Wanting to reduce gas usage - New Heating Design Circuit - will it work?

70sbudgie

Thank you @QrizB and @Solarchaser Yes it seems I was missing a fundamental of heat stores!

Is it this function that makes them more efficient? Are they more efficient?

Presumably then, it would take a couple days to get the heat store up to temperature.

Do your calculations for heat requirements not need to include DHW use? Or is that the calculation that gets you to the 500l tank - the total energy you can store?

Thank you for so patient with my questions.

Solarchaser

Sorry 70sbudgie,  I think our wires are a little crossed.
Its not that heat stores maintain themselves at that temperature,  its just they would not be useful under that temperature,  so thr assumption would be that you would either A. Not use them below that temperature,  or B. Set something up to start the heating process when it went below that.

If the store had never been used and you had just filled it with cold water at say 18C which my cold water is just now, then it would take 13kwh to heat the 500l to 40c, or a smidge over 2 hours with both 3kw elements running. 

This is just a simple water tank storing 500l of water, there is nothing fancy about it, using it as a thermal store really is just saying the water in the tank will not be used as potable water as you would normally expect with a hot water tank. The water in the tank will stay in the tank.

The only thing thermal stores hold over a humble hot water tank is increased insulation. 
And for me, I'm simply adding more insulation around it.
You could say this makes them more efficient storers of heat as less heat should be lost from the tank.

zeupater

70sbudgie said:

[ ... ]

What sort of timescales are you thinking of? I received my E7 October rates from Octopus at the weekend and was interested to see the day/night differential actually increase. I'm not convinced that the investment in the UK electricity network over the next 10 years is going to be suffient to remove the day / night differential. And if if it does, I think it will be replaced by a mix of different time of use tariffs. So having a heating system that can be flexible about charging / discharging will be beneficial. 

Perhaps it might be worth considering how to future proof the system - could an A2WHP replace the boiler?

Hi

As mentioned, the timescales are fully dependent on the take-up of the technologies mentioned and the steepness of the adoption S-curve that these kinds of 'disruptive' technologies will follow ...

My guestimate is that for EVs, even though sales have increased significantly we're only starting to notice the effect of exponential growth, which many don't perceive as drastically shortening the adoption timelines ... think of it this way:- in 10 years time the vast majority of UK vehicle sales (well in excess of 90%) will likely require charging & it could be possible that by then ~33%-50% of all passenger & commercial vehicles on UK roads will be electrified and the majority of energy required to charge them will likely be provisioned overnight. The issue here is that the typical overnight demand trough approximates to ~15GW below daytime peak levels, so allowing for 'peak rate' tariff times we're likely only looking at somewhere around 10-12GW of underutilised provision to tap into, which sounds a lot, but only represents ~1.5million vehicles being charged at ~7kW at any one time ... that's out of a total of around 40million currently on UK roads .. this in itself explains the very reasoning for introducing 'smart' charging regulations for EVs to prevent the creation of a new overnight demand peak ... https://www.gov.uk/guidance/regulations-electric-vehicle-smart-charge-points ...

I'm pretty sure that the simplistic and very basic 'first cut' logic would convey that it's more than sensible to predict that at some time pretty soon the current day/night demand differential seen as a trough in typical UK power demand curves (eg Gridwatch) will start to fill and that once started the speed of EV uptake will be the controlling factor in both scale & existence of overnight cheap electricity tariffs, and that's even before considering domestic battery & heat-pump uptake.

I agree with the comment that TOU tariff differentials will come into play, however, it seems that in similar situations where TOU has been implemented, the resultant was one more consistent with having to wield a big stick (punitive peak demand tariffs) because the opportunity to offer carrots (low prices overnight) expired, sometimes due to lack of capacity, but unfortunately sometimes because it could simply be employed to enhance supplier margins (per Canadian hydro smart meter customer tariff experiences!).

I fully agree with the point regarding the ability to future proof any current investment with the ability to easily switch the storage energy source to an alternative, be it heat pump, biomass or whatever, but that's simply a personal decision for whoever would be looking to take this approach to heat provision.

HTH - Z           

Freepost

Solarchaser said:

Thanks for your information,  I realised I read 500L telford and just assumed horizontal, my mistake.
So assume you are going for this?
https://www.cylinders2go.co.uk/shop/renewable-energy/telford-tempest-500-litre-twin-coil-solar-indirect-unvented-cylinder-twin-immersion/?gclid=Cj0KCQjw7KqZBhCBARIsAI-fTKKX4GfLjbbSVCzpu3R8IBMLy8mv4SjBcG_Dlbd4yhPHwogLVSXSb7saAh3ZEALw_wcB

Or some variation of it?

My coils are looped to around 1/3 of the bottom of the tank, but thats a horizontal tank, with a vertical tank that you specify, you could easily have the coils at the top, or say one at the top and one 1/3rd of the way down...  well I say that, I assume you could, my questions were all around the horizontal tanks, but I don't see why you couldn't.

For reference I used this guy on ebay
https://www.ebay.co.uk/itm/193247849462?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=AlZ0LTyyRca&sssrc=2349624&ssuid=DtbsXk1pRsq&var=&widget_ver=artemis&media=COPY as he has a direct line to telford and their custom build service 

This is what my coils look like inside the tanks, 6.9m long of 28mm coils (biggest and longest they did) equivalent to 25kw of heat transfer.



What you will hopefully see from those is that there are various straps going from the coils to the tanks to hold them in place.
So if you imagine your coils coiling around the top circumference of the tank,  they will always be at the hottest part,  say you use that one for central heating, and one closer to the middle for hot water, as your hot water doesn't need to be anywhere near as hot as your central heating radiators.

The top of the tank being hot and the bottom being cold is called stratification,  to stop this, or mix it up, you use a pump to destratify, a destratification pump, or in my case a central heating pump doing that job, but I need that really because of the cylinder being horizontal,  you probably won't.

2x 6kw heaters for 4 hours will get you 48kwh as you said, and you can specify 6kw heaters with the bespoke service, I did originally, (or buy them yourself of course) however solar diverters on the market will not run a 6kw element, as the resistance is too low, they will only run a 3kw (or sometimes a 3.6kw), so if your plan hinges on solar heating, id suggest perhaps 1x 3kw and 1x 6kw, but now in 4 hours of cheap rate you can only do 36kwh of heating.
This will dramatically reduce your heating from gas and will likely cover all but your coldest 2-3 months I'd wager, so probably not as big a downer as you might think.

The pumped loop, for me, I dont think it's necessary, when I changed to the tank I timed the furthest away hot tap, up around 4M and around 8M away horizontally and it took 11 seconds for hot water to come through.
I then changed the hot water piping from the tank to the mixer down from 22mm pipe to 15mm pipe and that dropped to around 7 seconds (that is on full flow though, takes longer on less flow).
Hot water circulating constantly at decent heat can be problematic in terms of legionella,  especially for dead legs or nearly dead legs, like the bathroom that isn't much used, imo it's safer to let those pipes be cool when they are not being used... plus it saves you a pump.

In terms of being a novice, honestly, me too, it's been a big learning curve all of this stuff, and I only know what I know, and picked up some bits and bobs from various jobs (like legionella from time working in hospitals), so if it seems like I'm trying to preach to you or similar, I truly apologise, I'm just trying to give you my experience. 

Anything mechanical will use energy, and anything mechanical will eventually break down, and there is always that principle of KISS, keep it simple stupid.

With that in mind, I'd say that if you spec a custom build with two coils, you negate the need for two plate heat exchangers and two pumps, which I'd imagine will end up around cost neutral (additional cost of custom tank) when you add it all together, but will be a simpler system.

If you then have the cold and hot inlets/outlets plumbed to your system boiler, you have your heating circuit without a 3rd coil.

On the flow detector, I haven't got mine to work.
It's essentially a paddle in the water flow, but the truth is that most of the time running a tap doesn't actually use very much water,  most tap hoses have an inner diameter of no more than 8mm, so trying to detect that flow in a 22mm pipe didn't work, and in a 15mm pipe didn't really work either. If I could convince you to remove the loop, then there is no need for the sensor either. But obviously it's your system and you need to decide how important instant hot water is.

It's reassuring that you found the same 45min *facts* about the 500l tank on searching, I have to admit it caused me to falter, but I eventually pressed on.

I couldn't find any real calculation for taking radiators of various sizes and including piping to get them from say 15C to say 55C and hold them there for hours in any kind of quantifiable way.

It's not really that cold just now, but the wife has had the heating on for the last few days for between 3 and 5 hours each night and around an hour each morning... roughly.
So I can emphatically and categorically rule out the 45Mins, but I do need destratification as I'm drawing heat out from one side of the tank, and unfortunately the myenergi add on board that does that, is still on back order for another couple of weeks (so far).
At one point a few nights ago, the tank was down to 58C in its mid point after the heating had been on 4 hours, from a starting point of 78C iirc, I told eddi to put on the 3kw element on the other side of the tank (I'm still messing about with what element to prioritise and getting the heating cut off at the right temperature) and within 5 mins I seen the tank go down another 5C to 53C, which essentially meant that the heater was causing some of the water to move about showing the central heating side of the tank was actually colder than it appeared.
For that reason I can't really do full facts about temperature until I'm destratifying while central heating is running as that's the only way I can see an accurate temperature of the whole tank.

Finally a couple of notes.
The telford cylinders come with extra bits.
They come with an inlet set, which is basically a pressure regulator which is set at 3 bar, so you don't need to buy that.
They also come with an equivalent expansion vessel, so 50L for 500l tank.
They also come with 1 motorised valve , a stat and a tundish (think simple overflow indicator)

That's got to be the longest post I've ever done.
I really hope it makes sense, and helps a bit.

Hi SC

Thank you for the links , I will be speaking to the guy this week, both links being to the same company, one direct the other via the auction site.

I hadn’t seen the coils in a tank before, well not since the old copper tanks many years ago where the coil was copper tubing. You say the coils could be suspended in the top I’ll check that out. It certainly looks like I may be able to dispense with the plate heat exchangers and consequently the associated pump and motorised valve. Also, the running of DHW would have no impact on the central heating, together with the 25kW of heat transfer looks very interesting. Although I am getting a little lost with the idea of two coils where couldn’t I just use the water in the tank for DHW? Of course it would probably be too hot and would need to be blended.

A good tip on the resistance of the 3 vs 6kw immersion heaters. With regard to the hot water loop, I have plumbed for it but I may not use it. Most of the pumps that I have seen for this application are equipped with timers so that you can set it for a couple of hours in a morning and again in the evening but there is always going to be a time when the pump isn’t running and consequently have to wait the 15 or 20 sec for hot water to arrive …… what an inconvenience that would be;-) …. I think it will be left out for the time being.

I am most definitely an advocate of KISS

Again, you have mentioned the coils and perhaps having the system boiler connected directly to the tank without the third coil, if I go for this then I most definitely need a coil for the DHW but wouldn’t I also require a pump to “mix it up a bit” or is that not necessary?

It’s good to know that you also had the 45mins fact thrown at you, it did stop me dead in my tracks for a day or so!

Thank you very much

F.

Freepost

70sbudgie said:

Freepost said:

2) Why a 500l tank, and why horizontal - My current gas consumption in the depths of winter (January) is around 70kW/day. With 2 6kW immersion heaters running for a 4hr period I can get near enough 50kW into the tank and the gas boiler will have to make up the short fall until I install batteries. Further to this and to give some idea about my arithmetic I used a formula of Volume of tank x 4 x temperature rise / 3412 = Power (kW) required from https://www.boilerguide.co.uk/articles/immersion-heaters where the tank is 500l and my available energy in a four hour period from the immersion heater is 48kw then a little bit of algebra delivers approx 80°C. .... The tank will be mounted vertically.

To me, this looks like an 80°C temperature rise? This seems a lot and might be problematic in the summer, when the cold water feed might be 15°C, or are you just calculating for the max and expect to modulate?

There also seems something not quite right about your units. You mention 48kW in a 4 hour period as the energy available. I think you mean 48kWhrs? If you were to switch to the 3kW + 6kW immersion heater as @Solarchaser suggested to utilise solar, then when doing so, you would be heating at a different rate. You may find that even in winter, a couple kWhrs from solar will be enough to get you closer to the 80° temp rise. I don't imagine there will be too many days when the 36kWhrs from Go wouldn't be enough. And its not like you can't do a short peak rate or gas boost. And don't forget that the temp rise is on the cold feed water temperature, not the ambient air temperature - there is less range on the former.

My gut feel is that your calculations have oversized your required capacity, but I don't know if that is because I am struggling to follow all the detail?

Hi 70sbudgie,

I don't think that I require an 80°C temerature rise I just did a little bit of algebra on the formula with 2 x 6kW immersion heaters and that delivered 80°C. Also, I believe that the immersion heaters are limited to 70°C.... but I would most definitely have to modulate!

With regard to the 48kW or kWh, I think you are right but in my defense I only used the formula as presented and that stated kW;-)

Regards

F.

Freepost

michaels said:

So definitely it will all work, just need to be clever with the mixing.  Not sure if you need the second heat exchanger or can just use the tank flow for the rads.

Hi michaels

Thank you for commenting on your experience with Plate Heat Exchangers, it's good to hear that the system worked.

With regard to the second PHE, my thoughts there were partly to do with keeping the central heating sludge out of the tank, maybe it's not so important if you use a good magnetic filter.

Thanks

F.

Freepost

zeupater said:

Hi

A very important consideration would be your expectations for the future of 'cheap rate' overnight electricity being available at a level of differential which supports the logic you've used.

Hi zeupater,

it's very good point and I am hoping that the system can use either energy source, there are no guarantee that Octopus won't at some point dispense with go!

Thanks.

F.

Solarchaser

Freepost said:

Solarchaser said:

Thanks for your information,  I realised I read 500L telford and just assumed horizontal, my mistake.
So assume you are going for this?
https://www.cylinders2go.co.uk/shop/renewable-energy/telford-tempest-500-litre-twin-coil-solar-indirect-unvented-cylinder-twin-immersion/?gclid=Cj0KCQjw7KqZBhCBARIsAI-fTKKX4GfLjbbSVCzpu3R8IBMLy8mv4SjBcG_Dlbd4yhPHwogLVSXSb7saAh3ZEALw_wcB

Or some variation of it?

My coils are looped to around 1/3 of the bottom of the tank, but thats a horizontal tank, with a vertical tank that you specify, you could easily have the coils at the top, or say one at the top and one 1/3rd of the way down...  well I say that, I assume you could, my questions were all around the horizontal tanks, but I don't see why you couldn't.

For reference I used this guy on ebay
https://www.ebay.co.uk/itm/193247849462?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=AlZ0LTyyRca&sssrc=2349624&ssuid=DtbsXk1pRsq&var=&widget_ver=artemis&media=COPY as he has a direct line to telford and their custom build service 

This is what my coils look like inside the tanks, 6.9m long of 28mm coils (biggest and longest they did) equivalent to 25kw of heat transfer.



What you will hopefully see from those is that there are various straps going from the coils to the tanks to hold them in place.
So if you imagine your coils coiling around the top circumference of the tank,  they will always be at the hottest part,  say you use that one for central heating, and one closer to the middle for hot water, as your hot water doesn't need to be anywhere near as hot as your central heating radiators.

The top of the tank being hot and the bottom being cold is called stratification,  to stop this, or mix it up, you use a pump to destratify, a destratification pump, or in my case a central heating pump doing that job, but I need that really because of the cylinder being horizontal,  you probably won't.

2x 6kw heaters for 4 hours will get you 48kwh as you said, and you can specify 6kw heaters with the bespoke service, I did originally, (or buy them yourself of course) however solar diverters on the market will not run a 6kw element, as the resistance is too low, they will only run a 3kw (or sometimes a 3.6kw), so if your plan hinges on solar heating, id suggest perhaps 1x 3kw and 1x 6kw, but now in 4 hours of cheap rate you can only do 36kwh of heating.
This will dramatically reduce your heating from gas and will likely cover all but your coldest 2-3 months I'd wager, so probably not as big a downer as you might think.

The pumped loop, for me, I dont think it's necessary, when I changed to the tank I timed the furthest away hot tap, up around 4M and around 8M away horizontally and it took 11 seconds for hot water to come through.
I then changed the hot water piping from the tank to the mixer down from 22mm pipe to 15mm pipe and that dropped to around 7 seconds (that is on full flow though, takes longer on less flow).
Hot water circulating constantly at decent heat can be problematic in terms of legionella,  especially for dead legs or nearly dead legs, like the bathroom that isn't much used, imo it's safer to let those pipes be cool when they are not being used... plus it saves you a pump.

In terms of being a novice, honestly, me too, it's been a big learning curve all of this stuff, and I only know what I know, and picked up some bits and bobs from various jobs (like legionella from time working in hospitals), so if it seems like I'm trying to preach to you or similar, I truly apologise, I'm just trying to give you my experience. 

Anything mechanical will use energy, and anything mechanical will eventually break down, and there is always that principle of KISS, keep it simple stupid.

With that in mind, I'd say that if you spec a custom build with two coils, you negate the need for two plate heat exchangers and two pumps, which I'd imagine will end up around cost neutral (additional cost of custom tank) when you add it all together, but will be a simpler system.

If you then have the cold and hot inlets/outlets plumbed to your system boiler, you have your heating circuit without a 3rd coil.

On the flow detector, I haven't got mine to work.
It's essentially a paddle in the water flow, but the truth is that most of the time running a tap doesn't actually use very much water,  most tap hoses have an inner diameter of no more than 8mm, so trying to detect that flow in a 22mm pipe didn't work, and in a 15mm pipe didn't really work either. If I could convince you to remove the loop, then there is no need for the sensor either. But obviously it's your system and you need to decide how important instant hot water is.

It's reassuring that you found the same 45min *facts* about the 500l tank on searching, I have to admit it caused me to falter, but I eventually pressed on.

I couldn't find any real calculation for taking radiators of various sizes and including piping to get them from say 15C to say 55C and hold them there for hours in any kind of quantifiable way.

It's not really that cold just now, but the wife has had the heating on for the last few days for between 3 and 5 hours each night and around an hour each morning... roughly.
So I can emphatically and categorically rule out the 45Mins, but I do need destratification as I'm drawing heat out from one side of the tank, and unfortunately the myenergi add on board that does that, is still on back order for another couple of weeks (so far).
At one point a few nights ago, the tank was down to 58C in its mid point after the heating had been on 4 hours, from a starting point of 78C iirc, I told eddi to put on the 3kw element on the other side of the tank (I'm still messing about with what element to prioritise and getting the heating cut off at the right temperature) and within 5 mins I seen the tank go down another 5C to 53C, which essentially meant that the heater was causing some of the water to move about showing the central heating side of the tank was actually colder than it appeared.
For that reason I can't really do full facts about temperature until I'm destratifying while central heating is running as that's the only way I can see an accurate temperature of the whole tank.

Finally a couple of notes.
The telford cylinders come with extra bits.
They come with an inlet set, which is basically a pressure regulator which is set at 3 bar, so you don't need to buy that.
They also come with an equivalent expansion vessel, so 50L for 500l tank.
They also come with 1 motorised valve , a stat and a tundish (think simple overflow indicator)

That's got to be the longest post I've ever done.
I really hope it makes sense, and helps a bit.

Hi SC

Thank you for the links , I will be speaking to the guy this week, both links being to the same company, one direct the other via the auction site.

I hadn’t seen the coils in a tank before, well not since the old copper tanks many years ago where the coil was copper tubing. You say the coils could be suspended in the top I’ll check that out. It certainly looks like I may be able to dispense with the plate heat exchangers and consequently the associated pump and motorised valve. Also, the running of DHW would have no impact on the central heating, together with the 25kW of heat transfer looks very interesting. Although I am getting a little lost with the idea of two coils where couldn’t I just use the water in the tank for DHW? Of course it would probably be too hot and would need to be blended.

A good tip on the resistance of the 3 vs 6kw immersion heaters. With regard to the hot water loop, I have plumbed for it but I may not use it. Most of the pumps that I have seen for this application are equipped with timers so that you can set it for a couple of hours in a morning and again in the evening but there is always going to be a time when the pump isn’t running and consequently have to wait the 15 or 20 sec for hot water to arrive …… what an inconvenience that would be;-) …. I think it will be left out for the time being.

I am most definitely an advocate of KISS

Again, you have mentioned the coils and perhaps having the system boiler connected directly to the tank without the third coil, if I go for this then I most definitely need a coil for the DHW but wouldn’t I also require a pump to “mix it up a bit” or is that not necessary?

It’s good to know that you also had the 45mins fact thrown at you, it did stop me dead in my tracks for a day or so!

Thank you very much

F.

Hi Freepost,  to be honest I didn't realise that guy was cylinders to go, I actually just googled 500l vertical cylinder twin coil and that was the first link.
I contacted him through ebay where his trading name was copper cylinders, so my intention was to give you two different company links. Meh!

For me looking at your proposed system, and mine as it is, I look at it as 3 separate circuits. 
1. The tank water/boiler
2. Central heating
3. Potable water

So keeping them separate would require two coils, but if you want to have the boiler and potable water together, fair enough, my thoughts on the tank is that its essentially dirty water, but its designed for it to be potable, so you can obviously use it as such.
My only concern would be if you were running the tank from solar for 6 months of the year say, then the water in the boiler and in the pipes would not move, this would be stagnant water and ripe for bacterial growth, so you wouldn't want to be drinking it, but most people won't be drinking hot water anyway.... in the back of my mind is the kids doing their teeth in the winter will probably blend in a bit of hot water.
You could probably negate this by running the boiler for say an hour a week, but for me, I wanted there to be as little chance as possible of any bacteria in the hot water, and a coil in very hot water does this.

Yes you are correct that the water out of the tank could be very hot, and so you would need to blend this with cold to have a consistent comfortable hot water.

The mixing up I need is because my tank is horizontal,  and my coils dangle into the bottom third of the tank, yours being vertical you will probably benefit from the stratification,  as you may have a half cold tank, but still get the heat you need for half the "cost", so in a vertical tank with the coils at the top, you will still have your coils in the heat.

I guess the only question mark would be where you have your heaters, id suggest 1 half way, and one at the bottom, normally heating by solar for the half way one means have of your tank will be hot using half the amount of energy more or less, and only when you have excess solar that you would power the bottom heater.

The I boost and myenergi eddi solar diverters both do sequential heating for this very reason.

michaels

I remembered who supplied our cylinder, DPS Heatweb.  Unfortunately they don't seem to be around anymore and the engineering drawings of the tank plus heat exchanger were on their webportal so also no longer accessible.  Apologies.

I think our set up was pretty like this:



Although only one heating zone and we didn't have the 'heat dump' radiator circuit.

Also we had a horizontal tank for loft space reasons with the 'diffusion' devices as per this image to prevent tank mixing which might impact on hot water flow rate, the aim was to keep the top of the tank as hot as possible for as long as possible using the fact water is naturally a good insulator are will allow the top layer to be hot whilst the lowest layers are cold.


Note the two thermostatic mixing valves in the first image, one on the boiler circuit to allow the boiler return to be at the most efficient temp for condensing and the other on the hot water supply.  Also note the flow switch controlling the pump on the plate heat exchange circuit. We may also have had a thermo mixer on the radiator supply to allow the rad temp to be lower than the tank temp.  I don't remember having 3 pumps so possibly the rad and boiler circuits were combined in some manner with a diverter valve or it could just be a memory thang.  Note no coils at all!

EricMears

michaels said:

I remembered who supplied our cylinder, DPS Heatweb.  Unfortunately they don't seem to be around anymore and the engineering drawings of the tank plus heat exchanger were on their webportal so also no longer accessible.  Apologies.

Still seem to be at https://www.heatweb.co.uk