Waste Heat

Strictly speaking there should be no "Waste heat" period. Certainly not in cold weather. We have been using energy so inefficiently for so long, engineers are hard pressed to think creatively outside of that box.

I think resale undermining been bad for the EV integration of the market by most automakers. I know people that I talk to are reluctant to take the plunge for a number of reasons, not the least of which is resale value insecurity. The current situation is surely casting that anxiety in stone for the next decade.

Aerowhatt

Aerowhatt said:

Strictly speaking there should be no "Waste heat" period. Certainly not in cold weather. We have been using energy so inefficiently for so long, engineers are hard pressed to think creatively outside of that box.
Aerowhatt

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Of course there is waste heat, just not nearly as much as with an engine. Here is an actual performance curve from an EV motor/inverter combo- just not our particular motor/inverter.



Generously assuming that we spend an entire drive in the efficiency sweet spot around 85% (usually it is worse), discharging 10 kWh over 30 minutes (highway driving) would yield motor and inverter losses of 1.5 kWh. That's a lot of waste heat, equivalent to running two ceramic space heaters continuously. Use that 1.5 Kwh in a heat pump, and we could make up to 6 kWh worth of heat.

jray3 said:

Generously assuming that we spend an entire drive in the efficiency sweet spot around 85% (usually it is worse), discharging 10 kWh over 30 minutes (highway driving) would yield motor and inverter losses of 1.5 kWh. That's a lot of waste heat, equivalent to running two ceramic space heaters continuously. Use that 1.5 Kwh in a heat pump, and we could make up to 6 kWh worth of heat.

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Absolutely, but even our terminology is wrong headed. It shouldn't be called "waste heat" to begin with. It's a resource (or should be). Add a phase change heat storage cell (Lighter and smaller than any other way) and the driver and occupants can use this heat reserve at their discretion without ever needing to dump it to the surrounding environment. Properly designed it could hold enough heat from your drive to work to heat the cabin during the beginning of the drive home. Preheat the cell from the grid before leaving and no significant climate control range hit would exist in most winter driving

Aerowhatt

Perhaps the posts relating to recovering heat from the coolant loop in both this thread and the thread solutions for windshield fogging should be merged into a new thread?

I've been working on adding a system into the car that can recover the heat and be used in the heater core, but also allow the stock heater to function.

https://www.dropbox.com/s/5zbpq49l9j7akt9/i-MiEV%20waste%20heat%20recovery%20-%20V2.png?dl=0

The secondary reservoir (top right blue box) could be any size, but the less coolant there is, the easier it is for the motor and charger to warm it up to temperature, but a large reservoir allows for a lot of thermal storage and enables the ability to use a roof-mounted solar panel to heat the reservoir while parked during the day. Also, a thermoelectric unit could be used to transfer heat from the coolant loop to the heater loop to achieve warmer cabin temperatures.

PV1 said:

Perhaps the posts relating to recovering heat from the coolant loop in both this thread and the thread solutions for windshield fogging should be merged into a new thread?

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Leaving the windshield fogging thread alone and simply created this one. Boy, the discussion sure got OT from pricing :!: :evil:

The sad thing is, a few other threads went off topic faster than this one. The problem stems from the mind's traveling thoughts. If we stayed 100% on topic and didn't skew on any tangents, most threads may only be 2 or 3 posts. We got onto this by discussing the incorrect feature listed about electric compressor heating being mentioned as a new feature for 2014, which turned out to be the same electric resistance heat found in the 2012.

Anyway, yesterday, the coolant loop was able to warm up to 15° F above 20° F ambient at 40-50 mph speeds, non-highway.

As for what we call it, right now it is waste heat since it is not utilized. If someone finds an effective way to utilize this extra thermal energy, then it won't be waste heat anymore. It'll be a "Rotary Cabin Heater" .

The simple act of insulating some of the piping surely helps. I wonder why Mitsubishi didn't do that?

JoeS said:

The simple act of insulating some of the piping surely helps. I wonder why Mitsubishi didn't do that?

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That is a must do if it still comes with resistance heating.

What these cars need is a water source heat pump (as someone else mentioned before) Specifically though it needs to use the system cooling water as the heat source. Much like an ICE keeps the coolant in the engine and cabin heater core bypassing the trip to the radiator until the cooling fluid gets to a certain temperature threshold. So in this system the coolant would skip the radiator until the heat pump (putting heat in the cabin) couldn't cool it fast enough alone. Just recirculating from the heat pump cooling coil to the inverter/motor and back again.

So the first question that comes to mind is why have a heat pump at all. Well, Because we don't have the massive heat dumped from an ICE to work with in an EV. Cars are like heating a greenhouse at night. The temps that the coolant water reaches (provided by the good work of members here) is not in the range needed to heat the cabin. The coolant in an ICE heater core is nearly 200F. So with a much lower input coolant temperature in an EV you need the heat pump to raise that temperature. That gets us into providing good cabin heating using about the power that the AC does (actually less most of the time). And using the coolant water from the other systems negates the low temperature source inefficiency inherent in heat pumps. Also now the energy draw to preheat the cabin is low enough to be effective at the 120 volt charging rate. At the beginning of a commute, or in extreme conditions the cabin heat would be refrigerating the coolant for the inverter/motor. That's fine though because both run incrementally more efficiently cold. Done right this system would take up less room than the current power hungry set up.

Aerowhatt

I keep giving some thought to this and try to design a workable solution. Thanks to new functionality introduced with CaniOn 135, we can see what the temperature of the electric heater is. With the temperature knob in the first red position, the heater maintains a temperature between 93 and 100 F, which is enough to keep the cabin warm after a pre-heat.

With a servo controlling flow to the radiator or bypassing it, there should be little problem in getting the coolant up to and maintaining 90 F, as the heater core is considerably smaller than the radiator. I'm at the point now where I'm trying to figure out how to plumb a heat recovery circuit. Simply connecting the front and rear reservoirs to the same loop will cause coolant to overflow if the car is pointed up or down hill. Having a quart-sized reservoir down low in the car with no refill cap should fix this problem, as the rear reservoir would be the highest point in the system almost regardless of vehicle tilt. An Arduino could control the two servos needed based on temperature and other sensor inputs.

Even if this only accomplishes a coolant temperature of 60 F, that would sure beat 10 F air coming in .

Keep checking back to the drawing below, as I will periodically improve the design.
https://www.dropbox.com/s/118fp8nz047qeyx/i-MiEV%20waste%20heat%20recovery%20-%20V3.png?dl=0

I think that before anything can be done in that direction we need to know what the temp of the coolant coming from the motor/inverter under normal operation. I've been meaning to place a remote sensor on the incoming line to the radiator to see what that is. Soon, I will be actually get it done. Perhaps a heat exchanger (water to water) taking the return water from the heater core and getting a boost on the way back to the electric heating unit from the hottest motor coolant headed forward. In most cases (if the motor coolant is warm enough (warmer than the heater core return water)) it would reduce the run time of the cabin heating element. Save power and use some of the waste heat for cabin comfort.

I'm afraid the motor coolant isn't hot enough to do much in the winter though. Heck I never heard the radiator fan run during the summer except when the AC was on. That's not a good indication of what might or might not be available. Perhaps a simple bypass up front where there is room to work, which skipped the radiator unless the coolant got nice and toasty would give enough supplement to make a difference?

Aerowhatt

I did a direct measurement on the hose leaving the motor. I taped a sensor to it and wrapped it with some thin insulation. With 29 F outside air at an average speed of 45 MPH on level roads, the coolant reached 41 F. On the highway with less than 20 F ambient (I can't remember the exact temperature), the coolant loop reached over 80 F. This is with full and normal flow to the radiator.

During our drive yesterday with 75 F outside air, the loop was over 130 F.

I like your approach, too. Using the coolant loop to pre-heat the coolant before it reaches the heater would work, too, except for one thing. If you have the heater on a higher temperature, you'll end up using more energy as it will try to heat the motor. According to CaniOn, the return temperature is only a few degrees below the output.

The diagram I posted includes provisions for using the electric heater as well. Once the Arduino controller senses that the forward reservoir is 2 F warmer than the coolant supply, it will flip the bypass valve so that the heated coolant doesn't flow to the motor or radiator. It will continue to moderate the coolant loop's temperature so that heat recovery operation can resume once the electric heater is turned off.

Either way, the radiator definitely has to have a bypass for this to work.

**Update***

After looking at the pictures I took of the underside of the car with the battery removed, the motor coolant pipes run next to the electric heater on their way to the radiator. There is also a cavity in front of the heater, which looks like a good location for the diverter (more correct term) valves and reservoir. The very short run between the heater and reservoir is also a benefit, as there would be less stranded heat after running the electric heater. The separate pump in my diagram would continue to circulate coolant from the front reservoir to the heater core.

OK. Just did an 18 mile drive home in 45 F outside air. According to my phone, the cabin temp was 59 F (but I don't believe it, probably closer to 50 F). At the end of the drive, the charger temperature (from OVMS, which reads the CAN bus) was 64 F and motor was 88 F. The last ten miles was mostly level road at 50 MPH. The first 8 miles was somewhat hilly, but at 35 MPH or less. The car sat outside all day in the shade, unplugged.

Of all the measurements I've taken, the coolant has been consistently 40 F above ambient temperature, sometimes higher in the city or in traffic.

Had to run the heat this morning. It was 30 F outside. I pre-heated to get the ice off the windshield, but did run the heater on the lowest temperature setting (1 click into the red) with the fan on medium/high. This was enough to keep the cabin comfortable with only a hooded sweater on over my shirt.

According to CaniOn, the coolant leaving the heater was at 90 F, and the return was 86 F. Over the 11.2 mile drive, I ran the heater for 7 miles. The summary usage was 2,382 Wh and the heater used 361 Wh. The heater used 18% of the total energy (not including regen, this was Wh out values only). Regen returned 432 Wh. If the motor is 85% efficient, it alone would produce enough thermal energy to provide similar heat to the heater on low. Of course, faster or more hilly driving would produce more heat as more total energy is consumed for propulsion, plus increased regen for hilly driving. Dumping heat through the radiator to ambient air, the motor coolant loop still reached 50 F, 20 degrees above ambient.

With properly timed charging, the charger alone could bring the entire loop up to 30 F above ambient (45 F ambient, charger and motor reporting 75 F in my case), which would allow the motor to bring the loop up to temperature even faster.

This method of heat recovery would provide the most benefit to those driving on the highway.

Now that almost a year has passed and I haven't done a thing with this, I just started thinking about it again the other morning.

After crawling under the car a few months ago to try to get a picture of the A/C compressor bracket, I noticed that there is a sizable void in front of the heater that is accessible even with all shielding in place. It should be quite easy to build the diversion equipment onto a frame and bolt it into place. I plan to get the car on a lift for rust removal and rustproofing before winter hits, so that may be the prime time to install the waste heat recovery system. I just ordered a Raspberry Pi for another project, but if it works well for that, I may use one to control this project (unless an Arduino is a better unit for driving servos).

Here is a more up to date drawing of what I have in mind:
https://www.dropbox.com/s/118fp8nz047qeyx/i-MiEV%20waste%20heat%20recovery%20-%20V3.png?dl=0

Thanks for sharing PV1.

Do you have photos of your installation?
From the dropbox link I see your diagram.

I am inspired to see how you have connected the loop to the heater core. Would this allow the use of only the fan without activating the A/C so the coolant heat would be used in the cabin?

I'm much interested in knowing more about experience using the heat from the power unitd.

I'm still in the design phase and haven't purchased or installed anything. I've done measurements through OVMS, CaniOn, and directly using thermometers, and am convinced that I should be able to at least get heat equivalent to the first click into the red on the HVAC controls.

Operating criteria I'm aiming to have:
1. Fan only operation with recovered heat (recovered heat will warm the cabin without the electric heater and with only the fan on).
2. Automatic heat recovery bypass when the cabin heater is turned on.
3. Automatic system bypass during Summer (system reverts the loop back to factory routing).
4. Automatic startup/shutdown with cabin fan.
5. Full-time, automatic temperature control of the coolant loop during Winter (dynamically send coolant to the radiator to prevent overheating).

I've arbitrarily set 60 F as the switchover between Winter mode and Summer mode. In Winter mode, the system makes coolant available to use for cabin heating, and will send coolant to the radiator if/as needed to prevent overheating (limits coolant loop to 100 F). In Summer mode, the system sends all motor coolant to the radiator and separates the coolant and heating circuits.

A side benefit is that one can use waste charger heat while level 2 charging (which can only normally be achieved by using the MiEV remote), since the car won't allow heater or A/C use while plugged in. Granted, this won't amount to much heat at all, but it's better than nothing when sitting at a lonely level 2 charger in the middle of the night (been there, done that...twice).

Appreciate your detailed sharing.

From your design I get the understanding you will flow the coolant through the A/C heater core. Did I get this right? (I have yet to get a complete overview of the components to involve just yet).
Are you sure you can mix the coolant from the charger, mcu and engine with the coolant running in the A/C heater core. Is it the same type of fluid?

I'm inspired by your approach and am curious how this would be possible to install.
I would much like to find a way to adjust the activation of the HV A/C heater so this only activates if pressing on a manual switch for extra heating. Of course QC will still need the A/C to cool the battery.
I pretty much only use the A/C to get the front windscreen clear in wet weather which is the season.

The cabin heating and motor cooling circuits meet and mix in a tank that'll be installed under the car. From here, a new pump will pump coolant to the heater core (the pump that currently does this will be used to pump coolant through the electric heater only). Yes, both circuits use the same coolant.

The way I have this designed, the car has no knowledge that the two circuits would now be one. The HVAC system would function just as it does now (so it doesn't interfere with QC cooling). I would install a switch to detect the position of the heater damper, which either directs air through the heater core or bypasses it. The system would only pump coolant through the heater core when both the cabin fan is on and this damper is directing air through the heater core.

So, to use recovered heat to warm the cabin, simply turning the fan on and leaving the temperature knob on the green dot should be sufficient. If there isn't enough heat in the coolant loop (or you want a boost), you simply turn the temperature knob up into the red to activate the electric heater and the HR (heat recovery) system will automatically separate the heating and cooling circuits while the electric heater is on, making it function just as the car does from the factory. When you want to switch back to recovered heat, leave the fan on and turn the temperature knob back down to the green dot (being careful not to accidentally click into the Blue portion. If you do, simply turn back into red, then to the green dot). The circuits will stay separate until the mixing tank falls back to the temperature of the coolant loop, and at that point, the two circuits will become one again.

The only caveat I'm aware of right now is that the front reservoir can't be used, as using two vented tanks would result in losing coolant. The coolant reservoir in the back of the car is vented, so the one that will be installed under the car must be ventless and must be below the vented tank (which being under the car, it would be).

This is very very interesting - From the moment i realised that there where to separate cooling systems i thought of some thing similar -

Do you know how the "Fansystem works" --

Is the air intake always thru the radiator no mather where the dial is cool/green/hot - or is there a motorised damper that changes the airflow around the radiator acording to the setting of the dial?

I first thought of this beacuse if I install a webasto heater (that turns on the fan) i need to know if the heater dial would have to be in the red zone to divert air thru the hot radiator ...


IF air always go thru the radiator the webasto install is easy - if it doesent the engine coolant should be easy - just always let it thru the radiator

It really really amazes me that the mitsu engineers have not pu more effort into this to achieve the optimal solution....

I'm guessing by 'radiator' you're meaning the heater core?

Installing a Webasto is fairly easy - Lots of folks in cold climates have done this and the car is perfectly set up for it

http://myimiev.com/forum/viewtopic.php?f=14&t=1248

If you live where it's cold, there is very little 'waste heat' to be had from the motor cooling circuit - You're not gonna stay warm trying to get heat from there

Don