Hot water tank degenerative disease

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Hot water tank degenerative disease

Postby jules » Fri Jan 13, 2017 9:19 am

I seek your thoughts please ...

400l mains hot water tank with 4,800W bottom element, roof solar X 2

Electricity controlled load bill over the last 12 months ...
3 month to Dec. '15, 2.35kWh per day
3 month to March '16, 1.25kWh per day
3 month to June '16, 6.13kWh per day
3 month to Sept. '16, 8.89kWh per day
3 month to Nov. '16, 10.7kWh per day
1 month to Dec. '16, a massive 12.39kWh per day!

As you can see, there is something close to a six fold increase in controlled load consumption over 12 months. Origin reckons the meter is ok and that seems right.

An electrician reckons the tank is ok and has no suggestions for the increase in kWh. There are no leaks in the tank. There are no dripping taps.

The number of people in the house has actually dropped from the first readings, down from 4 people to one or two. [the drop between the 1st and second bills was probably related to the number of people in the house at those times]

So it appears that something is degenerating but what? At the moment I'm wondering if a valve could have failed and there could be a reverse cycle thermo-syphon action happening at night, with the panels taking water from the top of the tank and cooling it down. There's some indications of this in the temp. of the pipe from the top of the tank to the solar panels but hmmm, probably wrong .... any thoughts out there?

Footnote ... we've turned off the power to the tank and things have been going just fine for a week without it. Water temp. is not noticeably different.
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Re: Hot water tank degenerative disease

Postby Gordon-Loomberah » Fri Jan 13, 2017 1:07 pm

Are you sure someone isn't taking really long showers? ;)
Just solar alone should supply more than enough energy over much of the year, with electric boosting only required in cloudy periods.

12.39kWh is enough energy to heat over 250litres by 40C (I don't know your source water temp or thermostat setting, so just an example), and that is assuming NO solar heating!

I'd be watching the temp/pressure release valve very closely, you may be losing a lot of hot water through it.
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Re: Hot water tank degenerative disease

Postby jules » Fri Jan 13, 2017 1:29 pm

Are you sure someone isn't taking really long showers? ;)


:) Absolutely certain. The generation of younger people who somehow lose sense of time in a shower, has left home and we're definitely very short showerers.

I've checked the release valve and the first time I opened it the water that came out looked as though it had been sitting in the outlet pipe [a metre or so long] for quite some time. There's no sign of any wetness anywhere around the tank.

The thermostat on the tank is set on 70C and hasn't changed.

This system is coastal NSW, Port Macquarie, so the water supply is never particularly cold.

The thing that stands out, is that this has been progressive and quite slow to develop ... 12 months or so, though there was a distinct starting point where the controlled load consumption seems to have jumped from a bit over 1kWh to around 6kWh per day.

I'm going to see what the "DeltaSol" computer controller for the unit can tell me, when I figure out its language.

Thanks for the reply Gordon.
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Re: Hot water tank degenerative disease

Postby davef » Fri Jan 13, 2017 4:51 pm

At the moment I'm wondering if a valve could have failed and there could be a reverse cycle thermo-syphon action happening at night, with the panels taking water from the top of the tank and cooling it down. There's some indications of this in the temp. of the pipe from the top of the tank to the solar panels but hmmm, probably wrong .... any thoughts out there?


To reduce running time on the solar hot water pump it was suggested to me to increase the flow rate to 6L/min and put the pump on a higher power setting. This reduced running time during sunny days BUT I also noticed that the lines to the roof were getting warm at night especially when the wood burner was going. The installer told me I had been given bad advice.

Good luck!
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Re: Hot water tank degenerative disease

Postby jules » Fri Jan 13, 2017 5:35 pm

Thanks davef.

I'm hoping the control module might at least give me a hint as to where the problem lies and I suppose I've got several months to figure it out when there's no need for any grid power heating right now.

I doubt that the problem will be with the pump power as that's not "controlled load" which is where the power is being used and it is HUGE @ 12kW per day in summer. I just can't see where so much power could disappear to.
Primary system: .8KW Trina panels; Plasmatronics PL40; 1,000Ah VRLA 12X2V battery bank; 1.7KW Selectronic inverter

Veteran system, semi retired: 6 X 55W Solarex 12V panels; Fangpusun CC; 6 X 2V, 35 year old 550Ah lead acid flooded cell batteries.
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Re: Hot water tank degenerative disease

Postby melmik » Sat Jan 14, 2017 3:25 pm

Hi Jules, that is a weird jump in consumption. Thinkibg about it practically, what parts in the system not working (or more importantly, failing progressively over the timeframe) could cause this?

1: top or bottom heating element gradually degenerating, or one failing? Leading to less efficient heating and therefore increased controlled load input. Maybe a second inspection by another tank specialist.

2: thermostat? Seems less likely to fail slowly.

3: pressure release valves? These do fail and do release enough water to need cold top ups and resultant increased energy use. BUT, as you said you havent seen any water leaks. Have you checked during the controlled load (1or2?) periods?

4: other leaks? As above it could be a cause but you havent seen any. Maybe check on roof near solar collectors? Do they have overtemp blow off valves?

5: meter? Did Origin actually check it? Or Ausgrid. My EM1200 meter recently had an unexplainable 10x jump in use on the 2nd circuit (not the controlled load circuit). Origin just dismissed it as a one off error. No physical check. Maybe record the actual hourly readings during the controlled load period to see how long, when it is boosting. Check the boost button, assuming yours isnt sealed like mine.

6: solar heating not heating? Leading to increased reliance on controlled load. Sorry, i know bugger all about the physical bits of solar heating.

I'm obviously no expert but it seems it must be something physical gradually failing and there arent many parts that do that.

Hope you solve it soon

Cheers
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Re: Hot water tank degenerative disease

Postby jules » Sun Jan 15, 2017 10:42 am

G'day Michael and thanks for applying your head to this problem.

On 1. I think there's a reasonable chance of this and I might contact the tank manufacturer with the symptoms to see what they think.

On 2. I agree and I think that if the thermostat had been failing to cut off at the set temp. there would probably have been boiling and pressure release through the valve but there were no signs of that, so maybe that supports 1.

On 3. I've replaced it, though I've yet to run a test since then.

On 4. The power has now been off for more than a week and the solar side of things has been supplying the heat which seems to be as hot as it ever was, so I'm thinking that this indicates there isn't a significant leak because, particularly with solar heating only, there should be a drop in temperature. Put another way, under circumstances where the element would have been using 12kWh per night its absence hasn't caused any noticeable change in water temp ... maybe that leads back to 1 again but have to keep an open mind :D

On 5 Aaagh. Origin reckon that if they come out to test the meter and it isn't at fault, there's a $300 charge. I think it can be ruled out though as there has been a meter change-over recently and it's telling the same story. Initially I thought it might be the meter till I went back and collated the figures showing a gradual rise over 12 months.

On 6 The solar is excelling and doing a good job of showing up the mains system, at least now, in the middle of summer.

There is a slight chance that this is a tech. problem as there's a small computer board managing the solar pump [and possibly overseeing the thermostats].

I'm surprised that the electrician didn't take on the symptoms and come up with an instant diagnosis. With so many of these thanks around, this has to be a common thing.

I'll tell you how it goes .....
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Re: Hot water tank degenerative disease

Postby Smurf1976 » Sun Jan 15, 2017 5:06 pm

Element won't be the problem. If power is being used via an element then heat is being produced and the efficiency won't change since it's always 100%.

My first thought is that the pump could be running at night thus circulating water through the solar and radiating heat away?

Or is the tank's temperature setting via the thermostat for boost heating such that it effectively stops the solar working during the day? Tank heats up overnight on off-peak power, too hot during daytime for the solar to activate, then draws power again that night to heat. I say that noting that 70 degrees for a booster is rather high - try 60 and see what happens.
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Re: Hot water tank degenerative disease

Postby davidg » Sun Jan 15, 2017 6:46 pm

Now I've read the posts properly. It strikes me that this appears to be likely a faulty check valve/s in the lines to/from the roof and the heat is leaking back out the panels on the roof at night, through thermal siphoning. #just saying

I know "thermal siphoning" was mentioned, but there's no mention of testing or checking of the "check valve/s" that would stop this occurring.
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Re: Hot water tank degenerative disease

Postby jules » Mon Jan 16, 2017 4:15 pm

Thanks davidg. That's helpful. I'm quite ignorant of the working of mains systems as my home system is basic thermo-syphon copper tank with home made solar /combustion stove [no fancy pump stuff].

I will work out if that's something I can look at, or if it's a situation for calling in another electrician with special tank skills.

Jules
Primary system: .8KW Trina panels; Plasmatronics PL40; 1,000Ah VRLA 12X2V battery bank; 1.7KW Selectronic inverter

Veteran system, semi retired: 6 X 55W Solarex 12V panels; Fangpusun CC; 6 X 2V, 35 year old 550Ah lead acid flooded cell batteries.
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