How the heat pump works

Faults and Technical chat for the Skoda Enyaq
User avatar
RichR
Posts: 1319
Joined: Thu Mar 11, 2021 11:53 am
Location: South end of North Yorkshire

Post by RichR » Tue Jan 25, 2022 12:23 pm

I've been reading the official VW training information for the MEB platform heat pump (thanks zice for letting me know it was now publicly available). If you want to read it, search for "ssp 881213". Now I have a far better understanding on how the heat pump system works, and I'd like to clear up some misunderstandings (which I've been guilty of too), due to the lack of any real information from Skoda/VW/Audi/Cupra on their retail websites and brochures, and also give a summary of how it works. Any mistakes, please let me know. :)

TL;DR: if you do mainly do journeys where a petrol/diesel engine struggles to get the cabin up to the temperature you want, a heat pump probably isn't worth it on an Enyaq. It's also most effective at temperatures around freezing, so if you don't drive much in winter then it also might not be worth it for you. For everyone else, it can reduce energy consumption to heat the car (particularly at higher speeds).


Here are some summary points:

The heat pump uses R744 as a refrigerant - this is normal CO2 gas. It's non-toxic and a natural component of the atmosphere. It is however at a very high pressure in the system (over 1000psi). There are sensors in the cabin to detect leaks. The non-heat pump cars use R1234yf, which is 2,3,3,3-Tetrafluoropropene. Extremely flammable and not nice to breathe in, but not as damaging to the environment as older refrigerants such as R134 and R12.

There is only one compressor. I previously thought there were two, but no, there's just one. What there is however is an assortment of valves, expansion valves, heat exchangers, condensers and evaporators in both the cabin and engine bay. So it's capable of both heating and cooling at the same time, by using different combinations of components. For example to dry and heat the air, it first cools intake air (to dry it) and then heats it using the heat it extracted from it whilst cooling it, plus a little more from the compressor. It's all about the flow of heat, not the temperature of fluids ;)

In normal operation, the heat pump uses waste heat from the motor and battery to heat the cabin. Exactly the same as a petrol/diesel engined vehicle does. The electric PTC heater is only used when a sudden increase in temperature is requested, or the motor/battery is very cold. On cars without a heat pump, this heat is simply lost to the environment through the radiator.

There are a number of other modes of operation for when the motor/battery coolant circuit is cold to help get it up to temperature (and hence increase the efficiency). In normal driving the 6kW battery PTC is not used. This is only used for pre-heating for departure schedules (and possibly for scheduled charging). If anyone's interested, I can post a summary of what it does in each mode. But I suspect this is going to be a long post as it is...

For cooling it's pretty much the same as a car without a heat pump, in that it uses the condenser behind the radiator to dump heat to the environment. But it can also cool the motor/battery independently of the cabin if it needs to (for example whilst charging) or at the same time (for example when driving immediately after charging).

Most of the time when the car is heating the cabin or the battery, the radiator and condenser are blanked off with an electric roller blind cover to improve aerodynamics. It will open this as much as it needs to in order to get the temperature difference across the radiator or condenser.

On cars without a heat pump, all heating comes from the 6kW PTC heater and all cooling/drying comes from the 5kW compressor. Demisting the windscreen could theoretically take around 10kW as result, though generally it'd be less than this.
On cars with a heat pump, the PTC heater is not used once there is sufficient heat in the motor/battery coolant system. All heating and cooling comes from the 5kW compressor, with the PTC only used for short periods until the temperature of the refrigerant fluid increases to meet the demand. Demisting a stone cold car will of course use the PTC, so be the same as the non-heat pump case. But once the car has driven for a few minutes the motor and battery will be hot enough not to need it.

It's this use of waste heat that gives the saving on electricity usage. For short trips, the motor and battery won't get hot enough to provide any heat - just the same as in a petrol or diesel car. But once it's up to temperature, that waste heat is able to heat the cabin air. It's most effective when the outside air temperature is below freezing, down to a point where the heat loss through the windows is more than the heat from the motor/battery can replace. At that point it'll use the PTC to supplement the heat pump.

Hopefully that should help people understand what the system does. It's much more sophisticated than the Stellantis (ie Peugeot, Citroen, Vauxhall, Fiat etc) system, and the Hyundai/Kia system - and they make you pay for it whether you want it or not. Personally, I think it would be better if Skoda/VW/Audi/Cupra made the heat pump standard like most other companies - but gave you the option to remove it to reduce the price, rather than it appearing as a very expensive option with no real description as to whether you would benefit from it or not.
Enyaq iV 80 Sportline, Energy Blue, Assisted Drive Plus, Infotainment Plus, Convenience Plus, Comfort Seat Plus, Transport Pack, Heat Pump, 125kW charging, Built Nov 2021.

Erakettu
Posts: 113
Joined: Sun Oct 24, 2021 8:49 am

Post by Erakettu » Tue Jan 25, 2022 1:45 pm

Nice summary. Thanks.

Do you have info, whether heat pump can also heat the battery? I'm thinking about the future updates that improve battery conditioning, possibly before arriving to charging stations.

User avatar
RichR
Posts: 1319
Joined: Thu Mar 11, 2021 11:53 am
Location: South end of North Yorkshire

Post by RichR » Tue Jan 25, 2022 1:56 pm

Sort of. As it takes the heat from the battery and motor as the primary heat source, it can't easily heat the same thing it's taking heat from. So the battery is mainly heated by the battery PTC or the heat from the motor via the cooling water system when the motor is hot.

There is a mode where it uses the compressor to help push some heat into the motor/battery coolant system, but this is only used immediately after starting from cold (ie when the battery PTC isn't used). Once the motor and battery are producing heat on their own it switches to a more normal mode of taking that heat for the cabin.

I suspect for pre-conditioning on approach to a scheduled charging stop it'll either reduce the amount of heat it's putting into the cabin by not cooling the battery if it gets over the 35C threshold that would normally cause the battery to be cooled when driving. Or it'd just disable cooling and turn on the PTC for a bit, and use a few kW to do it. Probably doesn't need to be on long to raise it a few degrees.
Enyaq iV 80 Sportline, Energy Blue, Assisted Drive Plus, Infotainment Plus, Convenience Plus, Comfort Seat Plus, Transport Pack, Heat Pump, 125kW charging, Built Nov 2021.

Erakettu
Posts: 113
Joined: Sun Oct 24, 2021 8:49 am

Post by Erakettu » Tue Jan 25, 2022 3:01 pm

Ok great. I understand how a basic refridgeration/heater unit works, but was wondering as you mentioned multiple evaporators etc.

User avatar
HarryHuk
Posts: 71
Joined: Wed Feb 09, 2022 8:58 pm

Post by HarryHuk » Mon Jul 25, 2022 10:50 pm

RichR wrote:
Tue Jan 25, 2022 12:23 pm
I've been reading the official VW training information for the MEB platform heat pump (thanks zice for letting me know it was now publicly available). If you want to read it, search for "ssp 881213". Now I have a far better understanding on how the heat pump system works, and I'd like to clear up some misunderstandings (which I've been guilty of too), due to the lack of any real information from Skoda/VW/Audi/Cupra on their retail websites and brochures, and also give a summary of how it works. Any mistakes, please let me know. :)
...

Skoda say very little about what it does, and why you would want one, and what they say is not very clear, you're right. The salesman wasn't much bothered whether I ordered it or not, which is nuts because it's his commission.
I was pretty sure I wanted one, knowing from my tumble dryer, and the heating system I'm getting installed that it's much more efficient than just a heating element.
60 Loft Graphite Grey ordered late Nov 2021, into production mid March 2022, shipped late May 2022, delivered late June 2022
Heat pump, chrome, transport, sport drive basic, assisted drive basic, parking basic, light and view basic

User avatar
RichR
Posts: 1319
Joined: Thu Mar 11, 2021 11:53 am
Location: South end of North Yorkshire

Post by RichR » Tue Jul 26, 2022 7:31 am

I think if there was just one line in the brochure that says 'uses waste heat from the motor and battery to heat the cabin' that would be all that's needed to give people an idea as to why it's more efficient than using electricity to provide heat directly. The subtleties of the other modes where it heats or cools the battery to improve efficiency may be more information than needs to go in the brochure, but perhaps implying something along those lines could be helpful.
Enyaq iV 80 Sportline, Energy Blue, Assisted Drive Plus, Infotainment Plus, Convenience Plus, Comfort Seat Plus, Transport Pack, Heat Pump, 125kW charging, Built Nov 2021.

Goaty
Posts: 1083
Joined: Sat May 22, 2021 3:27 pm

Post by Goaty » Tue Jul 26, 2022 8:10 am

/\

Your description explains it so succinctly and indeed - that’s all they need to say!!

I remember when I was looking in early 2021, there was no hint whatsoever that the HP uses heat from the motor and battery to heat up the cabin. If I remember correctly, the focus of the description was more along the lines of using heat from the heater to get the battery up to optimal temperature.. so basically the opposite 🤦🏼‍♂️


I suppose it may take a while to recoup the ~£1000 cost of the HP, when offset against the better range you should get (therefore more efficiency) on longer journeys in colder conditions.
iV80 Loft, ordered 25/5/21, del: 4/11/21. Black, 21” Betria, 125kW, Climate +, Asst Drive Basic. (company car, replaced BMW 520d). Tethered PodPoint.

MarkB
Posts: 45
Joined: Sat Mar 26, 2022 5:10 pm

Post by MarkB » Tue Jul 26, 2022 8:53 am

A very helpful description,. SKODA/VAG haven't done themselves any favours by providing inadequate information, and initially over claiming the benefits of the heat pump, I only added the HP to the order after finding out more about it, from the pumps manufacturer (TI fluid systems) and some of the EV pump research papers, I won't get a financial payback from fitting the pump, but that applies to other choices on the order as well
Last edited by MarkB on Tue Jul 26, 2022 12:27 pm, edited 1 time in total.
Ordered 26 March 22, Sportline 80, Graphite grey, Assisted Drive+, Infotainment Package+, Drive Sport+, Heat Pump. Zappi charger, 4 Aug notified Built in transit

User avatar
HarryHuk
Posts: 71
Joined: Wed Feb 09, 2022 8:58 pm

Post by HarryHuk » Tue Jul 26, 2022 12:16 pm

I wasn't really thinking about payback from improved economy, but wanted to minimise range reduction with the iV60 on winter trips.
(For me the iV80 would have been at least £5k more, from the difference in price and loss of grant eligibility)
60 Loft Graphite Grey ordered late Nov 2021, into production mid March 2022, shipped late May 2022, delivered late June 2022
Heat pump, chrome, transport, sport drive basic, assisted drive basic, parking basic, light and view basic

TheCorm
Posts: 57
Joined: Wed Jan 05, 2022 9:56 am

Post by TheCorm » Thu Aug 04, 2022 9:01 pm

How do you tell if an Enyaq has a heat pump?

(Like if you weren't aware of the option was added originally)
iv60 in Race Blue, Loft interior with 20" Vega wheels - Ordered Sep21, Delivered 25/07/22
Packs - Comfort seat plus, Family, Climate plus, Drive Sport, Assisted drive, Parking, Convenience, Heat Pump.

Post Reply

  • You may also be interested in...
    Replies
    Views
    Last post