Hot water tanks - measuring cooling
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Archie_tect
De Skieven Architek... aka Penfold + Horace
- Location
- Northumberland
Is there a reason why the airing cupboard vents to outside R?
Archie_tect
De Skieven Architek... aka Penfold + Horace
- Location
- Northumberland
Depends if it's a balanced flue type or an open burner type.
slowmotion
Quite dreadful
- Location
- lost somewhere
[QUOTE 2749910, member: 9609"]after a bit of research, it is most certainly an open burner.[/quote]
Do you have the make and model number?. There is usually a metallic looking plate with the rating etc somewhere in the boiler casing.
Do you have the make and model number?. There is usually a metallic looking plate with the rating etc somewhere in the boiler casing.
slowmotion
Quite dreadful
- Location
- lost somewhere
[QUOTE 2750000, member: 9609"]Ideal Mexico super 3 cf70
We seem to be heading away from evaluating heat loss from the hot water tank....[/quote]
No, not at all.
We seem to be heading away from evaluating heat loss from the hot water tank....[/quote]
No, not at all.
Smurfy
Naturist Smurf
- Location
- Smurfette's Kitchen
The water feed-in will be at the bottom of the tank, while hot water is drawn from an outlet at the top. There is no convective driving force for the layers of hot and cold water in the tank to mix, apart from perhaps a small amounts of turbulence where the water feeds in the bottom of the tank. Over time the temperature of the hot and cold water equalises by conduction up the copper tank wall. From this you can deduce that depending on where you make your measurements you may get very different results.
For example, my immersion heater is located at the bottom of the tank. It heats by convection, so is able to heat all the water in the tank above it. After using some of the hot water in the tank, the bottom of the tank is cold, but I can still draw hot water from the top. Twelve hours later, the heat has been dispersed, and all I have is a tank full of slightly luke-warm water. If I had two or more sensors I would be able to observe this dispersion of heat.
For example, my immersion heater is located at the bottom of the tank. It heats by convection, so is able to heat all the water in the tank above it. After using some of the hot water in the tank, the bottom of the tank is cold, but I can still draw hot water from the top. Twelve hours later, the heat has been dispersed, and all I have is a tank full of slightly luke-warm water. If I had two or more sensors I would be able to observe this dispersion of heat.
Archie_tect
De Skieven Architek... aka Penfold + Horace
- Location
- Northumberland
It's difficult R, because the hot water isn't evenly distributed throughout the tank so the top third may be far hotter than the rest.... it depends where the thermostat is located on the side... maybe best to put the boiler on constant for a couple of hours until the thermostat cuts in at a set temperature and take your readings at the thermostat position. Though I'm not sure what benefit it will have as the more insulation you have the less heat loss there will be regardless of the readings... where is the air vent in relation to the tank... could you isolate the HWT with rigid insulation board [use 50mm Styrofoam or Celotex RR to form a box and tape all the joints to stop air leakage then if you want to, fill the voids up with small polystyrene pellets to completely fill all the gaps... that's as good as you can do.
classic33
Leg End Member
If you want to do the maths
http://www.leaningpinesoftware.com/hot_water_heater_tank_insul.shtml
http://www.leaningpinesoftware.com/hot_water_heater_tank_insul.shtml
slowmotion
Quite dreadful
- Location
- lost somewhere
PM sent.
asterix
Comrade Member
- Location
- Limoges or York
Have done that to my French boiler/tank (electric) partly so it doesn't freeze over winter. Except I used rockwool to gap fill and also lined the compartment with reflective, multifoil insulation I had over. Very effective.
ArDee
Guru
- Location
- North of Buntingford, Hetfordshire
Also at the top of the cylinder use a 90 degree elbow as a takeoff, rather than a vertical pipe. A vertical pipe, especially if uninsulated, will lose a lot of heat and create convection currents with the colder water dropping back into the tank and hot water rising into the vertical pipe leading to more heat loss.
Over The Hill
Guru
- Location
- Ridden off into the sunset
The calculation has variables in the heat gain for the room from the tank may not be a loss and also the tank may take longer to cool but if that longer time is still before you use it again then it may not gain anything.
(say by insulating the tank the water cools in 20 hours instead of 4 hours but you only use the water to run one bath each day then the fact the water is kept warm for longer will not transfer into a saving unless the warmer water is then utilised. )
(say by insulating the tank the water cools in 20 hours instead of 4 hours but you only use the water to run one bath each day then the fact the water is kept warm for longer will not transfer into a saving unless the warmer water is then utilised. )
Smurfy
Naturist Smurf
- Location
- Smurfette's Kitchen
[QUOTE 2750130, member: 9609"]The strange world of heat dispersion in a HW tank.
After heating, the middle of the tank (top of heat exchanger) is hotter than the top, and it appears to take 6 to 8 hours for that to revert to the expected hotter at the top - I had Imagined the hottest water would have pooled to the top within minutes! (and I have interchanged the probes to test for discrepancies)
8pm top = 47.6 mid 52.1
1am middle = 47.4 mid 48.8
by the morning the top will be the warmer[/quote]
Yours will be a little different to mine. Certainly your boiler (and heat exchanger) setup will be a lot more powerful than my little electric immersion heater at the bottom of the tank. In that case the heating could be sufficiently fast that you get a hot spot where the heat exchanger is located. As you can see from your measurements, the heat in the tank is simultaneously spreading upwards, and being lost to the environment outside the tank. If you've got the time, I'd try a variety of measurement locations (maybe try 100mm intervals of elevation up the side of tank), and build up some measurements over a few weeks.
After heating, the middle of the tank (top of heat exchanger) is hotter than the top, and it appears to take 6 to 8 hours for that to revert to the expected hotter at the top - I had Imagined the hottest water would have pooled to the top within minutes! (and I have interchanged the probes to test for discrepancies)
8pm top = 47.6 mid 52.1
1am middle = 47.4 mid 48.8
by the morning the top will be the warmer[/quote]
Yours will be a little different to mine. Certainly your boiler (and heat exchanger) setup will be a lot more powerful than my little electric immersion heater at the bottom of the tank. In that case the heating could be sufficiently fast that you get a hot spot where the heat exchanger is located. As you can see from your measurements, the heat in the tank is simultaneously spreading upwards, and being lost to the environment outside the tank. If you've got the time, I'd try a variety of measurement locations (maybe try 100mm intervals of elevation up the side of tank), and build up some measurements over a few weeks.
