Calorifier

[claymore]

Well Nick, the Chents Cruise is almost upon us and it was there that this particular culinary delight shot to stardom. I've been eyeing one up in Dear Heart's polytunnel for a while now - it may well get to take a trip north...

[sahona]

As to the original question, - "yes" at last!
Tests today revealed that the engine still works, and the water in the calorifier gets heated. (short test, still ashore)
Nothing seems to match the advice sought and given on the web, but we appear to have lift-off.
What difference will it make ? - Less gas used by the geyser and more leccy sucked from the pontoon (if we ever get to one). More weight forrard, probably have to ditch 30m of chain to compensate. Oh yes, and a couple of hundred squids missing from the beer fund.

[Clyde_Wanderer]

The snag is that if you rest up for the night, have a decent nosh, do all the washing up etc, the tank then refils with cold water. So even though you might use say half a tank of hot, you end up with a full tank of only just warm enough for a wash the next morning.

I hesitate to comment, since I don't (yet) possess a calorifier, but the normal arrangement with a hot water storage tank is to draw the hot water off from the top and fill with cold at the bottom. That way the hot stays at the top (stratification) and doesn't mix with the cold to give a tank of tepid. The latter will happen if the tank contents are stirred, e.g. by briefly operating a low level immersion heater.

Dave, would it not be the case that as the bottom of the hot water at the top of the tank gets cooled by the cold water beneath it that it would gradually loose its density and sink hence mixing with the cold water in the tank, and after a long enough period the water at the top would be near enough the same temp as the water below it, Cool?

[DaveS]

No, I don't think the physics has changed since I posted this a year ago. What you are proposing is diffusion which does happen, but on a much slower timescale than concerns us here.

Now first a caveat, because I assume a static tank, i.e. like a domestic hot water cylinder (HWC). As I said, if the contents are stirred, either by operating an immersion or by shaking the tank (moving boat) then stratification can be destroyed, mixing will happen, and a tankful of tepid water will result. If there is no stirring stratification holds up remarkably well. This can be easily verified using a thermal imager or by scanning up and down the HWC with an infra-red thermometer: the hot / cold boundary is very obvious.

To give a practical example: in our last house the HWC was a well insulated 210 litre unit with high and low level immersion heaters (IH). The high level IH was meant for "boost" purposes, i.e. heating a relatively small volume of water quickly (an IH can only heat water which is at or above its own level). Because there were normally only two of us living there, this facility was only used about 5 times in 20 years: initially to prove it worked, then for parties, etc. The low level IH was switched on for 4.5 hours in the early hours of the morning, this being sufficient to fully heat the whole tank from cold: normally, of course, there was residual hot water, so the thermostat switched off long before this.

My wife generally had a largeish bath in the morning, using about a third of the stored hot water. By late evening, with no additional energy input, water drawn off was only about 1 degC cooler than that drawn off in the morning, confirming both the quality of the HWC insulation and that stratification had been undisturbed.

HWC designers sometimes incorporate a baffle at the cold water entry point to direct the incoming stream slightly downwards. This helps to avoid mixing.

[Clyde_Wanderer]

If only you were as knowledgable on anchors and rodes Dave, and were willing to share that knowledge wouldent life be just great.

[Rowana]

Many, many moons ago in my yoof, I used to go and fit immersion heaters part-time. It's how I made my beer money in those far-off days!

Anyway, the ones we used to fit were the Howden WE3. The heating elements were enclosed in a tube, with a hole at the bottom at the inboard end. At the outboard end, there was a hole in the top of the tube to which a vertical pipe was attached. The whole thing was installed low down in the hot water cylinder.

When you switched it on, the cold water came in the hole at the bottom, was heated and went out through the hole in the top, up the tube to the top of the tank.

If you left it on fot about 10 minutes, there was enough water to wash your hands, but you had to leave it on for quite a bit longer to heat the whole tank, but the whole idea was that it heated the water from the top down.

Our sales pitch was to wire it all up, then show the lady of the house where the switch was. Then leaving it on while we cleared up our tools, we then demonstrated how quick it was by having enough water to wash our hands! Amazing how many recomendations we got, and more heaters to fit! This was at the time when everyone was doing away with their coal fires.

Happy days!

[DaveS]

Ah, yes, the famous "circulator" type IH. Can be identified from outside the tank because the fixing uses studs rather than a big screw boss. Absolutely brilliant concept which allows a single IH to be used both for full tank charge and boost, with no risk of stirring. Excellent demonstration of stratification since it delivers the hot water right at the top of the tank, with the hot / cold interface slowly descending as the IH operates.

Virtually unknown south of the border, though, since it only works in soft water areas. Hard water scale clogs up the wee holes...