A/C and Fan Speed vs. Fuel Economy

:spy:Remember the A/C keeps your traction battery cool. If you look in your back seat right next to you rear passenger door you will see a vent. That is where the cool compartment air is sucked into and over the battery.

You also need to remember that you have an electronic A/C and it is not operated off a compressor attached to the engine via a belt like other cars.
So as it turns of and on you will not see any extra load placed on your engine.

 

A highly advanced climate control system like the Prius has, when set to AUTO, will take care of everything. Compressor operation, fan speed, air source (fresh vs. recirc) depending on, and associated with, cabin temp and humidity level.
Best bet is auto, set and forget. 77 deg summer, 68 winter.

Very few car owners really understand the proper relationship and operation of these A/C features, thus the development of auto mode. One thing is for sure, the Prius is most efficient when the HV battery is kept cool, if you want to fully expolit it's electric capabilities......

But that's another feature few owners really know how to maximizes. What a shame. If everyone understood how to take advantage of this car's electric and glide capabilities , it would be referred to as a 60 MPG car, instead of 47 MPG car by the media. Longer I have mine, the more I think of it as an electric car assisted by gas.

A few weeks ago someone made a post about how the compessor operation on the Prius was demand oriented (variable) and highly efficient. Someone else will point you to it.

 

i've always wondered about this myself ... in other words, is the Prius A/C control analog or digital?

 

The Prius does indeed run the compressor at different speeds depending on the A/C load.

Conventional cars have less variation, but they still have a suction throttling valve which reduces the load on the compressor when the cooling effort needed is less.

 

I dont know i try not to run it until the temps hit in the 90s..im fine in the 80s..will roll the rear window and driver side down in city traffic. Freeway i keep them up. Right now though with 109 temps. I set it on AUTO 75-78deg..it cools very well at this setting after 5 mins. No need for FULL BLAST.

thought it sucks the life out of battery at our long traffic lights..i mean major drain, sometimes i will click it off at red lights, especially coming from work were lights can be 5 mins.

 

Unlike a crappy petrol only car the 2004> Prius compressor speed is adjusted to the demands placed on it. If the system needs to cool quickly it runs fast if it is only maintaining the temperature it runs slower. The fan speed is controlled in a similar way.

A crappy petrol only car has the compressor speed determined by the engine speed and the compressor cycles on to cool then off when it is cool enough in the cabin. The TX valve allows for the varying flow rates caused by changing engine speeds. In really crappy cars the heater is used to moderate the cooling but this is stupid and something I don't think Toyota do, only American manufacturers use this method I believe.

Even though the air conditioner runs on electric energy it still uses petrol because petrol is used to generate the electricity.

 

Test it out...

Set the AC target temperature to 20 degrees below the outside air, the fan to medium and feel the temperature from the vents. (measure it if you want)

Now set the AC target for 3-5 degrees below the outside air and the fan at medium, again. Now feel the temperature from the vents. You should see the vent air "less cold" than before, more like cool"

This is due to the AC system adjusting the compressor to match the needs of the system. Less demand, less load, less fuel used. It is a great system.

Fan speed also changes fuel requirements. It takes more energy to run the fan faster. Turning on your headlights takes more energy as does turning on the cabin lights. For the most part, the energy used by the fan and lights has a minimal effect on FE compared to the compressor.

The variable load system in the Prius is far more efficient than most home AC units. Hmmmm...... now there is something to think about for saving overall energy.

Bob

 

I don't have any kind of data to back this up other than my gut feel, so if anyone has an issue please be gentle with me.

I really like the idea of varying the compressor to deliver air at a temperature depending on the need. When really cold air is needed, such as when you get home from work, it will drop the temperature quickly. When the difference is only a few degrees then just a little cool air is needed and the compressor would require very little power to take it down a few degrees. Once the desired temperature is reached it could, of course, shut down.

In combination with a variable speed fan it should make the house very comfortable. Some higher end systems use a two, or three, speed fan in an attempt to keep the house air temperature "even". To me that is the goal.

If you add radiant heat to a room of your house it operates at a temperature of maybe 100F, usually less. That is much more comfortable than using 180F and turning it off and on as needed.

Speculation
I "think" that a variable compressor combined with a variable speed fan and a smart control system (computer) should be able to produce a very efficient and very comfortable air conditioning system.

While typing this I heard my AC come on. A few seconds later I was hit with a blast of very cold air. It only ran for a few minutes and then shut off. That can't be very efficient. Right now I have a choice, determined by the thermostat, of VERY COLD air on no air.

Since I live in Florida I have a Heat Pump system. I would love to be able to take the AC unit out of the Prius and use it to cool or heat my house, scaled up, of course. In my mind is seems like it should be doable.

Maybe there are some engineering problems or economic issue I'm not aware of. Feel free folks, to tell me where I'm going wrong. Maybe it's a matter of scale? To me power is power and if the Prius AC is an efficient design for power reasons I don't see why it would change if the power came from the power grid as a source or a battery as the source.

Thanks for listening,
Bob