I have been investigating installing a solar water heating system that I wanted by use to provide pre-heated water to my combi ("the warmer the water feed, the less gas used to heat it" principle). I have spoken with a number of suppliers of Solar thermal systems and some say its possible whilst others say it will damage the combi. What is the "truth" here?
On Sun, 14 May 2006 10:13:41 +0100 someone who may be "Keith D" wrote this:-
The truth is that it depends on the combination boiler. Some will cope with heated water at the inlet others will not.
Depending on the answer to the obvious question there are then a range of options, depending on the house layout, hot water demand, condition of the boiler and determination.
I can't understand why you want to do that. Water from the solar system is warm or hot enough for most tasks on most days. If it needs a boost you can provide that from your programmer.
That's our experience, not theory.
Mary
Solar and combis are an awkward combination. It's do-able but probably expensive.
But before going further may I ask:
1: is your house already draught-proofed and insulated to the highest standards 2: does your heating system already have thermostatic radiator valves, a programmable thermostats and - if the house is not absolutely tiny - separate heating zones 3: is your combi already a high-efficiency condensing type?If the answer to any of these questions is No then improving the relevant area(s) is likely to make more sense both economically and ecologically than spending £1000s on a solar water heating system.
How would you achieve this "boost" without a hot water cylinder?
You do have a cylinder. It's not a problem :-) The OP didn't say that he didn't have one.
Mary
He said he has a combi which means that he doesn't have a cylinder. So it is a problem :-)
OK then, it means he *probably* does not have a cylinder. Better?
On Sun, 14 May 2006 16:43:29 GMT someone who may be John Stumbles wrote this:-
I know people that do. The combination boiler provides hot water to the kitchen, while a cylinder provides decent amounts of hot water for showers and baths.
Other than small houses with compact services, a variety of sources of hot water are often the best approach.
On Sun, 14 May 2006 14:23:09 GMT someone who may be John Stumbles wrote this:-
Cavity wall and loft insulation, to the greatest extent possible are certainly important, as well as cost-effective draught-proofing. Important for reducing heating costs.
However, none of these affect hot water production to any extent. What matters is the layout of the house and the services within it. Insulation of the hot water pipes is certainly a good move in many circumstances.
Important for reducing heating costs.
If it is not I would ask questions about how old it is. Replacing a relatively new boiler is not sound financially or environmentally.
Economically solar water heating is still a long term investment, at current fuel prices. However, the price of sunshine is not going to increase, unlike other fuels. There are also other advantages, such as being able to largely turn the boiler off in summer and thus (probably) prolonging its life. If it is the sort of combination boiler that has a small hot water cylinder this will also save some gas.
Environmentally solar water heating is an excellent investment.
I agree. I wish we'd done it years ago.
Mary
Here's one solution
OK, good boy ;-)
I that case you may want to investigate thermal store/heat bank systems to store the heat from the solar system. One arrangement that suggests itself to me it to have the store supply hot water (at mains pressure) directly to taps when the water is hot enough, and to use it as input to the combi when it's too cool to use directly.
However, depending on the design of the combi you may still be limited to the lower rate of flow that it can provide even though it's having to do less work, given pre-heated incoming water. A configuration that might give better flow might be to combine the output of the thermal store with the output of the combi via a thermostatic mixing valve: combi to hot input and combi to cold input of the valve. Again you'd only want this in-circuit when the store can't supply hot enough water.
In each case I guess you might use a 2-port or 3-port motorised valve to bypass the combi, controlled by a thermostat sensing the temperature of the store. Although these valves are only intended for closed systems with corrosion inhibitor they usually have brass bodies and some sort of rubber (EPDM?) actuator ball which should be OK (if not strictly kosher in terms of water regs and WRAS approval) for DHW.
Is your solar system going to be low or hi tech? E.g. old radiators in glass boxes or evacuated tubes. Depending on how much you're spending there are ways of DIY-ing thermal stores at low cost.
Anything with "Eco" in it is several times the price of everything else on the market.
Actually it is a long term non-investment as in most cases, and all commercially installed and maintained systems, it will never even break even.
There is no evidence that this is the case at all, and in all probability it will almost certainly reduce its life as seals and bearings in pumps and valves really dislike being unused for months on end and corrosion will also worsen.
In propaganda.
On Mon, 15 May 2006 23:36:55 +0100 someone who may be Peter Parry wrote this:-
At current prices DIY systems are long term investments. Systems where one pays someone to install it are probably not going to break even at current prices, but note the name of this newsgroup and that the price of sunshine is not going to increase, unlike other fuels.
Incorrect.
Pumps should indeed be turned over occasionally. However, that has no bearing on the life of the boiler.
No bearing on the life of the boiler either.
Corrosion where?
Incorrect. As I pointed out and you snipped, it can save more gas than people think.
You can keep trying with your incorrect assertions for as long as you like. However, because somebody may believe you, they will be rebutted whenever necessary.
You don't support that statement but in any case you're only talking about the effect on the buyer's pocket. There are other considerations.
Mary
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