Perhaps this clip is a better illustration of the multi geyser connections:
These valves are Ā£300 -Ā£400. I picked up one about a year ago for around Ā£40 on eBay.
I just checked eBay again on a whim.
Ā£25 each, more than 10 available. (Posts to ZA)
I just bought another 2. I hope they get to Ireland in time, but at that price I took a chance.
I was too afraid to ask what the price wasā¦
I have a recirculation setup on my heat pump. It has a temperature valve that keeps the water flowing through it at the optimum temp. (recycling the water if itās too cold)
Presently solar thermal geyser feeds my electric geyser, and the house draws off that.
So the solar geyser is like a pre-heat.
I am going to put this valve in place though.
Then I use less solar hot water because it is blended to a safe temperature, and still use the pre-heat when drawing on the electric geyser.
Disconnect it. I assume it is connected as a āprefeedā system, in other words the X-Stream tank feeds into the inlet of the Kwikot. If the sun heats the external tank somewhat, it means the internal tank has less work to do, and that is where you get your savings.
You will lose some overall hot water capacity. In winter, the water in the outside tank will be at best luke-warm, mostly cold, which means you have a total capacity of only 150 liters at a time. Right now you have 250 liters.
In summer the reverse happens, you have 250 liters and you hardly have to heat any of it, since the internal geyser is fed with boiling hot water from the outside one.
My source for this: I had the exact same setup at my previous house. We didnāt have enough hot water with just the X-stream tank, so we installed a Kwikot and changed it into a prefeed system, where the external tank is not connected to electricity at all. Iām in Somerset West.
My concern with such a setup would be that if it doesnt go above 55C at regular intervals that nasty bacteria could take hold in it. The ideal growth range for Legionella is between 32C and 42C.
You raise a valid concern there, and I had to do a bit of research.
What is required is luke-warm water, somewhere between 20Ā°C and 50Ā°C, and it has to be stagnant. The water in the bottom of the preheat tank can very likely provide such an environment.
The legionella will be killed within 10 minutes, once it gets to the second tank, so the risk is probably minimal, but you should not rely on ME for that answer 
If concerned, then I would say heating the outside tank to 55Ā°C once a day, preferably in the late afternoon after the sun has done its job, and close to the time that showering starts so as to have the least amount of cooldown before consumption.
Of course, the quoted numbers (the outside tank uses 12kWh, the inside one almost nothing) makes complete sense from that perspective too. The inside tank simply has nothing left to do, since the outside one did most of the work already.
Now for some math. It takes 1.16Wh to heat one liter of water by 1Ā°C. If you heat 100 liters of water in the X-stream tank, and use it pretty quickly afterwards (leaving the tank cold over night), and assuming ambient water is around 15Ā°C in winter, you need about 5kWh to heat that much water, and the inner tank then doesnāt use much at all until youāve used the 100 liters on the outside.
If the outside tank has a 2kW element, which I believe is common for those, then it needs to run about 2.5 hours per day, right around 4PM-ish.
So maybe thatās a solution. Set a 2.5 hour slot on the X-stream tank towards the end of the day. Let the internal tank do the rest of the work.
If youāre the second or third person to take a shower and the second tank is already down to below 50C then the bacteria from the first tank is going to pass through unscathed.
Thatās what I do.
I would guess that it takes multiple days for bacteria to multiply to dangerous levels, and even in our Cape Town winter weather thereās likely enough sunshine to cook the bacteria frequently enough to prevent that from happening. Iām not taking any chances though.
Depends who you ask If you want to convince someone that they need your product, then it takes only a few days. If you want to convince someone that itās no big deal, well then it takes two weeks of vacation with no water moving at all. The real answer is of course somewhere in the middle.
This I am not so certain about. When I still had that system, it really felt like it did absolutely nothing in winter, as if the water was at best lukewarm from the outside tank.
Even on my parentsā farm in Namibia, winter sunshine was good for maybe one hot bath. The rest of the colder water in the bottom of the tank is just sitting thereā¦ and no residual chlorine on a farm either. Of course there you would fire up the old ādonkieā and properly cook everything with a wood fireā¦
Anyway, @Tamara wanted to know how to get the bill down. If there is a timer on the outside tank, and it sounds like there might be, setting it for only 2 to 2.5 hours late afternoon, and then letting the internal tank do any of the rest of the heating, is probably a good first step. On my own system, we simply left it disconnectedā¦ and weāre all fine still. I thinkā¦
This would be a good start I reckon. If he then doesnāt have hot water then check the plumbing between the 2 geysersā¦
Iāve been thinkingā¦ always dangerous.
My existing system is 2x 150l geysers in series.
The usage one is electric and the solar thermal is a pre-heat. I think the Intasol valve is a far better way of handling that situation.
However, I digress, from the point I wanted to make.
I retro-fitted 200l geyserās worth of solar tubes on that 150l geyser. It was a few years ago and I havenāt had issues from the tenants.
Now for the thought experiment:
I like to over-panel a PV inverter, I now see from what I have done it is possible to over-tube a thermal geyser.
So what if I did this:
Installed a single bigger solar geyser with the solar thermal retrofit tubes.
But, instead of installing the conventional number of tubes
I put 300l worth of tubes on a 200l geyser, (or some similar combination) and never connect the electrical element.
There is over-temperature protection available that stops the circulating pump - install that.
Then install a 55C thermostatic mixing valve using cold water to mix with the hot water geyser outlet.
What I am trying to achieve is:
- The water can now and will get to nearly boiling point regularly enough, so legionnaires isnāt an issue. ( The bacteria take time to build up again).
- The water will attain a legionnaire-safe temperature even when the weather isnāt great, so no reliance on the electrical element.
- I now have a physically greater volume of hot water.
- I also virtually greater volume of hot water, because a % of cold water will be added to the mix. (Cold water is a legionnaire-safe temperature and it is only added at the time of use).
I suppose an electrical analogy is that my solar charger is bigger, my battery capacity is physically bigger and it is virtually bigger because I am running it at a higher voltage.
Unlike a real battery though where X voltage per cell is a limiting factor, I can go higher than 60C on a what is a thermal battery.
I think it equates to having enough free safe hot water after the initial capital spend.
Comments anyone?
This is something I never really thought about until @PierreJ mentioned it earlier, and I started reading about it.
There is some of this bacteria present in the cold water feed already. It is mostly controlled by residual chlorine, and generally not an issue. While cold, it is dormant, and there is no danger of growing.
It seems the time it takes to grow and become really bad, can be as little as a few days, but is usually closer to two weeks. It also needs a temperature somewhere above 20Ā°C but below 45Ā°C. Every time the temperature goes up a little bit (but does not exceed 45Ā°C), it grows a bit faster, every time it comes down again (in the evenings) it goes dormant. So over time, it is possible that it accumulates slowly.
So I am inclined to think that the time before critical levels is probably closer to two weeks, if not longer, than just a few days, since it can only grow for a few hours per day.
That would mean that as long as you get the solar tank hotter than 55Ā°C twice a month, you should be fine.
Now, is there ever a time when that does not happen? In Cape Town, maybe, but that will be once or twice a year.
So I would concede, that overpaneling a solar water heater may well be perfectly sufficient to contain this. Canāt prove it, but it is a gut feeling.
On this topic: I am now concerned about my heat pump setup. I donāt have my electrical element connected on the tank. The heat pump is the only source of heat. It heats to above 50Ā°C and keeps it there almost the whole day (Legionnaires dies within a few hours above 50Ā°C), so the risk should be minimalā¦ but all this talk has started to make me wonder if I should not perhaps connect the āboostā function of the heat pump controller so this can work properly.
Iāve read that 70C is instant death for those noo-noos.
As legionnaires is ubiquitous in water, I think that their recovery will take as long as rolling a snowball starting from a snowflake.
So hotter water may buy more time.
As have I.
Reading of all the plans and ideas in and around hot water, over years on multiple forums, me being me, starting thinking outside the box.
Like:
Long hot water pipe and kitchens kill hot water efforts.
Answer:
Under/over counter 5-10l geyser in kitchen. Just add a double pole plug in the DB for it, 16a max.
Solves the distance issue too.
Cents on the rand.
Showers:
Vertical 150l geyser, need to heat less water.
And it heats faster for showers.
Bath:
Law of Transvaal so all the best, see ya - unless you get a much smaller, by a mile, bath for those who insist.
And this SWAMBO āthing/dramaā:
Big SWAMBO/Little SWAMBO ā¦ you want it on on demand, then you feed the meter. Problem went away.
I am very attentive though to teeny weeny SWAMBO - till she grows older.
For now she has a little tub inside the bath. Sorted.
My point?
We spend so much time and money to heat hot water, that we sometimes miss the small solutions.
Hot water is going to cost, how much depends on how hard we apply our logic, change habits, approach to it.
Also helps the deeper thought processes when you sit for a week or more with no irradiation to heat hot water via tubes, flat panels or solar panels. It forces you to think differently fast.
It takes but the first replacement of said systems, to make you think very hard on why one needs to spend that amount of money, again, to keep on āsavingā. Only āsavesā the first time round.
We used to have a 300 litre direct-coupled thermosiphon geyser on the roof. The geyser was mounted above the panels, so no need for a pump. The downside of that was there was no way to switch it off. It would regularly hit 90+ degrees in summer and about once or twice a year the safety valve would open and it would spew boiling water all over the roof. Quite scary to witness.
When the geyser sprung a leak I decided to get rid of it and use the space on the roof for more PV panels. Iām now back to fully electrical geysers inside the roof - two 150 litre glass fibre geysers from X-Stream in a series configuration.
The upside is that I can better insulate the geysers so my standing losses are less, and I donāt have to worry about overheating. Thereās no moving parts so not a lot that can go wrong, and once the water is heated I can use the generated electricity for something else.
Yeah, 1.5kW element in those, you donāt even need a dedicated plug for it, and the proximity to the point of use saves a lot of water. Doesnāt save much money, as you point out, but it isnāt more expensive in the long run either, and it adds value to your life (no waiting around for hot water) and provides some separation of concerns (a burst geyser does not leave the kitchen without hot water).
Just one thing please: If you install it inside a cupboard, which is quite common, install a drip tray. They donāt make one specifically for these small heaters, so you may have to get creative (visit your local plastics shop and look for a properly sized plastic tray a few cm deep). If it burstsā¦ and they doā¦ it takes the cupboard with it. Ask me how I know.
I decided never to do that a long time ago.
Although the safety valve is regulation, the Ozzies have other over-temperature protection regulatory fittings that operate before the safety valve. (I think).
One is that the circulating pump is turned off. (Again, I think)
I take your point about more PV, I already intend to max out my roof with PV.
Jip, saw it happen to a fellow Victron enthusiast. Kitchen Island was tickets. The water, over the floor, bugger that!
Whilst looking at the fiasco, though silently, over the counter above the sync seems much more practical. Sorted.
Why the double pole?
Electrician pointed out:
- Electricity + exceptional close to water = KISS.
- So follow the same guidelines as a geyser.
I like common sense.
I decided, geysers WILL be vertically mounted outside.
- Not only for water damage mitigation.
- But also for easier safer replacement by the people having to do it.
ā¦ and if you do it right, when the geyser pops, catch the water by default in the water tanks if possible.
The hidden benefit of a small geyser dedicated to the kitchen is that whoever washes the dishes āis educatedā to put the plug in the sink when doing dishes.
YES!!!
Or like me, use the damn dishwasher right next to it for peteās sake dammit!
So what it takes a day to fill up ā¦ so what.
The wife, on her own, realized that the other day.