Is there an advantage to attaching the filter to the front of the fan so air is blown through it (as shown in the video) versus taping it to the back of the fan so air is sucked through it? Just curious if that would make any difference. It might be easier to get the filter to stay if it's getting sucked to the fan.
I’ve actually built this fan “mod” and when I change out the filter, I’m going to try attaching it to the back instead.
With the filter thoroughly taped to the front (nearly airtight), there’s a large amount of blowback. I suspect that this is reducing the overall efficiency of air filtration.
With it taped to the back, you don't get blowback, but there is significantly reduced airflow out the front. I used a filter of this type for ~2 weeks during the Thomas fire. Worked very well, though the proper filter I received from Amazon a week after I built this worked better. Two is better than one, though!
Placed in front it would catch particles coming off the motor like lubricant, bits of metal from bearings and carbon particles from the brushes if it's not a brushless motor.
Perhaps strain on the cheap box fan motor as it tries to pull its air through the filter. I've gone through a number of those style of cheap box fans over the years, any kind of long-term resistance very near the intake seems to cause the equally cheap motors harm and shorten their functioning life considerably. I haven't seen the same motor damage problem with resistance added to the exhaust side. In absence of that experience I would have guessed that similar resistance on either side would harm the junk motors all the same.
I used to put the high-efficiency filters on my furnace, my HVAC guy said these filters are so heavy that they put a strain on the blower motor. It's better for the motor to use a plain blue fiberglass filter (MSRP $1). You're not really filtering that much out of a closed house, unless you run your forced-air A/C or Heat with the windows open.
We upgraded to a "media filter" when we got new HVAC at my house. IIRC they are 4 inches thick, which gives a lot more surface area due to the deep pleats. You can then run fairly tight filters without putting undue strain on the motor - plus they last quite a bit longer. It made a moderate difference in our house in regards to dust in the air, but we also have 3 pets and live in a very dry, dusty area.
I did the same thing with my furnace. Just to try it I switched to a high merv filter rating and could immediately notice the considerable reduction in air flow that it was causing (and presumably increased strain on the furnace). Seeing as it was a bit more restrictive than I expected, I ended up ditching that and going back to a weaker merv rating filter (haven't gone back to the blue fiberglass style filters, just going with a weaker merv seems to do the trick, haven't had any problems with increased wear on the furnace in the last ~8 years).
You know, I'm going probably believe the guy that replaces blower motors day in and day out for a living as opposed to the group that sets up a "test box". Sorry.
1) If the filter is at the back, since the air is pulled through it, the dirty side is outside where people and kids can touch it as it builds up. If the filter is in the front, the dirty side is inside (towards the fan blade) while the clean side is outside.
2) If the filter is at the back, due to air's resistance it is possible, due to nooks/gaps in the fan, that the some of the air may be pulled from elsewhere and not all the air may pass through the filter. If the filter is in the front, it is easier to seal between the fan and the filter to make sure all air is pushed through it.
I can confirm what others said about air drag. I've done this in the past, assuming I needed the filter on the input side. I had to use two filters, some cardboard, and plenty of duct tape to create a triangular input in order to get a decent amount of airflow.
I wish the guy on the video would take an air reading measurement near the side of the filter. I'm guessing that a lot of unfiltered air is escaping out the sides.
FWIW if you tape the filter to the back then the fan doesn't get dirty as quickly. [Every now and then you should clean the accumulated dust off a fan.]
BTW you need not cover the entire area of the fan with filter material. So, for instance, if your fan's breaker is shutting the motor down b/c of the load of the filter, you can slide the filter up to cover less of the fan with the filter, reducing the load on the fan motor. While not all air passing through the fan will be filtered, over time most air will eventually pass through the filter and the room will be cleared of particulates.
Similarly, it is not necessary that the filter be the same shape or size as the fan, since with each pass at least part of the airstream is cleaned. Eventually all the air in a room will pass through the filter area.
I've been luring the Dyson hot and cool air purifiers, it's pretty silent from what I've heard, it also serves as both an electrical heater during the winter and a cooler during the summer. The price tag is the reason I've never bought one...
It's just a fan + heater. It's not an air conditioner, nor is it marketed as such.
I have one. It works pretty well. The air filter isn't as good as the massive Austin Air I use for my living room, but it's okay for a smaller room... not to mention much quieter, smaller, and easier to integrate with home automation.
Screw Dyson. Get a Winix HR1000. You can find them cheap ($200 or so) on eBay every so often. I picked up two a couple years ago and am very happy with them. You only need to replace the filters once a year. They've made a HUGE difference with my allergies. They automatically adjust airflow based on built-in air quality sensors. They are completely silent, aside from the "turbo" mode (~300CFM lol), but if you like white noise, it's great.
We recently got a Winix U300 (1) for about £150 new. It is basically a HEPA + Activated Charcoal filter and it claims it has some "plasmawave" thing that generates "free radicals" that kills odors and viruses. Initial searching suggests that this might be true, but I am unsure if there is any way to really test it. The air quality sensor certainloy works if you drink a strong coffee then go and blow into the sensor - the fans crank up the speed hugely to compensate for the stinking coffee breath! :)
Only criticism is that the U300 does not have wifi connection - only IR control... I am hacking up a esp8266 + some IR LEDs and photoresistors to monitor and control it via MQTT though which is fun. The "wifi connected" units seem to add several hundred GBP to the price for the same filtering performance.
We're not sure if we're noticing any actual improvements in air quality, or just imagining it...! :-) The placebo effect is quite good if nothing else. Noses feel less congested, and the air in the room feels less stuffy in the morning.
I bought one because of the fire near Chico, and I've been liking it. It's quiet enough to have in my bedroom, and the space heater aspect of it works well. It's cheaper than running the giant non-zoned furnace that heats our whole house.
I do this and it works wonders if you have pets.
Tips:
- run this homemade air purifier when you are vacuuming, as that tends to agitate particulates a lot
- get 2 filters, a cheap low grade and a premium, high-HEPA-rated filter. Stack them together and you can replace the cheap one frequently and the expensive one less frequently.
I am so tired of dust in my studio. There is no ventilation other than the small fan in the bathroom or the big sliding door in the front. So I leave the fan turned on overnight but because of pressure difference, very small particles keep accumulating all over my place. I’m really hoping this changes that.
Swedish tracing paper works well for a pre-filter. It's inexpensive for a long, seemingly inexhaustible roll, and can be washed numerous times.
It also works well by itself if you just want to cheaply filter large particulates. I used to use it in those cheap $40 Hamilton Beach air purifiers. The OEM filters for those cost almost at much as the new unit and wear out [for me] within a couple of weeks. That setup with Swedish tracing paper works well for dust, as a supplement for my HEPA filter purifier.
I used a very thick (4") filter rated for smoke particles when the wildfires this year blew their smoke down to Seattle. The filter went from white to a very interesting shade of grey in 3 days. Wife was able to sleep again though, so it does work very well in my experience. (20x20 fan, filter on intake side)
Out of curiosity, where were you able to find the big 4" thick filters in the 20x20 size? I wasn't able to find anything other than the usual 0.75 thick furnace dust filters in 20x20 for a box fan.
I was looking up air quality monitors but can't seem to find any on amazon with a calibration certificate that will accurately measure 0.3 micro particles. Am I the only one who thinks this is a great opportunity for a smart product with an app that has the features of a professional air quality monitor and simple UI / UX? If such product exists, does anyone know where I can find it?
With the recent California fires, I've been looking for a decent option. Unfortunately the Elgato Eve sensor is no longer sold, and the few other consumer products still hover in the $100+ range with poor reviews.
PurpleAir sells an indoor sensor, but it appears to be limited release and somewhat 3D printed.
https://www.purpleair.com/
Having both, I'd say that the indoor sensor is not worth it. It doesn't have both sensors so it isn't equipped to test them against each other. I do like the outdoor sensor though.
Their site is simple but it works great.
I "installed" my outdoor sensor by laying it on my desk inside and plugging it in.
Will move outside when fires end.
Why do you need an accurate measurement for consumer air quality monitoring? I believe even a DIY arduino project with cheap optical dust sensor, like PPD42NS or GP2Y1010AU0F, would be enough.
Why use a measurement device at all? Your nose is quite good enough, as long as it's neither clogged nor "calibrated" to city air. Putting a dust mask with a P3+carbon filter on for an hour or so tends to fix the latter.
Over the past two years as BC and WA have had terrible forest fires, this exact solution has become quite popular for people who are willing to DIY. the air quality in mid summer 2018 in Vancouver was really quite bad, exceeding Delhi or Beijing pm2.5 figures for weeks.
I been pondering about this solution for months since my air purifier died back early summer. I also have an additional idea to make it more automatic by using a raspberry pi, hooking it up to a powerswitch tail (essentially cutting power to a fan) and have it automatically turn on and off depending on time of day, etc.
I have mine on a homekit enabled outlet ($20) for scheduling and presence-based triggers. Unfortunately I haven't found a homekit enabled air quality sensor to pair with it.
Maybe you could even use it in conjunction with something like a laser particulate sensor, to scope how effective it is and track its progress from day to day. Kick it on when it detects a nasty bunch of filth in the air, and kill it once it reaches a set acceptable level.
I've been running a 3M Filtrete MPR 2800 in my furnace filter. https://www.purpleair.com/ confirms it works. There house averages maybe 60 PM 2.5 vs 200 outside.
Don't know how good it is for furnace, but it hardly runs otherwise in Northern CA.
I am relying on 2 purple air sensors 10 miles away in opposite directions for an outside estimate.
They are usually within 10%, and we are in the same valley, so should be close.
I also see when I stop the furnace fan, levels spike. Then drops when I turn on again...
Grainger [1] search for "industrial Blowers and Accessories" would probably be a good place to start looking. They tend to be expensive though. Take a look at McMaster-Carr [2] too.
Generally there are two classes of objects that you want to filter for.
Particulates and VOC (Volatile Organic Compounds).
Think of particulates as specs of dust with varying size and VOC's as random chemical compounds such as spray paint, smoke, oders.
The general go-to clean room/industrial filter stack is Prefilter(F5 Bag)->HEPA->Activated Carbon. The pre-filter catches all the big particulates to prevents clogging the HEPA filter. The HEPA filter catches all of the really small particulates. The activated carbon captures most of the VOC's/oder/smoke.
The official way to monitor when a particulate filter is bad, is to measure the pressure drop across the filter, and compare to manufacture specs. For the carbon filters, you would install a gas sensor measuring whatever chemical your trying to scrub. When there is a spike in that particular gas compound from your sensor. You know the carbon filter is saturated, and should be changed.
It looks like the the filter mentioned in the article video,combines all the filter products into a single product. Nice! If your air handler can manage the increased pressure drops, please buy the most legit filters you can buy. It's literally the cheapest insurance you can buy.
> “The general go-to clean room/industrial filter stack is Prefilter(F5 Bag)->HEPA->Activated Carbon.”
yup, i bought a blueair 211+ (https://www.blueair.com/us/blue/blue-pure-211/1695.html), that has exactly those filter elements in a nice (if bigger than expected) package. this model was recommended by both consumer reports and the wirecutter (until recently, cynically thinking they didn’t pay wirecutter’s “endorsement fees”). it’s effectively eliminated my constant coughing, sneezing and runny noses before i got it.
they don't, although if they recommend you, they'll ask you for a cut of sales (affiliate program). if you say no, they'll switch their recommendation to your competitor and never review your brand again.
I called out the inherent affiliate bias issue years ago but HN cult tunnel vision didn’t want to hear it and downvote me to hell. Wirecutter is not to be trusted.
When they link to a product on Amazon they then ask the brand to give them an additional cut of sales? I'm surprised Amazon allows sites to double dip like that.
I just bought the same model. What makes it so effective is that it has a filter on four large sides so it can process a large volume of air very quickly.
Does it spew out ozone? My memory may be off but I remember this model not meeting CA air purifier standards which was why Amazon couldn’t ship it to me
The purifiers I use have the activated charcoal before the HEPA. Probably doesn't matter that much though I sometimes findd a small amount of dust leakage from the pre-filter screen on the carbon filter which would just clog the HEPA.
Many don't have a prefilter and use the charcoal as the prefilter, essentially. I end up vacuuming mine or shaking it out (outside) every couple months to get rid of the build up.
For my air purifier, it generally reports better air quality in less than ten minutes of running at full speed. But, if you're in an area affected by the wildfires, then new particles will also be entering your home / bedroom, so you may want to keep it on low or run it in cycles.
Are you ok with white noise while you're sleeping and air flowing in the room? If you're ok with those things, run it while you're at home and sleeping. If you go to work during the day turn it off then, and turn it back on when you get home. It should rapidly clean up the air in a small bedroom.
The only real issue is any continual air flow into the room. There will be a big impact from what kind of air system you have in the greater building. For example, central air without a good filter on that system will make your fan-filter's job a lot harder.
The filters are relatively cheap to replace and will last a long time filtering a small bedroom. I get a solid year out of the filter on my central air system and it's filtering an entire home (non-smoking, no pets). Outside of the small electrical cost or annoyance from having the fan running, there's no reason not to run it very frequently if you derive a benefit. If you don't desperately need purified air for eg allergy purposes and your small bedroom isn't receiving inbound air (eg from a central air system), run it for 20-30 minutes, a few times per day, and that should easily do the job. If that's a hassle, just let it run more often than not.
I wonder if you'd put cotton wool, how effective it would be. Here is my set up:
- I bought XIAOMI Mi Air Purifier 2 straight from China for $137.00 and spent 1 euro on a EU plug. It's so quiet that I can sleep next to it, looks nice and it's quite compact, so doesn't take up much space. It has a particle detector to adjust the fan speed. The app is useless, so a cheaper version without WiFi and bluetooth would be great.
It will cost you less than 500$ to buy these and about 55$/year for new filters. It is worth the money. The air quality is much better (I'm allergic and I haven't had any problem with my sinus since).
What is more, is it worth it. It will save you time cleaning your place (about 10h/year)
Anyone has tried robot vacuums with mop or automatic dirt disposal function?
Wool fiber diameters are around 20 micron - HEPA can have glass fibers below 1 micron, and big box retail grades are often 5 - 10 micron. Smaller fibers = better filters.
Might be a stupid question but does this work for external air pollution? I live at the 20th floor in a city with terrible air quality and we open the windows once or twice a day.
I imagine it would help with particulate matter (such as smoke, whether visible or not), but I do not think it would have any effect on gases such as ozone, sulfur dioxide or nitrous oxide.
Nice synchronicity that this was posted the same evening I got a ~160 USD Xiaomi Air Purifier 2 (https://www.mi.com/global/air2/) delivered home. Might be a good alternative for those who want an off-the-shelf product, a pretty design and "smartness" like scheduling.
Huh! I independently "invented" this myself a couple of days ago when the Camp Fire blanketed the bay area in smoke. I got a 20x20 filter and some duct tape from Home Depot and a box fan from Target. (After discovering that Home Depot only sells fans in the summer.)
I don't think I was the only one, though. HD was doing a brisk trade in 20x20 filters, and I think I bought the last box fan at any Target in the entire bay area.
When you can't get house parts, try auto and computer parts.
Get some 120mm fans (or an array of 80mm, etc), and some engine air filters.
Don't change the filters too often:
"It is common, however, for servicing to occur when the filter appears dirty. Engine air filters are designed to actually increase their efficiency by using this initial layer of dust as an added filter layer. Initial filter efficiency is usually approximately 98% but increases to more than 99% by the
end of the service life of the filter.
Therefore, changing an air filter before the useful service life is achieved can result in premature engine wear."
I did this a couple years back. 2x 120mm fans and a rolled up filter in between with a cardboard box as the frame. I never thought it could do much, but also never left it running very long.
I've been begging for a good use of old computer fans...
Thank you for bringing this up ... in industrial settings, filters are "seasoned" for some period before they can be expected to perform at their published ratings.
Many air and water filters' performance continues to rise over their lifetime - the downside being decreased flow rate.
If you are filtering infectious agents with a water filter, I would be reluctant to run them past their lifetime because you could have things living in the filter and filter housing, etc., but if you're just dealing with particles, your filtration should continue rising over time.
The main reason why furnaces and cars have it on the incoming side is because the dust and particulate can damage the engine/blower. So you want to filter it out before it reaches there. In a system like this, the box fan will not be damaged by the particulate so you can instead push the air through the filter instead of pull it.
There are some cars that have circular air filters which fit almost perfectly over a "universal" radiator fan. IIRC some generations of Toyota Corolla and Tercel which spare parts should still be common enough for. Can be a solution if the more HVAC-type stuff gets sold out. You'll need a pretty beefy 12V DC power supply though.
When you decide to change out the filter I recommend using cheap painters or kraft tape instead of duct tape. I found that painters tape removes easily and tends not to leave adhesive behind.
I spent the weekend researching, implementing, etc. air filtration as one of those affected by the CA fires. It was worth it!
The first step for me was getting a device to measure particles in the air. The air quality index (AQI) is an aggregate score that is made up of contributions from several harmful components. Of these, the quantity (weight/volume) of small particles (<2.5um) is often the large contributor. This is called the PM2.5.
Directly measuring PM2.5 is very hard, requiring a device that eliminates the larger particles from the air (typically a cyclonic separator it seems) combined with some way of capturing and weighing of the very small quantity of remaining particles (we're talking ug/m^3).
Many home air quality sensors instead measure the count/volume of particles larger than 2.5 um and call that the "2.5um measurement". You can see the problem. I bought a laser particle counted called Dylos DC1100 Pro. The Dylos measures particles counts larger than 2.5um as is common, but also counts particles larger than 0.5um. Of these two numbers, the 2.5 count is only vaguely correlated with the actual PM2.5 measure, but the 0.5um count is highly correlated.
A bit of internet research (it seems many people have used the Dylos meter in various projects) and I was able to construct a scale to correlate 0.5um+ counts to PM2.5, and therefore AQI. (0.005*count~=ug/m^3)
OK, all that done, to the filtration. First, I installed 3M 1550 MPR furnace filters (~MERV11). The "1550" is a measure invented by 3M 'MicroParticleRating' (or something) and is supposed to speak to how well the filters remove small particles. However these furnace filters don't really knock down very small particle counts in once pass. Sure enough, putting the particle meter at an air duct, the large (2.5+) particle count was way down, but the small particle count was only down a little bit (15-25%?) from the ambient air. Net effect is that after running for several days my house numbers are about 1/3 of the outside air counts.
I also bought a BlueAir HEPA filter for my bedrooms. HEPA is supposed to be 99+% effective for particles 0.3um and up. This filter is in a whole different league. The particle counter placed on top of the filter returns near-zero small particle counts and does a much better job eliminating smells. The room they were in got down to 1/10 of outside levels.
Overall I'm glad I got both types of filters, we are sleeping better, and the meter was very helpful to understand what was going on.
Did you put the filter on the intake or outflow side of the fan?
I have built one of these (20x20 furnace filter on a box fan) and always put the filter on the intake side of the fan. However it seems like people are placing the filters on the outflow side of the fan instead, for reasons that are not clear.
Since it seems like you did some measurements, do you have any idea whether it's preferable to have the filter on the intake or outflow side of the fan? (I note that in furnaces and other air handling equipment, filters are almost universally on the intake, not the outflow, side, presumably because this keeps dust out of the blower/heating mechanicals.)
when you place it on the intake, it is sucked against whatever you are using to stop it pulling into the fan, if it is on the outtake, it can bubble out on the edges and the air can escape rather than pass through the filter. Intake is the only correct solution for these homemade devices without a metal diaphram.
Used an existing box fan. I had to buy duct tape ($3) and the filter I used one rated for 0.1micron pollen and viruses cost me $17 (rounding up after tax). I cut up a plastic safeway bag to make the seal around it. Seeing as most smoke particles is around 2.5-.5 micron I figured it'd be okay.
I threw this together at about 7am on Saturday after I woke up coughing my lungs out at 6am (I live in the bay area). Just a quick trip down the the Homeless Despot to get the parts and throw it together.
All things consider it works great. The air in my apartment is easy to breath, but if I leave without a respirator (even today) I cough uncontrollably.
---
As of Tuesday evening it has been running for 4 days straight (no overheating). And has started to become noticeably brown. Needless to say I'm thankful for it.
Can we talk about Molekule? Their team and some SF tech community folks have been plugging it all over Twitter during this tragic wildfire crisis. But it seems like snake oil to me. It’s $800. Certainly for smoke particles it can’t possibly offer any more protection than a standard HEPA filter. But even for its claimed ability to nuke VOCs, the claim seems ridiculous. While particles can deterioriate under prolonged exposure, the airflow must be too high and the exposure too short to make much of a difference.
What gets me is how these guys misuse “science marketing” to play on people’s fears about germs. Add the shameless exploitation of a real tragedy here.
I agree it seems sketchy. NYTimes writes, “Unlike virtually all other air purifiers—and all we’ve tested—Molekule is not HEPA-rated and does not claim to eliminate micron-scale particulates with a filter. Instead it claims to remove smaller, nanoscale pollutants, including VOCs and viruses, via a chemical rather than a physical process. Out of curiosity, we requested a model for testing for VOC reduction, but Molekule requested conditions around the testing that we could not agree to.”
While the New York Times Co. did indeed purchase The Wirecutter/The Sweethome, there’s no reason to start attributing Wirecutter reviews to the parent company.
This is especially true in the settings of reviews, since the NYT performs its own reviews.
I have a hard time taking them seriously. Some of their "independent" lab results are from some USF lab. The same lab one of the co-founders was a director for... Go figure. Some please correct me if I'm wrong. Read the results in technology, and then read the bios of the people.
1. CADR is really low to the point where the unit is near useless due to #2
2. In addition to a low CADR, it has the highest noise. It looks and sounds like a jet engine when you have this thing on high, which is needed due to the low CADR. This is the loudest air purifier that I’ve ever owned
3. If you get a defective main filter, the unit will emit an unpleasant metallic smell. I haven’t tested the particles yet but I doubt the air is clean.
4. Unlike other smart air cleaners in the same price range, it’s app and smart features don’t work. You can’t even create a schedule for it
5. The unit works using some LED light.
A. it is bright
B. It is not replaceable. Meaning after 2-4 years of operation, the unit becomes a throwaway. This is not a good thing for a unit that costs over $700
Insanely simple idea when you think about it. Side perk: My furnace uses the same size filters, so it won't even be a hassle to stock ones that fit a box fan.
I built my own air purifier in 2016, living in London, I was living in a basement and was having breathing problems due to mould. My landlady was gaslighting me at the time, so I built the air purifier. It worked for a while but mould spores cling to the paper filter and eventually grow into the filter material. I think Dyson uses glass fiber filter to stop this problem. My filter helped a lot, but eventually I had sclerosis infection on my brain and ended up in hospital with lung infection and brain lesion, still recovering after two years, and I will never be my old self again. I was subletting so had no grounds for complaint, I had to choose between homelessness or phoning a distant relative I hadn't spoken to for 24years, I chose the latter and I think it's the reason I'm still here.
Woah, this is pretty scary. Thank you for sharing. How did you know it was mold that was in the air? Is there some sort of test kit that you can buy to test for this. Mold is pretty hard to detect because you can't really see it because it typically hides between the walls.
You can notice black spots in your bathroom or other places where steam doesn't escape properly. I noticed it on my mattress also. I don't think I have any health issues because of that, it was 5 years ago, but it was rough.
By the time it is a health issue, it is usually visible. There is some air passage from within the walls to the living space, but not nearly as much impact as the visible mold on walls, furniture, etc. Sauce: Get paid to test sometimes.
Mold needs lack of ventilation /dampness. You see the dark spots (maybe that's too late?) and IMO nothing substitutes air flow, when possible. Even in winter, one needs to open windows and let the air flow freely at least for a while.
I know there is mould in my house. We do three things to deal with it:
1. Air Filter (more for pollution but it helps with mould)
2. Dehumidifier which we leave on 24/7 basically for the mould. This is the big one.
3. Wash any mould with vinegar to change the PH after it is wiped off to prevent it from growing back.
The mould is still there but the dry air stops it from growing and sporing which is what makes you stick. If humidity creeps up the mould will grow again. Be aware that mould is virtually everywhere and is only harmful if there is enough of it around sporing or if you touch it.
Dehumidifiers are expensive in power consumption, I don't know which model is more effectively. I'm living in SEA, and get humidity level to 50% 24/7 in my studio equally to double my monthly electricity bill.
I don't know if these are effective, but in my country we have passive dehumidifiers which are basically containers with a load of salt or something like that which draws the moisture out of the air. Good enough to keep caravans in storage mold free. Probably not good enough for e.g. living rooms or actually moist locations, but maybe it scales up. Of course, you'd then need a lot of salt or whatever the stuff is.
I used the passive variant that you explained in my previous apartment and while it may be effective at keeping humidity down, it's not very effective in bringing a high humidity down. I got an electric dehumidifier and it's drastically more efficient. It pulls over two liters of water per day out of the air if the air is sufficiently humid. I've since moved, so I don't use it routinely anymore, but I still have it and occasionally use it to speed up the drying of clothes on a drying rack.
The problem is, once the calcium chloride has absorbed the moisture from the air and is saturated, you have to take it out and dry it to make it effective again. That might be cheaper (in terms of energy) than refrigerant phase-change dehumidification, but it's a lot more labor intensive.
Vastly more different. A place like Houston is going to have “sealed” houses far more frequently than Scottsdale for instance. Sealed meaning the air conditioner will keep the indoor environment manageable. I remember as a kid my grandmother would use that god-forsaken attic fan in lieu of her window-unit air-conditioners and it was pretty much the zenith of misery in a Houston summer.
Natural airflow with the outside at 90% relative humidity isn’t going to do a thing other than make the interior occupants ornery.
The natural airflow design of Apple Park for example, that works incredibly well, but that same design in Houston or New Orleans would be catastrophically ridiculous.
I'm not really sure about keeping the humidity below 50% though. The UK and most of Northern Europe has rather high humidity in the winter. It commonly reaches 80-90 RH outside, so you'd have to heat your house to 25c/77F to bring the humidity below 50%.
Northern Scandinavia and west of Urals (I live here) have moist winters (70+% RH most of the time). Skin would dry anyway because water evaporation rate is proportional to a pressure (hence temperature) difference and convection makes a constant supply of fresh unsaturated air.
Cold air can simply hold less water overall, at 20C it can easily hold double as much water as it can at 0C.
There being a pressure difference is nonsense, you can get the same air pressure in the winter as in summer (though it tends to go on the Low side more often). What you probably mean is the vapor pressure, ie the natural pressure the liquid wants to be at in a closed container, though while it is largely depdenent on temperature, it does so in a linear/positive way, so at lower temperature, water will evaporate less (otherwise ice would more easily sublimate).
Once you go below zero a water content of a few grams can easily hit 100% RH which would barely manage 5% or less at 30C.
I think the relevant pressures are the vapor pressure of liquid water, the atmospheric pressure, and the partial pressure of gaseous H2O at the gas-liquid interface.
If you can blow dry air over its surface, you can evaporate liquid water (or sublimate water ice) even when the relative humidity is 100%.
You can think of air as a gaseous solution, and its water vapor content like table salt in aqueous solution. Temperature affects the solubility, and if the solution is saturated, no more can dissolve. You can still dissolve salt crystals sitting in a saturated cold saltwater solution by squirting warm freshwater onto the bottom of the container. If that then mixes with the rest of the solution, and everything cools down again, that dissolved salt can then precipitate out somewhere else (like rain), or form a suspension of tiny crystals (like fog or clouds).
The solubility of H2O vapor in atmospheric gas increases with temperature. But you can also do something with a gaseous solvent that you can't easily do with a liquid solvent, which is to change the pressure. Higher pressure lowers the solubility of water in air, but to a far lesser extent than a decrease in temperature. Even though the vapor pressure is dependent only on temperature, evaporation occurs whenever the vapor pressure exceeds the partial pressure of H2O at the interface. Increasing the overall air pressure also increases the partial pressure of H2O vapor by a proportional amount, so inhibits further evaporation. But water vapor is also less dense than N2, O2, and most other atmospheric gases, so the means of measuring pressures gets complicated.
When you involve wind, and stratified airflows, it gets even more complicated. The air blowing across water or water ice could have been previously warmed by the ground just enough to evaporate more water, then get pushed higher by an angled snowbank into colder, saturated air, and it will then dump the excess water as small ice crystals. A solid block of ice can then become "rotten" as a snowdrift forms downwind of it. The overall average temperature may say that ice should stay frozen, but the wind can still carry a tiny bit of water vapor at a time, thanks to local fluctuations, and with enough volume of air to move it, that ice will drift.
"The UK and most of Northern Europe has rather high humidity in the winter."
Indoors? No, not at all. In the winter the temperature in my house/office is 21-22C and 17 at the lowest at night, and I have to run a humidifier 24/7 to keep the humidity over 30% (otherwise the wooding floors shrink too much).
Currently in the bedroom (thanks Netatmo) it's 17.8° and 69% humidity (with one of the three windows open about 0.5"). That compares to 14.0° and 78% on the balcony. Looking at the graphs, 50% is the lowest indoor humidity over the last month.
Yes, bedrooms have the windows open more often, and usually less/no heating. How many hours a day do you have the windows open? Is there a heating source on or nearby? If you close the window, you'll see RH drop quite fast (in most houses). I'm going to try this same experiment tomorrow, I'm quite interested to know.
Still - mold in houses is not a problem in houses in Western/Northern Europe, except for the most pathological cases (for example, mold scores you iirc 2 points in Belgium on the 'uninhabitable property' test, where 9 gets your building declared unfit for living in. Having small holes in the roof or small cracks in the walls (still structural defects) gets you 3. That's how unusual mold is around here. OTOH when I lived in New Zealand, mold was met with 'eh, there's bleach in isle 5 at Countdown, just wipe it down.'. I was like 'wut?'.
We do have cold winters but that does not mean we have high humidity indoors. Relative humidity means the water contents of the air at 0 degrees is very very low. The higher temperature, the more moisture the air can hold. So when you heat up the air the same amount of water shares a much lower percentage of what the air can hold. In winter the hygrometer is showing 100% moisture outdoors (because ours can't measure below zero degrees C). When that air is heated up indoors, it holds about 20% of what it can hold [0], most likely thanks to warm water taps, us breathing and other moisture sources. This is why many people run their humidifiers so they can at least have 30-40% in winter. Less dry, cracked skin and nose bleed.
Yes, but that's my point. Where I'm currently living (UK, south coast) it's 15C at 77% RH outside, so to get below 50% RH inside the temperature needs to be at least 22C (which it isn't). It's not uncommon for the humidity to get up to 80-90% RH when it rains, and the temperature doesn't drop much.
When it gets to the cold part of winter it's obviously easier, but this time of year it's hard to get it below 50% RH inside just by controlling the temperature.
You can buy test kits that you expose to your rooms’ air for some time, and then a lab will grow the mold inside the Petri dishes to “amplify” what has been collected in your home. That may be expensive, though, and not easily available everywhere, and perhaps even prone to contamination “in transit”?
My first rental in London had bad mould problems. The landlord refused to fix them. We ended up with dehumidifiers throughout the house to keep it under control. When we left after a year, he complained at us for keeping dehumidifiers around when potential tenants came to visit - it raised too many questions! This was a 2200+/mo rental that he had bought for about 100k 15 years ago. What a crook.
A wet paper filter is the perfect place for mold to stick to and send spores all over the place. If you have a mold problem where you live and can't move out of the place, you need an air filter and a dehumidifier. Unfortunately, it's hard to jerry-rig a dehumidifier on the cheap. If you were in London in the winter, it might have been more practical to turn up the heat to keep the room as dry as possible.
And open your windows a tad. It's the best way to keep indoor humidity under control during winter. Being in a basement room though, I'm not sure this would have helped.
As someone else mentioned downthread, you need to maintain a rather high temperature (around 25C/77F) in order to reduce the relative humidity enough.
This might or might not have been feasible given OP's budget, heating arrangements, and general preference. I for one would not want to live in such a hot room for a whole season even if I could afford to. I keep my room cooler than that even in the summer!
Hmm, my house during winter is usually between 18-20. If I keep the window vents closed (most UK houses have vents above the windows specifically for this reason), I get a lot of condensation around the windows which gets mouldy. Leaving those vents open makes all the difference - no condensation, no mould. Also the house humidity seems to stay under 50% with the vents open.
Could mold grow inside of a dehumidifier as well? I mean, water is constantly passing the components inside. Or does mold need organic material (such as the paper inside the DIY filter) and thus will not grow on the dehumidifier that consists largely of plastic and metal?
We live in Hawaii and mold is a huge problem here. There are times during the day when the dewpoint spread is only a few degrees. This means that any object that is cooler than the air temperature will condensate. If you can't control the moisture you can't control the mold. Another major factor is the materials in your house. Things like unfinished birch plywood will absolutely mold if left in open air, where other woods like hardwoods don't have as many problems.
I was talking to a buddy that does construction work in a pretty wealthy area (Scottsdale, AZ). They are just finishing up a large luxury apartment.
Apparently, the contractor let the drywall get soaked while sitting on palettes during monsoon season, and since the roofing wasn't done there were inches of standing water that resulted in black mold.
They just drywalled right over it. In the US. In 2018. In a luxury condo.
So, you never know what nonsense you will have to put up with.
I'd imagine that's true on both counts, but with these things it's notoriously difficult to prove. You'd have to prove that the contractor knew about the damage, didn't do anything to mitigate it and then knowingly attempted to hide it. All of that is pretty tricky to pull off, given that a home damaged in this way might not show signs of the damage for a good while.
It's why bad actors (such as the ones described above) keep getting away with what they do.
Those are pretty easy to prove in this case. All you’d need to do is find, remove and test the bad dry wall. There’s no way someone installing it could reasonably claim ignorance of its condition.
You get one of the people who did the installation to admit to it. I'm sure you could find someone who has a conscience or doesn't think they are personally at fault who would be willing to own up to it.
Construction crews in Arizona? They aren’t going to own up to anything because a majority of those workers are in the country illegally. You aren’t going to find them going to depositions or signing affidavits any time soon. That isn’t mutually exclusive with “having a conscience” of course, but that does mean that you aren’t going to have much luck finding anyone who actually worked on that crew and if you did, they aren’t going to talk.
I can only speak for UK contractors/companies, but most of these guys will immediately close ranks on you if you try and pull this. The guys at the lower end of the chain won't want to say anything because it could affect their ability to get work at a later date. A lot of them are on temporary contracts, and these companies talk to each other. If they start making noise about these sorts of mistakes, they could well wind up on a blacklist.
What do you mean "they drywalled right over it"? They installed the damaged drywall and then _another_ layer of drywall on top of it? Sorry if this is a stupid question.
"They just drywalled right over it. In the US. In 2018. In a luxury condo."
This happens regularly in the SFBA, in Marin County. Every rainy season I see at least one house being built through Nov-Dec-Jan that is in the bare studs stage and gets soaked with a week or so of constant rain.
And then the sun comes out and they immediately tyvek wrap and seal the whole house up. Sopping wet, soaked studs, entrapped on both sides. I would love to open up the drywall in one of those two years later and see what the inside of the walls look like...
These are very expensive homes ... the four I am thinking of over the past two years were all 2M+.
This exact scenario is going to play out near my house over the next two weeks. SF Bay $2m houses. I should send pictures to the county building inspector.
The speaker is a little hammy, but he's doing (more or less) legitimate science, and he laid out a bunch of principles I didn't understand before.
In particular, the different layers of the wall (ballistic, water, insulation, vapor, structure) really need to go in the right order, and at literally every exterior joint in the house you need to match up all five layers. There are also several layers that it is crucial to vent/drain.
It's extremely complicated, and for the most part just obeying code and convention will only get you 80% of the way there.
It seems to me there are also anti-patterns ensconced in code and convention. The idea that insulation goes inside the structural layer for example. You want your insulation layer to be unbroken.
In order to take care of mold, you need to clean up what you can using hydrogen peroxide. It will foam up when it contacts mold. Keep applying until this is no foam up. Incidentally, peroxide in a spray bottle is great for cleaning showers and places that get mildew. Always use fresh peroxide.
For an air purifier, you need one with a UV light.
In my experience a one-two punch with chloride to kill the mold quickly, followed by a dousing with distilled white vinegar, results in a good short and long term solution for surface mold.
Safety advice: If you decide to try this at home, please keep in mind that mixing chloride based cleaning agents with an acid will release chlorine, which is toxic enough to have been used as a WW1 weapon.
Chloramine is responsible for the classic "swimming pool smell", as the chlorination in the pool reacts with urine, sweat, and other nitrogen-containing organics. Chloramine is a less effective disinfectant than free chlorine, and more irritating to swimmers, and diffuses out of the water more slowly, so this is why you shouldn't pee in the pool, and why you should rinse off in a shower for a minute before entering. Mainly, just don't pee in the pool.
If you smell "swimming pool" where no pool exists, it might be prudent to leave the area immediately and take a 1000 mg vitamin C tablet, before making any attempts to discover the source of the smell. (Taking vitamin C after the damage is already done won't help.) If the odor is especially strong, or if it causes any irritation to your nose and eyes, evacuate, and do not return. Call your emergency services number and tell them you smelled a strong chlorine odor.
Don't combine bleach cleaners with ammonia cleaners, ever. Don't even store them in the same place. Also avoid mixing bleach with acids, such as vinegar.
Chlorine can react with about anything that contains ammonia or amines to form chloramine, so shampoos, lotions, shaving foams, or conditioners could also be responsible. Amino acids are named thus for their amine groups, so anything containing proteins or protein fragments will react. Amine oxides and triethanolamine are used as surfactants in cosmetics. Sweat is unlikely to be the culprit. Check the ingredients in your cosmetics.
I guess I didn't realize someone would try this without letting the chlorine evaporate first. I should have worded it better: Chloride to kill the mold on contact, let dry, then vinegar to keep the mold away.
Different people suggesting different means against mold here, but in the end, you have to find the root of the problem and eliminate it. Otherwise, you are fighting symptoms.
1. Air filters might reduce the airborne spores, but if you have mold already growing behind some wardrobe you are wasting time.
2. Hydrogen peroxide, chloride, and isopropyl alcohol are all good tools to fight it when you find a place where it grows, but ultimately you have to solve the problem at a deeper level as mold has excellent survival skills (you might clean the wall but the spores in the air infect it again right afterward).
3. In order to eliminate mold, you have to change the environmental conditions. As most living organisms mold requires food and water. The water comes either from inside the wall (that is something only your landlord can fix) or from the air. So try to maintain a low humidity level within your apartment (<50% should be okay). The easiest way to achieve that is by using your heating and replacing all air within your apartment by opening all windows for 5 minutes (to let in cold air, no longer, as it will cool down the temperature of the wall otherwise), three times a day. Mold nourishes itself from organic material. Very often that means fabric, wood or wallpapers (yes removing your wallpaper might be a good idea). Since water condenses in cold spots first, those are the place you want to keep looking for (walls next to windows, corners of a room).
Three years ago I had a mold problem in my apartment. Following the above advice, the mold didn't come back (except for a few spots in the shower, but that is kinda difficult to keep dry).
I lived in a small studio in a damp part of SF and we discovered mold growing behind a beureu, I had cold like symptoms for months before which I think was related to a mold allergy.
We moved all furniture away from wall, cleaned with mix of bleach and water then invested in a $200 Frigidaire 50 pint dehumidifier (like this one Frigidaire FAD504DWD Energy Star 50-pint Dehumidifier https://www.amazon.com/dp/B00AU7GYXA/ref=cm_sw_r_cp_apa_n8i7...) and it solved the problem for us. It would pull a gallon or more of water out of the air everyday.
I tried some smaller/cheaper dehumidifiers but they really didn't compare.
I briefly lived inside an apartment that was previously a cave. There was a plaster wall separating from the outside, and after raining, it ended up covered in mold. We cleaned it with bleach, but moved out soon after. I hope I did not get too much exposure.
Do not forget that black mold release mycotoxins, which are carcinogenic.
Sorry to ask, but I’m not really sure I got it right: Do you think the DIY air purifier was the cause of these health problems? Or did it at least contribute by letting the mold come back (inside)?
As others have noted, a dehumidifier could help. But what prevents mold from growing inside these dehumidifiers as well? Sure, they’re mainly built from plastic and metal, so no paper as in your case. Will that be enough to prevent mold (or bacteria)?
Otherwise, a dehumidifier could turn into yet another health hazard over time.
354 comments
[ 3.3 ms ] story [ 291 ms ] threadWith the filter thoroughly taped to the front (nearly airtight), there’s a large amount of blowback. I suspect that this is reducing the overall efficiency of air filtration.
I used to put the high-efficiency filters on my furnace, my HVAC guy said these filters are so heavy that they put a strain on the blower motor. It's better for the motor to use a plain blue fiberglass filter (MSRP $1). You're not really filtering that much out of a closed house, unless you run your forced-air A/C or Heat with the windows open.
This graph of airflow vs. MERV rating isn't very conclusive in my mind: http://www.homeenergy.org/UserFiles/file/26-6_p34big(1).jpg
Granted there are about a million variables in all HVAC systems that could affect the results.
1) If the filter is at the back, since the air is pulled through it, the dirty side is outside where people and kids can touch it as it builds up. If the filter is in the front, the dirty side is inside (towards the fan blade) while the clean side is outside.
2) If the filter is at the back, due to air's resistance it is possible, due to nooks/gaps in the fan, that the some of the air may be pulled from elsewhere and not all the air may pass through the filter. If the filter is in the front, it is easier to seal between the fan and the filter to make sure all air is pushed through it.
I'm curious... doesn't #2 cut both ways? i.e. if you can seal the front, you can seal the back?
I wish the guy on the video would take an air reading measurement near the side of the filter. I'm guessing that a lot of unfiltered air is escaping out the sides.
BTW you need not cover the entire area of the fan with filter material. So, for instance, if your fan's breaker is shutting the motor down b/c of the load of the filter, you can slide the filter up to cover less of the fan with the filter, reducing the load on the fan motor. While not all air passing through the fan will be filtered, over time most air will eventually pass through the filter and the room will be cleared of particulates.
Similarly, it is not necessary that the filter be the same shape or size as the fan, since with each pass at least part of the airstream is cleaned. Eventually all the air in a room will pass through the filter area.
Where does the heat go?
I have one. It works pretty well. The air filter isn't as good as the massive Austin Air I use for my living room, but it's okay for a smaller room... not to mention much quieter, smaller, and easier to integrate with home automation.
Only criticism is that the U300 does not have wifi connection - only IR control... I am hacking up a esp8266 + some IR LEDs and photoresistors to monitor and control it via MQTT though which is fun. The "wifi connected" units seem to add several hundred GBP to the price for the same filtering performance.
We're not sure if we're noticing any actual improvements in air quality, or just imagining it...! :-) The placebo effect is quite good if nothing else. Noses feel less congested, and the air in the room feels less stuffy in the morning.
1 - https://winixeurope.eu/air_purifiers/winix-u300/ No personal connection to these guys, just a satisfied customer (so far after a few months)
I have no way to really measure its effectiveness, but it very quickly removes any cooking smells and has fixed my year-round allergies while indoors.
I am so tired of dust in my studio. There is no ventilation other than the small fan in the bathroom or the big sliding door in the front. So I leave the fan turned on overnight but because of pressure difference, very small particles keep accumulating all over my place. I’m really hoping this changes that.
It also works well by itself if you just want to cheaply filter large particulates. I used to use it in those cheap $40 Hamilton Beach air purifiers. The OEM filters for those cost almost at much as the new unit and wear out [for me] within a couple of weeks. That setup with Swedish tracing paper works well for dust, as a supplement for my HEPA filter purifier.
Fan --> Cheap Filter --> Expensive Filter
Fan --> Expensive Filter --> Cheap Filter
Cheap Filter --> Expensive Filter --> Fan
Expensive Filter --> Cheap Filter --> Fan
?
You put the filters on the intake, so that the airflow helps making a seal instead of creating leaks.
You put the cheap filter first everything that it catches will not clog the expansive one.
PurpleAir sells an indoor sensor, but it appears to be limited release and somewhat 3D printed. https://www.purpleair.com/
I've got a foobot, I like it. It was benchmarked by some gov't agencies and found to track pretty well.
They are hard to find and buy in the US, but very popular in China where many cities have major air quality issues. I picked one up on ebay.
Most of these consumer-grade PM2.5 monitors seem to use the same basic laser scatter sensor that measures 0.3um+ particles.
https://www.vox.com/energy-and-environment/2018/8/21/1776190...
https://hackaday.com/2018/10/09/hacking-the-zh03b-laser-part...
This one only goes down to one micron though, so it might not be usable for many allergens.
[1]: https://www.grainger.com
[2]: https://www.mcmaster.com/
Particulates and VOC (Volatile Organic Compounds). Think of particulates as specs of dust with varying size and VOC's as random chemical compounds such as spray paint, smoke, oders.
The general go-to clean room/industrial filter stack is Prefilter(F5 Bag)->HEPA->Activated Carbon. The pre-filter catches all the big particulates to prevents clogging the HEPA filter. The HEPA filter catches all of the really small particulates. The activated carbon captures most of the VOC's/oder/smoke.
The official way to monitor when a particulate filter is bad, is to measure the pressure drop across the filter, and compare to manufacture specs. For the carbon filters, you would install a gas sensor measuring whatever chemical your trying to scrub. When there is a spike in that particular gas compound from your sensor. You know the carbon filter is saturated, and should be changed.
It looks like the the filter mentioned in the article video,combines all the filter products into a single product. Nice! If your air handler can manage the increased pressure drops, please buy the most legit filters you can buy. It's literally the cheapest insurance you can buy.
yup, i bought a blueair 211+ (https://www.blueair.com/us/blue/blue-pure-211/1695.html), that has exactly those filter elements in a nice (if bigger than expected) package. this model was recommended by both consumer reports and the wirecutter (until recently, cynically thinking they didn’t pay wirecutter’s “endorsement fees”). it’s effectively eliminated my constant coughing, sneezing and runny noses before i got it.
https://news.ycombinator.com/item?id=16729408
The only real issue is any continual air flow into the room. There will be a big impact from what kind of air system you have in the greater building. For example, central air without a good filter on that system will make your fan-filter's job a lot harder.
The filters are relatively cheap to replace and will last a long time filtering a small bedroom. I get a solid year out of the filter on my central air system and it's filtering an entire home (non-smoking, no pets). Outside of the small electrical cost or annoyance from having the fan running, there's no reason not to run it very frequently if you derive a benefit. If you don't desperately need purified air for eg allergy purposes and your small bedroom isn't receiving inbound air (eg from a central air system), run it for 20-30 minutes, a few times per day, and that should easily do the job. If that's a hassle, just let it run more often than not.
- I bought XIAOMI Mi Air Purifier 2 straight from China for $137.00 and spent 1 euro on a EU plug. It's so quiet that I can sleep next to it, looks nice and it's quite compact, so doesn't take up much space. It has a particle detector to adjust the fan speed. The app is useless, so a cheaper version without WiFi and bluetooth would be great.
- Buy some HEPA filters to put into window ventilation. You may want to remove some plastic inside to increase the flow http://img.archiexpo.com/images_ae/photo-g/69621-5895915.jpg
- Buy roomba like vacuum cleaner https://www.goodcheapandfast.com/articles/best-robot-vacuums
It will cost you less than 500$ to buy these and about 55$/year for new filters. It is worth the money. The air quality is much better (I'm allergic and I haven't had any problem with my sinus since).
What is more, is it worth it. It will save you time cleaning your place (about 10h/year)
Anyone has tried robot vacuums with mop or automatic dirt disposal function?
Not very. Wet wool is better, but only as long as its wet and clean.
> XIAOMI Mi Air Purifier 2 straight from China
Interesting question. Does the removal of particulates offset the health impact of its cheap plastics?
Do you mean the health impact of when the device is thrown away?
have you tried it with hass (home assistant)? I've been considering getting one and running it via that instead.
I don't think I was the only one, though. HD was doing a brisk trade in 20x20 filters, and I think I bought the last box fan at any Target in the entire bay area.
My "creation": https://i.imgur.com/jeJfqeW.jpg
Is that the spot of use as well? I’d imagine the vicinity of the wall would limit the airflow.
I still have a sore throat, but I also have to go outside a lot, so maybe that's not surprising.
Get some 120mm fans (or an array of 80mm, etc), and some engine air filters.
Don't change the filters too often:
"It is common, however, for servicing to occur when the filter appears dirty. Engine air filters are designed to actually increase their efficiency by using this initial layer of dust as an added filter layer. Initial filter efficiency is usually approximately 98% but increases to more than 99% by the end of the service life of the filter.
Therefore, changing an air filter before the useful service life is achieved can result in premature engine wear."
https://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_2...
I've been begging for a good use of old computer fans...
Thank you for bringing this up ... in industrial settings, filters are "seasoned" for some period before they can be expected to perform at their published ratings.
Many air and water filters' performance continues to rise over their lifetime - the downside being decreased flow rate.
If you are filtering infectious agents with a water filter, I would be reluctant to run them past their lifetime because you could have things living in the filter and filter housing, etc., but if you're just dealing with particles, your filtration should continue rising over time.
There's often an electrostatic component that ties into a filter's efficacy, as well.
The first step for me was getting a device to measure particles in the air. The air quality index (AQI) is an aggregate score that is made up of contributions from several harmful components. Of these, the quantity (weight/volume) of small particles (<2.5um) is often the large contributor. This is called the PM2.5.
Directly measuring PM2.5 is very hard, requiring a device that eliminates the larger particles from the air (typically a cyclonic separator it seems) combined with some way of capturing and weighing of the very small quantity of remaining particles (we're talking ug/m^3).
Many home air quality sensors instead measure the count/volume of particles larger than 2.5 um and call that the "2.5um measurement". You can see the problem. I bought a laser particle counted called Dylos DC1100 Pro. The Dylos measures particles counts larger than 2.5um as is common, but also counts particles larger than 0.5um. Of these two numbers, the 2.5 count is only vaguely correlated with the actual PM2.5 measure, but the 0.5um count is highly correlated.
A bit of internet research (it seems many people have used the Dylos meter in various projects) and I was able to construct a scale to correlate 0.5um+ counts to PM2.5, and therefore AQI. (0.005*count~=ug/m^3)
OK, all that done, to the filtration. First, I installed 3M 1550 MPR furnace filters (~MERV11). The "1550" is a measure invented by 3M 'MicroParticleRating' (or something) and is supposed to speak to how well the filters remove small particles. However these furnace filters don't really knock down very small particle counts in once pass. Sure enough, putting the particle meter at an air duct, the large (2.5+) particle count was way down, but the small particle count was only down a little bit (15-25%?) from the ambient air. Net effect is that after running for several days my house numbers are about 1/3 of the outside air counts.
I also bought a BlueAir HEPA filter for my bedrooms. HEPA is supposed to be 99+% effective for particles 0.3um and up. This filter is in a whole different league. The particle counter placed on top of the filter returns near-zero small particle counts and does a much better job eliminating smells. The room they were in got down to 1/10 of outside levels.
Overall I'm glad I got both types of filters, we are sleeping better, and the meter was very helpful to understand what was going on.
I have built one of these (20x20 furnace filter on a box fan) and always put the filter on the intake side of the fan. However it seems like people are placing the filters on the outflow side of the fan instead, for reasons that are not clear.
Since it seems like you did some measurements, do you have any idea whether it's preferable to have the filter on the intake or outflow side of the fan? (I note that in furnaces and other air handling equipment, filters are almost universally on the intake, not the outflow, side, presumably because this keeps dust out of the blower/heating mechanicals.)
Used an existing box fan. I had to buy duct tape ($3) and the filter I used one rated for 0.1micron pollen and viruses cost me $17 (rounding up after tax). I cut up a plastic safeway bag to make the seal around it. Seeing as most smoke particles is around 2.5-.5 micron I figured it'd be okay.
I threw this together at about 7am on Saturday after I woke up coughing my lungs out at 6am (I live in the bay area). Just a quick trip down the the Homeless Despot to get the parts and throw it together.
All things consider it works great. The air in my apartment is easy to breath, but if I leave without a respirator (even today) I cough uncontrollably.
---
As of Tuesday evening it has been running for 4 days straight (no overheating). And has started to become noticeably brown. Needless to say I'm thankful for it.
HEPA filters are very very very good. Running through 2 of them isn't going to pull much more out because there just isn't much more.
Actually, you'd probably get less actual filtration due to the greatly reduced airflow.
If the first filter reduces 90% of pollutants, can we assume that the second filter reduces an additional 90%?
http://frugalvagabond.com/the-box-fan-dehydrator-experiment/
Although the price of that purifier is now $40 more then when I bought it, so it may make more sense to look at their other picks.
Air quality was bad and I’m still not sure what kind of filtering my condo building has.
What gets me is how these guys misuse “science marketing” to play on people’s fears about germs. Add the shameless exploitation of a real tragedy here.
https://thewirecutter.com/reviews/best-air-purifier/
While the New York Times Co. did indeed purchase The Wirecutter/The Sweethome, there’s no reason to start attributing Wirecutter reviews to the parent company.
This is especially true in the settings of reviews, since the NYT performs its own reviews.
1. CADR is really low to the point where the unit is near useless due to #2
2. In addition to a low CADR, it has the highest noise. It looks and sounds like a jet engine when you have this thing on high, which is needed due to the low CADR. This is the loudest air purifier that I’ve ever owned
3. If you get a defective main filter, the unit will emit an unpleasant metallic smell. I haven’t tested the particles yet but I doubt the air is clean.
4. Unlike other smart air cleaners in the same price range, it’s app and smart features don’t work. You can’t even create a schedule for it
It’s a very flawed device
5. The unit works using some LED light. A. it is bright B. It is not replaceable. Meaning after 2-4 years of operation, the unit becomes a throwaway. This is not a good thing for a unit that costs over $700
Any advice appreciated.
The mould is still there but the dry air stops it from growing and sporing which is what makes you stick. If humidity creeps up the mould will grow again. Be aware that mould is virtually everywhere and is only harmful if there is enough of it around sporing or if you touch it.
The problem is, once the calcium chloride has absorbed the moisture from the air and is saturated, you have to take it out and dry it to make it effective again. That might be cheaper (in terms of energy) than refrigerant phase-change dehumidification, but it's a lot more labor intensive.
Natural airflow with the outside at 90% relative humidity isn’t going to do a thing other than make the interior occupants ornery.
The natural airflow design of Apple Park for example, that works incredibly well, but that same design in Houston or New Orleans would be catastrophically ridiculous.
https://www.cdc.gov/mold/stachy.htm
I'm not really sure about keeping the humidity below 50% though. The UK and most of Northern Europe has rather high humidity in the winter. It commonly reaches 80-90 RH outside, so you'd have to heat your house to 25c/77F to bring the humidity below 50%.
Cold air can simply hold less water overall, at 20C it can easily hold double as much water as it can at 0C.
There being a pressure difference is nonsense, you can get the same air pressure in the winter as in summer (though it tends to go on the Low side more often). What you probably mean is the vapor pressure, ie the natural pressure the liquid wants to be at in a closed container, though while it is largely depdenent on temperature, it does so in a linear/positive way, so at lower temperature, water will evaporate less (otherwise ice would more easily sublimate).
Once you go below zero a water content of a few grams can easily hit 100% RH which would barely manage 5% or less at 30C.
If you can blow dry air over its surface, you can evaporate liquid water (or sublimate water ice) even when the relative humidity is 100%.
You can think of air as a gaseous solution, and its water vapor content like table salt in aqueous solution. Temperature affects the solubility, and if the solution is saturated, no more can dissolve. You can still dissolve salt crystals sitting in a saturated cold saltwater solution by squirting warm freshwater onto the bottom of the container. If that then mixes with the rest of the solution, and everything cools down again, that dissolved salt can then precipitate out somewhere else (like rain), or form a suspension of tiny crystals (like fog or clouds).
The solubility of H2O vapor in atmospheric gas increases with temperature. But you can also do something with a gaseous solvent that you can't easily do with a liquid solvent, which is to change the pressure. Higher pressure lowers the solubility of water in air, but to a far lesser extent than a decrease in temperature. Even though the vapor pressure is dependent only on temperature, evaporation occurs whenever the vapor pressure exceeds the partial pressure of H2O at the interface. Increasing the overall air pressure also increases the partial pressure of H2O vapor by a proportional amount, so inhibits further evaporation. But water vapor is also less dense than N2, O2, and most other atmospheric gases, so the means of measuring pressures gets complicated.
When you involve wind, and stratified airflows, it gets even more complicated. The air blowing across water or water ice could have been previously warmed by the ground just enough to evaporate more water, then get pushed higher by an angled snowbank into colder, saturated air, and it will then dump the excess water as small ice crystals. A solid block of ice can then become "rotten" as a snowdrift forms downwind of it. The overall average temperature may say that ice should stay frozen, but the wind can still carry a tiny bit of water vapor at a time, thanks to local fluctuations, and with enough volume of air to move it, that ice will drift.
Indoors? No, not at all. In the winter the temperature in my house/office is 21-22C and 17 at the lowest at night, and I have to run a humidifier 24/7 to keep the humidity over 30% (otherwise the wooding floors shrink too much).
Currently in the bedroom (thanks Netatmo) it's 17.8° and 69% humidity (with one of the three windows open about 0.5"). That compares to 14.0° and 78% on the balcony. Looking at the graphs, 50% is the lowest indoor humidity over the last month.
Still - mold in houses is not a problem in houses in Western/Northern Europe, except for the most pathological cases (for example, mold scores you iirc 2 points in Belgium on the 'uninhabitable property' test, where 9 gets your building declared unfit for living in. Having small holes in the roof or small cracks in the walls (still structural defects) gets you 3. That's how unusual mold is around here. OTOH when I lived in New Zealand, mold was met with 'eh, there's bleach in isle 5 at Countdown, just wipe it down.'. I was like 'wut?'.
Alas, it does not, but that's possibly because other windows are open around the place and there's relatively good airflow.
> I'm going to try this same experiment tomorrow, I'm quite interested to know.
I'll see how it goes tomorrow with the window closed and various doors closed to minimise the effect of the other windows.
[0] https://en.wikipedia.org/wiki/File:Relative_Humidity.png
When it gets to the cold part of winter it's obviously easier, but this time of year it's hard to get it below 50% RH inside just by controlling the temperature.
How does that work?
You may not be eligible for regular tenant protections, but you're still eligible for recourse through regular courts, no?
My first rental in London had bad mould problems. The landlord refused to fix them. We ended up with dehumidifiers throughout the house to keep it under control. When we left after a year, he complained at us for keeping dehumidifiers around when potential tenants came to visit - it raised too many questions! This was a 2200+/mo rental that he had bought for about 100k 15 years ago. What a crook.
This might or might not have been feasible given OP's budget, heating arrangements, and general preference. I for one would not want to live in such a hot room for a whole season even if I could afford to. I keep my room cooler than that even in the summer!
Apparently, the contractor let the drywall get soaked while sitting on palettes during monsoon season, and since the roofing wasn't done there were inches of standing water that resulted in black mold.
They just drywalled right over it. In the US. In 2018. In a luxury condo.
So, you never know what nonsense you will have to put up with.
It's why bad actors (such as the ones described above) keep getting away with what they do.
I know they're in the desert, but drywall really should happen after the building envelope is sealed.
Entering a rainy season without a roof being sheathed is also bad contracting.
This happens regularly in the SFBA, in Marin County. Every rainy season I see at least one house being built through Nov-Dec-Jan that is in the bare studs stage and gets soaked with a week or so of constant rain.
And then the sun comes out and they immediately tyvek wrap and seal the whole house up. Sopping wet, soaked studs, entrapped on both sides. I would love to open up the drywall in one of those two years later and see what the inside of the walls look like...
These are very expensive homes ... the four I am thinking of over the past two years were all 2M+.
This talk really gave me a foundation for understanding how moisture works in a building enclosure through seasons: https://www.youtube.com/watch?v=Ld8pzIu45F8
The speaker is a little hammy, but he's doing (more or less) legitimate science, and he laid out a bunch of principles I didn't understand before.
In particular, the different layers of the wall (ballistic, water, insulation, vapor, structure) really need to go in the right order, and at literally every exterior joint in the house you need to match up all five layers. There are also several layers that it is crucial to vent/drain.
It's extremely complicated, and for the most part just obeying code and convention will only get you 80% of the way there.
It seems to me there are also anti-patterns ensconced in code and convention. The idea that insulation goes inside the structural layer for example. You want your insulation layer to be unbroken.
For an air purifier, you need one with a UV light.
If you smell "swimming pool" where no pool exists, it might be prudent to leave the area immediately and take a 1000 mg vitamin C tablet, before making any attempts to discover the source of the smell. (Taking vitamin C after the damage is already done won't help.) If the odor is especially strong, or if it causes any irritation to your nose and eyes, evacuate, and do not return. Call your emergency services number and tell them you smelled a strong chlorine odor.
Don't combine bleach cleaners with ammonia cleaners, ever. Don't even store them in the same place. Also avoid mixing bleach with acids, such as vinegar.
https://en.wikipedia.org/wiki/Chloramine#Safety
1. Air filters might reduce the airborne spores, but if you have mold already growing behind some wardrobe you are wasting time.
2. Hydrogen peroxide, chloride, and isopropyl alcohol are all good tools to fight it when you find a place where it grows, but ultimately you have to solve the problem at a deeper level as mold has excellent survival skills (you might clean the wall but the spores in the air infect it again right afterward).
3. In order to eliminate mold, you have to change the environmental conditions. As most living organisms mold requires food and water. The water comes either from inside the wall (that is something only your landlord can fix) or from the air. So try to maintain a low humidity level within your apartment (<50% should be okay). The easiest way to achieve that is by using your heating and replacing all air within your apartment by opening all windows for 5 minutes (to let in cold air, no longer, as it will cool down the temperature of the wall otherwise), three times a day. Mold nourishes itself from organic material. Very often that means fabric, wood or wallpapers (yes removing your wallpaper might be a good idea). Since water condenses in cold spots first, those are the place you want to keep looking for (walls next to windows, corners of a room).
Three years ago I had a mold problem in my apartment. Following the above advice, the mold didn't come back (except for a few spots in the shower, but that is kinda difficult to keep dry).
I briefly lived inside an apartment that was previously a cave. There was a plaster wall separating from the outside, and after raining, it ended up covered in mold. We cleaned it with bleach, but moved out soon after. I hope I did not get too much exposure.
Do not forget that black mold release mycotoxins, which are carcinogenic.
Sorry to ask, but I’m not really sure I got it right: Do you think the DIY air purifier was the cause of these health problems? Or did it at least contribute by letting the mold come back (inside)?
As others have noted, a dehumidifier could help. But what prevents mold from growing inside these dehumidifiers as well? Sure, they’re mainly built from plastic and metal, so no paper as in your case. Will that be enough to prevent mold (or bacteria)?
Otherwise, a dehumidifier could turn into yet another health hazard over time.