Buffer Tank/Thermal Store addition to S Plan Plus & Unvented Cylinder?

[magician2905]

Hi sorry bit of an odd query here.
With the increases in energy costs now and in the future we are trying to find any way to reduce our exposure (retired couple on fixed incomes).
We are fortunate enough to have bought solar panels at the beginning of the year but as we head towards winter the solar generation will reduce and our use of gas will increase considerably.
Gas provides stove cooking, hot water and heating.
Our current system consists of an Ideal Logik Heat h15 Boiler which provides DHW and 2 zone central heating paired with a 210L Kingspan Trubune Xe Indirect Unvented Cylinder.
We don't want to rip out our existing system due to costs but if possible to add to it.
I have read various information regarding Buffer Tanks and Thermal Stores (including that a Buffer Tank can be a Thermal Store but a Thermal Store cannot be a buffer tank).
We currently have a good option to purchase a 90L Slimline Unvented Indirect Cylinder very cheap and wondered if it was possible to add this to our current system configured as a Thermal Store ie. within the heating loop, rather than for use with potable water?
Failing that, as the heating loop travels through the cylinder(s), can it be added to our current setup simply as an additional unvented cylinder?
We would then use excess solar and cheap rate "time of use tariff" to heat these via the immersion heating elements.
Hoping someone can help here.
Paul

 

[gmartine]

Just make better use of what you have...

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SolarImmersion monitors the PV production with a single clip on sensor and divert the surplus power for water heating, underfloor heating, battery charging etc.

solarimmersion.co.uk

 

[ShaunCorbs]

Or an eddi etc

 

[magician2905]

Thanks for your replies.
I am fully aware of the benefits of a Solar Immersion Diverter and would be looking to use one (or two) in the system.
Sorry if it wasn't clear what we are trying to achieve.

We are looking to use more of the Electricity available from Solar & Cheap TIme of Use Tariffs to reduce our Central HEATING cost not increase hot water production.

So as I currently understand a Thermal Store is effectively a hot water cylinder with a plate heat exchanger inside. This increases the surface area of the of heating loop inside the cylinder meaning that there is more heat transferred into the heating loop from the potable water in the hot water cylinder.

We are trying to discover whether we can add an additional unvented cylinder into the equation AND rather than using the cylinder in its normal operation - potable water which is heated by the heating loop - can we use the main compartment to act as a heat store for the Heating liquid. This would then be heated via an immersion element using a Solar Immersion Diverter/Time of Use Tariff.
I hope that clears that up.

 

[ShaunCorbs]

Better off using one of these and run it off your battery / cheap elec problem with cheap elec is it’s heated at night but will only last around 20-30 mins due to not being replenished

Slimjim Electric Flow Boiler | @electricheatingcompany

The SlimJim is traditionally installed in properties such as apartments, domestic dwellings, holiday homes & light commercial properties with limited space

www.electric-heatingcompany.co.uk

 

[magician2905]

This is what I think the diagram would look like....... (we have an S Plan + but that's mostly irrelevant for this query)

 

[magician2905]

Thanks for reply ShaunCorbs (tried using reply but kept insisting I was spamming.....)
That is a possibility but doesn't quite achieve the desired objective and there are a couple of pitfalls to that:
The battery which is getting installed will cover about 90% off the night time use (background appliances) that equation might change a little due to the cheap rate 4 hour tariff.
Whilst an Electric boiler is 100% efficient it is only aprox 27% efficient compared to a Gas Boiler due to energy density of gas (roughly 4 x) so until gas price reaches 4 times the cheap rate electric cost it doesn't work out. Its not there yet.....

 

[ShaunCorbs]

I think you’ve answered your own question

“Whilst an Electric boiler is 100% efficient it is only aprox 27% efficient compared to a Gas Boiler due to energy density of gas (roughly 4 x) so until gas price reaches 4 times the cheap rate electric cost it doesn't work out. Its not there yet....”

The store is exactly the same as an electric boiler / electric store

 

[magician2905]

I think you’ve answered your own question

“Whilst an Electric boiler is 100% efficient it is only aprox 27% efficient compared to a Gas Boiler due to energy density of gas (roughly 4 x) so until gas price reaches 4 times the cheap rate electric cost it doesn't work out. Its not there yet....”

The store is exactly the same as an electric boiler / electric store

I appreciate that you are trying to help and I welcome the discussion in general.

The current energy caps (due to increase in October 2022 and be reviewed every 3 months after that) are apprx Electric 27.63p/kwh Gas 7.282p/kwh (it depends on your location) represents Gas to Electric figure of 3.79x. Whilst it remains below 4x then it is still more efficient for us to use our existing Gas Boiler.

On Friday 26th the new price caps will be announced but considering that both electric and gas will both be going up it is still unlikely that we will reach the 4x.

Electric Store, eg batteries, yes as that stores energy in one form - electricity - to be utilized at a later time.
Electric boiler on its own, no - that is a point of use device - even being paired to batteries would be stretching the moniker of "thermal store".

There are many new style electric heating devices that use electricity to heat something up which can be used at a later time;

Electric Storage Heaters are an example that have been around since the 70's.
Tepeo Zero Emission Boiler (ZEB) - alternative to a Gas Boiler - uses electric to heat up a special concrete which can be used later to supply heating & DHW.
Caldera Warmstone (an alternative to LPG/Fuel Oil) uses some kind of Volcanic Rocks (similar to storage heaters but on a large scale) to provide heating & DHW.
Additional Solar Panels & Batteries would be great apart from the cost (anywhere from £1k each per 2kwh upwards depending on battery brand size etc) and roof orientation & space limitations.
Solar Thermal also isn't really ideal due to space, cost and the fact that it will only produce around 20% of heating during winter (typical is 70% across the year split something like 80/90% summer, 40% Spring/Autumn, 20% Winter)

However batteries would only provide additional Hot Water using a Solar Immersion Diverter or similar. They do nothing (or very little) to reduce the cost of providing wet central heating. They could be paired up with an Electric Boiler but that incurs additional cost.

If we could afford to rip out our current system and install something else we would but we don't have any more money for that.

An ASHP would run £16k approx less a government grant of ~£5k thats still £10/11k.
The Tepeo ZEB is still in development but considering its size and weight - about the size of a washing machine, 375kg in weight consequently needs to be floor mounted also wouldn't work. Our boiler is wall mounted in kitchen above worktop.

What gave me the idea was that ASHP regularly use Buffer Tanks as they are poor at supplying instant heat to Hot Water or central heating. Their principle is to maintain a steady heating state at a flow temp of 40-60'C, the lower the temp the better the efficiency.

A boiler (irrespective of Gas/LPG/Oil/Electric) generally operates at a higher flow temp but should be "tuned" to obtain the Delta T temp.

So we are trying to find out if it is possible to use a Thermal Store of Liquid within a Vented/UnVented Cylinder as an alternative connected to our existing Unvented system. This thermal store would be heated up using excess solar energy as available and every night from 12.30am to 04.30am and then used to reduce the heating burden on the central heating as and when required. We would try and heat the liquid in this Thermal Store to say 65'C and then through the day it will reduce in temp naturally (new cylinders are very efficient at retaining heat though). Should the heating be required to be turned on the boiler will not have to work as hard (ie. reduced gas useage) to heat the heating loop as there is an entire cylinder's worth of liquid being maintained as close to 65'C already.

Obviously the time when heating is required the most - winter - is also the time when the solar generation will be the least but 4 hours of cheap energy should make a significant dent in the gas being used to heat the central heating by our boiler.....?

 

[ShaunCorbs]

Problem is you will need a big store / buffer around 800l to heat your house for an hour so with a normal buffer you might only pre raise the temp 3-4 dc by the time it’s depleted so cost vs gas usage / not used vs a stnd system isn’t all it’s cracked upto be eg spending 1.5-2k and maybe saving £20 a month in winter at best

Better off putting the money in upgrading your system (well start to ) at a lower flow temp eg 50 flow etc as heat pumps correctly installed have a 1-4 ratio even a 1-5 if set to 45 flow