Can using CHG Mode be more efficient?

We have no gas line, but propane price usually follows very closely to gasoline and other petroleum products prices. I am sure it is higher now. Our oil burner is over 20 years old. I am seriously thinking of replacing it with a high-efficiency propane burner. But it is not going to be cheap. Here goes the money for Mach-E.

 

Agreed. Even with no changes in the driving style or mode, my day-to-day commuting shows wide fluctuations in both EV efficiency (miles/kWh or EV range) and HV efficiency (mpg without EV mode driven distance). Trying to keep constant SoC at 10% is just way too hard and still subject to a milieu of uncontrolled variables.

In any case, whatever the driving results I observe under my normal driving conditions are not likely to be universally applicable to all the PP drivers and vise versa. The only reason I am interested in testing CHG mode use efficiency was that with my rudimentary understanding of the law of physics that states conversion of one form of energy into another form always results in some loss (heat). Thus, I was firmly believing that using CHG mode to convert gasoline energy into electric energy for the traction battery will result in a loss of efficiency. This I thought was meant that driving on pure HV mode is always more efficient than using CHG mode and then EV mode from the charge. But, maybe under some conditions, it is not always the case. That is all I wanted to test.

BTW, as a side note about "conversion of energy", I am having an HVAC contractor stop by today to give me an estimate on our aging oil-fueled boiler system to a much more energy-efficient propane system conversion. I will see if the conversion makes sense financially and energetically ... or it may still be better to use the money to buy a Mach-E to forgo the gasoline engine in my commuter car. LOL

 

So, here is a formula-based calculation for driving the same route, same distance, under a perfectly controlled environment everything being equal, the only difference being the use of CHG mode and subsequent EV mode from the charge gained.

I made the following table on Excell. The only numbers I need to enter are in Green. Everything else is automatically calculated from the numbers entered. Two factors affect the CHG mode efficiency.

The first is the mpg factor which is how much mpg loss you will see when CHG mode is enabled compared to an identical drive situation with HV mode. From many observations by people experimenting with CHG mode, this number is about a 30 to 45% loss. That is if you were getting 60mpg on HV mode, then you will see 42mpg (best) to 33mpg (worst) when you use CHG mode. This of course will vary depending on the load, terrain, speed, etc. But for the sake of argument, we will assume everything stays the same before and after hitting CHG mode.

The second is the EV gain factor which is how many miles of EV range you gain by driving 1 mile of CHG mode. This of course will also vary depending on the speed of travel under CHG mode and EV mode and other variables. But again for the sake of argument, we will assume this is some constant number one can attain by driving CHG mode for a certain distance and using that charge on EV mode later. For my single experiment above this was ~1, that is 1 mile of CHG mode resulted in 1 mile of EV range, but for @KYBlue at a much faster speed, it was ~0.5, that is every 2 miles of CHG mode resulted in 1 mile of EV range. So this factor is somewhat still unknown or maybe a much wider possible range for now.

Once we have sufficient numbers of data and we can agree on numbers to use for those two factors, then the rest of the calculations are very simple. Assume your average HV mpg is EPA standard 54mpg and plan to travel 60 miles. CHG mode mpg is determined by the mpg factor above, and EV range possible is determined by EV gain factor above. So, for this 60-mile travel, driving 25 miles with CHG mode and driving 25 miles EV mode, and filling the rest with HV mode will give you the result below.



If the EV gain factor is more closer to @KYBlue which was 0.5. Still, I get the following result.



In fact for this travel, if I accept mpg factor of 30% loss and average HV mpg of EPA rated 54mpg, and 60 miles trip using 25miles CHG mode, CHG/EV is always better overall mpg until the EV gain factor is below 0.42, meaning for every ~2.4 miles of CHG mode you gain only 1 mile of EV range.



So, from those numbers, it seems unless EV miles gained by CHG mode is so poor, CHG/EV mode gives better overall mpg than HV mode.

I don't know how to upload an active formula containing a spreadsheet file, so the table above are all screengrabs. The real .xlsx file has all the underlying formulas to enter and change the values on the fly.

 

Yeah, for the purpose of comparison in silico, all I need is more data points for the two factors shown below. Anything else is extra that is not needed for the direct comparison.

• The first is the mpg factor which is how much mpg loss you will see when CHG mode is enabled compared to an identical drive situation with HV mode.
  
• The second is the EV gain factor which is how many miles of EV range you gain by driving 1 mile of CHG mode.

If anyone wants to experiment more in detail, then keeping EV ratio, Average MPH, driven miles on each section, SoC lever before and after, and type of driving conditions such as terrain, weather, temperature, loads in the car, wind, etc are good record-keeping but nor really necessary.

I realized that I can test and get more data points for those two factors on my routine 36 miles round trip commuting easily. All I have to do is drive the entire 36 miles on HV mode and record the mpg for each direction separately, then compare that to driving CHG mode one way on a separate day and record the mpg on the CHG mode direction and EV miles gained for that section. For completeness of comparison, I should do the CHG mode in both directions on separate days. If I do enough trials, then I should be able to get average numbers for those two factors I can use for my routine commuting route calculation.

Of course, the problem right now is that gas cost way too much to operate my PP. I would not have hesitated to do the testing when the gas was $2 and I had no free charge at work. But now, with the cost of gas at $3.25/gal. Using the single data point number for my commuting, it costs $1.95/day on HV, $1.77/day on CHG/EV. With the EV charge from the wall at home, it is now costing me only $1.32/day. And if I use a free charger at work, then it is $0.00/day

 

The idea is that with SoC above 10%, PP has more traction battery buffer for the HV mode to operate without firing the engine frequently. At low or no SoC, the PP is basically the same as the regular Gen4 Hybrid Prius but heavier. However, with my driving conditions of regular commuting ~36miles rural roads no heavy traffic going 30mph average, I did not find a noticeable difference in mpg with and without SOC. So if the SoC level affects the HV efficiency, it is not universally applicable to all driving conditions.

 

Yeah, had multiple contractors stop by and come up with a proposal. Two major issues with the heat pump. Cost and effectiveness. It cost more compared to oil or propane boiler replacement even with some federal and state incentives. And It is not likely will save any money on the cost of fuel either with our very high electricity rate. We currently have hot water baseboard-type radiators. There is no ductwork in our house. Meaning any forced air type conversion will require either having a central heat pump unit with retrofit ductwork which is almost impossible in our house with a completely finished basement and very little room in the attic, or mini-split units in each room meaning again not plausible for the cost of the unit and number of unit required. And, even the most advanced and most efficient air source heat pump is not likely to be effective in heating in the middle of winter when the temperature gets to low single digits to below zero F (-20C or below) requiring supplemental heat source for those days, meaning I have to keep the existing boiler and heating system in place.

If I am building a new house, then I may consider installing a geothermal heat pump, but in reality, if I am to build a new house, it will most likely be an off-grid tiny house with mostly passive solar heating.