The Class 180s air con

[whole diary]

[bobm]

I am far from an expert in such things, but I understand the aircon fitted to most if not all diesel trains depends in part on the air outside moving to cool things like heat exchangers.  It therefore follows that for the train to move the engine has to be running.  Whether it is different for electric stock I don't know.  There might well be issues with too much current being required for the infrastructure available.

They are not the same as air conditioning units fitted into buildings which require large amounts of current and are usually the first things to be switched off when the power fails and a generator kicks in.

[paul7575]

The power required for aircon is so significant that on most AC EMUs^▸ (Electric Multiple Unit) I can think of the aircon automatically goes off whenever the train passes under an OHLE neutral section.

Now as neutral sections are passed in a matter of seconds normally, and all the lights usually stay on, but the aircon is intentionally switched off, surely that tells us something doesn't it?  Another big clue is in the recent discussion about electric IEPs^▸ (Intercity Express Program / Project.) getting an auxiliary diesel engine just to support the 'hotel load' after a power failure...

Paul

[Gordon the Blue Engine]

I think I can help re some of the questions about air conditioning. 

The fan that blows the air through the coach takes relatively little power and is powered off the coach battery.  If the battery is fully charged before the charging supply is lost (eg engine stops, loss of power from overhead line or third rail) it can power the fan motor for several hours, thus providing air circulation in a sealed coach until the engine can be restarted, passengers moved to another coach etc. 

However, heating or cooling the blown air takes much more power, and more than can be provided by battery.  So this power is taken from the engine (mechanically and/or electrically) or overhead line etc depending on the type of train.  So if this power is lost, the heating or cooling will stop immediately.  However, the fan motor will continue to blow air into the coach.  Going through a neutral section in 10 seconds or whatever would have no noticeable effect on the temperature of the air being blown into the coach. 

The heat exchanger for the air-con (usually underneath the coach) has a fan to push air through it, so can function OK even if the train is stopped. 

edit: add (usually underneath the coach)

[ChrisB]

Just surprises me that no alternative is provided to power the aircon other than the engines... maybe like i said before ' this needs looking more into.'

(why doesn't the 'quote' button work no longer - I just get the green 'loading' banner' and nothing happens....)

Not sure it does, does it? You board roughly 10 mins from leaving (at the earliest generally) and its working within minutes once moving. I can think of far better things to spend money on that permanent aircon.

[IndustryInsider]

Also, just to clarify the situation should an engine not be working on a Class 180 in service, there is a cross-feed facility which automatically gets electrical power (including for the air-con) from an adjacent carriage.  That's unlike the Turbo units which have no cross feed.