Hi All,

I asked this question a while ago on someone else's thread but even though I got some good advice, I did not get a definitive answer with which I feel comfortable enough to do the installation.

I will try to embed some photos, but this is my plan. In the ceiling is a standard 150Lt 240V water heater with a 3Kw element. I have been given an 80Lt solar geyser with a flat plate collector, which I want to connect in series and hopefully rely on thermosyphon to keep both cylinders hot while using minimum grid input. If there is no alternative, I am happy to add a 12V solar circulation pump but would prefer not to. Is my diagram correct and what am I missing?

Hope this makes sense, thanks in advance

Solar Geyser Setup.pdf

Sorry I can't seem to open the PDF, hopefully you guys can see it

It looks like you want the flatbed to syphon into the small geyser and the small geyser should syphon into the big geyser... You need non return valves on both these circuits and without a pump they must open at very low pressures.

Thanks for the reply, I much appreciate the input. So where exactly must I install NRV's? Do I need to install vacuum breakers on the solar (lower) geyser? I am not averse to installing a circulation pump if it is the only way, where do I fit it or them in the system?

8 hours ago, dax021 said:

I am not averse to installing a circulation pump if it is the only way, where do I fit it or them in the system?

Personally, I would install a circulation pump - that would distribute heated water more efficiently than just relying on a thermosyphon. Also, if you do add a pump, have it circulate the water through both geysers, thus using the sun to heat up all the water, and not just that inside the small geyser. I would put the pump on a timer (and for "belts and braces" also on a light switch - the type that "makes" when a certain light intensity is reached, and "breaks" when the sunlight drops below the set level).

Thanks for the help. Ok, I will add the circulation pump, it makes sense. Now if someone could just confirm my drawing with advice on where to install the pump, NRV's and vacuum breakers, I be very appreciative. Thanks

The circulation pump I have runs on a small solar panel, so I assume this would be self regulating, i.e., it would pump while the sun shines and not at night or cloudy days

@dax021

My 2cents on your application. I just want to state beforehand that I am by no means a plumber just my input based on experience.

Your diagram won’t work as intended because you’re mixing a 4 kPa open-vented solar geyser with a 6 kPa pressurised (mains pressure)Kwikot in the same hydraulic loop.
The NRV does not isolate pressure the solar geyser will still be exposed to mains pressure unsafe/non-compliant.
Thermosyphon will only work within the solar collector solar tank loop, not between the solar geyser and the Kwikot.
So no, the solar unit will not siphon into the Kwikot. Keep the solar geyser on its own low-pressure (header tank) system and
use it as a preheat source only.
Solar hot outlet to Kwikot cold inlet and add a tempering valve or diverted valve (very important) and a add isolation + bypass line. No pump required if gravity feed is correct. Separate the pressure systems and use the solar as a pre-feed don’t try to thermosyphon between the two cylinders.

Hi TaliaB, thanks. So, in the edited drawing I have removed the line back to the 4Kpa geyser. Is this basically what you have suggested?

Solar Geyser Setup 1.pdf

2 hours ago, dax021 said:

Hi TaliaB, thanks. So, in the edited drawing I have removed the line back to the 4Kpa geyser. Is this basically what you have suggested?

Solar Geyser Setup 1.pdf

I missed your diagram in the original post - it's hidden to the side of one of the photos... Now that I've had a look at the diagram I can confirm: @TaliaB is correct. If your hater pressure is higher than the rated 4 kPa of the solar geyser then there is a risk that this geyser could burst or develop a leak, and is thus not suited to be coupled directly to your high-pressure water mains - just removing the line from the back of the tank won't solve this problem. You could run both geysers at the reduced 4 kPa pressure, but that would result in lower water pressure in your house.

9 hours ago, HennieL said:

If your hater pressure is higher than the rated 4 kPa of the solar geyser.

Oops... serious error here on my part - typical of contravening the first universal law of everything: Ensure brain is engaged before opening mouth (or posting in a forum...). Normal municipal water pressure varies between 400kPa and 600kPa, and I should have stated "400kPa" instead of "4kPa" - apologies to the OP for this... and thanks to @Scorp007 for pointing out my error in a PM - that's what friends are for 😄

20 hours ago, TaliaB said:

Your diagram won’t work as intended because you’re mixing a 4 kPa open-vented solar geyser with a 6 kPa pressurised (mains pressure)Kwikot in the same hydraulic loop

Apologies Gents I confused the issue between Kpa and Bar. Rather 4Bar and 6Bar or 400Kpa and 600Kpa.🫣Thanks @Scorp007

Edited April 15Apr 15 by TaliaB

Thanks for pointing this out. I started the confusion by getting the scale wrong to start with. So, if I add a 400kPa PRV to the cold inlet will my diagram work? I haven't tested my water pressure (I will), but suspect it is not 600kPa anyway

8 hours ago, dax021 said:

I haven't tested my water pressure (I will), but suspect it is not 600kPa anyway

I suggest you confirm that with your local municipality, or with a reputable plumber in the area where you live. Remember, the water pressure will increase or decrease depending on the water level in your feeder reservoir, and that could easily vary between 400kPa and 600kPa. At least, check the pressure over a number of days, and mornings and evenings, just to reduce your risk.

43 minutes ago, HennieL said:

confirm that with your local municipality

A PRV is better than anything the municipality says.

1 hour ago, TaliaB said:

@dax021

My 2cents on your application. I just want to state beforehand that I am by no means a plumber just my input based on experience.

Your diagram won’t work as intended because you’re mixing a 4 kPa open-vented solar geyser with a 6 kPa pressurised (mains pressure)Kwikot in the same hydraulic loop.
The NRV does not isolate pressure the solar geyser will still be exposed to mains pressure unsafe/non-compliant.
Thermosyphon will only work within the solar collector solar tank loop, not between the solar geyser and the Kwikot.
So no, the solar unit will not siphon into the Kwikot. Keep the solar geyser on its own low-pressure (header tank) system and
use it as a preheat source only.
Solar hot outlet to Kwikot cold inlet and add a tempering valve or diverted valve (very important) and a add isolation + bypass line. No pump required if gravity feed is correct. Separate the pressure systems and use the solar as a pre-feed don’t try to thermosyphon between the two cylinders.

Great reply @TaliaB I left my reply for the guys with the knowledge😀. I did however pick up the syphon if the height of the units are not correct. 1 problem less would be if the Kwikot of 600kPa is installed in a older house that has 400kPa regulators fitted and the last installer did not change it to suit the geyser. Less work as is common these days.

21 hours ago, HennieL said:

I suggest you confirm that with your local municipality, or with a reputable plumber in the area where you live. Remember, the water pressure will increase or decrease depending on the water level in your feeder reservoir, and that could easily vary between 400kPa and 600kPa. At least, check the pressure over a number of days, and mornings and evenings, just to reduce your risk.

I doubt the pressure is based on the level of the reservoir. If it was the houses next to it will suffer serious pressure handicaps. I belief pumps with regulating valves are used.

1 hour ago, Scorp007 said:

I doubt the pressure is based on the level of the reservoir. If it was the houses next to it will suffer serious pressure handicaps. I belief pumps with regulating valves are used.

The consulting engineering company that I work for does a lot of water engineering designs, amongst other things, and although my specialty is in a different field, I am regularly part of conversations regarding this field. To my knowledge *most* water pressure regulation in smaller cities, towns, and rural areas is done by using large gravity-fed "water tower" reservoirs. Larger cities do use Pressure Reducing Valves (PRVs) to ensure more uniform pressure, independent from water level height in the reservoir towers, but here in Bloemfontein I can personally confirm that our water pressure is primarily regulated by reservoir gravity feed, although they have installed a few PRV's (that don't work when the reservoir levels are low...).

Adjacent houses built on approximately the same level, and supplied by the same mains line, are not individually affected by a reservoir gravity feed. If, however, your neighbor's house is located substantially higher than your house, then his pressure would be seriously handicapped, as you stated.

Brand new Kwikot installed a month ago soon after I moved in here. First time I looked in the ceiling I noticed it was leaking in 2 places, so the seller had it replaced under her insurance. I still had to pay in R2500 excess, which I was not happy about. I don't see any other PRVs on my line, in fact I can't even find a shut off valve on either side of my meter. If I close the tap feeding the geyser, half the house's water supply is cut, but the rest is still open. Weird setup, in my mind.

The solar geyser came from a friend's house, he removed it when he did renovations to his bathroom. It is not open to atmosphere, but I remember it had vacuum breakers on it. Unfortunately, he didn't take note or photos of how it was connected, but it was mounted outside and had 22mm pipes going through his tiles and connected to his internal geyser.

I contacted the solar geyser manufacturer, but they said they can't help, get a plumber. I don't need this extra expense, and I am more than capable of connecting everything up safely, as long as I can get the correct info.

Thanks for all the advice, I really appreciate it, and am looking forward to more and coming up with a plan.

3 hours ago, HennieL said:

The consulting engineering company that I work for does a lot of water engineering designs, amongst other things, and although my specialty is in a different field, I am regularly part of conversations regarding this field. To my knowledge *most* water pressure regulation in smaller cities, towns, and rural areas is done by using large gravity-fed "water tower" reservoirs. Larger cities do use Pressure Reducing Valves (PRVs) to ensure more uniform pressure, independent from water level height in the reservoir towers, but here in Bloemfontein I can personally confirm that our water pressure is primarily regulated by reservoir gravity feed, although they have installed a few PRV's (that don't work when the reservoir levels are low...).

Adjacent houses built on approximately the same level, and supplied by the same mains line, are not individually affected by a reservoir gravity feed. If, however, your neighbor's house is located substantially higher than your house, then his pressure would be seriously handicapped, as you stated.

Thanks for sharing this info Hennie. Never to old to learn even if it is slow 😂