Immersion Heat lose!!

wasim21k

Hello everyone
I m taking temperature readings every minute for hot water, temperature drop from 50c at 1:00am to 30c at 10:00am, is this normal for heat loss for fully insulated immersion? Is there any thing i can do to avoid this?
Thanks

my3cents

Have you had a look to see what pipes get hot? Its possible the your hot cylinder of water is heating the pipes that come out of it and thats where you are getting heat loss. Can't put any figures on it but we still have warm water tonight after heating the water luke warm last night (first time of the year firing up the boiler in the multi fuel cooker).

Yeah you'll loose heat but you seem to be loosing it faster than I'd expect.

Sleeper12

How scientific are your tests?
If it were me I'd heat up the full cylinder by putting it on Bath for an hour and a half. Then you need to guarantee that no one uses hot water in the house during the testing period. By doing this you are ruling out any other possible ways that the water is cooling. I would test the water temperature at the nearest tap to the cylinder.
Your water temperature should be dropping by a degree or so over an 8 hour period with an insulated cylinder if no one is using the hot water.

my3cents

The test results look good on the graph and the way the temperature goes down gradually makes it look like no one is using the hot water, however I wonder if running the test is using up the hot water. If the test is being run at the tap then every times its run its using hot water to heat the pipes while it reaches its max temperature at the tap then leaving hot water to go cold in the pipes.

Maybe try the same test and only check the temperature every hour or even leave it a full 12 hours and see if there is the same drop as the first test.

Joe1919

Copper cylinders even when insulated still loose a fair bit of heat. I done tests a while back on various types of water heaters, and an insulated copper cylinders lost 3kw/day even in the 'sink' position. The green insulation is really only minimum and you could add additional insulation by wrapping cylinder in tin foil and fitting additional lagging jackets etc if there is room. Also lag pipes going to cylinder.

Also note that even if immersion was perfectly insulated, there is still two possible additional ways that heat can escape or temperature can lower.
1 Most immersions heat the top section of the copper cylinder but this water and heat can mix with the colder water at the bottom.
2. If boiler pipes are connected to side of copper cylinders, there can be some back gravity flow of heat if there are upstairs radiators or to higher pipes. (Also check that circulation pump is not running)

wasim21k

my3cents I can see your point, that is way I have insulated all pipes coming in or going out of immersion cylinder, heat loss from those pipes shouldn’t be this high. Sleeper12: wife left immersion on for 6 hours (she forget to turn if off), and now one used water after I turned immersion off, I have green insulated copper cylinder.

Joe, if electricity is used heat water temperature varies from top of the cylinder to bottom but when gas boiler is used to heat the water then temperature is somewhat same at top and at bottom, but in this case water was heated using electricity and left for 6 hours so I would image water temperature was same at top as bottom of the cylinder. I don’t think that back gravity flow would cause this much heat loss as I have motorized valve and they are shut when heating is not on in that zone.

Sleeper12

You have an inch of foam on that cylinder. The cylinder isn't the issue. I don't mean to disagree with Joe1919 but thats a very well insulated cylinder. The fact that you can't tell if the cylinder is hot or cold by touching the foam will tell you there is very little heat loss from it. There is no harm wrapping it in foil if you want but you'll find the cylinder itself is only loosing a degree or so over night. The problem is elsewhere imo.
I'm assuming that the element was set to bath for 6 hours rather than sink. Sink will only heat top of cylinder & you would expect temp drop like you are seeing especially if you are running off hot water to test it. You use 5 to 6 litres of hot water just to get hot water to the average kitchen sink. In other words you leave 5 to 6 litres of hot water in the pipes if you are testing at the kitchen sink. In fact even more hot water if you let it run to get really hot water. Average cylinder holds 130 litres of water, though yours looks bigger

wasim21k

Readings are taken at cylinder by removing little bit insulation To attach temperature sensor to copper wall of cylinder, no water was used durring this time, it was left on at bath, perhaps water leak somewhere? I don't see any obvious sign of water leaks anywhere.

Sleeper12 wrote: »

You have an inch of foam on that cylinder. The cylinder isn't the issue. I don't mean to disagree with Joe1919 but thats a very well insulated cylinder. The fact that you can't tell if the cylinder is hot or cold by touching the foam will tell you there is very little heat loss from it. There is no harm wrapping it in foil if you want but you'll find the cylinder itself is only loosing a degree or so over night. The problem is elsewhere imo.
I'm assuming that the element was set to bath for 6 hours rather than sink. Sink will only heat top of cylinder & you would expect temp drop like you are seeing especially if you are running off hot water to test it. You use 5 to 6 litres of hot water just to get hot water to the average kitchen sink. In other words you leave 5 to 6 litres of hot water in the pipes if you are testing at the kitchen sink. In fact even more hot water if you let it run to get really hot water. Average cylinder holds 130 litres of water, though yours looks bigger

Sleeper12

wasim21k wrote:

Readings are taken at cylinder by removing little bit insulation To attach temperature sensor to copper wall of cylinder, it was left on at bath, perhaps water leak somewhere? I don't see any obvious sign of water leaks anywhere.

You can rule out a leak by turning off the valve for the hot water & running the test again. Even if you test it going to bed and again first thing in the morning. Also with the hot valve off you can be certain no one is running hot water during the test.
It's a strange one

Wearb

Is that pipe coming out the top of cylinder insulated in the attic?
Do you have a pump over run on your boiler?

my3cents

Wearb wrote: »

Is that pipe coming out the top of cylinder insulated in the attic?
Do you have a pump over run on your boiler?

Add to that where is the take off for the hot water to the taps is it under than lump of insulation added to the top of the tank (where I'd expect it to be) or is it higher up?

I was loosing substantial heat from the cylinder, it turned out that the heat was going all the way upstairs to the bathroom radiator, no other radiator only the bathroom, I can't figure that one, anyway the cylinder is downstairs so heat rises etc.

The solution was in warmer weather to turn off all the upstairs rads. Even in winter if it's not so cold and I don't need so much heat I turn it off to keep the hot water.

my3cents

Deleted User wrote: »

I was loosing substantial heat from the cylinder, it turned out that the heat was going all the way upstairs to the bathroom radiator, no other radiator only the bathroom, I can't figure that one, anyway the cylinder is downstairs so heat rises etc.

The solution was in warmer weather to turn off all the upstairs rads. Even in winter if it's not so cold and I don't need so much heat I turn it off to keep the hot water.

Isn't that an old way of doing things where you had solid fuel and a direct connection to a HWC plus a bathroom rad as a sort of safety heat sink and a way of getting a good thermo siphon going.

I've no solid fuel, thankfully I got rid of that expensive dirt years ago.

It's just convection , the heat makes it's way up , if the cylinder was upstairs the heat would have nowhere to go.

Dtp1979

The pipe rising from the top of the cylinder, must run at least 457mm horizontally before it goes up to the attic to avoid one pipe circulation and cooling of the cylinder.

wasim21k

Wearb wrote: »

Is that pipe coming out the top of cylinder insulated in the attic?
Do you have a pump over run on your boiler?

it isn’t insulated, as mater of fact pipes aren’t insulated anywhere in the house.

my3cents wrote: »

Add to that where is the take off for the hot water to the taps is it under than lump of insulation added to the top of the tank (where I'd expect it to be) or is it higher up?

yes, thats right.

Sleeper12 wrote: »

You can rule out a leak by turning off the valve for the hot water & running the test again. Even if you test it going to bed and again first thing in the morning. Also with the hot valve off you can be certain no one is running hot water during the test.
It's a strange one

there is no shut valve for hot water but only cold feed into tank.

my3cents

wasim21k wrote: »

...
there is no shut valve for hot water but only cold feed into tank.

Thanks for the reminder I replacing one of our HWC's this week and hadn't thought to put a shut off valve in the supply, think I'll do that

Anyway have a very similar cylinder and once its up and running I'll do a temp test for you after heating with the immersion.

RJF

wasim21k wrote: »

it isn’t insulated, as mater of fact pipes aren’t insulated anywhere in the house.


yes, thats right.



there is no shut valve for hot water but only cold feed into tank.

The shut off on the cold feed into the CYLINDER (between storage tank and cylinder) is the shut off for the hot water. It is usually in the hot press but sometimes it is in the attic.