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Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Fri Feb 15, 2019 12:14 pm
by GetOffYourGas
LeftieBiker wrote:
Most of the new EVs sold today would do just fine in bitter cold with average commutes and letting the driver do whatever (s)he wants to do with heating settings.
Except for the ones who acquired their EV with range needs that approach the EPA range rating of the car. They, never having been told by the sales "people" about Winter range drop, are essentially screwed.
He said "with average commutes". The average commute is about 30 miles round-trip. There are no modern BEVs with an EPA range anywhere near that low.

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Fri Feb 15, 2019 12:48 pm
by iPlug
Private vehicle is ~25 miles mean average round trip according to 2017 NHTS. Would guess the not reported median is closer to 20 miles round trip.

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Fri Feb 15, 2019 8:43 pm
by iPlug
Can anyone here comment on the heating efficiency of EV heat pumps? Are they rated as residential heat pumps are, eg. HSPF?

Ok, found this thread but not updated recently:
http://www.mynissanleaf.com/viewtopic.php?t=15108

Looking for manufacturer specs on EV heat pumps or someone who has appropriately tested this on one's own.

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Sat Feb 16, 2019 8:46 am
by SageBrush
iPlug wrote: Looking for manufacturer specs on EV heat pumps or someone who has appropriately tested this on one's own.
I've looked without much success but you can pull up efficiency curves of different heat pumps that then give you a pretty good idea. The air to air pumps come in a couple of flavors:
1. By refrigerant
2. Vapor recirc (the Prius Prime e.g)
3. Variable Power. IIRC so-called inverter controlled are the best since they have what I call infinite gearing by analogy.

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Sat Feb 16, 2019 10:27 am
by iPlug
SageBrush wrote:
iPlug wrote: Looking for manufacturer specs on EV heat pumps or someone who has appropriately tested this on one's own.
I've looked without much success but you can pull up efficiency curves of different heat pumps that then give you a pretty good idea. The air to air pumps come in a couple of flavors:
1. By refrigerant
2. Vapor recirc (the Prius Prime e.g)
3. Variable Power. IIRC so-called inverter controlled are the best since they have what I call infinite gearing by analogy.
I’m having a hard time finding the efficiency curves of plug-in vehicle heat pumps. Able to find residential ones.

IIRC, Prime has one of the most efficient heat pumps in the plug-in vehicle market. Toyota says the heat pump in the Prime uses 63% less energy than conventional resistive heating and claims extend driving range up to 21%.

https://www.sae.org/news/2017/04/inner- ... p-revealed

I would presume the 63% is best yield achieved on an efficiency curve. By comparison our residential heat pump is HSPF 13.0 = 3.81 COP.

Someone can check my math, but that is a best case scenario 74% less energy than conventional resistive heating. So the Prime heat pump still has room for improvement compared to some of its stationary peers.

Of course, without ambient temperature efficiency curves to compare, we don’t know how well a plug-in vehicle heat pump is doing at say 0-20°F when heating demand would be highest and effiency the poorest.

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Sat Feb 16, 2019 12:20 pm
by SageBrush
Perhaps I was not clear -- you do not have to find a heat pump in a car, just match the engineering categories I mentioned earlier.

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Sat Feb 16, 2019 1:05 pm
by iPlug
I may not be completely understanding your position, and you may know substantially more about heat pumps. I was looking for hard specification numbers.

I would also suspect that by knowing the refrigerant type, if it has vapor recirculation tech like the Prime, and if it is single stage/dual stage/infinitely variable speed powered, etc. that this will give you some ballpark comparative ideas of efficiency, at least relative rankings.

Definitely an amateur on my end regarding heat pump systems, but can we say that if a fixed/residential heat pump system and plug-in vehicle heat pump system have the same refrigerant, recirculation tech, variable speed features, etc. and we know the HSPF/COP/efficiency curves of that residential unit, that the plug-in vehicle heat pump system therefore has identical efficiency specs?

My guess would be probably not off tremendously, but to get a heat pump system into a vehicle requires miniaturization/component engineering compromises and placement of components in perhaps suboptimal locations thus reducing efficiency, no?

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Sat Feb 16, 2019 1:44 pm
by LeftieBiker
The reason that most heatpump-equipped EVs have lower efficiency than a residential unit is that EVs,unlike houses, have to be heated quite a lot in a matter of minutes - or even a single minute - while units heating houses can take a little longer without complaints. So EVs use their resistance heating units (which are a backup only with residential units, IIRC) to speed up heating the cabin. The resistance heaters then shut down after the cabin has gotten warm enough for the heat pump to maintain the set temp. That's why we call the system in the Leaf a "hybrid" heating system: both heating units work together, speeding heating but lowering efficiency. The Prime appears to use a heatpump only, putting a definite lower temp limit on its usefulness, albeit with much lower energy consumption.

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Sat Feb 16, 2019 2:40 pm
by SageBrush
iPlug wrote:but can we say that if a fixed/residential heat pump system and plug-in vehicle heat pump system have the same refrigerant, recirculation tech, variable speed features, etc. and we know the HSPF/COP/efficiency curves of that residential unit, that the plug-in vehicle heat pump system therefore has identical efficiency specs?
No one would confuse me with a heat pump expert but the above is my understanding. Ballpark anyway

Re: AAA confirms what Tesla, BMW, Nissan electric car owners suspected — cold weather saps EV range

Posted: Sat Feb 16, 2019 2:43 pm
by SageBrush
iPlug wrote:but can we say that if a fixed/residential heat pump system and plug-in vehicle heat pump system have the same refrigerant, recirculation tech, variable speed features, etc. and we know the HSPF/COP/efficiency curves of that residential unit, that the plug-in vehicle heat pump system therefore has identical efficiency specs?
No one would confuse me with a heat pump expert but the above is my understanding. Ballpark anyway