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Solar geyser losing heat at night


Danger
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My solar geyser heats up to +65c during the day and then drops to 45c by the morning. I suspect the geyser is just siphoning water through all night long cooling it off. How do I prevent this? 

 

I've got 24 vacuum tubes accross 2x 200l in serie geysers. The "front" geyser is on geyser wise and the system takes cold water from the "back" geyser to feed warm water into the front geyser. 

Ive got geyser blankets and those pipe coverings on everywhere I could fit it. 

To make double sure it's not a temperature difference between the two geysers, I've electronically heated the rear one as well to 60c (normal element and thermostat) 

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1 hour ago, Danger said:

My solar geyser heats up to +65c during the day and then drops to 45c by the morning. I suspect the geyser is just siphoning water through all night long cooling it off. How do I prevent this? 

 

I've got 24 vacuum tubes accross 2x 200l in serie geysers. The "front" geyser is on geyser wise and the system takes cold water from the "back" geyser to feed warm water into the front geyser. 

Ive got geyser blankets and those pipe coverings on everywhere I could fit it. 

To make double sure it's not a temperature difference between the two geysers, I've electronically heated the rear one as well to 60c (normal element and thermostat) 

There should be a label on the geyser indicating the standing loss rate per hour. I lose about 4° overnight on my 200l evacuated tube geyser. Two kids have their showers at night and then the temp is about 52° at 8pm. At 7am the next morning the temp is down to 48°.

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Warm water will want to rise (thermal syphoning) so if the feeding geyser is higher than your main geyser (and you have a pumped system), this can be a problem.  We solved this problem by installing a non return valve.  Another solution if you have the space is to run the pipes downwards and then up to the feeder geyser.  The idea is that colder water collects at the bottom of the pipes effectively stopping the thermal syphoning.  This could be less maintenance over the long run as small particles can collect at the NRV's keeping them from closing properly.

 

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4 hours ago, Achmat said:

There should be a label on the geyser indicating the standing loss rate per hour. I lose about 4° overnight on my 200l evacuated tube geyser. Two kids have their showers at night and then the temp is about 52° at 8pm. At 7am the next morning the temp is down to 48°.

Tx. Our almost 20c drop is without anyone using hot water the evening. But thanks for the tip, will have a look. 

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4 hours ago, Niel said:

Warm water will want to rise (thermal syphoning) so if the feeding geyser is higher than your main geyser (and you have a pumped system), this can be a problem.  We solved this problem by installing a non return valve.  Another solution if you have the space is to run the pipes downwards and then up to the feeder geyser.  The idea is that colder water collects at the bottom of the pipes effectively stopping the thermal syphoning.  This could be less maintenance over the long run as small particles can collect at the NRV's keeping them from closing properly.

 

Makes sense! So basically put a kink in the pipes to prevent the warm water rising. Let me think it through, worried a vacuum might still push it through. 

 

I've heard the non returns valves don't last long and has to be replaced every few years. 

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Also check your TP valves (overtemp/overpressure) on both geysers,as I have seen these leak slowly and drop the temp overnight substantially, and consider if you don't have a hot water leak somewhere on one of the hot water pipes.

I once had a evacuated tube geyser that failed to heat, via solar or electrically assisted,  only to discover that the galvanized pipes had sprung a leak somewhere and the leak was not coming thru the walls or floors? They ended up running new piping to the taps and this sorted the problem. we could only find the issue with all taps closed and hen monitor the water meter, took a photo of the meter and 5 minutes later took anouther photo, we found the meter was turning over very, very, slowly :)

 

Good luck :)

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Non return valve on pump circulated system given up the ghost after a few years and hot water reverses into panels during the night. This will not happen with ordinary thermo geysers which have the panels below the geyser height.

 

Non return valves available in SA do not like hot water😀😀

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  • 3 weeks later...

Just to close this one off. I figured out my multi valve on the geyser is only 400kpa while the rest of the system is 600kpa. So part of what happened was that when the geysers got hot, they pushed water back out the multi valve on the mains (not to be confused by the TP valve...). 

 

While the guys was up there, I also got them to replace the non return valve leading to the solar tubes with a spring loaded version instead of a flap version. 

 

Between those two, the problem is now solved. Geyser works like a beast! Cut my daily consumption by 5 to 7kwhpd. The geyser is now actually overheating. New day, new problem. 

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11 hours ago, Danger said:

Just to close this one off. I figured out my multi valve on the geyser is only 400kpa while the rest of the system is 600kpa. So part of what happened was that when the geysers got hot, they pushed water back out the multi valve on the mains (not to be confused by the TP valve...). 

 

While the guys was up there, I also got them to replace the non return valve leading to the solar tubes with a spring loaded version instead of a flap version. 

 

Between those two, the problem is now solved. Geyser works like a beast! Cut my daily consumption by 5 to 7kwhpd. The geyser is now actually overheating. New day, new problem. 

I came here to say check your non-return. As for the multi valve, you won't push out much hot water before the pressure will normalize again.

The system should ideally also have an anti-syphoning loop - the return from the solar collector (hot side) should go lower than the cold outlet on the geyser near the geyser-like a U-shape. This should stop or minimize reverse syphoning even when the non-return fails.

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On 2021/02/18 at 8:32 AM, P1000 said:

I came here to say check your non-return. As for the multi valve, you won't push out much hot water before the pressure will normalize again.

The system should ideally also have an anti-syphoning loop - the return from the solar collector (hot side) should go lower than the cold outlet on the geyser near the geyser-like a U-shape. This should stop or minimize reverse syphoning even when the non-return fails.

I hear you on the multi valve, but it was dripping most of the day. So not 100% which one solved it more, I'm just happy. 

Just a pity I didn't pick this up before installed my pv solar system. Could have designed at least 6kwh/day smaller.... 

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  • 6 months later...

I had a solar system installed 4 months ago and after 2 I noticed the geyser temp drop overnight sometimes by 20 degrees.  Called in the technicians who checked the non-return valve (ball valve) and swear that its functioning properly.  Any suggestions?

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A ball valve and a non return valve are two different things. Ball valve closes off the water flow, non return valve only allows the water to flow in one direction. What type of solar system do you have: electric pump circulation or thermo circulation.

Temp should drop no more than 6 to 8 degrees on a winters night.

Get another technician to check it.

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Agree, get another technician to check it out.  Regarding NRVs, do not use the spring valves, they only handle up to 60C after which the rubber washer start to warp.  Install the swing valve at an angle, one without a washer as they can handle very high temps.

Scroll down on this link to see an example http://www.tecron.co.za/?controller=pages&view=load&id=spares_parts_and_accessories.  Also, if you install these with a ball valve on each side to close it off you can simply open the swing valve at the top and clean it out if dirty, close again and open ball valves for water to flow again.  I did that, so whenever I notice syphoning possibly taking place I do a 5 min cleaning with no need to replace the valve.  Very simple.

Rian

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