Recirculate and Outside Air Selection

You can switch between recirculate and outside air using a screen control or a steering wheel button. I am not sure about the default selection, but it seems to be recirculate when the air conditioner is turned on.

 

What is the big difference between the two. DOes either one of them offer a certain advantage or disadvantage?

 

The recirculate mode is best when using the A/C and it is hot outside. It recirculates air that is already cooled - thus making even cooler air and reducing the energy required to cool the air. It is also better to use this when traveling past refineries, farms (manure fertilizers), dead skunks, or any other thing that may smell because it keeps the outside air from entering the vehicle.

One thing to note that I've seen in other vehicle owner's manuals, but not in the Prius's manual: it is best to leave the recirculation mode off when parking the vehicle in hot weather. By keeping this valve open to the outside air, this allows the expanding hot air inside your vehicle to exit to the air around it. It also keeps the interior cooler, even if it slightly cooler, because the interior now breathes with the outside air. You will have fewer problems with your interior plastic if you do this. I've know many people who live in hot climates that have the dash panels crack over time.

 

I think this may be something of an age-old question for all cars -- i.e., when it's good (and not good) to switch the air to "recirculate".

Unless I'm following a smoking heap or a stench-burger in slow traffic, I have my 87 Civic switch turned to "outside air" rather than "recirculate". I seem to remember something in the manual indicating that it generally was a good idea not to leave the air switched to "recirculate" as a default.

Anyone know what the major reason for this would be? The "hot air expansion when parking" reason Whitey mentions? And have things changed since 1987 in this respect -- i.e., is it less (or even more) of an issue with modern cars?

Or, for that matter, live skunks. :mrgreen:

And speaking of skunks...

 

In "auto" the system starts in recirculation mode to quickly cool the vehicle. About 70% of the air is recirculated, leaving 30% incoming fresh air. Once near the target temperature, the "auto" system reverts to "outside" air.

While a real problem, this is not the cause. Outside air is not shut off, as mentioned above. Rather, a percentage of it is when the HVAC is operating. At rest, the temperature rise due to thermal conductivity is such that short of leaving the windows open, little reduction in interior temperature is possible. The recirculation setting does nothing in this case, as air must be forced through the HVAC vent system to cause any temperature reduction benefit. This requires either the operation of the fan motor or the motion of the vehicle and the resulting positive pressure generated at the base of the windshield, the location of the HVAC outside air intake. A parked car in the sun does not breath, it bakes.

 

Outside air: when the inside air is hotter than the outside air, this setting will cool the cabin faster.

Recirculate: this setting minimizes the amount of outside dust, Diesel exhaust and other crap that gets into the cabin air.


It's up to you to choose. By default the Prius will cycle between them as needed for maximum energy efficiency, or you can command it to use either one as you like.

 

These vents are called Pressure Relief Valves. They are there to release air when closing doors/trunk. The flaps probably do not work for small increases in pressure. If there are other "vents", I do not know of them. (I worked on several vehicle launches and never heard of other "vents").

 

On most cars, the main disadvantage that comes from being in the recirculating air mode is that when it's raining the windows are far more likely to 'steam up'.

If indeed recirculation mode on this car does use 30% outside air and 70% inside air as is suggested above, I'm going to stop switching to outside air unless the windows are starting to steam up.

It makes sense to use the cooler inside air as the source for air cooling. The air conditioner doesn't have to work so hard and thus doesn't have to use quite so much of the car's power (saves gas).

Driving with this most recent tank of gas (just filled it this morning), It's the first time I've filled it after using my air conditioner virtually full time (temperatures in the high 80s and low 90s). My mileage on the display this time has consistantly shown 2 mpg less than before and actual mileage calculated is even worse).

 

Anyone know why this posting on Prius climate control settings in in the, "Other Cars" catagory?