Solar water heating

[Doctor Drivel]

6 foot? This pipe will take water back to the tank, and may disturb stratification. You could have it horizontal above the tank water line and it sprays onto the surface not disturbing stratification. Best have the pipe small bore like 6mm to 8mm.

As hot water comes in from the panels you want this to stay at the top of the tank. You don't want to disturb any stratification aiming to reinforce it putting hot water at the top. Pumping it into the centre of the water body will make it warm with mixing. Not what you want.

Best have a tee under the lowest water level that acts as a spreader. Pipe in -> tee -> two lengths of pipe horizontal from each port of the tee to the edges of the tank -> cap on each end. Drill holes in speader pipe horizontally, so hot water does not flow downwards into the main water body and stays on the surface.

Now for the vent. Just before the speader tee insert another tee, this can be under the water line. Take a soft copper pipe, about 8mm, from the tee up and out of the water to the highest level in the tank, Bend it downwards in a "U". Depending on pump pressure and size of holes in the spreader pipes, water should take the line of least restisance and not work its way up the soft copper pipe, only exiting via the speader pipes.

[Mary Fisher]

?

That's the one we have, with which we are so well pleased.

You'll also note at the bottom of the page, "Solartwin offers minimum disruption when installing, and then is as equally easy to un-install and load in a van when moving house.

It'sguaranteed for up to (I think) three moves. So no potential buyer of the house need be put off and the happy owner won't be deprived.> :-) Mary

[Mary Fisher]

So does ours. It's not new.

Mary

[dennis]

You should explain to her that you don't need 50C for a wash. Set it to 40C or even 30C and save some energy.

[David Hansen]

On Fri, 10 Mar 2006 15:35:59 -0000 someone who may be "Mary Fisher" wrote this:-

Provided it is under enough pressure water can be heated to above

100C. It will not turn into steam, unless the pressure is reduced. Such systems are used in big heating systems.

However, this is very much something for those who know what they are doing. It is best to think of such high temperature hot water systems as liquid steam, because if it gets out the results are very nasty. My staff once had to recover the bodies of two men who had been killed by such a system and it haunted them.

The application to solar heaters is more complicated than I wanted to explain, but I will now. In any heating system one wants an adequate margin between what happens normally and what might happen in a strange situation. If an open vented solar water heating system was running with the water coming out of the collector at 95C then there is little margin between hot water coming out and the hot water turning into steam. There is little pressure because the header tank is likely to only just be above a roof mounted collector and thus the water will turn into steam at 100C. This isn't so much of a problem with flat plate collectors, which are unlikely to reach this temperature, but it will be with evacuated tube collectors.

With a pressurised system there is more margin, so that in odd conditions the collector could get to say 120C without too much risk of a problem. This could happen if the pump is not working for some reason, such as a power cut. With the Solartwin and Imagination systems the collector will never get to this sort of temperature anyway and the pump is solar powered and thus fewer things can go wrong with its electricity supply.

That is one of the advantages of the system. I think that if they could reduce the price of the unit they could corner a large slice of the market. When they started selling it some years ago ISTR a price of £1500, rather then the current £2000. However, reducing the price means increasing the volume sold and that depends on reducing the price...

[Tim Downie]

Does seem nice and simple but £2000 for the DIY kit buys a lot of gas heated hot water. Certainly our house would be very suitable for solar water heating (rear of house faces due south, v. little shade).

Tim

[meow2222]

What I'm suggesting is a 1/4" hole in the panel output pipe just above the top of tank, say 1/2" above. There will be close to no pressure there, and no possibility of any squirting.

NT

[David Hansen]

On Fri, 10 Mar 2006 17:02:26 -0000 someone who may be "Tim Downie" wrote this:-

If the price of gas were to remain the same the simple payback period would be around 20-25 years. However, unlike the price of sunshine, the price of gas is unlikely to remain the same.

There are also other reasons for installing such things, for example reducing greenhouse gas emissions and reducing the maintenance on/extending the life of the boiler (which can usually be turned off for several months a year).

[meow2222]

I realised this isnt so. Once the panel circuit fills with water, the pump is only pumping against the running friction, and not the head. The panel output piping is filled with water after a second or 2, so gravity has the same effect on both sides, so no extra pumping resistance.

NT

[meow2222]

When you choose sealed you're choosing not drainback, so the above doesnt seem to make sense, unless you know of a sealed drainback design?

I cant see how this is a problem. The loft is normally fine, sitting on the usual dividing wall. The tank is below the panels for drainbacks, it only needs to be above them for thermosyphons, which are not the usual choice.

again I dont see any downside with vented system maintenance. Sealed system maintenance does introduce extra issues, and for CH seems to result in more maintenance need in practice, as well as being less easy to work on.

That is one of the plusses for vented systems, that they will never go into that dangerous region of pressurised steam. Any sealed system that does requires extra certification, which isnt free, and must be designed to withstand much higher pressures. If it is not pressure safe then its just dangerous. Vented eliminates any such risk. Worst case for vented is steam coming out the overflow pipe, a non issue, or in the highly unlikely event of both a system boiling and a blocked overflow pipe, the steam simply comes out from around the tank lid. Safely.

Imho this is more the hype than the reality. The one advantage of a solar panel pump supply is simplicity, but thats all. The electricity created by the solar panel is the opposite of a worthwhile investment for 99% of end users. The control system is a bit crude, and will result in the system actively cooling your HW some of the time instead of heating it. In short it isnt worth it, unless you're just not skilled to do anything better.

NT

[nicksanspam]

Not if the pump turns off and the water drains down at 95C. For long life, EPDM-lined tanks should be less than 77C.

Nick

[meow2222]

Ah yes, ignorance. Our machines use cold fill because by the time the hot gets thru the pipes the machines have already had enough water. The water is heated electrically within the machine.

Cue silly statement about enormous pipes...

NT

[meow2222]

Pedant mode: they dont use the hot fill for most washes, only for the boiling washes will they use it.

NT

[meow2222]

Early dw machines can be seen on various net sites, and in books from the time. They used flow of hot water and soap to clean the dishes, and were only really effective on freshly used still wet food. They were used in large kitchens, being ineffective for smaller scale use. Restaurant machines are descended from these, todays home machines use somewhat different principles. The simplest early dishwashers were no more than a sink of hot soapy water with a pump to circulate it, plus a clean rinsing sink.

If you have any reference or link to sandblasting dishwashers I'd be curious to see it, but I'm doubtful.

NT

[Doctor Drivel]

Whites still need hot washes, no matter what they say.

[Doctor Drivel]

It is pumping against the head (pressure) always. Gravity asserts pressure. A 3 floor British house with attic. Inc' space between floor it could be 10 foot per floor. A radiator in the attic space and the pump at the bottom of the ground floor. The pump has to overcome 1 bar (~30 foot), one atmosphere, to get to the top, even in a sealed system. OK is assisted a little when the water is dropping from 30 foot on the return, but it still has to overcome one atmosphere plus system friction. Gravity doesn't care if it is open vented or sealed.

[dennis]

Hotpoints use hot for washes other than boil.

[Doctor Drivel]

Sealed and pressurised are two differnt things. You can have a sealed system with an air gap in the top of a cyldiner, yet it is not pressurised - only when heated. When cold it will be atmospheric.

It isn't a problem an open vented drainback system does not requires a header tank at all, just space in a tank or cylinder at a lower level for the panels to drain into.

It is true a solar powered pumps may reverse the panel/cylinder and dissipate heat. But it is its overall performance that matters over a year.

[Doctor Drivel]

Most will on 50C and above.

[Doctor Drivel]

Did you ever feel that powder? My first dishwasher would clean the chrome over grills and shelves spotless, as it sand blasted them. The powder was course and took a long time to dissolve. The new one does not. But the crockery is much cleaner.