Smart Immersion Timer

[JohnW2]

...the heatloss from a modern cylinder is negligable....

I'm not sure what you would consider to be 'negligible'.

See my post #13 in this thread. When I improved the situation from 'very well insulated' (~200 mm insulation in addition to what the cylinder came with) to 'ridiculously well insulated' (600+ mm all around, including top and bottom), it reduced my energy consumption by something like a further 1.5-2 kWh/day, so goodness knows how much higher it was before I added the initial ~200 mm of insulation (i.e. with just the cylinder, as supplied).

Kind Regards, John

 

[Gasguru]

Having a separate 12kW gas boiler just to do the unvented cylinder allows me to check the gas consumption...it's £10 to£12 per month for the 2 of us.
That's a cylinder with the manufacturers 50mm insulation layer (many years ago cylinders came with 25mm).
The cylinder is topped up as and when, the temperature is maintained 24/7. The miniscule heat loss is useful for clothes airing and background heat for 6 months of the year.
The pipework has 19mm thick insulation.

50mm insulation is optimal...the payback for any more would be decades and makes negligable difference.

 

[JohnW2]

Having a separate 12kW gas boiler just to do the unvented cylinder allows me to check the gas consumption...it's £10 to£12 per month for the 2 of us.

Can you perhaps translate that into kWh so I can do a comparison?

That's a cylinder with the manufacturers 50mm insulation layer (many years ago cylinders came with 25mm).

As I said, in my case with the manufacturer's insulation (not sure how thick) plus ~200mm more of mine, my cylinder was still losing a lot more than a 'miniscule amount of heat', since loss reduced appreciably when I upped that 200 mm to 600 mm - using E7 electricity, that change alone reduced water heating costs by £5 - £6.50 per month, so the saving relative to 'the cylinder alone' must be much more than that.

Kind Regards, John

 

[Gasguru]

The hot water is using around 9 to 11 kWh a day @ 3.3 p per kWh for gas.
Are you serious with 600mm of insulation...is it rockwool or something similar.
Did your cylinder come with any factory fitted PU insulation?
Is it installed in a garage or loft?
Do the heatloss calculations...once you go beyond 25mm of closed cell insulation the heat loss becomes minimal.
Is your electrical monitor reliable? Perhaps the cylinders poorly piped such that heat can be lost through conduction.

 

[JohnW2]

The hot water is using around 9 to 11 kWh a day @ 3.3 p per kWh for gas.

Thanks. That's a fair bit more that I am (now) using - which averages out at 5-6 kWh per day. However, as you can see from the graph below, before I upgraded from ~200mm to ~600mm in around May 2018 I was using not that much less than you (around 8-9 kWh/day. I therefore would imagine that before I had even that extra 200 mm of insulation, I was probably using at least as much, if not more, than you ...

Are you serious with 600mm of insulation...is it rockwool or something similar.

Yep, deadly serious It is a large cupboard with a 'floor area' of roughly 2m x 2m, and at least 2.5m tall. The cylinder is sitting on a slatted shelf a couple of feet about floor level, and behind a slatted door (seperating it from an 'airing' area, which still gets reasonably warm!) and the entire cupboard, is crammed (around all sides of cylinder, and above and below it) full of insulation - basically everything I had to hand, but mainly rockwool and fibreglass etc.

Did your cylinder come with any factory fitted PU insulation?

Yep - although, as I said, I'm not sure how thick - quite probably only 25mm, since it's fairly old.

Is it installed in a garage or loft?

No, but it's in a part of the house which is not heated all that much - as you can see in the above graph, there is, even now, still a fair bit of seasonal variation.

Is your electrical monitor reliable?

Extremely reliable. Over the period since my electricity meter was last changed, it has recorded a total of about 32,000 kWh, and the total recorded by my monitoring system during that same period differs from the meter by only about 30 kWh (i. an error lf less that 0.1%). Although probably not clear from the title of the above graph, it essentially relates to just the immersion circuit.

Perhaps the cylinders poorly piped such that heat can be lost through conduction.

I'm not sure what you mean by 'poorly piped' but, other than when water has recently been drawn through them, the pipes are not warm to the touch any significant distance from the cylinder.

Kind Regards, John

 

[mattyc94]

What a pointless device...the heatloss from a modern cylinder is negligable.
The noise must be immense heating up such a small volume, gravity circulation through such small pipework will be hopeless.

I run a dedicated boiler just to heat the cylinder and it runs 24/7. Any minimal heat loss contributes to the space heating for 6 months of the year and it's nice to have a slight background heat in an airing cupboard .
What you should have is an immersion heater in the main cylinder to give a proper backup in case the boiler fails.

Do we assume Northern Ireland?
I've no idea about the regs there (Scotland make up their own) but anyhow a modern economical system should allow full control.

Unless electric is as cheap as oil (unlikely) all the hot water should be heated by the boiler...only use electric when the boiler packs up.

Independent time control of the cylinder heating with a cylinder thermostat on the side of the cylinder to turn the boiler on and off once up to temp.

I guess Nest can control the rads but a TRVS should not be fitted where the Nest resides (otherwise they will fight each other).

Are there really no zone valves? How do you stop the cylinder from heating when the radiators are on?

Thanks for the reply.

1. Immersion Heater in the main cylinder - I'm not sure why the heater lives outside of the cylinder. Likely cost cutting from the original builder or the last owner. Will maybe look at a tank swap at some point.

2. NI - yes.

3. Independent time control of the cylinder heating with a cylinder thermostat on the side of the cylinder to turn the boiler on and off once up to temp. - OK I'd never heard of a cylinder thermostat before. I'll have to do some reading up but running the wiring back to the Nest thermostat may prove difficult as the `heatlink` lives on the floor below at the other side of the house.

4. Are there really no zone valves? How do you stop the cylinder from heating when the radiators are on? - Not that I am aware of. The cylinder always heats when the rads are on. I have no control over this.

 

[Gasguru]

The small cylinder with the immersion is a regional idea...and pretty pointless. Looks like the sort of thing semi retired diyers dream up.
Have a look at Honeywell S plan. The hot water just needs a cheap timeclock, cylinder thermostat and zone valve. No need for complicating it with smart stats.
These smart stats are pointless unless you have an efficient system to start with...no point adding the stat to save a few % when a fully pumped system with TRVs etc will save orders of magnitude more.

 

[mattyc94]

Just to follow up on this thread. I have carried out the following:

• Jacket added to Cylinder
• Nest swapped out for Tado with TRV's. Not proper zone's I know but gives a degree of more control
• Timeguard 'Smart Immersion' in place of existing switch

Thanks all for the tips and insight.

 

[Harry Bloomfield]

Those debates have been going on for decades. I've never really been able to make any sense (in terms of the laws pf physics) of the argument that some people try to produce that it can actually be cheaper to leave an immersion on for 24/7 but, as others have been said here the effect (additional cost) of leaving it on for 24/7 get smaller as the amount of insulation increases.

I agree. The hotter the cylinder contents, the greater the heat loss, the more frequently it will cut-in to reheat to bring it back up to stat temperature. That loss can be mitigated with good insulation, but it cannot be stopped. The only argument for having it on for an extended period, is one of convenience of having a cylinder of hot water ready to use, versus the small cost of maintaining the temperature if it is well insulated.

My cylinder is reasonably insulted and in my airing cupboard. The cupboard gets warm, which I think says it all.