car auxhilliary heater

[fred]

Thank you Clive George. You've restored my sanity. I was beginning to think I had imagined it.

[Adrian]

Cold country only option. Requires specific bodyshell. Fits into RH side transmission tunnel. Requires different trim, and leaves very little space under trim.

Sounds like something that'd be LHD only, tbh.

[fred]

Well I certainly wasn't speccing a LHD car when I saw it on an options list.

[Dave Plowman (News)]

Right - the mystery is solved. It's something which appeared in 2001 which explains why it was not on the options list for my '97 model.

It's not a lump of aluminium but a chemical reaction based on a salt solution.

[fred]

Nope. Doesn't solve the mystery for me. The last 5 series I bought was in 1997 and that is when I remember it from And I do not remember anything about chemical reactions what I remember was along the lines of a block of aluminium.

Perhaps BMW U.K. an elucidate.

[Thomas Prufer]

Sodium acetate solution phase change, releasing heat of crystallization.

Thomas Prufer

[Grimly Curmudgeon]

Ditto that. Never had a problem with it.

[Grimly Curmudgeon]

What?

[Adrian]

Likewise here. Even on heavily-frozen windscreens with pre-existing chips and cracks, I've never had them spread.

The really nice side-effect is that it warms the glass, so helps reduce misting on the inside.

[Johny B Good]

That utilises the latent heat of melting (in reverse) or phase change which is the only better alternative to simply using water as a heat store (water possesses a much higher specific heat than any solid or liquid metal, typically an order of magnitude better).

Using the latent heat of a salt offers a much better solution than simply reducing the temperature of a store of near boiling water by 20 or 30 degrees since the temperature stays constant at the transition temperature of the phase change for the material used until all the material (the salt solution in this case) has solidified before the temperature starts to drop again when all the material has solidified. The salt solution pack has to be well insulated if it's to act as a heat store for any reasonable length of time (say 24 hours for a 50% loss of the stored latent heat).

The salt is formulated to have a melting point just below the normal engine coolant temperature. It might be plumbed into the coolant circuit so that it's part of the bypass circulation created by the thermostat's normal operation that prevents flow into the radiator until the engine is up to temperature or it might have its own thermostat set just below the temperature setting of the normal engine thermostat in order to minimise warm up time from a 'totally cold start'.

In order for this to act as an engine pre-warming feature, an extra electric circulating pump will be required to transfer the stored heat into the engine block via either its own independent circulatory system or simply to set up circulation using the normal coolant circuit.

In either case, the flow could include the passenger compartment heater to provide both cabin heat and a supply of warm demisting airflow. I'm not acquainted with the details of any realworld examples so I'm just making an educated guess at how this particular cat gets skinned.

I've no doubt that there'll be several variations on this theme amongst the different car manufacturers and/or variations within each manufacturers' model range. At its most basic it could be used, without a pre-warming feature, simply as a means of accelerating the normal engine warmup period

A more sophisticated version my include the extra complication of an auxiliary electric pump and plumbing to pre-warm the engine to save wear and tear on both the engine and the starter motor as well as offer the comfort of instant cabin and demister heat during the several minutes of the pre-heating phase. It will be interesting to see exactly what variations in auxillary heating options are actually available.

[Dave Liquorice]

I guess the warning is for the brain dead who boil a kettle ful of water take it straight outside a lob it overe the screen. Rather than luke warm and carefully applied. Water straight form the cold tap would proably work just as well. When it's getting close to or below the ground frost point they water football pitches to keep 'em warm and unfrozen.

We regulary get frost on the inside...

[Dave Liquorice]

A clear night sky is at around -40 C. Thermo dynamics mean that the different temperatures try to equalise but space is a bit big and there isn't enough heat in the screen to warm up space. So the screen just radiates heat into space and cools and cools and cools...

Bit of cloud cover reflects the radiation back keeping things warm.

It's perfectly possible to get a hefty ground frost with the air temp remaining above zero.

[damduck-egg]

That's how water meadows used to work,it wasn't to make the grass grow like rice in paddy fields. A thin layer of water was trickled over the meadows by the "Drowners" and this warmed the ground enough to make the grass grow earlier in the season .

G.Harman

[Grimly Curmudgeon]

Was trying to see how the windscreen would be below air temp, but I had neglected the radiation component. Doh.

[Tim+]

I've literally poured jugs full of water as hot as I can get it from the hot tap over frozen screens for many years and have never had a problem. No pussy-footing around with applying it carefully, just drenching it.

Tim

[Tim Lamb]

In message , [e-mail] writes

Oh!

Not entirely sure I agree with that. Long before my time but, the ancient water bailiff who taught me to shoot, showed me where the temporary dams were located to flood our meadows. The river side grassland here is not dead flat so a considerable depth was needed to cover all.

I understand mist irrigation can be used to protect fruit blossom from frost.... something like providing a source of energy to supply the latent heat of melting ice rather than it being drawn from the blossom itself.

[dennis]

The mist freezes on the buds and insulates them from the really cold air. It releases heat when it freezes.

[damduck-egg]

There were local variations. There were long unused water meadows where I grew up near the river Torridge and I just assumed they were flooded paddy field style.

It wasn't till I joined a walking lecture tour around the remains of some given by a hydrographer who works for Wiltshire CC amongst others that the system as a described was described to me. This was on the Hampshire Avon which has a fairly broad flood plain.

Up the road towards Salisbury English Heritage were going to make some operable as a demonstration site but the rainfall of recent springs seems to have delayed the project.

Probably more than you want know here.

G.Harman

[Tim Lamb]

Umm.. not sure about that either.

Frost on East facing plants seems to cause more damage when melted by early morning Sun.

[Tim Lamb]

In message , [e-mail] writes

Interesting. Ta!

I think the meadow nearest the farmhouse must have been modified to grow Cress for London.