Heat pumps in EVs

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like2bike

Well-known member
Joined
Mar 23, 2013
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68
Location
Long Island, NY
Now that we have some experience with heat pumps. Please provide thoughts on whether they are a good thing to have in an EV. Not that they are available in other EVs yet, but at least may be available in the LEAF 2. I don't have a heat pump since I have the 2013 S.
 
Also having a '13S I'd don't have a heatpump but I see no negative to having one, in colder temps heatpump cars have a resistive heater like our S models and in warmer temps you get the benefit of less energy with the heap pump.
One thing I have wondered though is how dehumidifying works with a heatpump car, with ours a heat coil comes on and also the AC to dry the air out, since I'd assume the AC and heatpump can't run at the same time in such cars they must use the heat pump and resistive heater, basically resulting in a car like ours so if thats the case it wouldn't really be that more efficient than our S models during dehumidifying in cooler temps.....but I'm not positive.

I do see a big benefit to a heat pump in something like a Prius Prime(PHEV) where it can heat while on battery only, with the old Prius's anytime you wanted heat you had to run the ICE, and in states like mine that basically meant 6+ months of the year you couldn't really run on EV only :( (oh the Prius doesn't have a resistive heater, probably due to minuscule battery).
 
jjeff said:
Also having a '13S I'd don't have a heatpump but I see no negative to having one, in colder temps heatpump cars have a resistive heater like our S models and in warmer temps you get the benefit of less energy with the heap pump.
One thing I have wondered though is how dehumidifying works with a heatpump car, with ours a heat coil comes on and also the AC to dry the air out, since I'd assume the AC and heatpump can't run at the same time in such cars they must use the heat pump and resistive heater, basically resulting in a car like ours so if thats the case it wouldn't really be that more efficient than our S models during dehumidifying in cooler temps.....but I'm not positive.

I do see a big benefit to a heat pump in something like a Prius Prime(PHEV) where it can heat while on battery only, with the old Prius's anytime you wanted heat you had to run the ICE, and in states like mine that basically meant 6+ months of the year you couldn't really run on EV only :( (oh the Prius doesn't have a resistive heater, probably due to minuscule battery).

Actually, the LEAF heat pump system (at least on 2015 model) has two heat exchangers in the duct work in the dash and can run one to heat the air while the other dehumidifies the air. Since I have had both 2011 with resistance heater and 2015 with heat pump, I can say that the heat pump is a great improvement in my climate.

Gerry
 
There are more cars with heatpumps than just the Leaf and Prime. The higher end eGolf, the Kia Soul (IIRC) and the Hyundai Ioniq EV (higher trim levels), for example.
 
GerryAZ said:
....
Actually, the LEAF heat pump system (at least on 2015 model) has two heat exchangers in the duct work in the dash and can run one to heat the air while the other dehumidifies the air. Since I have had both 2011 with resistance heater and 2015 with heat pump, I can say that the heat pump is a great improvement in my climate.

Gerry
Totally agree on that! Even my '13S(without a heatpump) is a great improvement overy my '12SL, on heating anyway.
 
LeftieBiker said:
There are more cars with heatpumps than just the Leaf and Prime. The higher end eGolf, the Kia Soul (IIRC) and the Hyundai Ioniq EV (higher trim levels), for example.
Interesting, so the high mileage Bolt doesn't have a heatpump :? If not it must be a cost cutting measure by GM, they'll probably add that feature to higher trim models in a couple years, like Nissan did on the Leaf. Gotta give early adopters a reason to upgrade ;)
It's one reason I'd be leery to purchase a 1st or even 2nd year vehicle, Nissan made great strides on the Leaf moving into it's third year, whether planned obsolescence or they actually listened to early customers I just don't know.....I'd like it to be the latter but the skeptic in me says the first may also come into play...
 
LeftieBiker said:
Yeah, GM passed on using a heatpump, apparently to save money. They also passed on using real front seats.
Yes I've read as much, too bad as I might have been interested. I'm still going to give it a sit when they hit my state but have almost zero expectations I'll care one bit for the Bolt seats :(
Also interesting about the A/C being more efficient with a non heatpump car, of course living in MN A/C isn't nearly as important as a good heater so I'd still probably prefer the heatpump but I could see where a AZ or TX resident might think differently.
 
TomT said:
The larger the battery, the less difference a heat pump makes...

Until you actually need the range that is no longer there, thanks to a power-hungry heater.

I guess GM hasn't learned all the lessons from the Leaf.
 
I too will be test driving a Bolt next month, but assuming I haven't already picked up a 2016 Leaf at that point it still isn't extremely likely I'll lease one. Putting aftermarket cushions and seat covers on a $450 a month car (plus an aftermarket surround view system if the LT) just seems wrong. GM claims a motor heat recovery system that improves the resistance heater in the Bolt, but how much heat will the motor generate in 0F weather? I'm sure it will provide lots of waste heat when it's 90F outside... ;-(
 
webeleafowners said:
I was surprised to find them not available in the Teslas. Curious as to why.
IIRC Tesla uses waste heat from the battery to heat the cabin. They have hinted at a novel system for the Model 3.
 
LeftieBiker said:
I'm sure it will provide lots of waste heat when it's 90F outside... ;-(

I call it the "motorcycle heating system." Lots of heat when you don't want any, none when you're freezing your butt off.
 
RonDawg said:
LeftieBiker said:
I'm sure it will provide lots of waste heat when it's 90F outside... ;-(

I call it the "motorcycle heating system." Lots of heat when you don't want any, none when you're freezing your butt off.

That system is better, because even though your limbs and head freeze, it does actually provide heat in frigid weather, at least to your thighs. And, of course, you can always - carefully, avoiding the spark plugs! - warm your gloved hands while stopped.
 
My experience leads me to conclude the real world difference in efficiency between the 2015 heat pump and 2011 A/C for cooling in Phoenix summer temperatures is minimal. Either unit cools the LEAF well with minimal impact on range, but the black interior of the 2015 does absorb more solar energy.

Gerry
 
GerryAZ said:
Actually, the LEAF heat pump system (at least on 2015 model) has two heat exchangers in the duct work in the dash and can run one to heat the air while the other dehumidifies the air. Since I have had both 2011 with resistance heater and 2015 with heat pump, I can say that the heat pump is a great improvement in my climate.

Gerry

No. There are two heat exchangers but they never work simultaneously.
If HEAT and AC are both enabled (air drying in moist weather) compressor runs the AC (cooling, dehumidification) and PTC
heats the air after it has been dried. Aka it takes as much electricity as it takes on cars without heatpump.
Dehumidification is unnecessary and not possible in freezing weather. I've tried, doesn't work well enough.
Actually it is almost never needed. It is easier/more efficient to crank up the heat with heat-pump enabled vehicles.
Leaf with heat pump can generate 8-10kW of heat. That is more than enough to dry the windshield :D

Heat pump is not necessary if temperatures often drop down to 10C/50F and rarely drop below 4C/40F. Due to the fact that PTC
doesn't need a lot to heat the cabin moderately. Maybe this is why Bolt doesn't have it.
But near freezing the difference becomes bigger and bigger. Up to -10C/14F. 2-3x less consumption on heating.
Below -15C/ 5F heat pump is pointless. So it clearly depends on climate.
Estimations for warm Leaf cabin after warming up (w pump): 0C/32F - 300W, -5C/23F - 600W, -10C/14F - 1100W, -15C/5F - 2000W (PTC only).

Tesla doesn't have heat pump. Most likely the AC system is designed to be as powerful as possible in AC cycle. Because Tesla
does MAX out AC requirements in hot weather while SuperCharging. More is needed but that is not possible (no room for radiators).

I expect European version of Bolt and maybe even Model3 will be offered with reversible AC-system. It does make sense even more
if vehicle heats the battery to optimal temperature. Doing that at 200-400% efficiency saves on consumption while heating the pack.

Chevy tried very hard to keep the cost down. And, like I said, in warm climate, pump is not reasonable. Especially with 60kWh pack.
They will learn their mistake as soon as Canada or Europe starts to acknowledge Bolt as not 200mile EV on highway but rather 150 mile
EV for all year round use.

Driving for 3 hours in Bolt will draw 3x3kW=9kWh of heat in cold weather (14F). Aka 1/6th of the pack. At those temperatures heat pump makes sense.
 
Below -15C/ 5F heat pump is pointless. So it clearly depends on climate.

Many of us in the US have noticed that the heatpump stops helping range significantly below 15F. I don't dispute that it's still doing something below that, but it isn't helping range much at that point. I believe that 5F is where it stops working entirely.
 
Heat pumps are fascinating devices.

In terms of efficiency, COP is the unit to use, meaning how many units of heat can be moved from one space to another using one unit of energy. A resistance heater has a COP of 1.0; a heat pump has a range from 1 - 5ish, depending mostly on the temperature of the source. Standard heat pumps working as heaters shine when the source temperature is about 45F or greater and are down to a COP of 1.0 when temperatures hit about 20F. The temperature range can be improved using different gases. E.g, the Japanese use CO2 in their residential pumps which IIRC returns a COP of 2.0 at 5F.

Toyota put a heat pump into the Prime for this newest model that includes gas re circulation. I think that temperature performance rivals that of a CO2 pump.

Personally -- I don't really care much if my car has a heat pump or not because the heated seats work so well in conjunction with gloves and warm shoes and are low power devices.
 
LeftieBiker said:
GM claims a motor heat recovery system that improves the resistance heater in the Bolt,(
IIRC motors are about 97% efficient, so at 10 - 20 kW operation about 300 - 600 watts of waste heat are available for recovery.

That sounds like it might work nicely for a long road trip if the car is pre-heated, but I have no idea how well GM implemented the idea.
 
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