Is the near zero A/C power consumption trick real?

[padamson1]

I have read about the neat trick to lower A/C power consumption to nearly zero:

1. Turn on Climate Control.
2. Turn on A/C, then adjust the temp down to the minimum (60deg).
3. Adjust the fan to turn off Auto, use fan to regulate temperature.

If one has the Energy consumption display on you will see the Climate Control power level start around 1.5kW then drop to near zero within a few minutes. This is much lower than the reported value for Auto at a few degrees less than the outdoor temperature. I can't believe the power consumption with Auto active is that different than this manual technique (unless Auto does something totally stupid like turn the heater on). So I am thinking this is just a bug in the power monitoring SW.

For instance if the Energy Consumption screen was just the reflection of different reported sub-system power values and not total system power minus certain sub-systems, there could be 'invisible' power losses that aren't reported on the Energy display.

Can someone familiar with the CAN BUS protocol confirm that there is a Total System drain value as well as Engine, Climate control values? With just these three numbers the Energy display can be accurate (Other = Total - (Engine + Climate)), but if the protocol only had Engine, Climate Control, and other sub-system values then there is possibility for error in the display from ghost power losses.

 

[mkjayakumar]

Even I believe that the 'Energy Consumption' reading going down to near zero is bogus. Obviously the car is getting cooled, some power much greater than zero is getting consumed to keep the AC unit running.

The real measure is in actually driving with and without AC on and see the range difference, or directly get data from system interfaces.

 

[LEAFfan]

Yes, it works! Today, the energy meter went to a sliver in about a minute. When you use Auto and have the temp set above 60, the heater comes on to keep the set temperature and that's why it makes it use more energy.

 

[EVDRIVER]

This is all a result of improper testing and lack of understanding of how the LEAF systems actually work. This has already been proven using accurate methods with test equipment. If you use the fan with the AC button off you will not have AC and there is no way to disable the heat or ac while on without wasting much time playing with the temp setting. When the AC compressor cycles it will not use power for a while and the same for the heat but there is no trick and unless you have a CC mod you can't get full control of the system without constant monitoring and adjustment.

 

[smkettner]

I thought member ingineer confirmed the compressor and heater element do not come on at the same time.
I find power consumption drops quickly and stays low once the car is cooled.

 

[padamson1]

This is all a result of improper testing and lack of understanding of how the LEAF systems actually work. This has already been proven using accurate methods with test equipment. If you use the fan with the AC button off you will not have AC and there is no way to disable the heat or ac while on without wasting much time playing with the temp setting. When the AC compressor cycles it will not use power for a while and the same for the heat but there is no trick and unless you have a CC mod you can't get full control of the system without constant monitoring and adjustment.

Perhaps you misread the steps to the trick or I am misinterpreting what you are saying. The A/C is continuously active and cooling the car (I can feel it), temperature is simply controlled by adjusting the fan speed (not the temperature). Yesterday it was 80deg outside, the car was hot when I started and cooled quickly. However the Energy monitor showed little or no power consumption for Climate Control after only a minute or two (well before the car cooled) and never increased to more than a sliver.

This is the cause for my skepticism, the A/C compressor can't be cooling the air for free, so I am thinking there is simply a bug in the energy display SW. Normally I would confirm this with some sort of road test, but the routes that I drive do not have consistent topology and/or speed for me to perform a controlled test over a reasonable distance. Perhaps somebody in the flatlands somewhere (e.g. Arizona) can confirm there really is zero power cost, but the non A/C portion of the test might be too cruel to endure...

 

[GaslessInSeattle]

in any case, the Climate control uses very little energy to cool, no mater how you have it set. the most efficient cooling I've seen. the resistive heater is a whole other matter.

 

[EVDRIVER]

This is all a result of improper testing and lack of understanding of how the LEAF systems actually work. This has already been proven using accurate methods with test equipment. If you use the fan with the AC button off you will not have AC and there is no way to disable the heat or ac while on without wasting much time playing with the temp setting. When the AC compressor cycles it will not use power for a while and the same for the heat but there is no trick and unless you have a CC mod you can't get full control of the system without constant monitoring and adjustment.

Perhaps you misread the steps to the trick or I am misinterpreting what you are saying. The A/C is continuously active and cooling the car (I can feel it), temperature is simply controlled by adjusting the fan speed (not the temperature). Yesterday it was 80deg outside, the car was hot when I started and cooled quickly. However the Energy monitor showed little or no power consumption for Climate Control after only a minute or two (well before the car cooled) and never increased to more than a sliver.

This is the cause for my skepticism, the A/C compressor can't be cooling the air for free, so I am thinking there is simply a bug in the energy display SW. Normally I would confirm this with some sort of road test, but the routes that I drive do not have consistent topology and/or speed for me to perform a controlled test over a reasonable distance. Perhaps somebody in the flatlands somewhere (e.g. Arizona) can confirm there really is zero power cost, but the non A/C portion of the test might be too cruel to endure...

There is no trick and no cooling without consumption of energy of course. You may control the perceived temp (air volume) on you with the fan but the air temp is determined by the compressor cycling. The AC system is no different than any other in a car except it uses electricity to run as needed. There are lags in the metering at times on the dash based on input form controls.

 

[EVDRIVER]

in any case, the Climate control uses very little energy to cool, no mater how you have it set. the most efficient cooling I've seen. the resistive heater is a whole other matter.[/quote

Unless you live in a hot climate.

 

[EVDRIVER]

I thought member ingineer confirmed the compressor and heater element do not come on at the same time.
I find power consumption drops quickly and stays low once the car is cooled.

Yes, it does drop once cooled until needed again as it ramps quickly up. I'm not 100% on the heat and AC at the same time as it may based on humidity some times. I use AC only for defrost, in the SF area the AC is so low impact I leave it on, a mile loss in range over a long time unless in Napa, etc or more for those that sweat a bunch.

 

[TomT]

You are missing one salient point: The AC compressor does not run at a steady speed; it is throttled depending on demand. Thus, to maintain a given cabin temperature, you are going to expend about the same amount of energy over the long term regardless of how you do it.

And the only time it will use the heater is if the requested temperature is higher than the current cabin temperature, which should never be the case in the warm months when AC is necessary. It does not use the heater to modulate the temperature around the set point.

For AC, I usually just set a cabin temp and let it do it's thing, and the energy draw is very quickly just a very thin slice on the gauge. I suspect that the climate gauge is not actually even monitoring the actual power drawn by anything but rather is simply monitoring the CAN buss to see what is turned on and then using a look-up table to display power usage like the accessory gauge does...

The A/C is continuously active and cooling the car (I can feel it), temperature is simply controlled by adjusting the fan speed (not the temperature).

 

[Randy]

Ingineer posted a couple of weeks ago that the energy meter doesn't really measure power, it just displays presets for particular situations/devices.

 

[Stoaty]

I haven't seen any measurable effect of using the AC on my drive home in 85-90 degree temperatures. I am basing this on the number of Gids used for the round trip on my SOC meter. I drive very conservatively and predictably, and have a range of 105-120 Gids used for the round trip. The biggest factor is the traffic; if there is too much stop and go on the freeway it takes a few more Gids. Temperature is also a factor; if it is too cool I will use more Gids. Those two factors make a lot more difference than whether AC is used.

 

[EVDRIVER]

I haven't seen any measurable effect of using the AC on my drive home in 85-90 degree temperatures. I am basing this on the number of Gids used for the round trip on my SOC meter. I drive very conservatively and predictably, and have a range of 105-120 Gids used for the round trip. The biggest factor is the traffic; if there is too much stop and go on the freeway it takes a few more Gids. Temperature is also a factor; if it is too cool I will use more Gids. Those two factors make a lot more difference than whether AC is used.

Gids are not going to tell you about the AC consumption, rest-time KW usage will, particularly when turning it on and off. Regardless it is efficient in most cases.

 

[Nubo]

in any case, the Climate control uses very little energy to cool, no mater how you have it set. the most efficient cooling I've seen. the resistive heater is a whole other matter.

I can't speak to the compressor design, but one factor in favor of the LEAF's AC is that the condensor coils live in a much more favorable environment than in an ICE vehicle. Underhood temperatures are much lower and the condenser isn't sandwiched on top of a boiling hot radiator. Seems to me this has GOT to be a bonus for the thermal efficiency of the system.

 

[DaveinOlyWA]

**edited**

when the fan runs it does not change the energy screen when neither AC or heat is active which is wrong because the fan does use a enough power to register, but it does not. same with plugging anything into the accessory port.

i plugged a 250 watt heater into mine and it did not change the accessory power reading either.

you definitely want the A/C in the off position. this prevents "something" because i noticed a "freon-like" or maybe ozone like smell if you do not and the temp inside car is below your setpoint. i am guessing there is a slight rerouting of the air flow but i do not really know.

another thing is; the amount of power used by A/C is relatively small if the need is relatively small. granted, i live in an area where is does not get real hot most of the time so i am guessing this one characteristic of the Leaf is beneficial to me, but a few weeks ago when we were in the 80's a few days, i ran A/C and the gauge after a minute or so, read less than ¼ kwh.

i toggled it on and off and with SOC about 62% the GOM was fluctuating +/- 4 miles... pretty insignificant

**edited**

 

[Stoaty]

Gids are not going to tell you about the AC consumption, rest-time KW usage will, particularly when turning it on and off. Regardless it is efficient in most cases.

The Gids tell me plenty about AC consumption. Whether I drive with AC on or off, I use about the same number of Gids to make the journey. The AC draw is low enough that it is lost in the noise, and my SOC reads about the same when I get home whether I use it or not. That is all I need to know, not the exact number.

 

[garsh]

Ingineer posted a couple of weeks ago that the energy meter doesn't really measure power, it just displays presets for particular situations/devices.

IIRC, Ingineer stated that about the accessory meter, not the climate control or traction motor meters.

 

[EVDRIVER]

Gids are not going to tell you about the AC consumption, rest-time KW usage will, particularly when turning it on and off. Regardless it is efficient in most cases.

The Gids tell me plenty about AC consumption. Whether I drive with AC on or off, I use about the same number of Gids to make the journey. The AC draw is low enough that it is lost in the noise, and my SOC reads about the same when I get home whether I use it or not. That is all I need to know, not the exact number.

That is not an accurate measurement. The Gids are not granular enough for this low load measurement to give an accurate representation, You may use the same Gids but that really means little for several reasons.

 

[Ingineer]

The Climate control energy gauge is reasonably accurate, but heavily buffered, so it responds slowly to change. It will also not show you short bursts of energy usage, so don't depend on it for accurate metrics when trying to fine tune efficiency.

The accessory energy gauge is bogus. Do not rely on it for any useful metrics whatsoever.

The Leaf's A/C system is very efficient. It has an inverter driven compressor and will only run as hard as conditions merit. I believe this supposed trick is not real. Setting the A/C to a low temp and then running the fan manually at a low speed will cool the evaporator down to just above freezing and keep it there. This is actually less efficient because of the higher Delta-T, as well as it will remove even more humidity which will decrease heat conduction which will result in the cabin air "feeling" less cold for a given temperature.

The most efficient way to operate the system is to use the temperature to regulate the settings. Any perceived low energy saved by the "trick" is simply made up later. The Leaf's A/C system is so efficient that unless you are trying to squeeze absolutely every mile out of the pack, there is no reason not to use it.

One of the gauges I will likely add to LEAFSCAN is a total energy used by climate control per trip. Hopefully this will put an end to this type of stuff once and for all.

-Phil