Automotive Resistance Heaters

"Stupidru" (Schm1an) 01/30/2014 at 16:02 • Filed to: None

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People of northern descent, do you hate getting into a cold car and the few minutes it takes to heat your car up? (Sorry diesel owners, it may take hours for you) I've often wondered why cars don't use resistance heaters instead of blowing air from the coolant. Basically, these heaters would be hot as soon as your car is turned on. It's basically a little space heater inside each of the vents.

Does anybody know why these aren't used?

Nibbles > Stupidru 01/30/2014 at 16:03

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Engine heat has to go somewhere?

ddavidn > Stupidru 01/30/2014 at 16:04

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I can see that being used in addition to the regular heat, but the regular heating system seems pretty solid to me.

For Sweden > Stupidru 01/30/2014 at 16:04

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Engine heat is free heat. Resistance heaters mean increased electrical load. Though that doesn't stop the proliferation of heated seats.

Yowen - not necessarily not spaghetti and meatballs > Stupidru 01/30/2014 at 16:05

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It's probably far more efficient to use engine heat.

With battery life diminishing as it is due to all the electronics in modern cars, I wonder if putting that type of heater in would really kill the battery in a hurry.

Jeff-God-of-Biscuits > Stupidru 01/30/2014 at 16:09

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I think was discussed once before and the consensus was that the amps needed to be practical were enough that it would overload the car's electrical.

RamblinRover Luxury-Yacht > Stupidru 01/30/2014 at 16:09

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Comparative available wattage is *massively* in favor of the engine, and condensation/other problems are a death knell for large-scale resistance-heating past a certain age. Also, it's enough of an extra load that the car might not recover battery very fast at a time when it kind of needs to (after a wold-weather start). Also also, resistance heating works better at high voltages, and it's only recently you could economically pull high voltage AC in a car.

Strong argument to be made for non-diesel owners to have block heaters available too, though. Block heater - > reduced engine wear, semi-prewarmed coolant ->all around a better deal.

crowmolly > Stupidru 01/30/2014 at 16:10

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VW has this in TDI models. Aux air heater Z35, a strip in the vents.

It is not a primary heat source though. Power use would be too great I think.

willkinton247 > Stupidru 01/30/2014 at 16:10

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My 2010 Jetta does this! It heats up much quicker than normal cars.

puddler > Stupidru 01/30/2014 at 16:12

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i have no heater of any sort. so jacket & gloves FTW!

but i've got 2 heater cores to install as soon as i move. one on the firewall, one under the seat each will have a bi-directional fan, so i can eith blow the heat in, or blow it out.

Casper > Stupidru 01/30/2014 at 16:13

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Engine heat from the engine is free in a system where electricity is an after thought (actually it's an efficiency increase in that it's converting an unwanted by product to something usable). The more you take from the engine at the alternator, the less going to the ground to move the car and the more fuel it takes.

Stupidru > Casper 01/30/2014 at 16:16

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I get that- I'm a mechanical engineer, but as an engineer I also understand that if it's a trade-off between being cold for a few minutes or having immediate heat, people sometimes don't care about engine efficiency. Especially if you're able to use heat from the coolant after it reaches operating temperature. Engineering is a profession of managing compromises

Stupidru > willkinton247 01/30/2014 at 16:18

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+1 for VW. It's between VW and Subaru as my next vehicle and VW is winning the race so far

Stupidru > Nibbles 01/30/2014 at 16:20

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But keep in mind that anywhere north of the Mason-Dixon line, when it gets cold out and you're not on the throttle you can literally see the water temp needle going back down. I'm saying as long as your engine is making heat, use that heat to keep the engine warm. When the engine is warm, by all means use the coolant to heat the car, but until then, use the resistive heaters

You can tell a Finn but you can't tell him much > Stupidru 01/30/2014 at 16:21

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Using engine heat is essentially recovering "free" energy. Even a small resistance heater uses a ton of energy that has to come from somewhere.

Looking at Amazon, the first hair dryer that I see is 1875 W.

!!! UNKNOWN CONTENT TYPE !!!

The first alternator that I find for my 2002 GMC 1500 is a 145 A alternator. On a 12 V system we get a max power output of 145*12 = 1740 W. So at max power that alternator can't even fully power a hair dryer.

willkinton247 > Stupidru 01/30/2014 at 16:22

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Yeah, essentially the way it works is you turn the heat controls all the way up, where you'll feel a click and that turns on the electric heater. It's a fantastic feature, especially when combined with heated seats.

You can tell a Finn but you can't tell him much > For Sweden 01/30/2014 at 16:24

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Any idea what the wattage of a seat heater is? I'm sure it is much lower than what would be needed to heat the air, but I'm curious what those run at.

Arch Duke Maxyenko, Shit Talk Extraordinaire > Stupidru 01/30/2014 at 16:25

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Heated seats

Stupidru > Arch Duke Maxyenko, Shit Talk Extraordinaire 01/30/2014 at 16:26

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I don't drive with my hands under my butt cheeks, so... not quite.

Arch Duke Maxyenko, Shit Talk Extraordinaire > Stupidru 01/30/2014 at 16:26

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Gloves

Stupidru > Arch Duke Maxyenko, Shit Talk Extraordinaire 01/30/2014 at 16:27

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Don't get smart with me

Arch Duke Maxyenko, Shit Talk Extraordinaire > Stupidru 01/30/2014 at 16:28

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I'm only using logic.

Casper > Stupidru 01/30/2014 at 16:35

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Yes, but when one compromise involves increased complexity and cost for something that people haven't complained about and doesn't apply to many sales markets, it's generally going to be a non-issue.

The only way it could work is if everything else about the HVAC system were to remain the same, but somehow you heated the central exchanger so that it came up to temp before the engine was at temp, then could simply turn it's coil off via a thermostatic switch. That would keep the cost low, but the result probably wouldn't be fast enough still to justify the money/complexity. Most people will never care because they live in places that don't get extremely cold or use their garages.

Nibbles > Stupidru 01/30/2014 at 16:37

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Been living in Colorado for going on 10 years now, I've never actually seen that phenomenon.

Stupidru > Casper 01/30/2014 at 16:40

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Volkswagen seems to have done that in their cars since 2010...

Stupidru > Nibbles 01/30/2014 at 16:40

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Maybe my Subaru just sucks more and more in its later years

Casper > Stupidru 01/30/2014 at 16:41

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Well then there you go. You can buy a vehicle with it already implemented for you.

Stupidru > Casper 01/30/2014 at 16:42

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I've been contemplating buying a VW as my next car... it's been cold enough here as of late, that unless Subaru does something similar soon, I may end up driving a VAG

Nibbles > Stupidru 01/30/2014 at 16:43

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You may actually have an issue there, yeah. I should clarify: I've heard of the phenomenon, in other peoples vehicles, generally large trucks with massive radiators. Passenger cars shouldn't have this issue, I would think

The WB > Stupidru 01/30/2014 at 16:45

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Wattage, pure and simple. Your car engine rejects (very roughly) about 20% of the cars power output as waste heat. If you're using 20hp driving around town on average, you're putting somewhere around 4hp into the coolant, which is 3000W. If you're running at 70mph on the highway, you're probably using about 50hp (depending on car aerodynamics) which gives you 10hp, or 7460 Watts of available heating power. For reference, that's 25,000 BTU, which is enough to keep a 1000sq foot apartment warm in Minnesota winter.

To get just 3000W out of a typical 13.8V system, you're going to need 227 amps from the electrical system. That's about a third of the cranking capacity of a typical battery, and about double what modern alternators put out.

Stupidru > The WB 01/30/2014 at 16:48

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After reading some of the comments it seems that VW has figured out a work-around and has already implemented these into their cars since 2010... hmm... now to decipher those sneaky Germans

Casper > Stupidru 01/30/2014 at 16:49

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Why not just let your car warm up, get a block heater to help, or park in doors?

Stupidru > Casper 01/30/2014 at 16:58

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Warming your car up is actually bad for the engine. Being that I do periodic UOAs and have sold a car due to high chromium, I'd hate to put unnecessary stress on any more of my cars' engines.

I live in a townhome with no garages, so a block heater is out of the question and still would leave a void in the solution under the "leaving from work" column

jariten1781 > Stupidru 01/30/2014 at 16:58

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Some cars (I think most hybrids) have electrical heating elements on the radiator core to heat the coolant more quickly. I think this is a better option than trying to heat the air itself.

Casper > Stupidru 01/30/2014 at 17:05

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Whelp, this is where I get off this thread. Have fun with all that.

The WB > Stupidru 01/30/2014 at 17:19

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Well, even 500W is better than none. A VW golf has about 2.7 cubic meters of passenger volume, which works out to about 3.4kg of air. At a specific heat of 1kJ J/kg*C, 500W is 1000J/s, which means every second the temperature of 1kg of air increases .5 degree C. 3.4kg of air would increase 0.15C/second, or 8.8 degrees a minute. As long as they find a way to justify the extra complexity and ensure it is going to work for the lifetime of the car, it will work.

But to make an element small enough to package you'll have to make the temperature differential much greater to reject enough heat, which means a high operating temperature element, and lots of thermal stresses. The average hair dryer lasts only a couple years. Now put it on a road bouncing all over the place. That's what you have to compete with and why I would guess few manufacturers bother to do.

So engines make a lot MORE heat, but then you have 2 gallons of water to heat up, which takes a bit more energy, (4.2kJ to increase 1kg 1°C) which means you have 7.6kg of water to heat up. If you tried that with 500W, it would take you a minute just to raise the temperature 1 degree.

nafsucof > Stupidru 01/30/2014 at 18:30

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Right but with cafe standards cars rely more and more on fast start up to reduce the in efficient open loop warm up. It makes more sense to focus on fast warm ups. My focus st has grill shutters, and a water jacket exhaust manifold to improve warm up times. Manufacturers are more and more being pushed for higher fuel economy. What about seat warmers?

Rico > Casper 01/30/2014 at 19:32

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Wait, did he just say that warming up your car upon starting was a bad thing? Have I been misled all my life into thinking this was necessary especially when it's cold out?

Casper > Rico 01/30/2014 at 19:47

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Just keep walking, this is going to turn into one of those threads where people argue with completely anecdotal evidence as though it were gospel, someone will try to cite used oil analysis as scripture to as the health of an engine, and everyone gets mad.

Stupidru > nafsucof 01/31/2014 at 09:11

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Seat warmers are all good and great, but I guess an easier solution would be a heated steering wheel. It's my hands that get cold to that point that I don't even want to touch the wheel if I don't have to.

How do you like your ST? Why did you go with an ST over a GTI?

nafsucof > Stupidru 01/31/2014 at 10:27

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I'd love a heated steering wheel, I hate wearing gloves. I've always been a ford fan I guess. In high school when my buddies bought old gtis I bought a new then 00 focus zx3. Completely changed that to an SVT, then bought an SVT. The st seemed like the next logical step for me. The gtis are really nice but they don't feel as sporty to me. I drove a new one when I was looking last spring and I liked the faster turn in of the st. Makes the whole car feel more athletic. I wanted summer tires as oe. I like the busy interior of the st more than the classier, sedated interior of the gti as well. At 6'6" I would like some of the gtis extra interior room, but my st3 st fits me like a glove with just enough room for a helmet. Also I absolutely love ford's performance (spirit) blue. I know things changed with the new gti but I don't change cars that often.

nafsucof > Stupidru 01/31/2014 at 10:31

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I used to have a spirit rt, to keep it warm in the winter I blocked part of the radiator with tyvec foam insulation. Radiator was sized right for a performance car in the summer but too big for the winter.

Stupidru > nafsucof 01/31/2014 at 10:39

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Gotcha. I only ask because I'll likely be getting one or the other as my next car. I've test driven a few VWs and liked them, but my friends who bleed blue recommended I check out an ST before jumping to any conclusions... reviews between the two are mixed, so I just wanted an opinion

nafsucof > Stupidru 01/31/2014 at 10:43

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We'll my area director ordered a new gti and they said it'd be with the first truck of 2015 gtis in June. So you've got some time. The current model is fine but the mk7 is supposed to rock. That being said, I look forward to driving my car every opportunity I get. I say go with the st but that is heavily biased!

Stupidru > nafsucof 01/31/2014 at 10:43

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It's just when the temps here get below 0 and I'm off the throttle at speed. Once the engine gets fully up to temp, then the issue is almost non-existant

Stupidru > nafsucof 01/31/2014 at 10:49

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I've got quite a bit of time- 3 years until my wife's car loan is up would be the best case scenario, but with driving a 12 y/o car you never know what's going to happen next. I drive with far too many goons on the road everyday (52 miles round trip and 4 accidents spotted this morning) to assume that everything will be hunky-dory