I put a recording watt meter on the line to my WC hooked up to a 50 A breaker, charged the battery to 90% and let the car cool down over night in a 55 °F garage. In the morning cabin temp was 65 °F. Using the app I woke up the car and set the desired cabin temperature to 75 °F. Here's what I observed. The current demand went from 0 to approximately 5 kW. Within 3 minutes the cabin temperature was at 75 and still climbing. Close to 80°F the current demand began to decline getting down to about 1.4 kW steady state draw after about 40 min. In 1 hr 20 min a total of 2.94 kW hr had been drawn by the charger. Presumably most of this went to the climate system as the charge state did not change. Thus for a trip of an hour and a third where the weather conditions resemble those in my garage we could expect to lose about 2.9% of the battery or roughly 8 miles of range to the cabin heater. This is for approximately 20 °F rise. For 76° rise while moving at 65 mph the story is bound to be different and the average power drawn by the heater is likely to be close to the 5 or 6 kW it seems capable of handling.
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Obserations on Cabin Heat
- Thread starter ajdelange
- Start date
Probably should do the same test with the heat turned off before coming to conclusions. There's a lot of things that the car does in the first few minutes that can impact the current draw.
Also, assuming that the charge state didn't change probably isn't the best conclusion. How much would it change in that amount of time.
Also, did you have the AC set to stay on or did the car shutdown in a few minutes.
Not saying that the data is incorrect, I just don't necessarily draw the same conclusions.
Also, assuming that the charge state didn't change probably isn't the best conclusion. How much would it change in that amount of time.
Also, did you have the AC set to stay on or did the car shutdown in a few minutes.
Not saying that the data is incorrect, I just don't necessarily draw the same conclusions.
Obviously I can't know if the all the load is directed to the heating system but when the app says "Charging Complete" I take it to mean that charging is complete and the battery is not being charged. What I don't know is how much might be being drawn off to charge the 12V battery or how much to run the computers but I do know that when I turn climate control off the load drops to 0.
As to the fan - it was set to low which still allows the car to heat up (and overshoot in about 3 minutes). But it does speed up initially. I consider the fan part of the heating load so I'm not concerned about separating that out (not could I if I wanted to).
I'm glad to hear that the "heater use is not a big deal at modest temps" but that isn't quite as comforting as real data. I'll stick to the real data, thanks.
I think I have covered all the comments here. There is, of course, one other place appreciable energy can be going that I can't account for which no one mentioned and that is in warming the OBC. It is probably pretty efficient but not 100 %. Assuming that it is between 80 and 90% we might want to allocate 0.8 - 1 kW for that at the peak observed load and 140 - 280W for that in the steady state.
As to the fan - it was set to low which still allows the car to heat up (and overshoot in about 3 minutes). But it does speed up initially. I consider the fan part of the heating load so I'm not concerned about separating that out (not could I if I wanted to).
I'm glad to hear that the "heater use is not a big deal at modest temps" but that isn't quite as comforting as real data. I'll stick to the real data, thanks.
I think I have covered all the comments here. There is, of course, one other place appreciable energy can be going that I can't account for which no one mentioned and that is in warming the OBC. It is probably pretty efficient but not 100 %. Assuming that it is between 80 and 90% we might want to allocate 0.8 - 1 kW for that at the peak observed load and 140 - 280W for that in the steady state.
Perhaps. That would depend on how the outside air control is configured. For the measurements I took it was configured to admit fresh air. So at this point we know what the costs are if you want fresh air. I will repeat with this control set to recirculate cabin air. But we'll have to wait for the car to cool down.
Here's a graph of the power drawn in a run this morning after the car sat in the garage (mid 50's) and had a cabin temperature (according to the app - more on that in a bit) of about 65 °F. The battery was charged to 89% and, using the app, I set the charge level to 50% (so none of the rectifier's output would go to the battery) and the desired cabin temperature to 75 °F at about 8:30. The steps in the graph represent 1 minute averages. As you can see the power demand immediately went to 3 kW, then to over 5 (peak draw is about 5.5 kw but that's only for a few seconds) and then drops below 3 kW again within 15 minutes. From there it gradually declines dropping to below 2 kW and staying below 2 kW from 9:07 on. By 08:56 (26 minutes after turn on) the temperature in the cabin was 74.7 °F as measured by a Fluke thermometer. The application, however, indicated that cabin temperature was 81 °F at this time. From 08:56 on the system is holding temperature close to the set point. Observed temperatures went as high as 76.6 and as low as 73.2. I observed is that the car will, on its own, occasionally change the driver's side set point by a degree up or down. As soon as I spotted those I immediately went back to 75 °F. The other strange thing is that the app consistently reports the cabin temperature as being 3 - 5°F higher than it actually is. So I wonder where the sensor that reports to the app is located. It obviously isn't the same sensor that's used to compute the error used by the PID (or fuzzy) algorithm.
Keeping in mind that the graph shows the power going to the OBC, that it is not 100% efficient and that I was listening to the radio and the touch screen was on the graph does not represent the power going to the heater but heater (and fan) power is doubtless at least 90% of what is shown on the graph so knock off 10% if you like (or 47.62% if you want to) but it seems reasonable to assume that under the conditions (air source was set to recirculate) of measurements the graph is a pretty fair representation of the heating system demand. Thus it appears that to increase cabin temperature by 10 °F that representing a 20 °F rise WRT ambient is going to take about half an hour and cost you about 1.35 kWhr. But note that as the consumption graph shows you are most of the way to the set point within 4-5 minutes - that's why the power drops dramatically at that time. Once equilibrium is reached the demand drops to an average of 1.6 kW and will cost you about 1.6 kWhr per hour. For a 3 hour trip, thus the total demand for the heater (similar rise) would be approximately 4.8 kWhr or 4.8% of a 100 kWhr pack's charge.
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