AC compressor power use - help me compare!

[geordi]

Like everyone else, I'm always looking for more efficiency where possible. Also like everyone else, I'm asking myself the question "Is this normal for this car?" about things.

On this episode of "Is this normal?" The subject matter is the AC compressor. Here are the facts:
This is a 2016 MX 7 passenger with the dual AC.
When plugged in to AC power, the dash will show how much power is coming in, even when not charging (because other things like the AC are using it)
With only the fans running, the dash says I am consuming 1kw or 3-4 amps. This might be the lower limit of what it can display for watts. When I turn on the AC compressor though (button blue) the power usage shoots up to 5kw / 21 amps! That is with the temperature set at LO, fan speeds at max. My model S which should be nearly the same setup for AC compressor seems to use about 1-2kw per hour in camping mode, so this seems VERY excessive in the X and I'm just wondering if there's an issue here. The fan speed is also less than in my S, but that's for another time.

- The fans only............

- With the compressor on.

Ignore the error, it is obviously charging, and there may be something going on with the cable I'm using at my house (cheap connector) b/c it is working fine.

Based on that information from the dashboard - Please duplicate this setup and tell me what kind of power usage you are seeing, thanks!
Plug your X in, set the charge limit to something lower than whatever the current charge is - if you are at ~60% or more, set the limit to 50% so that it definitely is not charging. Turn on the fans, but not the AC compressor (button white) and you should see 1kw / 4amps being consumed. If you then turn on the compressor and set the temp on both front and rear all the way down.... What is the power consumption you see?

I've heard other X models outside and their condenser fans sound similar to mine (loud) so I don't think there's an issue there... But the compressor is just sucking down the juice. Maybe that's an issue, or is this normal?

 

[brainhouston]

Haven't tried that but just yesterday I was curious about AC n with car off sitting in the sun I started both fans max n SMT showed 4.5kw usage, can't recall what it was with rear off, maybe 3kw, we'll have to recheck...

 

[geordi]

Haven't tried that but just yesterday I was curious about AC n with car off sitting in the sun I started both fans max n SMT showed 4.5kw usage, can't recall what it was with rear off, maybe 3kw, we'll have to recheck...

Hmm, I'll have to look at SMT and see what that says if it compares with this. I HAVE noticed that in camping mode overnight, it seems to use about 2% per hour, which is near double what the S would do in the same usage.

Doing the math, just my fans on was 729 watts, and with the compressor it was 5019. The fans seem high too, but that seems awfully high for a compressor, honestly, but I don't know what it is actually rated at. My RV had a 15k btu air unit on it that used 1500 watts running.... That would cool more volume than this X has. For an electric vehicle, this power usage seems extreme.

 

[geordi]

SMT agreed with the dash display @brainhouston - and with the rear AC off, fan on 11 was around 4kw. With everything on max it was closer to 5kw. I still don't know if that's normal, but seems really high.

The loaner X I have right now (April 2017 75D) seems to be getting around 375 wh/mi on the highway at 80 where my 2016 X 90D is right at 500 wh/mi for the same road and speed. So there's definitely something going on with mine right now.

 

[mxnym]

The loaner X I have right now (April 2017 75D) seems to be getting around 375 wh/mi on the highway at 80 where my 2016 X 90D is right at 500 wh/mi for the same road and speed. So there's definitely something going on with mine right now.

Even if your A/C is running at max while you're driving (I'm guessing it's not) and the loaner A/C is off while you're driving (again, guessing it's not), that would only be 83 WH/mi @ 60 MPH (5000/60, and I'm guessing you're driving faster than that, which means it would be even less WH/mi). 375+83<500, and each of my 3 guesses imply the difference caused by the A/C would be less than that 83. A 90D weighs more than a 75D, and IIRC, a 90D has less efficient motors. Your 90D may also have larger wheels than the loaner 75D, so I wouldn't be too sure there is "something going on" from that comparison (I'd agree 500 seems high for a 90D, but 375 also seems high for a 75D AFAIK).

Regarding the A/C specifically, it seems you should be doing the same A/C test on the 75D, but the 75D is presumably a 5 seat, which means you'd need to be comparing to the 4kW number and some improvement between model changes may also exist, so brainhouston's test with a 90D seems more relevant there.

Regarding more efficiency where possible, operating under the assumption that similar improvements in aerodynamics would provide similar percentage benefits for similar shaped vehicles with difference efficiency profiles, and also understanding that aerodynamic impacts increase as speed increases, you might be able to get an ROI from lowering links (even if you also pay for a matching alignment kit). You'd have to make some assumptions of your own and do the math to see how many miles it would take to potentially bring an actual ROI, though, and if you saved money by skipping the alignment kit, tire cost might end up negating efficiency improvements. You'd also have to make sue you can find a place you trust for the install if you didn't want to do it yourself (and for the alignment if you also have that kit installed).

 

[geordi]

90D and 75D are both 7 pass versions.
75 has factory 22" wheels (heavy and big!) 90 has Tsportline 19" with 255/55 tires.
75 has a new 350 volt battery, 90 is the original 400v.
Both are base "D" versions, and being about 8 months apart, should be exactly the same motors.

I'm driving the same roads at the same road speed (80mph). The 90D originally was getting around the same 375 wh/mi at 80 but had been creeping up over the last 20k miles of ownership - masked by trailer usage.

Camping usage with AC on overnight draws down 2%/hour of usage. For obvious reasons I will not be able to do that with a loaner vehicle.

 

[brainhouston]

Haven't tried that but just yesterday I was curious about AC n with car off sitting in the sun I started both fans max n SMT showed 4.5kw usage, can't recall what it was with rear off, maybe 3kw, we'll have to recheck...

So it was 90F yest, was perfect for more testing. I have to update my previous claim...
With car sitting in the sun for 2hrs, immediately after turning on fan to 11, it reached 5.5kW per SMT, car off:

Turning rear fan on/off made no difference, turning range mode on/off made no difference...
However, AC pw usage quickly drops off, it only stayed on this high for few min and i purposely left drivers window open...
After about 10min of driving, only front fan on at 11, it was consuming 2kw (checked when stopped at traffic light)
Flipping range mode at this time only affected the pw by 0.25kW, didn't test rear (green light).

 

[geordi]

I'll have to mess around with SMT some more, it's good to see that these DO have a variable output compressor instead of just an on/off unit. What's interesting is that when camping in my 2014 S, I could hear the compressor kicking on and off fairly frequently when it wasn't having much asked of it.

 

[brainhouston]

I'm pretty sure all EV/Hybrid compressors are Scroll type and variable.
But if ur cabin Evaporator temp reaches ~32F it'll shut off AC to prevent freezing, so maybe just the right conditions happen for on/off cycling...

 

[SSonnentag]

My understanding is that the S can use up to 6kW for the climate system and the X can use up to 12kW due to there being two independent climate control systems, one for the front and the other for the rear. I believe the power draw will be significantly lower than that when only the AC is in use. The resistive heater can use more power and is probably the only time you'll see the full 6kW per system. But the X drawing double the power of the S under the same conditions is normal. On the X, you can manually turn off the rear climate control and only use the front, which should cut the power draw down, but since the interior of the X is larger than the S, the climate system will run longer and have a higher power draw anyway, it just won't peak at anything higher than 6kW if the rear climate system is off.

 

[Big Earl]

Like everyone else, I'm always looking for more efficiency where possible. Also like everyone else, I'm asking myself the question "Is this normal for this car?" about things.

On this episode of "Is this normal?" The subject matter is the AC compressor. Here are the facts:
This is a 2016 MX 7 passenger with the dual AC.
When plugged in to AC power, the dash will show how much power is coming in, even when not charging (because other things like the AC are using it)
With only the fans running, the dash says I am consuming 1kw or 3-4 amps. This might be the lower limit of what it can display for watts. When I turn on the AC compressor though (button blue) the power usage shoots up to 5kw / 21 amps! That is with the temperature set at LO, fan speeds at max. My model S which should be nearly the same setup for AC compressor seems to use about 1-2kw per hour in camping mode, so this seems VERY excessive in the X and I'm just wondering if there's an issue here. The fan speed is also less than in my S, but that's for another time.

View attachment 942883 - The fans only............ View attachment 942884 - With the compressor on.

Ignore the error, it is obviously charging, and there may be something going on with the cable I'm using at my house (cheap connector) b/c it is working fine.

Based on that information from the dashboard - Please duplicate this setup and tell me what kind of power usage you are seeing, thanks!
Plug your X in, set the charge limit to something lower than whatever the current charge is - if you are at ~60% or more, set the limit to 50% so that it definitely is not charging. Turn on the fans, but not the AC compressor (button white) and you should see 1kw / 4amps being consumed. If you then turn on the compressor and set the temp on both front and rear all the way down.... What is the power consumption you see?

I've heard other X models outside and their condenser fans sound similar to mine (loud) so I don't think there's an issue there... But the compressor is just sucking down the juice. Maybe that's an issue, or is this normal?

You aren't comparing apples to apples. On the X, you're using the power consumption for the system at maximum output. On the S, you're using the power consumption for the system at steady state over the course of several hours. If you camped in the car with the climate set to LO with fan at maximum output, you'd be freezing.

 

[brainhouston]

and the X can use up to 12kW due to there being two independent climate control systems, one for the front and the other for the rear.

Not true.
X has 2 PTC heaters (6kw each?) but only one AC compressor with 2nd loop for the back
In fact there isn't any car that i know of that has second AC compressor...

 

[Big Earl]

My understanding is that the S can use up to 6kW for the climate system and the X can use up to 12kW due to there being two independent climate control systems, one for the front and the other for the rear. I believe the power draw will be significantly lower than that when only the AC is in use. The resistive heater can use more power and is probably the only time you'll see the full 6kW per system. But the X drawing double the power of the S under the same conditions is normal. On the X, you can manually turn off the rear climate control and only use the front, which should cut the power draw down, but since the interior of the X is larger than the S, the climate system will run longer and have a higher power draw anyway, it just won't peak at anything higher than 6kW if the rear climate system is off.

The X with rear air has two evaporator coils but still only one compressor. Maximum air conditioning output is still around 6 kW, with 7.5 kW of resistive heat (6 kW front and 1.5 kW rear).

 

[SSonnentag]

Not true.
X has 2 PTC heaters (6kw each?) but only one AC compressor with 2nd loop for the back
In fact there isn't any car that i know of that has second AC compressor...

OK, good to know. Then I'd chalk up the power draw differences to either a larger compressor on the X or simply the X compressor having to work harder than the S due to cabin size and the cabin taking longer to cool down. I'm pretty sure Tesla utilizes variable speed compressors, so a hotter interior will cause the compressor to work harder (more power draw).

 

[geordi]

You aren't comparing apples to apples. On the X, you're using the power consumption for the system at maximum output. On the S, you're using the power consumption for the system at steady state over the course of several hours. If you camped in the car with the climate set to LO with fan at maximum output, you'd be freezing.

That's reasonable based on what I had said - but also my mistake for not explaining it fully.

Most definitely the AC in either vehicle is powerful enough to turn the interior into a meat locker.
I have camped in both, in similar external conditions and have seen where the S uses around 15% of the battery overnight, while the X is pushing ~2%/hour for 25%. It definitely could be as simple as the fans using more power since they are both running - I kinda wish there was an option for only the rear and not the front, but what I've been doing is setting the front at 1 or 2, and the rear at a higher fan speed.

I need to play around with the analytics in Tessie to see what the actual power consumption has been, b/c the two cars have different battery ages so the X is at a disadvantage on the total available power as well as the specific consumption.

 

[Big Earl]

The X is a larger vehicle with more glass. It stands to reason that it would require more energy to maintain comfort.

I’ve found HVAC consumption to be higher in mild weather than when in moderately warm weather. The reason: in moderate weather, the system runs the heating and cooling together to better control humidity (cooling the air to dry it out, then reheating it so you don’t get too cold), while in warm weather, it can use just cooling by itself. It just so happens that car camping usually happens in milder overnight weather. You can reduce this effect by not running the compressor if the weather is comfortable for fan-only.

 

[beachmiles]

You can reduce this effect by not running the compressor if the weather is comfortable for fan-only.

In the model 3/y there is no fan only setting, does the X really have a fan only setting where you don't have to set the temp to LO and disable the AC button?

I want to get cold when I have the AC and the temp inside/outside is hotter than my 1 temp setpoint. During this time I only send watts to the AC evaporator to keep the cabin temp from going above this 1 temp setpoint.

I don't want to shoot myself in the foot by also sending 400-1000 watts to also heat the car when there is plenty of hot air outside the car. Having to use LO mode to disable the cabin heater and use a low fan speed of 1-3 to control the temp is fairly ridiculous way to control the cabin temp without wasting watts shooting myself in the foot.

Here in the desert where it seems to always be over 80F I only need to heat the cabin about 3 days out of the year and also use the cabin heat to defrost the front window maybe 7 days out of the year. The rest of the time I NEVER am looking to add heat to my cabin when im in the car. If the car wants to zap some heat after I exit the car to reduce the risk of mildew in the air filters then thats fine otherwise I am fine replacing them every year. I've been running with the LO setting for a couple years now and haven't had the mildew smell since I changed my filters a couple years ago.