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TomT
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Re: Heat pumps in EVs

Mon Feb 06, 2017 9:32 am

The point is that the larger the battery, the less likely that is to happen... On a 24 or 30 Kwh pack, it is much more of a concern...

RonDawg wrote:
TomT wrote: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.
59,991 miles/12 bars/289 Gids/68.54 AHr/101% SOH/101.64% Hx 7May15 w/ new Lizard (barely made the warranty).
71,770 miles/12 bars/256 Gids/59.04 AHr/88% SOH/87.92% Hx 3Mar16 at lease return.

Now driving a 2016 Volt Premier. Model 3 reserved.

RonDawg
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Re: Heat pumps in EVs

Mon Feb 06, 2017 4:40 pm

TomT wrote:The point is that the larger the battery, the less likely that is to happen... On a 24 or 30 Kwh pack, it is much more of a concern...

RonDawg wrote:
TomT wrote: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 don't know how much of the Bolt's advertised 238 mile range is affected in winter, but if you advertise a car's range as being x, and the heating system takes a huge chunk out of it, it doesn't matter what the battery size is. It still leads to consumer disappointment, especially if that consumer is new to the EV world and wasn't made fully aware of that prior to purchase/lease.
Blue Ocean 2012 Leaf SV, lost that 1st bar on 11/21/2015 at 26,435 miles.
Lease returned on 12/23/2015. Final LeafStat figures: 225 Gids, 17.44 kWH, SOC 91.89%, SOH 82.36%, 69.49% HX, 54.57 Ahr, battery temp 61.8 F
Now driving a 2015 VW eGolf SEL

arnis
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Re: Heat pumps in EVs

Mon Feb 06, 2017 6:33 pm

Today was a perfect day to test heat pump at the extreme. It was -12C (10F) and super dry (worst for heat pump).
It took a lot of time (more than 25 minutes of driving) to totally heat the cabin up (wasn't able to preheat) but when
ready compressor consumed 1750-1850W. Cabin warm (17-20C, 60-70F), CC at AUTO (3bars), temperature set to low.
I expect COP around 1.5-2.0. Haven't had a Leaf without heat pump in 10F weather. Any feedback on that?

I had to raise temperature setting as when cabin fully warmed up CC slowed down to 2 bars and consumption dropped
to around 900-1100W. That is not enough and I felt cold (I wear shorts and a t-shirt, don't ask).

During warmup cycle with blower at max stable consumption is 1800-2000W HP + 1500-2250W PTC. I usually limit fan to 4 bars,
this results PTC going too hot and consumption drops to 1800-1900W HP +250-750W PTC. This should generate about
3,5-4kW of heat.

In a little bit warmer weather (20F -6C) heat pump is more capable, can draw 2400W while PTC can add 3500W.
This generates around 10kW of heat. That continues for a minute or two. Cabin warm fast, reduces to stable warmup load.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

jjeff
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Leaf Number: 422121
Location: MSP MN

Re: Heat pumps in EVs

Tue Feb 07, 2017 6:57 am

arnis wrote:.... Haven't had a Leaf without heat pump in 10F weather. Any feedback on that?

At 10F my '13S with the resistive heater does pretty well, takes a lot of power but heats well. My '12SL OTH also takes a ton of power but doesn't do so well due IMO to the poor implementation of using glycol liquid to transfer the heat instead of direct air heat on the '13S. To make matters worse apparently the '11/'12 Leafs didn't insulate the glycol lines very well(if at all??) so you get lots of wasted heat to the outside of the cabin.
Personally I would NOT suggest a '11/12 for very cold areas, the resistive heater on the S models does heat quite well, just take quite a bit more power than Heat pumps in moderate to not so cold temps. Of course in -F temps both systems probably draw about the same.

A question for anyone who might know, is the resistive heater on a S model larger(more Kw) than the resistive heater on a Heat pump equipped Leaf? Might make sense since a Heat pump vehicle could be designed for the Heat pump to provide some heat while the S model would rely on resistive heat only. If that were the case then in -F temps the S model should heat better than non S models.....
My S model doesn't tell me Kws drawn by the climate control system but my '12SL does and in the bitter cold it's not unheard of for me to see 6+Kwh being drawn by the liquid heater. I do know I need a EVSE setting of at least ~18a@240v to keep up with extreme morning warmup, a standard 16a@240v EVSE will lose ground in charging. Note the '12SL Leaf only has a 16a@240v max internal charger so in such bitter cases it always loses charge when preheating.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
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IssacZachary
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Re: Heat pumps in EVs

Tue Feb 07, 2017 3:14 pm

Here's my dos centavos.

I drive every day with the heater on for three to six hours (usually charge for an hour during lunch). Today it was snowy and cloudy which didn't give much solar heat, so I had to use the heater more. I noticed that I got much better range today with the heat pump running than on -20*F days (and especially nights) with the resistive heater running.

There was a comment about lack of humidity making the heat pump less efficient. Wouldn't it be the other way around because more humidity would cause more icing??

Also, how does the heat pump make the A/C less efficient?
2013 SL 45,000 miles.
12 bars until 44,300 miles on June 2, 2017. :D
11 bars current. :)
The Nissan Leaf is the fourth best long distance car for highway driving. >>Best Long Distance Cars<<

arnis
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Re: Heat pumps in EVs

Tue Feb 07, 2017 3:20 pm

jjeff wrote:
arnis wrote:.... Haven't had a Leaf without heat pump in 10F weather. Any feedback on that?


A question for anyone who might know, is the resistive heater on a S model larger(more Kw) than the resistive heater on a Heat pump equipped Leaf? Might make sense since a Heat pump vehicle could be designed for the Heat pump to provide some heat while the S model would rely on resistive heat only. If that were the case then in -F temps the S model should heat better than non S models.....
My S model doesn't tell me Kws drawn by the climate control system but my '12SL does and in the bitter cold it's not unheard of for me to see 6+Kwh being drawn by the liquid heater. I do know I need a EVSE setting of at least ~18a@240v to keep up with extreme morning warmup, a standard 16a@240v EVSE will lose ground in charging. Note the '12SL Leaf only has a 16a@240v max internal charger so in such bitter cases it always loses charge when preheating.


OK, I have lots of fresh data :ugeek:

I believe air PTC element on S and on HP equipped Leafs is the same.
Right now it is 0F outside. I made some measurements (open windows for stable readings). Heat pump is disabled at 5F.
Maximum fan speed (only possible if air is blowing to defrost only), maximum temperature setting, fresh air only. Outside -17C (0F).
Heat pump equipped Leaf's PTC element maxes out at 4000W. I have a hunch that this is the maximum rating. Can not verify.
S-trim will most likely have exactly the same PTC element (sad, that you don't have LeafSpy, you could extract power draw from there).
Actually it falls down to 3750W after fast warmup. And stays there forever. In addition, I measured some other max values (max temp settings):
1bar fan 1250W
2bar fan 1500W
3bar fan 2000W
4bar fan 2750W
This is how much PTC element on new Leaf will draw. It will go little higher at temperatures below 0F, but this data is exactly for 0F.
If Leaf is plugged in, maximum draw is limited to 2750W no matter what. During preheating cycle recirculation is engaged automatically.
With recirculation even at 0F cabin will warm up normally with 2750W PTC heat. Fan will draw 300W and computers some more. This is why at 240V 16A battery will very slightly discharge. Usually 0,5-1,5%

Why I think air PTC element is 4kW? Because air that exits from the vent while fan is at full is not as hot as it is when fan is at 4 bars.
There is a maximum air temperature that can not go higher for PTC element. PTC just works that way. Leaf can control PTC output by
PWM signal. When it sends 100% command PTC heater is always activated. But resistance of that element raises dramatically when it
gets hotter. Even if you keep PTC element at 100% it will never go above it's maximum temperature (unknown value). So, theoretically,
if we feed air that is even colder, PTC element can draw more as cold air will result PTC to be able to consume more electricity. But that doesn't mean air temperature going out will be hotter. It should stay the same. If I won't fall asleep I will measure air out temperature at
different fan settings while it is 0F outside. I will mark that down. In theory air exiting vents on newer Leafs will never be hotter than one specific value, no matter, is it -20F or 120F outside. Exception is heat pumps radiator maximum temperature. For home units it's around 70C 160F.

More information about heat pump. Few hours earlier it was -14C and then fell to -15C. I was driving at that exact time.
What I found out is that heat pump is limited with one more thing. Fan speed setting. This applies to temperatures between -15C and -10C (5F 14F). If the fan speed is above 4 bars heat pump will IMMEDIATELY slow down. As soon as 1-4 bar fan speed is selected, heat pump
will resume at higher power. I was fiddling more with that. Temperature fell to -15C (heat pump extreme value for Leaf). Pump was able to work at 1600-1900W (which on its own is not full power any more). As soon as selected fan speed 5, compressor slowed down to 900W. Then fell and fell and fell, until minute later it died at around 500W and locked out. I stopped the vehicle, heated the inside condenser with recirculation, switched vehicle off, waited a minute, switched on and pump was enabled again. Everything worked like before. I used recirculation mode and did the trick again, still, pump immediately slows down at 5+bars. BUT, this time, it didn't die. It kept on running at 500-1000W rating.
This means that complicated pump design is protected with some intelligence and some sensors (gas pressure and inside radiator temperature). It knows that somewhere between -10C -15C there is a risk of pressure going out of limits (or wrong refrigerant state) due to the fact that inside radiator is too cold. I do know that heat pumps for homes are not designed to work when inside radiator is too cold. Most likely same reason. Luckily it is always above freezing indoors. But car must suck fresh air from outside and PTC is AFTER heat pump. The only way to keep it running is to wait a moment when inside radiator gets warm and never chill it down to not acceptable temperature. CC software is set to distinguish 4-5bar fan setting. But it will still die if it gets too cold. Temperature fell to -16C and heat pump was not initiated any more.
This is why last year I noticed many times that heat pump spins up but doesn't work for long. Because CC sets fan speed to full on AUTO. This freezes inside radiator and disables pump for that trip.
Conclusion: at temperatures between 5F and 14F set your fan speed to no more than 4 bars at warmup. This will allow heat pump to work normally and it shouldn't lock out.
Also at temperatures above that limiting fan speed will result in minimal PTC usage, even during warmup cycle.
Changing temperature settings doesn't change absolutely anything ... besides how long warmup mode is engaged.
Minimal temperature selection vs Maximum selection changes nothing. Heat pump does what it can, PTC element the same.
Until interior temperature sensor reaches set temperature, then heating capacity will be reduced, starting with PTC.
The only way to minimize PTC usage during heatup is to limit fan speed. Keep CC draw between 1500-2000W for ideal results.
This usually results in PTC working up to 250W as heat pump's nominal (ideal) load is somewhere around 1000-1850W.

And something else. It appears heat pump does have acceptable COP even at -15C 5F. Because at the end of warmup phase consumption
was around 1300W HP + 250-500W PTC. While as soon as HP is killed (same temperature) more than 2000W was drawn. I would not say COP was above 1.5, but 50% reduction is still a reduction.

PS! there is around 100-200W additional load while HP runs at vehicle speeds below ~60km/h (outside fans). This is not measured anywhere.
PS2! Heat pump is limited to 1000W while vehicle slower than 25km/h due to noise. I've heard that Tesla also limits AC compressor speed at lower travelling speeds now.

IssacZachary
If there is too much humidity (usually at 0C 32F and few degrees below that) and Leaf detects condenser icing it will disable heat pump until defrost cycle (need to plug in). Defrost starts 1 minute after pluging (SOC above 15%) and runs for 6 minutes.
Heat pump plumbing is more complicated. Maybe this somehow reduces overall efficiency during cooling compared to system that can't switch to heating mode.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
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User avatar
EVDRIVER
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Joined: Sat Apr 24, 2010 7:51 am

Re: Heat pumps in EVs

Tue Feb 07, 2017 3:25 pm

I think the Tesla heater is 6kw or even more and there is an econ mode. It is a power hog and a heat pump for long trips would have been nice.

sendler2112
Posts: 214
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Location: Syracuse, NY USA

Re: Heat pumps in EVs

Tue Feb 07, 2017 4:24 pm

arnis wrote:And something else. It appears heat pump does have acceptable COP even at -15C 5F. Because at the end of warmup phase consumption
was around 1300W HP + 250-500W PTC. While as soon as HP is killed (same temperature) more than 2000W was drawn. I would not say COP was above 1.5, but 50% reduction is still a reduction.

Had you been driving when you saw this?Can the heat pump outside element be gaining heat from the EV drive cooling system?

arnis
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Re: Heat pumps in EVs

Tue Feb 07, 2017 4:38 pm

EVDRIVER wrote:I think the Tesla heater is 6kw or even more and there is an econ mode. It is a power hog and a heat pump for long trips would have been nice.


Tesla's heater is 6kW, cabin, and another 6kW, for battery. Cabin heater is Air PTC, battery heater heats the coolant.
In range mode battery heater is disabled. If plugged in to reasonable EVSE preheating Tesla does much more than preheating Leaf.
Leafs with heat pump lose as much/more range due to freezing battery than from heater consumption :cry:

If I were Mr Musk I would definitely consider Heat pump for battery and cabin.
But that would make a complicated system even more complicated:
http://insideevs.com/wp-content/uploads ... gineer.jpg
http://insideevs.com/wp-content/uploads ... gineer.jpg
At least 100-1000W heat from drivetrain is redirected for battery heating (second photo).
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

arnis
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Re: Heat pumps in EVs

Tue Feb 07, 2017 4:41 pm

sendler2112 wrote:
arnis wrote:And something else. It appears heat pump does have acceptable COP even at -15C 5F. Because at the end of warmup phase consumption
was around 1300W HP + 250-500W PTC. While as soon as HP is killed (same temperature) more than 2000W was drawn. I would not say COP was above 1.5, but 50% reduction is still a reduction.

Had you been driving when you saw this?Can the heat pump outside element be gaining heat from the EV drive cooling system?

I don't think so. If I'm not wrong, Leaf kills coolant pump at freezubg temperatures. There is only one on newer models.
Motor-inverter are after condensers. If coolant is not circulating there is no heat in the coolant radiator. At all.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

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