Willis Water Heating System

[ericmark]

Now you are seeing my point, we know it does work, not how.

 

[Harry Bloomfield]

I don't get that diagram at all - i.e. I cannot see how it could work.

If the pipework were of similar size for the connections to the cylinder and Wallis heater were the same, when you turned on a hot tap, you'd get a roughly 50:50 mixture of (cold) water from the cylinder and heated water from the Wallis.

More to the point, what you depict could not supply more hot water than (the small) volume contained in the Wallis heater (mixed with cold from the cylinder, as above), since there is no way that it would get from the heater into the cylinder.

Water rises out of the Wallis, permeates into the top of the cylinder, more cold is then drawn into the bottom of the Wallis all by convection. The amount of hot in the cylinder will gradually increase, the longer the Wallis runs. Assuming the Wallis's heated water flow is gentle into the cylinder, the hot to cold water interface will be well defined.

 

[JohnW2]

Now you are seeing my point, we know it does work, not how.

As you've shown it, I really don't think it could work - for reasons I explained.

Kind Regards, John

 

[JohnW2]

Water rises out of the Wallis, permeates into the top of the cylinder ...

Not per eric's diagram, surely? Water 'rising out of the Wallis' can surely only rise into the expansion pipe, it would have to 'fall', through colder water, to get into the cylinder, and what would make it do that? I suspect that eric's diagram is not correct....

Kind Regards, John

 

[JohnW2]

The Willis system creates hot water externally and feed it into the top of the cylinder while removing cold water from the bottom of the cylinder.

@bernardgreen ... maybe I'm just being dim, but I am continuing to struggle to understand how that is achieved - as I wrote to Harry, I certainly don't see how it would work per the diagram posted by eric (which is the first hit one gets with a Google search for an 'image' of the Willis system).

Looking at that diagram (or, come to that, any other arrangement I can think of), where the feed from the output of the external heater joins onto the take-off pipe from the top of the cylinder (which is initially 'full of cold water'), the pressure in both will be the same and the temperature of the water coming from the heater will be higher than that in the cylinder - so what could/would cause the heated water to travel 'downwards' into the cylinder? All I can see happening is the (small volume of) water in the expansion pipe getting heated, primarily by convection, with the cylinder just remaining full of cold water.

What am I missing?

Kind Regards, John

 

[Harry Bloomfield]

All I can see happening is the (small volume of) water in the expansion pipe getting heated, primarily by convection, with the cylinder just remaining full of cold water.

Convection currents will cause water in the Willis to expand and rise, drawing cold water in at the bottom. The cold water coming in at the bottom, will be drawn from the cylinder, thus drawing the hot from the Willis into the top of the cylinder. Before cars had water pumps in the cooling systems, they relied upon convection currents to circulate water up through the engine, out of the head, into the top of the radiator, then eventually back to the bottom of the engine. Water rising as it took on heat from the engine, then falling as it cooled, in the radiator.

 

[bernardgreen]

The hot water rising up out of the heater is replaced by cold water taken from the bottom of the cylinder. The replacement cold water cannot come from the cold water tank because if water from the tank entered the system then the level of the water in the vertical expansion pipe would rise to be above the level of the top of the water in the tank. That is physically not possible, water finds it's own level.

 

[JohnW2]

Convection currents will cause water in the Willis to expand and rise, drawing cold water in at the bottom. The cold water coming in at the bottom, will be drawn from the cylinder, thus drawing the hot from the Willis into the top of the cylinder.

The hot water rising up out of the heater is replaced by cold water taken from the bottom of the cylinder. The replacement cold water cannot come from the cold water tank because if water from the tank entered the system then the level of the water in the vertical expansion pipe would rise to be above the level of the top of the water in the tank.

Clearly a case of "Great minds', but I'm still somewhat struggling.

If some of the water within a contained mass of cold water is heated, then the density of the heated water wilkl reduce, so that it will 'rise' ('float up') to the top of that mass of cold water. However, it will not, and cannot, rise to above the top of that mass of cold water, thereby creating some sort of 'voiud' which requires more water to be drawn into the system from somewhere.

Thinking of eric's diagram, heated water from the Willis will 'rise up' to the top of the column of (initially cold) water in the expansion pipe. Eventually, the entirety of the expansion pipe will be 'hot' and, until heat starts getting lost, nothing further will then happen.

There will be a very slight increase in the volume of water in the expansion pipe, due to water having literally 'expanded' during heating, but less than a 1% increase for a temp rise from 20°C to 60°C. Depending on the height of the expansion pipe relative to the water level in the supply tank, that tiny amount of water may or may not 'overflow' into the storage tank ('wasting' a tiny amount of heated water).

However, other than that (possible) tiny amount, no water has been 'lost' from the system, so there is seemingly no need for any cold water to be drawn into the Willis heater from the borrom of the HW cylinder (which, if it happened, would 'draw' some of the heated water into the top of the cylinder.

If a hot tap is turned on, what comes out will be a mixture of (cold) water from the cylinder and (hot) water from the external heater (none from the expansion pipe), but that will only remain hot/warm until the (small) volume of heated water within the external heater is exhausted.

I therefore must still be 'missing something'. What is it?

Kind Regards, John

 

[EFLImpudence]

Isn't the answer "it just does"?

That is - the heating element or heated water will act like a pump.

If there was just a loop from heater top to heater bottom, would the water not "just" circulate?

 

[Harry Bloomfield]

However, other than that (possible) tiny amount, no water has been 'lost' from the system, so there is seemingly no need for any cold water to be drawn into the Willis heater from the borrom of the HW cylinder (which, if it happened, would 'draw' some of the heated water into the top of the cylinder.

It obviously does work and did work for the vehicles with no pump, using convection alone.

If a hot tap is turned on, what comes out will be a mixture of (cold) water from the cylinder and (hot) water from the external heater (none from the expansion pipe), but that will only remain hot/warm until the (small) volume of heated water within the external heater is exhausted.

I see your point, but that has me equally puzzled too - unless there is some sort of valve, or restriction of some sort which is ommitted from the diagram.

 

[JohnW2]

Isn't the answer "it just does"?

Maybe, but I have spent most of my professional life having to be unsatisfied with such 'explanations'!

That is - the heating element or heated water will act like a pump.

I see no way that (at least with the arrangement we've been shown) it could 'pump' hot water into the top of a cylinder full of cold water.

If there was just a loop from heater top to heater bottom, would the water not "just" circulate?

The top and bottom of the external heater? If so, then yes, but 'so what?' - that wouldn't help the hot water to get into the main cylinder, which is what this system seems to be all about (except in those situations in which one does not need more hot water than the (small) amount within the external heater).
Kind Regards, John

 

[EFLImpudence]

The top and bottom of the external heater?

Yes.

If so, then yes, but 'so what?

So, make the cylinder part of the loop.

 

[Harry Bloomfield]

The top and bottom of the external heater? If so, then yes, but 'so what?' - that wouldn't help the hot water to get into the main cylinder, which is what this system seems to be all about (except in those situations in which one does not need more hot water than the (small) amount within the external heater).

John, it does certainly work - another example for you to consider...

An ordinary water filled central heating radiator. It has water passages, heat comes in at one end, rises straight to the top, then gradually falls down the various passages towards the return. That works, whether the pump is running or not.

 

[JohnW2]

It obviously does work ...

Yes, I have to accept that - I am not suggesting thatvthe Irish are deluded into believing that it works when it doesn't, but ...

... and did work for the vehicles with no pump, using convection alone.

I don't really understand what analogy you're trying to draw. As you previously wrote ...

... Before cars had water pumps in the cooling systems, they relied upon convection currents to circulate water up through the engine, out of the head, into the top of the radiator, then eventually back to the bottom of the engine. Water rising as it took on heat from the engine, then falling as it cooled, in the radiator.

Indeed so - and not only in car engines, but entire CH systems worked on that principle. However, in that situation the water is constantly circulating, in a 'convection loop'. In what is being described here, there is no such loop, hence no circulation - and certainly no way I can see of getting hot water into the top of the cylinder (initially full of cold water) without either having a pump or else introducing the hot water into the cylinder below the top (hence all the disadvantages of having to rise through/mix with cold water before it gets to the top).

I see your point, but that has me equally puzzled too - unless there is some sort of valve, or restriction of some sort which is ommitted from the diagram.

As described, it really makes no sense to me.

Yes, if there were a substantial restriction in the outlet from the cylinder it would 'work' to some extent, but (a) that would not help hot water to get into the top of the cylinder (in fact, quite the converse), and (b) it would limit the amount of hot water available to the small volume within the external heater (which I gather is usually around 3-5 litres).

In fact, as one approached the situation in which such a restriction were 'total', then one would be approaching the situation in which one had replaced the (large) HW cylinder with a tiny one (aka the Willis Heater), probably just 3-5 litres, with obvious consequences in terms of the amount of hot water available.

Kind Regards, John

 

[JohnW2]

So, make the cylinder part of the loop.

Exactly. IF one fed the output of the external heater into the cylinder at some distance below it's top, then there would be a 'loop', and that would work ...

... BUT, then would effectively have exactly the same situation as if one had an immersion element at the place in the cylinder where the external heater was connected - with the potential disadvantages (of the hot water having to rise through, and 'mix with' colder water on its way up to the top of the cylinder. In other weirds, it would offer no advantages over haviing the heating element within the cylinder.

However, it seems clear that such is not how they do it, even though such systems obviously must 'work' if people are using them -, so I remain mystified.

Kind Regards, John