On October 28 I took delivery of a new 2016 Volt. It is an LT version in Kinetic Blue Metallic with the Light Ash/Dark Ash interior. Optional equipment includes the Comfort Package, Leather, and Bose stereo. What an excellent car!
For the first 750 miles or so, I had been driving in EV mode exclusively (except for testing the total range on the first day and testing Hold mode). My lifetime efficiency peaked at 115 MPGe.
After three weeks of ownership, I decided to use the Volt for a 200-mile business trip from New Hampshire to Massachusetts and back. My planned route would involve about 50-percent interstate driving, 40-percent rural driving (speeds of 40 to 55 mph), and about 10-percent urban driving. The weather forecast called for morning lows in the 20s, and highs later in the day in the 40s and 50s.
Staying Comfortable While Maximizing Range
I typically try to minimize the amount of electrical energy used for cabin heating, however, the windshield on the second-generation Volt seems to need a great deal of defrost on cold days. I believe this is due to its steep slope and large surface area. This large surface cools quickly, condensing moisture from within the cabin.
In addition, while I am willing to accept some level of low temperature in the cabin, I don’t want to be freezing. Therefore, I have the car’s “Engine Running Due To Temperature (ERDTT) set to engage at 35° F outside air temperature, and I have my own logic for this setting. If I want to be somewhat warm at 35° F and below, the car will require more and more electrical energy. This reduces my EV range.
However, if I run the Internal Combustion Engine (ICE), not only do I get 42 mpg, I also get free heat! Since heat is a byproduct of running the ICE, I feel it is more energy efficient when it gets cold to utilize the ICE to provide heat and reserve the battery for propulsion.
As the U.S. EPA observes, a gallon of gasoline has an equivalent of 33.7 kilowatt-hours of energy. With a 30-percent efficient ICE, this leaves over 23 kilowatt-hours of waste heat. That’s 65 percent more than the entire 14.0 kilowatt-hours that is usable in the battery pack!
Thus, I planned my trip to strategically utilize the battery and ICE to provide the best range and interior comfort.
The owner’s manual states:
Use Hold Mode on a trip where it is expected that all of the electric charge will be depleted. Use Hold Mode mainly during highway or high speed driving to maximize both EV miles and fuel efficiency.
Therefore, my strategy was to use EV mode on urban and rural sections of the route, and utilize Hold mode on the interstates. I also planned to use Hold mode on some of the faster rural routes as well.
At 6:05 on a Wednesday morning I left my home. I had a fully charged battery and the temperature in the garage indicated 56° F (see Figure 2, please excuse my blurry photos). The odometer read 759 miles and the coolant temperature was 60° F. The indicated EV range was 60 miles (see Figure 3).
I utilized the steering wheel heater from the start of the trip, and that is a true blessing. My intent was to drive several miles in EV mode, and then switch to Hold mode to get cabin heat. I kept the cabin heat in ECO mode with a low fan setting and the cabin temperature set to 70° F
However, since it was only 20° F that morning, in less than 1 mile of travel, the ICE started and the message “Engine Running Due to Temperature” appeared on the driver’s display. Also at this time, the windshield began to fog up. The normal defrost did not seem to defrost the windshield fast enough for me to maintain good visibility, so I needed to use Max Defrost. This cleared the windshield quickly, but likely utilized some of my battery energy.
On the DIC, I was monitoring coolant temperature. I noticed that the ICE continued to run until the coolant temperature reached 145° F. Then the ICE shut down. This worked well, for soon after the engine shut down, I was able to proceed at 35 mph through a small town in EV mode.
Once I had gone through the town, I stopped to get a picture of my energy usage (see Figure 4). As I continued on my journey at 50 mph, ERDTT kicked in again. My observations from this trip (and subsequent trips that I have taken) is that ERDTT will run the ICE until your coolant temperature reaches 145° F, at which point the ICE shuts down. Once the coolant temperature cools to 120° F, the ICE starts again. So my observation is that ERDTT maintains the coolant temperature nominally between 120° F and 145° F.
I continued the first leg of my journey, utilizing Hold mode on the faster stretches of rural roads, and returning to normal mode for urban and slower driving scenarios. This enabled me to maintain reasonable cabin temperature, keep the windshield defrosted, yet utilize only a portion of my electric range, and reserve my battery for propulsion purposes only. With the warm coolant temperatures, it seemed that no electric power was being consumed for climate control (or defrosting).
After about 1 hour of driving rural and urban roadways, I got on an Interstate for approximately 8 miles. I was traveling at 65 to 70 mph and the coolant temperature was about 190° F when I exited the Interstate.
From here I drove about 7 miles on more rural roads to reach another Interstate highway. I was able to utilize the heat stored in the 190° F coolant for heating/defrost for the next 7 miles and travel in EV mode, however, since there was a great deal of stop and go traffic on this road (typical morning commute delays), by the time I reached the next Interstate highway, my coolant temperature was nearing 120° F, and ERDTT was about ready to engage. Fortunately, I reached the entrance ramp just prior to this point, went into Hold mode, and zoomed up the entrance ramp.
I will just briefly touch upon the performance difference between EV mode and Hold mode. Acceleration certainly feels stronger when the ICE is running, especially at speeds above 30 mph. I have no data or facts to back up this statement, only my perceived “seat of the pants” reaction.
Once on this second stretch of Interstate highway, I used cruise control to the best extent possible, and traveled at 70 mph, plus or minus a few mph. The coolant temperatures increased to between 180° F and 205° F. With all this heat energy available, I changed the climate control settings to Max, set the cabin temperature to 78° F, and increased the fan speed to about 75 percent. After a few minutes, I felt very warm and cozy, and decided to maintain this setting until I exited the highway, at which time I would resume Eco settings. Between the heat stored in the cabin and the heat stored in the coolant, once I exited the highway, I was able to reach my destination that morning in EV mode with plenty of warmth. Final coolant temperature at my destination was still 154° F.
While traveling on the Interstate, the DIC indicated at times that the ICE was providing all propulsion power. On small inclines, I would sometimes see motor power providing boost. On some downhill sections, I would see the engine running and the motors in regen (green color). There was no particular trend that I could establish.
At one point in the Interstate drive, the traffic slowed, and basically kept moving, but at speeds from 10 to 40 mph. During this slow drive, the ICE shutdown, and the car was propelled by electricity exclusively, even though I was still in Hold mode! As the traffic began to increase speed, the ICE started and went to a high rev status. As I continued to drive, the ICE speed subsided to more normal speeds.
Although I again don’t have positive proof, it appears that in Hold mode, the ICE will build a buffer in the battery. When conditions are right (like slow speed driving), the ICE shuts down and the motors propel the car utilizing the energy in the buffer. Once speed increases, the ICE starts, and may need to operate at higher power settings to restore energy to the buffer (i.e. bring the battery back to its original energy level when placed in Hold mode).
Another example of this buffer was noticed when I exited the Interstate. Upon leaving the highway, I restored the car to normal mode, and the ICE shut down. I looked at my gas mileage, and the reading was about 38 mpg. However, as I continued to drive the last 6 or 7 miles of my journey on a 40 mph urban road, the miles were still being recorded as gasoline miles, even though I was in normal (EV) mode! Again, I believe this is the Volt utilizing the battery energy that was placed in the battery buffer by the ICE. After a few miles of driving, the miles then were recorded as EV miles, however, the indicated gas mileage had increased to 40.0 mpg!
The first leg of my trip was just under 90 miles, and I used just over half of my battery’s usable capacity. The trip took just over 2 hours and interior cabin heat was a little low on the first part of the trip, but much improved when the coolant temperatures got up to 150° F and above. Figure 5 indicates that I got 120 MPGe on electricity and 40.0 mpg on gasoline. The ambient temperature had warmed from 20° F to 34° F. Figures 6 and 7 show the energy used for climate control was 0 percent, while the coolant temperature at my destination was still 154° F.
For my return trip, temperatures in MA had warmed to the low 50’s, while in NH they were only in the mid 40’s. Also, I had other business to complete, so my return trip was longer (mostly more rural/urban driving).
Utilizing the same driving strategies during the drive to MA, I was able to complete my entire trip using very little energy from the battery for climate control (0 percent indicated). Figure 8 shows that I returned home with a total trip length of 202.7 miles. Of that distance, 57.5 miles were EV miles, and gas mileage was 44 mpg.
Recently, I took another trip of 98.4 miles (more than you would want to attempt in a Leaf). I utilized the same strategy as in the 200-mile trip. On this day, the temperatures started in the upper 30’s, rising to the low 50’s by the return home. As seen in Figure 9, I traveled 60.8 EV miles and got 49.9 mpg for the non-EV miles. Due to defrosting needs early in the morning, I used 2 percent of my battery for climate controls.
In summary, strategic use of the battery energy and thermal energy derived from the ICE can help to maximize EV range and still provide good levels of comfort within the cabin.