Willis Heating System

[Harry Bloomfield]

Thanks. Right, I think I maybe starting to 'get it'.

Have you never opened a hot tap, and listened to the noise the water makes, as it drops into the sink/basin? The noise changes quite noticeably, as the water out of the tap, changes from cold, to hot. The last few drops of cold water, is much more reluctant to drain from an upturned cup, than is hot water, from a hot cup.

 

[EFLImpudence]

Thanks. Right, I think I maybe starting to 'get it'.

Ok.

However, as I've been saying all along, I can't really see how the process you refer to could result in water in cylinder B being heated to significantly below the level of the immersion in A,

Who said it would?
and
Is that what you have been saying?

since the overall ('average') density in B would then be less than in A - which presumably would mean that 'circulation' would happen in the 'opposite direction'?

So - whatever happens the tanks will end up the same.

 

[JohnW2]

Have you never opened a hot tap, and listened to the noise the water makes, as it drops into the sink/basin? The noise changes quite noticeably, as the water out of the tap, changes from cold, to hot. The last few drops of cold water, is much more reluctant to drain from an upturned cup, than is hot water, from a hot cup.

No, I can't say I've ever noticed that. Nor am I really sure of its relevance to the discussion we're having!

 

[SUNRAY]

What is trying to be 'level' with what? With convection, there is no 'net movement' of water - all that happens is that rising hotter water 'swaps places' with cooler water which was above it.

If you can bear with me, let me try to get my thinking straight about all this, starting with 'first principles'. Forget Willis for now and consider just the simple system depicted in this first diagram here, with (for added simplicity) no thermostat. My belief is that, as times goes on (and despite what some people seem to believe) the immersion does not heat ever increasing amounts of water in the cylinder but, rather, progressively increase the temp primarily of just the water above it (ultimately until it boils, if there is no stat) - as per my diagram. Do people agree or disagree with me?

View attachment 408711

If you agree with me about the above, consider this diagram below, in which a second cylinder (full of cold water) is connected, top and bottom, to the one with the immersion. Do people really believe that water in the second cylinder is going to get appreciably heated and, if so, how/why? Thanks for any insights.

View attachment 408712

regardless of anything else continuing to apply heat to tank A the water will try to 'flow' and as there is an escape route and a possible inflow from B it will escape. Therefore there very well may be more hot water in B than A.
It certainly works that way in the big calorifiers where the vessel basically sit on the floor and the immersion tanks are above the floor.

 

[Harry Bloomfield]

No, I can't say I've ever noticed that. Nor am I really sure of its relevance to the discussion we're having!

Really - obviously, water becomes more fluid as it heats up.

 

[JohnW2]

Who said it would? ... and ... Is that what you have been saying?

Unless I have completely misunderstood, some people seem to have been saying that a Willis system can (eventually) heat the entire contents of the main cylinder, but I have (I hope) been consistently saying that I don't understand how it can significantly heat water in the cylinder which is 'lower' than the Willis heater.

So - whatever happens the tanks will end up the same.

Sure, except that I don't believe it could happen. If the density in B did somehow get below that in A, such that the circulation was reversed, cold water would move from the bottom of A into B (hardly a method of 'heating' the water in B), wouldn't it?

 

[JohnW2]

Really - obviously, water becomes more fluid as it heats up.

What do you mean by 'more fluid' - less viscous, perhaps?

Whatever, as I've said, I have not noticed the phenomenon you describe with water. With some things (honey, syrups, oils etc.), increasing temp can dramatically reduce viscosity.

...but I still don't really see what this has got to do with our discussion

 

[JohnW2]

regardless of anything else continuing to apply heat to tank A the water will try to 'flow' and as there is an escape route and a possible inflow from B it will escape.

Yep, as you will have seen, I have 'got' that much.

Therefore there very well may be more hot water in B than A.

... but, as you will also have seen, I don't yet get that. More hot water in B than A would mean lower overall density in B than in A - in which case it seems to me that 'flow'/circulation would be in the opposite direction from that which would heat B - so I don't seee how that situation could arise.

 

[EFLImpudence]

Unless I have completely misunderstood, some people seem to have been saying that a Willis system can (eventually) heat the entire contents of the main cylinder, but I have (I hope) been consistently saying that I don't understand how it can significantly heat water in the cylinder which is 'lower' than the Willis heater.

Sure, except that I don't believe it could happen. If the density in B did somehow get below that in A, such that the circulation was reversed, cold water would move from the bottom of A into B (hardly a method of 'heating' the water in B), wouldn't it?

Yes, but I was referring to your diagrams.

 

[JohnW2]

Yes, but I was referring to your diagrams.

Fair enough.
However, to get things clear in my mind, are you one of the people who believe that the arrangement in my diagrams (or a Willis heater) can result in the entire contents of the 'non-heated' cylinder ending up full of hot water?

 

[EFLImpudence]

However, to get things clear in my mind, are you one of the people who believe that the arrangement in my diagrams (or a Willis heater) can result in the entire contents of the 'non-heated' cylinder ending up full of hot water?

As the question is written, I am not sure there was or would be anyone who would claim such a thing.

 

[SimonH2]

I would tend to say the opposite - that, since the the additional cost/complexity/space is, as you say, only slight (particularly in relation to the 'big picture' of an entire heating system), if people really believed that the Willis system offered a "very clear advantage" we would have been seeing it in pretty widespread use in domestic installations, both in the UK and most countries of the world.

When you have an industry with people with an attitude like "I would never suggest anything other than a combi" (yes, I've seen a plumber express that) then it's hard to get alternatives into the minds of the punters. The majority will simply accept whatever the plumber suggests will be best for them (even if it is fraudulent because they won't consider anything but their "standard" offering). This was in a thread discussing thermal stores - where a number of others expressed an attitude that they would never ever suggest one regardless of the situation.

In the electrical world, it would be like an electrician saying he would never ever consider anything but a ring final, 2.5mm T&E, 32A MCB for a socket circuit regardless of the situation - so no radials with a single socket fed from a 20A or 16A MCB, no lollipops, now radials with 4mm cable and 32A MCB, ... EVER. We all know that some other circuit arrangements can have benefits over RFC in some situations, but some people would never fit them.

I suspect knowledge (to a level where they actually understand the benefits and downsides) of Willis heaters among the plumbing trade is even lower than that of thermal stores - which means they'd only get fitted if it's a particularly clued up customer (remember we are an untypical self-selected group here) or a particularly clued up plumber, and it's a situation where it would be better. And don't forget, the far more common arrangement in this country is a gas (or oil) boiler with an immersion for backup - hence a Willis wouldn't have all that much benefit.

 

[Echo the husky]

Betamax and VHS there was a third V2000 where you turned the tape over, Philips special.

Totally not relevant to this thread, but last year I worked in a house where the elderly customer was frequently recording TV programs in the day to watch when she got back in from the farm in the evenings on a Philips V2000 machine. I instantly recognised the design of the tapes, of which there were many! Must have been heading for 40 years old now.

 

[SUNRAY]

And don't forget, the far more common arrangement in this country is a gas (or oil) boiler with an immersion for backup - hence a Willis wouldn't have all that much benefit.

Except in commercial installations where it is quite common to have the heat exchanger external to the storage vessel, in other words instead of the immersion heater in a Willis system. However due to the lower temperatures involved it is likely the secondary into the vessel will be pump assisted.

However an unpumped gas/oil boiler directly heating a hot water storage vessel is as close as one can possibly get to a Willis system and such systems were still being installed only a few few decades ago.

 

[robinbanks]