# [EVDL] Reversible air conditioning



## EVDL List (Jul 27, 2007)

You can't reverse the compressor to reverse the system.

You have to add some valving and such to convert an AC into a heat pump. 
You will also have to improve the control system, such as the installation 
of a outside coil temp sensor, otherwise you will experience evaporator 
(outside) coil ice-up on cold days and the system will stop working.

There are some automotive heat-pump systems on some cars, but for DIY, the 
expense and complexity compared to a ceramic system is not worth it IMHO.

Another option is to use a fuel-fired heater that provides hot water to the 
existing heater core. This is how my system works. Only a few gallons per 
winter fuel usage.

-Phil
http://evalbum.com/1413

----- Original Message ----- 
From: "Tom Parker" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Sunday, December 23, 2007 3:47 AM
Subject: [EVDL] Reversible air conditioning


>


> Metric Mind wrote:
> >> BTW, I'm negotiation distributorship with Masterflux to add their
> >> systems to the line of products I have. Later on their inverter
> >> will have to be replaced by simpler version but today it can be used as
> ...


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## EVDL List (Jul 27, 2007)

On Dec 23, 2007 10:01 AM, ( Phil ) <[email protected]> wrote:

> You will also have to improve the control system, such as the installation
> of a outside coil temp sensor, otherwise you will experience evaporator
> (outside) coil ice-up on cold days and the system will stop working.
>

Yup, heat pumps don't really work below about 40F or so, because they
start icing the evaporator coils. Typical heat pumps for heating
houses switch on an electric heating element at lower temperatures.
Since most of the time that you want heat in a car is when it's below
freezing (to defrost the windows, etc), you'd be using the electric
resistance heating most of the time anyway.

Doesn't the prius have a heat pump system though?

Z

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## EVDL List (Jul 27, 2007)

A heating element is almost 100% efficient. One of the few things out
there that is. Why mess with that?

The vapor compression refrigeration cycle is more efficient that peltier
but less than the magnetic(which we have yet to see make it in a car.)

Absorption is more efficient than compression, It never made it into car
A/C, other than RV refrigerators. Ammonia is rather poisonous and the
vapor compression is much faster initially. There is a compression
absorption but it is complicated.

How about this idea. two tubes filled with calcium chloride there is a
valve and a heat exchanger to another vessel. this is charged with ammonia.
when charging, the ammonia is driven off the calcium chloride by the
heaters while a fan blows across the heat exchanger to liquefy the
ammonia into the second vessel.

When you are driving, the valve is opened and the fan is reversed and
the ammonia is allowed to go from pressurized liquid to gas and be
reabsorbed onto the calcium chloride. IT gets VERY cold when this
happens. In fact the valve will have to be modulated to prevent the air
coming out of the duct from being too cold.

Why two sets? well for longer drives in really hot areas, you can start
with two charged tubes and when you are on the second set, the first one
can be recharged off of pack or regen energy.

http://www.solarhaven.org/AmmoniaAbsorptionIcemaker.pdf


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## EVDL List (Jul 27, 2007)

Sorry, but even though an electric heater is pretty efficient (not 100% but 
close), it's almost always "cheaper" to move heat from somewhere else than 
to make it.

But it's not always about efficiency. The complexity of an in-car heat pump 
is probably out of reach of a DIY operation.

-Phil
----- Original Message ----- 
From: "Jeff Shanab" <[email protected]>
To: <[email protected]>
Sent: Sunday, December 23, 2007 12:46 PM
Subject: Re: [EVDL] Reversible air conditioning


>A heating element is almost 100% efficient. One of the few things out
> there that is. Why mess with that?
>
> The vapor compression refrigeration cycle is more efficient that peltier
> but less than the magnetic(which we have yet to see make it in a car.)
>
> Absorption is more efficient than compression, It never made it into car
> A/C, other than RV refrigerators. Ammonia is rather poisonous and the
> vapor compression is much faster initially. There is a compression
> absorption but it is complicated.
>
> How about this idea. two tubes filled with calcium chloride there is a
> valve and a heat exchanger to another vessel. this is charged with 
> ammonia.
> when charging, the ammonia is driven off the calcium chloride by the
> heaters while a fan blows across the heat exchanger to liquefy the
> ammonia into the second vessel.
>
> When you are driving, the valve is opened and the fan is reversed and
> the ammonia is allowed to go from pressurized liquid to gas and be
> reabsorbed onto the calcium chloride. IT gets VERY cold when this
> happens. In fact the valve will have to be modulated to prevent the air
> coming out of the duct from being too cold.
>
> Why two sets? well for longer drives in really hot areas, you can start
> with two charged tubes and when you are on the second set, the first one
> can be recharged off of pack or regen energy.
>
> http://www.solarhaven.org/AmmoniaAbsorptionIcemaker.pdf
>
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
> 

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## EVDL List (Jul 27, 2007)

couldn't a refrigerator be used. a matter of selecting which end you 
want fanned into the cabin and which out to the environment.
or why not use a car AC and supply whatever function is missing. seems 
like the simplest way to get it right

Dan

( Phil ) wrote:
> But it's not always about efficiency. The complexity of an in-car heat pump 
> is probably out of reach of a DIY operation.
> 

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## EVDL List (Jul 27, 2007)

Driving stock compressor (plumbed into already built A/C system in any 
car) with external motor is simplest way to go. At minimum you need only 
one DC motor running off the traction pack to do it. Not so slick 
solution is pulley from the tail shaft of now idling traction motor, 
this already been discussed on EVDL many times.

A heater, liquid or ceramic, IMO should be separate (and is indeed very 
simple) sub-system.

Other advantage of separation - if one subsystem fails, the other
keep functioning. A heat pump is more suitable solution for OEM
ground up EV. Doable, but requires too specialized skills and machining.

Just an opinion.

Victor



> Jeff Shanab wrote:
> > A heating element is almost 100% efficient. One of the few things out
> > there that is. Why mess with that?
> >
> ...


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## EVDL List (Jul 27, 2007)

> Tom Parker wrote:
> ...
> >> http://metricmind.com/ac.htm
> >
> ...


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## EVDL List (Jul 27, 2007)

On Sun, 2007-12-23 at 22:21 +0100, Dan Frederiksen wrote: 
> couldn't a refrigerator be used. a matter of selecting which end you 
> want fanned into the cabin and which out to the environment.
> or why not use a car AC and supply whatever function is missing. seems 
> like the simplest way to get it right

Conceptually that is the simplist, "create a system of ducts, fans and
boxes to house the evaporator and condensor, with a door to select which
recirculates cabin air and which has outside air pass through it".

However when you want to pack it into a very small car and you want
something close to the original sized condenser you are asking for the
impossible. If you made everything quite small and you were clever, you
could probably make it all fit, but I would expect the cooling mode to
be seriously compromised by the small condenser.

If you had all the parts to make a reversible heat pump it would likely
be far superior.

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## EVDL List (Jul 27, 2007)

> Metric Mind wrote:
> > > Due to the wonders of British engineering, my car has completely
> > > separate heating and cooling units. I'd like to drop the heater as it's
> > > noisy and I can save some weight by integrating it with the air
> ...


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## EVDL List (Jul 27, 2007)

> Driving stock compressor (plumbed into already built A/C system in any 
> car) with external motor is simplest way to go. At minimum you need only 
> one DC motor running off the traction pack to do it. Not so slick 
> solution is pulley from the tail shaft of now idling traction motor, 
> this already been discussed on EVDL many times.

Doesn't necessarily have to idle. On my Mariner hybrid the AC is powered 
by the ICE and shuts off when the engine is off. At a long light the air 
coming out gradually gets warmer but as soon as I start moving again and 
the ICE kicks in the air gets cold again. There's a max setting which 
keeps the ICE running but I rarely find it necessary.

I agree, though, that a separate DC motor is the better way to go. 
Especially if you live somewhere hot where you really would want the AC 
on all the time.

--Rick

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## EVDL List (Jul 27, 2007)

Tom,

I may have misunderstood but I got the impression that the Aptera has a
heating/cooling system that does what you want - it was referred to in the
Pop Mechanics' recent video as a 'heat pump' and 'reversible' (the relevant
bit of the clip is at 5m40sec). This might be an area you would want to
investigate further.

Regards, Martin Winlow

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Tom Parker
Sent: 23 December 2007 11:48
To: Electric Vehicle Discussion List
Subject: [EVDL] Reversible air conditioning



> Metric Mind wrote:
> > BTW, I'm negotiation distributorship with Masterflux to add their
> > systems to the line of products I have. Later on their inverter will
> > have to be replaced by simpler version but today it can be used as is.
> ...


----------



## EVDL List (Jul 27, 2007)

The aptera uses a heat pump for air conditioning.
>
> If you had all the parts to make a reversible heat pump it would likely
> be far superior.
>


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