alozzy
Posts: 1039
Joined: Fri Jan 20, 2017 4:25 pm
Delivery Date: 18 Jan 2017
Location: Vancouver, BC
Contact: Website

Re: Still can't understand my heat pump!

Mon Mar 05, 2018 4:09 pm

As I stated before, I don't really care if the cabin reaches the temperature set point - I just want a clear windshield. So, for my purposes, cycling the heat + AC in order to clear the windshield is definitely more efficient than heat only...

When relatively warm air hits the colder glass of the windshield, the temp of the air drops to the saturation point, at which point some water vapour condenses on the windshield and fogs it up. By using heat + AC, the much dryer air produced by the AC mode results in a higher capacity for that air to take up water vapour, despite the air temperature being lower than with heat only mode. Fast defogging is what I'm after, in the most efficient way possible - which is why I keep saying that heat + AC is more efficient.

I get what you are saying about the intuitive physics, the heat pump should be more efficient than the PTC and; therefore, using heat only mode on an SV/SL should be more efficient than heat + AC - if the end goal is to heat the cabin to the temperature set point. With AC enabled, the heat pump should switch the reversing valve and the evaporator coil becomes the condensor and visa versa. As you stated, the PTC is heating the air, the heat pump is cooling and drying that same air, and the total energy usage is higher in heat + AC - but only if you are running it continously and wanting to reach the temperature set point.

The problem, as noted by BuckMkII, is that the LEAF's "Climate Control" graph is super misleading and therefore confusing.
Vancouver, CA owner of a 2013 Ocean Blue SV + QC, purchased 01/2017 in WA
Zencar 12/20/24/30A L1/L2 portable EVSE
1-1/4" Curt #11396 hitch
After market, DIY LED DRLs
LeafSpy Pro + Konnwei KW902 ELM327 BT OBDII dongle
Loving my first BEV :D

LeftieBiker
Posts: 9063
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 31 May 2013
Location: Upstate New York, US

Re: Still can't understand my heat pump!

Mon Mar 05, 2018 5:03 pm

If you had just written at the beginning that you were talking specifically about efficiency in clearing the windshield without heating the cabin, we could have saved me some typing! The majority of BEV drivers want cabin heat as well, though. I suppose that I should add to Tips & Tricks the technique of setting the CC for defrost with heat and A/C, and then just using the climate control On/Off button as needed to keep the windshield clear. Again, though, that would be for people who choose to drive with little cabin heat and just want maximum Winter range while keeping the windshield clear.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

alozzy
Posts: 1039
Joined: Fri Jan 20, 2017 4:25 pm
Delivery Date: 18 Jan 2017
Location: Vancouver, BC
Contact: Website

Re: Still can't understand my heat pump!

Mon Mar 05, 2018 6:37 pm

Sorry for any confusion, I tend to fixate on maximizing range and forget that others keep the heat running all the time to have a toasty warm cabin. I'm so looking forward to getting a longer range EV in a few years, when I don't have to think about range anymore :-)
Vancouver, CA owner of a 2013 Ocean Blue SV + QC, purchased 01/2017 in WA
Zencar 12/20/24/30A L1/L2 portable EVSE
1-1/4" Curt #11396 hitch
After market, DIY LED DRLs
LeafSpy Pro + Konnwei KW902 ELM327 BT OBDII dongle
Loving my first BEV :D

LeftieBiker
Posts: 9063
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 31 May 2013
Location: Upstate New York, US

Re: Still can't understand my heat pump!

Mon Mar 05, 2018 10:03 pm

I have the same desire, although it looks like every EV on my list has at least one substantial defect. The Leaf has about three of them.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

alozzy
Posts: 1039
Joined: Fri Jan 20, 2017 4:25 pm
Delivery Date: 18 Jan 2017
Location: Vancouver, BC
Contact: Website

Re: Still can't understand my heat pump!

Mon Mar 05, 2018 11:01 pm

If my wife can forgive my defects, I can find it in my heart to forgive my next EV a few too :D
Vancouver, CA owner of a 2013 Ocean Blue SV + QC, purchased 01/2017 in WA
Zencar 12/20/24/30A L1/L2 portable EVSE
1-1/4" Curt #11396 hitch
After market, DIY LED DRLs
LeafSpy Pro + Konnwei KW902 ELM327 BT OBDII dongle
Loving my first BEV :D

specialgreen
Posts: 97
Joined: Sun Mar 26, 2017 1:21 pm
Delivery Date: 26 Mar 2017
Location: Minnesota

Re: Still can't understand my heat pump!

Sat Apr 07, 2018 3:59 pm

When it's below 10F, I see 3 defogging methods:
- Defrost: what Nissan thought we'd do. Lots of air is directed at the windshield (good!), 100% of air from outside (very dry), but needs to be heated 60F (bad). And A/C runs.
- Partial Recirculation: with heat on lower register, a bit of air still hits the windshield (sorta good). About 1/3 of air is drawn from outside, which lowers humidity but needs heating. This is basically "Defrost Lite" without the A/C. If this clears the windows, great. But it did not work at 0F with a full car (I had to Defrost).
- Full Recirculation: Alozzy's method(?). With heat on lower register, plus dehumidification: there is zero outside air to heat, but there is lots of dehumidification.

Has anyone compared energy consumption using Partial Recirc heating vs. Full Recirc heating + A/C? If you have resistive heat (or it's too cold to pump), then the Alozzy Method may be better.

LeftieBiker
Posts: 9063
Joined: Wed May 22, 2013 3:17 am
Delivery Date: 31 May 2013
Location: Upstate New York, US

Re: Still can't understand my heat pump!

Sat Apr 07, 2018 5:42 pm

Has anyone compared energy consumption using Partial Recirc heating vs. Full Recirc heating + A/C? If you have resistive heat (or it's too cold to pump), then the Alozzy Method may be better.


In order to use less power, the 'Alozzy method' has to involve running the climate control for only short bursts, and waiting as long as possible between them. It relies on faster defrosting, combined with the system (blower excepted) being off most of the time, to save power. In continuous use, partial recirc with heat only is better as long as it can keep the windshield clear with lower fan speeds. I remember one trip the Winter before this last one: the air was pretty dry, so I was able to use partial recirc with the fan on the lowest setting. The energy consumption was dramatically lower than usual - more like using the A/C in Summer.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

alozzy
Posts: 1039
Joined: Fri Jan 20, 2017 4:25 pm
Delivery Date: 18 Jan 2017
Location: Vancouver, BC
Contact: Website

Re: Still can't understand my heat pump!

Sun Apr 08, 2018 12:28 am

LOL, I have a method now :D

The method I use in winter works well in the PNW climate, where my LEAF resides (Vancouver, BC), as we typically have high humidity and so condensation forms really fast on the windshield. I find that AC + HEAT very quickly generates dry, warm air that defogs the windshield in under a minute. Once the windshield is defogged, I switch to partial recirc with heat only. Inevitably, the windshield fogs again, so I have to repeat - over and over again.

The method does become tedious, I wish there was a climate control option to have the LEAF do that sort of cycling automatically. Typically, I use the above process only when I need the range or if I'm feeling extra patient :-)

Trying to defog using partial recirc with heat only just doesn't work. I could of course switch to HEAT only, four bars of fan speed and that eventually clears the fog. Doing so uses tons of energy though. That's exactly what I do for shorter trips in winter. Also, it's nice to stay warm ;)

I'm guessing that in drier climates, defogging is less of an issue, in which case it likely makes more sense to use partial recirc with heat only and a low fan speed.
Vancouver, CA owner of a 2013 Ocean Blue SV + QC, purchased 01/2017 in WA
Zencar 12/20/24/30A L1/L2 portable EVSE
1-1/4" Curt #11396 hitch
After market, DIY LED DRLs
LeafSpy Pro + Konnwei KW902 ELM327 BT OBDII dongle
Loving my first BEV :D

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