[doug]

http://opel-ampera.com/wp_en/2012/02/16/on-board-cogeneration-of-electricity-and-heat/

This Ampera (Volt) blog post got me wondering how the Karma is dealing with waste heat from the engine. Does the Karma use it to heat the cabin or the batteries?

 

[SoCalGuy]

Good question...

 

[Nimisys]

The ICE is on its own cooling system (High temp) from the rest of the other cooling systems (low temp for the motors/inverter and the battery has it's own loop) and supplies the coolant for the heater core. there is a seperate PTC High Voltage heater to warm the coolant and electric pump to circulate coolant into the HVAC heater when the ICE is shutoff and the coolant cold.

 

[Sigurd]

I have noticed that when driving in stealth mode there is a little cold air (when it's in the 30s outside) coming in through the vents. I use my seat heater to keep my butt toasty. But when I go into sport mode and the engine is warm, the air turnes warm. All this with the climate control system off. So, my guess is that there is a little air being forced through the system as I'm driving and recirculation is not engaged and this air is ambient temperature unless waste heat from the ICE warms it.
Cheers,

 

[Fabulist]

I have noticed that when driving in stealth mode there is a little cold air (when it's in the 30s outside) coming in through the vents. I use my seat heater to keep my butt toasty. But when I go into sport mode and the engine is warm, the air turnes warm. All this with the climate control system off. So, my guess is that there is a little air being forced through the system as I'm driving and recirculation is not engaged and this air is ambient temperature unless waste heat from the ICE warms it.
Cheers,

I posted a question about this on this thread, and everyone was convinced that I had my climate control system on and just did not realize it. It's good to know other people have experienced the same thing. I think the ambient air that is drawn into the cabin is getting warmed up somehow by the ICE waste heat.

-- Fab.

 

[ct-fiskerbuzz]

I have noticed that when driving in stealth mode there is a little cold air (when it's in the 30s outside) coming in through the vents. I use my seat heater to keep my butt toasty. But when I go into sport mode and the engine is warm, the air turnes warm. All this with the climate control system off. So, my guess is that there is a little air being forced through the system as I'm driving and recirculation is not engaged and this air is ambient temperature unless waste heat from the ICE warms it.
Cheers,

I've always observed a little bit of outside air gets forced into the cabin even with everything turned off, in every car I've owned. It's speed-dependent, so there is more outside-air "leakage" at 70 mph than at 30.

In my existing cars (which have all had slider controls for outside vs recirc) you can slide over to recirc to avoid the leakage, or (assuming the engine is warm and you want heat rather than A/C) adjust the temperature knob.

Diagnosis: perfectly normal, but harder to control in an electric car and/or one with fancy cabin-temperature settings (including separate driver and passenger temperatures).

 

[doug]

there is a seperate PTC High Voltage heater to warm the coolant and electric pump to circulate coolant into the HVAC heater when the ICE is shutoff and the coolant cold.

Wait. Are you saying to heat the cabin electrically, they heat the coolant in the heater core, not the air directly?

 

[kabalah70]

That is what I understood which seems efficient from a weight and space perspective, but not from any other perspective. It would seem to me to be more efficient that they would use the inverter loop since those would always be producing heat that needs disapated. Just my two cents.

 

[doug]

The inverter cooling loop likely doesn't produce enough heat to adequately heat the cabin.

I would think they'd just put a resistive heating element in the same air path between the heater core and the cabin. It doesn't make sense to me to be electrically heating the water in the heater core. One, it's a waste of energy. And two, you'd have to overcome the thermal inertia of the heater core before you start blowing warm air, instead of the almost instant warm air you get from heating the air directly.

So I guess they're not using a heat pump either.

 

[Nimisys]

there is a seperate PTC High Voltage heater to warm the coolant and electric pump to circulate coolant into the HVAC heater when the ICE is shutoff and the coolant cold.

Wait. Are you saying to heat the cabin electrically, they heat the coolant in the heater core, not the air directly?

Just about EVERY automotive HVAC heater ( i honestly can't think of any production exceptions) uses a coolant fed heater core that the cabin air is blown across.

The inverter (low temp) loop can not exceed 150F, which means for effective cabin heat, you would need to be running your inverters and motors at the upper end of their thermal limits, which would be a bad thing. The ICE on the otherhand is quite happy in the 190-220F range, which is why the heater works soo much better when the ICE is running.

Heater cores have had decades worth of engineering at this point, not to mention the coolant does a decent job of holding the heat (a prius can hold its coolant above 150f for 48 hours in an insulated thermas), where a resistive heater will require a continual electrical current.

 

[ct-fiskerbuzz]

Just about EVERY automotive HVAC heater ( i honestly can't think of any production exceptions) uses a coolant fed heater core that the cabin air is blown across.

The obvious place to look for exceptions is in pure-battery cars. What does the Leaf use, and what will Tesla be using in the Model S? (I'd add the Think City here but it's pretty close to zero on other creature comforts so I'm not sure they put much work into cabin heating. :dodgy Nissan's FAQ just says that they use resistance heating, without going into any specifics.

 

[Don A]

there is a seperate PTC High Voltage heater to warm the coolant and electric pump to circulate coolant into the HVAC heater when the ICE is shutoff and the coolant cold.

Wait. Are you saying to heat the cabin electrically, they heat the coolant in the heater core, not the air directly?

From what I have read this is the same approach that is used by the Volt / Ampera

 

[Nimisys]

Just about EVERY automotive HVAC heater ( i honestly can't think of any production exceptions) uses a coolant fed heater core that the cabin air is blown across.

The obvious place to look for exceptions is in pure-battery cars. What does the Leaf use, and what will Tesla be using in the Model S? (I'd add the Think City here but it's pretty close to zero on other creature comforts so I'm not sure they put much work into cabin heating. :dodgy Nissan's FAQ just says that they use resistance heating, without going into any specifics.

Currently, the LEAF, the Tesla Roadster, and the MiEV all use a heater core with a seperate circulating coolant pump and PTC resistance heater to warm the coolant. The Ampera/Volt (as well every other GM Hyrbid) all combine the ICE coolant and PTC as well for cabin heat.

 

[doug]

Well I guess the question would be what's the heat capacity of the heater core. As long as can be isolated from the rest of the engine, I guess that's reasonable. Some thermal inertia makes it easier to regulate the temperature.

 

[ct-fiskerbuzz]

Well I guess the question would be what's the heat capacity of the heater core. As long as can be isolated from the rest of the engine, I guess that's reasonable. Some thermal inertia makes it easier to regulate the temperature.

Same principle as oil-filled space heaters: more thermal mass = better temperature regulation.

(In the case of fluid-cooled engines, you also get "free" heat, of course. In the Karma, that means when in Sport or range-extending modes.)