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Air Conditioning hope

Air Conditioning hope

I hope that the A/C in Model 3 is the reverse-cycle type so that heating is far more energy efficient. I have a Gen 1 Leaf with resistive heating and I can tell you it sucks (the battery) big time, whereas even intense cooling barely moves the needle.

Gen 2 Leafs onwards have reverse-cycle A/C. Tesla would not want to bring a new car to market in 2017 and be outdone on something so basic.

A resistive heater could be part of the Cold Weather package, should people need it for that reason.

My 2c.

graylan.janulis | March 5, 2017

Well i don't think Tesla can really do much better than they already do. they are still new in the game give them a few more years to get down the Mod Cons, Nissan has been doing it for many many years now.

Frank99 | March 5, 2017

I agree with you, bj. For a majority of drivers, a heat pump would solve the vast majority of their heating needs with much less impact on range; a backup resistive heater for really cold days would handle the rest.

Fugacity | March 5, 2017

Model S has a cold weather package with heated seats. Reverse-cycle heating and heated seats should be good for cold weather. I should say that I live in Phoenix where 40 is a cold day.

Badbot | March 5, 2017

remember that making heat pumping below zero air outside the car sucks too.
plus the Teslas batteries are a tiny bot bigger than a leaf battery.

andy.connor.e | March 6, 2017

The reason heat draws more, is because resistive heat uses 100% of the energy put into for heat production.

Electric A/C does not. A/C uses less energy at a lower efficiency to give you cold air.
Electric Heat uses more energy at a higher efficiency.

topher | March 6, 2017

"Electric A/C does not. A/C uses less energy at a lower efficiency to give you cold air.
Electric Heat uses more energy at a higher efficiency."

No, the efficiency of A/C or heat pumps are about 3 to 4 times *greater* than the efficiency of resistive heat, by tricks of accounting mostly. The energy required to move heat is less than to create it. Note: A/C is often doing a lot of dehumidifying, which also takes energy, but which won't appear in a naive energy balance.

Thank you kindly.

Rutrow | March 6, 2017

How about a resistive heat source for warming up the car before you get in while still plugged in to its charger, then a more efficient process (heat pump/resistive, I'll stay out of the thermodynamics debate) to maintain warmth while underway. Maybe they could install small turbines to harness wind resistance... oh nevermind.

andy.connor.e | March 6, 2017

You do not understand how resistive heating works? 100% of the energy put into the heater is used. 100W in, ~100W out. Its the equivalent of hooking up resistors to a battery. On the (-) terminal side, there is 0V. 100% of the energy was used, and only 1 component absorbed the energy.

topher | March 6, 2017

"How about a resistive heat source for warming up the car before you get in while still plugged in to its charger, then a more efficient process (heat pump/resistive, I'll stay out of the thermodynamics debate) to maintain warmth while underway."

If you have a more efficient system why wouldn't you use it whenever you need heat?

Thank you kindly.

bj | March 6, 2017

@andy.connor.e - ignoring thermodynamics for a moment, the Leaf energy monitor has a separate dial for the accessories, which shows A/C cooling uses about 300W and resistive heating uses about 1200W. Four times as much energy is used to deviate the cabin temperature from ambient. There's little reason to doubt that a heat pump would also use about 300W since the thermodynamic process is the same, just in reverse.

I think what you're missing is that while 100% of the energy put into the resistive heater is used, most of that goes into making a coil of metal get really hot and glow red. Air is a terrible conductor of heat (to wit, double glazing) so only a small portion of that energy is successfully conducted to heating the air around it.

topher | March 6, 2017

"There's little reason to doubt that a heat pump would also use about 300W since the thermodynamic process is the same, just in reverse."

Actually not, the A/C process also includes dehumidification, so it isn't the same just in reverse.

"so only a small portion of that energy is successfully conducted to heating the air around it."

Nope. Where would it go then? Some of it gets radiated to surfaces nearby, but that quickly reaches equilibrium, other than that, all that power needs to be transferred away or the unit will fry. That is why there is a fan in there to increase air flow.

Thank you kindly.

bj | March 6, 2017

@topher - "the A/C process also includes dehumidification, so it isn't the same just in reverse" if you want to nit pick, yes, but does dehumidification change the total power consumption? Not to any significant amount, which is the substantive topic here.

"Nope. Where would it go then?" - as you know heat can be tranferred by conduction, convection, and radiation. The conduction to the air with resistive heaters is poor. Radiation is better, but the element is under the hood not in the cabin, so that doesn't help the occupants. Conduction and radiation to the chamber and mounting hardware is where a lot of the energy goes and in turn that's not well transferred to the air.

As to all that stuff reaching temperature equilibrium, of course it does, but if you're losing heating energy to keeping the chamber and mounting hardware hot and not very successfully transferring that heat to the air that goes into the cabin (e.g. re-radiated to the air outside instead) then it's still inefficient.

If resistive heating was efficient and most of the watts went in to heating the air instead of being wasted, then it wouldn't take 1200 watts to make you feel warm, but only 300 watts to make you feel cool.

Anyway why are you taking issue with this when the Leaf energy consumption dial substantiates your earlier point that "the efficiency of A/C or heat pumps are about 3 to 4 times *greater* than the efficiency of resistive heat". The Leaf data completely agrees with you! You have been vindicated! Woo hoo!

Frank99 | March 6, 2017

As long as the outside air temperature isn't "too low", a heat pump will put out (as Topher pointed out) 3-4 times as much heat as a resistive heater when the two are matched by power draw. For example, here in Phoenix where the occasional night in winter drops to 0C/32F, most houses are heated quite nicely with heat pumps. Some houses have an auxiliary resistive heater for those nights that drop so low that their heat pump stops working. If resistive heating were more efficient, EVERYONE would use one all the time.

There's a great chart 2/3 of the way down this page:
https://asm-air com/hvac/heat-pump-vs-furnace-pros-cons/
(Direct link to image: https://asm-air com/wp-content/uploads/2014/11/heat_pump_vs_furnace_annual_heating_cost.jpg)
showing

Carl Thompson | March 7, 2017

bj:
"Radiation is better, but the element is under the hood not in the cabin, so that doesn't help the occupants."

Why can't the element be in the cabin? Maybe in the floor or roof...

Carl

luwong.8888 | March 7, 2017

The floor would be the best location. Takes advantage of heat rising. Con, that is where the batteries are, so another chamber above the batteries will make the vehicle taller, thicker floor. If we put the heating element in the roof, thicker roof, less head room.

topher | March 7, 2017

"but does dehumidification change the total power consumption? Not to any significant amount, which is the substantive topic here"

Yes, it does. Lowering the temperature of 1 pound of air involves 0.24 BTUs. Condensing 1 pound of water, 970 BTUs. Look up the Enthalpy of various humidity levels on a Psychrometric chart.

Thank you kindly.

topher | March 7, 2017

Pet Peeve: "Takes advantage of heat rising." Heat does not rise. Warmer fluids rise relative to cooler fluids (that's convection).

Thank you kindly.

topher | March 7, 2017

"Conduction and radiation to the chamber and mounting hardware is where a lot of the energy goes and in turn that's not well transferred to the air."

And then where does it go? If you are putting energy continuously into an object, it either needs to transfer it somewhere else or it just keeps getting hotter.

"but if you're losing heating energy to keeping the chamber and mounting hardware hot"

There is no such thing as "keeping something hot". Conservation of energy says that they stay the same temperature unless they lose that energy to somewhere else.

"then it wouldn't take 1200 watts to make you feel warm, but only 300 watts to make you feel cool."

That is just nonsense. what it takes to make you feel warm is dependent on a large number of things, most of which have nothing to do with those watts. Mean radiant temperature, air temperature, humidity, air flow, clothing, etc.

"You have been vindicated! "

I am not looking for vindication, I am looking to educate. The thermodynamics of creature comfort are not obvious or well known.

Thank you kindly.

Red Sage ca us | March 7, 2017

Uhm... Isn't all this why Tesla chose to put heating elements in the seats?

Carl Thompson | March 7, 2017

topher:
"And then where does it go? If you are putting energy continuously into an object, it either needs to transfer it somewhere else or it just keeps getting hotter."

I think his point was that because the heating element is outside of the cabin under the hood much energy is lost due to heating the _outside_ air surrounding it.

Carl

bj | March 7, 2017

@topher - maybe you are being mischevous, but I'm intrigued. If all those watts going into a resistive heater are not being wasted in heating up things other than the cabin air to make the occupants feel warm, then you are implying resistive heating is in fact very efficient (since apparently not much energy is being wasted heating other irrelevant things).

But that would contradict your earlier claim that a heat pump has 3x - 4x better efficiency. You can't have better than 100% efficiency, so even if a heat pump was 100% efficient, the implication is that resistive heating is no better than 25-33% efficient.

So maybe you should tell us roughly what proportion of the energy going into a resistive heater is successfully transferred to the cabin air? And where is the remainder of that energy going?

Happy to be educated.

Rocky_H | March 7, 2017

@bj, Quote: "But that would contradict your earlier claim that a heat pump has 3x - 4x better efficiency. You can't have better than 100% efficiency, so even if a heat pump was 100% efficient, the implication is that resistive heating is no better than 25-33% efficient."

It seems a little counterintuitive until you read about it, but yes, heat pumps do achieve higher than 100% efficiency. That is because they are not directly converting energy from electricity to heat. That could never get higher than 100%. Heat pumps use mechanical means to move heat energy from one place to another, so they can use 500W of energy to make a 1,000W difference in the heat in an area.

It's called a "coefficient of performance".
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatpump.html

https://en.wikipedia.org/wiki/Coefficient_of_performance

bj | March 7, 2017

@Carl - "Why can't the element be in the cabin? Maybe in the floor or roof..."

Sure, it could be put in lots of places, but whether the regulators would ever approve it... Anything accessible that is hot to touch would be a safety risk.

bj | March 7, 2017

@Rocky_H - "It's called a coefficient of performance".

OK, got it now. So a resistive heater is a one-trick pony, it can't pump heat energy from one place to another, to make one place hotter while it makes another place cooler (and vice versa).

Which reinforces my OP - Tesla should put a reverse-cycle (aka heat pump) A/C in the Model 3.

Carl Thompson | March 7, 2017

Rocky_H:
"...they can use 500W of energy to make a 1,000W difference..."

Wow. That would be a neat trick.

bj:
"Sure, it could be put in lots of places, but whether the regulators would ever approve it... Anything accessible that is hot to touch would be a safety risk."

Who said it would have to be too hot to the touch? If a large enough surface area (floor + roof maybe) were heated to say 100F it would be enough to heat the car quickly but not hot enough to be uncomfortable if you were to touch it.

Carl

dsvick | March 8, 2017

@carl - "If a large enough surface area (floor + roof maybe) were heated to say 100F it would be enough to heat the car quickly ..."

The problem you run into there is in all those cars with dual climate control (which I never understood anyway). If you're arbitrarily heating the entire cabin then you'll end up with some people who won't like the fact that they can't control their own little micro-climate.

Your other problem will be location, I'm not sure the floor will work because then your putting a large heat source very close the battery. In some cases that might be good, in others not so much. And the roof will only work in those cars that have the metal roof option, even then I think the area would be too small to do anything effectively.

Rocky_H | March 8, 2017

@Carl, Rocky_H:
"...they can use 500W of energy to make a 1,000W difference..."

Wow. That would be a neat trick.

I was actually being conservative. Many large scale building heat pump systems that use a ground source for the constant temperature to draw from get coefficient of performance of 3X or 4X.

topher | March 8, 2017

@bj: "But that would contradict your earlier claim that a heat pump has 3x - 4x better efficiency. You can't have better than 100% efficiency, so even if a heat pump was 100% efficient, the implication is that resistive heating is no better than 25-33% efficient."

My apologies for not making this clearer. It is explained well by others above, but another way to think of it is that a heat pump is getting energy from two places, 1) the electricity you put in, 2) heat energy from outside. The *total* energy input is (of course) less than the useful energy output. Since you are only *paying* for the electricity it looks (from your perspective) that you are getting greater than 100% efficiency. If you parked your car inside your house (or other areas that you pay to heat), you would be paying for *all* of the energy, and they would cost the same (AOTBE). This is the 'tricks of accounting' to which I alluded.

Hard to know exactly what portion of the energy input in a car resistive heater is going to the occupants comfort. Given a reasonable design, I would expect about 80-90%. Some of that heats the air, but most of it heats solid things in the passenger compartment (via the air). The remaining bit heats the outside through various other paths. But cars are not very insulated, and the cabin heat escapes pretty fast, which is why you need to keep your heater on most of the time in really cold weather.

Thank you kindly.

Carl Thompson | March 8, 2017

@Rocky_H

You quietly corrected yourself there. What you actually originally said was:

"It seems a little counterintuitive until you read about it, but yes, heat pumps do achieve higher than 100% efficiency. "

No, that's not possible. But your self-corrected version is accurate:

"...coefficient of performance of 3X or 4X"

Much better.

Your quote:

"...they can use 500W of energy to make a 1,000W difference in the heat in an area."

Is similarly incorrect for a couple of reasons. 500W of energy always makes 500W of difference (however you define that). And "1,000W difference in the heat in an area" is meaningless primarily because watts are a unit power and not a unit of "heat" (whatever that would be). Maybe what you meant to say was something like "500W of power is can be used to produce the equivalent affect on cabin temperature as a 1000W resistive heating element." Though if that's what you meant I'd want to see sources.

Sorry if I was a bit flippant in my response, though.

Carl

Rocky_H | March 8, 2017

Wow, someone wants to be a GIGANTIC douche.
Carl, someone has something he wants to say to you.
" I can see that you can technically make that argument. I think it's sad that you'd want to win a debate by resorting to a technicality but, OK."

Carl Thompson | March 8, 2017

@Rocky_H

I was just responding to _your_ comment to _me_. That's allowed, right?

What you wrote simply made no logical sense and was thus devoid of actual meaning. That's not simply a "technicality." I'm not saying you're a bad person. You just made a mistake. Just because I point out a mistake in something you said to me doesn't make me a "GIGANTIC douche" and saying so doesn't advance the discussion.

Carl

Red Sage ca us | March 8, 2017

OK, a used, rotting douche, that gave its original owner toxic shock syndrome. Is that better?

Rocky_H | March 8, 2017

@Carl, But your response was (1) Incorrect and then (2) Nitpicking and unhelpful

First there was this part about the greater than 100% efficiency.
"No, that's not possible. But your self-corrected version is accurate:"

I was being accurate. The coefficient of performance is the efficiency rating of a heat pump system. It is always higher than 100% efficient. So you just wanted to argue and falsely tell me I was wrong.

Then the part about the 500W and 1,000W was just picking on my phrasing. Yes, I did mean that the energy use rate of 500W through a heat pump could yield the same amount of heating as 1,000W from a regular resistive heater. That does seem really self-explanatory.

Quote: "Though if that's what you meant I'd want to see sources."

Sources? I gave sources when I was explaining it to @bj.
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatpump.html
https://en.wikipedia.org/wiki/Coefficient_of_performance

And here's another one:'
http://www.industrialheatpumps.nl/en/how_it_works/cop_heat_pump/

I'm sorry, everyone that it is having to devolve into this.

gavinfaulkner | March 8, 2017

Getting back on topic. Tesla could consider incorporating heat batteries.. Something similar to what Robert Lewellyn (aka Kryton from Red Dwarf) introduced on his Fully Charged youtube blog. Sunamp solar heat batteries.

Clearly heating is difficult to do efficiently but if you could store thermal energy for sufficiently long periods you could solve some of the problems already mentioned in this thread. (Plus, as a bonus it could be used to regulate battery temperature in cold environments and act as a heat sink/heat exchanger in warm environments)

Rocky_H | March 8, 2017

Let me offer this.
@Carl Thompson, I am sorry for the douche remark. That was name calling and wasn't right.

Carl Thompson | March 8, 2017

Rocky_H:
"I was being accurate. The coefficient of performance is the efficiency rating of a heat pump system. It is always higher than 100% efficient. So you just wanted to argue and falsely tell me I was wrong."

Well, you asked. You could have left it alone if you didn't want me to explain why you were wrong. Efficiencies greater than 100% are not possible for _anything_... including heat pumps. Even 100% efficiency is not possible. I'm really not trying to offend you but it was very unclear just what you were trying to say. If you misuse words and scientific concepts then it's going to be tough to follow you.

It's OK about the name calling. I am a bit too sarcastic myself sometimes. It's just a sign that people are really excited about Tesla and electric cars. We just need to make sure there's room for other points of view and for (hopefully polite) disagreement!

Carl

Bill Korea | March 8, 2017

For heating, the heat pump can be very efficient when the source heat (ambient air for a car) is close to or beyond the target temperature. If the ambient air is cold enough, the heat pump can be completely useless for heating. Some of us northerners have learned to be somewhat critical of some of the energy ideas coming from our southern neighbors.

Carl Thompson | March 8, 2017

This is a good conversation with great information. It's made me realize that it could be a good idea to switch my house from gas heating to a heat pump. It's a small house, I live in the SF Bay Area where it rarely gets below 35F and my solar panels make more electricity than I use. Seems like it would be a good fit for my situation. Does anyone know of any negatives?

Thanks,
Carl

Frank99 | March 9, 2017

From an environmental POV, the heat pump will cause fewer pollutants and CO2 to be released to the atmosphere especially since you have excess solar capacity. And you'll never have to worry about carbon monoxide poisoning from leaks in the flue.

If you didn't have solar, it's likely that the gas furnace would cost you less per month to run than the electric heat pump. At least, that's been my experience in the past, but I don't have a clue what relative energy costs are in the Bay Area. With solar, the cost question is complicated because most of the heating costs would come at night.

The Heat pump should do fine for you. I live in Phoenix where the winter lows are generally in the 30's with occasional (one or two nights a year) excursions to the high 20's, and our heat pump keeps us toasty warm. If your location ever drops below this, I'd look closely at the low-temp performance of any proposed heat pump.

Carl Thompson | March 9, 2017

Frank99:
"If you didn't have solar, it's likely that the gas furnace would cost you less per month to run than the electric heat pump."

Really? I thought the whole point of heat pumps was that they were cheaper than gas when temperatures aren't too cold?

Carl

Haggy | March 9, 2017

The Model S has heated front seats even without the cold weather package. It's far more efficient to heat the seats than to heat the cabin. But unless you will be coming anywhere close to using up your range, it won't make a practical difference.

Frank99 | March 9, 2017

Carl -
Heat pumps are cheaper than Resistive heat, but not necessarily Natural Gas. There are two completely different delivery systems and taxing systems for gas v. electricity; due to fracking, the cost of natural gas has gone down significantly in the last few years. It all really depends on your local costs of gas, electricity, the age and efficiency of your furnace, and the cost/efficiency of the new heat pump.

Here's a good series that talks about it: http://sensiblenergy com/home-energy-efficiency-blog/cost-comparison-gas-vs-oil-vs-electricity-part-4/

Carl Thompson | March 9, 2017

@Frank99

Thanks for the info!

topher | March 9, 2017

" it's likely that the gas furnace would cost you less per month to run than the electric heat pump"

Around here, heat pumps are slightly cheaper than natural gas (also far more available). But if you want to see a comparison you can go to http://www.greenfret.com/calculators/fuels.html and add your own values for price and efficiency, to see what would be cheaper for you.

Thank you kindly.