Ditching gas, going electric immersion only, a wee project

Solarchaser

I suppose what I'd say is there are thermocouples and there are thermocouples. 

I have rather a few years experience of making and remaking, replacing and being let down by thermocouples. 
You are of course correct that many are made for industrial applications, and can be robust, but they don't tent to be cheap.

However if you are looking from the point of view of precision, then I'd definitely agree.
But I actually don't really need precision.

In the brighter months I'll have a massive excess of solar, so I'll be supping it up until the tanks are hot hot, and that should carry me over any dull days, so it won't matter too much.

In the darker months I'll be giving the tanks 36kwh of heat every night pretty much regardless of what they are at (within some reason).
Going above 100C will trigger the T&P valve, but if I can set the thermostats at 90C and 95 reset I think I should be fine.
My problem right now is they are set somewhere around 70C ish, and they are all different.
Standardisation of 85-90C I *think* will be fine. 

What I need is a bit of headroom above 40C to be able to store 36kwh of heat, and I don't have that with them set at 70C odds

The other thing is my elements have these thermostats as part of their power circuit, they spade into the elements, so the safety is part of the circuit, and the fact its mechanical takes away the issues of electronic shorts, pcb failures etc, and the secondary cut out, for something like this, I like an extra layer of safety.... or more accurately I wouldn't want to lose a layer of safety which I would do employing an outside controller.

I guess I see thermocouples as an elegant, precise solution,  but really I have a dumb but reliable one already installed.
The other part is obviously cost.
This whole thing was at least partially about saving money... don't get me wrong, it's as much a project as a cost saving, but I don't want to be continually throwing money in.

Anyway today I picked up a calibrated heat block (thanks old workplace) which I can set to the heat I want and insert the thermostats I have, and use their mechanical screw to set them to where I want.
This should address the variation in switching.
I'll be having two elements controlled by 1 Eddi, and so a little hysteresis isn't a bad thing in terms of spreading the load between the two rather than the 1st one always kicking back on quickly, though to be fair the destrat running would probably work against the load spreading. Hmm
Got me thinking, perhaps I should put a delay in the destrat to encourage the second element to have more working time?? Dunno, one to ponder there.

Interestingly... or perhaps not, it's a heat block I used to use to calibrate thermocouples, accurate to 0.01C so should be good enough for my plans I guess, well I'll find out soon.
I plan to test this out at the weekend after replacing the failed one way valves in the tanks.

Fingers crossed the thermostats are more accurate than we both suspect they are 😉

Solarchaser

Changed the single check valves /one way valves for double check valves yesterday,  and with a fairly sunny day today was able to heat the tank to 72C to test if they held back the thermosyphon. 
This was the old single checks


And this is the double checks

The piping before and after are insulated, which is why the pump looks warmer, but its cool to the touch, so looks like mission accomplished on that part.

So just the central heating to do, adding double checks and U's.
It's mostly done, but sore knees and leg cramps have convinced me to give it up for today.

Freepost

Hi SC,

I can clearly see that installation of the double check valve solved the problem around the pump but I don't understand why. If I am correct, a double check valve is basically just two single check valves connected in series, both types of check valves require back pressure to close, so if the pump isn't running then the back pressure should close the valve feeding the pump. Perhaps it's a case of the single check valve doesn't fully close but pressure between two check valves would be greatly increased ..... I don't know?

Also, excuse my ignorance but what does the 'U' do for you?

F.

Solarchaser

Hi Freepost, id say first off there are two different types of check valve, one type is closed by back pressure, the other (which I bought) is closed by a spring, so doesn't require back pressure.

I can only pass on what I've read rather than knowing, but basically a single check valve when it shuts can let a little fluid through, the double check valve stops this,  however this isn't really what's different for me.
Single check valve opened really easily, not sure of pressure, but tiny amounts. 
The thing about heat is it rises, the elements in the main tank are at the bottom, and when the heat rises it basically pushes up through the water, and more cold water moves down in its place... or that's how I understand it, and if that's wrong, I'm happy to be corrected.

So it seems when the heat rose it pushed through the single check valve with ease.
The double check valve requires 300mbar to open (0.3bar) and so the thermosyphon isn't enough to push through the valve.

On thermal stores they usually state if they are to be added into the heating circuit via heat exchanger,  they should be situated at the top of the circuit,  I can only assume this is also for thermosyphon. 

Which brings me onto the U's, they are two fold.
1. Heat rises, so if you put in a point in the system where the pipes go down, heat cannot syphon through, the U does this (so I've read, and logically it makes sense)
2. I've added double check valves to the start of the heating circuit, so the assembly is now too tall to have the pump and return on top of the check valves (I'd hit the ground floor floor boards) so I have to bring the piping down to still have the pump and magnetic filter vertical, you can argue I could put them horizontal, but I feel they both work better as vertical units.

I finished this off (I hope) tonight and pressurised the heating system, and ran the central heating for about 40 mins.
All seems to work well, though the furthest away radiator is taking a bit longer than usual to heat up, so I think I need to close the return valves on the other radiators a little to increase flow to it.

I noted that when running, the temperature in the tanks dropped approximately 0.9C -1C over 10 mins.

I didn't take note of the start temps, (was running around bleeding rads and checking for leaks) so don't know what the initial drop rate is, and obviously end of August is milder weather than mid December,  so I'd think it will use more then, but for right now it would basically be 3kw per hour to keep the 500l tank at the same temperature while it's running
(1kw for 1 hour in 1000l raises by 1C, so 3kw in 500L raises 6C in an hour, which will be same as I'm using)

Freepost

Hi SC,

Thanks for the explanation, that makes sense and with the 'U' almost common sense;-) I didn't know that there are two different types of check valve, again I'm educated.

 With the drop in temp of 1°C over 10mins, that 6°C over an hour when running, I assume as the room temps increase that rate of drop will decrease, will you have enough stored energy to get you through the day? I'm most definitely not trying to pore cold water on your idea/project, I think it's great and of course, you will have done the maths, perhaps several times.

 Excellent stuff, I wish you all the best.

F.

Heedtheadvice

"bleeding rads"

Language! :-)

Solarchaser

I have done the calculations and they are by no means fool proof.
In fact they really need for a few assumptions to be correct. 
And you know what they say about assume.
Last year I used 50kwh of gas per day.
Combined hot water and heating.
I assume... the gas to be 75% efficient so I need 37.5kwh to do the same job.
I can put in 36kwh in the 3 hours of octopus go faster.

I've added pex loops at the back of the livingroom to heat it up faster as I assume I'm using more heat heating the rest of the house before the livingroom. 

I assume I'll use less electricity on electric showers,  so I'll have excess in my batteries to top up the tanks if need be.

I dont think it can be a total failure, but it can definitely be an expensive solution 

70sbudgie

Can I recommend Eco camel shower heads for your showers? The power shower replacement limits the water flow to 7l/min (I think). I know that they also do an electric shower version, though I don't have enough details to share. My husband usually just tolerates my eco mods, but the showerheads is something that he even commented on being an improvement!

Solarchaser

You can, and you did 🙂
You recommended the shower heads on the 5th or 6th post 👍

70sbudgie

Solarchaser said:

You can, and you did 🙂
You recommended the shower heads on the 5th or 6th post 👍

Sorry for repeating myself!