5 ms·

The hotter the coils the higher the amount of energy that's required to maintain it.

by BrianOnHN 6y ago

anamexis 6y ago
Well yes, but also the faster it dries your clothes and shuts off.
- BrianOnHN 6y ago
  Yes, but it's not a simple linear use of energy. For example, it might use 10x energy to dry twice as fast. That's a gain if you're in a hurry, but not so much if you're relaxing at home, on a tight budget, and/or have unusually high cost of electricity.
  - anamexis 6y ago
    It might, but does it actually? Or does it use 2.05x energy to dry twice as fast, making the energy use difference negligible? Edit: Consider also that the shorter you run the dryer for, the shorter you are running the (substantial) motor and fan, as well as less time spent heating the shell of the dryer and the air surrounding it.
    - BrianOnHN 6y ago
      Idk about the rest but the ratio of energy used by the heater compared to the motor is greater than 10:1. Edit: 20:1 mentioned here https://qr.ae/pGNTie https://qr.ae/pGNTie
      - anamexis 6y ago
        If we assume for just a moment that the time to dry clothes scales linearly with heat applied, we can try to run some numbers: Total power usage for full heat is (5000W + 250W) * 0.5h = 2625 Wh Total power usage for half heat is (2500W + 250W) * 1h = 2750 Wh So that's a 4.6% increase in efficiency for using full heat over half heat. So the big question remains, does lower heat dry clothes more efficiently, and if so, how much? The Stack Overflow answer you linked raises some interesting points, but doesn't seem rigorous.
        BrianOnHN 6y ago
        From an industry pdf I stumbled across, it looked like moisture sensing improvements were the best bet to save the most energy. Though, I didn't see anything about comparing heat settings in that doc, which may be telling.
    - bluGill 6y ago
      Depends, for most dryers the temperature is limited because water evaporation is taking all the energy. The motor takes the same energy per time, so twice as fast actually uses less energy. However there is a limit to this, eventually (the end of the cycle) you reach the point where water isn't evaporating fast enough to use up all the input energy and temperatures go up to heating clothing fibers to no useful purpose and this is wasteful.
    - adrianmonk 6y ago
      Also, is the dryer located in a climate-controlled part of your home? If so, the air that it exhausts will be made up in equal volume by outdoor air pulled into your living space. How much extra energy does that make your heater or AC use?
- bkor 6y ago
  That's not true though. The additional energy to create that heat doesn't have to equal the time saved. You'll notice this in heat pump dryers. They cannot generate the same amount of heat. They take way longer to dry the clothes. But they're way more energy efficient than other forms of dryers. Edit: I thought of another example. Heating your home with hot water running through radiators. It's significantly more energy efficient to reduce the temperature of the water. This outweighs the additional time it takes to heat up your home. There are various drawbacks and considerations though, e.g. if the house has terrible insulation (noticeable draft) then it'll not be beneficial. There's various other things that'll significantly reduce energy usage, this while anyone would assume that generating heat is already very efficient.
  - contravariant 6y ago
    To some extent drying clothes is generating heat (evaporation heat). If you're clever about it you might be able to avoid heating the (wet) clothes and rest of the contents of the dryer (or the outside!) too much. However evaporating water requires an incredible amount of energy, even if you just boil water away then most of the energy is still spent evaporating the water rather than heating the water, so it's not really too clear-cut that running a dryer hot is massively inefficient. Edit: Also it's not that using lower-temperature water to convey heat is somehow more efficient, the thing with heat pumps is that they are more efficient at heating things to a lower temperature. If you're burning gas it doesn't really matter either way, you just get the energy out you put in.
    - BrianOnHN 6y ago
      So would microwaves be the way to go? Edit: too much metal on clothing...
      - peterburkimsher 6y ago
        Ultrasound might work! https://www.energy.gov/eere/articles/no-heat-no-problem-ultrasonic-dryer-dries-clothes-half-time https://www.energy.gov/eere/articles/no-heat-no-problem-ultr...

The hotter the coils the higher the amount of energy that's required to maintain it.

anamexis 6y ago

Well yes, but also the faster it dries your clothes and shuts off.

BrianOnHN 6y ago
Yes, but it's not a simple linear use of energy. For example, it might use 10x energy to dry twice as fast. That's a gain if you're in a hurry, but not so much if you're relaxing at home, on a tight budget, and/or have unusually high cost of electricity.
- anamexis 6y ago
  It might, but does it actually? Or does it use 2.05x energy to dry twice as fast, making the energy use difference negligible? Edit: Consider also that the shorter you run the dryer for, the shorter you are running the (substantial) motor and fan, as well as less time spent heating the shell of the dryer and the air surrounding it.
  - BrianOnHN 6y ago
    Idk about the rest but the ratio of energy used by the heater compared to the motor is greater than 10:1. Edit: 20:1 mentioned here https://qr.ae/pGNTie https://qr.ae/pGNTie
    - anamexis 6y ago
      If we assume for just a moment that the time to dry clothes scales linearly with heat applied, we can try to run some numbers: Total power usage for full heat is (5000W + 250W) * 0.5h = 2625 Wh Total power usage for half heat is (2500W + 250W) * 1h = 2750 Wh So that's a 4.6% increase in efficiency for using full heat over half heat. So the big question remains, does lower heat dry clothes more efficiently, and if so, how much? The Stack Overflow answer you linked raises some interesting points, but doesn't seem rigorous.
      - BrianOnHN 6y ago
        From an industry pdf I stumbled across, it looked like moisture sensing improvements were the best bet to save the most energy. Though, I didn't see anything about comparing heat settings in that doc, which may be telling.
  - bluGill 6y ago
    Depends, for most dryers the temperature is limited because water evaporation is taking all the energy. The motor takes the same energy per time, so twice as fast actually uses less energy. However there is a limit to this, eventually (the end of the cycle) you reach the point where water isn't evaporating fast enough to use up all the input energy and temperatures go up to heating clothing fibers to no useful purpose and this is wasteful.
  - adrianmonk 6y ago
    Also, is the dryer located in a climate-controlled part of your home? If so, the air that it exhausts will be made up in equal volume by outdoor air pulled into your living space. How much extra energy does that make your heater or AC use?
bkor 6y ago
That's not true though. The additional energy to create that heat doesn't have to equal the time saved. You'll notice this in heat pump dryers. They cannot generate the same amount of heat. They take way longer to dry the clothes. But they're way more energy efficient than other forms of dryers. Edit: I thought of another example. Heating your home with hot water running through radiators. It's significantly more energy efficient to reduce the temperature of the water. This outweighs the additional time it takes to heat up your home. There are various drawbacks and considerations though, e.g. if the house has terrible insulation (noticeable draft) then it'll not be beneficial. There's various other things that'll significantly reduce energy usage, this while anyone would assume that generating heat is already very efficient.
- contravariant 6y ago
  To some extent drying clothes is generating heat (evaporation heat). If you're clever about it you might be able to avoid heating the (wet) clothes and rest of the contents of the dryer (or the outside!) too much. However evaporating water requires an incredible amount of energy, even if you just boil water away then most of the energy is still spent evaporating the water rather than heating the water, so it's not really too clear-cut that running a dryer hot is massively inefficient. Edit: Also it's not that using lower-temperature water to convey heat is somehow more efficient, the thing with heat pumps is that they are more efficient at heating things to a lower temperature. If you're burning gas it doesn't really matter either way, you just get the energy out you put in.
  - BrianOnHN 6y ago
    So would microwaves be the way to go? Edit: too much metal on clothing...
    - peterburkimsher 6y ago
      Ultrasound might work! https://www.energy.gov/eere/articles/no-heat-no-problem-ultrasonic-dryer-dries-clothes-half-time https://www.energy.gov/eere/articles/no-heat-no-problem-ultr...