On Thu, 31 Mar 2022 12:54:36 -0000 (UTC), nib <news@ingram-bromley.co.uk> wrote:

>On Thu, 31 Mar 2022 13:25:47 +0100, Roland Perry wrote:
>
>> In message <t244v0$lku$2@dont-email.me>, at 11:57:20 on Thu, 31 Mar
>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>On Thu, 31 Mar 2022 12:48:31 +0100, Roland Perry wrote:
>>>
>>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>>>On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>>
>>>>>...
>>>>>
>>>>>> If only. Unless there's a decent movement of air and there arn't
>>>>>> many people in the train then the air inside pretty much stays there
>>>>>> in the 20 secs or so the doors are open.
>>>>>>
>>>>>...
>>>>>
>>>>>But I think there must be air changing. Apart from the cooling aspect
>>>>>there is the matter of ensuring breathable air.
>>>>
>>>> No-one denies the air is flowing/changing to some limited extent.
>>>> However adding aircon makes it change much more often (as well as the
>>>> input air being cool rather than hot). That's the whole point.
>>>
>>>If the air is changing fast enough to keep the air fresh then it is
>>>changing several times per hour. More than enough to take the heat out
>>>as well.
>>
>> It's not taking enough of the heat out, therefore the carriages are hot
>> and sweaty.
>
>Don't confuse heat (flow) and temperature. It is taking the heat out. It
>just needs a higher source temperature to drive it.
>
>>>The air-con doesn't need to change the refresh rate, just cool the fresh
>>>air coming in.
>>
>> It's not fresh air, of course - it's hot, stale, air inside the tunnels.
>
>It's fresh in that it's not full of CO2! The air in the tunnel is
>ultimately refreshed via deliberate flow, mostly forced in at stations
>and out at ventilation shafts (I think, with the trains pushing it
>around).

Yes, plus fresh air gets pushed in at the tunnel portals of most lines. Obviously the Drain, Victoria and Bakerloo lines
get much less benefit from that source.

On Thu, 31 Mar 2022 13:25:47 +0100, Roland Perry <roland@perry.co.uk> wrote:

>In message <t244v0$lku$2@dont-email.me>, at 11:57:20 on Thu, 31 Mar
>2022, nib <news@ingram-bromley.co.uk> remarked:
>>On Thu, 31 Mar 2022 12:48:31 +0100, Roland Perry wrote:
>>
>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>>On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>
>>>>...
>>>>
>>>>> If only. Unless there's a decent movement of air and there arn't many
>>>>> people in the train then the air inside pretty much stays there in the
>>>>> 20 secs or so the doors are open.
>>>>>
>>>>...
>>>>
>>>>But I think there must be air changing. Apart from the cooling aspect
>>>>there is the matter of ensuring breathable air.
>>>
>>> No-one denies the air is flowing/changing to some limited extent.
>>> However adding aircon makes it change much more often (as well as the
>>> input air being cool rather than hot). That's the whole point.
>>
>>If the air is changing fast enough to keep the air fresh then it is
>>changing several times per hour. More than enough to take the heat out as
>>well.
>
>It's not taking enough of the heat out, therefore the carriages are hot
>and sweaty.

Yes, because the air in the tunnels might be pretty warm in the summer, so you need a huge amount of it to reduce the
carriage temperatures. And if that air is at, say, 30C, it's not going to cool the carriages below that (very
uncomfortable) temperature. Even at 25C, the blast of ventilation air won't make the carriages particularly comfortable.

On Wed, 30 Mar 2022 17:23:54 +0100, Roland Perry <roland@perry.co.uk> wrote:

>In message <t1v84h9ptb8p1ckhakmm7milqbichufdoo@4ax.com>, at 16:53:20 on
>Wed, 30 Mar 2022, Recliner <recliner.usenet@gmail.com> remarked:
>
>>>>>>>> Air conditioning is new to the tube.
>>>>>>>
>>>>>>> One thing that I don't understand is how the NT4L address the question
>>>>>>> of heat dissipation within the tunnel. IIRC, this has always been an
>>>>>>> issue for tube trains and the main reason why up till now there never
>>>>>>> was air conditioning.
>>>>>>>
>>>>>>> Having said that, I note that the cabs on 95ts have air conditioning.
>>>>>>
>>>>>>Including the aircon, these new trains will use significantly less energy
>>>>>>(ie, produce less heat) than the ones they replace.
>>>>>
>>>>>The heat people are concerned abut isn't that generated by the train
>>>>>motors or even the aircon motors, but that which is pumped out by the
>>>>>aircon as it cools the people, the interior fittings, and the on-train
>>>>>air. The latter two in particular get "recharged" every time the doors
>>>>>are open on surface sections of the line, as well as by solar gain on
>>>>>those sections of line. The former is recharged every time hot and
>>>>>bothered pax board the train (on all sections of the line).
>>>>
>>>>The heat people are concerned about is caused by the energy consumed by
>>>>the train, which turns into heat in the tunnels.
>>>>That will be lower with the new trains, despite the power consumed by
>>>>the aircon compressors.
>>>
>>>And what of the heat pumped out from the inside of the train?
>>>
>>>Wikipedia cites a broken link to the Times for:
>>>
>>>"Conventional air conditioning was initially ruled out on the deep lines
>>>because of the lack of space for equipment on trains and the problems of
>>>dispersing the waste heat these would generate. Different systems were
>>>proposed to cool Underground trains, including the use of large blocks
>>>of ice inside the train."
>>>
>>>Maybe as a subscriber, you would have better luck getting the fuller
>>>text.
>>
>>I remember those proposals, but nothing came of them.
>
>And the tunnels kept on heating up. Just because they didn't implement a
>particular rather wacky cooling system doesn't detract from that.

I'm not sure if the tunnel temperatures are continuing to rise, as LU has taken measures to mitigate it (eg, dumping
heat into the cool ground source water it pumps out, and increasing ventilation).

On Thu, 31 Mar 2022 13:23:35 +0100, Roland Perry <roland@perry.co.uk> wrote:

>In message <t24581$b7s$2@dont-email.me>, at 12:02:09 on Thu, 31 Mar
>2022, Recliner <recliner.usenet@gmail.com> remarked:
>>Roland Perry <roland@perry.co.uk> wrote:
>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>> On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>
>>>> ...
>>>>
>>>>> If only. Unless there's a decent movement of air and there arn't many
>>>>> people in the train then the air inside pretty much stays there in the
>>>>> 20 secs or so the doors are open.
>>>>>
>>>> ...
>>>>
>>>> But I think there must be air changing. Apart from the cooling aspect
>>>> there is the matter of ensuring breathable air.
>>>
>>> No-one denies the air is flowing/changing to some limited extent.
>>> However adding aircon makes it change much more often (as well as the
>>> input air being cool rather than hot). That's the whole point.
>>
>>Actually, with aircon, the air will probably be changed *less often* than
>>with simple pressure ventilation.
>
>I'm not so sure about that, but the overall effect means the passengers
>are more comfortable, so job done.

Yes, and it's achievable with lower volumes of air, simply because it's cooler and drier. But there obviously still
needs to be enough flow to keep CO2 levels down.

On Thu, 31 Mar 2022 12:42:27 -0000 (UTC), nib <news@ingram-bromley.co.uk> wrote:

>On Thu, 31 Mar 2022 12:02:09 +0000, Recliner wrote:
>
>> Roland Perry <roland@perry.co.uk> wrote:
>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>> On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>
>>>> ...
>>>>
>>>>> If only. Unless there's a decent movement of air and there arn't many
>>>>> people in the train then the air inside pretty much stays there in
>>>>> the 20 secs or so the doors are open.
>>>>>
>>>> ...
>>>>
>>>> But I think there must be air changing. Apart from the cooling aspect
>>>> there is the matter of ensuring breathable air.
>>>
>>> No-one denies the air is flowing/changing to some limited extent.
>>> However adding aircon makes it change much more often (as well as the
>>> input air being cool rather than hot). That's the whole point.
>>>
>>>
>> Actually, with aircon, the air will probably be changed *less often*
>> than with simple pressure ventilation.
>
>OK, some numbers to play with. Basis: a person breathes out 400 mL/min of
>CO2; a tube train is about 17x3x2 m so 100 m^2 volume; crush loading is
>about 120 per carriage; background CO2 is about 350 ppm (0.035%); fatal
>CO2 is about 8%; poor air quality is about 0.15%.
>
>So our stuffed carriage will be adding 48 litres of CO2 per minute, which
>in 100 m^3 will be increasing the CO2 concentration by 0.048% per minute.
>
>That gives fatal levels in about 2.7 hours.
>
>An FOI request I saw from measurements on running Vic line trains in a
>busy period showed CO2 varying with an average of 0.1% and a peak of
>0.22%. To get to that 0.22% from background level would take nearly 4
>minutes. So if the levels are kept below that we can assume that the
>ventilation is doing a complete change of air at least every 4 minutes;
>or 15 changes per hour.

Surely, to maintain any particular level of CO2 (high or low) would only require enough ventilation air to remove at
least 48 l/min (ie, remove 0.05% CO2 per minute)? Obviously to reduce the levels would require a higher rate.

>
>The recommendation for trains is 6 to 8 changes per hour, but another FOI
>answer I found, actually about Covid, said that Tube trains have a higher
>rate than this of 20 changes per hour.
>
>So quesswork scribbling and that datum seem to confirm than the air in
>the tube carriage is changed completely about every 3 or 4 minutes.
>
>Any obvious errors?

Yes, I think so. You're calculating how many changes would be needed to reduce the concentration from the peak to the
background level, rather than the minimum number of changes to stop the concentration increasing.

On Thu, 31 Mar 2022 14:32:39 +0100, Recliner wrote:

> On Thu, 31 Mar 2022 12:42:27 -0000 (UTC), nib
> <news@ingram-bromley.co.uk> wrote:
>
>>On Thu, 31 Mar 2022 12:02:09 +0000, Recliner wrote:
>>
>>> Roland Perry <roland@perry.co.uk> wrote:
>>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>>> On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>>
>>>>> ...
>>>>>
>>>>>> If only. Unless there's a decent movement of air and there arn't
>>>>>> many people in the train then the air inside pretty much stays
>>>>>> there in the 20 secs or so the doors are open.
>>>>>>
>>>>> ...
>>>>>
>>>>> But I think there must be air changing. Apart from the cooling
>>>>> aspect there is the matter of ensuring breathable air.
>>>>
>>>> No-one denies the air is flowing/changing to some limited extent.
>>>> However adding aircon makes it change much more often (as well as the
>>>> input air being cool rather than hot). That's the whole point.
>>>>
>>>>
>>> Actually, with aircon, the air will probably be changed *less often*
>>> than with simple pressure ventilation.
>>
>>OK, some numbers to play with. Basis: a person breathes out 400 mL/min
>>of CO2; a tube train is about 17x3x2 m so 100 m^2 volume; crush loading
>>is about 120 per carriage; background CO2 is about 350 ppm (0.035%);
>>fatal CO2 is about 8%; poor air quality is about 0.15%.
>>
>>So our stuffed carriage will be adding 48 litres of CO2 per minute,
>>which in 100 m^3 will be increasing the CO2 concentration by 0.048% per
>>minute.
>>
>>That gives fatal levels in about 2.7 hours.
>>
>>An FOI request I saw from measurements on running Vic line trains in a
>>busy period showed CO2 varying with an average of 0.1% and a peak of
>>0.22%. To get to that 0.22% from background level would take nearly 4
>>minutes. So if the levels are kept below that we can assume that the
>>ventilation is doing a complete change of air at least every 4 minutes;
>>or 15 changes per hour.
>
> Surely, to maintain any particular level of CO2 (high or low) would only
> require enough ventilation air to remove at least 48 l/min (ie, remove
> 0.05% CO2 per minute)? Obviously to reduce the levels would require a
> higher rate.
>
>
>>The recommendation for trains is 6 to 8 changes per hour, but another
>>FOI answer I found, actually about Covid, said that Tube trains have a
>>higher rate than this of 20 changes per hour.
>>
>>So quesswork scribbling and that datum seem to confirm than the air in
>>the tube carriage is changed completely about every 3 or 4 minutes.
>>
>>Any obvious errors?
>
> Yes, I think so. You're calculating how many changes would be needed to
> reduce the concentration from the peak to the background level, rather
> than the minimum number of changes to stop the concentration increasing.

Ta! Yes!

The amount of extraction air needed is lower the higher the concentration
you are prepared to accept. Imagine you are prepared to accept a maximum
of twice the background. Then imagine implementing that by allowing the
concentration to increase to double with no air-flow and then changing
all the air. In our figures that would mean changing the air every 0.75
minutes. If you are prepared to accept the 0.22% or 5 times the
background, it comes down to the 4 minutes.

But I'll try again. As you say we need to get rid of 0.048 m^3/min of
CO2. We are assuming we are achieving a maximum of 0.22% concentration,
the worst figure from the TfL measurements. The air coming in has already
the background level so we need to shift the concentration of the air by
0.18% or so. That takes 0.048 / 0.0018 = 26 m^3/min of air. So a full
change every 4 minutes, roughly.

nib

In message <t24di4$lku$5@dont-email.me>, at 14:24:04 on Thu, 31 Mar
2022, nib <news@ingram-bromley.co.uk> remarked:

>But I'll try again. As you say we need to get rid of 0.048 m^3/min of
>CO2. We are assuming we are achieving a maximum of 0.22% concentration,
>the worst figure from the TfL measurements. The air coming in has already
>the background level

Why doesn't it have a higher level on account of all the CO2 expelled
from the trains in front.

>so we need to shift the concentration of the air by
>0.18% or so. That takes 0.048 / 0.0018 = 26 m^3/min of air. So a full
>change every 4 minutes, roughly.

--
Roland Perry

In message <t248ab$lku$4@dont-email.me>, at 12:54:36 on Thu, 31 Mar
2022, nib <news@ingram-bromley.co.uk> remarked:
>On Thu, 31 Mar 2022 13:25:47 +0100, Roland Perry wrote:
>
>> In message <t244v0$lku$2@dont-email.me>, at 11:57:20 on Thu, 31 Mar
>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>On Thu, 31 Mar 2022 12:48:31 +0100, Roland Perry wrote:
>>>
>>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>>>On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>>
>>>>>...
>>>>>
>>>>>> If only. Unless there's a decent movement of air and there arn't
>>>>>> many people in the train then the air inside pretty much stays there
>>>>>> in the 20 secs or so the doors are open.
>>>>>>
>>>>>...
>>>>>
>>>>>But I think there must be air changing. Apart from the cooling aspect
>>>>>there is the matter of ensuring breathable air.
>>>>
>>>> No-one denies the air is flowing/changing to some limited extent.
>>>> However adding aircon makes it change much more often (as well as the
>>>> input air being cool rather than hot). That's the whole point.
>>>
>>>If the air is changing fast enough to keep the air fresh then it is
>>>changing several times per hour. More than enough to take the heat out
>>>as well.
>>
>> It's not taking enough of the heat out, therefore the carriages are hot
>> and sweaty.
>
>Don't confuse heat (flow) and temperature. It is taking the heat out. It
>just needs a higher source temperature to drive it.

Passengers don't like the higher temperatures, although their dry
cleaners might.
--
Roland Perry

On 31/03/2022 11:49, Recliner wrote:
> nib <news@ingram-bromley.co.uk> wrote:
>> On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>
>> ...
>>
>>> If only. Unless there's a decent movement of air and there arn't many
>>> people in the train then the air inside pretty much stays there in the
>>> 20 secs or so the doors are open.
>>>
>> ...
>>
>> But I think there must be air changing. Apart from the cooling aspect
>> there is the matter of ensuring breathable air. Not sure of guessing, but
>> a few figures from Googling suggest that say 100 people rammed into a
>> tube carriage won't have to wait long before the CO2 levels become
>> elevated, less than an hour to levels that might be fatal. That this
>> doesn't happen might suggest that the air inside does exchange with the
>> tunnel/station air?
>>
>> What part of it is through the doors I wonder, rather than through other
>> paths?
>>
>
> I'm sure the ventilation must be strong enough that even if a packed Tube
> train gets stranded in a tunnel for an extended period, the passengers
> don't suffocate. They may get hot and bothered, but nobody suffers from CO2
> poisoning.
>

IIRC, at least some EMU trains have emergency fans in the event that
main power is out.

On Thu, 31 Mar 2022 16:09:08 +0100, Roland Perry <roland@perry.co.uk> wrote:

>In message <t24di4$lku$5@dont-email.me>, at 14:24:04 on Thu, 31 Mar
>2022, nib <news@ingram-bromley.co.uk> remarked:
>
>>But I'll try again. As you say we need to get rid of 0.048 m^3/min of
>>CO2. We are assuming we are achieving a maximum of 0.22% concentration,
>>the worst figure from the TfL measurements. The air coming in has already
>>the background level
>
>Why doesn't it have a higher level on account of all the CO2 expelled
>from the trains in front.

Yes, it will, to some degree, but it won't be much above background level, as the CO2 is dispersed in a far larger
volume of air, and there's quite a bit of ventilation from stations.

<Muttley@dastardlyhq.com> wrote:
> On Wed, 30 Mar 2022 21:23:29 -0000 (UTC)
> Recliner <recliner.usenet@gmail.com> wrote:
>> Roland Perry <roland@perry.co.uk> wrote:
>>> The non-airconditioned train will heat up while in the tunnelled
>>> sections, possibly very uncomfortably so, and cool off later while out
>>> on surface sections (especially when doors are open). Rinse and repeat.
>>
>> You seem to forget that the trains stop in stations every couple of minutes
>> and open all the doors (three or four per carriage). The hot, humid air in
>> a non-airconditioned train will largely discharge into the station platform
>
> If only. Unless there's a decent movement of air and there arn't many people
> in the train then the air inside pretty much stays there in the 20 secs or
> so the doors are open.
>
Here I agree with you. You’d need both sides of door to open, which isn’t
going to happen at most stations. It’s remarkably difficult to get air
exchange through a doorway. At work we have two rooms with a connecting
door. One has a powerful air conditioner, the other doesn’t. Propping the
door open on a hot day makes almost no difference to the hot room. Even
putting a powerful fan in the doorway makes little impact.

Roland Perry <roland@perry.co.uk> wrote:
> In message <t248ab$lku$4@dont-email.me>, at 12:54:36 on Thu, 31 Mar
> 2022, nib <news@ingram-bromley.co.uk> remarked:
>> On Thu, 31 Mar 2022 13:25:47 +0100, Roland Perry wrote:
>>
>>> In message <t244v0$lku$2@dont-email.me>, at 11:57:20 on Thu, 31 Mar
>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>> On Thu, 31 Mar 2022 12:48:31 +0100, Roland Perry wrote:
>>>>
>>>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>>>> On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>> If only. Unless there's a decent movement of air and there arn't
>>>>>>> many people in the train then the air inside pretty much stays there
>>>>>>> in the 20 secs or so the doors are open.
>>>>>>>
>>>>>> ...
>>>>>>
>>>>>> But I think there must be air changing. Apart from the cooling aspect
>>>>>> there is the matter of ensuring breathable air.
>>>>>
>>>>> No-one denies the air is flowing/changing to some limited extent.
>>>>> However adding aircon makes it change much more often (as well as the
>>>>> input air being cool rather than hot). That's the whole point.
>>>>
>>>> If the air is changing fast enough to keep the air fresh then it is
>>>> changing several times per hour. More than enough to take the heat out
>>>> as well.
>>>
>>> It's not taking enough of the heat out, therefore the carriages are hot
>>> and sweaty.
>>
>> Don't confuse heat (flow) and temperature. It is taking the heat out. It
>> just needs a higher source temperature to drive it.
>
> Passengers don't like the higher temperatures, although their dry
> cleaners might.

Which is why they're going to so much trouble to cool the new trains and
ventilate the tunnels.

For example, look at this substantial LU ventilation shaft built at Euston
as part of the HS2 works:
https://www.gzconsultants.com/wp-content/uploads/1652_EUSTN.pdf

Tweed <usenet.tweed@gmail.com> wrote:
> <Muttley@dastardlyhq.com> wrote:
>> On Wed, 30 Mar 2022 21:23:29 -0000 (UTC)
>> Recliner <recliner.usenet@gmail.com> wrote:
>>> Roland Perry <roland@perry.co.uk> wrote:
>>>> The non-airconditioned train will heat up while in the tunnelled
>>>> sections, possibly very uncomfortably so, and cool off later while out
>>>> on surface sections (especially when doors are open). Rinse and repeat.
>>>
>>> You seem to forget that the trains stop in stations every couple of minutes
>>> and open all the doors (three or four per carriage). The hot, humid air in
>>> a non-airconditioned train will largely discharge into the station platform
>>
>> If only. Unless there's a decent movement of air and there arn't many people
>> in the train then the air inside pretty much stays there in the 20 secs or
>> so the doors are open.
>>
> Here I agree with you. You’d need both sides of door to open, which isn’t
> going to happen at most stations. It’s remarkably difficult to get air
> exchange through a doorway. At work we have two rooms with a connecting
> door. One has a powerful air conditioner, the other doesn’t. Propping the
> door open on a hot day makes almost no difference to the hot room. Even
> putting a powerful fan in the doorway makes little impact.
>

The Tube train doorways extend into the train roofs, so hot air will rise
from them. I suspect your connecting door doesn't do that. And the
ventilation fans in the saloons will help move the air through the doorway.

But we all agree on the need for airconditioning in trains, particularly
those running through the small, hot tunnels under London.

nib <news@ingram-bromley.co.uk> wrote:
> On Thu, 31 Mar 2022 14:32:39 +0100, Recliner wrote:
>
>> On Thu, 31 Mar 2022 12:42:27 -0000 (UTC), nib
>> <news@ingram-bromley.co.uk> wrote:
>>
>>> On Thu, 31 Mar 2022 12:02:09 +0000, Recliner wrote:
>>>
>>>> Roland Perry <roland@perry.co.uk> wrote:
>>>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>>>> On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>> If only. Unless there's a decent movement of air and there arn't
>>>>>>> many people in the train then the air inside pretty much stays
>>>>>>> there in the 20 secs or so the doors are open.
>>>>>>>
>>>>>> ...
>>>>>>
>>>>>> But I think there must be air changing. Apart from the cooling
>>>>>> aspect there is the matter of ensuring breathable air.
>>>>>
>>>>> No-one denies the air is flowing/changing to some limited extent.
>>>>> However adding aircon makes it change much more often (as well as the
>>>>> input air being cool rather than hot). That's the whole point.
>>>>>
>>>>>
>>>> Actually, with aircon, the air will probably be changed *less often*
>>>> than with simple pressure ventilation.
>>>
>>> OK, some numbers to play with. Basis: a person breathes out 400 mL/min
>>> of CO2; a tube train is about 17x3x2 m so 100 m^2 volume; crush loading
>>> is about 120 per carriage; background CO2 is about 350 ppm (0.035%);
>>> fatal CO2 is about 8%; poor air quality is about 0.15%.
>>>
>>> So our stuffed carriage will be adding 48 litres of CO2 per minute,
>>> which in 100 m^3 will be increasing the CO2 concentration by 0.048% per
>>> minute.
>>>
>>> That gives fatal levels in about 2.7 hours.
>>>
>>> An FOI request I saw from measurements on running Vic line trains in a
>>> busy period showed CO2 varying with an average of 0.1% and a peak of
>>> 0.22%. To get to that 0.22% from background level would take nearly 4
>>> minutes. So if the levels are kept below that we can assume that the
>>> ventilation is doing a complete change of air at least every 4 minutes;
>>> or 15 changes per hour.
>>
>> Surely, to maintain any particular level of CO2 (high or low) would only
>> require enough ventilation air to remove at least 48 l/min (ie, remove
>> 0.05% CO2 per minute)? Obviously to reduce the levels would require a
>> higher rate.
>>
>>
>>> The recommendation for trains is 6 to 8 changes per hour, but another
>>> FOI answer I found, actually about Covid, said that Tube trains have a
>>> higher rate than this of 20 changes per hour.
>>>
>>> So quesswork scribbling and that datum seem to confirm than the air in
>>> the tube carriage is changed completely about every 3 or 4 minutes.
>>>
>>> Any obvious errors?
>>
>> Yes, I think so. You're calculating how many changes would be needed to
>> reduce the concentration from the peak to the background level, rather
>> than the minimum number of changes to stop the concentration increasing.
>
> Ta! Yes!
>
> The amount of extraction air needed is lower the higher the concentration
> you are prepared to accept. Imagine you are prepared to accept a maximum
> of twice the background. Then imagine implementing that by allowing the
> concentration to increase to double with no air-flow and then changing
> all the air. In our figures that would mean changing the air every 0.75
> minutes. If you are prepared to accept the 0.22% or 5 times the
> background, it comes down to the 4 minutes.
>
> But I'll try again. As you say we need to get rid of 0.048 m^3/min of
> CO2. We are assuming we are achieving a maximum of 0.22% concentration,
> the worst figure from the TfL measurements. The air coming in has already
> the background level so we need to shift the concentration of the air by
> 0.18% or so. That takes 0.048 / 0.0018 = 26 m^3/min of air. So a full
> change every 4 minutes, roughly.
>

My gut feel is that's on the high side, but I'm not complaining if they
achieve or beat that figure.

On Thu, 31 Mar 2022 16:29:32 +0000, Recliner wrote:

> nib <news@ingram-bromley.co.uk> wrote:
>> On Thu, 31 Mar 2022 14:32:39 +0100, Recliner wrote:
>>
>>> On Thu, 31 Mar 2022 12:42:27 -0000 (UTC), nib
>>> <news@ingram-bromley.co.uk> wrote:
>>>
>>>> On Thu, 31 Mar 2022 12:02:09 +0000, Recliner wrote:
>>>>
>>>>> Roland Perry <roland@perry.co.uk> wrote:
>>>>>> In message <t23utr$lku$1@dont-email.me>, at 10:14:19 on Thu, 31 Mar
>>>>>> 2022, nib <news@ingram-bromley.co.uk> remarked:
>>>>>>> On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>>>>>>
>>>>>>> ...
>>>>>>>
>>>>>>>> If only. Unless there's a decent movement of air and there arn't
>>>>>>>> many people in the train then the air inside pretty much stays
>>>>>>>> there in the 20 secs or so the doors are open.
>>>>>>>>
>>>>>>> ...
>>>>>>>
>>>>>>> But I think there must be air changing. Apart from the cooling
>>>>>>> aspect there is the matter of ensuring breathable air.
>>>>>>
>>>>>> No-one denies the air is flowing/changing to some limited extent.
>>>>>> However adding aircon makes it change much more often (as well as
>>>>>> the input air being cool rather than hot). That's the whole point.
>>>>>>
>>>>>>
>>>>> Actually, with aircon, the air will probably be changed *less often*
>>>>> than with simple pressure ventilation.
>>>>
>>>> OK, some numbers to play with. Basis: a person breathes out 400
>>>> mL/min of CO2; a tube train is about 17x3x2 m so 100 m^2 volume;
>>>> crush loading is about 120 per carriage; background CO2 is about 350
>>>> ppm (0.035%); fatal CO2 is about 8%; poor air quality is about 0.15%.
>>>>
>>>> So our stuffed carriage will be adding 48 litres of CO2 per minute,
>>>> which in 100 m^3 will be increasing the CO2 concentration by 0.048%
>>>> per minute.
>>>>
>>>> That gives fatal levels in about 2.7 hours.
>>>>
>>>> An FOI request I saw from measurements on running Vic line trains in
>>>> a busy period showed CO2 varying with an average of 0.1% and a peak
>>>> of 0.22%. To get to that 0.22% from background level would take
>>>> nearly 4 minutes. So if the levels are kept below that we can assume
>>>> that the ventilation is doing a complete change of air at least every
>>>> 4 minutes;
>>>> or 15 changes per hour.
>>>
>>> Surely, to maintain any particular level of CO2 (high or low) would
>>> only require enough ventilation air to remove at least 48 l/min (ie,
>>> remove 0.05% CO2 per minute)? Obviously to reduce the levels would
>>> require a higher rate.
>>>
>>>
>>>> The recommendation for trains is 6 to 8 changes per hour, but another
>>>> FOI answer I found, actually about Covid, said that Tube trains have
>>>> a higher rate than this of 20 changes per hour.
>>>>
>>>> So quesswork scribbling and that datum seem to confirm than the air
>>>> in the tube carriage is changed completely about every 3 or 4
>>>> minutes.
>>>>
>>>> Any obvious errors?
>>>
>>> Yes, I think so. You're calculating how many changes would be needed
>>> to reduce the concentration from the peak to the background level,
>>> rather than the minimum number of changes to stop the concentration
>>> increasing.
>>
>> Ta! Yes!
>>
>> The amount of extraction air needed is lower the higher the
>> concentration you are prepared to accept. Imagine you are prepared to
>> accept a maximum of twice the background. Then imagine implementing
>> that by allowing the concentration to increase to double with no
>> air-flow and then changing all the air. In our figures that would mean
>> changing the air every 0.75 minutes. If you are prepared to accept the
>> 0.22% or 5 times the background, it comes down to the 4 minutes.
>>
>> But I'll try again. As you say we need to get rid of 0.048 m^3/min of
>> CO2. We are assuming we are achieving a maximum of 0.22% concentration,
>> the worst figure from the TfL measurements. The air coming in has
>> already the background level so we need to shift the concentration of
>> the air by 0.18% or so. That takes 0.048 / 0.0018 = 26 m^3/min of air.
>> So a full change every 4 minutes, roughly.
>>
>>
> My gut feel is that's on the high side, but I'm not complaining if they
> achieve or beat that figure.

Well yes, it's only an order-of-magnitude guess, not a study! But it's
fun and good when it gives a sensible answer. That FoI request that gave
the actual figure is here:

<https://tfl.gov.uk/corporate/transparency/freedom-of-information/foi-
request-detail?referenceId=FOI-0219-2122>

nib

On Thu, 31 Mar 2022 10:49:46 -0000 (UTC), Recliner
<recliner.usenet@gmail.com> wrote:

>nib <news@ingram-bromley.co.uk> wrote:
>> On Thu, 31 Mar 2022 08:24:27 +0000, Muttley wrote:
>>
>> ...
>>
>>> If only. Unless there's a decent movement of air and there arn't many
>>> people in the train then the air inside pretty much stays there in the
>>> 20 secs or so the doors are open.
>>>
>> ...
>>
>> But I think there must be air changing. Apart from the cooling aspect
>> there is the matter of ensuring breathable air. Not sure of guessing, but
>> a few figures from Googling suggest that say 100 people rammed into a
>> tube carriage won't have to wait long before the CO2 levels become
>> elevated, less than an hour to levels that might be fatal. That this
>> doesn't happen might suggest that the air inside does exchange with the
>> tunnel/station air?
>>
>> What part of it is through the doors I wonder, rather than through other
>> paths?
>>
>
>I'm sure the ventilation must be strong enough that even if a packed Tube
>train gets stranded in a tunnel for an extended period, the passengers
>don't suffocate. They may get hot and bothered, but nobody suffers from CO2
>poisoning.
>
>Tube train doorways extend well into the roofs of the carriages, so hot air
>from the carriages will naturally rise out of the train in stations.
>
They all have vents (and/or fans) near/above cantrail level, usually
more evident from outside.

On Thu, 31 Mar 2022 16:08:22 -0000 (UTC)
Recliner <recliner.usenet@gmail.com> wrote:
>Tweed <usenet.tweed@gmail.com> wrote:
>> Here I agree with you. You’d need both sides of door to open, which isn’t
>
>> going to happen at most stations. It’s remarkably difficult to get air
>> exchange through a doorway. At work we have two rooms with a connecting
>> door. One has a powerful air conditioner, the other doesn’t. Propping the
>> door open on a hot day makes almost no difference to the hot room. Even
>> putting a powerful fan in the doorway makes little impact.
>>
>
>The Tube train doorways extend into the train roofs, so hot air will rise

Barely. Plus it makes very little difference especially if people are standing
in the doorway. I think we can surmise you've never commuted on the tube for
any length of time.

<Muttley@dastardlyhq.com> wrote:
> On Thu, 31 Mar 2022 16:08:22 -0000 (UTC)
> Recliner <recliner.usenet@gmail.com> wrote:
>> Tweed <usenet.tweed@gmail.com> wrote:
>>> Here I agree with you. You’d need both sides of door to open, which isn’t
>>
>>> going to happen at most stations. It’s remarkably difficult to get air
>>> exchange through a doorway. At work we have two rooms with a connecting
>>> door. One has a powerful air conditioner, the other doesn’t. Propping the
>>> door open on a hot day makes almost no difference to the hot room. Even
>>> putting a powerful fan in the doorway makes little impact.
>>>
>>
>> The Tube train doorways extend into the train roofs, so hot air will rise
>
> Barely. Plus it makes very little difference especially if people are standing
> in the doorway. I think we can surmise you've never commuted on the tube for
> any length of time.

I commuted on the Tube for many years, but tried to avoid travelling in the
peaks.

On Wed, 30 Mar 2022 11:46:59 -0000 (UTC), Anna Noyd-Dryver
<anna@noyd-dryver.com> wrote:

>I suspect that, like S Stock IIRC, it'll only get used at termini, or when
>the train stands for more than a few minutes at stations. Procedure: train
>arrives, all doors open. After a few minutes with nobody passing through,
>each set of doors will close itself and the door buttons become active.

45 seconds on S stock.