How could battery powered trains (such as Class 230) be heated?

[Harpers Tate]

All electric heaters are basically 100% efficient. The heat output is (give or take a small "on" light, a slight red glow of the element and maybe a quiet buzz) exactly the same as the power input. The output cannot be more than the input in kWh....

True, but a heat pump is not an electric heater in the conventional sense and therefore this traditional logic isn't applicable. For anyone who does not know, simplistically a heat pump setup is a refrigerator working "in reverse" using a coolant gas in a closed system to effectively cool the world outside and throw the "waste" heat into the environment you want to heat. Thus, electricity is not used directly to heat anything; it is merely used to pump the refrigerant around the system.

 

[Bletchleyite]

True, but a heat pump is not an electric heater in the conventional sense and therefore this traditional logic isn't applicable. For anyone who does not know, simplistically a heat pump setup is a refrigerator working "in reverse" using a coolant gas in a closed system to effectively cool the world outside and throw the "waste" heat into the environment you want to heat. Thus, electricity is not used directly to heat anything; it is merely used to pump the refrigerant around the system.

True, I thought the post I was replying to was referring to the electric car heater which isn't a heat pump. (A conventional car heater is in a very rudimentary sense using waste engine heat).

 

[Clip]

Whilst all this talk of heating it and what could be used some of you may have forgotten that its a short stretch of line with many stops so in the bitter cold when the doors open its going to get chilly again so will need something powerful to get that back up to a nice temperature quickly before the next stop - a heat pump may be the best solution than any storage heaters which would lose their heat much quicker in operation.

 

[samuelmorris]

True, I thought the post I was replying to was referring to the electric car heater which isn't a heat pump. (A conventional car heater is in a very rudimentary sense using waste engine heat).

Some electric cars do use heat pumps for heating, mine does. A lot of them use elements which are much less energy efficient but faster.

 

[Bletchleyite]

Some electric cars do use heat pumps for heating, mine does. A lot of them use elements which are much less energy efficient but faster.

I thought it was more usual just to use a heater matrix, which is basically a radiator fed from the engine coolant water, and blow air over it. That being why if your engine overheats putting the heater on full whack can buy you a bit of time.

 

[gordonjahn]

I thought it was more usual just to use a heater matrix, which is basically a radiator fed from the engine coolant water, and blow air over it. That being why if your engine overheats putting the heater on full whack can buy you a bit of time.

For combustion engine vehicles, this works - I believe my engine has a triple-stage cooling system so the smallest (and first) coolant loop takes the initial heat from the engine as it warms round the smallest circuit to get the heater matrix warm first. Only when the first loop is hot do valves open to bring in the second and third coolant loops (that end in lots of coolant and the radiator under the bonnet being in use).

Coming back to the 230, it seems unlikely that this is even used on diesel-powered sets - the desire for a removable raft means there aren't coolant loops up to rads in the passenger saloon - I'm sure they've said it's fuel, exhaust and electrical connections from the raft to other underframe equipment. That likely means the same electrical heaters that were used on the Underground remain. For the battery version, it might just be that a power management system throttles the consumption of the elements during the day, but they get left plugged in overnight to keep them warm on depots.

 

[notlob.divad]

I thought it was more usual just to use a heater matrix, which is basically a radiator fed from the engine coolant water, and blow air over it. That being why if your engine overheats putting the heater on full whack can buy you a bit of time.

In a car with an internal combustion engine. Not in an entirely electic car, which (hopefully) has very little waste heat to utilise. As they get more efficient overtime that 'waste' heat will get even less. From what I am led to believe from my previous job, one of the limitations on electric cars is that you actually need a bit of heat in the car, not so much for the comfort point of view, but for the safety of de-misting the windscreen. As a result the range and efficiency of some cars is limited as much by the need to produce some heat for this very purpose.

 

[Bletchleyite]

Coming back to the 230, it seems unlikely that this is even used on diesel-powered sets - the desire for a removable raft means there aren't coolant loops up to rads in the passenger saloon - I'm sure they've said it's fuel, exhaust and electrical connections from the raft to other underframe equipment. That likely means the same electrical heaters that were used on the Underground remain. For the battery version, it might just be that a power management system throttles the consumption of the elements during the day, but they get left plugged in overnight to keep them warm on depots.

If those sets will have aircon, it probably deserves a bit of a rethink. The railway approach to aircon (as it sort-of is with older petrol/diesel cars) tends to be to cool air to a quite low temperature and whack it in at ceiling level (or sometimes, e.g. 390s, from the bottom of the luggage rack), and to have traditional electric heaters in conduits at foot level to cook your feet and heat the air up at the bottom of the vehicle, then convection of the hot and cold air mixes it up. This works reasonably well and is quite simple, but it's not exactly energy efficient as you're always both heating and cooling the same air except when it's extremely hot or cold. If energy efficiency becomes more important, then it's time to consider proper climate control possibly with some recirculation, so you're only ever doing one of the two to the required level (or neither, if the outside air temperature is spot-on).

 

[Bletchleyite]

you actually need a bit of heat in the car, not so much for the comfort point of view, but for the safety of de-misting the windscreen

Drying the air by way of aircon can also achieve this, though it obviously doesn't stop you needing your coat on. I'd also be interested to see if any work is going into developing windscreen-safe double glazing which might well avoid the issue entirely (or reduce it) by reducing the temperature gradient on a single piece of glass and stop the condensation forming in the first place just as it does in your house.

 

[notlob.divad]

Drying the air by way of aircon can also achieve this, though it obviously doesn't stop you needing your coat on. I'd also be interested to see if any work is going into developing windscreen-safe double glazing which might well avoid the issue entirely (or reduce it) by reducing the temperature gradient on a single piece of glass and stop the condensation forming in the first place just as it does in your house.

Solutions to the problem are in development, (or at least were when I was last involved a couple of years ago) they may well be pre-market products by now but it is unlikely they are yet in any forecourt vehicles. One thing is sure though laminate double glazing won't be the solution due to the cost and in-particular weight compromises that would require.

 

[reddragon]

A heat pump typically provides at least 3x the amount of heat compared with the energy used so is 300% efficient.

https://en.wikipedia.org/wiki/Air_source_heat_pumps

Most electric cars use heat pumps, with only early models not doing so, as these heaters use 1/3rd of the power compared with traditional heaters. The latest iterations of EVs now extract heat from the battery & electric motors, rather than the air so use minimal energy.

 

[samuelmorris]

A heat pump typically provides at least 3x the amount of heat compared with the energy used so is 300% efficient.

https://en.wikipedia.org/wiki/Air_source_heat_pumps

Most electric cars use heat pumps, with only early models not doing so, as these heaters use 1/3rd of the power compared with traditional heaters. The latest iterations of EVs now extract heat from the battery & electric motors, rather than the air so use minimal energy.

Indeed, though as said earlier the removable battery raft on the 230s may limit the available options, depending on how easily that can be connected.

 

[Andrew*Debbie]

Heat pump in my LEAF typically draws about 1.5kW for a few minutes and then tapers off to a few hundred watts. In cold weather (0C) the auxillary resistance heater comes on too. The total draw is 4-5kW for about 5 minutes, dropping down to about 1kW once the car starts to warm up.


A 230 could use a mix of heat pump and resistance heat, but with a considerable range penalty. Every time the doors open the resistance heater would have to come on. My guess is they would use a diesel air heater. The current 230 doesn't have enough battery margin and a Webasto RV heater is easier to retrofit.

 

[superkev]

As I posted on the 230 thread battery technology has a long way to go to match a few gallons of diesel. Only so many electrons to be had in a lump of lithium.
The things that may improve significantly are cost (currently around £300 kw/hr) and hopefully life (currently around 7 years)
Because of the cost of the additional battery to give 10kw of heat for say 4 hours (40kw/hr @ £300 a kw £12000) most electric buses have diesel heaters.
Interesting many bus companies are converting there government green grant funded hybrid buses back to straight diesel when faced with a £35k bill to replace the battery after typically 7 years.
K

 

[Emblematic]

As I posted on the 230 thread battery technology has a long way to go to match a few gallons of diesel. Only so many electrons to be had in a lump of lithium.
The things that may improve significantly are cost (currently around £300 kw/hr) and hopefully life (currently around 7 years)
Because of the cost of the additional battery to give 10kw of heat for say 4 hours (40kw/hr @ £300 a kw £12000) most electric buses have diesel heaters.
Interesting many bus companies are converting there government green grant funded hybrid buses back to straight diesel when faced with a £35k bill to replace the battery after typically 7 years.
K

Lithium isn't the limiting factor, it's the surrounding chemistry that comprises most of the bulk and mass of a Li cell. If it can be made to work well enough, Li-air cells will provide 50 to 100 times the energy density of best present Li-metal cells. Amongst Li-metal, there is a wide range of energy densities. Nissan Leaf has gone from 24 kWh to 60 kWh in under a decade (with 90 kWh rumoured for next year) with the same size and mass of battery. There is huge potential to increase the capacity of rechargeable cells, and multiple parallel development streams mean no single technology can yet be identified as the future winner.
I'd be interested to know some details of the companies de-hybridising their buses. Certainly isn't happening in London, in fact I understand the reverse is being trialled. Of course some of the earlier hybrid buses were complete lemons (yes Boris Bus, I am looking at you!)
To desperately try to get this back on topic, I think the point is that whatever heating solution is fitted now to the 230s, very likely the first battery refresh will give plenty of spare capacity to power electric heaters or reverse cycle AC. Webastos will do in the meantime.

 

[MarkyT]

I'd be interested to know some details of the companies de-hybridising their buses. Certainly isn't happening in London, in fact I understand the reverse is being trialled. Of course some of the earlier hybrid buses were complete lemons (yes Boris Bus, I am looking at you!)

This is probably because the green subsidies for the original hybrids only provided an eagerly accepted one-off capital injection, coupled with no obligation on a commercial operator to permanently convert a a route, an area etc to a lower emissions model. In a free market environment, how could any such arrangement work anyway? London is entirely different, with emissions policies, charging zones and a centrally planned network and contract structure. Even the small number of municipally operated provincial companies have converted fleets of hybrids to diesel only. I remember Reading Transport doing this a few years ago, but they have to keep costs under control as some previous senior management found out to their cost when they signed up to a long term supply contract for biodiesel (portrayed as a fantastic developmment by all at the time) . . . just before the world price of oil dropped dramatically (after which the bosses were castigated ceaselessly for profligacy and some senior individuals had to resign I believe). Yes the Borises were bad but I believe the later models just before the programme was abandoned were much better than the earlier ones.

 

[AlastairFraser]

Reading Buses' latest enterprise is natural gas buses with the first wave of single-deckers being introduced on my local route, the 25 and the 2 and later the 9, 7 and 11. They were intended for medium-capacity suburban/rural routes in the Greater Reading area. The next phase was the latest with the 33 and 17 receiving new double deckers for their urban/suburban, high-capacity routes mostly within the Borough of Reading. These buses are all Alexander Dennis I think and Reading Buses have been buying a lot from them, the first buses being the diesel hybrids previously on the 17 that have now been cascaded to Caversham routes. As my local routes I am very happy, they are really nice buses, they accelerate quickly and the seats are very comfortable.

 

[Emblematic]

This is probably because the green subsidies for the original hybrids only provided an eagerly accepted one-off capital injection, coupled with no obligation on a commercial operator to permanently convert a a route, an area etc to a lower emissions model. In a free market environment, how could any such arrangement work anyway? London is entirely different, with emissions policies, charging zones and a centrally planned network and contract structure. Even the small number of municipally operated provincial companies have converted fleets of hybrids to diesel only. I remember Reading Transport doing this a few years ago, but they have to keep costs under control as some previous senior management found out to their cost when they signed up to a long term supply contract for biodiesel (portrayed as a fantastic developmment by all at the time) . . . just before the world price of oil dropped dramatically (after which the bosses were castigated ceaselessly for profligacy and some senior individuals had to resign I believe). Yes the Borises were bad but I believe the later models just before the programme was abandoned were much better than the earlier ones.

A lot of these so-called green incentives go awry. Take the example of the subsidies and tax breaks for PHEVs, where many commercial operators ran them exclusively on petrol and never charged the from the electric supply during their whole period of ownership. And, on a whole other level of incompetence, the Renewal Energy Incentive in NI - farmers being paid to heat empty farm buildings, ffs.
Fortunately we're passing through the tipping point where the 'green' solutions can stand up against the old technology without crude incentives or penalties skewing the market. Battery powered trains should be in the mix commercially, any time now.

Oh and the last Borises may have been better, but still striving for mediocre. Trouble is London is stuck with them for the foreseeable, no-one else would be daft enough to buy them. Just don't get me going...

 

[Greybeard33]

A heat pump typically provides at least 3x the amount of heat compared with the energy used so is 300% efficient.

https://en.wikipedia.org/wiki/Air_source_heat_pumps

Most electric cars use heat pumps, with only early models not doing so, as these heaters use 1/3rd of the power compared with traditional heaters. The latest iterations of EVs now extract heat from the battery & electric motors, rather than the air so use minimal energy.

"Efficiency", defined as (Heat Energy Out/Electrical Energy In)*100%, is a rather misleading concept when applied to heating systems, in that all heat pumps have an "efficiency" of more than 100%. Heat pumps are normally compared using the Coefficient Of Performance (COP), defined as simply (Heat Energy Out/Electrical Energy In). So a pump with a COP of 3 has an "efficiency" of 300%. But the COP varies with the temperatures of the heat source and heat sink. The COP value is only meaningful when these temperatures are specified.

For an air source heat pump, the COP decreases as the ambient air temperature falls - the pump has to work harder to push the heat further "uphill". Therefore power consumption of the system varies more with temperature than for resistive heating - the heat pump is most advantageous in mild weather. In cold, damp weather, frost can form in the cold matrix of the external heat exchanger, restricting airflow and further reducing performance. If a higher temperature heat source, such as the cooling air exhaust from the traction motors and batteries, can be used instead of ambient air, performance is improved.

The true efficiency of a heat pump can be determined by comparing its COP with that of an idealised Carnot cycle heat engine. The latter can be calculated as (TH/(TH-TC)), where TH is the temperature of the saloon air and TC is the temperature of the source air, both in Kelvin. http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatpump.html#c3. For example, if the source temperature is 0C (273K) and the saloon temperature is 20C (293K), the ideal COP = 293/(293-273) = 14.6. Real systems can never get close to this; for one thing the temperatures of the external and internal heat exchanger matrices have to be respectively well below/above the air temperature to transfer sufficient heat. If these temperature differences are each 30 degC, the Carnot COP becomes 323/(323-243) = 4.0. After taking account of losses (e.g. fans), a practical system might have a COP around 3 in these conditions, similar to the battery car heaters mentioned above.

The % of battery capacity that must be reserved to power the heating system will be highly dependent on the limiting design cases. If it is considered necessary to provide supplementary resistive heating on a very cold day, the benefit of heat pumps would be greatly reduced. The train must be able to complete its working, with adequate battery margin, on that very cold day. Also important is the maximum en route delay during which it is required to maintain heating. In the rare events when a conventional EMU loses power, it is accepted that the heating will go off. But would it be acceptable to shed the heating load every time a battery EMU is brought to a stand at a signal? Or shed after 5 minutes? Or what?

Diesel heaters (and gas heaters/boilers) are also relatively wasteful in that they convert the high grade chemical energy of the fuel directly into low grade heat energy, then throw some of it away in the hot exhaust gases. It would be more fuel efficient to use a heat pump driven by a small diesel engine.

 

[randyrippley]

There are a couple of technologies that would work and wouldn't need excessive weight.
One option would be to fit microwave emitters in coaches. These would heat any water containing bodies - i.e. passengers, without wasting heat on the surrounding air. Before anyone shouts "rubbish", don't forget the microwave oven is a spinoff from research intended to find a cheap way to keep lab rats warm.
The other option would be to use Britain's stockpile of redundant nuclear fuel to fit the carriages with Radioisotope heater units. (See https://en.wikipedia.org/wiki/Radioisotope_heater_unit for details of this technology). We have a stockpile of Pu-238 which we have no use for - use in in our trains!

 

[Bald Rick]

An air source heat pump is a very interesting idea. I wonder how easy it would be to apply that to a train.

Easy. In fact I’m 99% sure the 442s had them when new. Not sure if they still do.

 

[randyrippley]

just found this research paper from 2010 which discusses the savings possible through using carbon dioxide in a heat pump system in trains: technology can only have improved since
http://www.r744.com/files/pdf_662.pdf "REVERSIBLE R744 (CO2) HEAT PUMPS APPLIED IN PUBLIC TRAINS"