Half a croissant, on a plate, with a sign in front of it saying '50c'
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Low-energy Automobile HVAC

Heat, cool, and ventilate the car, as if it were a house
(+3, -3)
  [vote for,

This idea is to incorporate as many of the techniques for efficiently heating, cooling, and ventilating a home, into heating, cooling, and ventilating a car.

First, as other HB'ers have already suggested, use a loop of heated/cooled water to heat or cool the seats. And the floors, and the roof.

Second, better insulation. I know cars already have some insulation, but surely it could be better -- for example, silicon aerogel is a superb insulator, and has a very low density. Sure, it's a bit pricey, but the combination of low weight and high R-value should result in a good return on investment. Also, we would want to make the cabin as close to airtight as possible, to minimize leakage of conditioned air out of the vehicle.

Third, the cabin air ventilation system should be either a heat recovery ventilator or an energy recovery ventilator.

Fourth, a dehumidifier. This would suck excess humidity out of air that's been partially conditioned by the HRV or ERV system. To make it energy efficient, it would use an adsorption or absorption system (powered by the engine's waste heat), not a vapor compression system (powered mechanically).

Fifth, a humidifier. Of course, since refilling a humidifier with water is a hassle, our humidifier would actually be the dehumidifier, operating in slightly backwards manner -- specifically, sucking water out of the engine's exhaust, and transferring it to the cabin air. If done right, only the water will be moved, not the pollutants.

Sixth, built in, fully retracting curtains. The curtains on the side windows could go up and down the same way the windows do. The curtains for the front and rear windshield would need a different mechanism, but it wouldn't be impossible. And there'd need to be a mechanism to automatically open the curtains when the car is in drive. Curtains can provide thermal insulation, acoustical insulation, and privacy -- a must have for the adventurous teenager ;)

Seventh, make the windows dichroic mirrors, reflecting infrared and ultraviolet light, while passing visible light.

Either, make the rear windshield, and perhaps the front as well, into a semi double paned window. The outer pane would be regular glass, the inner pane would be a thin film of plastic, stretched taught. The air gap between the film and the glass would have low enough pressure air, that the film would be curved to the same shape as the glass.

For those who are worried that chilled seats, floor, and roof will result in condensation on those surfaces (and water damage), well, that's what the dehumidifier is for. If the dew point of the air is lowered sufficiently beforehand, condensation won't happen.

goldbb, Oct 22 2009


       Heavy, heavy, heavy and not needed.   

       The biggest problem with modern cars is that they are far too heavy. While you might save a few Joules here and there with better insulation etc, the engine needs to drag all this extra crap around all the time, using more energy to do so.   

       Do we really expect a machine (whose purpose is to move us and our stuff from one place to another) to provide a perfect environment for the comfort of the most discerning occupants?   

       Of course, there will always be a market for luxury cars, but the much bigger market is for functional cars that do the job and provide a reasonable degree of comfort.
Twizz, Oct 23 2009

       I'll bun it only if the driver's seat can spin round, recline, and have access to a plasma TV and mini-fridge. The rear seat should be long enough for a 2m bloke and lady friend to sleep on. And throw a bog in for good measure.   

       Oh wait, this is a motorcoach.
bdag, Oct 23 2009

       Wow, so much to cover. First many of the ideas are bad and/or lethal such as the air tight cabin and recovering waste water from the exhaust to humidify the air in the cabin. I realize you said //If done right, only the water will be moved, not the pollutants.//, but you have to realize that in the real world some things go wrong and when this goes wrong it will poison everyone in the car. If you don't believe me ask anyone who ever had an old VW that used exhaust heat for cabin heat.   

       Next, some of the ideas are dumb, such as heating the roof and floor, which just provides an easy pathway for heat loss or gain.   

       Then there are some good, but mostly baked ideas, such as the dehumidifier based on absorption, the curtains and the idea of insulating the cabin. The later seems excessive and unnecessary but as cars get more efficient, engines get smaller and waste heat gets scarce, this is a necessity in certain climates. I used to drive to Syracuse, NY in the winter in an old 77 Scirocco and several times the motor temp dropped into warm up mode just keeping the windows defrosted in the bitter cold at highway speeds. I'm sure several issues occur in extremely hot climates.   

       All in all I don't see any good unique idea in here, so (-).
MisterQED, Oct 23 2009

       The only part of that I support is the curtains, and that's already pretty much baked. The rest would add weight, which lowers fuel economy.   

       Can't a company come up with an aftermarket kit to power part of your a/c with a solar panel, like the prius?
DIYMatt, Oct 23 2009

       bdag, nothing prevents the driver's seat from spinning around, so long as you don't mind that it won't be able to make a 360 degree turn -- the electrical wires that power the reclining function, and the tubes for the hydronics, just won't be able to accommodate that. For that matter, you'll also need to temporarily adjust the driver's seat to full upright, or even leaning forward, while turning it, to get the back of the seat past the door.   

       As for making the rear seat wide enough to lay on, it would be much easier to make the car longer, and design the back of the rear seat to fold flat, making it into part of a bed.
goldbb, Oct 25 2009

       MisterQED, Why is making the cabin airtight (and adding a heat recovery ventilator) a bad idea? If we can completely control where air enters/leaves the cabin, then we can ensure that all the air that enters is appropriately heated or cooled, and humidified or dehumidified.   

       As an example of a cabin that *isn't* airtight, I cite my own car -- if I open the sun roof while on the highway, a draft comes in through the door, somewhere in the vicinity of the door handle.   

       In regard to using exhaust air as a source of water, consider that the US army was or is developing a system to produce drinking water out of a humvee's exhaust, so it shouldn't be impossible.   

       But if it's really that bad an idea... well, there's no reason not to use our dehumidifier to suck water out of atmospheric air, and move it into the cabin.   

       I'll admit, that it's not especially useful to heat the roof, or to cool the floor.   

       However, doing the opposite (heating the floor, cooling the roof) isn't a dumb idea, provided there's a reasonable amount of insulation inside the floor (below the heating tubes) and inside the roof (above the cooling tubes).   

       The main point of adding insulation isn't to contain heat in winter, but to keep heat out in summer. Assuming a compression based air conditioner, there's a load of about 5-6 horsepower. If the car were insulated, this could be vastly reduced.   

       Obviously, if we could use an absorption based air conditioner, then air conditioning would be "free" because it' would powered by the engine's waste heat, not the engine's mechanical power, but even then, I think that adding insulation would improve comfort.   

       And for an electric car, insulation becomes very important, since batteries only produce a small amount of waste heat.
goldbb, Oct 25 2009

       I've been thinking about how to provide humidification for the car (in winter, when the air is typically uncomfortably arid).   

       If the cabin is fully airtight, with all of the air circulation coming from the energy recovery ventilator (ERV), and the car contains a vapor barrier, then the *only* way for moisture to be lost is through the ERV.   

       If the ERV is sufficiently efficient, then moisture added to the air by the passengers (breathing, sweating) might be enough to maintain humidity at comfortable levels.   

       An artificial humidifier might be completely unnecessary. And if it is necessary... well, the best place to suck water from (other than perhaps the exhaust), will be the stale air which has passed out of the ERV.
goldbb, Oct 26 2009


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