AC *and* Heater simutaneously reducing efficiency?

[occ]

I have a friend who just picked up his LEAF yesterday. He questioned/argued with the sales rep there about the LEAF AC compressor. The question was "does the AC compressor works with the heater to keep the cabin to the temperature you selected, or does it just cycle the AC compressor for that?"

Common sense says if you have "AC" on, then the heater has nothing to do with cabin temperature. The sale guy say that if you use AC, to not set the temperature too high (say 78F) because both AC and heater will be used, causing reduced efficiency.

There's a thread that indicates that the heater does play a roll during de-frost, (actually the other way around: the AC compressor plays a roll during window de-frost, which primarily use the Heater so both will be on).

So any truth in what the sales guy said?

Maybe the right question would be: if "AC" is ON...will setting the temperature high cause both to AC and Heater to be used?

 

[planet4ever]

Well, it is certainly my experience that in many ICE vehicles the "free" heat is used to moderate the temperature of the air coming from the A/C. So it makes sense that a salesman might think the LEAF works that way, whether it is true or not.

Ray

 

[derkraut]

Well, it is certainly my experience that in many ICE vehicles the "free" heat is used to moderate the temperature of the air coming from the A/C. So it makes sense that a salesman might think the LEAF works that way, whether it is true or not.

Ray

I almost always set my temp to 77-79 when I run the AC, because otherwise it is too cold in the car. If I step into my car, and it's 95-100deg in there, I find it hard to believe that the heater will come on if I set the temp to --say---79. :?

 

[LEAFfan]

So any truth in what the sales guy said?
Maybe the right question would be: if "AC" is ON...will setting the temperature high cause both to AC and Heater to be used?

No, the sales guy is absolutely mistaken. I always have my A/C temp set above 80...usually around 84 or higher depending on the outside temp. The heater NEVER comes on as one can tell from the energy screen. What does happen though is the fresh air mode comes one to keep it at the higher temp. And after ten minutes or so, the energy usage drops to almost nothing (-1 to -2m/kW h).

 

[johnr]

No, the sales guy is absolutely mistaken. I always have my A/C temp set above 80...usually around 84 or higher depending on the outside temp. The heater NEVER comes on as one can tell from the energy screen. What does happen though is the fresh air mode comes one to keep it at the higher temp. And after ten minutes or so, the energy usage drops to almost nothing (-1 to -2m/kW h).

Yes, my experience is the same. The LEAF's A/C operation is really well thought out. As long as the temperature you set is lower than the actual temperature, the heater doesn't seem to come on. The A/C starts out at full power, then as desired temperature is reached the power level is reduced. If you look at the energy info screen it appears that, rather than mixing with the heater, it reduces the A/C power to minimal and actually cycles it on and off. So once the desired temperature is reached it takes very little power to maintain. In heating mode however, sometimes it will mix in some A/C to prevent fogging up the windows.

 

[shay]

So any truth in what the sales guy said?
Maybe the right question would be: if "AC" is ON...will setting the temperature high cause both to AC and Heater to be used?

No, the sales guy is absolutely mistaken. I always have my A/C temp set above 80...usually around 84 or higher depending on the outside temp. The heater NEVER comes on as one can tell from the energy screen. What does happen though is the fresh air mode comes one to keep it at the higher temp. And after ten minutes or so, the energy usage drops to almost nothing (-1 to -2m/kW h).

It still cools really well in eco mode. The temperature here has been 100+ for a good part of the summer here. Even with it hitting 105 and 106, I have never thought that this AC does not cool well. I do have Huper Optik tinting which is lowering the heat gain.

 

[occ]

Thanks guys. That's what I thought. I've never tried setting the temp higher than 77F since I like it cool in the car. And yes, I think the LEAF AC is very efficient...but I also have ceramic tinting done for AC efficiency reason, so I've never seen climate control takes up more than 2-3 miles on the screen (haven't use heat yet).

 

[EVDRIVER]

It's a poorly thought out system for an EV, if you want to use fan only with no AC it will often turn the heat on when you don't want it and are unaware. I constantly find the heat coming on and it's really annoying.

 

[TomT]

Yep! When I want fan only, I turn the temp all the way down, set the A/C off, and then manually set the fan speed to the level I want. It should have had an "Econ" mode like most ICE cars do that runs only the fan...

It's a poorly thought out system for an EV, if you want to use fan only with no AC it will often turn the heat on when you don't want it and are unaware. I constantly find the heat coming on and it's really annoying.

 

[pasowino]

I agree that the system is poorly designed. I do the same thing (lower the temp setting down as low as it goes) to make sure the heat stays off when I only want some fresh air.

Today I was driving home from work and it was about 90 F outside and I had the A/C set to about 75 F. It was cool in the cabin and I was getting close to home, so I turned the A/C off by depressing the A/C button. Watching the climate control energy meter on the energy screen, with the A/C off it was still pulling about 500 watts. I thought that it needed a few seconds to catch up, but it stayed up there. So, I lowered the temp setting down and the climate control load dropped to nothing.

So, that is my beef at the moment. Why in the world was the heater running at the same time the A/C was running with the outside temperature at 90F?

Another question about heating, why doesn't the Leaf steal waste heat from the motor and battery pack vs. use a resistance heating element? Seems pretty silly to not use the waste heat from the drive motor.

 

[smkettner]

It should have had an "Econ" mode like most ICE cars do that runs only the fan...

I find LEAF does not even have as much airflow as I would have expected with the system off. Should have been designed better to allow natural pressure to come through the vents more. Or am I missing something?

 

[highcountryrider]

Another question about heating, why doesn't the Leaf steal waste heat from the motor and battery pack vs. use a resistance heating element? Seems pretty silly to not use the waste heat from the drive motor.

+1

 

[EVDRIVER]

Another question about heating, why doesn't the Leaf steal waste heat from the motor and battery pack vs. use a resistance heating element? Seems pretty silly to not use the waste heat from the drive motor.

+1

It's insignificant and not worth capturing plus all the parts to do it would be extra weight for pointless gain.

 

[evnow]

It's a poorly thought out system for an EV, if you want to use fan only with no AC it will often turn the heat on when you don't want it and are unaware. I constantly find the heat coming on and it's really annoying.

Hmmm ... never had that problem. I switch the climate control on - switch the AC off and set the temperature a few degrees below what the dash shows. Seems to work fine.

 

[EVDRIVER]

A better question is why Nissan did not use a heat pump and used an antiquated water-tank system. Why? Because the used basic conversion parts from an ICE car even though they like to call it ground up. This is the most inefficient system they could use on an EV and it was also poorly implemented.

 

[evnow]

A better question is why Nissan did not use a heat pump and used an antiquated water-tank system. Why? Because the used basic conversion parts from an ICE car even though they like to call it ground up. This is the most inefficient system they could use on an EV and it was also poorly implemented.

I guess they decided this is the most efficient way to bring Leaf to the market

 

[EVDRIVER]

A better question is why Nissan did not use a heat pump and used an antiquated water-tank system. Why? Because the used basic conversion parts from an ICE car even though they like to call it ground up. This is the most inefficient system they could use on an EV and it was also poorly implemented.

I guess they decided this is the most efficient way to bring Leaf to the market

Quickest.

 

[Smidge204]

Has anyone tried to cross-reference components from the Leaf's HVAC system with other vehicles they make? I'm very skeptical they did it the way they did just to save money on standard parts. Best I can figure, trying with limited success to parse the service manual's descriptions, is the water system provides an advantage of control over air temperature - especially if you pre-condition the vehicle before unplugging.

By having ~2 liters of good thermal mass you can provide very consistent air temperatures across varying air inlet temperatures. A bare heating element would have short but noticeable heat up and cool down times, but the coolant loop is a good buffer that will hold temp until the heating element can adjust. Of course, you sacrifice efficiency in the form of "standby losses" for a heating system you may never use.

I suspect the heater core is always at a temperature appropriate for whatever the desired cabin temp is, regardless of heating/cooling mode. Immediate air heating is controlled by the mixing dampers (5 & 6) while the water temp is adjusted on setpoint and other conditions. Even if you set the temp all the way down and turn the A/C off, best I can tell from the manual all that does is keep damper 5 open and 6 shut... the heater is probably still working.

Seems like a good mod to try and disable the heating element via switch to save a few watts.
=Smidge=

 

[vegastar]

If there is a fuse for the heater element we could just remove it. Anibody with the service manual can check that?

 

[kmp647]

disabling the heater element will render the auto temp control inoperative as the system will not be able to maintain a set temp by mixing a/c and heater core air together

a 10 year old could have designed a better HVAC system for an EV

how about a heatpump with a toaster coil backup for starters !

that would be my choice