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Discussion Starter #1
Well in the great white north winter has come. Lots of people talking about the horror of the engine firing up to create heat. Ah but in trying to get to the bottom of just how this works, I discovered a couple little nuggets.

How does heat get created? 3 ways.
1. Well obviously the engine fires up and heats up the coolant which goes through the heater core which is basically just a radiator by the firewall right? OK check. Runs at a steady RPM (about 2000) to maximize efficiency of the engine while putting out enough heat to matter. Even runs at stop lights. During this process you are recovering energy through electricity generation (it charges the batter) as well as waste heat of course.
2. I think effectively every new car has this but it's still a big deal. New cars heat up really quickly. One reason is that there's a exhaust heat exchanger. The coolant loop goes into a heat exchanger that is mounted around the exhaust pipe where it comes down off the engine. i.e. again a radiator. The hot exhaust is transferring heat into the coolant loop. So this accelerates warm up considerably and again increases overall efficiency of the total process.
3. Ah...but here's the hidden nugget. I didn't know this. There's a THIRD heat source. There is a resistive electric heater mounted on the out port of the cabin heater. It heats the air coming out of the heater after the air has gone through the heater core and before entering the cabin. It's an electrical 'boost' heater called a PTC (Positive Temperature Coefficient...i.e. resistive heater). Apparently Prius has one too as do many small engine cars not just EVs. Used where the engines are so efficient they don't generate enough heat to heat the car. Power? Well looking at the fuse and parts diagrams there appears to be 2, 50 amp relays. Seems like that translates on 12v to roughly 1 kw....I'm not that familiar with how it operates though...someone correct my power assumption. Certainly smaller than the cabin heater on a pure EV but nonetheless indeed there is partial electric heating of the cabin. And this is why the engine won't kick on until the coolant cools off to about 130F (can't remember where I read but it was 55C...maybe it was even 55F). The booster heater can add to the water heat sufficiently until that point apparently.
 

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I've seen some diagrams that appear to show a PTC in the Niro (and Ioniq). No one has been able to find that it is using voltage, or that it is actually producing heat. If it did, all those PHEV owners would not be complaining so much.
 

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Well in the great white north winter has come. Lots of people talking about the horror of the engine firing up to create heat. Ah but in trying to get to the bottom of just how this works, I discovered a couple little nuggets.

How does heat get created? 3 ways.
1. Well obviously the engine fires up and heats up the coolant which goes through the heater core which is basically just a radiator by the firewall right? OK check. Runs at a steady RPM (about 2000) to maximize efficiency of the engine while putting out enough heat to matter. Even runs at stop lights. During this process you are recovering energy through electricity generation (it charges the batter) as well as waste heat of course.
2. I think effectively every new car has this but it's still a big deal. New cars heat up really quickly. One reason is that there's a exhaust heat exchanger. The coolant loop goes into a heat exchanger that is mounted around the exhaust pipe where it comes down off the engine. i.e. again a radiator. The hot exhaust is transferring heat into the coolant loop. So this accelerates warm up considerably and again increases overall efficiency of the total process.
3. Ah...but here's the hidden nugget. I didn't know this. There's a THIRD heat source. There is a resistive electric heater mounted on the out port of the cabin heater. It heats the air coming out of the heater after the air has gone through the heater core and before entering the cabin. It's an electrical 'boost' heater called a PTC (Positive Temperature Coefficient...i.e. resistive heater). Apparently Prius has one too as do many small engine cars not just EVs. Used where the engines are so efficient they don't generate enough heat to heat the car. Power? Well looking at the fuse and parts diagrams there appears to be 2, 50 amp relays. Seems like that translates on 12v to roughly 1 kw....I'm not that familiar with how it operates though...someone correct my power assumption. Certainly smaller than the cabin heater on a pure EV but nonetheless indeed there is partial electric heating of the cabin. And this is why the engine won't kick on until the coolant cools off to about 130F (can't remember where I read but it was 55C...maybe it was even 55F). The booster heater can add to the water heat sufficiently until that point apparently.
I have a US spec PHEV and there is no resistive heater. How do I know this? It takes about 3 min before any heat can be felt. This observation is not consistent with the existence of a resistive heater which would get hot in a matter of seconds.
 

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There is a large difference in a PTC heater and one such as a pure EV might have. The PTC is very small in comparison. The diagrams I saw were for the HEV, but if it really has it, it would be found on the PHEV too.
 

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If my PHEV has a PTC heater, it certainly isn't doing much.


1) My engine always turns on ANY time that the engine coolant is cold and the heater is on, even if the climate control is set to a temp barely warmer than ambient temp.


2) The vents do not blow warm air until the engine coolant is warm.


3) The temperature of the air coming out of my vents almost always exactly correlates with the coolant temperature indicated on my dashboard display. There is never a time where the vents blow warm air and the engine coolant is cold, it seems to be physically impossible.


4) The engine only shuts off while the heater is running if the coolant reaches normal running temp. But then it immediately kicks back on once the coolant temp drops.



If anything, a PTC heater (if it exists) is nothing more than a mild "booster" for the heat coming out of the vents, increasing the temperature by maybe a barely noticeable 5 degrees F, at most.


All that said, I'm not one of the people complaining about it. The effect on my MPG has been negligible. I'm still getting 45mpg in HEV mode on average, with 80 miles of daily driving. Since I do plug it in every night, I'm getting more like 60-65mpg when using combined EV/HEV modes, even with the engine doing its thing to keep my cabin warm. That's not much different than what I was getting during the summer and fall.
 

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There is a large difference in a PTC heater and one such as a pure EV might have. The PTC is very small in comparison. The diagrams I saw were for the HEV, but if it really has it, it would be found on the PHEV too.
since I see no evidence of a resistive heater in the us spec PHEV then, by your reasoning, there is none in the HEV either.

do you have any evidence?
 

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Pictures are all the evidence I have. Of course they make the heating completely different in different models. My logic is completely flawed.
 

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Now that it's gotten cold I can say that I agree that there is no electric cabin heater in my EX Premium PHEV Niro.

My last car had an auxiliary electric cabin heater (2010 VW Golf TDI) since it took so long for the diesel engine to warm up in cold weather and it was quite obvious when it was working. You could actually hear the relay closing when you turned it on. In the Golf it was a 1KW heater which means that it could draw up to 80A! :eek: When it turned on the ECU actually raised the idle RPM to provide the required current.

It was nice on really cold mornings. The diesel was so efficient that it could take 10-15 minutes of steady driving to get the engine warm enough to provide cabin heat. In really cold weather the engine temp would actually drop at stoplight. Too bad it was a big cheater, I loved that car. >:)

TL;DR, if your Niro had one, you would know it. :D
 

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Conjecture:

The PHEV alone can accept an external charge. If the PHEV is outside in very cold conditions then a high charge rate and a very cold battery is a problem. The non PHEV HEV doesn't have to draw any more power than to start the engine the engine heat ( ICE's are only 20% efficient so 80% is just waste heat) can then be used to heat the battery prior to charging it from either regen or the ICE.
The PHEV battery alone is vulnerable to being charged when cold so a resistive heater is probably solely for the battery when being externally charged.
 

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Discussion Starter #15
Hey guys...I didn't say it somehow operated instead of but rather in assistance of the heater. It is clearly not as strong as say something that was trying to be a full on cabin heater. It is in the manual and it is in the parts diagrams. Period. Now if you use hte Prius as an example that PTC is a booster to the main heat which of course comes from the coolant. Presumably this functions exactly the same way. Now for those who say 'it takes 3 minutes to throw heat'. Holy crap, a regular ice vehicle takes 10. How exactly is this super efficient engine which by definition is making less fire than a regular ice somehow heats up quicker? Simple. Via the 3 mechanisms I describe. The other morning it was 5F. Neither the engine, the exhaust, or ANY heater is going to get up to speed in less than 3 minutes.

So then:
1. It doesn't exist because I didn't look and haven't read the manuals.....is not logic.
2. It doesn't exist because I have to wait x minutes.....is not logic. Almost certainly the assist feature will NOT kick in until the coolant reaches some minimum temp via the other two means which would be operationally different then a resistive heater only.

So during that time when the engine is running at 2000 rpm accelerating the heatup as compared to an ice, the heater exchanger on the exhaust is also adding heat (after a minute or two of course), then when the coolant temp gets to a threshold (lower than normal ice heater threshold but not super cold...somewhere it says 55 degrees but I can't find that just now) the resistive assist kicks in. Thus the 2000 rpm engine turning chargine the battery is coming back to some degree via the electric assist. The total efficiency of that system is going to be substantially higher than a regular ice.
 

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Discussion Starter #16
Now that it's gotten cold I can say that I agree that there is no electric cabin heater in my EX Premium PHEV Niro.

My last car had an auxiliary electric cabin heater (2010 VW Golf TDI) since it took so long for the diesel engine to warm up in cold weather and it was quite obvious when it was working. You could actually hear the relay closing when you turned it on. In the Golf it was a 1KW heater which means that it could draw up to 80A! :eek: When it turned on the ECU actually raised the idle RPM to provide the required current.

It was nice on really cold mornings. The diesel was so efficient that it could take 10-15 minutes of steady driving to get the engine warm enough to provide cabin heat. In really cold weather the engine temp would actually drop at stoplight. Too bad it was a big cheater, I loved that car. >:)

TL;DR, if your Niro had one, you would know it. :D
That's exactly how this one works.
 

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That's exactly how this one works.
Well, if it is indeed installed it either doesn't do what we think it should do or it doesn't do it very well. In the Golf the aux heat turned on immediately to provide some (not much admittedly) heat to the cabin on startup.

What would be the point of waiting for the engine coolant to warm up to some level before turning on the PTC heater?

The Owner's Manual lists not one but two 50A relays for the PTC. This implies that the heater is approximately the same size as the one in the Golf (1kW). For all that I don't notice much effect.
 

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"Efficiency and emissions are further improved via the Niro’s exhaust heat recovery system, which speeds engine warm-up by routing coolant to a heat exchanger in the exhaust system. "

https://www.kiamedia.com/us/en/media/pressreleases/11952/2017-niro-overview

I think this is consistent with the ~3 min time to heat I observe. Faster than your typical ICE but much slower than a resistance heater.
 

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Discussion Starter #19
Basically all hybrids have one it turns out, but it may not be obvious. Yes the TDIs in VW also added one but not awhile back...they were notorious for not enough heat as they were too efficient. All diesels suffer from that. Here's how one functions by the way.

PTC heater for electric and hybrid vehicles allows for dual temp zones | eeNews Automotive

When it's cold the resistance is low and the power pull is high. As the heater core gets warmer, the resistance increases and the power pull/boost of the ptc decreases.

In the PHEV, Niro the engine shuts down once the water is hot. The heater continues to operate and then once that water temp his threshold (again 55 degrees..can't find it right now but that might be C not F) the engine kicks back on. The ptc would be varying pull throughout that temp swing.

One other little note I found? The block temperature is held at a hotter temp than the head. The engine has a separation ability on water flow.
 

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In my experience, there is some heat after 4 minutes. However, I don't turn climate on before that (and often wait 6 minutes) as I don't like being blasted by cold air. Temperature is defaulted to high, but it would be silly for the PTC heater to be using battery power when there is no call for heat with climate off.
 
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