What difference will tank lagging make, I have noted pre-lag kWh, what will be the result a week from now?

[Harry Bloomfield]

Here is mine, for comparison, a 120L cylinder....

It fires up on schedule, at 3pm. bring the water to 60C, in two sessions. Fires again, at 5pm, for washing up, then again at 7:30 to make up from drawing a bath.

 

[Johntheo5]

@ericmark, I think i've asked before, when the immersion cuts out after a full reheat, is tthe HW temperature at at the same consistent temerature and has the immersion ever tripped since the installation. Of the 27" elememt.

 

[ericmark]

Thermostat is never touched, so assume same temperature, and never tripped.

 

[Rodders53]

My OSO unvented HW cylinder (210 litres) is supposedly well insulated but the makers quote it at 81 Watts or nearly 2kWh of loss every 24 hours.
Certainly our airing cupboard (press for the Scots and Irish readers) gets warm and is used to finish drying clothes (and a wet towel this morning).

Your cylinder will likely have a similar nominal loss rate in the specs. Telford cylinders that look similar have numbers ranging from 60 Watts to 95 Watts depending on size of cylinder (and 40mm thick insulation foam).

Now I'd expect your consumption and losses to increase:
27 inch depth of hot water cf 9 inch (and 6 inch of that is within the reducing dome diameter). Possibly up to 4x the HW volume and area of the tank, certainly more than 3x...

Now my EV rate of 6.7p inc VAT 0000-0700 might work out almost as cheap as Kerosene oil (on daily for 1 hour, never seem to run out) as I bought a 1000 litres at 55p/l inc VAT this month... But a timer investment to use the cheap rate would never recoup the investment, and the HW usage exercises the boiler as well as not wearing out the emergency HW backup facility. I'd avoid for that reason alone in my case.

 

[lostinthelight]

Where have I said 26.5 kW? That is a 115 amp, main fuse is 60 amps, no way could I use that much power. Have I missed of a h somewhere? To heat the whole tank from cold, I would think around the 15 kWh and would take 5 hours at 3 kW. But not worried about that, clearly I do run off some hot water, but be it 9" at top or 27" the amount of hot water used is about the same. So 10 kWh per week approx extra is lost by heating the extra 16" of water, that seems a lot of extra energy.

A week today I will have answers, but until the jacket has been on a week, don't really know what it will save. I do wonder if the extra water being heated has resulted in a thermal flow though some pipework?

Wouldn't a longer heater element be heating a greater volume of water in the tank?
A 9" element would heat just the top of the tank where 27" would heat 3x more

 

[Harry Bloomfield]

Wouldn't a longer heater element be heating a greater volume of water in the tank?

Yes, a longer element will heat a greater volume/depth of water in the cylinder. The greater the depth of heated water, in the cylinder, the greater the heat lost from the surface of the cylinder.

 

[lostinthelight]

Yes, a longer element will heat a greater volume/depth of water in the cylinder. The greater the depth of heated water, in the cylinder, the greater the heat lost from the surface of the cylinder.

That's what I was thinking which would account for op energy use increase.

 

[ericmark]

Yes, a longer element will heat a greater volume/depth of water in the cylinder. The greater the depth of heated water, in the cylinder, the greater the heat lost from the surface of the cylinder.

Correct, but loses will be from the cylinder not pipe work in that case, so adding more insulation around the cylinder should reduce heat loss. But last 7 days, read on Friday (27) 16.48 kWh, Saturday (28) 16.49, Monday (30) 16.45 kWh. So there has been no reduction in the energy used after fitting the jacket.

Looking over one day, it is chance when the immersion switches on/off, so over 7 days we should be seeing a reduction, and I have not, so @polesapart and @flameport where it seems correct, adding the jacket has not helped reduce the losses.

 

[Munroast]

Since I have an iboost+ I can read what energy has been used yesterday, last 7 days etc. 16.48 kWh in last 7 days, 34.64 kWh in last 28 days, but not a good reading as there was a 9-inch immersion heater, now a 27-inch immersion heater been in around 2 weeks. Yesterday 2.80 kWh, today 2.3 kWh at 5:30 pm.

With the 9-inch immersion, we were using around 4.5 kWh for 7 days, never hit the 5 kWh for 7 days, but we were not really getting much hot water, the over temperature trip was tripping 3kW it seems is too much for such a small immersion, but I use solar to heat the water, so want enough stored to bridge the bad days. OK 35p average per day to heat DHW and £20.68 for the jacket, it will take some time to break even. At least 3 months.

But most don't know how much energy is being used by the immersion, I am one of the odd few that do.

Do you still have gas ?

If you still have gas then that is by far cheaper than electric, even if you have solar

I export leccy at 15 per unit, so if I use any of that for HW then it is in efect cotingme 15p per kWh

Gas is only 6p, and even an old boiler at 80% inefficiency would knock that up to 7.5p per unit, which is half the price of your electric

 

[ericmark]

Do you still have gas ?

No oil, and I have seen a huge reduction in oil use since using the immersion heater. I have no tank thermostat, so I had to guess how long to run the boiler for, I found ½ hour 4 times a week would give me warm water, but not hot water like I am getting now, and the boiler would turn off after around 20 minutes so more like 25 kWh per week used with oil, and I could simply turn down the thermostat with the immersion heater, so looking at 10 kWh extra to heat with oil.

The cost of oil v electric is not the only consideration, as the oil heats up pipes which go through me living room, so also heating up the living room more.

You are correct about the 15p/kWh I would get if exported, so I have set the iboost+ to also use off-peak, as that is only 8.5p/kWh, but there is no way to stop it using solar, and the cost of fitting a time switch instead of the iboost+ is not really worth it.

It does seem I got it wrong, I really did think the jacket would half the energy used, but it seems no, seems it does not save a thing, the airing cupboard is only just big enough for the cylinder, so maybe the cupboard its self was doing most of the insulation?

 

[Munroast]

No oil, and I have seen a huge reduction in oil use since using the immersion heater. I have no tank thermostat, so I had to guess how long to run the boiler for, I found ½ hour 4 times a week would give me warm water, but not hot water like I am getting now, and the boiler would turn off after around 20 minutes so more like 25 kWh per week used with oil, and I could simply turn down the thermostat with the immersion heater, so looking at 10 kWh extra to heat with oil.

The cost of oil v electric is not the only consideration, as the oil heats up pipes which go through me living room, so also heating up the living room more.

You are correct about the 15p/kWh I would get if exported, so I have set the iboost+ to also use off-peak, as that is only 8.5p/kWh, but there is no way to stop it using solar, and the cost of fitting a time switch instead of the iboost+ is not really worth it.

It does seem I got it wrong, I really did think the jacket would half the energy used, but it seems no, seems it does not save a thing, the airing cupboard is only just big enough for the cylinder, so maybe the cupboard its self was doing most of the insulation?

more insulation will save money, (half the costs was wildly over optimistic) but it will save money in the long term, these things are sometimes difficult to quantify but more insulation will reduce heat loss, and this will be a saving

 

[Harry Bloomfield]

more insulation will save money, (half the costs was wildly over optimistic)

It follows a rule of diminishing returns - the more you add, the less likely the extra will make much improvement. The saving half the costs, were likely based on a cylinder, with no insulation.

 

[lostinthelight]

ericmark said:
"but there is no way to stop it using solar, and the cost of fitting a time switch instead of the iboost+ is not really worth it."
I boost operates when it senses export which I suppose yours are metered as opposed to deemed ? so have you tried either removing the sensor off the mains wire or removing the batteries to see if it prevents solar signal to activate the boost?

 

[ericmark]

Possibly, had not considered removing batteries.

 

[ericmark]

Well it seems I am saving around 2 kWh per week, down from 16 kWh to 14 kWh, so around 30p/week cheaper.