5 ms·

> Using the heater does not affect range in a gas powered car. It typically does (though not as much as the chiller would). There's two costs to using the hea

> Using the heater does not affect range in a gas powered car. It typically does (though not as much as the chiller would). There's two costs to using the heater: 1. The electricity to power the fan comes from the engine. I'm not sure how much of an impact this actually is (depends on the power the fan needs) but there's something there. 2. The heat from the heater comes from the engine block, which cools the engine. On cold days (<15 F) this can have a huge impact on the engine's temperature and will often cool the engine well below it's most efficient operating temperature.

pdonis 14y ago
The electricity to power the fan comes from the engine. I'm not sure how much of an impact this actually is The fan practically never runs in cold weather. The only time it's needed is in hot weather, when you're stopped or at low speed and there's not enough airflow over the radiator and/or condenser. In cold weather the thermostat controls engine temperature, not the radiator, so the fan never gets told to turn on.
- modoc 14y ago
  Not the radiator/cooling fan(s), the climate control system/vent fan(s.
  - pdonis 14y ago
    Ah, ok. That actually does draw a significant fraction of the available power on the 12V electrical system (in my car the interior lights dim perceptibly when the climate control blower is on high), but by the standards of the engine it's still not much.
eli 14y ago
Isn't it using electricity that is already being generated by the alternator whether the heat is on or off?
- tbrownaw 14y ago
  Not exactly... the alternator provides "up to" a certain amount of electricity, but as more of that electricity is actually used for things it gets harder for the engine to spin the alternator and so you end up using (slightly) more gas. The alternator (or really any electric generator) has a magnetic field, and a lot of coiled up wire. Moving the wire thru the field generates electricity, the faster the wire moves the higher the voltage is. But the more current is moving thru the wire (more load, more things using the electricity), the more it pushes back against the magnetic field (because that current in the wire generates its own field) and so the harder it is to make it move.
- deleted 14y ago
  [deleted]
- function_seven 14y ago
  No. The greater the electrical load placed on the alternator, the greater the parasitic load on the accessory belt. That being said the amount of electricity, and thus the load on the belt, to run the fan is very very tiny compared to the energy required to heat the air. In an ICE, the heat energy is literally free. You were going to dump it anyway, might as well be into the cabin.
- jessaustin 14y ago
  I agree with siblings that we're not talking about a significant effect on mileage, but technically there is still an effect. When the ventilation fan kicks on, this will be an additional current draw. Since the voltage regulator is an analog device, it will respond to the resulting slight dip in system voltage by increasing the alternator field strength slightly. The engine will then have to apply slightly more torque to the alternator, which will burn slightly more fuel. Since engine speeds vary greatly, having a dumb alternator that provided power scaled in proportion to RPM would be a disaster.
- MertsA 14y ago
  That's not how a generator works. Take a DC motor and spin it with your hand and it'll generate a bit of a voltage potential across the terminals on the motor. If you short those together and then try to turn the motor you'll notice that it's significantly harder to turn.
bathat 14y ago
Look, electric cars are great, and I'm looking forward to the day when I can buy one, but this is BS. First, the power the run the fan is minuscule. On the order of a few Watts. Maybe a few tens of Watts at most. It's an order of magnitude less than what is needed to run seat heaters (and those have almost no measurable effect on a Model S's range, which is why "range mode" uses seat heat in favor of air conditioning). The energy use you're talking about is enough to move the car an extra few hundred feet after a multi-hundred mile drive. Second, every ICE has a thermostat on the radiator. It greatly reduces coolant flow to the radiator when the car is warming up, or any other time that the coolant is below optimal temperature. I spent many years in the northern (continental) United States and never encountered a situation where the coolant temperature gauge on an ICE car failed to show normal operating temperature after 10-20 minutes of warm-up time. The cold-weather fuel economy difference in a conventional car mostly comes down to greater air density.
- bradleyjg 14y ago
  Wouldn't colder air, and thus higher air density, be more efficient, not less efficient?
  - stcredzero 14y ago
    Drag goes up proportional to the density of the fluid. Having more oxygen to run your engine will give you more energy, but I suspect that it won't keep up with increases in drag.
    - pdonis 14y ago
      Oxygen density is also proportional to the density of the fluid, so this should be a wash.
    - bradleyjg 14y ago
      Yeah I suspect this is it. The density is inversely proportional to temperature and drag is proportional to to density. Even if the engine is more efficient (in a steady state) with denser air, the relationship is probably sub-linear.
ken_railey 14y ago
This is reaching a bit. 1) The nominal amount of electricity used by a heater blower motor is not going to measurably affect the range of your trip (this is most likely the same for the Tesla) 2) The heat from the engine block is waste heat from the relatively inefficient combustion process. This heat has to be actively dissipated in most driving conditions (typically even in winter). It is essentially free to pipe this heat into the cabin. Now contrast this with the Tesla's 400 electrical resistance heater, which has to directly compromise range to generate cabin heat.
- DannyBee 14y ago
  I'm mildly curious why they use direct electrical resistance. It's not like you can't make heat pumps that operate down past 0F. My mitsubishi mini-split: 1. Can produce it's full BTU load all the way down to 5F, and 75% BTU load down to -13F. 2. Doesn't bother to blow air until it's warm :) They aren't even that much larger than a resistance based coil system (though I could imagine the model S may not be able to fit them)

pdonis 14y ago

The electricity to power the fan comes from the engine. I'm not sure how much of an impact this actually is The fan practically never runs in cold weather. The only time it's needed is in hot weather, when you're stopped or at low speed and there's not enough airflow over the radiator and/or condenser. In cold weather the thermostat controls engine temperature, not the radiator, so the fan never gets told to turn on.

modoc 14y ago
Not the radiator/cooling fan(s), the climate control system/vent fan(s.
- pdonis 14y ago
  Ah, ok. That actually does draw a significant fraction of the available power on the 12V electrical system (in my car the interior lights dim perceptibly when the climate control blower is on high), but by the standards of the engine it's still not much.

eli 14y ago

Isn't it using electricity that is already being generated by the alternator whether the heat is on or off?

tbrownaw 14y ago
Not exactly... the alternator provides "up to" a certain amount of electricity, but as more of that electricity is actually used for things it gets harder for the engine to spin the alternator and so you end up using (slightly) more gas. The alternator (or really any electric generator) has a magnetic field, and a lot of coiled up wire. Moving the wire thru the field generates electricity, the faster the wire moves the higher the voltage is. But the more current is moving thru the wire (more load, more things using the electricity), the more it pushes back against the magnetic field (because that current in the wire generates its own field) and so the harder it is to make it move.
deleted 14y ago
[deleted]
function_seven 14y ago
No. The greater the electrical load placed on the alternator, the greater the parasitic load on the accessory belt. That being said the amount of electricity, and thus the load on the belt, to run the fan is very very tiny compared to the energy required to heat the air. In an ICE, the heat energy is literally free. You were going to dump it anyway, might as well be into the cabin.
jessaustin 14y ago
I agree with siblings that we're not talking about a significant effect on mileage, but technically there is still an effect. When the ventilation fan kicks on, this will be an additional current draw. Since the voltage regulator is an analog device, it will respond to the resulting slight dip in system voltage by increasing the alternator field strength slightly. The engine will then have to apply slightly more torque to the alternator, which will burn slightly more fuel. Since engine speeds vary greatly, having a dumb alternator that provided power scaled in proportion to RPM would be a disaster.
MertsA 14y ago
That's not how a generator works. Take a DC motor and spin it with your hand and it'll generate a bit of a voltage potential across the terminals on the motor. If you short those together and then try to turn the motor you'll notice that it's significantly harder to turn.

bathat 14y ago

Look, electric cars are great, and I'm looking forward to the day when I can buy one, but this is BS. First, the power the run the fan is minuscule. On the order of a few Watts. Maybe a few tens of Watts at most. It's an order of magnitude less than what is needed to run seat heaters (and those have almost no measurable effect on a Model S's range, which is why "range mode" uses seat heat in favor of air conditioning). The energy use you're talking about is enough to move the car an extra few hundred feet after a multi-hundred mile drive. Second, every ICE has a thermostat on the radiator. It greatly reduces coolant flow to the radiator when the car is warming up, or any other time that the coolant is below optimal temperature. I spent many years in the northern (continental) United States and never encountered a situation where the coolant temperature gauge on an ICE car failed to show normal operating temperature after 10-20 minutes of warm-up time. The cold-weather fuel economy difference in a conventional car mostly comes down to greater air density.

bradleyjg 14y ago
Wouldn't colder air, and thus higher air density, be more efficient, not less efficient?
- stcredzero 14y ago
  Drag goes up proportional to the density of the fluid. Having more oxygen to run your engine will give you more energy, but I suspect that it won't keep up with increases in drag.
  - pdonis 14y ago
    Oxygen density is also proportional to the density of the fluid, so this should be a wash.
  - bradleyjg 14y ago
    Yeah I suspect this is it. The density is inversely proportional to temperature and drag is proportional to to density. Even if the engine is more efficient (in a steady state) with denser air, the relationship is probably sub-linear.

ken_railey 14y ago

This is reaching a bit. 1) The nominal amount of electricity used by a heater blower motor is not going to measurably affect the range of your trip (this is most likely the same for the Tesla) 2) The heat from the engine block is waste heat from the relatively inefficient combustion process. This heat has to be actively dissipated in most driving conditions (typically even in winter). It is essentially free to pipe this heat into the cabin. Now contrast this with the Tesla's 400 electrical resistance heater, which has to directly compromise range to generate cabin heat.

DannyBee 14y ago
I'm mildly curious why they use direct electrical resistance. It's not like you can't make heat pumps that operate down past 0F. My mitsubishi mini-split: 1. Can produce it's full BTU load all the way down to 5F, and 75% BTU load down to -13F. 2. Doesn't bother to blow air until it's warm :) They aren't even that much larger than a resistance based coil system (though I could imagine the model S may not be able to fit them)