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LTLFTcomposite
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Re: Heater

Sat Apr 24, 2010 5:23 pm

Add that to the feature content list for Leaf 2.0 - reverse cycle A/C for heat

One problem you have with heat pumps/reverse cycle AC for heating is they lose effectiveness at lower temps.
LTL
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daniel
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Re: Heater

Sat Apr 24, 2010 6:39 pm

LTLFTcomposite wrote:From what I saw on the evening news, nobody there is yet concerned about declining population.
Just wait until they start having water outages!
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KarenRei
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Re: Heater

Sat Apr 24, 2010 7:01 pm

LTLFTcomposite wrote:Add that to the feature content list for Leaf 2.0 - reverse cycle A/C for heat

One problem you have with heat pumps/reverse cycle AC for heating is they lose effectiveness at lower temps.
Indeed. But they're still a lot more efficient than resistive.

To simplify it, an air conditioner is a device that moves heat from one radiator to another, wherein the one having heat removed from it has a fan over it that leads into the vehicle, while the one having heat pushed into it has a fan over it that blows to outside air. A reversible heat pump can change which radiator is which. Another alternative is to keep the radiators the same, but simply switch where the ducts are leading.

It's just a matter of ducts and solenoids.

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sjfotos
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Re: Heater

Sat Apr 24, 2010 7:13 pm

I'm guessing the problem for an 'all heat pump' solution is the problem faced by my original heat pump installation here in Pennsylvania for my house. Once it gets down into the 30's (F) it just can't keep up. In any event, it will be interesting to see how it all works in a real application in the North.
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KarenRei
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Re: Heater

Sat Apr 24, 2010 7:16 pm

daniel wrote:
LTLFTcomposite wrote:From what I saw on the evening news, nobody there is yet concerned about declining population.
Just wait until they start having water outages!
Eh, what'll happen is that agriculture fed by the Colorado River will start getting pushed out of business. Farmers can't afford to pay nearly as much for water as people can pay for water for their homes. If it gets bad enough, you'll see desalination plants in California and an adjustment of the Colorado River Compact, with the upper states helping pay the cost in exchange for more of the river's water. Desalination water is generally too expensive for agriculture, but again, what's too expensive for agriculture isn't necessarily too expensive for homes.

Also, there's some interesting new desalination techs out there. My favorite -- although it'll require some massive-scale high-throughput ion-selective membranes or salt bridges to work -- is this really clever one involving evaporation ponds. So, basically, black-bottomed open-air evaporation ponds aren't very expensive. They're a *lot* cheaper than covered ones that try to collect condensation from the evaporation. So you can get very salty brine, many times saltier than seawater, really cheap. Now, that's the opposite of what you want, right? You want freshwater. So what they do is they link it up to two different ponds of normal concentration seawater with ion-selective channels -- one pond gets positive ions, like sodium, and the other pond negative ions, like chlorine. Now, obviously, the ions *really* want to travel out of this super-concentrated brine into these other ponds so they can all be equal saltiness... but they can't. If they did, they'd be mismatched! So, they bring into play a third pond of regular seawater. It also provides an ion channel to each of the other two seawater ponds, of the opposite type -- that is, the pond that has a positive ion channel to the brine gets a negative one, and the one that had a negative ion channel to the brine gets a positive one. So the brine gets to push ions down from its extreme concentration, so long as an opposite ion gets sucked out of the third seawater pond. Since the ions *really* want to leave the super-concentrated brine, that's no problem. And so what you end up with is all of the salt being sucked out of the third seawater pond in the process. Freshwater, with no electricity input! Again, though, the issue is making said membranes high enough throughput and low enough cost.

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garygid
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Re: Heater

Sat Apr 24, 2010 7:21 pm

One dual-port valve to re-direct the refrigerant's flow right after it leaves the one-way compressor?

Either to the inside radiator (cabin heating) or to the outside radiator (cabin cooling).
No air-duct switching needed.
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LTLFTcomposite
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Re: Heater

Sat Apr 24, 2010 7:26 pm

KarenRei wrote:
LTLFTcomposite wrote:Add that to the feature content list for Leaf 2.0 - reverse cycle A/C for heat

One problem you have with heat pumps/reverse cycle AC for heating is they lose effectiveness at lower temps.
Indeed. But they're still a lot more efficient than resistive.

To simplify it, an air conditioner is a device that moves heat from one radiator to another, wherein the one having heat removed from it has a fan over it that leads into the vehicle, while the one having heat pushed into it has a fan over it that blows to outside air. A reversible heat pump can change which radiator is which. Another alternative is to keep the radiators the same, but simply switch where the ducts are leading.

It's just a matter of ducts and solenoids.
I've never seen a reverse cycle system that worked that way. Converting an automotive ac system to a heater with ducting doesn't sound to practical. The condenser is out in front where it gets airflow (probably why you still see a fairly sizable grill). The usual approach of reversing the gas/liquid flow would be a lot easier IMO.

As for reverse cycle systems being more efficient than resistive, that's true up to a point. In really cold temps they don't work at all.
LTL
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2013 Volt replaced after 36 months/30k miles with ICE Rogue
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mitch672
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Re: Heater

Sat Apr 24, 2010 7:27 pm

wow KarenRei , I though I was one of the brightest people here, I see now I am not worthy :(
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LTLFTcomposite
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Re: Heater

Sat Apr 24, 2010 7:30 pm

garygid wrote:One dual-port valve to re-direct the refrigerant's flow right after it leaves the one-way compressor?

Either to the inside radiator (cabin heating) or to the outside radiator (cabin cooling).
No air-duct switching needed.
If the compressor is powered by a DC motor maybe you can switch between heat and AC by just switching the polarity! :-)
LTL
White 2012 SV delivered 10 Dec 2011 returned 25 Nov 2014 replaced with stopgap ICE Sentra
[35 months] [35K miles] [9 Bars]
2013 Volt replaced after 36 months/30k miles with ICE Rogue
2016 SV-adjacent May 2016 lost 4th bar March 2018

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garygid
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Re: Heater

Sat Apr 24, 2010 7:57 pm

Yes, switching the motor direction is easy.

However, I suspect it is difficult to design a compressor that works efficiently in both directions.
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2011 LEAF, 2014 Tesla S85
2018 & 2019 Tesla Model 3
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