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has anyone actually measured the efficiency of the heat pump

Posted: Sun Nov 24, 2013 10:53 pm
by johnrhansen
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.

Re: has anyone actually measured the efficiency of the heat

Posted: Sun Nov 24, 2013 11:01 pm
by pkulak
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.

Re: has anyone actually measured the efficiency of the heat

Posted: Sun Nov 24, 2013 11:22 pm
by surfingslovak
pkulak wrote: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.

Re: has anyone actually measured the efficiency of the heat

Posted: Sun Nov 24, 2013 11:25 pm
by surfingslovak
johnrhansen wrote: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.

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Re: has anyone actually measured the efficiency of the heat

Posted: Mon Nov 25, 2013 12:27 am
by DaveEV
johnrhansen wrote: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.

Re: has anyone actually measured the efficiency of the heat

Posted: Mon Nov 25, 2013 4:15 am
by davidcary
+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?).

Re: has anyone actually measured the efficiency of the heat

Posted: Mon Nov 25, 2013 5:48 am
by johnrhansen
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

Re: has anyone actually measured the efficiency of the heat

Posted: Wed Nov 27, 2013 12:11 pm
by pkulak
surfingslovak wrote:
pkulak wrote: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

Re: has anyone actually measured the efficiency of the heat

Posted: Wed Nov 27, 2013 1:28 pm
by TimLee
pkulak wrote:
surfingslovak wrote:
pkulak wrote: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

Re: has anyone actually measured the efficiency of the heat

Posted: Thu Nov 28, 2013 6:42 am
by Rauv
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.