Free hot water with a solar water heater

[Zasso Nouka]

From what I read Brett the increased efficiency is in the order of around 5% overall but that figure varies a lot on different sites and the main locations evacuated tubes outperform flat panels is in more northerly locations like Canada and northern Europe. Further south where we are the difference is probably negligible and at the end of the day if you have piping hot water a few percent efficiency hardly matters. Supposedly on cloudy days or if the unit can't be orientated to the south the evacuated tubes should be better suited but again if you have a tank of piping hot water by the evening that's all that counts.

We couldn't mount a panel on the roof because most of our roof is non weight bearing, it forms the passive solar heater for keeping the house warm in winter, so had to site the water heater on the ground and MMC's free standing unit works well then. As you mention flat panel units are don't seem that much cheaper these days and when we contacted an installer the price including installation was totally unrealistic, whereas the MMC installer was happy to cut costs and have us do the manual labouring and he brought his mum along to look after our hatake

I'm thinking of putting another unit on the cafe (which can go on the roof) and currently looking at the options, is your flat panel unit pressurised and refilled by the domestic cold water system as you draw off hot water ? I'd need that to be able to hook it up to the water intake of the gas boiler.

As you and Ian have said the one drawback is how it empties most of the tank when it gets too hot, we've only had to let off excess heat two or three times this year but I'd prefer it if we didn't have to ever. I'm sure there is a solution for this and am currently looking into it.

I couldn't agree with you more Brett that given the savings made with any type of solar heater I'm really surprised that not every house in Japan is using them. Would seem to me to be a win/win situation for the householder to me.

e2a:

Sorry forgot to say. Ian when fitting the relief valve was it a temperature and pressure relief valve or purely a pressure relief valve ? I'm wondering if fitting a more expensive American or European one would solve the problem.

[BrettRas]

Yes, I think you are right ZN. Down here in Kyushu the difference in efficiency is likely to be inconsequential.
I am curious how folks adapt their setups for areas where hard freezing occurs. It's easy to take for granted how simple things can be piped when freezing is not an issue.

The flat panel model is not pressurized, it relies on gravity to provide the force (unless you add something yourself). It is refilled automatically by the domestic hot water as the hot water is drained off though. It operates with a simple ball valve similar to what you often find in toilets.

Sounds like these MMC units might be the way to go these days if the prices of the flat panel units stay this high.
Like you say, I'd imagine one could replace the relief valve easily enough.

[Ian]

Brett - great to hear you are using solar hot water there too and the wood fired boost when needed is a great option.

ZN - We put in a temperature/pressure relief valve from MMC, the right one in the pic, with the red probe. The left one is a pressure relief valve at the cold water inlet side of the tank. A chance of that one dripping to release pressure.

Next weekend I will pipe (flexible metal) the outlet of the hot water relief valve back into one of our water storage tanks. Don't like to waste any water. And just thinking now, will try and also loop the cold water relief valve outlet back to the storage tank too, or even to the kiwifruit. Why do I always create more work for myself?!

MMC says when the top temp/pressure relief valve activates to drain boiling water and cold water enters the tank, then the water temperature should come down to around 40C.

Sure was a very, very satisfying shower today, both in the morning and after getting covered in dirt later in the day. A bit of tweaking of the system to suit our usage and we should be laughing, without gas.

[Zasso Nouka]

Just a little assistance in the winter if it has been cloudy, or if it has been cold and rainy for a couple days. It's actually almost unfortunate some times, as the wood fired bath water feels so good!

It's interesting you say that Brett, Quite a few houses in our village still have wood fired baths and folk that have them also say how much they prefer them to gas boilers or eco cutes so there really is something to that. Whether it's part of the ritual, preparing and lighting the fire or it just feels a whole lot more organic I don't know but there seems to be something to it.

In answer to your point about freezing conditions, lagging/insulation on the pipes. Lots and lots of the stuff, I think we've got around 40 - 50mm in the incoming pipes and maybe around 60mm on the hot water pipes.

There seem to advantages and disadvantages to both systems, an unpressurised tank doesn't have to dump most of the hot water when it starts to boil and can divert small amounts down the overflow pipes. However on the other hand a pressurised tank may possibly be slightly easier to connect into a gas boiler or eco cute. Two different design philosophies that basically do the same thing. From what Ian says changing the temp and pressure valve may make no difference but I think it still worth looking into to see what other folk do as there may be another option.

Thank for clarifying what MMC have to say Ian, I do wish it didn't have to drop the temp so dramatically. Ok, for us it doesn't happen that many times a year but I'd rather it didn't happen at all, it just seems wasteful. You have exactly the same relief valves we do, why do you think they include a cold water relief valve, I couldn't work out why that would be necessary. Sounds like a good idea feeding the relief pipes back into your storage tanks so it isn't wasted.

Whichever system one chooses it is very satisfying indeed knowing that lovely hot shower or bath isn't costing you a single yen.

[Ian]

The hot water relief valve pipe now goes into one of our 10,000L water storage tanks.

Also came across the same valve made by a Chinese company.
http://sell.lulusoso.com/selling-leads/ ... valve.html

And it looks like they make the MMC frame too.
http://www.weiku.com/products-image/724 ... CH-35.html

[Zasso Nouka]

Nice find on the T/P valve and frame, at least we know where to source a new one when these rust through and nice job on routing the relief flow into your storage tank, at least you know now that water isn't going to be wasted.

With regard to the over heating issue it appears you can get some pretty nice covers to put over some of the tubes at times of year it is a problem or you aren't there and you can even fit heat dumps. However I did find this

Andrew in regard to my last contact re excessive hot water venting I have changed the inlet to directly under the temp relief valve plus 100 mm pipe protrusion into the tank & now when it vents it only lets quite a small amount go and stops as the cold water reaches it quite quickly A vast improvement

From here

Looks like an interesting possibility, that way cold water entering the tank would hit the T/P valve fairly quickly and might stop it venting quite so much of the hot water or it might lead to the tank seriously overheating and exploding :o

From that same thread here is another interesting post

Another option for overheat problems apart from covering a % of the collector is to ask your installer to install a Cold water Expansion valve(CWEV) at the cold inlet to your tank , this valve is preset at a lower expansion rate(750kpa i think from what i can remember) the CWEV is generally set 200-300kpa expansion point less than the PTR , which means when your tank gets hot and the pressure is up to 750kpa it will expel cold water from the CWEV , when the valve opens and water is expelled it also replaces that expelled water in the bottom of the tank with colder water therefore the sensor will tell the sensor at the collector that it needs more heat reducing stagnation time of the collector and the chance of the PTR to go off and totally dump the hot water contents of your tank.

Still more reading required I think

[gonbechan]

I have always wondered if a system like this could be hooked up in winter to heat floors Korean Ondol style and did a bit of poking around to find this
http://www.bestmadeinkorea.com/product- ... ystem.html
I know it is probably a closed system but if you could vent the hot water through something like an ondol system and then back to the tank when it cools, you wouldn't be wasting water when it dumped.

The Koreans use ondol even in summer and it keeps their homes dry and mold free.

[Ian]

Good info ZN and Gonbechan. Will also read more, thanks.

For now, I’ve put a few pipe insulation covers over some of the tubes while we aren’t there. Chances are we’ll need more, but will wait and observe the system first. Today was a clear day and at around 6 p.m. we had 68C water in the unit.

[Zasso Nouka]

You possibly could run an underfloor heating system from one of these but the vented water comes out unpressurised so not sure how that could be fed into the floor heating system, that's not to say it can't be done, Ian would probably be able to tell you as he's a far better plumber than I. I'd have thought the underfloor heating system would possibly be a closed loop, with venting valves for over heating and an inlet for topping up, you might not want to introduce water back into the domestic pipes that has been sitting around in underfloor pipes for a while, specially if you are using unchlorinated well water but I still wouldn't rule it out.

Great idea with the insulation covers, they look far better than lashing a blue sheet over some of the tubes. They really blend in with the whole unit, snap on snap off, awesome.

Re the ideas in that thread, I'd be somewhat concerned that the part of the tank away from the cold water inlet might carry on heating up and produce steam under pressure. As the whole thing is designed not too mix the hot water with incoming cold as you draw off water for domestic use could the temp down the hot water outlet end get too hot with these ideas ? I'd really rather not turn the tank into a pressurised steam bomb

[CYEK]

Ive got an old solar tube system on the roof here in Kyushu and was thinking of taking it up to the other place and seeing how it works in minus 10. Its been disconnected here for a while and currently Im using a toyu boiler at around 2000 yen for 2 or 3 months during winter mainly December to February. Boiler up north is gas and averages around 7000 yen during winter. Strictly cold water showers during the other seasons in Kyushu but up north hot water used from about October to April.