megaflow, solar and combi boiler...possible??

[kevineaton]

hi guys hope you are well.

ive got a 4kw solar system that is doing fantastically well (2300 kw produced since february). ive cut my electricity bill by 75%!! im looking to see what other efficiencies i can get and thought i could get my gas bill reduced as well.

i have a combi boiler (potterton performa 24 eco he)

is it possible to get a system so that a hot water tank is constantly kept hot by the solar system during the day which would also work with the combi boiler we have - the idea being that the free solar gets us a tank full of free hot water all the time, and if needs be the heat to the shower / taps can be topped up by the combi if needed on demand. i have plenty of space in the loft for a storage tank and believe there is plumbing going up there already because thats where the old immersion heater was.

i hope this makes sense!

if its possible - what do i need and any idea of costs please??

thanks in advance.

 

[solarsavings]

It's possible with a direct unvented cylinder in you have at least 1 bar incoming water main pressure. You would need an heatbank or new mains if it's less than one bar. You would also need something like the Intasol combi solar diverter and possibly something like the immersun switch.

It think it would be impossible to price without seeing the job.

 

[kevineaton]

thanks for this.

the pressure here is really good (our shower which is straight off the combi is fab) but i dont know what it actually is.

can you give a ballpark for the cost of parts assuming pressure is above a bar?

just want to know if its worth considering.

 

[solarsavings]

I would expect it to cost somewhere in the region of £2500-3500.

 

[kevineaton]

ok, thanks for that. - does anybody have experience with the kind of savings its possible to make doing this please? another very vague question i know!

 

[sedgy34]

There is a Worcestor boiler that can take warm water and it just tops up the temperature saving on gas

 

[kevineaton]

already got a new combi boiler 2 years ago so not keen on replacing it to be honest!

 

[solarsavings]

There is a Worcestor boiler that can take warm water and it just tops up the temperature saving on gas

There are many boilers that can take pre-heated water but the water regulations mean that water must be 23c or below.

 

[BruceB]

......but the water regulations mean that water must be 23c or below.

can you point me in the direction of those please?

 

[Gavin A]

can you point me in the direction of those please?

I believe it's actually HSE guidance specific to the use of combi boilers with solar water heating, as the water when flowing through the combi isn't heated for long enough to kill off any legionella etc that might have been breeding in the luke warm solar tank.

Though it may also be in the water regs for the same reason I suppose.

not sure of where the document is to be found, but I have read it previously and such guidance definitely exists and does make sense as well from an H&S point of view IMO.

 

[Gavin A]

Any hot water storage vessel displaying thermal stratification and maintaining temperatures in the range of 20 to 45
O
C is very likely to contain legionella bacteria in
significant numbers, unless regular pasteurisation of the entire contents of the vessel
takes place at temperatures of 60OC or above. Solar pre-heat cylinders that are subject
to thermal stratification would be equally susceptible to legionella contamination.
Solar heated vessels that do not reach 60OC and notably those maintaining
temperatures below 45OC would be particularly prone to contamination with high
levels of legionella bacteria.

Where these devices supply water via a combi-boiler in
order to raise the hot water temperature to 60OC, then according to the work of Stout
et al., the boiler would need to maintain the water temperature at 60OC for 3.2 mins to
reduce the concentration of legionella bacteria by 1 log (90%).

In systems where combi-boilers receive water from solar pre-heat cylinders that are not able to raise the water temperature to 60OC or above, then consideration
should be given to programming the system to automatically activate the combi-boiler
to heat the water to 60OC and recirculate this through the pre-heat cylinder, at a preset time daily.
10. This should provide effective pasteurisation of legionella bacteria colonising the
pre-heat cylinder. Where this pasteurisation programme is in place, the volume of
potentially contaminated water that can pass through the heating system before a
temperature of 60OC is reached (approx 20 litres), should then present little risk of
legionella infection. If this pasteurisation programme occurred daily, shorter contact
times of less than one hour may still prove effective in controlling legionella bacteria
in solar pre-heat cylinders, particularly in smaller systems. Alternatively, as legionella
bacteria grow relatively slowly, even when at optimum growth temperatures, then less
frequent cycles of pasteurisation (e.g. twice weekly) where the entire contents of the
vessel are maintained at 60OC or above for at least one hour, may also achieve
satisfactory control of residual legionella bacteria.

I think this is the report for the WRAS that really raised the issue. I'm not entirely sure where it now appears in the guidance though.

 

[Worcester]

The Best way to do it is a thermal store, basically a bog tank of water purely used as a 'heat bank' (think of it as batteries for heat ) you can have mutlipe inputs to them, immersion, solar, wood burner, trad boilers etc, and then draw off hot water, central heating via built in coils (heat exchangers) that way you maximise your renewables when they are available and top up only with non-renewables as needed.

Gledhill do the torrent multi fuel store : Torrent MultiFuelStore Solar - Hot water cylinders | Indirect hot water cylinders | Gledhill cylinders | Pressurised hot water cylinders | Domestic hot water cylinders
Though these guys do the same for a lot less RM Cylinders - Envirocyl - Heat Pump Cylinders (and will sell directly )

 

[Gavin A]

so from that, it probably is actually possible, as long as there's some means for ensuring the entire tank get's heated fully at regular intervals eg once or twice a week. I'm actually working up a system for a customer at the moment to work with a combi, so will report back once I've sussed it, as it's a couple of years since I last looked into it.

eta - but worcester's right, a thermal store is likely to be the best way to go, providing you've got the room for it, which my current customer hasn't.

 

[Worcester]

Thermal stores get over the legionella issue - hence why they are popular. - You don't bathe in that water it's just a store.

Give RM a chance / opprtunity if you need their type of prodcut - they are really helpful guys on the phone as weelas the good prices - (and we're not connencted to them ! )

 

[Worcester]

Has anyone used or looked at this : Renewable Energy Systems - Willis Renewables ?

Just wondered how efficient it was and wether it really works!, they have a similar designed immersion heater product as well.
Willis Renewables - Solasyphon - How it works
and
Willis Renewables - Immersion syphon - How it works