5 ms·

Trees are swamp coolers. Consuming freshwater for outdoor air conditioning isn't necessarily a bad idea, but you aren't cheating thermodynamics.

ComputerGuru 3y ago
Native, grown trees need no watering, even in a (one- or two-off) drought.
- jjoonathan 3y ago
  Sure, but less evapotranspiration = less cooling. You aren't cheating thermodynamics.
  - ComputerGuru 3y ago
    Apparently a good part of the reason (parts of) the Midwest can get uncomfortably humid some summers despite being so far from large bodies of water is the evapotranspiration from the crops (mostly the corn). So too much evapotranspiration is not always a great thing! (Of course those are being watered regularly.)
kgermino 3y ago
Trees are so much more than swamp coolers. Leaves block the Sun relatively high off the ground, meaning people are in the shade during the hottest part of the day and feeling as much radiation off buildings and streets in the evening. Beyond cooling they’re also good for water management. Most street trees don’t need any watering (at least in the Midwest) they live off rainwater. When it rains, water pools on the leaves and evaporates from there, reducing the amount of run off and keeping the street drier and less humid on days with light rain. In cooler months (and places where this is relevant) the leaves fall and you can still get the warming benefit of sunlight.
- jjoonathan 3y ago
  I love trees and want more of them in our cities, my only point is that they are not usually a substitute for HVAC unless your climate is in a precise sweet spot of plentiful water, dry air, and not too much heat. Rather than letting wishful thinking snowball into bad policy and disappointment, let's promote trees by focusing on what they do well (what you've mentioned plus aesthetics and sound damping) rather than by ignoring the limitations of evaporative cooling.
  - kgermino 3y ago
    I guess we disagree on what trees do well. I’m in the Midwest with warm semi humid summers. Trees keep the area around them massively cooler, not by evaporation but by shading. Maybe it’s a disagreement of terms? I guess they aren’t technically “cooling” the area in an active sense, but they absolutely keep it cooler even when it’s 95 and the dew points over 70
    - jrockway 3y ago
      The shade is the important effect. Air conditioners have to use energy to remove heat from the indoors. That means that if the indoors are less hot, then you need to move less energy out of the room. Trees are great here, because the trees stand in the way of our solar system's largest energy source and the indoors. To be fair, things like insulation are also good here. You want something outside to get hot when the sun shines on it instead of whatever space you're cooling. (There are, of course, many heat sources inside that are annoying. I was running some fuzz tests yesterday and was annoyed to watch my air conditioner scale up in power to remove the heat that was wasting. I guess that's why people use The Cloud for everything. You can heat up someone else's city while enjoying the comforts of home!)
    - freddie_mercury 3y ago
      Dew point over 70 doesn't sound that high? I live in Vietnam. It is 8am right now and the dew point is 80. It only 80 at the moment but is supposed to get up to 90 later in the day. I assume the dew point will also go up to around 90. AccuWeather says the "RealFeel" will be 97 and "RealFeel Shade" will also be 97, so being in the shade does almost nothing, since it is overcast and raining very slightly at the moment. We're not in a heat wave or anything, this is just normal weather basically year round. If anything it's been especially rainy and cool the past few weeks. Trees are nice but are not remotely a substitute for air conditioning. Trees do not lower humidity enough to stop the average European/American from sweating constantly just sitting still here.
uoaei 3y ago
With enough trees the microclimate changes enough that precipitation is more likely in that immediate area, which compounds the cooling effects on average.

ComputerGuru 3y ago

Native, grown trees need no watering, even in a (one- or two-off) drought.

jjoonathan 3y ago
Sure, but less evapotranspiration = less cooling. You aren't cheating thermodynamics.
- ComputerGuru 3y ago
  Apparently a good part of the reason (parts of) the Midwest can get uncomfortably humid some summers despite being so far from large bodies of water is the evapotranspiration from the crops (mostly the corn). So too much evapotranspiration is not always a great thing! (Of course those are being watered regularly.)

kgermino 3y ago

Trees are so much more than swamp coolers. Leaves block the Sun relatively high off the ground, meaning people are in the shade during the hottest part of the day and feeling as much radiation off buildings and streets in the evening. Beyond cooling they’re also good for water management. Most street trees don’t need any watering (at least in the Midwest) they live off rainwater. When it rains, water pools on the leaves and evaporates from there, reducing the amount of run off and keeping the street drier and less humid on days with light rain. In cooler months (and places where this is relevant) the leaves fall and you can still get the warming benefit of sunlight.

jjoonathan 3y ago
I love trees and want more of them in our cities, my only point is that they are not usually a substitute for HVAC unless your climate is in a precise sweet spot of plentiful water, dry air, and not too much heat. Rather than letting wishful thinking snowball into bad policy and disappointment, let's promote trees by focusing on what they do well (what you've mentioned plus aesthetics and sound damping) rather than by ignoring the limitations of evaporative cooling.
- kgermino 3y ago
  I guess we disagree on what trees do well. I’m in the Midwest with warm semi humid summers. Trees keep the area around them massively cooler, not by evaporation but by shading. Maybe it’s a disagreement of terms? I guess they aren’t technically “cooling” the area in an active sense, but they absolutely keep it cooler even when it’s 95 and the dew points over 70
  - jrockway 3y ago
    The shade is the important effect. Air conditioners have to use energy to remove heat from the indoors. That means that if the indoors are less hot, then you need to move less energy out of the room. Trees are great here, because the trees stand in the way of our solar system's largest energy source and the indoors. To be fair, things like insulation are also good here. You want something outside to get hot when the sun shines on it instead of whatever space you're cooling. (There are, of course, many heat sources inside that are annoying. I was running some fuzz tests yesterday and was annoyed to watch my air conditioner scale up in power to remove the heat that was wasting. I guess that's why people use The Cloud for everything. You can heat up someone else's city while enjoying the comforts of home!)
  - freddie_mercury 3y ago
    Dew point over 70 doesn't sound that high? I live in Vietnam. It is 8am right now and the dew point is 80. It only 80 at the moment but is supposed to get up to 90 later in the day. I assume the dew point will also go up to around 90. AccuWeather says the "RealFeel" will be 97 and "RealFeel Shade" will also be 97, so being in the shade does almost nothing, since it is overcast and raining very slightly at the moment. We're not in a heat wave or anything, this is just normal weather basically year round. If anything it's been especially rainy and cool the past few weeks. Trees are nice but are not remotely a substitute for air conditioning. Trees do not lower humidity enough to stop the average European/American from sweating constantly just sitting still here.

uoaei 3y ago

With enough trees the microclimate changes enough that precipitation is more likely in that immediate area, which compounds the cooling effects on average.