PV1
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Re: Waste Heat

Fri Nov 06, 2015 12:08 pm

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.
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PV1
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Re: Waste Heat

Sat Nov 07, 2015 6:44 pm

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.
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
Solar-powered since 10/10/2013

"Koorz" - 2012 Cool Silver Metallic ES with QC - 1/5/2015

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PV1
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Re: Waste Heat

Mon Nov 09, 2015 8:00 am

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.
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
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PV1
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Re: Waste Heat

Fri Oct 07, 2016 11:21 am

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/118fp8nz047qe ... 3.png?dl=0
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
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Dani
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Re: Waste Heat

Fri Oct 07, 2016 11:53 am

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.
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PV1
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Re: Waste Heat

Fri Oct 07, 2016 12:32 pm

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).
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
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Dani
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Re: Waste Heat

Fri Oct 07, 2016 12:55 pm

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.

PV1
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Re: Waste Heat

Fri Oct 07, 2016 1:28 pm

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).
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
Solar-powered since 10/10/2013

"Koorz" - 2012 Cool Silver Metallic ES with QC - 1/5/2015

2017 Bolt EV LT in Orange with QC - 7/31/2017

Driving electric since 2-21-2013.

meier
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Location: Denmark / EU

Re: Waste Heat

Fri Oct 07, 2016 2:34 pm

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....
c-zero - 2011 - 35000km

Don
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Re: Waste Heat

Fri Oct 07, 2016 3:06 pm

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

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
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1994 Miata 60K miles - Soon to be sold
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