BuckMkII
Posts: 195
Joined: Sat May 06, 2017 8:04 am
Location: Seattle

Still can't understand my heat pump!

Sun Mar 04, 2018 9:42 am

OK, I'm being an idiot, but I give up: how can I tell when the heater is operating in heat pump mode vs. resistance mode? After 3/4 year of fairly regular looking at LeafSpy, I still don't get it. Maybe I need to RTFM for the car *again,* but it's more fun to ask here.

Unless I want fan-only operation, I always turn on both the Heat and A/C buttons, since I assume that having the A/C off would disable the heat pump. Is that correct?

I mostly keep the app on the Summary screen. When the temp setpoint is roughly 20 degrees above the outside temp, I'll usually see the heater bar pulling 1500 to 2000 watts for a couple of minutes, then ramp down to 500 watts or even 250. I almost never see the AC bar come on. Friday afternoon I did see it show a bit of AC usage, which was surprising since it wasn't that warm out, the car was parked in shade and I didn't expect the system to call for cooling. However, I shut off the climate control switch without bothering to check for cold air, so I'm not sure what it was doing. Does the Summary screen "Hetr" bar distinguish between resistive and heat pump heating, or does it just show the amount of power being used by either of those?

Should I be using the Table screen instead? I have run it occasionally, but it seems that it always says "HVAC" if I have both Heat and A/C buttons on, so I haven't found that to be informative. Maybe I'm just not watching it closely enough?

I doubt that my resistance heater NEVER comes on, because sometimes I do smell the hot metal odor associated with a hair dryer heater coil, but I haven't been able to associate this with any other indicator.
Last edited by BuckMkII on Sun Mar 04, 2018 6:40 pm, edited 1 time in total.
2013 SV no QC, built July 2013
car grew up in San Jose CA, purchased 5/31/17 in Seattle
on 6/16/17: AHr = 56.4; SOH = 86%; Hx = 84.3; ODO = 39,250
bar 12 lost 8/21/17
on 2/2/18: AHr = 56.1; SOH = 85.7%; Hx = 81.5; ODO = 44,444

LeftieBiker
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Re: Still can't understand my heat pump!

Sun Mar 04, 2018 2:24 pm

I just talked about this in another thread. You do NOT need to have the A/C on as well to activate the heat pump! In fact, when both Heat and A/C are selected, you are PREVENTING the heat pump from providing heat, because it is being made to provide A/C, and this system can't do both at once. Just use the Heat button and let the car select the heater(s) it uses. If you have plenty of heat, and A/C when needed, then the heat pump is working.
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alozzy
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Re: Still can't understand my heat pump!

Sun Mar 04, 2018 6:39 pm

FWIW, if, like me, you don't really care if the temp set point is reached and you just want to keep the windshield defrosted, then using heat + AC seems to be the most efficient - as long as you turn off the climate control as soon as the windshield is defrosted and only turn it on again to defrost.

If you like a warm cabin and want the LEAF to reach the setpoint, then heat only does seem to be more efficient.

Like you, I find it confusing that the heat pump, which provides both heating and cooling, is automatically active in heat only mode. I likewise assumed that AC had to be on to enable the heat pump. Thanks, LeftieBiker, for clearing this up :-)

For SV/SL trims, Nissan should have added a separate "heat pump" switch, which would have made things less confusing...

BTW, the owner's manual doesn't explain this well at all.
Vancouver, CA owner of a 2013 Ocean Blue SV + QC, purchased 01/2017 in WA
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LeftieBiker
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Re: Still can't understand my heat pump!

Sun Mar 04, 2018 7:12 pm

The main - really the entire - reason for the heatpump is to provide the most energy efficient heat possible. The A/C in the PTC-only Leafs is actually more efficient at providing cooled air. Given these two facts, I think that Nissan thought it a safe assumption (and I agree with them, for once) that people would understand that the heatpump would run automatically in Heat mode. The source of the confusion is apparently the way the energy info screen identifies the heatpump when it runs: it apparently calls it "A/C." They should have updated the software for the energy monitor when they added the heatpump in 2013.
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.

BuckMkII
Posts: 195
Joined: Sat May 06, 2017 8:04 am
Location: Seattle

Re: Still can't understand my heat pump!

Mon Mar 05, 2018 6:25 am

When the heat pump is operating, how many watts does it usually pull?
2013 SV no QC, built July 2013
car grew up in San Jose CA, purchased 5/31/17 in Seattle
on 6/16/17: AHr = 56.4; SOH = 86%; Hx = 84.3; ODO = 39,250
bar 12 lost 8/21/17
on 2/2/18: AHr = 56.1; SOH = 85.7%; Hx = 81.5; ODO = 44,444

jake14mw
Posts: 155
Joined: Sun Nov 12, 2017 9:53 pm
Delivery Date: 13 Nov 2017
Location: Connecticut, USA

Re: Still can't understand my heat pump!

Mon Mar 05, 2018 7:45 am

I didn't know that there was so much to know about the heating! Why should I care when the heat pump is operating? Also, does the A/C button work differently in this car than my other cars? I always thought the A/C button was used to run the A/C compressor, drying the air?

Of course the most common use of A/C is to cool and dry the air in the summer. I would think that the use of the A/C button in the winter would be solely for running the compressor to dry the air in order to more quickly defog the windows?

alozzy
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Delivery Date: 18 Jan 2017
Location: Vancouver, BC
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Re: Still can't understand my heat pump!

Mon Mar 05, 2018 9:52 am

Did some more observations last night and discovered a few things...

The biggest takeaway is that the "Climate Control" graph on the energy info screen shows ONLY kW usage for generating heat with PTC and/or the heat pump, nothing else.

So, energy used to run the heat pump compressor and the blower fan are NOT included.

Also, the energy usage of the PTC does not increase when the AC is turned on, which explains why that graph value is consistently lower in that mode (heat+AC) - it's reflecting the fact that the heat pump is no longer in "heat" mode. The main difference between "heat" and "cool" cycles for a heat pump are just the direction of the reversing valve - the compressor runs in both modes of operation and it's the compressor that draws the most current.

LeafSpy also doesn't show energy usage of the heat pump's compressor. With heat + AC, LeafSpy shows heat pump energy usage to generate heat as "AC" - guess that's an estimated kW usage. With heat only, LeafSpy shows the "AC" value drop to zero and the heat (PTC) values stays about the same (even drops a bit on my LEAF).

So, based on the LEAF's instrumentation, it's pretty hard to know which mode is more efficient.
Last edited by alozzy on Wed Mar 07, 2018 10:34 am, edited 1 time in total.
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

GerryAZ
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Re: Still can't understand my heat pump!

Mon Mar 05, 2018 12:20 pm

The energy use display on the navigation screen shows climate control power which includes both resistance heater (PTC heater) and compressor in the graph for climate control. Blower fan consumption is included in the graph for 12-volt system load. LEAF Spy display shows compressor consumption as A/C regardless of heating or cooling and the PTC consumption as heater load.
Gerry
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
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LeftieBiker
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Re: Still can't understand my heat pump!

Mon Mar 05, 2018 12:39 pm

I always thought the A/C button was used to run the A/C compressor, drying the air?


In the heatpump-equipped Leafs the A/C comes from the heat pump - there is no "A/C compressor" as a separate unit. When you select both heat and A/C you get heat from the PTC heater and A/C from the heatpump, which consumes the maximum amount of energy for a set temperature. I'm beginning to be glad that I don't obsess over energy usage graphs, because that display seems to be really confusing some of you.

Given the lack of complete info, it's pretty hard to know which mode is more efficient.

Does the heat pump's compressor run in heat only mode? If it does, then heat + AC seems to be more efficient.


You have a heatpump that uses the least amount of energy currently possible to provide heat, and just a tiny bit more energy than a dedicated A/C compressor to provide cooled air. You have a resistance heater (aka PTC) that uses much, much more energy to create the same amount of heat rather than simply move it from outside the car to inside. When you select Heat, both the heatpump and the PTC run at first, for maximum warming speed. Then the PTC throttles back or turns off, depending on the outside temp and the set temp inside. Once this happens, you are using less power to get heat than you would be using the PTC heater alone.

If, on the other hand, you select Heat and A/C, then the PTC heater runs alone to provide heat, and uses more power overall then the heatpump+PTC, because it can't throttle back as much. At the same time the heatpump is ALSO running, to provide the chilled, dried air you requested with the A/C button (this doesn't happen at frigid temps, AFAIK). So unless adding chilled air to the mix somehow reduces the amount of heat required (instead of increasing it, which is what happens*), you are feeding power to both units, which are then working against each other to provide the set temperature. This is as clear as I can make it. Stop looking at the damned energy use screen and look at the physics of heating, please.

* If your only purpose is to defog the windshield, then Heat + A/C can be more efficient if you run it only briefly and turn it off when not needed.
Last edited by LeftieBiker on Mon Mar 05, 2018 2:28 pm, edited 1 time in total.
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.

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IssacZachary
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Re: Still can't understand my heat pump!

Mon Mar 05, 2018 2:00 pm

BuckMkII wrote:OK, I'm being an idiot, but I give up: how can I tell when the heater is operating in heat pump mode vs. resistance mode?


Stand in front of the car. Do you hear the radiator fan? Any time the heat pump is working, either for heating or cooling, the radiator fan is on. So if your heat is on and the radiator fan is off then you know you are using the resistance heater.

If both A/C and heat buttons are on you may be using the resistance heater too. Turn off A/C for heat pump to heat and not cool, but turn it on to defog windows more quickly.
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