advice please,add a cylinder to combi to utilise solar pv

[numnutss]

Hi all, ive been googling for days now and still no closer to getting a plan together,
Ive got a vaillant ecotec 837 combi which has been serviced regularly and wont be replacing,
i just had a 4kw solar pv system fitted along with an immersun gadget which is designed to make the most of any electricity that would be going back into the grid.
Im looking for a way to connect a cylinder with an immersion into my combi,

Is it possible to make it into a storage combi?
Any advice greatfully recieved

 

[Agile]

I am a little confused at what you are trying to achieve!

If you have a feed in tariff of over 22p per unit then why not takje it?

To heat your water you buy your gas at 4p per unit !

It seems that you want to lose your feed in tariff !

Tony

 

[numnutss]

Hi tony thanks for showing an interest, you might find this hard to believe as i did, you get the feed in tarriff whether or not you use the electric thats been generated,
I'm just looking at ways to cut the bills.

 

[muggles]

Is it possible to make it into a storage combi?

Not in the way you want to do it I don't think, no. A bunny might come along and say different, but AFAIK your boiler can't take preheated water and it would need to be able to in order to achieve your aim relatively simply. There is, I think, a more complex solution involving some very interesting motorised valve arrangements, but you'd be in danger of spending so much money doing it that it would take several years to recover the installation cost.

 

[Agile]

Yes, I did rather think that although its not logical.

The best way to save is to have a large unvented cylinder ( 300 li ) fitted in the feed water to the boiler. But most combi makers don't advise it because of legionella risks and because the boiler cannot control its output temperature properly.

The reality is that you have too much energy in the summer and not enough in the winter!

Tony

 

[numnutss]

Hi muggles, yes cost is an issue, i was hoping to be able to do what is with a used cylinder once i know the best way to tackle it.

I contacted vaillant and the boiler is OK as long as the input water temperature is below 60 degrees c.

I also read about the legionaires issue with wras, that's the big problem.

This is what I keep going back to
[urlhttp://www.solartwin.com/solartwin-features/basic/plumbing-in-solar-thermal-to-a-combi-boiler-combination-boiler-geyser[/url]

http://www.solartwin.com/solartwin-...l-to-a-combi-boiler-combination-boiler-geyser

If you switch the solar hot water panels for solar to an immersion in the cylinder.

 

[ScottishGasMan]

I would have a concern fitting the output of a cylinder to the boiler given the size of the boiler, thats a big combi, and wont be able to modulate very low, so when "medium" temp water is coming into it, it will fire and then start to cycle as it wont be able to keep on low enough fire to heat the water "just that little bit"

an alternative I have seen, was a balanced cold supply to cylinder and boiler, with the two hot outputs attached using a mixing set up/changeover valve, so when the cylinder output starts to cool it switches to the combi output, these combis can also be set in the D.codes not to fire straightaway on HW demand, but set to wait a few sec and wait for slightly higher flow rate which might also be useful.

Alternatively work out the cost of a cylinder and explain how long in real life its gonna take to pay back!

 

[numnutss]

The reality is that you have too much energy in the summer and not enough in the winter!

Yes your right ive only had about 1.5kwh spare electricity each day this week so wouldnt be enough to raise the temperature in a cylinder much, i might install a stove with back boiler in the future.

The best way to save is to have a large unvented cylinder ( 300 li ) fitted in the feed water to the boiler. But most combi makers don't advise it because of legionella risks and because the boiler cannot control its output temperature properly.

Tony

If i were to use a cylinder with a coil and have the hot water feed flow through the coil, and have the bulk of water in the tank being heated by the immersion, that would have pretty much the same as a thermal store(i think) would the heat transfer fast enough. That would remove the risk of legionaires?

Thanks for the advice, please keep it coming

 

[oldbuffer]

You could consider splitting the hot water system, say to have the kitchen directly off the combi, and install an indirect cylinder for the bathroom(s).

The cylinder would be heated by the boiler as a separate zone, but could have an immersion fitted to use the PV electricity when available.

However, would need to have the feed temperature high enough to heat the hot water, which might be too high for the heating if you want it to run in condensing mode.

Is is all worth it? I'd doubt it for 1.5 Kw on the occasional sunny day.

 

[Agile]

Its a nice feeling to gain some free energy.

The real solution is to store the energy as hydrogen and to use a fuel cell to provide an electric supply.

There was a unit for that at the show, costing £36k ! It could provide 3 kW and store about 7 kWh with the standard small cylinder but that was upgradeable.

A very high tech and expensive solution but a very good way to do it!

Tony

 

[numnutss]

hi scottishgasman, yes its powerful, great for the shower, that was the reason i got it originally, i was advised that vaillant were the best, it turned out to be a pile of rubbish when i first had it installed about 7 years ago, in the first 3 years i bet it had every part replaced, since then its been great with regular services by the vailant engineer who i got to know quite well at the time. i think i was just unlucky as my brother and dad both had the same boiler fitted with no bother at all.

is this what you mean?


im going to have to try and draw a schematic of what your sugesting to get my head around it.
thanks Joe

 

[Agile]

There are some very interesting blogs in that link.

Not enough time for me to read them though!

 

[numnutss]

Its a nice feeling to gain some free energy.

The real solution is to store the energy as hydrogen and to use a fuel cell to provide an electric supply.

There was a unit for that at the show, costing £36k ! It could provide 3 kW and store about 7 kWh with the standard small cylinder but that was upgradeable.

A very high tech and expensive solution but a very good way to do it!

Tony

a bit out of my my price range

 

[numnutss]

You could consider splitting the hot water system, say to have the kitchen directly off the combi, and install an indirect cylinder for the bathroom(s).

The cylinder would be heated by the boiler as a separate zone, but could have an immersion fitted to use the PV electricity when available.

However, would need to have the feed temperature high enough to heat the hot water, which might be too high for the heating if you want it to run in condensing mode.

Is is all worth it? I'd doubt it for 1.5 Kw on the occasional sunny day.

hi old buffer, thanks for the input, id rather not split the hot water.
i only had the solar fitted on monday and its been a bit cloudy in Barnsley this week so the 1.5kwh as been poor, its nice and sunny this morning so i just checked my figures and i ve exporteed 3.9kwh today and its only 11.30, so although there will be days when its pretty useless(especially through the winter), there will be others when it pays. i havent done any calculations for money saved v cost but if i can work out the best way to do it(wih a little help from y friends on here)safely without risking legionaires, i it should be cost effective over a few years.hopefully.(especially if i can buy a used cylinder)

the

 

[ianmcd]

What you are trying to achieve is very similar to the Alpha solar smart, which heats the water with solar thermal where you want to use PV and an immersion heater and use a vaillant boiler instead of the Alpha boiler, no reason why you couldnt

http://www.newaveheating.co.uk/alpha-solarsmart.php