Thermal inertia–brillant…Thanks, Stanistan. Your post was very close to what I intended to post but yours is probably better written than any effort I would have made. Come on Tom and Ray, simple Thermo (which I almost failed - yuck hated that class(es)) the greater the difference in temperature between two object the FASTER the rate of heat exchange. Sure the air temperature (at the thermostat – I don’t even want to get into air currents and fan speeds – hated Fluid Flow even more than Thermo) might not get warmer quicker (dependent on how the control system is designed - What if it is an overdamped system like the gas pumps that slow down the closer you get the pre-paided amount of gas? That would slow it down.) If you heat the air temp higher your cold jacket, clothes, finger and toes warm up to a comfortable temp quicker then you back it down to the nice 72 comfort level.
Slightly off the track here, but…I usually keep the temp control on the lowest until I see the temp gauge move. Keeping the heater core out of the cooling circuit. Would that not let the engine heat up faster? If really cold outside I sometimes turn on the AC - the theory being that the increased load will cause the engine to heat up even faster! (I usually wait in the house when I do this, but of course defrost deploys the AC, too)
I drive a '94 Olds Ninety-Eight with 2-zone Automatic Climate Control. On cold days I crank it to 90 degrees and as the engine temp comes up, the fan speed comes up as well. I agree with the guy who said that everything else in the car has to become warm as well and not just the air temperature. Once everything is warm, (seats, steering wheel, armrests, etc.) I back the thermostat down to 75 for the rest of the trip. If the passenger wants any different, he/she can use the thermostat that regulates that side of the car.
Crank it up. I’ve got a 2004 Accord with an automatic temperature control, and if it’s set on AUTO, the system gets much more active when I roll it from 82 (or whatever the maximum number is on the readout) to HI. It definitely puts the fan on the highest speed, and I suspect that it also switches over to recirculate.
-Craig
Here’s the meat of what we wrote to Tom and Ray:
Like most of this sort of physics problem, the answer is to look at energy transfer in the system.
Also, notice that the problem is not to warm the car, but the people in the car. Truth is, this is a comfort issue, and that is in turn a safety issue, isn?t it?
Transferring energy into the driver and passenger as quickly as possible is better accomplished by blowing as much warm air across them as possible. (The on air discussion implied higher thermostat settings resulted in higher blower settings.)
As long as the air is even a few degrees above the temperature of the thermal ?system? representing the passenger, increasing the number of collisions with air molecules per unit time will increase the transfer of energy into the passenger.
Even more significant is the delta T factor. Assume that the passengers are insulated by some sort of warm clothing; the passenger compartment (being largely comprised of air, a low thermal mass material) will come to temperature far sooner than the passenger (a much higher thermal mass material, hidden behind a slow, insulating interface).
The higher that target temperature, the greater the delta T across that interface. The air in the car will come to temperature relatively quickly, even if that temperature is a few degrees higher than normal (say, 90 vs. 72). But that extra delta T will transfer energy faster, raising the temperature of the bodies in the car faster, even if only a little bit.
And as you know, when it?s cold, every little bit helps.
–Tom and Kay
Cure= Move to the Bahamas for the winter.
My recollect is that Tom and Ray are Course 10 grads not Course 2. Maybe one of them is Course 8; but I am positive neither one is course 2.
You said it right, Stanistan the manistan. Shame, shame on the car talk guys for flubbing the old thermostat question. There’s no doubt that the temperature of the thermostat itself will get to 72 degrees at the same time whether the temperature is set to 72 or 90, but the goal of the exercise is to get your frozen toes to 72 degrees, not the thermostat. Those of us who drive the more classic cars that are not endowed with thermostat controlled heating systems know that the quickest way to warm the car is to turn the heat on full blast until we feel hot, and then back it down to a comfortable temperature. In more technical terms, the simple thermostat control is economical for maintaining the temperature setpoint in the steady state, but does not do an optimal job of slewing to a new setpoint.
That’s interesting. Wonder how many cars with climate control systems have a simple on/off thermostat, and how many have a more complex proportional control system. Can you manually turn off the AC when you don’t want it running? If so, you could still heat your body faster by initially turning the temperature to a high setting and backing it down when the car warms up.
Excellent! But here’s a correlative question: Would the engine, hence the car, heat up faster if Denise set the heater to off until the engine temp started to rise?
Truckers use radiator curtains or flap vents usually only when they’re parked. Because those big old diesels aren’t under a load, (driving down the road), the radiator cooling fan runs while the engine is running. Stopped at a truck stop or other parking spot does not allow the cooling system to get up to normal operating temperatures. Some trucks need to idle to keep electrical systems working without killing their batteries. Using a ‘curtain’ or other type of a grill cover allows the engine to warm up and stay warm thus helping to keep the coolant system warm thus allowing the heater and defroster to work properly. Don’t forget about all of the electronic gizmos trucks have nowadays. Satellite T.V.; computers, interior lights, G.P.S., etc.
Truckers use radiator curtains or flap vents usually only when they’re parked.
Really? I see trucks and school buses running all the time with the curtains mostly closed up. Are they being used incorrectly?
the radiator cooling fan runs while the engine is running.
So these big trucks are using directly-driven (off the engine) fans, and not thermostatically controlled electric fans like most cars do? That doesn’t make sense to me. With the price of a rig and the price of fuel, if going to electric fans resulted in even a small fuel savings (from not overcooling), I’d think truckers would be all over it.
Some trucks need to idle to keep electrical systems working without killing their batteries.
New York forbids trucks from idling more than 5 minutes at a Thruway rest stop.
A woman convinced against her will,
is of the same opinion still!
Which is a fancy way of saying,“Forget it! You can’t win!” The only true option is to find another way to deal with it - hopefully one that indicates to her “I love you.” When I had an Austin Healey I would heat an iron skillet and wrap it in a towel. When she got in I would hand it to her and say,“Here. Stuff this in your jacket.” I really don’t know if it made her any warmer, but it did melt her heart. To this day I still carry lip balm in the glove box! Good luck!
New trucks are coming with APUs (auxiliary power units) so they can keep things running without idling the main engine. I think NY is not the only place that forbids long-term idling.
Au contraire, mon ami! Under these circumstances, the temperature will DROP rapidly, esp. in the proximity of the woman’s shoulder.
Aw, c’mon - Florida, south of Alligator Alley, is divine during the winter. There has never been a frozen orange.
Let’s make it more complicated. Some Automatic Temperture Control systems have an infrared sensor on dash that measures core (I read body) temperature of passenger(s).
Sorry guys, I think that women who listen to car talk don’t show much skin - especially in winter. And I’ll bet they ware sensible shows in winter.
What are you talking about a thermostat. I thought cars just had a dial that was red and blue and fan speed. I just crank it all the way up and the car warms up fast:)h
Sorry, but I have to side with Denise. But, first I have to say that I wouldn?t turn on the heater until the car is warmed-up ? it only blows cold air until the engine is warmed.
Now, back to Denise. I agree with her. Once the engine is warmed (or as it is warming), having the thermostat set at 90 degrees would make the air coming out of the vents hotter than the 72 degree air at the lower setting. This would get the car?s interior to 72 degrees faster than a 72 degree setting. That?s my two cents worth.