Poll: Heating Concepts

[Harry Bloomfield]

Eh?

You seem to be querying how UFH works?

 

[EFLImpudence]

I've repeatedly said that thermostat location appears to be crucial to everything we've been discussing but, despite my having repeatedly asked the question, no-one has yet told me where the thermostat is in a Willi system,

That wouldn't take much searching.
It's in the Willis, which is just an immersion heater in a tube.

so I have been guessing/assuming that it is within the Willis heater.

Of course.

If so, the situation is identical to that with an internal immersion, with the stat switching off the heating when the desired water temp gets level with the Willis.

No it isn't. It is dependent on the temperature in the tube; not in the cylinder.

One variant of 'common sense' would tend to agree with that.

Then use that variant.

However, if that's what happens, I presume it would have to be (probably slowly) by conduction, since I can't see why ('by convection') heated water should fall through the cooler water below the heater?

So what? If some hot has risen then some other not quite so hot must fall.

As above, if the Willis has a thermostat (which I strongly suspect that it probably does), then I see no difference from any other immersion+stat.

Because the Willis gets a supply of water from the bottom of the cylinder.

 

[EFLImpudence]

When this is settled, are you familiar with magnetism?

 

[ericmark]

Warm air, or water, rises. The heat source is in the floor, the floor area will be warmer the air above it, therefore it will rise. The air current will be rising in the middle, because the walls will be cooler. Basic common sense, in my view!

Good point. Looking at round houses

your answer is clearly correct. Which is why I selected "it depends" also with under floor heating the air current would be up in the centre and down the sides.

Centre of house, internal wall of living room, we have an open fire. I have made a unit to connect it to the AC, so no need to open a window in the summer for the exhaust, it has never been used by me to heat the house, main problem is air goes up the chimney and is replaced through every crack and gap in all doors causing drafts, as there is no ducting for combustion air, so it is for emergency use only as a fire.

The room has two radiators at 90° to each other on outside walls, under windows, not ideally placed, but they work, both with electronic TRV heads which do not connect to the wall thermostat, which clearly can't be opposite to both of the radiators, and the room L shaped, so no ideal place for either radiators or wall thermostat, but it works.

I have no idea how the air circulates, it clearly does, but at moment thermometer on table 21.3°C wall thermostat 21°C (only shows in 0.5°C increments) radiator behind me 20°C (only shows in 1°C increments) and other radiator 17.2°C behind a settee, and been a warm day today, so heating has not been running. The room below living room showing 17.8°C. There is a lot if insulation between the rooms, as it was a garage. In the main today room has been heated with inferred from the sun, so warmer than the rest of the house. Wife's bedroom North side of the house, 15°C with so many easy read temperatures my bedroom 19.1°C and the utility room unheated 13.8°C and hall 15°C TRV and 18°C wall thermostat, and dinning room 14°C on the TRV the rest do not connect to phone or PC, there is with the heating not running a huge variation throughout the house. Even within the same room. Some can be explained away by height of the sensor, or proximity to outside, but my feet are not cold, so the air clearly does circulate to some extent.

 

[Harry Bloomfield]

When this is settled, are you familiar with magnetism?

Pleeeeaaase, not another endless thread!

 

[ericmark]

When this is settled, are you familiar with magnetism?

ELECTRIC LOVE
My love is like a dynamo
With woven wire for hair,
And when she brushes it at night
The sparks run crackling there.
Oh she is the magnetic field
In which I pass my days,
And she will always be to me
ELECTRIC in her way.
No insulated force is she;
Galvanic rather , seeing
Hers is the current keeping bright
My filament of being
Oh yes,my love's a dynamo
Who charges all the air ;
My love is an Electrolux
Who sings upon the stairs..

 

[ericmark]

I got

Look for the positives. Whilst waiting you will have plenty of time to think about another pointless post on the forum.

so not doing too bad with

Pleeeeaaase, not another endless thread!

But 252 replies will take some beating.

 

[JohnW2]

That wouldn't take much searching. ... It's in the Willis, which is just an immersion heater in a tube.

As I said, that's what I've been assuming.

No it isn't. It is dependent on the temperature in the tube; not in the cylinder.

Can I remind you of your 'levelling' theory/explanation? - which, ironically, was one of the things which helped me to understand (I though/think) how the Willis system works.

Then use that variant.

The problem with using what I described as 'one variant of common sense'(which I probably should have called 'intuition') is that it may well be flawed - e.g.perhaps by ignoring the fact that heating water below the level of the heat source might be an extremely slow process, primarily dependent on conduction through the water and the material of the cylinder.

However, if that's what happens, I presume it would have to be (probably slowly) by conduction, since I can't see why ('by convection') heated water should fall through the cooler water below the heater?

So what? If some hot has risen then some other not quite so hot must fall.

Yes, but only in the region above the heat source. There is no heat source below that, so what could have created 'hot water' to rise in that region?

Because the Willis gets a supply of water from the bottom of the cylinder.

Where are you suggesting that an immersion 'gets its supply of water from', and how does it importantly differ in this respect from the Willis?

 

[JohnW2]

You seem to be querying how UFH works?

Not really, but I certainly am querying how on earth UFH got into this discussion

 

[JohnW2]

The air current will be rising in the middle, because the walls will be cooler. Basic common sense, in my view!

Good point. Looking at round houses View attachment 409358your answer is clearly correct.

In the round house depicted in your drawing (and many others) the 'heat source' (the fire) is surely 'in the middle', which would seem to be a very good reason why 'a current rises in the middle, wouldn't it?

 

[ericmark]

In the round house depicted in your drawing (and many others) the 'heat source' (the fire) is surely 'in the middle', which would seem to be a very good reason why 'a current rises in the middle, wouldn't it?

Yes which was one of the reasons for the depends on vote. As I said with my own living room, because of the shape, and the radiators being on a wall, it will start circulation, otherwise far corner from radiator would be very cold, shape of the room or tank matters.

 

[Harry Bloomfield]

John - it is so very simple, and obvious....

In a normal cylinder, using a normal immersion heater, the heater will only heat the water, which is above the element, and perhaps slightly below - all due to the heat convection currents set up by the element, which begin soon after the element is switched on.

Now, imagine a vertical element, contained within a narrow tube, only open to the cylinder at the top, and the bottom. The convection current then is rather different. The heated water flow has to exit at the top of the tube, and has to be drawn in at the bottom. That process will continue, until the water drawn in at the bottom, causes the stat to open, because the stat is measuring the temperature of the water going past it. Thus, the system has the ability to heat water in the cylinder to a lower depth, than the end of the element, almost down the cold inlet.

Now imagine that same tube, mounted alongside the main HW cylinder, with a pipe connecting it top and bottom - we get the very same flow of hot in the top, cold out the bottom, from the HW cylinder - that is a Willis. Again the stat will remain closed, until it begins drawing hot water from the lower pipe, once the level of HW has 'spread' down that far. Thus, the length of the element in a Willis system, has little bearing on the ability of the system, to heat the entire contents of the HW cylinder.

A major difference, is that a normal immersion heater installation, when switched on, gradually heats the entire water contents, which is above the lower tip of the element - whereas, the Willis process does not quite so much, mix cold with its hot. The result is a gradually increasing store of HW, better defined, at the top of the HW cylinder.

 

[ebee]

The way I see it is what we learned at school, three methods by which heat might travel, conduction, convection or radiation so all three might come into play to some extent. Heat rises is not correct. Heat will go in any direction it can and to any extent that it can by any of those three methods. Hot water (or air etc) is less dense therefore will tend to rise and subsequently transfer heat to its surroundings by any or all of those methods. Conduction will occur thru a medium (metal might be a good example) and radiation can radiate thru no mediums such as space (outer space) .

Therefore I reckon that the prime mover of hotter water in our example is convection of the water as it is heated and it lines up accordingly, then some transfer to the surrounding via conduction . Although some conduction will occur at the bottom of the heater it will not be that much in the scheme of things.

Convection is the main driver within any cylinder or any Willis and associated pipe work. Outside the cylinder itself then even radiation could come into play along with the two others,

That’s my tenpennorth

 

[ericmark]

This and this I would not expect to heat in the same way, the latter this is likely heating nearly the whole tank, but not with the tall tank. As to how wide the tank needs to be to see the change, not sure.

 

[ebee]

This View attachment 409425and this View attachment 409426I would not expect to heat in the same way, the latter this View attachment 409427is likely heating nearly the whole tank, but not with the tall tank. As to how wide the tank needs to be to see the change, not sure.

Certainly interesting to see how and to what extent such baffles might affect the characteristics and whether that might make some plus or minus differences that could be helpful or could be best avoided according to need too Eric