a) heat recovery ventilation (HRV) and b) heat pumps. An HRV system passes filtered air through a heat exchanger from the inside to the outside and vice versa. The air passes through a heat exchanger that ensures the interior and exterior remain the same temperature. You end up with fresh, clean air inside your house that has been filtered without changing the interior air temperature. Combining an HRV with a heat pump completes the picture, giving you both fresh air and a comfortable temperature, with no need to open the windows and let smoke in.