Is cabin heat "free" if a Prime is in HV mode?

For those of us who live in cold climates, driving without interior heat is not an option.
Nevertheless, heated seats and heated steering wheel are welcome.

 

Of course, it is not free if you turn on the A/C (heat pump), which uses a lot of electricity. But:

If you don’t turn on the A/C (heat pump), you can still get some heat from the heater core, which circulates engine coolant. Adjust the temperature to the desired heat. You can turn on the fan only without the A/C (heat pump) and still adjust the temperature. The fan alone should not use that much electricity.

I need to turn on the A/C (heat pump) occasionally in Southern California because the windshield fogs up. I then set it to DEF vents. It is more efficient than using the DEF button, which is much more aggressive and also activates the mirror defoggers.

 

Studies have shown that people who put up with cold weather regularly live longer and stay healthy longer... And yes it is true the ICE heat is the most efficient source of cabin heating costing less than pennies on the dollar via what you pay as mpg.

One thing that could change this is battery pack temperature optimization. The battery runs most efficient at very specific temperatures. And being able to monitor that temperature and how efficient the car manages it versus you needing to manage is significant. It may well be that lots of cabin heat in cold weather improves EV range in some scenarios.

On one end of the spectrum you have a Prime like yours living in a heated garage and plugged in. On the other end of the spectrum you have a Prime like yours living on the street with no home charging in sub-freezing temperatures.

 

I owe the fact that I am still alive to the fact that I have tried to eliminate all stress in my life. Endlessly fine-tuning settings and driving habits to extract maximum fuel economy is not my idea of reducing stress. I am happy to take the benefits of driving my car normally. I know I am reaping an enormous benefit just by owning a Prius.

 

I believe the Prime has a heat pump so it still uses electric in Hybrid node.That is my guess. Otherwise in EV mode the heat pump would need to heat up engine coolant too, which would be counter-productive,

 

I don't know whether the Prime does include a conventional heater core as well as the heat pump. For purposes of discussion, let's assume it does.

The question is still a bit more involved than you're making it. If you have an OBD-II device you can plug in and watch live data, you can watch the coolant temperature. Whenever that number exceeds the thermostat-opening temperature, you have "waste heat" and you can use some in the cabin for "free". It would be going out the radiator otherwise.

In even a regular hybrid, you can often find the engine running with the coolant temperature not above the thermostat-opening temperature. At those times, your cabin heat is not "free"; every joule of heat you're taking out has to be made up from gasoline to maintain the operating temp.

 

Yes, in hybrid mode with a warm engine, the cabin heat comes from engine waste heat.
The car will also turn on the engine for that heat when it isn't possible for the heat pump to provide the required heat, like with the defroster turned on.

 

Also in Sub-Zero °f - temperatures the ice will turn on to assist for defrosting

 

IMHO; it's a moot point. You've already paid for the equipment (sunk cost); why not use it? We are actually talking about pennies and yes they do add up over time; but you waste all that at the bar, coffee shop, or interest on your credit card debit anyways. I'm too old and crusty to be freezing my hiney off when there's a perfectly good heat source within arms reach.
This reminds me of my cheap friend that won't turn-on his AC because it burns a few more drops of gasoline; but he'll roll down the windows and create more drag on the highway instead. BTW; the AC unit was a $1K option that he paid for, on that old car when he bought it new. They are standard equipment now-a-days.

FWIW; my Prime seems to automatically fire the heat pump; w/o lighting up the AC button and you can't manually turn it OFF. I get heat out of the vents in manual mode, unless I crank the temp. setting down to Lo. Don't have a techstream to monitor this; just my observations. As stated earlier, on a gen4 - hitting the windscreen defroster option on the HVAC panel will fire the ICE to defrost the glass. That's also the quick and easy way to circulate the engine oil after a change.

YMMV

 

My response is based on an ordinary base hybrid model, not a prime.

In my car running heat can impose a substantial penalty because

Using heat may change a journey on which the engine would run 40% of the time to one in which it runs 70%. The swing I've noticed would be from high 50 miles per gallon to a flat 40mpg in single digit cold in stop and go traffic.

The tip someone here left me was to run heat but not at 68 or 70 - to keep it in the low 60s F.

This observation doesn't mean that the entire difference is attributable to the interior heat. The tires will also show a lower pressure and maybe the engine keeps kicking on because it isn't us to a reasonable running temp after being off for a few minutes in 5F weather.

 

Toyota PHEVs have an electric heat pump for HVAC to minimize running the engine. They may also have supplemental electric heat for cold temperatures.

 

The OP that originated this post has a PHEV, which has a heat pump setup.
In the single digit; IMHO you should be running your cabin heater. Your traction pack would benefit by the batteries getting closer to room temperatures; if it's still using cabin air to heat/cool the pack. I know the gen5 has moved some of those packs to the bottom of the car and being cooled by the AC refrigerant. Not sure about your non-PHEV.
ANY car running under those conditions WILL burn more gas. What are your ICE cars doing under those same conditions or BEV???? Adjusting your cabin heat might get you an additional mile per gallon, because you can't fight physics.

 

Not free, in most instances.
In a gasser, it is free because the engine is running all the time

 

Which is not the case for a Toyota hybrid or PHEV. For a Toyota hybrid, cabin heat lowers mpg more that running air conditioning in the summer, generally.

 

See my post above. The Prius Prime (Gen 4 and Gen 5) has an engine-coolant heater core. If you don’t turn on the A/C (heat pump), only the heater core will be used for heating in the HEV mode, and you can still use the temperature control. You can turn on the fan only and adjust the temperature control.

 

The A/C button in the PHEV does not select whether or not the heat pump is used in general.

It replicates the traditional user interface behaviour of specifying whether you want a heat pump to be used for cabin cooling and dehumidification.

The heat pump will be used for cabin heating or battery cooling regardless of the A/C button.

 

That's been my observations in a gen4 PHEV too.
Have you tried adjusting your temperature setting to Lo to terminate the heat pump operations. I'm curious if that will also work on the gen5? If you have duo zone climate control; I'm pretty sure you'll have to get both temp settings down to Lo. If it's too cold outside; the engine will kick ON anyways.

YMMV

 

I don't believe it wastes hot engine coolant when it's available. My car doesn't provide heat to the interior until the engine coolant warms up.