Another maths question...

[hotponyshoes]

So if I had 2 large tanks, A & B.
I frequently want to electrically pump water from one of them to the other and back again..

Tank A must be at ground level.
Tank B could be mounted above, below or the same level as tank A.

Now, if I mount tank B either above or below tank A then I could use gravity to either drain or fill tank A meaning I would only have to pay the electricity bill to pump water in one direction.

If i mounted tank B at the same level as A I would have to pump water in both directions but I would not need to pump against so much of a head.

Which will be the cheapest system to run?
Feel free to show the maths needed!

 

[gaz1]

not if you used compressed air

if your draining a tank from above into the bottom tank then compressed air will push it back up again

as long as the below tank is used in a vertical position spout facing down

it would gravity feed when letting the air out of the tank

 

[jerrytug]

Same level would save your amps.
A balance pipe would allow the water to occupy the tanks equally at the same level. Then you would have only half of it to pump from one tank to the other.
Obviously this would involve opening and closing the correct cocks etc.

 

[Rrobson]

Can you connect the two tanks towards the bottom with a pipe and a valve in the middle? That way you would only have to pump half a tank every tine you need to empty one?

I think either way you will need to move a tanks worth of water, regardless of position to do a complete empty and fill of either.
Unfortunately my little pea brain wouldn’t be able to calculate the extra energy required to pump liquid up into another tank if one was above the other, but it’s probably slightly less than if both were at ground level...

 

[armalites]

If the tanks are at the same level link them at the bottom with a valve then when you open it you'll do half you work for nothing and pump the rest.

 

[jerrytug]

If the tanks are at the same level link them at the bottom with a valve then when you open it you'll do half you work for nothing and pump the rest.

Exactly

 

[hotponyshoes]

So say there is 1000L of water to be transferred.
If both tanks are at the same level I could open the valve, 500l of water would self level into both tanks.
I then pump 500l of water accross to fill one tank.
To swap the tanks I have to reverse the process so another 500l pumped.

If one tank was mounted underground all 1000L would drop but I would have to pump 1000l back up hill again.

I can see there would be less wear on the pumps moving from left to right but I would gain more floor space if i only had one tank at ground level.

In terms of pure electrical cost would there be any difference where the tanks were?

 

[armalites]

Why not mount them both on platforms with hydraulic rams, you could pump them by hand so the full one was higher and let gravity move the water, no electricity involved.

 

[jerrytug]

So say there is 1000L of water to be transferred.
If both tanks are at the same level I could open the valve, 500l of water would self level into both tanks.
I then pump 500l of water accross to fill one tank.
To swap the tanks I have to reverse the process so another 500l pumped.

If one tank was mounted underground all 1000L would drop but I would have to pump 1000l back up hill again.

I can see there would be less wear on the pumps moving from left to right but I would gain more floor space if i only had one tank at ground level.

In terms of pure electrical cost would there be any difference where the tanks were?

Ok just for the sake of argument reductio ad absurdam, imagine if one tank was a mile above the other one. The water could obviously drain down, but a lot of energy would be used pumping it back up to the top tank.
The same unneccessary pumping would still be happening if they were one yard above each other, although a smaller loss it's still a waste of leccy.

 

[jerrytug]

Why not use one big tank instead of two small ones

 

[Barking Mat]

Can't you pump it up at night, using cheap rate electricity.

Like that pumping station somewhere?

I know what I mean.

 

[julianf]

Moving half a tonne 500mm off the ground twice is going to require the same energy as moving half a tonne 1000mm once.

But then you would still need to move the other half tonne.

You've got other things going on, like if you have them side by side, at the start, depending on where your outlets and inlets are, you are not moving the fluid 500mm. Likewise if the tanks are stacked in top, at the start of the session, you are only moving from the top of one tank to the bottom of the other. But then to maintain that gain, you need floating pipe terminals, or you will be working against the Syphon rather than with it...

But, yeah, moving half a tonne over 500 mm twice is half the work than moving a tonne (double the weight) over 1000mm (double the distance) once. Roughly.

 

[julianf]

Something I somtimes forget and then remember...

We have a mortgage here. Every square foot of volume is costing me each month.

Have a pile of junk in the corner? You're renting that space off the bank and just using it to store junk.

When you start talking money, there are so many trade offs. That bit of extra electricity to take up less space in a Manhatten penthouse would seem very worth while.

Somwhere else, and, maybe the power would seem more important than the space.

So it's not just simple maths. Not that it's simple maths anyway.

 

[gaz1]

 

[CornishPete]

Screwfix do a 350w Karcher pump for £63 capable of 167l/minute. By my reckoning that means in 1hr it will use 0.35kwh of electricity and have pumped 10020 litres, so in about 3 hours it will use just over 1kwh and have pumped 30000litres. For the princely sum of about 14p! Obviously it depends on your exact circumstances, what your pumping, and how accurate Karchers' specsb are but as an illustration I wouldn't fret over running costs or be faffing with gravity or hydraulic lifters to save a few pence!

 

[CornishPete]

As a caveat, if I've got the maths wrong, it is pretty late!

 

[Screwdriver]

So if I had 2 large tanks, A & B.
I frequently want to electrically pump water from one of them to the other and back again..

Tank A must be at ground level.
Tank B could be mounted above, below or the same level as tank A.

Now, if I mount tank B either above or below tank A then I could use gravity to either drain or fill tank A meaning I would only have to pay the electricity bill to pump water in one direction.

If i mounted tank B at the same level as A I would have to pump water in both directions but I would not need to pump against so much of a head.

Which will be the cheapest system to run?
Feel free to show the maths needed!

No maths, logic: one tank must be at ground level, you want to fill one from the other and v.v.

But there is an ambiguity in the question.

You say you want to pump <the> water from "one of them to the other and back again" which suggests you want the actual contents of one tank to be transferred to the other.

You then say "either drain or fill tank A" which implies you're only concerned with filling or emptying one or other tank with water and not specifically transferring the particular contents of one to the other.

Assuming you are connected to a mains water supply (!) then the obvious answer is Tank A at ground level, tank B above and always fill tank B from the mains. You can fill A from B using gravity. Empty tank A into a pond, tank B fills from the mains. If you're not on a water meter, you're golden and you get a free pond. Even if you are on a meter, the actual volumetric cost of usage (which is low compared to the service charge) is offset against the cost of the energy used to shift it.

Without specifying the precise reason for needing to shift water "from one tank to the other" it is difficult to quantify the probability you will require A or B to be full/empty since if the requirement is random and <B is always full> then you won't need to expend any energy exactly half the time and if A happens to be full, you will need to wait for B to fill from the mains and for A to drain which only costs you the time it takes.

I think I probably ought to go to bed. Can we have some real maths questions please?

 

[hotponyshoes]

Ok I will add a bit more detail!
The application is a water filled treadmill for horses.
Basically a big box with a watertight door on one end and a treadmill in the bottom.
It starts empty, you walk the horse in with it dry and teach it to use the treadmill. You then fill it with water. You need to drain the water back out again before removing the horse at the end of the session.
A water capacity of about 4000L with a max of a 1.2m head.

Fill/drain time needs to be no more than 5mins either way. (Emergency drains are manual)

The main requirement for having more than one tank is the water needs to be heated and that will obviously be the biggest running cost.
The horse tank has to have an open top so the storage tank will be insulated and the heating will be done in that.

Potentially 3 extra tanks would be required for warm/ambiant/chilled water.
These will be gojn in a barn that is not yet built so he option of mounting them underground may not cost much more to install than building the extra floor space to have them at ground level.

Sessions last about half an hour start to finish so possible that the treadmill would be drained & filled 10-12 times a day.
If the tanks were underground then that would give space for a 2nd & 3rd treadmill to be added at a later date.

My head is saying that to pump water from side to side (pumping half of it twice) should be cheaper than pumping it up from underground (pumping all of it once) but as it ends up as the same amount of water being pumped to the same place are the costs actually any different?

 

[cheb]

Use the trained horse to power a pump connected to a dry treadmill.

@barking mat: Pumped storage power stations: Cruachan, near Oban, and Dinorweg, near Snowdon. Both have excellent visitor centres and do tours.

 

[8ob]

Why can't both the tanks be mounted on a big rotisserie, no pumps needed just rotate so the full tank rotates to the top and gravity empties. Sod the pumps.

Bob