Solar heating with a combi

GasWorks · Joined: 03 Sep 2005 Posts: 18

My company has started installing Worcester Bosch green skies solar systems which are installed typically in conjunction with regular boilers. Trouble is that there are a lot of houses out there that have converted to combination boiler, but may not want to be excluded from the solar/heat pump club - or have to convert back to a regular boiler....

So that I can include these households I hope to install a single coil unvented cylinder which will be heated by the solar system, and will supply pre heated mains water to the combi for 'topping up' if neccesary.

Given that the water temperature could range from around 10 degC to 60 degC, what would be the effect be on the combi? (in terms of reliability). I'm pretty sure that the minimum output in DHW is going to be v important

OK. I know this may be a difficult one to answer, and that the answer will depend on the make and model of combi, but any info will be greatly appreciated

Regards
I McL
The Gas Works NW Ltd

ronwagen · Joined: 18 May 2006 Posts: 6

Have you tried contacting the boiler companies? I like you're idea though. Sorry for not being very helpful

Agile · Joined: 09 Jan 2003 Posts: 3422 Location: NW London

Its unlikely that you will find a boiler manufacturer who will agree that you may do that.

In practice it will work fairly well except that the temperature regulation will be poor when the inlet temperature exceeds about 30°C.

Tony

GasWorks · Joined: 03 Sep 2005 Posts: 18

Thanks for replies. I have just seen Alphas system which is designed for combi's, and uses a special wax cartridge valve to swap hot water flow directly to taps or through the combi for further heating where needed. They seem to suggest that it will be OK for existing (non Alpha boilers).

Not unsurprisingly they do not mention any temperature regulation problems. Are these problems worse with boilers that cannot modulate very low on hot water? (Baxi 105 can only drop to about 11KW before switching off completely).

If this is the case then I'm guessing that more technologically advanced boilers - like ones designed to operate with modulating thermostats, would be better for this situation.

Iain McL
The Gas Works NW Ltd

johnb · Joined: 27 Dec 2002 Posts: 176

There are some 'high class' combis around which have a built-in blender valve to ensure that the temperature at the tap stas constant. Alpha's latest solar gadget, with the combi being used or not, according to whether the solar system is delivering hot or just warm, is a clever development. Most, if not all, condensing combis can modulate down to very low burner rates so feeding these with warm (if not hot) water should be OK, I'd have thought. I've yet to see a maximum cold inlet temperature specified for a combi....

jmsgas · Joined: 31 Aug 2005 Posts: 16

hi was looking to get in to the solar side but don't know if there is much call for is anyone having much call for it? i

is the anyone doing training course for it?

has the prices come down yet?

cheers john

SimonD · Joined: 08 Jan 2003 Posts: 123

There is a company selling a unit that was initially designed with a Viessmann boiler in mind.

It sits in line with the flue and turns the boiler into a fully condensing unit - a small solar panel can be added to it.

Some combis get confused if the incoming water temperature is higher than expected.

Frankly I can't see the point in solar for combis; the cost of the equipment and payback period make solar for small domestic rather pointless. The only way I can see it costing in is if the Government funds it. And then it is a fools game, because we are all paying out in taxes to keep solar installers and manufacturers in business.

HSP · Joined: 29 Jul 2007 Posts: 69 Location: London

solar with a combi is best with the cylinder used as a thermal store via the panels.
The preheated water runs thru the boiler and fires only when necessary!!

I imagine only a few boiler on the market can take pre heated water

ATAG is one and
Rinnai hot water heaters are the other

the alpha blends it back to 30 so no real advantage if you ask me
_________________
Dont cha wish your bouyfriend was a plumber like me !!!

SimonD · Joined: 08 Jan 2003 Posts: 123

The Alpha is interesting because there is no easy way to ensure the stored water temperature is not in the dangerous region for bacterial contamination.

In theory the Alpha valve can be used with other boilers but there is a rumour that the regulatory testing houses are now getting concerned and may be reconsidering and stalling any further approvals. Only rumours, mind.

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