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Low budget air flow visualization

 
steward & bricolagier
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Location: SW Missouri
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In this thread: Most effective ceiling fans? I kind of derailed it (apologies!), by asking what the poster considered effective in a fan. I personally find "blasts lots of air all over" to be fairly ineffective for what I do. In later posts I got into how fans work is WAY more interesting than people give them credit for, and that I use them oddly to get really good results in a rental with a lot of bad design, including a very badly designed (stuffed in randomly, actually) heat pump system.
The Original Poster asked

Mike Benjamin wrote:How did you develop your expansive fan-related knowledge? Any resources for someone like me?

 
And I really had no good answer. I have been thinking on it, and I may have some answers that make sense enough to be able to type them up.
What I said to him in that thread:

Pearl Sutton wrote:A lot of trial and error, living in a very hot climate with no A/C worth mentioning, looking at wind tunnel results, and learning how to move pretty much only the air I want moved at one time.

I don't go for blasting air indiscriminately, like most fans do, I move high air or low air where I want it to go, and I use focused fans for specific areas. Keeping the circulation moving how I need it is a lot of it.

So, no, I don't know how to tell you to look it up. I have never found anyone teaching this kind of information. Seeing air flow and wind tunnel visuals might help a lot. Turbulence and straight line movement are both effective at cooling the human body, but they have very different results in how the whole house, as a system, cools. I'm fascinated by the system of how it all works.

A random example from this rental in Missouri is an 8 inch fan I have hanging from the ceiling in the hallway, set to it's low setting, and left on 24/7. It moves high air and excess heat from the bedrooms to the body of the house, and cooler low air replaces the hot air. The bedrooms are closed up well during the day, so little heat comes in their windows, and the air in the bedrooms is never stagnant, due to that fan. So the bedrooms are cooler at night, when we get there to sleep.

This place has SERIOUSLY bad air flow patterns, there is nothing high I can open, all windows open at the same height, and stagnation is a major issue here, causing hot and cool spots in the house, with the worst area being where the thermostat sensor is located in the hall. The 8 inch fan in the hall breaks a lot of that stagnation at the east end of the house, and that keeps the thermostat from reacting to the stagnant air temperature in the hall (which never relates to anyplace else in the house) and kicking on the heat or A/C.

And that's what one little fan is doing, the rest of them do equally odd things, specific to the crappy design/construction of this rental. The upshot of it all is the neighbor's A/C's run 18+ hours a day, ours runs about 2 and it's quite comfortable in here. These heat pump systems were layered in on top of old, badly done, construction, and they are very ineffective. There HAS to be a better way to make stuff work than this. There really does.


So your ceiling fan, in my eyes, would depend on what exactly you are trying to do, what the rest of the house is contributing to it all, and what other factors (like A/C or not, windows, etc) are doing to the house as a whole system.

I really vote to try running the fan in reverse mode, see what it does. It changes the air flow pattern in the room, and it might tell you whether you need a bigger fan, or to change the flow a different way. Unfortunately, most of the fans you can buy will not tell you blade pitch, so, as far as I know, the only way to figure out the pitch of a blade is to look at them in the store.  My phone has a circular level on it, putting it on a blade of a display fan tells you the angle. Too steep, and the fan motor works way too hard, adding motor heat to your room. Too level and the fan isn't effective.

I just looked up "ceiling fan air flow pattern" and some of those videos might make more sense that I can by typing  :D



After all that intro, I think I need to start my actual writing in a new post.... Keep reading if you are interested!
 
Pearl Sutton
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I think the major parameter to be aware of is the input and output air of a house. All houses both have and need air input and output, and the design of most common 2x4 type constructed houses doesn't pay attention to either one.

Outputs include things people notice, like stove hoods, dryer vents, and bathroom vents. The question there is where is the air they are moving out coming in? Most houses it comes in through a lot of little gaps. Negative pressure in a house, caused by using output fans (especially oversized ones) will pull air in through teeny tiny cracks that are not even visible, unless they pull in enough moisture with them in humid climates to make a drip, or make an obvious draft that people notice.
If you are putting air out of a house, it HAS to come in someplace, CHOOSE where you want the air to come in.

Example: If you are going to run a stove hood that outputs outside, especially a high flow one, make sure you give it an input you choose. Open a window in the same room if you want just that room air shifted, if you want the whole house aired, open a window at the far end. What are you bringing in then? What temperature/humidity? Is it worth it to you to have to deal with all that different air coming in? Is there a better place you can pull it from? (Do you need to run the stove hood in the first place? Why? Can you change what makes you need to use it?)
Example: If your bathroom is up to code it has an exhaust fan (known as a fart fan to the builders.) Where is it pulling air from when it runs? Where does the output go? (I found out the fart fan at this rental outputs upward into an unheated attic space, in winter if you shower and run the fan, the moisture condenses when it gets in the cold part of the tube in the attic, and it rains in the bathroom. That's a bit extreme, but it shows what can be happening that is bad. I disarmed and covered the whole mess, I'd rather have no fart fan in the bathroom than rain in the bathroom. If it was cold enough in winter, it condensed without the extra humidity from the shower, and without the fan being turned on. It's mounted right above the toilet. Ice cold rain on the potty in winter is NOT OPTIMAL!!!) So where is the air coming in? Where is it going? Are they both good places? (That same bathroom has a window that does not seal, it pulls in cold air to the floor, makes your feet cold, then the rising air out the fan makes it rain. I don't approve of nonsense like that, I REALLY don't. It doesn't do it any more.)

How do you track how the air moves through the house? I have odd tools I use to visualize the air flow. Lowest tech is to dampen your hand, put it into an area you want to understand, and note (and draw, it helps) where one side of your hand is cooler as the air flow hits it.

Using smoke to see patterns works too, I use incense sticks because if you get too much smoke it dissipates and you can't tell what it's doing anymore. Those are good for finding very small input air leaks. Turn off the lights, and use a small flashlight to watch the smoke.

My favorite way (because I'm a silly person) to visualize the major air flows in a building is mylar helium filled balloons. Use clay or something similar that you can add or subtract exact amounts of weight on the bottom where the string goes, and adjust the weight so the balloon floats at the level you are interested in. A group of them, at high, medium, and low altitudes, allowed to float around for several days (you have to tweak the clay as the helium leaks out) will let you find the slow current patterns. Where do they go and hide? There's a problem there, figure out what. (I had one at medium level that would NOT stay out of the front closet in this rental. Took me a while to find the leak there, bad corner joint in the wall.) Where do they run to? Opening a door will always change their pattern, and it's interesting when they run toward the door, and when they run away. (I had a house in college that when the heat was on, and I had drapes over the cat door, the cat coming in made the balloons run to the cat door. My cat killed one balloon when he was attacked by it!)

Once the balloons have found your basic air flow, start adding fans to see how they change it. Something people find surprising is it's pretty rare for a ceiling fan to hit one of the balloons. It usually takes something like the door being opened and the air flow suddenly changing to make a balloon get hit. So in the example in the post above, about the 8 inch fan in the hall, when we got here the balloons totally avoided the hall, stagnant air. The 8 inch fan hung from the ceiling ( it faces west down an E-W hall) made it so the high balloons go west now, and low ones go east. This moves the summer heated high air out of the bedrooms toward the bulk of the house, where the other systems can cool in or remove it. (Using heavy drapes and opening and closing windows at the right time modulates them too, but that end of the house was never consistently comfortable till I put that fan in.) I tried it on the floor pointing east, but it was more effective (according to the balloons) in the ceiling location, plus we don't trip over it.

An interesting factor is the wind direction on a house, especially depending on the roof shape, will make a negative pressure area outside the house, that can be either be a problem (if there are cracks there, they will pull heated air out,) or be used to your advantage. The wind in this area is most often from the southwest or northwest, giving me two common low pressure areas to deal with.  If I'm trying to pull air through, I'll open windows in the negative area wider, in the positive area not as wide, which makes it pull the air through the house more effectively than having them both open the same, as it increases the turbulence in the incoming air. (Ask a balloon! It'll tell you these things.) If I am trying to keep the air from going out, I'll make sure that area is sealed up well.

My last home I put a big clerestory on the roof, angled for the wind flow. I needed it to cool the house, in Southern New Mexico, that's a requirement. After having the negative pressure actually blow out a window when everything was shut (!!! Oh, that sucked !!!) I got it down to one particular window up there on the negative side opened in spring, closed in fall, always at about 3 inches wide. That was enough let out enough hot air to drop the temperature in the house about 20 degrees, without the input air heating the house back up. Balancing the pressure let the inputs from things like opening the door not flood the house with much hot air, as only an exact amount came in. If I had been running a serious air conditioner, it would have been different. I'd have asked the balloons what I needed to do then.

Turbulence is another factor, that I'll go into another time. That is what does surface cooling on the skin, and it is fun stuff to think about.
:D
 
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https://www.youtube.com/@matthiasrandomstuff2221]Matthias[/youtube]  Wandel (aka, the wood gears guy) has been performing scientific experiments with whole-house airflow and fans lately.


I think there are several interesting take-aways from this:
1)  the wind speed/volume of the fan isn't everything because extra air beyond what the fan produces winds up becoming "entrained" in the air flow.  His experiments conclude that the thrust of a fan (which can be measured by something like a skateboard and a scale) is more representative of how much air flow it will create.
2) Because of the entrained air effect, generally speaking, putting a fan several meters(yards) back from a window/door will cause more air flow
3) Interestingly, since speed/volume doesn't matter, you can get good airflow amount using a high-speed -OR- high volume -- that is, instead of a large diameter fan for a whole-house fan, you could conceivably use something like an electric leaf blower -- a potential option if installation space is the limiting factor.
 
Pearl Sutton
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Turbulence in air flow is when things get REALLY interesting. At the farthest end of the science of turbulence, you get the serious math and computer modeling that makes the stealth planes fly differently than a jet, and that makes all the new cars look the same. I'm looking at the low end though, how it works in house heating and cooling, visualized through low tech/low budget eyes, and my words, which may not be the proper technical terms for what I'm describing.

Water and air turbulence is very similar in some ways (only in some ways, but that gets into the high math stuff above) and you can see water, so I'll start there.
If you pour water carefully from a pitcher, it's a smooth stream, minimal turbulence.
If you put a hose into a kiddie pool pointed along one wall of it, you can make it into a whirlpool, as all the water will start moving the same way, controlled turbulence.
If you put a pressure sprayer on that hose and aim it in the middle of the kiddie pool, the waves and bubbles will go all over, chaotic turbulence.

All of these turbulence styles are in the air too, and we can use them to our advantage.

**The human body is cooled by air movement across it, it dries the sweat, lowering the skin temperature. That's lovely in the summer, and miserable in the winter.
**Heated air is slightly less dense than cooler air, and air at rest tends to end up stratified, layers, like some of the weirder alcoholic drinks that look striped.  :D
**Fan motors add a bit of heat to the room, not a lot, but they ARE adding to the temperature, NOT lowering it, despite the cooling air movement.

Any kind of turbulence will move air across the body, so all of them are effective for surface cooling the body. Where they are more or less effective is in the rest of the house, and depending on what is needed.

Minimal turbulence is great when you don't want the air mixed up much. A small fan moving heat from one area to another (like the 8 inch one hanging from the ceiling in the posts above) is most effective at it's job with minimal turbulence. If it was mixing the cool air from the floor into the hot air it's moving, it would end up still being a stagnant air hallway, just with with lots of chaotic turbulence. It would feel cooler to the body as you walk through it, but the air moving from here to there would not happen.

Controlled turbulence is excellent when you know what you need. I have a small fan on the floor of the bathroom in summer, on very low, pointed at about a 60 degree angle upward. It takes the cold air off the floor (due to problems with the heat pump system here cold air puddles on the bathroom floor) and bounces it up so the bathroom feels cool, without the floor being so cold. It stirs the air enough to be comfortable without making cold drafts when you come out of the shower. The air is stirred, but only how I want it.

Chaotic turbulence is how I vent the house pre-dawn in the summer. I open the correct windows, and put a huge noisy fan pointed diagonally at the correct wall. It gets the whole house air moving in and out, and around. If I point it straight out a window, it would pull the air through, but by bouncing it off the wall I get a spiraling effect going on, which gets the stale air in all the corners moving too. If I'm trying to cool thermal mass, I'll put a lot of chaotic turbulence around it, so all of the surface gets cooled, and the mass cools well. My last home had rock interior walls, my nighttime cooling fans (different climate than here, in Missouri I do pre-dawn) pointed diagonally at the wall, took the mass temperature down most effectively. My heaters in winter pointed diagonally at the wall too, to heat the mass the same way.

So what does this mean for cooling the house?

Stratification, when the air is still and the cooler air is low, the heated air is higher, is either something you WANT to encourage (to keep the heat up there away from you) or discourage (to affect the whole temperature of the space.)  Breaking stratification also is excellent for keeping the air moving in places it doesn't want to naturally, like in stagnant areas that are between two areas that flow well.

An oscillating fan (goes back and forth) will make chaotic turbulence, great for moving all the air in it's path around. Which also means if it's getting the hot air from a sunny window, or the stove, it's mixing it into all the cooler air in the shady parts of the room. So an oscillating fan feels good as it goes by, but quite possible makes the rest of the room feel worse as the heat is more spread out. Depending on how it's pointed, it might break the stratification. So if you are laying in bed at night, and want a cool breeze on you, oscillation across you feels great, but if it's a stifling hot and you point the fan more upward, it breaks the stratification, and all the heat in the room is mixed, and now at bed level, and you have made your bed hotter.

Ceiling fans break the stratification of the affected air too. They make a sort of torroidal shaped pattern (like an inner tube shape,) where the air comes down, banks back up and goes back into the fan to come down again. So any heat by the ceiling is coming down in the air that is supposed to be cooling you. Sometimes that is fine, sometimes that's too much heat, so be aware that's happening, factor it in if you need to.  Ceiling fans in reverse (so they blow upward) on high speed work very much the fan pointing down, except you get the bounce off the ceiling, which increases the turbulence, making the spread of the fan's effect felt farther away. So it feels like it's cooling a larger area, although it's also moving the heat from the ceiling. On slow speed going upward they break stratification really effectively. A ceiling fan set as slow as you can get it to run, going upward, will keep the room warmer feeling in the winter without making a draft.  This rental has a dead spot in the kitchen where there is a ceiling fan I keep set to blow upward and slow all year, wish I could slow it down more. It makes it so the air from the adjoining rooms can move through the kitchen. It's amazing what it does, winter and summer, and I wish I could put it on a lower speed, it would work even better.

Single point fans, that do not move, do minimal turbulence in front of them, and if pointed straight ahead pull most of their air from the level they are at. So if you have one on the floor, it's mostly moving the cooler air, if you have it at body level, it's moving the air temperature at that level. If you point it upward or downward, it behaves like a ceiling fan, moving the stratified heat, whether you mean to or not.

This still hasn't explained what all of this means for cooling the house, Pearl!

When you look at light fixtures in a room, they are classified as ambient (light up the whole room, like a big ceiling fixture,) task (light up the area you are working, like the kitchen counter) and accent (light up a specific object, like a painting, or a doorway.) I see air flow as the same pattern.

Moving the air in a large area, with a ceiling fan or something pointing to break stratification is chaotic turbulence, and ambient cooling, it affects the whole room, which is both good and bad. Good as in the all of the air is affected, bad as it stirs all the heat around and isn't really focused anywhere.

Using a fan to move the hot or cool air to accomplish a specific goal is controlled turbulence, and task cooling. It's very effective for exact purposes, like moving air to better places or breaking stratification.

Moving the air in a specific spot, like a fan pointed at you while you sleep, is minimal turbulence and accent cooling, most effective for feeling cool in a specific spot.

Look at what you actually NEED as far as cooling. Can you make it so you need less cooling to start with? (Check air inputs and outputs) Do you need it to be controlled or chaotic? Do you need the stratification broke or all the heat to stay up high? Do you need specific areas? Where does the air move, where does it not? Is it's movement or not making you feel hotter or cooler?

Think on it that way, and start watching the patterns of air flow and need. This is a classic permaculture pattern recognition skill, used in a way that is less familiar to people. We are used to looking at water flow, less used to looking at air flow. Balloons are really a great tool for this,  cheap helium filled mylar balloons come from the dollar stores here, and any kind of clay or putty that doesn't dry up works as a weight. It lets you see the air flow sort of like it was water, so you can figure out where it needs to move and where it does not.

:D
 
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Thanks for doing this!
 
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