Amber - HVAC Power Consumption Question

[oilerlord]

Hi Amber,

It's been discussed that the heater draws 9kW from the battery. Does the heater always use 9kW when it's in operation? It would be reasonable to assume it consumes less than 9kW once the cabin reaches the desired temperature, but we don't know if that's the case.

Please post specific power consumption values for automatic climate control operation for the heater and A/C at outside temperatures of 32F, 72F, and 90F respectively. Let's also assume that the driver has set the cabin temperature at 72F and the car has been parked outside in in all three scenarios.

Thanks.

 

[SeanNelson]

Please post specific power consumption values for automatic climate control operation for the heater and A/C at outside temperatures of 32F, 72F, and 90F respectively. Let's also assume that the driver has set the cabin temperature at 72F and the car has been parked outside in in all three scenarios.

It sounds to me like you're asking her to perform an experiment, which I expect is outside the scope of her job description.

But hopefully she can at least answer the question of whether the power consumption of the heater is fixed at 9KW or not. I'd be very surprised if it doesn't vary depending on load. Or it may be the heater element simply cycles on and off when full power is not needed, so even though the element itself always consumes a fixed 9KW, shortening its duty cycle will lower the average power consumption.

 

[michael]

It surely varies depending on the amount of heat and the fan speed needed to maintain the thermostat setting. Do we know that 9 kW is the peak power? If so, this applied continuously would roast the passengers except in very cold weather.


The Focus had a climate power display. This varied from a maximum of 6 kW down to zero as necessary to heat or cool. I'm certain the Bolt works in a similar manner.

 

[oilerlord]

It sounds to me like you're asking her to perform an experiment, which I expect is outside the scope of her job description.

But hopefully she can at least answer the question of whether the power consumption of the heater is fixed at 9KW or not. I'd be very surprised if it doesn't vary depending on load. Or it may be the heater element simply cycles on and off when full power is not needed, so even though the element itself always consumes a fixed 9KW, shortening its duty cycle will lower the average power consumption.

Sean, what I'm trying to avoid is a general PR response such as "To preserve range, and to allow you to reach your destination, we suggest using the heater sparingly in the event your battery is at low capacity". GM probably has all of the data we're asking for (or close to it), the question is if Amber has access to it, or will share it with us.

There are five pages of spit balling on how much the heater uses:

http://www.mychevybolt.com/forum/viewtopic.php?f=11&t=5752

Instead of pages of debating, and various opinions on this subject, wouldn't it instead be nice to have definitive answers?

 

[ChevyCustomerCare]

Hi Amber,

It's been discussed that the heater draws 9kW from the battery. Does the heater always use 9kW when it's in operation? It would be reasonable to assume it consumes less than 9kW once the cabin reaches the desired temperature, but we don't know if that's the case.

Please post specific power consumption values for automatic climate control operation for the heater and A/C at outside temperatures of 32F, 72F, and 90F respectively. Let's also assume that the driver has set the cabin temperature at 72F and the car has been parked outside in in all three scenarios.

Thanks.

Thanks for your outreach, oilerlord! The power gauge in the Enhanced Layout on the IP screen includes HVAC power consumption. By turning HVAC on and off, you can determine what the HVAC system is consuming at any point. In addition to tracking HVAC energy consumption on power meter, you can also visualize instantaneous range changes as you change your HVAC settings. This feature is new in the Bolt EV.

If you have additional questions/concerns, please let me know.

Amber G.
Chevrolet Customer Care

 

[oilerlord]

Thanks for your outreach, oilerlord! The power gauge in the Enhanced Layout on the IP screen includes HVAC power consumption. By turning HVAC on and off, you can determine what the HVAC system is consuming at any point. In addition to tracking HVAC energy consumption on power meter, you can also visualize instantaneous range changes as you change your HVAC settings. This feature is new in the Bolt EV.

If you have additional questions/concerns, please let me know.

Amber G.
Chevrolet Customer Care

I was hoping for more of a technical answer than a how-to, but thanks for your reply.

We do have some data...@devbolt provided this info when preconditioning his car:

"Max draw from the wall when pre-conditioning is indeed the max that the EVSE can provide. However, the car will consume any additional power it needs from the battery pack to heat or cool the car. I saw 7.35 kW being drawn from the wall (30A at 245V = 7350 watts), and an additional 2 or so kW being drawn from the battery pack when I had the heat turned up to max. If I had the heat turned down to a more reasonable level like 75, the car only pulled what was absolutely necessary, which was somewhere between 3 and 4 kW."

I'm assuming that the heater initially draws 7.35 kW, and over 9 kW when heater is set to "max". A setting of 75F is between 3-4kW. This is when the car is plugged in.

Preconditioning & driving the car may have different results. If a Bolt owner has the time, and for the benefit of the group, please do a couple of tests with the heater & A/C and post them here.

Thanks!

 

[SeanNelson]

A setting of 75F is between 3-4kW.

The actual power draw, of course, depends on how far the cabin is from 75F - that dictates how hard the HVAC system has to work to get the that temperature. If, for example, the ambient temperature is 30F then the HVAC system will have to use a lot more energy than if the car is at 70F.

 

[oilerlord]

The actual power draw, of course, depends on how far the cabin is from 75F - that dictates how hard the HVAC system has to work to get the that temperature. If, for example, the ambient temperature is 30F then the HVAC system will have to use a lot more energy than if the car is at 70F.

Using some common sense, that kind of goes without saying, doesn't it?

The guy was preconditioning his car, and posted two examples with results - the heater to "max" (9kW) and a "more reasonable level like 75" (3-4kW). He didn't say what the ambient temperature was.

 

[gpsman]

This is a piece of cake to understand.

Run your heater in your car while in park.
Watch your power consumption display.
Adjust the temperature controls to your heart's content.
Write down the results or comit them to memory.
Post the results here save the next 5,000 people with the same question some time.

My only question is mostly a curiosity as laws of physics already give me a pretty good idea of what WILL happen without performing the experiment.

My question is:

Does the heater modulate on and off to keep a steady temperture (as in a gas fired home furnace with thermostat) or does it dial down the power input and run continuously?

As stated earlier, the total power used per hour will be the same in eithet case. It takes a fixed, finite amount of energy to warm your car from x to y in condirion z.

 

[LeftieBiker]

It takes a fixed, finite amount of energy to warm your car from x to y in condirion z.

That's quite true with resistance heaters like the Bolt's, but heat pumps are more complicated, because their efficiency varies with temperature.

 

[SeanNelson]

The actual power draw, of course, depends on how far the cabin is from 75F - that dictates how hard the HVAC system has to work to get the that temperature. If, for example, the ambient temperature is 30F then the HVAC system will have to use a lot more energy than if the car is at 70F.

Using some common sense, that kind of goes without saying, doesn't it?

Hence the "of course" in my comment. But I wanted to point out the obvious because I've seen people take posts just like that one, leap to the wrong conclusion, and start running around like Chicken Little with it.

 

[SeanNelson]

My question is:

Does the heater modulate on and off to keep a steady temperture (as in a gas fired home furnace with thermostat) or does it dial down the power input and run continuously?

It's an interesting question, but the answer is probably of no practical value. Unlike a furnace, power to the heater could potentially be modulated on a millisecond basis so that unless you use an oscilloscope you really couldn't perceive the difference.

And although the belt-driven A/C units on ICE cars had to cycle on and off in order to modulate their output, I don't think I've ever seen anyone fret about it (although I've always wondered how durable the A/C clutch is with all those on/off cycles).

 

[peteblair]

For what it's worth i've run my heater at max (while parked) when outside temps were in the mid teens (think it was 16 degrees that night) and I never saw my draw hit 9kw. I never saw it go higher than 7kw and once the temps were reasonable within the car it was sitting closer to 3kw most of the time.

The days I have run the heater while driving the range predictor almost always tells me about 9 - 13 miles difference in range.

Granted, I know this isn't scientific, I wasn't doing any direct measurements and I just relied on the car telling me what it was using.

Seems reasonable though knowing the car uses a heat pump system that initial draw is going to be higher than what you would expect during normal running while the car is already heated up.

 

[oilerlord]

For what it's worth i've run my heater at max (while parked) when outside temps were in the mid teens (think it was 16 degrees that night) and I never saw my draw hit 9kw. I never saw it go higher than 7kw and once the temps were reasonable within the car it was sitting closer to 3kw most of the time.

Seems reasonable though knowing the car uses a heat pump system that initial draw is going to be higher than what you would expect during normal running while the car is already heated up.

Wait a minute...your car has a heat pump? Sounds like GM is already shipping Bolt V1.1. I'll bet they fixed the seats in your car too. Amber, any news on this?

 

[LeftieBiker]

More likely the salesman just told them it has a heat pump.

 

[devbolt]

If you have the climate control system I n auto mode, the car will automatically adjust the amount of power it is drawing to cool/heat the cabin to the set point you have selected, partially based on what the outside ambient air temperature is. I.e if it is 35 degrees out, and you set the temp to 85, it will draw the max it can to get up to 85 inside the cabin, and then ramp down the power drawn to maintain that 85 degrees, cycling the system on/off as necessary.

If, on the other hand, you put the system in manual mode, crank the temp up 85, it will continue to pull the full 9kw to pump out 85 degree air until the battery is exhausted.

These days with any car that has an auto temp feature, I enable auto mode, and adjust the temp up/down to get airflow where I need/want it and to make myself comfortable. I'll let the system decide when to cycle the A/C compressor on/off, or turn on the heat.

 

[LeftieBiker]

If you have the climate control system I n auto mode, the car will automatically adjust the amount of power it is drawing to cool/heat the cabin to the set point you have selected, partially based on what the outside ambient air temperature is. I.e if it is 35 degrees out, and you set the temp to 85, it will draw the max it can to get up to 85 inside the cabin, and then ramp down the power drawn to maintain that 85 degrees, cycling the system on/off as necessary.

If, on the other hand, you put the system in manual mode, crank the temp up 85, it will continue to pull the full 9kw to pump out 85 degree air until the battery is exhausted.

These days with any car that has an auto temp feature, I enable auto mode, and adjust the temp up/down to get airflow where I need/want it and to make myself comfortable. I'll let the system decide when to cycle the A/C compressor on/off, or turn on the heat.

That isn't how the climate control works in the Leaf. We rarely use Auto mode because it draws more power, not less. If the car is in Eco mode then HVAC draw is restricted, to about 3kw in cars with the heat pump. I would be surprised if the Bolt didn't have a similar feature.

 

[peteblair]

More likely the salesman just told them it has a heat pump.

You would be correct. I assumed what they told me was correct so i've never looked into it.

Not really a shocker that a dealer got it wrong, I mean it is a completely new model.

 

[michael]

Perhaps the dealer gave the answer that would have been logical...a heat pump. Too bad they didn't actually provide one in the Bolt

 

[peteblair]

Perhaps the dealer gave the answer that would have been logical...a heat pump. Too bad they didn't actually provide one in the Bolt

That is my assumption as well.