Heat pump vs resistive heater

Hi, I'm not sure which forum to post this in (mods, feel free to move it if there's a more suitable location).

I was curious to know more about the heat pump in some Leafs. If I understand correctly, Leafs with heat pumps also have resistive heater which is used in very cold temperatures. What's the cutoff for heat pump vs resistive heater usage? Is it something that is factory set or can the dealer or the owner change it? How much power does the heat pump use compared to the resistive heater? Is there a way to tell which mode it's in?

I'm curious because I have 15 SV and I just had the heater control unit replaced because it would not work at all on resistive heater (Down to about -10 to -12C (10F), I would get some heat (presumably from the heat pump) and it didn't appear to take very much power on the energy monitor (although I didn't take any data before the fix). But below that temperature, there was absolutely no heat coming from the heater (i.e. it appears that the switch-over to resistive wasn't happening or the resistive heater wasn't heater or something). I brought it in and they fixed it on warranty and now I have plenty of heat but today it's -7C (20F) and according to the energy monitor, I'm using a lot of power to heat so I think it's just using the resistive heater.

Let me know. Thanks,
Mike

Hi Mike.

The heat pump uses less power because it is extracting heat from the outside air and "moving" it into the cab. It's essentially an air conditioner acting in reverse. Since it is only "moving" heat, it is less power hungry than the electric heating element which is using electrical energy to create heat energy.

This is also why the heat pump doesn't work well when it is extremely cold outside. There is not much heat in extremely cold air that can be extracted and moved into the cab.

The electric heating element converts electricity into heat. To generate a significant amount of heat requires a significant amount of electricity. No way around that.

Blow dryers, curling irons, electric frying pans, space heaters, all have the same challenge. They draw a LOT of power.

As far as the specific settings in the Leaf's control systems, someone else will have to answer that for you. I have no idea.

Dave

You can't change the settings - they are based on physics more than personal preferences. The changeover is gradual, too. The resistance heater starts to help the heat pump at roughly 32-35F. By 20F it's the other way around, and below about 14F you get just a little heat from the heatpump, as you learned. At roughly 0F the heat pump shuts off.

Thanks for the quick response. That's good to know.

How much consumption should I expect on the energy meter for climate? At around 18-20F, with the climate set to 70F and on AUTO, it was mostly at 3.5kW but would go down to 1.5kW for some periods.

Let me know,
Mike

Look for the "Tips & Tricks" topic here. If you want more range with heat, you want the vents on floor only, fan on 2, partial recirculate engaged, temp on 70-75F. That can give you 1.0-1.5 kw consumption at those temps.

EDIT: here it is. http://www.mynissanleaf.com/viewtopic.php?f=38&t=23297

Thanks, I'll try that and see what my power consumption is.

In some experiments, I found that I could get the resistance heater to come on at relatively high temperatures by having the interior set point temperature set high. I also found that the heat pump would provide all of the heat needed down as cold as it got the past two "winters" here if I was careful to set the interior set point temperature to my minimum comfort level. It seems that the controller's determination of whether to use heat pump, resistance, or combination depends upon the difference between outdoor ambient temperature and inside set point temperature unless it is too cold for the heat pump (then it uses resistance heat only). Also, it will probably use a combination of heat pump/air conditioning and resistance heat for defrost, depending upon outside temperature. I have also noticed that the car usually uses the resistance heater when preheating while plugged in (at least on L2) so that is a way to verify that the resistance heater is functional.

GerryAZ said:

I have also noticed that the car usually uses the resistance heater when preheating while plugged in (at least on L2) so that is a way to verify that he resistance heater is functional.

Click to expand...

In my 2014 SV I I assumed the heat pump was used to preheated the car as it is when precooling. Just checked the 6.6kW ESVE draw after turning preheat on though. Initially was 2400-2500 watts then jumped to ~2800W I don't hear the pump running. It is 6F here this morning. I'll check it again on a warmer day to see if that makes a difference.

IBeLeaf2 said:

In my 2014 SV I I assumed the heat pump was used to preheated the car as it is when precooling. Just checked the 6.6kW ESVE draw after turning preheat on though. Initially was 2400-2500 watts then jumped to ~2800W I don't hear the pump running. It is 6F here this morning. I'll check it again on a warmer day to see if that makes a difference.

Click to expand...

I edited my previous post to fix a small typo after reading your post. Your preheat power draw looks similar to what I measured when I was experimenting with the new car in February 2015. I have not used preheat very much, but, in my case, the car has always used the resistance heater when plugged in.

GerryAZ said:

IBeLeaf2 said:

In my 2014 SV I I assumed the heat pump was used to preheated the car as it is when precooling. Just checked the 6.6kW ESVE draw after turning preheat on though. Initially was 2400-2500 watts then jumped to ~2800W I don't hear the pump running. It is 6F here this morning. I'll check it again on a warmer day to see if that makes a difference.

Click to expand...

I edited my previous post to fix a small typo after reading your post. Your preheat power draw looks similar to what I measured when I was experimenting with the new car in February 2015. I have not used preheat very much, but, in my case, the car has always used the resistance heater when plugged in.

Click to expand...

Using the heat when plugged into a QC (with the car turned on) does run the heat pump. I'll have to investigate the QC/preheat scenario next time I'm on a trip.

You are correct--heat pump will run if you start a QC session and then turn the car on to keep warm while charging. Also, the heat pump will run if you start preheat remotely when the car is not plugged in (presumably to minimize power consumption from the battery).

GerryAZ said:

Also, the heat pump will run if you start preheat remotely when the car is not plugged in (presumably to minimize power consumption from the battery).

Click to expand...

That is actually optional, can be set on or off with NissanConsult. My car did run HP while unplugged and preheating, now it doesn't.



Heat pump is always used except if system detects it being iced up. In this scenario outside fans stop and only resistive heater is used.
With 99% probability heat pump is used at temperatures down to -12*C. With 99% probability it is switched off at -15*C or below.
Compressor is capable to draw up to 2500W. Usual load is 1200-2150W in cold weather.
At near 0*C and after cabin warmup period normal draw is 350W with no help from resistive heater.