ck123

when using climate control does it use gas?

I cant tell the difference between that and AC...

jpt

The automatic climate control is just a thermostat and some logic to decide whether and how to switch on the AC/heater/fan. Using the air conditioner (which will be on if your CC setpoint is lower than the current temp, obviously) does use some small amount of power (and hence cause your car to consume slightly more fuel). The fan uses an even smaller (completely negligible) amount of power. The heater uses none at all -- it just redirects waste heat from your engine to the cabin instead of the world outside.

BulldogHockey

Does the A/C will place more drag on the driveline through the alternator, or does it have it's own separate power generator? Do different fan speeds draw different demands of A/C current? Does the climate control just cycle the A/C on and off, or does it draw less current as the cabin temperature is near the setpoint?

Always wondered those things. I don't think it makes a huge difference on mileage, but probably some.

jpt

The air conditioner compressor is belt-driven, not electric; it places a load directly on the crankshaft when active and clutch disengages to remove the load when it is not. I think (but am not sure) that our A/C does not have multiple speeds -- the compressor is either on or off. To modulate the temperature of the air blowing out the vents more finely, the heater (which essentially blows the air over an auxiliary radiator connected to your main engine cooling system) must be activated.

The actual cabin fans are electric (this is why you can use them, but not the heater or A/C, with the engine off) but do so little work as to be completely negligible.

BulldogHockey

All right good to know, I had always assumed the A/C was electrically driven. So there is no savings to fuel consumption then to have it set at 77 F where it is mixed with warm air, and 67 F where it is full A/C. That's assuming the A/C is on/off only.

That seems to be the case with other cars with dumb controls, the graduated dial that goes from "blue" to "red".

jpt

On cars without automatic climate control, the dial you're talking about affects the heater: the air conditioner is still on or off, but you can blow the air-conditioned air over the car heater to modulate the temperature at which air comes out of the vents. This is the same thing our climate control does, although it may also run the AC compressor at a lower duty cycle (i.e. turn it off for a brief period then turn it back on to maintain cabin temperature and humidity) -- I'm not sure.

jlukja

Im pretty sure the temperature setpoint does make a difference in fuel economy. Lets say its 85 outside. If you set it at 67 the A/C compressor will kick on more often and stay on longer than if you had it set at 77. My

curls

That's the way I see it, too.

I tend to set it at 22 or 23*C on average in the summer, but when the temps get to like 34*C outside, I tend to set the climate control even higher -- say 24 or 25*C. Still uses AC, and keeps me cool enough, but doesn't use the A/C ALLLLL the time (which I find to be too much anyhow, if I'm wearing shorts and sandals...)

ck123

the ac light should come on when you set it too low but it doenst

jpt

What I'm not sure about is if the CC computer decides to leave the compressor on for dehumidification purposes and uses the heater to modulate the temperature, or if it just shuts the compressor off completely when you are at or near target temp. I could believe either way.

jlukja

Maybe you have A/C turned off. I turn off the A/C frequently and rely on the ventilated outside air to keep the cabin at a certain temperature. If the temeprature setpoint is lower than the outside air then the fan clicks up a notch or two but the A/C doesn't come on. Remember that if you hit "auto" then everything is automatically set. Once you make adjustments after you hit "auto" then you are effectively removing those adjustments from being controlled automatically. At least that's the way it works on my non-navi 04 TSX.

STEELTOWN

Just remember, nothing is for free. People use the term negligible like it does not matter, but it does because all those pennies make a dollar. Small items that add up to burn extra gas:
1) Sunroof up or open
2) Full tank of gas (extra weight)
3) Headlights, foglights
4) Fans, seat heaters, Cd player on
5) Windows down
6) Trunk with items

There are a few so-called negigible items that can add up with other negligible items to impact your mileage. Also, pennies everyday for a few years can be significant, so you gotta watch that term negligible, its very overused and misunderstood. A drip in your sink may not cost you much by the end of the week, but take a look over a year or two. Just drive and enjoy, we will all be riding mopeds at the rate these prices are going...

jpt

These six things have energy costs that are orders of magnitude apart. An open sunroof at highway speed costs MUCH more than the weight penalty of 100lbs of gasoline in a full tank (weight affects your car only when accelerating, and the energy cost is reclaimed when coasting to a stop, and let's not forget that not filling up your gas tank means more wasteful trips to the petrol station), which costs MUCH more than the 80W cost of having two headlights on. Of the items you listed only sunroof and windows are going to be more significant than, for instance, taking one second longer to get to 60 each time. Certainly none of the items you list are worth giving up for the minuscule fuel savings you get out of them.

You need to recalibrate your sense of scale. To wit, a drip in my sink that leaks 10ml of water a minute would waste 2,778 gallons in two years, costing me a total of twelve dollars -- not enough to cover the cost of fixing the sink. I'd be far more likely to fix it because the drip is annoying.

Um, no. At $3.40 a gallon, gas is cheap. Driving my TSX to work costs me about two bucks a day in fuel, and I get way more value than that out of it.

Penny-pinching can be more dangerous than overspending, because people who overspend at least usually know they have a problem, whereas compulsive misers will happily make sacrifices that make absolutely no sense while proclaiming their superior rationality.

STL

I'm almost certain that in full AUTO mode the "A/C" compressor is always on (for dehumidification purposes) -- at least that's how my car seems to work. When it's cool enough outside, I'll select AUTO then turn the A/C OFF; that way it seems to still try to control the climate with the compressor off.

DLTSX6MT

Probably a dumb question, because I'm sure the answer is "no", but does the climate system monitor cabin humidity? Otherwise, how does it know when to use the A/C to dehumidify when the temp is below the setpoint but it's humid?

It just could be, like STL said, that the A/C is ALWAYS running (or at least, always cycling) when in AUTO mode.

STEELTOWN

You are speaking without facts, please provide the actual gas usage provided by the items listed, seat of your pants and guessing don't cut it

psteng19

Every accessory uses some gas to an extent.

If it uses electricity, it requires the alternator, which is cranked by the engine which is powered by gas.

youngTL

That's not even necessary. Sure, more drain on the alternator uses more gas, but just accelerate a BIT slower and you've MORE than made it up! Personally, I would rather be comfortable and not have my windows fog up. My CC is on auto most of the time in my Accord except when I have the windows down or the sunroof open (that's when I press A/C off). To put it in perspective, I can go ~90-100 miles on 1/4 tank in the city. I have the 6MT. It's because I drive gently but not like a grandma. Smooth driving keeps fuel costs down.

Power1Pete

Yes, A/C is always on when you press the AUTO or the Defrost button.

Ellas9

A question was asked during the thread that has not been answered yet.

Does the AC work harder when the climate control is set to different temperatures/settings and given various outdoor temperatures.

I have read in some owners manuals for other cars that if you re-circulate the indoor cabin air that the AC compressor works less hard because the air being recirculated is cooler as opposed to taking in hot outside air and having to cool that on a hot day. My guess is that your better off (for fuel efficiency and putting less strain on the system) running the AC for 5 or 6 minutes at 'Lo' temperature with the fan at a fairly high speed with recirculation on and then after the 5 or 6 minutes, turn the AC off and lower the fan speed and wait until it gets somewhat uncomfortable before turning the AC back on.

vidgamer

With my previous car, it often was too cool, so to save energy, I often turned off the A/C rather than try to modulate it by adding heat. But then I'd just have to turn it back on in a few minutes, and that was a hassle. SO, when I got the TSX, I thought, great! Let it turn the A/C on and off. But, like many of you have asked, is that how it works or does it just mix in heat too?

Also, when you accellerate, is it smart enough to disengage the A/C? (Put that DBW to work...)

SoCaliTrojan

I would like to see your facts as well, Mr. Scrooge =)

Heck, add #7 to your list...driver's weight. Let's all eat bread and water to squeeze every pound out of ourselves ;-)

#8, driver's clothes...don't weight long pants and shoes when you can wear shorts and sandals ;-)

#9, passengers...charge them money to ride with you, otherwise they're on their own.

#10, baby seat...bah, let them use a regular seat belt ;-)

#11, stereo...all of the speakers, tweeters, and headunit takes power...just turn it all off and have a conversation with a passenger or yourself.

TSX owners spent more to enjoy their car, not to be stingy. We buy 91 octane for our cars. Sure, it gives us better fuel efficiency and performance, but you could probably get away with even 89 octane and granny driving.

#12, get an accord hybrid

Yes, small things can add up. An adult book costs 0.25 cents a day when late at a library. Return 1 book late, and you only pay a quarter. If you checked out 20 books a day (yes, there are many who do), then turning it those books late costs $5.00.

One question to ask is how much it costs you for each item on the list. Another might be if it's possible to "gain" back some of the loss (think about coasting, injector's off, car is in gear...).

In the end, everything leads to entropy...

STL

That's one thing I was looking forward to also (with the climate control in the TSX), but sadly I don't think it works that way.

Still Water

The Question: Does climate control use gas?

The Answer: Yes

The Reason: Belt drive + pulley + engaged A/C compressor clutch = Drag

What to know how it all works: Think heat lost = Heat gained, then introduce airflow.

It's simpler than you think. How does a CC system work? Think thermostat.





My favorite A/C setting, once I cool off the interior, is to set the air vent flow for arrow floor & arrow front vent. No auto setting other than me (you can call me Otto) adjusting the temp and fan speed. Works for me.

Still Water

Add to the above @ "= Yes*"



*In temp range that needs to use the A/C to cool the car. Also A/C is used to defrost (dehumidify) the interior (Known in the trades as your car taking a piss when you park it) and the windows while using the heater core to heat the air.


-Sorry 'bout that.

STL

Actually, I think if your in AUTO mode the A/C compressor is on all the time.

Ken1997TL

The real question is.. does the compressor work with various power levels? Or is it simply on/off?

Still Water

I've yet to get the definitive answer to that question. One way to tell is to have the CC on at a relative high temp setting, lift the hood and check to see if the A/C compressor clutch is engaged. Then change the temp settings and check again. Not long after I got my TSX I got in the habit of turning off the A/C not for better mileage but rather better engine response. Consequently I haven't revisited this question because in my part of CA it's usually either cold, mild or hot. When it's hot turn on the A/C.

jpt

To get a semi-definitive answer to the question of whether the compressor is off when temp is set to high, I set my CC temp to "HI" on the drive into work this morning (the things I do for science ). Water still dripped from the front of the car, implying that the air conditioner was on along with the heater.

I think we can therefore conclusively state that having the climate control set to auto uses the same amount of fuel regardless of the temperature setpoint.

In response to Ellas9's question about whether the compressor does less work when the interior air is cooler, the answer is no. The air compressor does the same amount of work regardless of the interior and exterior air temperature. However, cooling performance is decreased when the interior air is cooler, and increased when the exterior air is cooler (this should not really be a surprise).

Still Water

That's way I use the CC between my ears and hit the A/C on/off button.

jpt

The 5hp isn't worth it for me, I leave it on auto and my cabin is always comfy. Except right when I get in and the black leather melts my skin off... I really need some tint

STEELTOWN

Hardly Mister Scrooge. My original post said there are plenty of things that use gas and just enjoy your car. How some posters decided I wanted anything different is beyond me. Quotes like this show how many people have missed the point (and basic physics classes):


Originally Posted by jpt
These six things have energy costs that are orders of magnitude apart. An open sunroof at highway speed costs MUCH more than the weight penalty of 100lbs of gasoline in a full tank (weight affects your car only when accelerating, and the energy cost is reclaimed when coasting to a stop, and let's not forget that not filling up your gas tank means more wasteful trips to the petrol station), which costs MUCH more than the 80W cost of having two headlights on. Of the items you listed only sunroof and windows are going to be more significant than, for instance, taking one second longer to get to 60 each time. Certainly none of the items you list are worth giving up for the minuscule fuel savings you get out of them.

Weight affects your mileage ALL THE TIME, not just when accelerating. Its called Rolling Friction which takes into account the weight of the car F(r)=u(r)*W, where W is the weight of the car. This rolling friction in addition to the force of air resistance F(air)=1/2CApv^2 must be overcome while cruising, not to mention heating/cooling, pumps, etc and many other inherent losses in a car. Unless you live in Texas, you will encounter hills which will really magnify the weight penalty while going up the hill. You WILL NOT gain this loss energy back by coasting into a stop. Work=FD. That means the gas you burn driving to sell your unread physics books to the book store over twenty miles will not be magically given back to you while coasting to a stop in 50 ft. Accelerating is yet another formula that also must be accounted for.

So for someone to dismiss the weight of a full tank and loaded trunk as negligible without knowing the full impact just does not make sense. Depending on how fast you are going the impact of weight in your car can be greater than air resistance (sunroof up, windows down). Notice the squared function in the F(air) equation, that is why the higher your velocity the lower your gas mileage. Rolling resistance is independent of velocity, that is why one can be greater than the other at a given speed. Lower speeds, weight plays a greater roll, higher speeds air resistance takes over.

As I said before, you should not use the term negligible unless you know what the answer is. Class has been dismissed. Sorry for the thread jack, many people read some of these posts and accept them as truth without question.

jpt

The coefficient of rolling resistance of typical tyres on asphalt is about .03. The rolling resistance added by 100 lbs is therefore 3 lbf = 0.5 hp at 60mph. That's not much (much less, like I said, than the drag created by opening a sunroof, and more than the 80W of turning on your headlights) and, of course, in a 3500lb car+driver it is only 1/35 of the total rolling resistance. By far more power (about ten times as much) is used to accelerate that 100lbs to 60, and that kinetic energy is then recovered if you coast to a stop.

... which are not mass-dependent.

Kinetic energy put into the car must be lost to friction with either the tires, air, or engine internals. These energy-sinks are roughly the same regardless of the car's weight (only rolling resistance, which accounts for about a third of energy consumption, is dependent at all on weight), so in a trip of a given distance I'm going to spend about the same total amount of energy. If I do not use the brakes when coming to a stop (which implies it would probably take more than fifty feet...) then the kinetic energy put into that physics book I'm lending you so you can brush up on the basics would keep my car rolling longer, so I don't have to use gas to cover the last (or first, depending on your point of view) few feet to the stop sign. Similarly the energy I have to put into the car to go up a hill is recovered when I don't have to burn gas to go down the hill.

That's why I said "at highway speed." But at low speed, fuel consumption is not dominated by rolling resistance, but rather the cost of idling the engine. That's why cars are less fuel efficient at low speed (the optimum, for our car, is around 90kph as tested by sauceman).

Well, now I told you what the answer is (apparently you didn't know either, which must be why you haven't posted a single number in your off-target rants), and I still say 100lbs of added weight makes a negligible difference to fuel economy, and is certainly not worth making any sacrifices to avoid.

jlukja

The engineers are strong in this thread.

jpt

I don't know why I even bother getting into arguments like these. I need to remember the flame war mantra. ("Flame wars are like the special olympics, even if you win...")

jlukja

That wasn't a criticism. I'm an EE. But you're right about arguing over the internet...

youngTL

I don't believe that you can model air resistance by a simple equation like that. The equations of fluid dynamics are actually a set of coupled partial differential equations and are extremely complex to solve. The relevant equations are called the Navier-Stokes equations.

And secondly, at least with the Accord V6, I've noticed that the A/C off doesn't do all that much. I made a same-day trip to Calgary (297.1km from the Esso in St. Albert to the first gas station I saw in Calgary) there and back. The ambient temperature in the later morning was 11°C, so I drove with the A/C off, CC set to 22°C and used 19.4L of gas (filling up at a Petro Canada in Calgary), netting me 6.53L/100km. I had reset my trip meter and filled up at the Esso as I was leaving (resetting it at the gas station). Highway 2 is uninterrupted, so there's not too many traffic lights to screw things up except near the gas stations (and that's negligable). I was traveling in 6th gear on cruise control at exactly (as close as I could get to) 100km/h in the slow lane since the speed limit is 110 and going slower saves gas.

On the way back, since I'd driven around the city, I stopped at the Petro Canada again, reset my trip meter and filled up to full. Then, it was 24°C outside, so I used the climate control on AUTO set at 22°C. I traveled in 6th gear at 100km/h and then filled up at the Esso again when I got back. I somehow traveled an extra 0.2km, I don't know how. So I got 7.23L/100km according to my calculations since the pump told me I used 21.5L of gas.

So there we have it. I think the extra $2 I spent on a 3 hour trip was freakin worth it for my comfort. I could have had the A/C off and allegedly saved $2.02, but so what? And don't forget, the A/C needs to go on sometimes to lubricate the parts.

STEELTOWN

No, I never argue, I try to enlighten. Having a friendly conversation with AcuraZines finest help get through a long day. So, my last attempt to enlighten my electrical engineer friend (hopefully he has paid more attention in Circuits than Physics):

The original point of my post was the term negligible can not be used unless you know the answer. 100 lbs seems to be an easy number to remember, so lets work with that. My friend has given out values for instaneous power, but you have not included time, which plays a role. One gallon of gas has roughly 35e6 Joules of energy. That 358 J/s (converted from HP) over the course of an hour will use 1.3e6 J of energy. My commute at an hour cruising (make it easy) each way to work/5 times a week means I will burn an extra gallon of gas every 27.2 hours with that extra weight. That is not counting accelerating that weight (more realistic, which burns more gas). So working 50 weeks out of the year, I will spend (@$3.10 gallon gas) an extra $57.00. That is low ball because we didn't work in accerlerating that weight over the course of my commute/year. So I guess there are a few people here who have better things to do with $57.00 than to toss it out the window, we can't all be money making Electrical Engineers.

Unless you have invented a new science, the energy loss carrying 100 lbs over 10 miles and accelerating it will not be gained back coasting into any stop light or sign at even 1000 feet. I don't recall ever stating which losses were the greatest, I have only made a point of going over losses you say are negligible. So how about taking a poll and find out if people think $57.00 is a neglible amount that can be saved relatively easy, by unloading the trunk. I hardly think that is a sacrifice. I have not talked about the extra gas in the tank because that becomes an integral function, that liquid weight is being reduced over a given distance. That works in everyone's favor. But it all adds up.
Unload the trunk, drive with half a tank of gas instead of filling it up each time (unless you live in the Amazon and don't pass eight gas stations during your commute, you shouldn't have to go out of your way to find a Petrol station).

So I am finished with this post, your P.Diddy money is obviously greater than mine, so I am headed out to unload my trunk...

youngTL

Unloading your trunk is a good idea. Might as well if you have heavy stuff in there for no reason.

I think he has a point though about the obese part. Someone who's obese should lose weight to get better fuel economy. I mean look at Texas...about 2/3 of people there are overweight or obese IIRC. Imagine how much gas North Americans would save as a total if those of us that were fat lost weight. And they'd save money by not eating at fast food (which is a hell of a lot more than $57 a year if you eat it even once a week).

sauceman

You also need to take in consideration that increased weight will increase the pressure a tire applies on the pavement, and the rolling resistance will increase accordingly.