How to measure Hot Water Head

[doitall]

I will do know such thing

Try again.

If the cylinder is on the ground floor, the top of the cylinder is say 4m below the tank, so the head at that point is 0.4bar.

Now run a hot pipe to the 1st floor and the head at the outlet is now 0.2bar, if you stick a shower rose on the wall the head will be shall we say 0.1 bar.

Stick with me.

Now bring the cylinder up a floor, and the head at the top of the cylinder is now 0.2 bar, and shall we say a maximum 20 Ltrs/mim, as you say physics head x pipe size = flow.

Now run a pipe from the cylinder to the kitchen, the head does not increase, and neither will the maximum flow from the cylinder.

Still with me.

Now raise the cylinder even more, the higher you go the lower the head, and the smaller the flow rate becomes, as you said physics.

As far as this thread is concerned the top of the cylinder is virtually level with the bottom of the tank, therefore the head will be very very low.

Try and remember what you get out of the cylinder is all you get, 5 Ltrs/min in the loft, cannot be turned into 20 Ltrs/min in the kitchen.

 

[doitall]

I certainly seem to have started something here...

See, you didn't read what I said after all.

You'd said 'head' could be from cylinder to loft pipe, steved101 had it only as far as showerrose. I was just double checking who had it right...

... I have a feeling the cylinder may also be stood up in the loft.

All that's in the loft is the cold storage tank. How water cylinder is in the utility room.

As far as this thread goes, can I take it that 'cylinder' = Hot, 'tank'=Cold? Maltaron speaks of a 'header tank' - is that another term for cold tank?

Anyway, I have this graph from the manufacturer - temperature of water in hot cylinder on one axis, 'Hot water head' (in metres) on the other. I just want to know if I fit into the area on the graph of 'acceptable performance'. So there's my hot cylinder in the utility room, cold tank in loft, H&C feeds to the new Trevi have been made in the loft space. Trevi is on same level as hot cylinder (bungalow).

I'm guessing my Hot Water Head is just over a metre (distance between showerhead and the pipe running along the rafters). Can anyone confirm or suggest otherwise?

Sincere thanks to all contributors - for the entertainment as well as the info.

So you are say the cylinder is below the loft, and the hot pipe from the cylinder goes into the loft and drops down to the shower. ?

If that is the case then the head will be from the storage tank to the pipe.

 

[cmother1]

Naah... still don't get this. I've just done experiment 2 with the hot water in the downstairs shower. Removed shower head, turned on H/W & pointed hose at the tiles at a distance of 2 feet. At a height of 6 feet the jet of water dropped 10" over that distance. At 1 foot above the ground it dropped 8". How does this square with your theory.

PS. What was my self-contradiction?

PPS. The cylinder is on the 1st floor.

 

[doitall]

Naah... still don't get this. I've just done experiment 2 with the hot water in the downstairs shower. Removed shower head, turned on H/W & pointed hose at the tiles at a distance of 2 feet. At a height of 6 feet the jet of water dropped 10" over that distance. At 1 foot above the ground it dropped 8". How does this square with your theory.

PS. What was my self-contradiction?

PPS. The cylinder is on the 1st floor.

Ok we have all the information now, so it should be easy.

Storage tank in loft.
Outlet of cylinder, say 2m below, (head = 0.2bar)

So by your theory a shower rose at this point would give you a head of 0.2bar, what will happen in your theory if you raise the shower rose to the ceiling, correct the head will get less the higher you go, as will the flow of water.

Now take the real thing, leaving the cylinder where it is at 0.2 bar, but you run the pipe from the cylinder up into the loft correct you lower the head and reduce the flow.

 

[electronicsuk]

Ok, I'm no plumber, and that's probably not the ideal way to start a post when contradicting someone in the plumbing forum, but I also agree with all those who think that doitall is wrong.

If the cylinder is on the ground floor, the top of the cylinder is say 4m below the tank, so the head at that point is 0.4bar.

Ok, so before we go any further, every metre of head = 0.1bar assumed difference in pressure, for the sake of your example at least. No problem.

Now run a hot pipe to the 1st floor and the head at the outlet is now 0.2bar, if you stick a shower rose on the wall the head will be shall we say 0.1 bar.

So, presumably, the shower head in the example must be 3 metres above the HW tank, which also means that it must be 1 metre below the bottom of the CWS tank, as we're saying there's 4 metres of head between CWS and HW tank. I have no problem with your theory here, 1 metre = 0.1bar pressure at the shower head.

Now bring the cylinder up a floor, and the head at the top of the cylinder is now 0.2 bar, and shall we say a maximum 20 Ltrs/mim, as you say physics head x pipe size = flow.

Still with you here, as we're assuming 2 metres floor to ceiling height, so distance from bottom of CWS tank to top of HW tank is now approximately 2 metres, hence 0.2bar AT the HW tank outlet.

Now run a pipe from the cylinder to the kitchen, the head does not increase, and neither will the maximum flow from the cylinder.

Still with me.

No, this is where I'm not with you. I can't fathom how you've come to this conclusion, but it makes absolutely no sense at all. The HW tank does not somehow suddenly 'create' a new level to which we must now reference the head, as you seem to believe, as it is still backed by the additional 0.2bar pressure we already have between CWS and HW tank. Go down another 2 metres vertically to the kitchen and we have 4 metres of head, or 0.4bar if you will.

By your logic, if the HW tank was on the second floor with 2 metres between top of HW tank and bottom of CWS tank, any head measurements would start from the top of the HW tank. So, you're trying to tell me that despite their being an additional 2 metres of head between the two tanks, the outlet at the top of the HW tank will have a head of 0 metres? In which case, there would be absolutely no flow, which you know will not be the case. Physics tells us this, but it's demonstrated in my house where the shower head is ABOVE the top of the HW tank, but BELOW the bottom of the CWS tank.

In essence, if you ignore the heat exchanger, the HW tank is simply a VERY large diameter pipe. It DOES NOT alter the system head at all, just as a section of pipe does not alter the head in anything other than its vertical drop.

Now raise the cylinder even more, the higher you go the lower the head, and the smaller the flow rate becomes, as you said physics.

As far as this thread is concerned the top of the cylinder is virtually level with the bottom of the tank, therefore the head will be very very low.

No no no no no! It's all about the difference in height between the bottom of the CWS tank, and the outlet, be it a tap, shower, or anything else. Let me try one final example to convince you...

My previous house had a HW tank with integrated header tank, the header being integrated onto the top of the cylinder although normal in every other respect, i.e. float valve filler, overflow, etc. Distance between bottom of header tank and top of cylinder was ZERO, where the CWS tank ends, the HW tank starts. By your reckoning, I have zero head, but lo and behold... water came out the taps! What's more, the dynamic pressure on upstairs taps was very poor, but dynamic pressure (and flow rate) on downstairs taps was excellent. Not coincidentally, the HW tank was located upstairs!

If you were correct, there would have been poor HW flow rate everywhere, in fact, as there's no head (by your definition, not mine) there should have been NO flow to ANY of the taps. It just isn't true.

Try and remember what you get out of the cylinder is all you get, 5 Ltrs/min in the loft, cannot be turned into 20 Ltrs/min in the kitchen.

Again, wrong, for all the reasons above. This just IS NOT true, and it goes against the laws of physics. Did you not have a toy in nursery school which was essentially a tube with a bunch of holes drilled at different levels in the side? Water from the bottom hole projected a lot further than from the top, as the pressure was higher down there. The principle is the same.

 

[doitall]

Well Matthew I suggest you stick to sparky things things because you know nothing about about plumbing.

Lets try it another way.

The inlet head, is the distance from the storage tank to the bottom of the cylinder, that dictates the absolute maximum pressure and flow, you cannot get more out whatever you do.

Now consider cmother 1 example, where he raised the shower rose and the pressure dropped the higher it was, because he was reducing the head.

Back to the cylinder.

Before the water can go anywhere it has to go to the top of the cylinder, reducing the head by that distance, so at this point we have say 0.2 bar and 20Ltrs/min, happy, that's the maximum we are going to get out of the cylinder, running a pipe to the kitchen on the floor below, cannot increase the head or the flow, it is set be the height of the outlet. to do that I would need to take the cylinder down a floor.

Ok back to cmother 1 by the same token, the higher I take the out pipe from the cylinder the lower the pressure will be, (pressure/head being related)

 

[kirkgas]

i have read all this post (I think) my take on this is:
a comment usually made and correct is "the position of the cylinder is irrelevant to the flow from the tap, it is the distance between the water level in the tank and the outlet (this is the variable bit as the water level drops the head/flow reduces, and is something we all agree on) so when calculating head available it is best to take the level at the bottom of the tank as this is the least head it can ever be. this is bourne out when you check the flow in an upstairs bathroom and a downstairs kitchen, this is also something we all agree on
if you simply relocate the cylinder and leave all the pipework where it is the flow will be exactly the same, what we should actually be considering is the vertical distance between the water level in the tank and the highest pipe (which someone has already said) we are all agreeing it is a gravity thing so the water drops out of the tank into the cylinder and out of the pipe at the top, if the pipe at the top of the cylinder rises right into the loft and across the loft then back down to the tap the head will be the distance between the water level and the pipe (the u tube effect mentioned)
this was supposed to be a quick reply stick with me

on a traditional cylinder system say you added an ensuite bathroom with 2 whb's,and for arguement's sake connected them from 2 different places 1st one simply cut into the expansion pipe to run a supply to 1 whb at a height of about 3' above the loft floor(nearly as high as the water level) and the 2nd one you cut a tee into the existing hot supply 3m below the water level, REMEMBER THE 2 WHB'S ARE FED FROM THE SAME CYLINDER AND ARE AT THE SAME HEIGHT AS EACH OTHER so depending who you agree with do you say the pressure at both taps is the same or vastly different
(i say vastly different)

 

[doitall]

if you simply relocate the cylinder and leave all the pipework where it is the flow will be exactly the same, what we should actually be considering is the vertical distance between the water level in the tank and the highest pipe (which someone has already said) we are all agreeing it is a gravity thing so the water drops out of the tank into the cylinder and out of the pipe at the top, if the pipe at the top of the cylinder rises right into the loft and across the loft then back down to the tap the head will be the distance between the water level and the pipe (the u tube effect mentioned)
this was supposed to be a quick reply stick with me

on a traditional cylinder system say you added an ensuite bathroom with 2 whb's,and for arguement's sake connected them from 2 different places 1st one simply cut into the expansion pipe to run a supply to 1 whb at a height of about 3' above the loft floor(nearly as high as the water level) and the 2nd one you cut a tee into the existing hot supply 3m below the water level, REMEMBER THE 2 WHB'S ARE FED FROM THE SAME CYLINDER AND ARE AT THE SAME HEIGHT AS EACH OTHER so depending who you agree with do you say the pressure at both taps is the same or vastly different
(i say vastly different)

A couple of comments Kirkgas Nice that someone else knows what they are talking about.

In you example with the two basins the head will be the same, however the flow would be different because of the resistance in the pipe.

Another example with the two basins side by side.

Connect one from the same height as the cylinder, and the other one by running the pipe up into the loft and dropping down to it.

The head will be the distance it is from the top of the cylinder to the pipe, less than the 1st basin.

 

[picasso]

have to agree with dia, had the same discussion on another forum and was eventually convinced he was right,we had pictures, diagrams , drawings ,tears and tantrums, isint plumbing wonderful

 

[doitall]

have to agree with dia, had the same discussion on another forum and was eventually convinced he was right,we had pictures, diagrams , drawings ,tears and tantrums, isint plumbing wonderful

We did didn't we

Another example with the basin.

I stand a basin next to the cylinder and connect the hot from the top of the cylinder, and I tee into the cylinder cold feed just before the cylinder connection for the cold.

Which tap has the biggest head/pressure

 

[kirkgas]

if you simply relocate the cylinder and leave all the pipework where it is the flow will be exactly the same, what we should actually be considering is the vertical distance between the water level in the tank and the highest pipe (which someone has already said) we are all agreeing it is a gravity thing so the water drops out of the tank into the cylinder and out of the pipe at the top, if the pipe at the top of the cylinder rises right into the loft and across the loft then back down to the tap the head will be the distance between the water level and the pipe (the u tube effect mentioned)
this was supposed to be a quick reply stick with me

on a traditional cylinder system say you added an ensuite bathroom with 2 whb's,and for arguement's sake connected them from 2 different places 1st one simply cut into the expansion pipe to run a supply to 1 whb at a height of about 3' above the loft floor(nearly as high as the water level) and the 2nd one you cut a tee into the existing hot supply 3m below the water level, REMEMBER THE 2 WHB'S ARE FED FROM THE SAME CYLINDER AND ARE AT THE SAME HEIGHT AS EACH OTHER so depending who you agree with do you say the pressure at both taps is the same or vastly different
(i say vastly different)

A couple of comments Kirkgas Nice that someone else knows what they are talking about.

In you example with the two basins the head will be the same, however the flow would be different because of the resistance in the pipe.Another example with the two basins side by side.

Connect one from the same height as the cylinder, and the other one by running the pipe up into the loft and dropping down to it.

The head will be the distance it is from the top of the cylinder to the pipe, less than the 1st basin.

perhaps then we are getting a bit mixed up with the terminology, i agree with your comments on my post, head is the same flow is less, but some posters have been commenting that the head is critical (which it is) but the way it is piped will drastically decrease the flow, as in my example so if i agree the head is critical, in my example IS the head is the same or should we take the head as distance between water level and pipe half way up tank for 1 whb and for 2nd whb head is water level to outlet of cylinder, we all agree (i think) that in my example if we cut into the expansion pipe above the water level of the tank no water would come out of the whb so how could you explain no water at 1 whb with the same head of water as the whb next to it with water coming out of the tap.

 

[Tipper]

Sorry.

Head is distance from the surface of water in a tank to the level of the outlet.

Plain and simple.

Look at it this way...

Q. What is the head at the outlet from a tank?

A. The depth of the water = surface to outlet distance.

Therefore wherever the outlet of a system is, the head is the distance from water surface to outlet. All the pipework in between only goes to reduce the head due to resistance to flow.

 

[doitall]

Sorry.

Head is distance from the surface of water in a tank to the level of the outlet.

Plain and simple.

Look at it this way...

Q. What is the head at the outlet from a tank?

A. The depth of the water = surface to outlet distance.

Therefore wherever the outlet of a system is, the head is the distance from water surface to outlet. All the pipework in between only goes to reduce the head due to resistance to flow.

I'm not disagreeing with part of your post Tipper.

You are measuring static pressure, not operating pressure, and yes like gas there's a very big difference.

The minute you open an outlet and the water level drops your calculations go out the window, so are meaningless the same as static pressure at a gas meter.

Therefore wherever the outlet of a system is, the head is the distance from water surface to outlet. All the pipework in between only goes to reduce the head due to resistance to flow

This you have partly wrong but it maybe the way it's worded.

The distance from the water to the outlet (being the top of the cylinder) you cannot increase it from this point.

The head is not reduced through resistance, the volume will be.

The higher you raise the pipe from the outlet the lower the head will be.

 

[cmother1]

Pooksahib - please get rid of your shower. It's causing too many arguments!

 

[doitall]

Kirkgas/OP

You can increase the flow/volume of water by increasing the pipe sizes.

You could increase the head by dropping the hot pipe in the loft to below the shower rose.