[Atlant]

I'm cautiously optimistic my future EV (several still on order, including ID.4, now for the past 8 months) will be able to meet my expectations in this type of weather. We haven't had a particularly cold northeast winter in a while, but we already have had a stretch of <25F weather for the past few days. Late January into February usually brings a few week-long stretches of <0F. I'd love to have more sub-zero F (-20C and below) temperature data to put my mind at ease that this car won't be a mistake.

Driving my usual commute (1/2 time at ~75 MPH, 1/2 time at ~40 MPH), the initial Guess-O-Meter reading on my 2021 AWD Pro S is down to 151 miles in the mornings. This morning it was 21°F / -6°C in New Hampshire.

 

[Atlant]

Heatpump is crucial for keeping decent range in winter. VW ID.4s in this test were NOT equipped with a heatpump:

Winter & Cold Weather EV Range Loss in 7,000 Cars

The bad news is that all electric cars experience some degree of range loss in cold weather. The good news is that this range loss is temporary.

www.recurrentauto.com

When you're down below freezing, I'm not sure a heat pump helps.

What probably DOES help, at least a little, is to recycle the waste heat from the drive into the passenger compartment (assuming that there's any to spare after heating the battery). But the ID.4 doesn't do that, either.

 

[Atlant]

I wonder how much heat is really there to use. My cooling loop temperature always hovers slightly above ambient in the winter.

'Depends whether it's dumping all to the radiator or not, doesn't it?

 

[Atlant]

In the only plug-in passenger van in America (the Pacifica Hybrid), the coolant heater which warms the cabin also draws 5 kW from the battery. That's an interesting coincidence with the Buzz and ID.4. Must be some sort of calculated value?

FYI: The 2011-2016 Volts use the same 5KW value.

 

[Atlant]

One reason R744 is making a comeback. Heat pumps designed to operate down in the -20C range are dependent on R744 to get a useful COP at those temps.

Frost build up in the evaporator is still a problem and no refrigerant can beat Sadi Carnot.

 

[Atlant]

Not sure what you are getting at with the reference to Carnot. Heat pumps are not heat engines in the Carnot sense

Of course heat pumps are heat engines, they're just running in reverse. And I never claimed they violated thermodynamics, I was just (obliquely) making that point that pumping heat from a colder reservoir to a warmer reservoir takes more and more energy as the cold reservoir gets colder, just as Carnot predicts.

 

[Atlant]

COP of 1 at ultra cold temperatures is perfectly acceptable to me as well, but at those temperatures, a completely frozen evaporator would stop the heat transfer entirely, no?

Right! That's why heat pumps operating in the regime where their evaporators go below 32°F/0°C MUST have some way of defrosting their evaporator coils (whether its an external electric heater or briefly running in cooling mode or what-have-you). As you say, once the evaporator coil is full of frost, it's not going to acquire much heat from the air that can no longer pass through it.

 

[Atlant]

Several folks have told me that I'm wrong about waste heat from the electrical system not being able to be discharged into the passenger cabin of the ID.4.

I do not for a moment claim that I am never wrong, but I guess I do need further explanation.

Here's the diagram of the non-heat-pumped ID.4's battery and electric drive cooling system from MC-10186407-0001.pdf, the “Self Study Program 811213 The High-Voltage System in the ID.4”:

The only question is what is component 6, the “Heat Exchanger for Heat Condenser”? To what does that exchange heat?

Meanwhile, please note that there doesn't seem to be any direct path for waste heat from the drive electronics to reach the cabin air; the waste could warm the battery and any remaining heat in the battery exhaust coolant that isn't routed right back to the drive electronics could reach the mysterious component 6, but that's a pretty indirect path.

 

[Atlant]

If equipped with heat pump it will use #6 heat exchanger block for heat harvest from battery pack to assist in cabin heating.

Thank you for that clarification — That's EXACTLY the situation that I expected.

 

[Atlant]

#6 is heat exchanger block .....refrigerant to coolant ( heating or cooling if necessary)

Just to get this completely explicit:

So in a North American car without a heat pump, which portion of the Air Conditioning refrigerant loop is this heat exchanger dumping its heat into? (I'd assume a cool/cold part of the refrigerant loop?)

 

[Atlant]

It dumps any waste heat into the battery, nothing in AC loop. There is not much heat because the car is so efficient, so it rarely warms the battery above 50F if its <32F ambient. At a coolant temperature of 59°F (15°C) or higher the thermostat opens, allowing battery coolant to flow to the radiator (passive cooling). It starts using the AC loop to cool the battery at 86°F (during charging) or 95F when driving.

The picture doesn't show that, though, does it? It shows hot fluid entering this heat exchanger and cool fluid leaving it. (It also ignores the fact that the PTC Heater heats the fluid, but showing heating/cooling on the same diagram was probably viewed as too confusing).

BTW, my Volt has the exact same heat exchanger that @VW TECHNICIAN is describing and it's for exactly the same purpose: cooling the battery (and the drive electronics? I can't recall.) cooling loop in the summertime when its hard to reject heat to the ambient air via the radiator.