Which situations? I really am confused.
You started by wondering how the Willis worked at all in its intended configuration.
Willis Heating System
- Thread starter JohnW2
- Start date
You started by wondering how the Willis worked at all in its intended configuration.
The situation you were considering when you presented your 'levelling' argument and the rather weird stuation (with the high-up heater) that Sunray (I think) introduced.
I did,and to some extent, with some help from you, I think I have now got to grips with that.
However, maybe I'm sticking my neck out, but the more we discuss this the more I am becoming inclined to my view that the behaviour of the Willis system should be more-or-less identical to having a horizontal immersion of the same power in the main cylinder, at the same height as the Willis heater - in other words, it seems to me that the only difference is whether the 'heater' in inside or outside the cylinder, and that difference probably makes no appreciable difference to hoow the system behaves.
... but, of course, I have to yet again repeat my caveat that "maybe I'm missing something"
Was that not only in response to your two cylinder diagram after it was modified?
I think there are too many variations in the thread to be certain what is being discussed.
The main point I have been trying to discuss is a very simple and basic one, but 'answers' so far have been varied and confusing - namely what, if anything, can a Willis system do that a horizontal immersion heater (at a similar 'height') cannot do?
That's hardly the main point but I suppose the answer is deliver a smaller amount of hotter water more quickly.
Plus I suppose is there any choice with the height of a horizontal immersion heater?
I'm not sure about that, given that some people are claiming that it offers "very clear advantages".
That is a variant of one of the things that is being said, but which I don't really understand. Starting from 'switch-on' with 'everything cold', I don't see why the amount (and 'hotness') of rapidly-available heated water should be appreciably different with a Willis system than with a 'high up' immersion of the same power.
I don't know how much variation exists in terms of available cylinders but, once the system is installed, there is obviously no choice - but nor is there any choice about the height of a Willis heater once it has been 'plumbed in' - so I'm not sure what the difference is meant to be.
No, because the rising flow is channelled/directed. Hot water will rise over the top, cool down a little, and then fall down the vertical pipe, into the main cylinder.
My experience with commercial large calorifier systems using external unpumped heater batteries is: The whole storage vessel will heat and that is to below the level of the heater vessel, all the time heat is applied the water will flow and the hot water has to go somewhere,
Don't forget the heater vessel is very small, only big enough to accomodate the heating element, I'd guess domestic versions from the images I've seen on line only hold 1L so would boil very quickly if given a chance. As we all know the top will be hotter than the bottom and there is very little space to circulate internally, all the while there is an external flow available it will flow.
Perhaps this more restricted diagram may help influence thoughts.
Whereas this
will allow lots of circulation within the heater vessel and far less flow into the flow pipe until it gets very hot and the pressure will push water in both directions, except of course the lack of cooling water will causde the thermostat to open before any incorrect operation occurs.
Don't forget the heater vessel is very small, only big enough to accomodate the heating element, I'd guess domestic versions from the images I've seen on line only hold 1L so would boil very quickly if given a chance. As we all know the top will be hotter than the bottom and there is very little space to circulate internally, all the while there is an external flow available it will flow.
Perhaps this more restricted diagram may help influence thoughts.
Whereas this
I don't see why a high up horizontal immersion should be appreciably different from that, since heat from the vicinity of the element will rise up to the top of the main cylinder. The only issue (possible 'difference') if that if the immersion is appreciably below the top of the cylinder that rising water will have travelled though cold water on the way up, and hence cooled a little. However, I can assure you that,in practice, water too hot for one's hands appears at the top of the cylinder (available to be drawn) very quickly after the immersion is switched on!
As for "... cool down a little, and then fall down the vertical pipe, into the main cylinder" that may happen as a result of water being 'pushed', but it certainly will not 'fall down' by convection, since it will be hotter, hence less dense, than the water in the vertical pipe below it.
Yes, and no! A Willis intake/bottom connection could likely be placed lower than your bottom immersion heater could be located, and could therefore enable a greater volume of hot water to be produced.
Your bottom immersion heater, assuming you only have the one element, would mean that you are waiting much longer for a small quantity of hot water, because the hot will be diluted, by the circulation currents, resulting from the hot element. The Willis system, provides a much more instantaneous small 'batch' of water, at the top of the cylinder, undiluted by the cold further down the cylinder, making it potentially more economic to run.
You also have the advantage of being able to stop the Willis producing hot water, all at your desired temperature, at any point which you decide is enough, simply because the boundary moves gradually down from the top, with none of the mixing, you would get with your bottom mount immersion.
I agree, your two element, goes some way towards addressing the limitations of your system.
The Willis has other advantages, mainly useful in commercial systems, in that there can be multiple Willis units, contributing to one HW cylinder, and each can be isolated for maintenance and repair, leaving the system still able to operate.
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I don't think it makes much, if any, difference whether or not water in the 'heating vessel' (or associated pipework) does any circulating within that vessel - my problem (and I think maybe also EFLI's?) is in understanding how it can result in appreciable heating of water in the main cylinderbelow the level of the heat source.
My bottom immersion is extremely close to the bottom of the cylinder, so I don't think that's an issue.
We seem to be overlooking the fact that the whole point of having a DHW cylinder is that one nearly always has plenty of stored hot water, so all this talk about 'how long one has to wait' is, in practice, not very relevant.
As above, if one has stored water, one expects it to usually always be available, so there is rarely a need for a "more instantanous small 'batch' of heated water". However, if all the stored water had been used up (and replaced by cold) and one had such a need, one certainly would not use the 'bottom' immersion to achieve that, for the reason you give.
As I recently wrote, the one issue with an immersion is that heater water has to rise through cooler water (hence getting cooled a little) on its way to the top of the cylinder. However, thatbecomes less of an issue the higher up the immersion is - and I presume that if it were possible to install the immersion 'right at the top' of the cylinder, then it would behave identically to the Willis system.
Again, if one has a 'stored hot water' system, one will rarely completely run out of immediately available hot water - but, if one did, and wanted a small amount of hot water quickly, one certainly would not be advised to use a 'bottom' immersion for that.
I'm glad you agree to that extent. I would go a lot further and say that it goes a very long way to achieving what I want, and what I don't believe would be appreciably bettered by a Willis system.
One further observation/question occurs to me. If people have a 'hot water storage cylinder' but are often running out of hot water and need to generate some quickly, does that not mean that their storage cylinders are too small and/or inadequately insulated? As I have explained, although I have a 'top' immersion, I very very rarely use it, since a cylinder full of hot water is more than enough for us (and stays plenty hot enough) during the 20 or so hours between 'top ups' (heated by the bottom immersion).
Economiser (Willis) External Immersion Heater | Elemex
The Economiser (Willis) Heater: for fast, economical domestic hot water. The Elemex Economiser is a compact, inexpensive external immersion heater.
www.elemex.ie
They are not compulsory.
John - you seem to be forgetting the fact that other people have very different needs to yourself. I am not a salesman, attempting to sell you a Willis system, I am simply pointing out the differences to what you have, and potential advantages. With that, I will leave the thread, as it is becoming simply repetitive.
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