Utah Teens Invent Better Air Conditioner 755
Carl Youngblood writes "Two recent Utah high school graduates won the first-ever Ricoh Sustainable Development Award for inventing a better car air conditioner based on the Peltier effect. The peltier chips used in the device are more energy-efficient, last between 20 and 30 years, are solid-state, and don't harm the environment with ozone-depleting freon like today's car air conditioners."
No more freon in cars (Score:2, Informative)
freon? (Score:2, Informative)
Ahem. "Today's" cars use R134a refrigerant, not ozone-depleting freon. This has been the standard for a little less than ten years now.
Google Cache (Score:5, Informative)
Freon isn't used in new cars! (Score:4, Informative)
Newer car air conditioners use refrigerant R-134a. This is *not* an ozone destroyer, but it is still a greenhouse gas.
Peltier coolers use electricity, which is generated by the horribly inefficient internal combustion engine which produces greenhouse gasses and other toxins by the boatload.
It's all bad.
Re:Peltiers (Score:1, Informative)
This seems unlikely to me, simply from a conservation-of-energy perspective. Every first-semester Physics course teaches that even 100% efficiency is unattainable in the real world; there will always be losses due to friction or whatever.
But if you've seen an air conditioner with 400% efficiency-- then why are we working for better energy sources? This would be the magical Infinite Energy Box! Let us all dance and celebrate!
Re:Peltiers (Score:5, Informative)
RSDA Press release (Score:2, Informative)
(PDF)
The problem is the power supply from the Altenator (Score:5, Informative)
No one notices a few Kilowatts disappearing. Except ricers.
Peltier devices come from the Altenator with an output capacity of around 1Kw or less, And most of that is used by Lights, Engine management etc... And for charging the battery
There's not a lot of electricity spare to run a Peltier based cooling device.
I've built something similar myself for a car once, but it only provides piped air - and didn't have to cool the whole cabin.
A 12 amp peltier device consumes a LOT of power... About 150 watts Not all cars can spare that much. And it doesn't cool much either.
I'm sorry I can't get the article up though. I really wanted to read it
Good on them though for experimenting
GrpA.
Re:Freon isn't used in new cars! (Score:5, Informative)
Not to nitpick, but the compression cycle of regular car AC is also powered by the motor...
Plus, if your alternator can handle it, the peltier is probably much lighter, and certainly much smaller, further improving your engine efficiency.
m
this is not a sig
Re:Peltiers (Score:2, Informative)
It is entirely possible to move 4 watts of heat energy out of the car with only 1 watt of electricity energy.
Bad Link - better one (Score:5, Informative)
No ozone depletion from hfc134a either (Score:5, Informative)
The current refrigerant, hfc134a contains no chlorine (the ozone damaging part of R12) and has an ozone depletion potential of zero.
The idea of using Peltier devices is interesting, because there'd be no mechanical parts to wear out, or refrigerants to leak out, so the system should be much more reliable, but I thought Peltiers would require a huge amount of current to do as much cooling as a car A/C system delivers.
Re:What an ironic twist. (Score:2, Informative)
2) The trib moves the URL after it's no longer in the day's news
3) The trib isn't a Mormon paper. The Mormon paper is Deseret News (www.desnews.com)
But I have to admit, the poor Trib probably isn't used to getting slashdotted
Re:No more freon in cars (Score:3, Informative)
Freon != R-12
Re:Peltiers (Score:2, Informative)
AC's have a Coefficient of Performance (COP) around 4-5 (or 400%-500%)
This is similar to effiency, but obviously not the same.
COP of a cooling device is measured as:
(Energy Removed from Cold Reservoir) / (Work Done on the device)
AC's don't cool, they just move the heat, and moving the heat doesn't require a lot more energy.
If this new device has higher efficience, it will have a similarily higher COP.
Re:No more freon in cars (Score:5, Informative)
R134a A/C systems have evolved over the years. Granted, the early systems left a lot to be desired, but the output of the recent systems rival that of old R12 systems. R134a systems are very pressure-dependent, far more than R12, and must be precisely charged for maximum effectiveness.
It's hot here in Texas, at or above 100F in the summer, and both of my Chevy trucks (an '02 and an '03) blow frigid air.
Re:Freon isn't used in new cars! (Score:5, Informative)
#13120684: Normal peltiers have an efficiencies of less than 30% Modern air conditioners have an efficiencies approaching 400%.
#13120746: Modern aircon works by using matter phase change and using pump to move the fluids. It transfers more heat than the energy consumed in moving the fluids.
So while I don't have one of these, I'm really really sceptical that the CO2 and other greenhouse emissions per unit of cooling by a peltier can get anywhere near a modern air conditioner.
Re:/.ed (Score:5, Informative)
"Today, the young inventors say, U.S. drivers use about 7.9 billion gallons of fuel each year to run their air-conditioners, which draw power from the engine. By adopting their contraption - which taps into the electrical system, using fans to blow hot air through five Peltier chips and then releasing cold air - they say the country stands to save 3.9 billion gallons of fuel annually, or about $10 billion based on current gas prices."
Re:/.ed (Score:4, Informative)
Re:The problem is the power supply from the Altena (Score:3, Informative)
Not necessarily. The Toyota Prius, for example, uses an electric (144V AC) A/C compressor. Of course, it's the exception, not the rule. The Prius has a high-voltage battery system and a powerful inverter.
"A 12 amp peltier device consumes a LOT of power... About 150 watts Not all cars can spare that much. And it doesn't cool much either."
True. 150W is a lot to ask of a typical car. But a hybrid vehicle, like the Prius, can put out 5+ KW continuously without breaking a sweat.
"Good on them though for experimenting
Well, if they have developed a peltier system that rivals an electric-powered vapor-phase system in efficency, their technology could very well find its way into future hybrid vehicles.
Bad pics at wilki (Score:2, Informative)
Re:No more freon in cars (Score:2, Informative)
Re:Freon isn't used in new cars! (Score:5, Informative)
The parent poster is absolutely correct, R134a is a greenhouse gas. However, that statement should be qualified: it is only a greenhouse gas when it is released into the atmosphere. Modern technicians use recovery equipment to remove refrigerants from cooling systems (everything from your freezer to your central A/C). The refrigerant is either recycled, or disposed of properly.
As long as we are all conscious about our environment (and we all should be, lest anyone turn us in to the EPA, causing us to have to fill out the reams of paperwork!) there is no problem. Oh, and there is always that pesky thing about preserving the planet for generations to come
I, for one, am quite sick of people blowing things out of proportion when there is no real problem. Having said that, kudos to the two teens for their inventive spirit. Maybe with some refining, the invention will prove more efficient and ultimately prove commercially useful!
Re:No more freon in cars (Score:1, Informative)
Re:Peltiers (Score:3, Informative)
Efficiency is a measure of how much useful energy you get out of a system compared with what you expend in doing so (contrast that with efficiacy).
Going by this a bar heater is 100% efficient, since any energy lost in the cable, etc is radiated as heat, which is useful energy for the purpose of heating a room.
Now heat pumps usually consume electricity to move heat from one sink to another. Once the cycle is started, the useful energy that is transferred is much greater than the energy you're expending to drive the pump. Therefore you're getting more energy out than you're consuming.
By consuming I of course mean converting energy from one form to another. And no this does not violate principles of thermodynamics since we're not converting the heat into another form.
Re:No more freon in cars (Score:3, Informative)
Other companies around the world do pay for pensions and health care as well. Not by setting up their own insurance funds, but by paying higher salaries (to compensate for the higher income taxes on those salaries) and by paying sometimes quite high employer fees. The difference is really that in state-run system everybody shares the cost, while for the US carmakers they are stuck with the bill for a lot of workers all by themselves.
Re:/.ed (Score:1, Informative)
Ok, get this straight... from the article and what I know of the peltier effect (yes, I'd like a better primary source concerning the structure of the students' system given GM's naysaying), this is only a modification of an air conditioner system in the sense that it still has an internal loop for conditioned air cooled by a heat exchanger/evaporator (for lack of a better description of the peltier equipped analogue) -- the system no longer has a compressor, condenser, and coolant loop.
Instead, the peltier drives one side of the heat exchanger/evaporator to cool the conditioned air loop, and SIMULTANEOUSLY pumps the absorbed thermal energy and the peltier waste energy to the other side of the heat exchanger to dump the heat into a waste air stream.
I.E. - no coolant liquid (water, ammonia, R12, or R134a) and no inherent moving parts in the core cooling system (compressor), at the price of significantly higher electrical energy demands (the A/C system is mechanically driven and does not require a mechanical/electrical conversion step).
THIS IS NOT A CASE OF "PLUG IN THE MAGIC CHIP". It's the difference between installing a peltier CPU cooler and one of those phase changing multi hundred dollar monstrosities.
Re:New car electrical system (Score:3, Informative)
The article I had read at the time stated that the standard would be implemented in 2005. Does anyone know about this?
The only car I know of with an electric sealed compressor instead of a belt driven compressor is the 2005 Prius. It runs off the 400 volt hybrid battery, not the low voltage side of things. They didn't bother to stop at 48 volts.
Re. Whatever ... (Score:3, Informative)
The chips are semiconductor chips that when current is applied exhibit the peltier effect. One side gets warm, the other cooler. Essentially a solid state heat pump. No compressor, no liquid refrigerant needed. Instead just blow air over the device and its "cold sink" (same essentially as the expansion side air handler for a liquid refrigerant system in principle). So fewer moving parts. Especially the blasted compressor clutch assembly which in some cases makes it cheaper to replace the whole compressor with a rebuilt one than separate the clutch from it. The clutch causes the pulley to spin freely and not drive the compressor when cold is not demanded by the air temp controls, hopefully thermostats, but n ot always in cars.
in your disk drive analogy, it would be like coming up with a cheap flash drive that beat the specs for lifetime and cost to those spinning magnets you mentioned. It makes it last longer by eliminating wearing spinning parts that rub against each other roatating and moving up and down and up and down
Re:Bad Link - better one No Just Bad Science (Score:3, Informative)
Since when do they hand out awards for bad research at best or out-and-out lying. A peltier effect heat pump has a COP of around
They would have to increase the size of the alternator several times to power this a peltier effect heat pump and you would have the unavoidable inefficiencies of converting mechanical energy into electrical to boot.
Why didn't they just mention that this thing runs off of cold fusion - and maybe they could get the University of Utah to endorse it
Re:New car electrical system (Score:1, Informative)
It's Actually 42v (Score:3, Informative)
It looks like there is the Toyota Crown Royal which uses 42v and a "new SUV from GM" that will use 42v as well. Source. [66.102.7.104]
Re:Peltiers (Score:3, Informative)
If I recall my physics even somewhat correctly, the amount of energy it takes to convert a gram of water at 32F from solid to liquid state is 80 calories. That same amount of energy will then increase that same gram of water from 32F to 176F.
Re:No ozone depletion from hfc134a either (Score:5, Informative)
The car's electrical system is not suited to supplying significant amounts of power. A typical alternator tops out at about a kilowatt of power (80A or so). Due to the low voltage, ridiculously large currents are necessary.
Of course, a peltier is much less efficient than a compressor system. A compressor typically has a coefficient of performance (COP) of around 3, meaning that it removes 3 units of heat for every unit of supplied work. For peltiers, this value is around 0.4, which is a huge difference. Thus, the peltier would consume about 7x more energy to supply the same cooling capacity. This is the main reason cars don't use peltier A/Cs.
Re:Freon isn't used in new cars! (Score:2, Informative)
Heat pumps are cheaper to run because they don't _create_ or _take_ any more energy than necessary to compress and move the fluid through the system. The temperature difference between the hot and cold side, combined with phase change properties in the fluid is what makes air conditioners so efficient.
You have to power the pump, but no more.
Compare a 20,000 BTU strip heater's power consumption with a 20,000 BTU heat pump.
Simply put, you need to check your facts before you post cheeky stupid comments.
Furthermore, the people who gave this award to these kids are most definitely graduates of the New Math way of thinking, ie., no point in obeying proven facts when we can make up what we want along the way to make older proven and better technology look bad by putting kids faces on it.
The educated know what New Math was really about --- but it has been corrupted into what we see here in this article, which is just plain stupidity and laziness about checking facts.
A Peltier Junction emits more heat than it moves, and fails the test for good technology at the scales where a compressor is not too much of a burden on the rest of a design. In addition, running a current drain system like a peltier junction off of 12Vs at the size required for a car (20,000 BTU or more), would require a alternator that would be so inefficient at out of rpm conditions, that twice the amount power wasted at the peltier, at least, would need to be wasted just to keep the stupid alternator rotating against the humongo bearings and cooling fan necessary to cool the damned thing.
Geez people, read the physic manuals before you make stupid assessments.
TurboD
Re:No more freon in cars (Score:4, Informative)
I briefly discussed this topic recently [slashdot.org] when we were talking about keeping computers cool. The heat problem is becoming so critical that Intel is actually designing a Pulse Tube cooler for their microprocessors!
Re:Peltiers (Score:1, Informative)
Deseret News Article [deseretnews.com]
Re:"can't tell"? (Score:3, Informative)
Re:Peltiers (Score:3, Informative)
If you need 1kW (or 1kJ/s) to displace 10kW (10kJ/s), the COP is 10. This means the displaced energy is ten times as much as the energy used to move it.
Now, the catch with Peltier elements is that they have high COP only at very low power and small temperature difference, usually around 5-10% of the power rating and 10C temperature difference. Unless they are operated under these optimal constraints, their COP quickly drops under five. So, to produce a highly efficient TEC AC able to handle 1000W, one would need a 1kW TEC bank operated at ~80W. Considering that a TEC costs about $0.25 per rated watt, this efficient solution would cost over $250, roughly twice the price of an average room AC... and it gets worse: 1kW is barely enough to cool one square meter worth of solar heating, car and house windows have a much larger surface area total than that.
Note: a TEC's 100% rating is where the TEC barely manages to pump its own heat away from the cold side. TECs used for thermal regulation usually operate in the 30-50% range. The high-efficiency range is usually somewhere around 5% with COPs sometimes reaching over 15. For comparison, the theoretical limit for freon (and many substitutes) is around 16 but the best practical implementations only reach around 12.
Now, a typical room AC pumps from 5kW to 12kW with a temperature delta around 20C with a COP around 10. So, to beat the phase-change system's efficiency, the TEC solution would have to be beefed up by about 20X (10X the load, 2X the delta), bringing the cost around $5k, which is 20X as expensive as good classic AC.
Until they find materials that offer both better electrical conductivity and better thermal insulation to improve their overall performance (widen their sweet spot and move it up the power curve), TECs will remain a somewhat marginal cooling solution.
Re:No ozone depletion from hfc134a either (Score:3, Informative)
Pelters aren't very efficient.
Furthermore, if they were a good means of cooling things, we would use them for everything, but they don't thus why some kids build it, and corporations don't. If would be massively cheaper for them to use and have nothing but benefits. But they suck for the job, thats why they don't use them.
But people seam to be missing that part of this thing. I'm guessing all the articles are gone cause someone pointed out how bad a story it was.
Re:No more freon in cars (Score:3, Informative)
Re:No more freon in cars (Score:3, Informative)
You're right that the AC keeps you cooler, though...
Re:/.ed (Score:3, Informative)
Of course it is possible that the Peltier chips are more efficient, but considering the ones found on most electric coolers are around 60watts each I doubt it, considering you'd need 10-20 of them to keep up with the heat (the summers in CA are tough).
The real advantage would be that they are simple and wouldn't need to be connected directly to the engine. So if 1-5 broke you might not even notice.
Re:/.ed (Score:2, Informative)
Let's not let facts get in the way of a good story though.
Re:/.ed (Score:3, Informative)
Re:No more freon in cars (Score:2, Informative)
98.6 is a fairly bogus number with respect to significant digits. It is just 40C converted to Fahrenheit, but even that number is plus or minus a degree or two for normal population distribution.
It's just 37C converted to Fahrenheit. 40C is 104F.
Re:Freon isn't used in new cars! (Score:4, Informative)
The seemingly trivial change of having a light colour roof can substantially reduce air conditioning requirements (although it can also increase heating requirements).
That depends on what was done when changing the roofing materials. For a couple summers when I was in college, I had a job as commercial roofer. We would rip off the layers of tar and rocks that had built up over the years. In its place, polyurethane foam insulation would be sprayed down and then coated with a thick rubbery paint. We would normally see a big difference in how much the A/C units were running before we were even 1/2 way done. The cost savings due to using less energy all year round usually paid for the roofing in a couple years.Re:/.ed (Score:5, Informative)
Domestic fridges are the most reliable applicances in the home because they are built as a completely sealed unit.
Comment removed (Score:3, Informative)
Re:No more freon in cars (Score:2, Informative)
Re:Peltiers (Score:3, Informative)
COP is defined as HEAT_RATE_REMOVED_FROM_COLD_RESEVIOR/WORK_RATE_RE
(also written as Q(dot)[L)/W(dot)[pump]). A simple thermodynamics course in Mechanical Engineering will tell you that THE maximum efficiency an refrigderator (reverse heat-pump, such as an air conditioner) can reach is T(L)/(T(H)-T(L)) where T(L) is the absolute* scale temperature of the low heat resevoir and T(H) is the absolute scale temperature level of the high heat resevoir. This value can exceed unity (1) and generally ranges from 2-5.
Efficiency of the heat pump or refridgerator is defined as USEFUL_WORK_PRODUCED/ENERGY_REQUIRED. For a refridgerator, this is written as Q(L)/W(in). Since Q(L) for a no-loss system is defined as Q(L)==Q(H)-W(in)** Through some equation manipulations shown on page 7-24 of the referenced book(see end of post) it's shown that Q(L)/Q(H) = T(L)/T(H) and that the efficency is defined as 1-T(L)/T(H) and that this value is always less than one as by definition of T(H) > T(L).
Appendices:
Source: Thermal-Fluid Sciences: An Integrated Approach 3rd ed, Dr. Stephen R. Turns Ph.D., 2003, Published by the Pennsylvania State Universit Department of Mechanical & Nuclear Engineering.
A heat pump/refridgerator is defined as a high temp resevior and a low temp resevior sufficently large that any instantanious heat added or subtracted by the system will not significantly affect their temperature. Between these reseviors is a pump that moves heat from the low temp to the high temp by performing work on the system. It receives the energy to perform the work from outside the system. The second law of thermodynamics*** says that because the natural entropy of the system would be an equalized temperature between the reseviors, the energy required to move heat the other direction must be greater than the actual energy moved (thus the efficency can never be greater than 1).
Q(dot)[L] => Rate heat is removed from low temp resevior
Q(dot)[H} => Rate heat is added to high temp resevior
W(dot)[pump] => Rate work is used by the pump
Q(L} => Heat removed low temp resevior
Q(H) => Heat added to high temp resevior
T(L) => Absolute temperature of the low temp resevior
T(H) => Absolute temperature of the high temp resevior
W(in) => Work required by the pump
* Absolute scale can be either Kelvin, Rankine, or any other linear proprietary temperature scale where there is no negative temp and that sets its lowest temperature at the temperature at which all molecular movbement stops (absolute zero)
** There is no such thing as a no-loss engine in real life. There will always be friction, drag, and/or head loss (for turbine/pump/fan driven air conditioners) or electrical resistance (for things such as peltier coolers). So the real equations is: Q(L)==Q(H)-W(in)-W(loss) where W(loss) is the total work lost overcoming internal forces such as drag, resitances, etc..) That W(loss) makes the maximum heat removed from the low temp resevior even less, thereby reducing the efficiency.
*** Among other things, it says: "Work can be converted entirely into heat. Heat cannot be converted entirely into work."
-Ab
ps. "Lisa, in this house, we obey the laws of thermodynamics!" -Homer Simpson
Re:/.ed (Score:5, Informative)
Older cars had horribly inefficent AC systems, and larger vehicles that have the equilivant of a house sized AC system also have horribly inefficent AC systems.
One of the most efficent AC setups in current production vehicles is in the Honda Insight and Toyota Prius. using less than 72 watts of electricity to run the electric compressor and a synthetic compressor oil + newer coolant technology.
you can not get near the efficency of a phase change cooling system with peltiers.
Re:/.ed (Score:3, Informative)
A few points (Score:3, Informative)
Here are a few of the things that become possible with that kind of available power:
Re:/.ed (Score:5, Informative)
Completely false. This statement is a common urban legend, and nothing more.
Using your AC taps mechanical power from the engine. This requires you to use more gas to maintain the same speed. Opening your windows adds some wind resistance, but doesn't add the same amount of loss as engaging the AC compressor. (you should watch mythbusters sometime, its a great show!)
Re:/.ed (Score:3, Informative)
Didn't the Mythbusters prove this one false (albeit in a somewaht flawed test)? The car with the open window ran significantly longer on the same amount of fuel.
Re:No more freon in cars (Score:2, Informative)
IAASAEM (Society of Automotive Engineers Member), I don't work in the automotive field, but I'm a geek interested in cars. From their magazine: The automotive industry calculates cost to the penny, and if there was some technology that was cheaper, improved mileage, or help cut emmisions (by not working the engine as hard), they would probably use it. There are numerous technologies in the works, but changing the A/C involves changing a massive infrastructure from manufacturing to maintanence.
Mythbusters (Score:2, Informative)
Yeap, Mythbusters did prove this theory wrong. 2 SUV's were loaded up with 5 Gallons of gas and driven around the track. One had the AC on and windows rolled up, the other had the AC off and windows rolled down. If I'm not mistaken, The first test was inconclusive. However, the next test I believe proved this theory wrong. They decided to fully gas up the SUV's instead of trying to accurately measure and fill up only 5 Gallons. The test showed (and I'm not sure on these numbers) somewhere around a 5% to 10% loss of MPG on the AC SUV. While the AC SUV had to pull over, the windowed SUV kept on trucking!! So yeah, they busted that myth.
Re:/.ed (Score:4, Informative)
Change the speed to typical highway speeds (70MPH here in Michigan) and I bet the story would change quite a bit. I know that my car (a standard smallish sedan) drags quite a bit when you open the windows at highway speeds. Windows up and AC on, the throttle doesn't have to be depressed nearly as far in order to maintain higher speeds.
I'd agree that at 45MPH and below the AC is less efficient, but start getting up to faster speeds where the turbulance caused by open windows creates a *lot* of drag and I think the difference will be pretty obvious.
Re:/.ed (Score:2, Informative)
Because of the huge demand for current in modern cars (when's the last time you saw a window crank?), the automakers are trying to move to a 42V electrical system, but they're having a hard time bringing down the costs of all those gas-tight connectors, not to mention devising safe procedures for jump-starts etc.
Re:/.ed (Score:3, Informative)
Completely true. While the A/C taps power from the engine, rolling down windows taps more power from the engine to overcome drag.
I have a 2001 Chrysler Sebring sedan with the 2.7 V6 and one of those nifty trip computers. I use synthetic oil. At 75mph, I get around 31MPG. With the A/C on, that drops to 29 MPG. With the A/C off and one window down, that drops to 26 MPG. (This is with the cruise control on - so no lead foot to take into account.)
Care to back up your assertion with some facts?
Re:Freon isn't used in new cars! (Score:2, Informative)
There are some basic physics nits to pick, I'd recommend reading up on guys like Carnot, Boyle, etc. When A/C coils pass heat to the outside surroundings, they are *not* creating a net increase in overall heat, they are simply moving existing heat from one place to another. The heat you feel coming off the back of your fridge is simply the heat that was contained in the interior of the unit. Once cool, the A/C only has to work to maintain a temperature difference, pushing already existing energy back to the outside--it doesn't continually pump heat willy-nilly into the atmosphere or create it from nowhere.
If left at rest, your fridge or office building would gradually warm as the energy migrates back in through conduction and convection, until everything is at equilibrium. Using your argument, if everyone turned off their A/C at once, we would risk global cooling as all of that outside heat gets sucked back into the buildings!
The only net heat increase happening is due to mechanical and electrical inefficiencies in the motor and compression cycle. All mechanical systems do this.
Re:Mythbusters (Score:3, Informative)
The next test was to be a 55MPH run around the race track to determine which of the test vehicles would run out a full tank of fuel first. Safety officials did not allow this because of concern over tire failure (and possible subsequent vehicle rollover) and possible driver fatigue (maintaining the concentration required to handle the vehicle for the 6-8 hours required for the test would be difficult). Instead the test was run at 45MPH with 5 gallons of fuel.
The power required by the AC on full is constant regardless of the engine speed. The effect of drag on the vehicle is dependent on the speed, and the nearly 20% reduction in speed may have eliminated the slight difference seen in the first test.
Also, the fuel was removed from the vehicles using a hand pump, and it was not shown that any effort was made to clear the fuel from the in-tank pump all the way to the fuel rail in the engine. It is possible that the two vehicles did not have the same amount of fuel.
They did not show that other conditions where checked, such as identical engine parameters (the computers in modern vehicles tune themselves depending on how they are driven, if the two SUVs were driven before the test they might have had different computer parameters, resulting in different fuel consumption rates).
In short, the experiment was very rough, and had little in the way of controls. It is likely that at low speeds it is better to have the windows down, and at high speeds it is better to have them up. Also, it is unlikely that the AC would be run at MAX the entire time, so there would be fuel savings there as well.
The episode was entertaining, and did mostly answer the question "Would a big SUV use more fuel driving at 45mph with the windows open and AC off, or with windows closed and driver shivering under continious MAX AC?"
To test more accurately would have required several trials of the same vehicle at several different speeds with an accurate flow meter on the fuel lines (both delivery and return lines). Throttle position at all times would have to be carefully controlled to avoid any serious variations in computer tuning. Trials would ideally be run in two opposite directions, similar to how land speed records are controlled.
Re:/.ed (Score:4, Informative)
I have always had small 4-cylinder cars, and in them, when you turn on the A/C, it feels like the car just hit a construction barrel. It's pulling a much larger percentage of power from the engine than on those big SUVs. That large percentage of power would translate significantly to lost fuel efficiency.
The other aspect about the Mythbusters test that was messed up was that they were running them around a closed-in, banked racetrack. The handling limitations of the SUVs on that track forced them to keep their speed down to about 45mph. Those two factors--the low speed and the sheltered from the wind environment pretty much take the wind resistance factor out of the equation.
So, myth: The Mythbusters show proved something about the A/C vs. windows debate? BUSTED!
Re:/.ed (Score:4, Informative)
1- When they tested the car at 55MPH using the computer it showed that using the AC was more efficient. Jamie wrote this off as "Yeah but the computer was measuring airflow and not fuel consumption." Modern engines use O2 sensors and closed feedback to maintain stoichiometry. As a result if you use less air the engine will inject less fuel to maintain stoichiometry or the appropriate air-fuel balance.
2- When they did the objective testing they drove at 45MPH and not the 70-80 commonly done on American highways (Don't claim people don't drive this fast- get on any highway in New Jersey, New York, Mass, or Maryland where I drive). Drag increases exponentially so this can make a _huge_ difference.
3- Instead of draining the fuel tank they siphoned it out instead. They could have missed the fuel in the sump on one car and gotten it on the other. As the difference in economy was only about 15 miles (less than a gallon of gas) it could have made the difference on it's own.
4- They used two different vehicles for the test- as the difference was so small then it could simply have been a result of engine differences, tire pressure differences, air cleaner performance differences, transmission slippage, etc.
-sirket
New AC (Score:1, Informative)
Re:/.ed (Score:3, Informative)
One old and simple example is the kerosine refridgerator. In that case the compressor is a reservior of water, ammonia is the working fluid, and kerosine is used to provide flame to get some heat input to keep it all moving before the expansion nozzle.
It's a lot easier to compress the working fluid/gas, run it through a cooling system (for example the exposed copper piping with a big surface area on the back of old refridgerators), then expand it. Gasses that we can do this to easily are the ones that are used as the working fluid - with air it's a lot of hard work to get the CO2 out so you don't get solids and then compress the nitrogen down to a liquid. It's far easier to cool something else and blow the air past it than to compress and expand nitrogen.Re:No more freon in cars (Score:3, Informative)
The overall 12.5% jobless rate is clearly not a result of unionization or social programs as you imply, but from re-unification problems. I dare say that if Mexico were added to the US overnight our unemployment rate would skyrocket too.