AC/fan setting vs. mpg

How much effect does recirculation vs. outside air have in cold weather on ICE turning on? Am I correct in assuming that using the outside air option (I'm not sure what it's called in English) will cool the engine more when ICE is off, thus resulting in more ICE usage to actually heat the engine?

 

That makes sense. You might have to resort to outside air, though, if window fogging becomes a problem.

 

This.

Recirculation does better at heating and not using the ICE as often. However, it traps moisture in the car.

You can help combat this by keeping your windows clean on the inside. I use about 1/3 cup of white vinegar, a shot of liquid dish detergent and 2 cups of hot water. Apply with one hand cloth. Remove with a second dry cloth. Oil and such on the glass is the primary thing that makes it fog up so fast. Clean glass clears and stays clear easier.

 

One of those little windshield paddle brushes makes cleaning the windshield a lot easier.

 

The amount of energy the a/c can transfer isn't constant. The greater the temperature difference it must operate against, the higher the head pressure the compressor has to operate against and the lower the cooling capacity. Maximum cooling capacity at 120F outdoors will be much less than at 75F outdoors.

If indoor fan speed is increased the air flow across the evaporator coil increases and the temperature of the air leaving the coil rises which reduces the temperature difference the refrigerant circuit sees and the amount of cooling available increases. The supply air won't feel as cold but there will be more of it.

I often set air flow at less than maximum or at less than the auto control would choose but it is to get quieter operation even though there is some loss of cooling capacity. If the interior is really hot I live with the noise to let the car cool down as quickly as possible.

 

Wow! You guys are extreme. Not that that's bad. I just go by the rule that if I'm uncomfortable with the heat I use the a/c, gas mileage be damned! haha! Keep rollin'!!

 

I agree - I'm not determined enough for that either. I'm in my car an hour and half a day, I'd rather be comfortable and get 50 than sweat for 55-60

 

The biggest difference comes from using re-circulation.

Keeping higher temperature setting in auto+recirculation mode gives best MPG.

 

Well that's pretty much how I use it, so that's good! It's only been 90-95 here in Texas lately and it's almost too cold for me at anything less than 76...the Prius has a good a/c I feel like

 

I guess hot climes are a doubly-whammy for hybrids, more AC loading, and tough on the batteries.

 

I know having a light interior and window tint goes a long way around here

 

Summer was pretty hot (and very dry) up here, at least for us. One issue that bothered me was parking the car after an extended drive, in an uninsulated, very hot garage, that it might be slow-cooking the hybrid battery.

If I just shut all the garage doors, then went back in there an hour later: it was like slow-death, super-hot from the garage itself coupled with the residual engine heat. I took to popping/raising the hood, leaving the garage windows open, and placing a fan in one of them, in an attempt to exhaust some of the hot air.

That's one time the hybrid battery temp really goes through the roof, sitting on a hot day after a fully warmed up drive. The hybrid battery fan does not run on after the car is shut down, I'd entertain some sorta mod that could move air over the battery, post shutdown.

 

Good point. Not a "mod," but you can fake it to the extent you have patience, by sitting a minute in READY after stopping. Battery current is so low then that I assume it would cool some, if the fan is running. However, if the car's parked in full sun on a hot day with air conditioning off, the interior is going to get so hot so fast the driver would soon want out, and air entering the fan would soon be too hot to help much.

 

You bring up a good point, but do you really think that's a serious problem? Don't you think we'd hear about a battery problem here in the desert southwest where daytime temps in Phoenix are well above 110 in the shade for much of the summer?

 

Well southern states is where leaf batteries started losing charge capacity; yeah, I think it's a factor.

 

Not arguing, but that's an all-electric vehicle. I have no doubt the battery temp might rise when shut off in a warm garage, I'm sure the ICE does, but I'm not educated enough to know how big of a problem it is. Of course, blowing that warm air over the battery is probably not a solution. I know you open the hood to disburse some of the hot air under the hood, it's just that when it's 115+ outside, I'm not sure how much good that would really do me. Also, the garage is probably cooler than the parking lot at the mall.

 

Parking lots are inherently bad: giant expanses of black tar, very efficient solar collectors.

 

Raising the hood on the car only allowed the heat to escape into the garage more rapidly, which in turn raised the garage temperature. The hybrid battery is located towards the rear of the car, so engine temperatures have no effect on battery temperature.

I wouldn't worry about hot garages damaging the battery; NiMh can be stored at 130 F, and Li-ion are rated to 140 F.

 

It depends on if the car has excess heat that it's loosing through the radiator, or if the car is failing to maintain proper operating temperatures. I'd imagine that winter in the Netherlands is a struggle for the Prius to maintain operating temperature, and setting the fan mode to recirculate the air is more efficient. Even more efficient than that would be to grill block. I wouldn't recommend doing a grill block unless you have a gauge to monitor the coolant temperatures. The car isn't likely to overheat since it has 2 cooling fans, but you don't want the fans to run excessively since this will reduce fuel economy.