has anyone actually measured the efficiency of the heat pump

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johnrhansen

Well-known member
Joined
Aug 12, 2013
Messages
1,100
Location
Seattle, WA
I'd be interested to know just how much more efficient the heat pump installed on the premium 2013 leafs are compared to the basic resistance heaters installed in the s type. My recent experience driving in cold weather has shown that the heat wasn't as energy consuming as I thought it would be when I looked at all the other range reducing factors that the cold weather subjects my car to, and actually compared the range with the heater on or off in the same conditions.

Last summer I installed the most efficient 12000 btu mitsubishi mini split heat pump in my home and with this colder weather I was able to measure the power consumption of my new unit. It was drawing 1500 watts. If I calculated it correctly thats only 2.3 times better than resistance heat. This whole experience makes me think the heat pump on the leaf performs similarly, probably worse because it is a mobile unit that can't have as large or as heavy evap and condser coils as a stationary unit can.

looking at amount of power consumed by the traction motor vs the heater and the other factors reducing range in cold weather, I cant imagine having a heat pump would increase your range that much vs the resistance ones.
 
What was the temperature when you took that measurement? Heat pumps approach the efficiency of resistance heat as they get closer to some point just below freezing. Which also means they are most efficient in mild temperatures, like I have where I live.
 
pkulak said:
Heat pumps approach the efficiency of resistance heat as they get closer to some point just below freezing.
This was discussed and debunked a few months ago. The heat pump should offer a tangible albeit diminishing benefit all the way down to 0 F.
 
johnrhansen said:
I was able to measure the power consumption of my new unit. It was drawing 1500 watts. If I calculated it correctly thats only 2.3 times better than resistance heat. This whole experience makes me think the heat pump on the leaf performs similarly, probably worse because it is a mobile unit that can't have as large or as heavy evap and condser coils as a stationary unit can.

looking at amount of power consumed by the traction motor vs the heater and the other factors reducing range in cold weather, I cant imagine having a heat pump would increase your range that much vs the resistance ones.
The heat pump on the LEAF offers a similar benefit, and according to Nissan, it substantially helps preserve usable range in wintry conditions.

I did my best to find the data presented at the 2013 LEAF introduction last year. I tried to get higher resolution, but I couldn't. I'm sorry, but I hope that this puts it to rest.

To be clear, this is not the first time that I see the effectiveness of the heat pump used in an EV to be questioned. According to the data presented by the LEAF engineering team, a significant benefit can be expected around 0°C, and the ambient temperature would have to go down to about -15°C for the heat pump to stop offering a benefit over the heater used in the previous model year. If you find more relevant references, please post it.

12h5rYH
 
johnrhansen said:
Last summer I installed the most efficient 12000 btu mitsubishi mini split heat pump in my home and with this colder weather I was able to measure the power consumption of my new unit. It was drawing 1500 watts. If I calculated it correctly thats only 2.3 times better than resistance heat.
I highly doubt you calculated it correctly - for one - it sounds like you are assuming that it always pumps out 12000 BTU of heat, but that's very rarely the case.

I'm not aware of any easy ways to measure heat-pump efficiency unless you have a resistance heater to compare it to.
 
+1

A Mitsu minisplit would have a far better COP than 2.3 down to any temp that you have reached this year.

Typical COPs are 4 at 47 degrees and 2 at 17 degrees. Obviously there is a lot of variability and a mobile unit is not likely very efficient. That being said, a Mitsu minisplit would do better that that and I am pretty sure Olympia hasn't been that low yet (ever?).
 
I must have calculated it wrong. My space is 1500 square feet and that 1500 watts easily heats the whole space at 40 degrees. I just converted watts to btu hrs and divided it out
 
surfingslovak said:
pkulak said:
Heat pumps approach the efficiency of resistance heat as they get closer to some point just below freezing.
This was discussed and debunked a few months ago. The heat pump should offer a tangible albeit diminishing benefit all the way down to 0 F.

Hey now, 0 is below 32. I stand behind my point. :D
 
pkulak said:
surfingslovak said:
pkulak said:
Heat pumps approach the efficiency of resistance heat as they get closer to some point just below freezing.
This was discussed and debunked a few months ago. The heat pump should offer a tangible albeit diminishing benefit all the way down to 0 F.

Hey now, 0 is below 32. I stand behind my point. :D
0F is a substantial amount below freezing.
Good you can find humor in posting about something you aren't competent about. :D :D :D
 
I have measured (and will post a graph hopefully this weekend) of the load from the wall after a full 100% charge, followed immediately by a pre-heat session. I have done this several times and the load from the wall during the pre-heat is around 1500 watts, to get heat rise from 30 deg. F ambient to 65F in the 'cabin'.

I am making the assumption that after a full charge (8 hours+balancing) followed by a pre-heat, means that all of the load from the wall effectively goes to heating the cabin. Maybe that is not the case and the traction battery provides some energy to heat the cabin even while plugged in? Maybe LEAF Spy will expose whether or not the traction battery assists in heating the cabin even while still plugged in.

I'll try to post LEAF SpyPro data on the same graph if I can figure it out in Excel. Maybe the best test is for someone with the proper DC current meter to actually pull load data during a pre-heat session at various ambient temps to see at what low temp the resistance heater kicks in to help the heat pump.
 
Rauv said:
I am making the assumption that after a full charge (8 hours+balancing) followed by a pre-heat, means that all of the load from the wall effectively goes to heating the cabin. Maybe that is not the case and the traction battery provides some energy to heat the cabin even while plugged in?
I don't know whether the heat pump runs from 12v DC or 400v DC, but surely it doesn't run from AC, either 120v or 240v. Therefore the on-board charger has to be running during your preheat. That means the cooling system is also running, and the DC/DC converter is likely to be running to supply the 12v for the cooling system, if not also the heat pump. Both the charger and the DC/DC converter are water cooled, and the heat the coolant extracts goes to the outside of the car, not the cabin.

So you still have a number of variables for your test.

Ray
 
As someone who has had both a '12 and a '13 Leaf in Wisconsin winters, I can testify that the '13 heat pump is noticeably more efficient. I don't have real numbers, just anecdotal evidence from the Energy Monitor screen that I always have up while driving. We only run the heat when it's well below freezing. My '12 Leaf would be a solid 5kW to start, and then steady 3-4kW after that. The '13 is usually 4kW to get started, and then 1.5-2kW after that to maintain. Big difference. It also heats up WAY faster and hotter than the old one. This was actually one of the primary reasons we traded in for the '13.
 
I have no idea how efficient is the Leaf's heat pump, however the DoE did a test on the Mitisubihi split heat pump and rated it with a coefficient of performance in the heat cycle of 4.2. That means for every watt going in, the unit produces the equivalent of 4.2 watts of heat. I believe COP is measured at 50 degrees and drops off significantly as the temperature drops.

http://www.nrel.gov/docs/fy11osti/52175.pdf" onclick="window.open(this.href);return false;

Since COP drops off as the outside temperature drops my understanding is the heat pump is pretty useless as the temperature drops near zero. As such, they require resistive heat to supplement, and this draws heavily on the battery. It would be nice it there was instead, a propane powered catalytic heater to supplement the heat pump. I don't think heating directly from a catalytic heater is a good idea as they deplete oxygen from the air, but using it to pre-heat the air going to the heat pump would eliminate this danger. Propane could come from the standard 1lb propane tanks that are widly used with camping equipment.
 
LKK said:
Since COP drops off as the outside temperature drops my understanding is the heat pump is pretty useless as the temperature drops near zero. As such, they require resistive heat to supplement, and this draws heavily on the battery.
This not quite correct, and has been debunked on this forum several times. While the efficiency of the heat pump drops with lower ambient, it offers a significant benefit over a resistive heater all the way down to 0F. You can see that on the graph below, which Nissan used during the launch presentation of the 2013 LEAF. The heat pump and the resistive heater were set to 77F, and the range was then measured at different ambient temperatures.

12h5rYH


LKK said:
It would be nice it there was instead, a propane powered catalytic heater to supplement the heat pump. I don't think heating directly from a catalytic heater is a good idea as they deplete oxygen from the air, but using it to pre-heat the air going to the heat pump would eliminate this danger. Propane could come from the standard 1lb propane tanks that are widly used with camping equipment.
Volvo did this, but they used ethanol instead of propane. Arguably, in some parts of the world reliable source of heat can be a matter of survival.
 
now that winter is here I'm really noticing how poorly the resistance heater is working in my 2013 s. It really gobbles up power. I've checked more thoroughly the difference berween heat on and off, especially in the slow city driving I do so much. I really wish I had bought the SV with a heat pump. I use about twice as much energy when the weather gets really cold. I should have researched more when I bought it. I don't want to lose my shirt trading it in, so it looks like I'm stuck with it. I take back everything I said before. When it gets really cold and rainy, I just drive my ice truck now. It needs a workout now and then anyway. The leaf is really a fair weather car. Might as well be a convertible.
 
johnrhansen said:
now that winter is here I'm really noticing how poorly the resistance heater is working in my 2013 s. It really gobbles up power. I've checked more thoroughly the difference berween heat on and off, especially in the slow city driving I do so much. I really wish I had bought the SV with a heat pump. I use about twice as much energy when the weather gets really cold. I should have researched more when I bought it. I don't want to lose my shirt trading it in, so it looks like I'm stuck with it. I take back everything I said before. When it gets really cold and rainy, I just drive my ice truck now. It needs a workout now and then anyway. The leaf is really a fair weather car. Might as well be a convertible.

i just got my S yesterday and the difference due to the special on the S would have been $100 a month. After driving my 2011 with no heated seats or steering wheel, the 2013 has been a dream but then again, it has not been below 42º and I am well prepared for cold. First thing I did was turn seat heaters from high to low. High was just a bit too warm for me. Cant wait to see how it works when temps hit the 20's...
 
It's always heated very well and defogged just fine regardless of how cold or damp it was, and if you don't have far to go, it works just fine. I see you are in olympia and I drive down there periodically. When it gets really cold, I can't make it there from Seattle unless I stop at the blink charger in fife. One time I was only getting 3 miles per kwh. When it's warmer and the heat is off I can make 4.8 easy., and arrive there with 20 percent to spare. Driving a leaf is a lot like being an old time bush pilot. You need to be really cognizant of the weather and of your machine or you won't make it. From now on I dont leave king county in it unless the weather is decent. Just too much to think about.

DaveinOlyWA said:
johnrhansen said:
now that winter is here I'm really noticing how poorly the resistance heater is working in my 2013 s. It really gobbles up power. I've checked more thoroughly the difference berween heat on and off, especially in the slow city driving I do so much. I really wish I had bought the SV with a heat pump. I use about twice as much energy when the weather gets really cold. I should have researched more when I bought it. I don't want to lose my shirt trading it in, so it looks like I'm stuck with it. I take back everything I said before. When it gets really cold and rainy, I just drive my ice truck now. It needs a workout now and then anyway. The leaf is really a fair weather car. Might as well be a convertible.

i just got my S yesterday and the difference due to the special on the S would have been $100 a month. After driving my 2011 with no heated seats or steering wheel, the 2013 has been a dream but then again, it has not been below 42º and I am well prepared for cold. First thing I did was turn seat heaters from high to low. High was just a bit too warm for me. Cant wait to see how it works when temps hit the 20's...
 
Rauv said:
I have measured (and will post a graph hopefully this weekend) of the load from the wall after a full 100% charge, followed immediately by a pre-heat session. I have done this several times and the load from the wall during the pre-heat is around 1500 watts, to get heat rise from 30 deg. F ambient to 65F in the 'cabin'.

I am making the assumption that after a full charge (8 hours+balancing) followed by a pre-heat, means that all of the load from the wall effectively goes to heating the cabin.
This is with a heat pump car? Still no one has done this test with a space heater car? Maybe 4 Kw on high instead? A 40 mile highway commute will use up 10kWh and take 45 minutes. The space heater worst case would be 3kWh vs 1kWh for the heat pump. The total would be 13kWh vs11 if the space heater really stayed that high the whole time. So maybe about 15% highway range advantage to the heat pump car on a 0C day.
 
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