Water Immersion Tank linked to E7 meter

r2015

There is significant energy lost from hot water cylinders.

Before I got rid of my HWC and got a combi my hot water cylinder lost 2 kWh a day without me using any hot water.

Cardew

Smiley_Dan wrote: »

Sorry, my previous reply to Cardew wasn't posted for some reason.

It is a problem. There is significant energy lost from hot water cylinders.

I don't agree that it is 'significant'. In any case what is the alternative?


http://media.wix.com/ugd/4acd2a_0c96762bf30b460d8dcf9432115bfaf1.pdf


Tested to a British Standard with water at 65C typical losses over 24 hours are shown above e.g 150 litre tank the loss is 1.31kWh.


I doubt few people keep their HW tank at 65C continuously, so the losses will be considerably less than shown above.


In many cases a Combi loses more heat. Every time you demand water the Combi fires up and the boiler itself gets warm, and then cools down. How many time a day does this happen for washing hands, baths, showers, washing up etc?


Given we want a readily available supply of hot water, I think the cost is minimal.

Richie-from-the-Boro

Smiley_Dan wrote: »

Sorry, my previous reply to Cardew wasn't posted for some reason.

It is a problem. There is significant energy lost from hot water cylinders.

It has nothing to do with "eco" or green-wash, it is physics, only far more complex than the simplistic assessment procedures allow.

In terms of finances I agree it is not a big issue. At the moment.

Unless you can quantify your assertion of "significant energy lost from PartL hot water cylinders" I'm out of this thread. So how much is lost per cylinder size ?

Hot water for domestic use 150 litre tank [bath shower washing up etc] from a 27kW system on day rate is going to cost a 'day rate' fortune. Heat loss from pipework etc is going to be similar / same to the [cough] heat loss from pipework.

Liquid, such as water, is heated from the bottom, the layer of water closer to the heat source expands and hence becomes less dense compared to the water layer above it. Expanded water is less dense than the surrounding water and therefore it rises. The cooler regions of the water in the upper part of the flask, being denser, sink. This movement of liquid due to a difference in density sets up a convection current.

So the water heated [ hot ] by the bottom element in a PartL cylincer pushes up and forces the cooler water down over the thermostat which in turn is heated until the whole volume of the tank reaches your pre determined setting then the stat switches the leccy off. Its a bit atomic science and the random motion of atoms and all that, but sufficient to say that's why the top down element is rubbish at heating a full tank of water. That's physics.

Smiley_Dan

Cardew wrote: »

I don't agree that it is 'significant'. In any case what is the alternative?

http://media.wix.com/ugd/4acd2a_0c96762bf30b460d8dcf9432115bfaf1.pdf

Tested to a British Standard with water at 65C typical losses over 24 hours are shown above e.g 150 litre tank the loss is 1.31kWh.

That doesn't mean the tank is heated for 24 hours. It means the total energy losses over 24 hours.

Plus, it has minimal allowance for pipework.

Cardew wrote: »

I doubt few people keep their HW tank at 65C continuously, so the losses will be considerably less than shown above.

Agree, but there are valid scenarios where that does happen (input from uncontrollable sources).

The point is that it's not good enough to point at the sticker and say that's how much your tank is losing. It's likely a lot more than that.

Cardew wrote: »

In many cases a Combi loses more heat. Every time you demand water the Combi fires up and the boiler itself gets warm, and then cools down. How many time a day does this happen for washing hands, baths, showers, washing up etc?

I'm not necessarily advocating a combi, although they are likely to be a bit better. EST measured this as a few % better (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/180950/In-situ_monitoring_of_condensing_boilers_final_report.pdf section 8.4).

Cardew wrote: »

Given we want a readily available supply of hot water, I think the cost is minimal.

Again, I don't disagree with that. What I'm saying is that that only holds for the current situation of low energy prices. Although, who knows what will happen to that...

Smiley_Dan

Richie-from-the-Boro wrote: »

Unless you can quantify your assertion of "significant energy lost from PartL hot water cylinders" I'm out of this thread. So how much is lost per cylinder size ?

It depends. Massively. That's my point. It is not as simple as pointing at the sticker on a tank.

Richie-from-the-Boro wrote: »

Hot water for domestic use 150 litre tank [bath shower washing up etc] from a 27kW system on day rate is going to cost a 'day rate' fortune. Heat loss from pipework etc is going to be similar / same to the [cough] heat loss from pipework.

I didn't suggest that. Modulating instantaneous water heaters only heat water on demand.

Richie-from-the-Boro wrote: »

Liquid, such as water, is heated from the bottom, the layer of water closer to the heat source expands and hence becomes less dense compared to the water layer above it. Expanded water is less dense than the surrounding water and therefore it rises. The cooler regions of the water in the upper part of the flask, being denser, sink. This movement of liquid due to a difference in density sets up a convection current.

So the water heated [ hot ] by the bottom element in a PartL cylincer pushes up and forces the cooler water down over the thermostat which in turn is heated until the whole volume of the tank reaches your pre determined setting then the stat switches the leccy off. Its a bit atomic science and the random motion of atoms and all that, but sufficient to say that's why the top down element is rubbish at heating a full tank of water. That's physics.

I'm beginning to wonder if I'm posting in the wrong thread