You're missing an important figure here: the outside temperature. For a heat pump (either cooling or heating) the efficiency depends on the ratio of the temps (in kelvins) on the two sides of the pump. So, even if the cabin were perfectly thermodynamically sealed from the outside world, it would still take more energy for a given delta T if it's hotter outside (for AC).
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You're missing an important figure here: the outside temperature. For a heat pump (either cooling or heating) the efficiency depends on the ratio of the temps (in kelvins) on the two sides of the pump. So, even if the cabin were perfectly thermodynamically sealed from the outside world, it would still take more energy for a given delta T if it's hotter outside (for AC).
Of course, sorry if I assumed that was obvious.
Suffice it to say that the Roadster can't maintain a 20C cabin at 40C, but it can easily do that at at 0C. The heater has more oomph.
The AC in the 2.x roadsters (can't comment on 1.5) uses a variable speed compressor so power consumption rises and falls as demand changes. I think it averages around 1KW IME traveling at 20-25*C rising to 3KW when it's working flat out to cool the battery.
Perhaps the system felt the battery needed cooling and was running flat out; Benji4, did you hear the compressor running at full speed?
Perhaps the system felt the battery needed cooling and was running flat out; Benji4, did you hear the compressor running at full speed?
In order to save power, I'm using the recirculate mode (is that what it's called?) on the AC. Since the air gets cold in 20 seconds or something, after that it just needs to keep the already cool air cool.
Yes, some of the time it was running, but not all the time. I've just taken the car in for service and they are going to check it as well as the very load sounds the fans make.
Once my car gets back, and who knows when that will be since I saw something like 10 other Roadsters in the shop, I'm thinking about doing a test where I crank the AC with the car stationary for 1 hour and see how many ideal miles I lose from that. That would be pretty accurate wouldn't it?
edit: sorry, I see that experiment was done already from reading the earlier posts here.... about 3.4% of a full charge is used per hour with the AC cranked. That would be about 8 or 9 ideal miles per hour, and I suppose that could be worse depending on how hot it is outside.
By the way, I got to see the top-secret Tesla workshop in Tokyo the other day when I took the car in. I was told not to disclose the location as it is not open to the general public. It's really hidden and you have no clue what it is until they open a garage door which reveals a huge, beautiful garage with lots and lots of Roadsters in it. There was even a gorgeous burnt orange fully loaded Roadster Sport. There were blue ones, green ones, black ones, it's really surprising how many cars were there. I guess they are selling pretty well in Tokyo now!
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dhrivnak
Active Member
In my 1.5 Roadster the AC does seem to consume about 7A or about 2.6 KWH as I go from 1-2 amp at idle to 9 amps with the AC on. It seems to have a noticable effect on my range in the 10-20% range. So I normally go with the top down. It is a lot more fun that way.
Possibly OT a little but, I was experimenting with the AC today, I have been for a few weeks. Trying to eek out the last ounce of cool air.
I've looked at the temperature of the air coming out of the vents to see what seems to work and played around with the flow a bit. All my testing was carried out with the demand from the battery being low, i.e. battery temp was down at rest.
One thing I did find was that the recirculate does actually work; having no discernible change in sound between on/off I did wonder but, with re-circulate on the air temp coming out of the vents does reliably drop 1-3*C after a minute or so.
It seems that the typical temperature of the output is around 7-10*C. It doesn't seem to fall lower and seems able, even in 38*C outside temps to stay in that range. This temperature is higher than other cars and why I think the AC appears weak.
So, how to keep cool? Well, I got to reasoning that, if the AC can keep up with demand then the problem is how to direct the output for the best effect. I found that pointing the vents directly at me is good for a few seconds but then you get that, what's it called, AC burn? where your body gets used to it and still feels warm. So that was out. I tried the control at 3 O'Clock directing the bulk of the air to the screen; the theory here was that, as heat rises the cool air should be directed to cool that hot air. This worked to a good degree and I found that I could stay comfortable for an hour at fan 1 in 30*C so, progress but, I was getting condensation on the windscreen - cooling energy was being wasted cooling the glass. So the next and final configuration worked for me.
To get the best effect, aim the vents at the source of the heat (physics students, stop laughing... this is my journey of discovery. So, rotate the side vents to direct the air straight at the side windows; about 10 O'clock on the drivers side, and the centre vents upside-down and 50% open to direct cooing air straight up towards the roof - make sure no vent airflow is hitting driver or passenger directly. Set the output control at 9 O'clock to direct most air to the vents but leave some to cool the legs. Re-circ: ON. Fan at 1-3 as demand increases - Even at 3 the AC is able to keep up. The result is that a gentle cool air keeps your head cool (great phycological effect) whilst the thermal load from the windows is nullified by a wall of cool air to either side. Some air still leaks from the screen vents to prevent the build up of hot air under the windscreen.
One more thing; don't make the mistake I did and leave the temp control anywhere other than very minimum; I previously thought that the AC ran at some fixed rate (it does in the MINI) and that, as long as the heat wasn't on, it was cold; nope! If you turn the control up the AC power is reduced and the air from the vents does go up - Doh!
One regret; I wish the AC would output cooler air. I hear the compressor running at low to medium speed even with the fan (i.e. demand) at 3. I've heard the compressor run much faster... there's more life in her! Perhaps the external radiator is unable to shed the heat fast enough.
At this high level of demand total car power consumption is at 5A.
These are my findings, try them out, let me know if you can find another ounce of cool air; it'd be much appreciated!
I've looked at the temperature of the air coming out of the vents to see what seems to work and played around with the flow a bit. All my testing was carried out with the demand from the battery being low, i.e. battery temp was down at rest.
One thing I did find was that the recirculate does actually work; having no discernible change in sound between on/off I did wonder but, with re-circulate on the air temp coming out of the vents does reliably drop 1-3*C after a minute or so.
It seems that the typical temperature of the output is around 7-10*C. It doesn't seem to fall lower and seems able, even in 38*C outside temps to stay in that range. This temperature is higher than other cars and why I think the AC appears weak.
So, how to keep cool? Well, I got to reasoning that, if the AC can keep up with demand then the problem is how to direct the output for the best effect. I found that pointing the vents directly at me is good for a few seconds but then you get that, what's it called, AC burn? where your body gets used to it and still feels warm. So that was out. I tried the control at 3 O'Clock directing the bulk of the air to the screen; the theory here was that, as heat rises the cool air should be directed to cool that hot air. This worked to a good degree and I found that I could stay comfortable for an hour at fan 1 in 30*C so, progress but, I was getting condensation on the windscreen - cooling energy was being wasted cooling the glass. So the next and final configuration worked for me.
To get the best effect, aim the vents at the source of the heat (physics students, stop laughing... this is my journey of discovery
. So, rotate the side vents to direct the air straight at the side windows; about 10 O'clock on the drivers side, and the centre vents upside-down and 50% open to direct cooing air straight up towards the roof - make sure no vent airflow is hitting driver or passenger directly. Set the output control at 9 O'clock to direct most air to the vents but leave some to cool the legs. Re-circ: ON. Fan at 1-3 as demand increases - Even at 3 the AC is able to keep up. The result is that a gentle cool air keeps your head cool (great phycological effect) whilst the thermal load from the windows is nullified by a wall of cool air to either side. Some air still leaks from the screen vents to prevent the build up of hot air under the windscreen.One more thing; don't make the mistake I did and leave the temp control anywhere other than very minimum; I previously thought that the AC ran at some fixed rate (it does in the MINI) and that, as long as the heat wasn't on, it was cold; nope! If you turn the control up the AC power is reduced and the air from the vents does go up - Doh!
One regret; I wish the AC would output cooler air. I hear the compressor running at low to medium speed even with the fan (i.e. demand) at 3. I've heard the compressor run much faster... there's more life in her! Perhaps the external radiator is unable to shed the heat fast enough.
At this high level of demand total car power consumption is at 5A.
These are my findings, try them out, let me know if you can find another ounce of cool air; it'd be much appreciated!
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NigelM
Recovering Member
True. I posted my original figures (which indicated about a 4.5A draw at full blast) during the day with an outside temperature in the mid 90's. After reading the bolosky's post I checked it again last night: Same conditions - Car stationary, immediately after charging and full blast on the AC - but with outside temperature of 85F. The start-up draw was the same 1Amp, but with the AC running I was now drawing about 3.5A.
Basic (unscientific!) conclusion: at 95F my AC draws 4.5A and at 85F it only draws 3.5A.
This difference in draw related to the outside temperature got me thinking about the effects of air density on range at sea level (my elevation indicator has never been above 100ft and spends most of the time at 0ft) and the subsequent effects of down-force incorporated into the Roadster design and whether that was a contributing factor in Dragon almost losing his rear end up in those mountain passes?
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NigelM
Recovering Member
Maybe yours is wrong/broken? :wink:
Seriously though, I am starting to realize there are too many unmeasurable variables to draw any conclusions. I also have the latest software upgrade which is supposed to improve the energy efficiency/distribution; so that may be causing a difference. Plus I am not sure what you mean by "full throttle"; the AC on full? Yes, that's what I used also.
Yes, it tends to change back and forth, so I unscientifically called it 3.5.
I had a long freeway drive yesterday, so put the car in cruise control and then looked at the Amp draw with the AC on and off. I learned nothing whatsoever, as the ammeter changes all the time as the car adjusts to gradients, wind etc to maintain exact speed.
Although others use words like "anemic" to describe the Roadster AC, on my long drive freeway yesterday I actually turned it down to the middle setting as I was getting too cold. Outside temperature was 97F.
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DrComputer
TeslaClubLA President
I'd have to say when I first got my Roadster (2.0) I would have described the A/C as anemic. But with the latest firmware and the new fan shroud, the A/C actually gets very cold even on hot days. I think they finally decided that the batteries don't need to be cooled as much and that when the car first turns on (on a hot day) they let the compressor give freon to the cabin for a long while before trying to cool the battery. This makes the A/C very usable now.
kgb
Member
How recent is this firmware? Would my 2.5 benefit? I have found, to my chagrin, that sometimes my AC just cuts out. I hope that it is doing this to cool the battery, but I'm not too sure. There does not seem to be much logic to it. When it happens, I check the temp of the battery, PEM and motor, and sometimes when this happens, those parts will not be as hot as other times when the AC is actually working. Even when it is working, the AC is still anemic. I have even tried radiant barrier from another thread.
P.S. I also paid for the solar guard option
Every time I see this thread's title, "How much power does the Roadster's AC use?" I can't help but think to myself, "NOT ENOUGH!"
DrComputer
TeslaClubLA President
Let me clarify my observations. Last summer when it was really hot out and I would get into the car and turn on the A/C, the car would give full priority to cooling the battery pack and give nothing to the cabin for quite a long time (5 minutes or so). Then when it would decide to cool the cabin it would give cool air to the cabin for about two minutes then give it back to the battery for another 5 minutes. This process would continue that way and that cabin would never cool down. Now, it seems to give the cabin first priority when you turn the car on and when it does switch between the cabin and the battery the intervals are shorter and more priority if give to the cabin at first so the cabin actually cools down on a hot day.
Hi,
I read a couple of Times now, that the AC is used and prioritized for the battery cooling.
But what about if we use the Roadster as it was build for, Top off? is there an automatic to switch on the AC to cool down the battery pack, or is it needed to switch ON manually when the battery starts overheating?
If there IS an automatic, is there a difference between Standard and MaxRange mode to prevent loosing range?
What are your experiences?
Cheers
Mischa
I read a couple of Times now, that the AC is used and prioritized for the battery cooling.
But what about if we use the Roadster as it was build for, Top off? is there an automatic to switch on the AC to cool down the battery pack, or is it needed to switch ON manually when the battery starts overheating?
If there IS an automatic, is there a difference between Standard and MaxRange mode to prevent loosing range?
What are your experiences?
Cheers
Mischa
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