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Ingineer
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Delivery Date: 13 Jul 2011
Leaf Number: 6969
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Re: Why hot water heating?

Tue Nov 22, 2011 9:40 am

cwerdna wrote:
Ingineer wrote: The biggest disappointment is the lack of a heat-pump system. This would have enabled heating at a much lower energy cost, all for the addition of an $18 reversing valve (my cost at the local refrigeration supply house) and some software. Toyota has done it on the plug-in-Prius!
Regarding the PiP, you sure about that on the production model? See http://priuschat.com/forums/prius-hybri ... ost1389049" onclick="window.open(this.href);return false;.
Wow, you are right, according to Doug, they scrapped it for the Production models. I studied it thoroughly on the demos, it was a nice setup, and it's definitely not for the reasons Doug is claiming; Weight/Complexity? Weight is total B/S, it's just basically an aluminum reversing valve with a small solenoid. Complexity might be a partial truth; the real reason is probably to save a few $.

After all, in a car that will probably only drive 15-20 minutes on Electric, the cabin pre-heat is enough to keep it warm until the ICE kicks in. But in a BEV like the Leaf, it would be a great benefit!

-Phil
Easily Learn Electricity HERE! - - - - Website: http://evseupgrade.com/[/size] - - - - Like us on Facebook: EVSE Upgrade

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EVDRIVER
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Re: Why hot water heating?

Tue Nov 22, 2011 9:42 am

It was because the LEAF is not a ground-up EV as Nissan would like everyone to believe. They use many parts form ICE cars and trucks including the heat which is simply an ICE system with an inefficient and slow tank heating system. This is the EXACT same system used in an ICE conversion for years when one is too lazy or it is too difficult to use another type of heater. A heat pump would have been vastly better, far more efficient, and lower weight with fewer parts and not to mention faster. At the very least they could have designed it so it would not always come on when it's not needed, it's like a double hit on efficiency.

HighDesertDriver
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Re: Why hot water heating?

Tue Nov 22, 2011 9:47 am

Ingineer wrote:The biggest disappointment is the lack of a heat-pump system. This would have enabled heating at a much lower energy cost, all for the addition of an $18 reversing valve (my cost at the local refrigeration supply house) and some software. Toyota has done it on the plug-in-Prius!
And where is this project on your growing and interesting list of potential improvements for development?! I'm guessing that labor for installation might be the biggest piece of this mod because opening and restoring the refrigerant loop requires equipment not found in most home garages. On a personal note, all of your efforts are applauded and of interest to this LEAF owner. Thanks for contributing!
2011 Glacier Pearl SL QC
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vegastar
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Re: Why hot water heating?

Tue Nov 22, 2011 9:50 am

For really cold weathers a heat pump alone would not work. The best would be a heat pump and the current system. Up to 0ºC (32ºF) a heat pump is enough and very efficient, below that it would be necessary a resistive heating element.
2011 Nissan LEAF since 2011-07-07, 151000 km on 2018-03-03, 7 bars, 37.9Ah.

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EVDRIVER
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Re: Why hot water heating?

Tue Nov 22, 2011 10:22 am

vegastar wrote:For really cold weathers a heat pump alone would not work. The best would be a heat pump and the current system. Up to 0ºC (32ºF) a heat pump is enough and very efficient, below that it would be necessary a resistive heating element.

The Think had a electric heating element like many EVs. it would heat in 10 seconds. That could be used in conjunction with a heat pump. Nissan also blew it by not making heated seats standard in all cars or at least an option, at a couple hundred watts total it would beat using the heater in many cases.

jkirkebo
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Re: Why hot water heating?

Tue Nov 22, 2011 10:33 am

vegastar wrote:For really cold weathers a heat pump alone would not work. The best would be a heat pump and the current system. Up to 0ºC (32ºF) a heat pump is enough and very efficient, below that it would be necessary a resistive heating element.
Modern heat pumps work well down to at least 0F/-18C. For example the newest Toshibas has a COP of between 2,07 and 2,25 at -15C (5F). So you'd need about 2kW input to get 4.5kW output in 5F weather. A big improvement IMHO. The 5kW resistive element should be retained of course, it can get colder than -40 (C or F) over here some places.

edatoakrun
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Re: Why hot water heating?

Tue Nov 22, 2011 10:42 am

jkirkebo wrote:
vegastar wrote:For really cold weathers a heat pump alone would not work. The best would be a heat pump and the current system. Up to 0ºC (32ºF) a heat pump is enough and very efficient, below that it would be necessary a resistive heating element.
Modern heat pumps work well down to at least 0F/-18C. For example the newest Toshibas has a COP of between 2,07 and 2,25 at -15C (5F). So you'd need about 2kW input to get 4.5kW output in 5F weather...
In automotive applications?
no condition is permanent

jkirkebo
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Re: Why hot water heating?

Tue Nov 22, 2011 10:46 am

edatoakrun wrote:
jkirkebo wrote:
vegastar wrote:For really cold weathers a heat pump alone would not work. The best would be a heat pump and the current system. Up to 0ºC (32ºF) a heat pump is enough and very efficient, below that it would be necessary a resistive heating element.
Modern heat pumps work well down to at least 0F/-18C. For example the newest Toshibas has a COP of between 2,07 and 2,25 at -15C (5F). So you'd need about 2kW input to get 4.5kW output in 5F weather...
In automotive applications?
I don't see why automotive applications would be any different ? You can use more or less the same components.

vegastar
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Re: Why hot water heating?

Tue Nov 22, 2011 12:20 pm

Those new Heat Pumps that work well in sub freezing temperatures are very expensive and I don't know if they are possible in a space restricted area as an automobile. Of course if possible they should be used as long as the price can be kept low.
2011 Nissan LEAF since 2011-07-07, 151000 km on 2018-03-03, 7 bars, 37.9Ah.

Smidge204
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Re: Why hot water heating?

Tue Nov 22, 2011 12:26 pm

jkirkebo wrote:I don't see why automotive applications would be any different ? You can use more or less the same components.
It's not. It's all about how good your compressor is: Can you create enough suction to boil the refrigerant at the low ambient temperature? Can you also create enough pressure so the discharge gas is hot enough (via heat of compression) to do useful heating?

The limiting factor is usually the discharge temperature. As outside temperature drops the compressor is doing more and more work to keep the gas hot, and at some point if becomes difficult to keep things operating efficiently. The larger the the temperature difference, the larger the portion of energy the compressor contributes, and the COP drops like a stone.

A heat pump with electric element assist is the best option IMHO. The water in the system does provide some pre-heat buffer which is nice, but I'm not sure that was really the full intention plus it's extra weight you might not really need to carry. Get as far as you can with the heat pump and boost it with a direct-to-air heater element. Bonus points if you can scavenge any waste heat off of the motor/inverter system as input for the heat pump (would probably backfire in the cooling season, though!)
=Smidge=

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