More details on heating - Kia Niro Forum
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post #1 of 43 (permalink) Old 12-13-2018, 12:53 AM Thread Starter
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More details on heating

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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post #2 of 43 (permalink) Old 12-13-2018, 08:43 AM
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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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post #3 of 43 (permalink) Old 12-13-2018, 09:57 AM
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Very interesting ! thanks for the info!
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post #4 of 43 (permalink) Old 12-13-2018, 01:24 PM
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Quote:
Originally Posted by brandent View Post
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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post #5 of 43 (permalink) Old 12-13-2018, 05:02 PM
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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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post #6 of 43 (permalink) Old 12-13-2018, 06:04 PM
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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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post #7 of 43 (permalink) Old 12-13-2018, 07:43 PM
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Originally Posted by yticolev View Post
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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post #8 of 43 (permalink) Old 12-13-2018, 08:21 PM
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The part exists.. https://kiaparts.penceauto.com/p/Kia...7192G2000.html

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post #9 of 43 (permalink) Old 12-13-2018, 10:06 PM
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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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post #10 of 43 (permalink) Old 12-13-2018, 10:08 PM
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Originally Posted by Roadkill401 View Post
very interesting!

Less than $100. I certainly would have been happy to pay an extra $100 for the capability.

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