# The Naked Scientists Forum

### Author Topic: Do swimming pools get hotter with more people in them?  (Read 5405 times)

#### paul.fr

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##### Do swimming pools get hotter with more people in them?
« on: 15/02/2008 22:38:01 »
If a pool is heated to 20c and 30 people get in, does their body temperature increase the heat of the pool?
« Last Edit: 04/03/2008 23:34:15 by chris »

#### opus

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##### do swimming pools get hotter with more people in them?
« Reply #1 on: 15/02/2008 22:48:35 »
Depends how big the pool is doesn't it....?

#### lightarrow

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##### do swimming pools get hotter with more people in them?
« Reply #2 on: 16/02/2008 08:17:20 »
If a pool is heated to 20c and 30 people get in, does their body temperature increase the heat of the pool?
If the pool's water is constantly recycled (as it should be, but not always and not everybody do it), then it also constantly passes through a heat exchanger (hope to have translated well) wich measure water's temperature and adjust it to the correct value, so temperature couldn't vary.

#### lyner

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##### do swimming pools get hotter with more people in them?
« Reply #3 on: 18/02/2008 23:29:32 »
The best way to think of this is in terms of 'dilution'.
A pool, 2m deep by 5m by 10m has a mass of water of  100 thousand kg.
Ten bodies would, at most, have a mass of one thousand kg (100kg each represents pretty large people).
The people would represent only 1% of the water's mass.
If you replaced the people with 1000kg of water at 40 degrees Celsius and the pool temperature was 20 deg Celsius and if you mixed it up well, the rise in pool water temperature would be about 0.2degrees Celsius.
In practice, most of the heat inside the bodies would be kept there by body insulation so, initially, the temperature rise would be much much less.
However, if these people lived in the pool for a long time, some of the energy in their food would eventually go towards warming the pool - every kg of warm wee would contribute, for instance.
The bottom line is that it people would have virtually no effect.

#### Bored chemist

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##### do swimming pools get hotter with more people in them?
« Reply #4 on: 19/02/2008 19:39:58 »
How much power does it take to run a pool heater? (OK, I realise there are too many variables to answer that sensibly). Each person in the pool would (assuming the pool was cooler than body temperature) contribute about 100W of heat. That would warm it up, at least slightly.
"However, if these people lived in the pool for a long time, some of the energy in their food would eventually go towards warming the pool - every kg of warm wee would contribute, for instance."
Even if they got out of the pool to go to the toilet they would still heat the pool the rest of the time. The Calories in your food nearly all end up as heat and there's nowhere else for it to go but into heating the pool.

#### lyner

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##### do swimming pools get hotter with more people in them?
« Reply #5 on: 19/02/2008 21:52:12 »
Pool heaters must be pretty high power - Tens of kW - if they are to have much effect. Very expensive to run. The transparent insulating covers that people use are probably more effective in many cases (bearing in mind that there is about 500W of useful energy flow from the sun arriving  at each square metre  and eliminating evaporation plus 'double glazing' over the top will reduce heat loss significantly.
You might expect more than 100W per body altogether but that could hardly be enough to make a difference. In my experience, the only time when you can produce your own warm  water is when the small amount in your wet suit warms up. The water that pours out of my wet suit socks feels warm enough to make tea (not really).

#### turnipsock

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##### do swimming pools get hotter with more people in them?
« Reply #6 on: 19/02/2008 22:27:41 »
The pool will be controled by a thermostat.

#### lyner

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##### do swimming pools get hotter with more people in them?
« Reply #7 on: 20/02/2008 09:50:13 »
The pool will be controled by a thermostat.
and . . . ?

#### turnipsock

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##### do swimming pools get hotter with more people in them?
« Reply #8 on: 20/02/2008 10:02:43 »
The pool will be controled by a thermostat.
and . . . ?

the pool won't change in temperature.

Even if the people did cause the water to change temperature, the thermostat would compensate by not running the heating so much.

#### DoctorBeaver

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##### do swimming pools get hotter with more people in them?
« Reply #9 on: 20/02/2008 10:26:49 »
It would warm up if they all peed in it

(I'm sorry. I was waiting for someone else to say but no-one did & it really did have to be said  [:I] )
« Last Edit: 20/02/2008 10:32:39 by DoctorBeaver »

#### JimBob

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##### do swimming pools get hotter with more people in them?
« Reply #10 on: 20/02/2008 13:35:30 »
Or if it were Romanized - AKA Roman Polanski pool party

#### Bass

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##### do swimming pools get hotter with more people in them?
« Reply #11 on: 20/02/2008 18:33:25 »
It would warm up if they all peed in it

Went to one of those Mexican resorts years ago- gigantic pool had a swim-up bar with underwater bar stools.  Was enjoying a margarita until I learned that the guy next to me had been drinking beer in copious amounts for the last 4 hours without moving from his barstool. [xx(]

#### DoctorBeaver

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##### do swimming pools get hotter with more people in them?
« Reply #12 on: 20/02/2008 19:27:14 »
It would warm up if they all peed in it

Went to one of those Mexican resorts years ago- gigantic pool had a swim-up bar with underwater bar stools.  Was enjoying a margarita until I learned that the guy next to me had been drinking beer in copious amounts for the last 4 hours without moving from his barstool. [xx(]

#### lyner

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##### do swimming pools get hotter with more people in them?
« Reply #13 on: 20/02/2008 19:55:42 »
It would warm up if they all peed in it
Yebbut not a lot. The taste would change before the temperature, I suspect. (Wee didn't want to know that did wee?)

#### DoctorBeaver

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##### do swimming pools get hotter with more people in them?
« Reply #14 on: 20/02/2008 20:02:34 »
You could have said to me "Urine trouble now"

#### turnipsock

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##### do swimming pools get hotter with more people in them?
« Reply #15 on: 20/02/2008 22:33:25 »
I know that if my bath is too hot I sometimes loose control of my body functions.

How many people would need to be in an olympic sized swimming pool before the tiddling point is reached?

#### The Naked Scientists Forum

##### do swimming pools get hotter with more people in them?
« Reply #15 on: 20/02/2008 22:33:25 »