Solar Water Heaters linked to Combi boiler

[John Rumm]

Perhaps I have missed some critical detail, but it seems to me that the solution you are proposing only seems to make use of the solar heat to reduce the costs of your hot water supply.

If this is the case it will do nothing to reduce the costs of your heating. Since you are probably spending less that 10% of the total gas bill for the boiler on hot water in the first place, you are going to make it very hard to get any meaningful payback on this.

Even if you could achive a 50% saving (highly unlikely as a year round average) in your hot water costs with the use of solar, you are only going to see a reduction in *total* costs of 5% or less. This will never payback the investment in solar kit and your time.

The usual purpose of this "complexity" is to aggregate the output of several sources of heat into a thermal store of some sort. This in turn can be used to reduce both *heating* costs (and possibly hot water as well).

No sure I follow that...

Well, it does mean you can use less of it and hence achieve a faster combined flow rate. So faster bath filling etc.

Perhaps you use more hot water than me, but I doubt I spend more that £100/year on it. How much are you hoping to save?

Most regulate the heat input based on the *output* temperature of the water. So implicitly that takes account of the input temperature.

On old ones "yes", on modern ones "no" (in general).

[Doctor Drivel]

In some homes DHW cost more than the heating. 10% is way too low

Most an get 70% plus, and 95% in summer. It depends on how many solar panels you have on the roof.

** snip ignorant of solar musings **

[Doctor Drivel]

It is best to have a heat bank with a solar coil. The panels heat the heat bank. A simple cheaper boiler heats the heat bank. The CH is taken off the heat bank. So, solar heat can go towards CH and DHW. Also a Grundfos Alpha pump can be be on the CH circuit and TRVs on all rads. If you want proper solar, to do the CH and DHW, then have a large thermal store (heat bank) and a large solar panel array...but you must have low temperature underfloor heating, as in spring and winter the panels may not generate high water temperaures, thus making UFH the ideal choice.

As mentioned, in the US they preheat the water into a multi-point (tankless water heaters over there) a lot. They reason they do this with multi-points is that the CH is forced air.

See for cheap solar equipment

[David Hansen]

On Sat, 25 Feb 2006 01:49:30 +0000 someone who may be John Rumm wrote this:-

There is nothing wrong with this, not the least because it avoids complexity. Given that it is sunnier in the summer when heating is not needed such complexity adds little in the way of gains.

Sounds unlikely to me, except for particular circumstances.

That rather depends on how well the system is matched to demand. With the right sized system this should be possible in many buildings. A properly designed system may well produce nearly all the hot water from Easter to late Autumn. Even in winter a properly designed system will produce a useful amount of hot water, though not all of it.

It is certainly the case that if one is just interested in money there are better investments. However, money is not the only reason for doing something. Replacing windows in a "conventional" house with double glazing is certainly not cost-effective if looked at in simple payback terms. However, it is worthwhile if looked at in broader terms.

[meow2222]

The OP would save far more with solar hot air panels than DHW, and at lower install cost, but hasnt shown much interest in working through it all so far. Solar heat is one of those things where you need to do the calcs, or its not likely to work satisfactorily. Perhaps one of the reasons for its unpopularity.

NT

[Doctor Drivel]

double and especially triple glazing reduces/eliminates cold spot in a room enhancing comfort conditions.

[Doctor Drivel]

The OP would save far more with solar hot air panels than DHW, and at lower install cost, but hasnt shown much interest in working through it all so far. Solar heat is one of those things where you need to do the calcs, or its not likely to work satisfactorily. Perhaps one of the reasons for its unpopularity.

[John Rumm]

In the case of windows, perhaps... but will solar water heating add to the asthetic appeal of a house (let's assume we are not talking PVC windows here!), reduce noise, or improve comfort levels though? The only real operational benefit I can see is the increased flow rate potential, although is it is likely to give you the biggest boost at the time of year you need it least.

Remember it is not only a cost issue, you need to make savings of at least the energy required to manufacture all of the solar kit in the first place to justify the use of it on environmental grounds.

[Tony Bryer]

On a place built to modern standards, DHW accounts for about 1/3 of energy usage. But the economics are still dubious at best.

[John Rumm]

What proportion of the UKs housing stock is built to modern standards I wonder?

[meow2222]

Solar space heating is simpler than DHW, and the available returns are higher. Yes it works in winter.

Money is roughly a measure of total energy input, both direct and indirect. If one measure doesnt pay, another that does pay will save more money & energy, so on energy saving enviro grounds it still isnt worth doing things that dont pay.

Solar DHW is one of them in most cases. You have to be creative on design, and either a heavy HW user, or be happyto work for naff all to get a system that pays.

NT

[David Hansen]

On Sat, 25 Feb 2006 14:05:57 +0000 someone who may be John Rumm wrote this:-

Obviously.

However, the energy required to make all the bits depends on what those bits are precisely. A real DIY system using an old radiator and other salvaged bits is somewhat different to one using new evacuated tubes and a host of other bits.

[David Hansen]

On 25 Feb 2006 22:45:13 -0800 someone who may be [e-mail] wrote this:-

Really. Why is that?

Given that this is a DIY group, the latter point can be assumed.

[Matt]

Less than 1% of the UK housing stock is replaced or added to per annum. (circa 200,000 builds out of a total housing stock of 25 million)

How many comply completely with the building regs is an exercise for those with nothing better to do. Paging Dr Dribble?

[meow2222]

Primarily because a) theres no plumbing or water involved. b) theyre usually mounted on the wall instead of the roof

not in the least. Many of us value our time.

NT

[David Hansen]

On 26 Feb 2006 07:45:14 -0800 someone who may be [e-mail] wrote this:-

What form of space heating are you proposing?

[meow2222]

Flat plate solar hot air space heating. Much cheaper than HW and more payback.

NT

[David Hansen]

On 26 Feb 2006 11:38:26 -0800 someone who may be [e-mail] wrote this:-

Using what as the storage? The building fabric itself?

Hot air heating has the disadvantage of using a larger area to transmit the same amount of heat as a water system. Large ducts appeal to some, but not all.

[Doctor Drivel]

In a well designed system, yes. Solar air heaters outpace solar wet systems by a mile.

The ducting can be embedded in the building fabric. I have seen retrofitted forced air with ducts under wooden floors and laid in the attic.

Foced air heat recovery and vent laugh all over a wet system.

[Tony Bryer]

A formal study has been done - I couldn't find it via Google but the results were IIRC that as-built compliance is far from 100%