Switching alternative energy devices

[PeTe33]

I was contemplating a project for a long time in the future, and stumbled upon an idea...

Our boiler MAN (ecohometec) can use pre-heated water to reduce/eliminate required heat boiler input into DHW. Logical use of this is a Solar heated water bank thing before the boiler. That's the easy bit. Next idea was on Wind power. Our home is in an ideal location to catch the SWesterly winds blowing up the Bristol channel see S.W. picture here:

assuming I could get planning to erect a 2.5KW turbine, the ideal scenario would be have the turbine feeding an immersion heater in the heat bank (something like the following: Solar by summer and wind by winter, but with the magical bit happening when heatbank/store is satisfied....

Electricity being switched by tank thermostat and divered into ring main as per usual method.

Can anyone see a possible flaw in my plan? Currently we wouldn't be go the solar route as we only have East/West sloping roof but that can be sorted with a future flat roof replacement over the garage.

As it is, it's a "hmmmmm....." plan with much smaller things to be sorted first, I thought I needed to get some thought on the idea before I waste more time on theoretical pipe runs and Mast locations etc. :¬)

Cheers Pete

[Roland Mösl]

""Pet @

;¬)"" schrieb im Newsbeitrag news:PeANg.17841$ [e-mail]...

Shure and very easy.

It's not modern to have the DHW in a boiler.

Solar and heat pump systems loose efficiency at high temperatures, but temperatures between 40 and 60 Celsius love Legionella to breed.

So the solution is to have a closed loop storage for hot water The DHW is warmed up by a plate heat exchanger

this with a heat pump combined and with photovoltaic / heat combinded system

[The Natural Philosopher]

Sadly, its not very green to not do it either. DHW requirements are trivial compared with house heating requirements. Well ours are.

Maybe we use 250litres of DHW a day.. raised by what/..40C? say 10 megajoule..3KWh? about 1Mwh per year, or about £130. Even on electric heating, which it aint. Say £60 worth of oil..

The central heating spend is > £1000 these days..spend a thousand or two to heat hot water, or a thousand or two to knock 10% off the heating bill..I know which I'd rather do...

Whats the energy payback of solar heating? Compared with energy to make the units? Ditto windmills.

Once the BCO has gone I am going to block up half to three quarters of the roof ventilation and the underfloor ventilation. I reckon that will save me £300 a year easy. Its a howling icy GALE up there in winter, and under the ground floors as well.

[meow2222]

You can do things these ways if you wish, but in neither case will it give you anything close to the best possible payback ie max energy harvest from the equipment used. Solarthermal technology is at the point today where it takes proper design effort to make a system that can pay its way in the long term. Slap it together designs like this just dont pay back.

Details:

First solar hw collector efficiency depends on water temp, the colder the water being heated the more energy is harvested. So the idea is to put them in the coolest part of the system where the output will be useful. That means either heating the bottom of the hot tank / heatbank, or running ufh, or using a solar preheat tank.

2nd windmill heating HW is using high price energy (electricity) to do the job of low cost energy (oil & gas). This step alone divides your payback by about 3.

3rdly, solar dhw just doesnt compare to solar space heating. Space heating is much cheaper, more efficient, yields far more energy payback, and costs in the region of a tenth the price to install. If you want good payback, solar space heating is the way.

There are newsgroups with expertise on this stuff, alt.solar-thermal and alt.solar.pv.

NT

[Doctor Drivel]

Your Eco-Hometec (rebadged German MAN) is a combi version (DHW and instant CH in one box) I assume. Roland seemed to be showing a heat bank - a thermal store using a plate heat exchanger and pump for DHW take off for the cylinder. Look at this web site for an explanation.

Eco-Hometec cylinder is a normal unvented cylinder with a solar coil. It needs to be fitted by an approved installer and cost around £60 to £100 per year for an annual service. Any gain via solar or wind is negated by the service charge, so a no. no.

Try a vented heat bank (variant of a thermal store using a DHW plate heat exchanger) heated directly by the boiler (no heating coil in the cylinder). Heat the cylinder via the CH section of the boiler. The wind turbine can heat an electric immersion heater in the cylinder. Any solar can be via a solar coil, or even directly into the cylinder using an auto drain down system. This way any energy gained by wind or solar may be used for CH or DHW, not just DHW. The CH circuit can be taken off the heat bank cylinder using a Grundfoss Alpha auto variable speed pump.

The cold mains pipe goes through the DHW plate heat exchanger.

Now you have a redundant DHW instant section on the combi boiler. This can be used for backup if the DHW pump fails on the heat bank, by inserting some valves in the DHW cold mains supply by isolating the combi or the heat bank.

This is the best approach for you.

[Roland Mösl]

250 litres * 40 C * 1,16 Wh for 1 litre to warm 1C = 11,6 kWh

11,6 kWh per year * 365 = 4234

It's fascinating, that people oposing solar energy can not calulate

[Doctor Drivel]

He also lives in a poorly insulated house that is far too large and has a bath of around 750 litres. The oil companies love him.

[Doctor Drivel]

You can do things these ways if you wish, but in neither case will it give you anything close to the best possible payback ie max energy harvest from the equipment used. Solarthermal technology is at the point today where it takes proper design effort to make a system that can pay its way in the long term. Slap it together designs like this just dont pay back.

Details:

First solar hw collector efficiency depends on water temp, the colder the water being heated the more energy is harvested. So the idea is to put them in the coolest part of the system where the output will be useful. That means either heating the bottom of the hot tank / heatbank, or running ufh, or using a solar preheat tank.

2nd windmill heating HW is using high price energy (electricity) to do the job of low cost energy (oil & gas). This step alone divides your payback by about 3.

3rdly, solar dhw just doesnt compare to solar space heating. Space heating is much cheaper, more efficient, yields far more energy payback, and costs in the region of a tenth the price to install. If you want good payback, solar space heating is the way.

There are newsgroups with expertise on this stuff, alt.solar-thermal and alt.solar.pv.

[Dave]

ng

You could make better use of the DHW part of the combi by feeding the mains input to the boiler with the output from the plate heat exchanger. The combi will boost the hot water temperature if the thermal store is empty or not hot enough.

[Doctor Drivel]

You could make better use of the DHW part of the combi by feeding the mains input to the boiler with the output from the plate heat exchanger. The combi will boost the hot water temperature if the thermal store is empty or not hot enough.

[Dave]

ge

The O.P. did not mention any need to increase DHW flow. If the combi flow is poor get a new one or just remove the restrictor.

Keeping the thermal store cool (by not heating with the boiler) will maximise the solar heat input.

[PeTe33]

Exactly.

[PeTe33]

That's what I suggested... a Solar pre-heat tank.

I know this, but, as I wouldn't be able to get a big enough mill (6KW) on the space available (or planning) I can't realistically export surplus energy to the grid, so when energy is being produced during times of minimum power consumption (all hours outside 07:00 to 09:00 and

17:00 to 23:00) so about 16 hours of the day, I thought it better to initially use electricity to "top-up" heat-bank (Water pre-heater)before switching to ring main feed.

Of course, if I get a few PC's and servers running then I doubt I would over produce anything anyway.

But our South facing wall has a big window across it which I'd prefer to keep!

And... the sun is a bit arse about face when it comes to space heating requirements.

:¬)

[PeTe33]

Doesn't this negate the benefits of the condensing aspect of the boiler though?

[Doctor Drivel]

You don't suffer low water flows when you can have high flows easily.

Have you seen the price of a MAN? No need to get rid of the combi at all. The DHW section can be made redundant and the heating side just heat up the heat banks cylinder. It is only fit for backup.

You heat the cylinder right at the bottom where it is coolest. You design the system so that DHW and CH returns are always cool back into the cylinder to promote more effective solar and promoting cooler return condensing efficiency.

[Doctor Drivel]

See above.

[Doctor Drivel]

Not at all. The body of water in the cylinder stratifies and leaves only cool water at the bottom, which is returned to the boiler for more efficient boiler operation. The body of water in the cylinder runs though the boiler, not via a coil.

[meow2222]

Right. Next then comes the question of matching the collector technology to the app. Flat panels are best for preheating, not vac tubes. Flat panels with added concentration work better and more in winter as well. If you want some vac tubes as well, I'd use those on a separate circuit to heat the main hw tank or heatbank, as theyre best suited to heating high temp water.

Yes, its one problem generating it, then another problem setting up a a system to make use of it. A windmill would not be very high on my list of alt nrg choices.

So dont put it on the house. It can be on a fence, freestanding, or on an outbuilding. This is by far the best option if you have some space to put such a system in. An insulated air duct to the house is not a big barrier.

NT

[PeTe33]

Ah... I was presuming it went through a coil....

OK, if the hot from the boiler goes to the top of the tank and the return from the bottom, then surely the turbulence of the pumped flow would mess up any stratification. Our boiler modulates the pump to ensure a 20 degree C difference. If the return was significantly lower than the flow, presumably the boiler would ramp up the output to maximum heat and pump speed until such difference was achieved. This would I'm sure create a significant "mixing" of the water and again cause boiler confusion and loss of any significant condensing benefit would it not?

[PeTe33]

But my theoretically "better half" would be. :¬)

And it still only works best both in the seasons and the time of day you don't require heat (if you work away from home), and you can't store warm air for use later. :¬(