I've used the Vic line a few times over the last few weeks and have
been struck by the heat. These weren't very busy trains and the days
weren't that hot. I think someone posted here recently about a problem
facing parts of the tube of heat buildup, with trains and passengers
adding more heat during the day than can be removed overnight.
I know that various ideas have been floated but the only thing visible
to mitigate underground heat are large fans in subterranean walkways
on the Vic and other lines.
Surely these simply add to the problem? These are huge, heavy things
that must use a couple of hundred watts doing work on air and
generating heat in the motors.This heat goes directly towards warming
up the system.
OK, they feel nice for a second as you walk past but they're
counterproductive,aren't they?

Ken <ken@birchanger.com> wrote:
> I've used the Vic line a few times over the last few weeks and have
> been struck by the heat. These weren't very busy trains and the days
> weren't that hot. I think someone posted here recently about a problem
> facing parts of the tube of heat buildup, with trains and passengers
> adding more heat during the day than can be removed overnight.
> I know that various ideas have been floated but the only thing visible
> to mitigate underground heat are large fans in subterranean walkways
> on the Vic and other lines.
> Surely these simply add to the problem? These are huge, heavy things
> that must use a couple of hundred watts doing work on air and
> generating heat in the motors.This heat goes directly towards warming
> up the system.
> OK, they feel nice for a second as you walk past but they're
> counterproductive,aren't they?

For decades heat has been pumped into the tube network by virtue of electric
trains (and their braking) heating up the air, more than can escape. That
eventually heats up the tunnels, the buildings, the rocks, everything.
Things have got better of late with trains that regen, so there isn't quite
so much heat going in now as there used to, but if the surrounding rock has
been heated it's not going to cool rapidly.

The only way to cool is to transport the heat out. Fans are the most
efficient way to do this: move warm air through the station and out of a
ventilation shaft, allowing cooler air to come in. Air conditioning would
offer cooler air but very much more energy intensive. I think water systems
are in use in some places.

If a train is 1MW, a 200W fan doesn't sound so bad?

Theo

On 25 Sep 2022 14:47:13 +0100 (BST)
Theo <theom+news@chiark.greenend.org.uk> wrote:
>Ken <ken@birchanger.com> wrote:
>> I've used the Vic line a few times over the last few weeks and have
>> been struck by the heat. These weren't very busy trains and the days
>> weren't that hot. I think someone posted here recently about a problem
>> facing parts of the tube of heat buildup, with trains and passengers
>> adding more heat during the day than can be removed overnight.
>> I know that various ideas have been floated but the only thing visible
>> to mitigate underground heat are large fans in subterranean walkways
>> on the Vic and other lines.
>> Surely these simply add to the problem? These are huge, heavy things
>> that must use a couple of hundred watts doing work on air and
>> generating heat in the motors.This heat goes directly towards warming
>> up the system.
>> OK, they feel nice for a second as you walk past but they're
>> counterproductive,aren't they?
>
>For decades heat has been pumped into the tube network by virtue of electric
>trains (and their braking) heating up the air, more than can escape. That
>eventually heats up the tunnels, the buildings, the rocks, everything.
>Things have got better of late with trains that regen, so there isn't quite
>so much heat going in now as there used to, but if the surrounding rock has
>been heated it's not going to cool rapidly.

If it was rock it probably wouldn't be so bad, but most (all?) of the tube
tunnels are dug through clay which is wet and water holds on to heat better
than most other substances.

On 25 Sep 2022 14:47:13 +0100 (BST), Theo
<theom+news@chiark.greenend.org.uk> wrote:

>Ken <ken@birchanger.com> wrote:
>> I've used the Vic line a few times over the last few weeks and have
>> been struck by the heat. These weren't very busy trains and the days
>> weren't that hot. I think someone posted here recently about a problem
>> facing parts of the tube of heat buildup, with trains and passengers
>> adding more heat during the day than can be removed overnight.
>> I know that various ideas have been floated but the only thing visible
>> to mitigate underground heat are large fans in subterranean walkways
>> on the Vic and other lines.
>> Surely these simply add to the problem? These are huge, heavy things
>> that must use a couple of hundred watts doing work on air and
>> generating heat in the motors.This heat goes directly towards warming
>> up the system.
>> OK, they feel nice for a second as you walk past but they're
>> counterproductive,aren't they?
>
>For decades heat has been pumped into the tube network by virtue of electric
>trains (and their braking) heating up the air, more than can escape. That
>eventually heats up the tunnels, the buildings, the rocks, everything.
>Things have got better of late with trains that regen, so there isn't quite
>so much heat going in now as there used to, but if the surrounding rock has
>been heated it's not going to cool rapidly.
>
>The only way to cool is to transport the heat out. Fans are the most
>efficient way to do this: move warm air through the station and out of a
>ventilation shaft, allowing cooler air to come in. Air conditioning would
>offer cooler air but very much more energy intensive. I think water systems
>are in use in some places.
>
I'm not talking about the huge fans in ventilation shafts; I'm talking
about the freestanding ones in passenger circulation areas. These
don't move a molecule of air in or out of the system.

>If a train is 1MW, a 200W fan doesn't sound so bad?
>
>Theo

In uk.transport.london Ken <ken@birchanger.com> wrote:
> I'm not talking about the huge fans in ventilation shafts; I'm talking
> about the freestanding ones in passenger circulation areas. These
> don't move a molecule of air in or out of the system.

But there are inevitably dead spots in the ventilation. There will be a
particular main flow from the shaft fans, but heat can build up in pockets
that aren't directly ventilated. Adding extra fans to mix the air around
smooths out temperature differences between (for example) the running
tunnels (which might be directly ventilated) and the platform cross-passages
and escalator lower tunnels (which might not). Plus it also makes a breeze
which is appreciated by passengers.

A bit like a fan oven, the fans make the temperature more even and so you
need less power to achieved the desired heating/cooling outcome.

Theo

On 26 Sep 2022 13:08:17 +0100 (BST)
Theo <theom+news@chiark.greenend.org.uk> wrote:
>In uk.transport.london Ken <ken@birchanger.com> wrote:
>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>> about the freestanding ones in passenger circulation areas. These
>> don't move a molecule of air in or out of the system.
>
>But there are inevitably dead spots in the ventilation. There will be a
>particular main flow from the shaft fans, but heat can build up in pockets
>that aren't directly ventilated. Adding extra fans to mix the air around
>smooths out temperature differences between (for example) the running
>tunnels (which might be directly ventilated) and the platform cross-passages
>and escalator lower tunnels (which might not). Plus it also makes a breeze
>which is appreciated by passengers.

The amount of air they move around is probably insignificant compared to
the trains themselves. All they do is provide a breeze for pax walking past.

<Muttley@dastardlyhq.com> wrote:
> On 26 Sep 2022 13:08:17 +0100 (BST)
> Theo <theom+news@chiark.greenend.org.uk> wrote:
>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>> about the freestanding ones in passenger circulation areas. These
>>> don't move a molecule of air in or out of the system.
>>
>> But there are inevitably dead spots in the ventilation. There will be a
>> particular main flow from the shaft fans, but heat can build up in pockets
>> that aren't directly ventilated. Adding extra fans to mix the air around
>> smooths out temperature differences between (for example) the running
>> tunnels (which might be directly ventilated) and the platform cross-passages
>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>> which is appreciated by passengers.
>
> The amount of air they move around is probably insignificant compared to
> the trains themselves. All they do is provide a breeze for pax walking past.

For this relief, much thanks!

Sam

--
The entity formerly known as Sam.Wilson@ed.ac.uk
Spit the dummy to reply

<Muttley@dastardlyhq.com> wrote:
> On 26 Sep 2022 13:08:17 +0100 (BST)
> Theo <theom+news@chiark.greenend.org.uk> wrote:
>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>> about the freestanding ones in passenger circulation areas. These
>>> don't move a molecule of air in or out of the system.
>>
>> But there are inevitably dead spots in the ventilation. There will be a
>> particular main flow from the shaft fans, but heat can build up in pockets
>> that aren't directly ventilated. Adding extra fans to mix the air around
>> smooths out temperature differences between (for example) the running
>> tunnels (which might be directly ventilated) and the platform cross-passages
>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>> which is appreciated by passengers.
>
> The amount of air they move around is probably insignificant compared to
> the trains themselves. All they do is provide a breeze for pax walking past.
>
>

I've always presumed that that's what they're for - to provide a breeze to
make the heat feel less unpleasant.

Anna Noyd-Dryver

Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
> <Muttley@dastardlyhq.com> wrote:
>> On 26 Sep 2022 13:08:17 +0100 (BST)
>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>> about the freestanding ones in passenger circulation areas. These
>>>> don't move a molecule of air in or out of the system.
>>>
>>> But there are inevitably dead spots in the ventilation. There will be a
>>> particular main flow from the shaft fans, but heat can build up in pockets
>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>> smooths out temperature differences between (for example) the running
>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>> which is appreciated by passengers.
>>
>> The amount of air they move around is probably insignificant compared to
>> the trains themselves. All they do is provide a breeze for pax walking past.
>>
>>
>
> I've always presumed that that's what they're for - to provide a breeze to
> make the heat feel less unpleasant.

Yes, they're just a low cost stop-gap until the temperatures can be reduced
using better surface ventilation, or using ground water for cooling.

Recliner <recliner.usenet@gmail.com> wrote:
> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>> <Muttley@dastardlyhq.com> wrote:
>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>> about the freestanding ones in passenger circulation areas. These
>>>>> don't move a molecule of air in or out of the system.
>>>>
>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>> smooths out temperature differences between (for example) the running
>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>> which is appreciated by passengers.
>>>
>>> The amount of air they move around is probably insignificant compared to
>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>
>>>
>>
>> I've always presumed that that's what they're for - to provide a breeze to
>> make the heat feel less unpleasant.
>
> Yes, they're just a low cost stop-gap until the temperatures can be reduced
> using better surface ventilation, or using ground water for cooling.

Of course; at higher temperatures humans mostly use evaporative cooling -
we’d die at external temperatures anywhere near 37 C otherwise - and
increasing the airflow increases the cooling so long as the air doesn’t
have very high relative humidity.

Sam

--
The entity formerly known as Sam.Wilson@ed.ac.uk
Spit the dummy to reply

Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
> Recliner <recliner.usenet@gmail.com> wrote:
>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>> <Muttley@dastardlyhq.com> wrote:
>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>> don't move a molecule of air in or out of the system.
>>>>>
>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>> smooths out temperature differences between (for example) the running
>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>> which is appreciated by passengers.
>>>>
>>>> The amount of air they move around is probably insignificant compared to
>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>
>>>>
>>>
>>> I've always presumed that that's what they're for - to provide a breeze to
>>> make the heat feel less unpleasant.
>>
>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>> using better surface ventilation, or using ground water for cooling.
>
> Of course; at higher temperatures humans mostly use evaporative cooling -
> we’d die at external temperatures anywhere near 37 C otherwise - and
> increasing the airflow increases the cooling so long as the air doesn’t
> have very high relative humidity.
>

Yes, but of course the powerful fans themselves contribute to the heat
build-up in the system.

In message <ti0qaj$pcp5$2@dont-email.me>, at 09:57:40 on Mon, 10 Oct
2022, Recliner <recliner.usenet@gmail.com> remarked:
>Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>> Recliner <recliner.usenet@gmail.com> wrote:
>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>> <Muttley@dastardlyhq.com> wrote:
>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>
>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>> particular main flow from the shaft fans, but heat can build up
>>>>>>in pockets
>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>> smooths out temperature differences between (for example) the running
>>>>>> tunnels (which might be directly ventilated) and the platform
>>>>>>cross-passages
>>>>>> and escalator lower tunnels (which might not). Plus it also
>>>>>>makes a breeze
>>>>>> which is appreciated by passengers.
>>>>>
>>>>> The amount of air they move around is probably insignificant compared to
>>>>> the trains themselves. All they do is provide a breeze for pax
>>>>>walking past.
>>>>
>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>> make the heat feel less unpleasant.
>>>
>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>> using better surface ventilation, or using ground water for cooling.
>>
>> Of course; at higher temperatures humans mostly use evaporative cooling -
>> we’d die at external temperatures anywhere near 37 C otherwise - and
>> increasing the airflow increases the cooling so long as the air doesn’t
>> have very high relative humidity.
>
>Yes, but of course the powerful fans themselves contribute to the heat
>build-up in the system.

Only as a second or even third order effect. What's the relative power
consumption of a fan, compared to an escalator, or one train every two
minutes, or even a hundred bodies a minute?

Hint: the latter is around 100W each, you can look up the escalators and
trains yourself.
--
Roland Perry

Recliner <recliner.usenet@gmail.com> wrote:
> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>> Recliner <recliner.usenet@gmail.com> wrote:
>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>> <Muttley@dastardlyhq.com> wrote:
>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>
>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>> smooths out temperature differences between (for example) the running
>>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>>> which is appreciated by passengers.
>>>>>
>>>>> The amount of air they move around is probably insignificant compared to
>>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>>
>>>>>
>>>>
>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>> make the heat feel less unpleasant.
>>>
>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>> using better surface ventilation, or using ground water for cooling.
>>
>> Of course; at higher temperatures humans mostly use evaporative cooling -
>> we’d die at external temperatures anywhere near 37 C otherwise - and
>> increasing the airflow increases the cooling so long as the air doesn’t
>> have very high relative humidity.
>>
>
> Yes, but of course the powerful fans themselves contribute to the heat
> build-up in the system.
>
>

What power are the fans, typically? Are we just considering the waste heat
from the motors, or also the contribution of the energy they impart to the
moving air?

How does the heat contribution of a handful of fans compare to that of
thousands of people and hundreds of trains?

Anna Noyd-Dryver

Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
> Recliner <recliner.usenet@gmail.com> wrote:
>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>> <Muttley@dastardlyhq.com> wrote:
>>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>>
>>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>>> smooths out temperature differences between (for example) the running
>>>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>>>> which is appreciated by passengers.
>>>>>>
>>>>>> The amount of air they move around is probably insignificant compared to
>>>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>>>
>>>>>>
>>>>>
>>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>>> make the heat feel less unpleasant.
>>>>
>>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>>> using better surface ventilation, or using ground water for cooling.
>>>
>>> Of course; at higher temperatures humans mostly use evaporative cooling -
>>> we’d die at external temperatures anywhere near 37 C otherwise - and
>>> increasing the airflow increases the cooling so long as the air doesn’t
>>> have very high relative humidity.
>>>
>>
>> Yes, but of course the powerful fans themselves contribute to the heat
>> build-up in the system.
>>
>>
>
> What power are the fans, typically? Are we just considering the waste heat
> from the motors, or also the contribution of the energy they impart to the
> moving air?

The total energy consumed by each fan (a few hundred watts) gets added to
the heat in the system.

>
> How does the heat contribution of a handful of fans compare to that of
> thousands of people and hundreds of trains?

It's only a very small increment, but it's nevertheless contributing to the
heating, rather than reducing it.

In message <ti0svo$pjqu$1@dont-email.me>, at 10:43:04 on Mon, 10 Oct
2022, Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>Recliner <recliner.usenet@gmail.com> wrote:
>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>> <Muttley@dastardlyhq.com> wrote:
>>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>>
>>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>>> particular main flow from the shaft fans, but heat can build up
>>>>>>>in pockets
>>>>>>> that aren't directly ventilated. Adding extra fans to mix the
>>>>>>>air around
>>>>>>> smooths out temperature differences between (for example) the running
>>>>>>> tunnels (which might be directly ventilated) and the platform
>>>>>>>cross-passages
>>>>>>> and escalator lower tunnels (which might not). Plus it also
>>>>>>>makes a breeze
>>>>>>> which is appreciated by passengers.
>>>>>>
>>>>>> The amount of air they move around is probably insignificant compared to
>>>>>> the trains themselves. All they do is provide a breeze for pax
>>>>>>walking past.
>>>>>>
>>>>>>
>>>>>
>>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>>> make the heat feel less unpleasant.
>>>>
>>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>>> using better surface ventilation, or using ground water for cooling.
>>>
>>> Of course; at higher temperatures humans mostly use evaporative cooling -
>>> we’d die at external temperatures anywhere near 37 C otherwise - and
>>> increasing the airflow increases the cooling so long as the air doesn’t
>>> have very high relative humidity.
>>>
>>
>> Yes, but of course the powerful fans themselves contribute to the heat
>> build-up in the system.
>
>What power are the fans, typically? Are we just considering the waste heat
>from the motors, or also the contribution of the energy they impart to the
>moving air?

Both, I think.

>How does the heat contribution of a handful of fans compare to that of
>thousands of people and hundreds of trains?

Tick.
--
Roland Perry

Recliner <recliner.usenet@gmail.com> wrote:
> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>> Recliner <recliner.usenet@gmail.com> wrote:
>>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>>> <Muttley@dastardlyhq.com> wrote:
>>>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>>>
>>>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>>>> smooths out temperature differences between (for example) the running
>>>>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>>>>> which is appreciated by passengers.
>>>>>>>
>>>>>>> The amount of air they move around is probably insignificant compared to
>>>>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>>>> make the heat feel less unpleasant.
>>>>>
>>>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>>>> using better surface ventilation, or using ground water for cooling.
>>>>
>>>> Of course; at higher temperatures humans mostly use evaporative cooling -
>>>> we’d die at external temperatures anywhere near 37 C otherwise - and
>>>> increasing the airflow increases the cooling so long as the air doesn’t
>>>> have very high relative humidity.
>>>>
>>>
>>> Yes, but of course the powerful fans themselves contribute to the heat
>>> build-up in the system.
>>>
>>>
>>
>> What power are the fans, typically? Are we just considering the waste heat
>> from the motors, or also the contribution of the energy they impart to the
>> moving air?
>
> The total energy consumed by each fan (a few hundred watts) gets added to
> the heat in the system.
>
>>
>> How does the heat contribution of a handful of fans compare to that of
>> thousands of people and hundreds of trains?
>
> It's only a very small increment, but it's nevertheless contributing to the
> heating, rather than reducing it.
>
>
>

A human emits around 100W give or take. So the fan is around the equivalent
of one extra person standing next to a perfect fan that consumes no power.
Small in the scheme of things.

On Mon, 10 Oct 2022 09:57:40 -0000 (UTC), Recliner
<recliner.usenet@gmail.com> wrote:

>Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>> Recliner <recliner.usenet@gmail.com> wrote:
>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>> <Muttley@dastardlyhq.com> wrote:
>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>
>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>> smooths out temperature differences between (for example) the running
>>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>>> which is appreciated by passengers.
>>>>>
>>>>> The amount of air they move around is probably insignificant compared to
>>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>>
>>>>>
>>>>
>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>> make the heat feel less unpleasant.
>>>
>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>> using better surface ventilation, or using ground water for cooling.
>>
>> Of course; at higher temperatures humans mostly use evaporative cooling -
>> we’d die at external temperatures anywhere near 37 C otherwise - and
>> increasing the airflow increases the cooling so long as the air doesn’t
>> have very high relative humidity.
>>
>
>Yes, but of course the powerful fans themselves contribute to the heat
>build-up in the system.

Which was my original point! It's taken some time.

On Mon, 10 Oct 2022 12:44:19 +0100, Roland Perry <roland@perry.uk>
wrote:

>In message <ti0svo$pjqu$1@dont-email.me>, at 10:43:04 on Mon, 10 Oct
>2022, Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>Recliner <recliner.usenet@gmail.com> wrote:
>>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:

>>
>>What power are the fans, typically? Are we just considering the waste heat
>>from the motors, or also the contribution of the energy they impart to the
>>moving air?
>
>Both, I think.
>
Of course. It doesn't matter how efficient or inefficient the fans
are. They produce waste heat via resistive heating and friction and
any useful work they do on the air increases its temperature.

>>How does the heat contribution of a handful of fans compare to that of
>>thousands of people and hundreds of trains?
>
>Tick.

Ken <ken@birchanger.com> wrote:
> On Mon, 10 Oct 2022 12:44:19 +0100, Roland Perry <roland@perry.uk>
> wrote:
>
>> In message <ti0svo$pjqu$1@dont-email.me>, at 10:43:04 on Mon, 10 Oct
>> 2022, Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>
>>>
>>> What power are the fans, typically? Are we just considering the waste heat
>>> from the motors, or also the contribution of the energy they impart to the
>>> moving air?
>>
>> Both, I think.
>>
> Of course. It doesn't matter how efficient or inefficient the fans
> are. They produce waste heat via resistive heating and friction and
> any useful work they do on the air increases its temperature.
>

So, while the fans briefly cool the people walking past them, they actually
warm up everyone else in the station, who just experiences the extra heat
without benefiting from the breeze.

Ken <ken@birchanger.com> wrote:
> On Mon, 10 Oct 2022 09:57:40 -0000 (UTC), Recliner
> <recliner.usenet@gmail.com> wrote:
>
>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>> <Muttley@dastardlyhq.com> wrote:
>>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>>
>>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>>> smooths out temperature differences between (for example) the running
>>>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>>>> which is appreciated by passengers.
>>>>>>
>>>>>> The amount of air they move around is probably insignificant compared to
>>>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>>>
>>>>>>
>>>>>
>>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>>> make the heat feel less unpleasant.
>>>>
>>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>>> using better surface ventilation, or using ground water for cooling.
>>>
>>> Of course; at higher temperatures humans mostly use evaporative cooling -
>>> we’d die at external temperatures anywhere near 37 C otherwise - and
>>> increasing the airflow increases the cooling so long as the air doesn’t
>>> have very high relative humidity.
>>>
>>
>> Yes, but of course the powerful fans themselves contribute to the heat
>> build-up in the system.
>
> Which was my original point! It's taken some time.
>

Some years ago I had an argument with an accountant colleague who thought
that leaving a fun running in a hot room would cool it down, so it should
be left on, even if no-one was in the room. I simply couldn't convince him
that doing that would actually make the room even hotter.

It's a bit like the many people who think that the flash should be used
whenever pictures are taken in low light, even in large stadiums or
firework displays. Or, even worse, when taking pictures of objects behind
glass.

Recliner <recliner.usenet@gmail.com> wrote:
> Ken <ken@birchanger.com> wrote:
>> On Mon, 10 Oct 2022 12:44:19 +0100, Roland Perry <roland@perry.uk>
>> wrote:
>>
>>> In message <ti0svo$pjqu$1@dont-email.me>, at 10:43:04 on Mon, 10 Oct
>>> 2022, Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>>
>>>>
>>>> What power are the fans, typically? Are we just considering the waste heat
>>>> from the motors, or also the contribution of the energy they impart to the
>>>> moving air?
>>>
>>> Both, I think.
>>>
>> Of course. It doesn't matter how efficient or inefficient the fans
>> are. They produce waste heat via resistive heating and friction and
>> any useful work they do on the air increases its temperature.
>>
>
> So, while the fans briefly cool the people walking past them, they actually
> warm up everyone else in the station, who just experiences the extra heat
> without benefiting from the breeze.
>

The waste heat is probably trivial compared to everything else pumping heat
into the system. Even the lighting is quite a load in the quantity
deployed.

Recliner <recliner.usenet@gmail.com> wrote:
> Ken <ken@birchanger.com> wrote:
>> On Mon, 10 Oct 2022 09:57:40 -0000 (UTC), Recliner
>> <recliner.usenet@gmail.com> wrote:
>>
>>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>>> <Muttley@dastardlyhq.com> wrote:
>>>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>>>
>>>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>>>> smooths out temperature differences between (for example) the running
>>>>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>>>>> which is appreciated by passengers.
>>>>>>>
>>>>>>> The amount of air they move around is probably insignificant compared to
>>>>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>>>> make the heat feel less unpleasant.
>>>>>
>>>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>>>> using better surface ventilation, or using ground water for cooling.
>>>>
>>>> Of course; at higher temperatures humans mostly use evaporative cooling -
>>>> we’d die at external temperatures anywhere near 37 C otherwise - and
>>>> increasing the airflow increases the cooling so long as the air doesn’t
>>>> have very high relative humidity.
>>>>
>>>
>>> Yes, but of course the powerful fans themselves contribute to the heat
>>> build-up in the system.
>>
>> Which was my original point! It's taken some time.
>>
>
> Some years ago I had an argument with an accountant colleague who thought
> that leaving a fun running in a hot room would cool it down, so it should
> be left on, even if no-one was in the room. I simply couldn't convince him
> that doing that would actually make the room even hotter.
>
The lack of even a basic understanding of science is the undoing of a huge
chunk of the population.

In uk.transport.london Recliner <recliner.usenet@gmail.com> wrote:
> Some years ago I had an argument with an accountant colleague who thought
> that leaving a fun running in a hot room would cool it down, so it should
> be left on, even if no-one was in the room. I simply couldn't convince him
> that doing that would actually make the room even hotter.

Actually that can and does work. The reason is that masonry walls are a
temperature moderator: because they change temperature slowly they stay
warmer in the nighttime and cooler in the daytime.

A blowing fan increases the airflow on the walls and thus the heat being
exchanged from the air (which may have heated rapidly from say the midday
sun) with the cooler walls. There's a lot more potential heat flux from the
walls than the ~20W added by an efficient domestic fan.

Obviously YMMV - not so much in a large room, and destatifying the air may
have an opposite effect if the hot air has collected near a high ceiling.
But not quite a simple as just calculating energy in.

Theo

Tweed <usenet.tweed@gmail.com> wrote:
> Recliner <recliner.usenet@gmail.com> wrote:
>> Ken <ken@birchanger.com> wrote:
>>> On Mon, 10 Oct 2022 09:57:40 -0000 (UTC), Recliner
>>> <recliner.usenet@gmail.com> wrote:
>>>
>>>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>>>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>>>> <Muttley@dastardlyhq.com> wrote:
>>>>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>>>>
>>>>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>>>>> smooths out temperature differences between (for example) the running
>>>>>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>>>>>> which is appreciated by passengers.
>>>>>>>>
>>>>>>>> The amount of air they move around is probably insignificant compared to
>>>>>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>>>>> make the heat feel less unpleasant.
>>>>>>
>>>>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>>>>> using better surface ventilation, or using ground water for cooling.
>>>>>
>>>>> Of course; at higher temperatures humans mostly use evaporative cooling -
>>>>> we’d die at external temperatures anywhere near 37 C otherwise - and
>>>>> increasing the airflow increases the cooling so long as the air doesn’t
>>>>> have very high relative humidity.
>>>>>
>>>>
>>>> Yes, but of course the powerful fans themselves contribute to the heat
>>>> build-up in the system.
>>>
>>> Which was my original point! It's taken some time.
>>>
>>
>> Some years ago I had an argument with an accountant colleague who thought
>> that leaving a fun running in a hot room would cool it down, so it should
>> be left on, even if no-one was in the room. I simply couldn't convince him
>> that doing that would actually make the room even hotter.
>>
> The lack of even a basic understanding of science is the undoing of a huge
> chunk of the population.

But as Theo’s parallel post points out, the lack of a more subtle
understanding of science may also be doing us a disservice. In the case of
the Underground fans they (may) make travel bearable for passengers in the
short term while also making it situation more difficult in the longer
term.

Sam

--
The entity formerly known as Sam.Wilson@ed.ac.uk
Spit the dummy to reply

Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
> Tweed <usenet.tweed@gmail.com> wrote:
>> Recliner <recliner.usenet@gmail.com> wrote:
>>> Ken <ken@birchanger.com> wrote:
>>>> On Mon, 10 Oct 2022 09:57:40 -0000 (UTC), Recliner
>>>> <recliner.usenet@gmail.com> wrote:
>>>>
>>>>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> wrote:
>>>>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>>>>> <Muttley@dastardlyhq.com> wrote:
>>>>>>>>> On 26 Sep 2022 13:08:17 +0100 (BST)
>>>>>>>>> Theo <theom+news@chiark.greenend.org.uk> wrote:
>>>>>>>>>> In uk.transport.london Ken <ken@birchanger.com> wrote:
>>>>>>>>>>> I'm not talking about the huge fans in ventilation shafts; I'm talking
>>>>>>>>>>> about the freestanding ones in passenger circulation areas. These
>>>>>>>>>>> don't move a molecule of air in or out of the system.
>>>>>>>>>>
>>>>>>>>>> But there are inevitably dead spots in the ventilation. There will be a
>>>>>>>>>> particular main flow from the shaft fans, but heat can build up in pockets
>>>>>>>>>> that aren't directly ventilated. Adding extra fans to mix the air around
>>>>>>>>>> smooths out temperature differences between (for example) the running
>>>>>>>>>> tunnels (which might be directly ventilated) and the platform cross-passages
>>>>>>>>>> and escalator lower tunnels (which might not). Plus it also makes a breeze
>>>>>>>>>> which is appreciated by passengers.
>>>>>>>>>
>>>>>>>>> The amount of air they move around is probably insignificant compared to
>>>>>>>>> the trains themselves. All they do is provide a breeze for pax walking past.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>> I've always presumed that that's what they're for - to provide a breeze to
>>>>>>>> make the heat feel less unpleasant.
>>>>>>>
>>>>>>> Yes, they're just a low cost stop-gap until the temperatures can be reduced
>>>>>>> using better surface ventilation, or using ground water for cooling.
>>>>>>
>>>>>> Of course; at higher temperatures humans mostly use evaporative cooling -
>>>>>> we’d die at external temperatures anywhere near 37 C otherwise - and
>>>>>> increasing the airflow increases the cooling so long as the air doesn’t
>>>>>> have very high relative humidity.
>>>>>>
>>>>>
>>>>> Yes, but of course the powerful fans themselves contribute to the heat
>>>>> build-up in the system.
>>>>
>>>> Which was my original point! It's taken some time.
>>>>
>>>
>>> Some years ago I had an argument with an accountant colleague who thought
>>> that leaving a fun running in a hot room would cool it down, so it should
>>> be left on, even if no-one was in the room. I simply couldn't convince him
>>> that doing that would actually make the room even hotter.
>>>
>> The lack of even a basic understanding of science is the undoing of a huge
>> chunk of the population.
>
> But as Theo’s parallel post points out, the lack of a more subtle
> understanding of science may also be doing us a disservice. In the case of
> the Underground fans they (may) make travel bearable for passengers in the
> short term while also making it situation more difficult in the longer
> term.
>
> Sam
>

If you put a high power fan at a pinch point, where perhaps the
temperatures peak, it may be sensible in as much as it lowers the peak
perceived temperature at the expense of a slightly higher average
temperature.