Revisiting small 12v heater discussion

will do on sunday, you and me both!

 

Wasn't me. Been busy with solar panels on my roof.

 

Is everyone in this thread remembering that we've got about that much electric heat already built into our Prii?

The only official figures I've got are for my Gen 1, where all models have 330 watts of electric elements integrated into the heater core, and northern US/Canada models have an additional 330 watts (two more 165 watt elements) that live in the footwell duct. So that's a total of 660 watts of electric heat available (for comparison, when the coolant is up to temp, heat transfer from the heater core is rated 5300 watts). The electric elements switch on when (1) the coolant isn't up to temp, (2) the amplifier is requesting max heat, (3) the DC/DC converter says the power is available. The converter has its own dedicated signal circuit, IDH, it can use to tell the heater amplifier to drop the electric heat if too much power is needed elsewhere.

As for how much of a difference it makes, well, I've long been considering wiring in a couple LEDs just to see when these elements are on, 'cause in cold weather I sure couldn't say I feel 'em at all ... but probably I would feel colder longer if they weren't there.

I don't have the manuals or exact ratings for the later generations, but looking through the parts diagrams at Village Toyota, I can see that Gen 2 kept pretty much the same arrangement as Gen 1, with both the fancy liquid/electric heater core and the extra electric-only elements for some regions. With Gen 3, including the Plug-in, it seems they went back to a simple liquid-only heater core, but there is a separate electric-only element and in the picture it looks pretty big. Without a 2010 New Car Features Manual to look at, I can't say how many watts it is.

Wikipedia says a gallon of gas is worth about 33.3 kWh, so full use of the coolant-powered heater (5300 watts in Gen 1) is worth not quite a sixth of a gallon per hour.

I don't have heated seats or steering, but the cheap 40 watt blanket I bought a couple years ago at Menards is the greatest thing since sliced bread. In another thread I looked at how long it would be possible to stay cozy on one tank of gas (if stuck on the roadside, for example) compared to using the cabin heat.

-Chap

 

40 watt 12v blanket? i would be shocked if the pip had any electric heat, but as you say, you can't go by feel.

 

Prepare to be shocked: 87710-12020.

Anybody with a copy of the pip's New Car Features Manual can look up the wattage, but I'd guess it's somewhere in the 300 to 700 watt range, by comparison to what's in the Gen 1.

-Chap

 

Added to my shopping list for next winter. Thanks for the tip!

 

i can't even imagine. is there anyway for someone with a scanner to see the electrical usage? when exactly does this bad boy come on?

 

I get the feeling your EV range is going to shoot up from now on

 

Given the fact that the Prius engine must run at operating temp to function, and the fact that IC engines produce a lot of waste heat...

Why the hell would anyone be talking about 12V heat?

 

...while putt-putting down the road, about 10 minutes after startup.

• Chapman sits in his stationary car.
• My wife would like to feel warmer during the first ~ 10 minutes of driving while waiting for the ICE to warm up.
• Bisco probably wants to stay in EV during a cold, short commute

We all want to run the ICE less, or not at all.

 

It's a hybrid car, not an electric car after all, and that means it's designed to burn gasoline as efficiently as possible. To do this, the engine has to run. In doing so, heat is produced, which incurs no additional mileage penalty; in comparison to "12V heat" which would incur a higher penalty.

 

actually, on short trips for the pip, running the engine for heat is a waste of gas and only produces 30mpg or so. you're free to disagree of course, as we're free to drive all ev if our hearts so desire.

 

It's also designed to have significant intervals of burning no gasoline at all. During those intervals, if you have the heat on, the electric water pump is still circulating the coolant through the heater core and you are extracting heat from it. This measurably shortens the time for the coolant to drop below 60 C where the engine has to start again, so it isn't free.

Once started, the engine won't stop again until the coolant exceeds 70 C. (These temps are from my Gen 1, I don't know if the setpoints are different in later models.) That takes measurably longer when the heater core is extracting a few thousand watts of heat from the coolant, so it's not free then either.

What you're thinking is clear enough, but it might be based on older, less efficient engines that produce a lot of waste heat. The heat you steal for the cabin is 'free' if it is waste heat that would otherwise have to be dumped out the radiator in the front of the car. In the Prius, many of us are able to run a grille block from early fall well into late spring, and still never see the ScanGauge coolant temps even arrive at the thermostat opening temperature except on moderately long trips. The rest of the time, the game is just to get the engine up to operating temperature and keep it there. Bob Wilson has piles of graphs of the effect of heater operation on that short-trip and warm-up efficiency.

So I guess we're talking about 12 V heat partly because it doesn't seem to be common knowledge that Toyota already built some into the car, and partly because it's interesting how comfortable you can stay with under a hundred watts of heat placed where it's needed, as opposed to a few thousand watts to heat the air in the cabin.

-Chap

 

It's a mistake to think that further gains can come from running the engine less. That would be true, only if the the operating temperature could be maintained for a longer time, but that would require re-engineering. It's also necessary when the battery level drops below a threshold, and the only way to restore the voltage level is to run the engine.

Expecting the engine to run less to "save fuel" is a bit like expecting a cow to produce milk more efficiently by eating less.

 

How's this for "smug":
Who else has managed to engineer a better hybrid in the world today, which delivers the greatest number of overall benefits across the board?

If you are that "engineer" please step forward, otherwise accept the Prius as the current state-of-the-art.

 

LOL.

There are good reasons why Greg is a climate change denialist.

 

That's an idiotic statement. I made it abundantly clear that the problem with the debate was it's dysfunctionality. You are living proof.

I'm denying nothing. Massive denial being practiced by the both opposing parties in the climate debate.

 

I'm not following your math ... could you show a few more of the details you're skipping?

Just as the car is currently engineered, a person can easily watch the coolant temperature and battery state of charge, and see at what levels the engine will start and stop to maintain each. A ScanGauge is all it takes.

With just that much instrumentation, a person can then change various parameters in the situation, the heater settings for example, and observe the results. That's been done in this thread and various others.

It's possible that the question you are focusing on is whether there would be an efficiency gain by replacing the coolant-based heater core with an equivalent capacity (ca. 5300 watt) electric heater. When that's the question, your instinct is quite right - the power to the electric element includes all the conversion losses through MG1, inverter, into battery, out of battery, DC/DC, etc. No way to come out ahead.

But I don't think that's the question of interest to others in this conversation. Toyota already builds into the car an electric heater, but only of around 600 watt capacity, roughly one order of magnitude less than the coolant-based heater. They don't use it to replace the main heater, but to cover certain operating conditions where engine heat is less available or better used for other things. It's also interesting that if you put some electric heat where it's needed, on the driver's body, you can have comfort with more like 60 watts of heat, or two orders of magnitude less than the main heater. Sure, those 60 watts still have to go through all those stages of conversion loss, but if you're achieving comfort with a factor of 100 less power, you've got some room for that in your budget.

Now granted, as soon as you're cruising on the highway or a moderately long trip, the coolant is up to thermostat-opening temperature and the engine is running for other reasons than to keep it there, at that point your heat from the coolant is arguably free. But those aren't the only circumstances Prii get used in.

I'm pretty much with you there - I'm pretty impressed with Toyota's design, and I figure I can probably even learn something from why they included electric heat in it.

-Chap