Maths Puzzle For You

[H2oDunc]

Hi, a friend has a pool that is leaking. The pool is 12 mtrs by 4 mtrs and loses 25mm every day. In litres how much water is he losing ? Cheers guys

[bkkjames]

Hi, a friend has a pool that is leaking. The pool is 12 mtrs by 4 mtrs and loses 25mm every day. In litres how much water is he losing ? Cheers guys

apparently enough for you to start a thread about it.

[jackr]

1,200

[ukrules]

1,200

That's what I came up with too, 1,200L per day.

Edited September 17, 2009 by ukrules

[H2oDunc]

I told him a lot but 1,200 litres is more than I expected I think he needs to get it sorted rather quicker than he planned Cheers Jack

[bkkjames]

I told him a lot but 1,200 litres is more than I expected I think he needs to get it sorted rather quicker than he planned Cheers Jack

H20, with all the rain we are getting, he should be good until November.

[harrry]

May not be leaking. Sun and wind cause evaporation.

[chrgrims]

how much water can you lose without a leak in the Thailand sun?

[cdnvic]

May not be leaking. Sun and wind cause evaporation.

Possible, but that's unlikely to be the cause of everything. Does he have a cover on it? Is it being used, and how much? What is the temp/humidity there?

[Crossy]

how much water can you lose without a leak in the Thailand sun?

You don't actually need to know. Try the bucket test http://www.americanleakdetection.com/tips-bucket-test.php

[chrgrims]

yes, i understand that crossy. I just wonder if i dont have a leak, how much water can i presume to lose every day from other factors? i know its not directly to the OP, but i posted it here anyway, because its related.

[Crossy]

yes, i understand that crossy. I just wonder if i dont have a leak, how much water can i presume to lose every day from other factors? i know its not directly to the OP, but i posted it here anyway, because its related.

Try this

M-dot= (A)(42.6+37.6V)(Pw-Pa)/Hv

where:-

m-dot= evaporation rate, kg/hr

A= surface area, m^2

V= air velocity over water surface, m/s

Pw= saturation vapour pressure at water temperature, mm Hg

Pa= saturation vapour pressure of air dew point, mm Hg

Hv= latent heat of vaporization of water at pool temperature, about 2270 KJ/Kg

For a vapour pressure calculator goto: http://www.csgnetwork.com/vaporpressurecalc.html

To calculate the Dew Point you need to know the relative humidity (from the weather man if you don't have a hygrometer):-

Td = T - (100-RH)/5

(T and Td are in degrees Celcius)

You wouldn't want me to do your homework for you, would you?

[chrgrims]

hmm. guess i will stick to the old equation of "look and see, put in more if lose a lot".

[Crossy]

hmm. guess i will stick to the old equation of "look and see, put in more if lose a lot".

Sorry

Calculating for 10m2 pool.

Right now in BKK:-

T = 30C

RH=66%

Windspeed = 11 km/h = 3 m/s

So Dew Point = Td = 30 - (100-66)/5 = 23.2C

Let's assume the pool is at 25C

Pw = 23.71 mmHg

Pa = 31.74 mmHg

M-dot= (A)(42.6+37.6V)(Pw-Pa)/Hv = 10(42.6-18)(23.71-31.74)/ 2270 = 10x24.6x8.03 /2270 = 0.87 kg per hour = about 1 litre per hour

Of course I may have done the sums wrong (it's been a very long while), but it looks reasonable

Any disturbance by circulation pump, swimmers, water features etc will increase the rate of loss

[chrgrims]

ok, very nicely done. you have put 25 degrees celsius, so i guess we can close to double this in the sun?

[Crossy]

ok, very nicely done. you have put 25 degrees celsius, so i guess we can close to double this in the sun?

Actually not having a pool I don't know how warm they get relative to the air, it's easy enough to re-calculate using a higher pool temp. The pool of our condo in KL was actually cooled, kept the locals out

The evaporation itself will tend to reduce the temperature (think sweating).

[harrry]

This may give a guide.....Carnavon would be a fair starting point

.

[robertsonmartin]

hmm. guess i will stick to the old equation of "look and see, put in more if lose a lot".

Sorry

Calculating for 10m2 pool.

Right now in BKK:-

T = 30C

RH=66%

Windspeed = 11 km/h = 3 m/s

So Dew Point = Td = 30 - (100-66)/5 = 23.2C

Let's assume the pool is at 25C

Pw = 23.71 mmHg

Pa = 31.74 mmHg

M-dot= (A)(42.6+37.6V)(Pw-Pa)/Hv = 10(42.6-18)(23.71-31.74)/ 2270 = 10x24.6x8.03 /2270 = 0.87 kg per hour = about 1 litre per hour

Of course I may have done the sums wrong (it's been a very long while), but it looks reasonable

Any disturbance by circulation pump, swimmers, water features etc will increase the rate of loss

The vapour pressure calculator link doesn't seem to calculate correctly. If using the

Td = T - (100-RH)/5 formula.

From the formula using figures of 30degC air temp and RH of 66, this gives a dewpoint of 23.3degC

Using the calculator with 30degC air temp and dewpoint of 23.3degC gives a RH of 94.53%

Something not quite right somewhere.

Edit - Sorry, talking a load of <deleted>. Works out at 67.05%

Edited October 3, 2009 by robertsonmartin

[H2oDunc]

Here's another poser for you guys. The pool guy says I have to reduce the pool level by 10cm to repair the leak. How much water am I going to have to get rid of to do this ? and where the hel_l am I going to put it ? Cheers again

[cdnvic]

That's 4800 litres. You could hire a guy with a water truck to hold it for a few hours quite cheaply I bet.

[Singtoo]

I have only recently gained some experience in swimming pools.

The subject is now evaporating.

We had the same experience in the months April and May, our pool of Huai Yai (Chonburi Province).

Our pool has an L shape largest measures 6.46 x 5.35 meters.

But there goes a piece off to the terrace.

Total 27 sqm water surface.

Mean depth 1.56 meters overflow + 2.5 m³ / circulation tank = total 41.7 m³

So the difference between our pools is a few square meters.

First I doubted that what the water went away it could not only by evaporation.

(My friend with the same pool who had the idea that he suffered from leaks in his pool.)

Our overflow tank was empty in 3 days.

Nearly 2.5 m³ in 3 days.

Seemed very much to evaporation.

So again refilled the tank.

Simply open the tap into the overflow tank and the city water runs.

And just wait and see what happens.

And again the tank was in 3 days as good as empty.

So what the case shows nearly 2.5 m³ evaporated in 3 days.

This is a 800 liter per day in the air.

I had a conversation with a few people from a pool service company.

So they said, surprised, together you see that Farang says also that a 2.5 m³ tank is empty evaporated in 3 days.

The point of the story is the temperature and wind.

In April and May it was very hot and very little rain with us.

So just evaporated.

(This is 1 of the same reasons I do not let service at the pool while we are not in Thailand. But that is a different subject.)

Now since we are away it seems to rain every day.

Yes, then the circulation tank / overflow tank is full.

Then there is certainly water evaporates.

But if a big rain falls then there may be 1 m³ of water.

And so there goes water out through the overflow pipe to the sewer.

So the conclusion on very hot days in Thailand evaporates there is indeed a substantial amount of water.

[Singtoo]

I have now during our absence, the entire pool covered with 2 sheets.

For that several reasons.

Evaporation prevention.

And the 2nd reason prevention of dirt blow in.

Now, with the rainy season, the rainwater runs between the separation of the 2 to the overflow tank dress and then the excess into the sewer.

And then I just put the whole place stopped.

Yes I know the algae growth.

With the information I had received here and elsewhere seemed to me that all things considered for me the best solution.

So when I come back, and in between watching my friend there is one in sometime, where I discovered what the situation is.

I did not want to, may not be reliable pool service, 1600 Thai Bath by paying for one months or 6 while we are not there.

Shame on me that I do not trust Thai.

Also we than have no cost of electricity and water.

And possibly worse a broken pump that runs dry.

Precisely because the serviceman not come look when he realizes that we are apparently away for along time.

But if you are away over 6 months there too can go to much wrong I think.

When we get back the chloride and pH value are to cry.

Perhaps I should just water pumping and refilling all bad.

That cost me a 600 Bath water I treasure.

45 m³ x 13 bath per m³

But first i try to restore the present water I think.

And clean the whole pool.

It is never too late to learn.