solar geyser "sucks" air

[BangCrash]

Hi folks

I have installed a solar heated geyser. There is a flat panel collector that is connected to the geyser via a small recurculating pump controlled by a geyser max "computer".

Further pertinent info: I have an off-the-grid home so there's no water-mains. Instead the home is fed with a pump from harvested rain-water. Nothing fancy: opening the tap drops the pressure which switches on the pump and water flows.

The problem which has me vexed is this: As the geyser temp reaches above 40degC, when the recirculating pump between the solar collector and the geyser switches on... for some reason there is a pressure drop in the geyser and it begins to suck air from the vacuum breaker.

This is a bit of a noisy affair and is a bit irritating. But nothing near as irritating as when we open a hot water tap later in the day and have water spitting and spurting at us until the bubbles are all expelled.

Now the thing is this: if, just as the vacuum breaker begins to such air, we open a tap and in so doing switch the mains pump on, then there is no problem. The mains pump pressurizes the system and the geyser sucks no more air.

What I don't understand (and don't have the experience to even begin to guess) is:
1. Why the recirculating pump switching on causes a partial vacuum to form in the geyser - and why only at temperatures above 40degC.
2. And why this drop in pressure in the geyser doesn't anyway trigger the mains pump.
3. And MUCH more importantly, how to fix this problem.

If any of you can help me with this I would be much obliged!

 

[transam]

??



So are u drawing water directly out of the solar panel than ?? that than gos into the geyser thingy (?) i.e your rain harvestor pumps water directly into the solar panel upon demand ?? when a tap is opened ?

Or am I competely off track here ??

 

[Agile]

Hello Baba

I am sorry but without a diagram of your setup or seeing it personally I cannot guess whats involved.

Who designed this layout?

Tony

 

[BangCrash]

uh...

Okay so there are PV panels that provide electricity. This is NOT what I am talking about. There is something entirely separate which is a solar water heater panel. Water from the geyser is pumped into this panel. It collects heat from the sun and heats the water. When the water temp in the panel rises 7degC above the temp in the geyser the controller switches on the recirc pump which drives this hotter water back into the geyser. The water in the geyser is now a little warmer than before. This process repeats all day and the geyser gradually builds up heat.

When I open a hot tap the main pump switches on and pressurizes the geyser and hot water flows.

But this is not a novel technology. Pretty standard if you live in places where the sun actually shines a bit.

The "rain harvester" is equally not anything spectacular. Its basically big drums that the gutter system feed into via some clever filters. Nothing exciting. The point is just that I don't have a council (or whatever local government you have) supplied high pressure system.

 

[Agile]

Yes Baba!

I understand what you have!

What I dont know is how the system is pressurised to enable the water to flow to your tap outlets and thus why air is being sucked in.

Tony

 

[BangCrash]

okay.

I guess I should have done a bit more reading before posting my Q on this forum. I didn't realise it was, essentially, a UK forum. All the little Union Jacks should have given it away, right?

So anyway, clearly my setup, which is not madly unique here in South Africa, is totally from another planet for you folks.

Fair enough. You know... I don't know even one person here that has double glazing? Not one that has central heating? We never even think of "excluding drafts" or anything like that. Because none of that stuff belongs in our reality.

What we have is sunshine and lots of it. So clearly what we are doing with plumbing and house building is very, very different.

So.. all good. Lesson learned. I guess I'll go looking for a forum that serves Aussies and Yanks (the southern variety) and other warm weather types.

Thanks all the same...

 

[BangCrash]

Sorry Tony

I was replying to the post before yours. Our lines got crossed.

I don't know if there is really a point pursuing this here. Unless you are just interested. I'd be happy to tell you more but, as I say, I think I should chat to folks that are more familiar with what I have.

 

[Agile]

The only places that I have seem where some properties dont have mains water are in Seweto and similar shanty towns!

Everywhere else either has mains water or a borehole and a ntaka on a tower !

Tony

 

[BangCrash]

Hi Tony

Okay, I guess shanty town dwellers don't have mains water. But theirs is a far cry from my situation. I made a carefully chosen life-style choice to leave behind city life. I moved to the most beautiful pristine forested area in the mountains where I have built and off-the-grid home. So, yes, I don't have mains water. I also don't have a sewerage servitude. I also don't have municipal electricity. But all of this is easily dealt with and the pay off is that I also don't have noise, pollution, traffic congestion, neighbors (no-one as far as the eye can see) and all the grime and crime that goes with city living. I have have forest views all around me and wildlife that visits my garden. I breathe the freshest cleanest air on the planet and I have no stress.

You see, Tony, I swapped trivial benefits like municipal mains water and electrical servitudes for... well... paradise.

I have put in place all the systems I need to live a very high quality life-style. I use a photo-voltaic system to electrify my home and so have all the modern conveniences that one could want. I use a carefully laid-out constructed wetland to clean the house's effluent. And yes, I have no water mains. But this is no challenge. I simply collect rainwater from the roof, via a rainhead filter into large reservoirs beneath the house. There is a pressure-switched pump that draws from the reservoirs that keeps all the water in the plumbing lines at a constant 3 bars. If one opens a tap then the pressure drops and this causes a pressure switch on the pump to close and the pump activates. The water flows uninterrupted. When one closes the tap the pump continues to run for a few seconds to ensure that the pressure is stabilised back at 3bar and then goes to standby mode.

So that is the cold water situation.

The hot water is just one small added complication. Solar electrical systems are not ideally suited to using electricity for heat. So my geyser has no heating element. It is essentially just a pressurised container. It has the usual input and output to the house's plumbing lines. There is, however, an additional loop that takes water out of the geyser, via a small recirculating pump, to solar heating panels. When the sun shines it warms the water in the pipes in the panel. As the water warms, so a controller detects that the water in the panel is warmer than the water in the geyser and the recirc pump runs. It drives water around the loop pushing ever warmer water back into the geyser. This slowly brings the geyser temp up over the course of the day. By the end of the day the geyser is nice and warm and baths or showers are in order.

Inside the home this is indistinguishable from any other domestic plumbing situation. You open the tap, water flows, no problem.

So anyway. I have a perfectly balanced functional off-the-grid home. There is just this one little niggle that I can't figure out. It is, as described, the fact that the main pressure pump keeps all the plumbing lines under a constant pressure of about 3 bar. But when the little recirculating pump kicks in to send water from the geyser to the solar heating panel and back... then there is this rattle-and-thump from the roof as the vac breakers suck air. I don't know why. More vexing is that I don't know why, if the pressure has dropped, it doesn't switch on the main pump (it switches on automatically with the pressure drop of an opened tap so why does this not switch it on). And why does this only happen when the geyser gets to above 40degC? This one little issue I have not been able to resolve.

Could it be something arcane like water having a different density at 40+ degrees than it does at, say 20? I don't know. But whatever the case, I will gladly forgo satisfying my academic curiosity as to why this happens if I can just find a solution that stops it from happening in the first place!

I tried using a anti-siphon loop on the geyser and then I tried using a non-return valve instead. Neither resolves the situation. I don't know what else to try.

And there you have it. That's my situation.

 

[mysteryman]

Good to know you have a wonderful lifestyle. Enjoy! Meanwhile, we need a diagram of what you have had installed before we can help.

 

[Agile]

Thats an interesting description of your lifestyle. Only problem is that it needs considerable capital to put in place. You may also be some way from shops and supplies etc.

If I had to make a bold guess I would say somewhere to the NW of Joburg but in such a large country of could be anywhere.

Its difficult for me to guess at what you have however I assume you have auto air vents at the top of the panels. I dont know what the vac breakers are or what they are designed to do.

How is the system protected against overheating?

Presumably the circulating pump is on the flow side? You only need a very tiny flow rate, can you reduce that?

At a pressure of 3 Bar there is no way that any air should be able to be drawn into the system. I am assuming that the panels take the primary water and its not an isolated secondary system.

Has it always done this or is it something that has started?

Tony

 

[doitall]

Vac breakers are to stop a vacuum and prevent implosion in a sealed system.

The opposite to a PRV.

 

[Agile]

So would an auto air vent ( but it was I who suggested he would have them and perhaps he just has the vac breakers instead as they would also expell air ).

Tony

 

[silverback]

Contact http://www.genersys.co.za/ ask to speak to Mike Leighton, they install thermal,solar systems in South Africa and I am sure will be able to assist with your problem

 

[BangCrash]

Hi Mysteryman

I didn't mean to come off quite so self-congratulatory. I guess I was really just trying to point out that this isn't a shanty installation and I got carried away.

Okay. So a diagram. I haven't done a plumbing diagram before so I'll have to give that a little thought. I think I remember seeing a guide to plumbing diagrams on the 'net. I'll find that and come back when I have something for you.

___

Tony, yes, one doesn't put an off-the-grid system in primarily because it is cheap. We did it because it allowed us to live where we want to live and the way we want to live. Its also a choice to live more sustainably. Its a part of the self-sufficient lifestyle we have where we pretty much live entirely off of our own land. But that is another WHOLE topic. Point is, no, it isn't cheap to install at all. but the up side is I will never see another utility bill ever. If you amortise the cost of such a system over the lifetime of the various components then it really does pay for itself quite comfortably.

Not near Joburg no. In the Garden Route. You see somewhat familiar with South Africa?

The panels are like this:
http://en.wikipedia.org/wiki/Solar_thermal_collector#Flat_plate_collectors

Vacuum breakers? Uh... perhaps you have a different name for them. These are two brass attachments mounted 30cm above the geyser. A quick search brought this:
http://www.dripsanddrains.com/tag/geyser-maintenance/page/2/
What would you call these over there? Is this an auto air vent, Tony?

The system isn't likely to overheat on purely solar heating. But if you add a back-up heater then it can. In that event there is a Temperature/ Pressure Relief valve on the geyser.

Yes, the recirculating pump is indeed on the flow side. Its a small 22w unit. I don't know what the actual flow rate is but it can't be much. It's specified particularly for this purpose. I hear what you say about reducing the flow rate. That would not be my first choice though. Ideally I'd like to know why this is happening and to fix the problem rather than reducing the efficacy of the system to compensate.

I agree totally that it shouldn't be pulling in any air. It should be pressurised and that should be that. And yet...

Yes, there is only one primary system.

Yes it has always done this. Or, as I say, when the geyser temperature sensor shows more than 40degC. Then it rattles and shudders up on the roof for a little while as it sucks the air and then that too settles down. It has done this from the beginning.

Thank you for your interest, Tony!

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Silverback - thank you very much for your suggestion. I'll give them a call but what are the chances they will tell me they need to send someone out to have a look. I mean there is no problem with wanting a service and then paying for it but when the service call means a very, very, very long drive on rural roads then billing becomes an interesting exercise. Which strongly encourages a DIY response in the home owner. But thank you none the less for the suggestion. I will follow up.