Odd question perhaps - has anyone tried to improve how their immersion heater heats water?

[SteamyTea]

3 minutes ago, MrTWales said:

That spike looks like those random (to me!) spikes that I see sometimes

Count the LED pulses on the meters.

Posted up details on how to do it.

 

 

[MrTWales]

Thanks, I'll have a go!

[Radian]

3 hours ago, MrTWales said:

If it was consumption of 6kw I think the orange line would be at 6kw,

 

"Consumption" does indeed sound like local power demand - be it supplied by solar PV, battery or grid (or combination thereof) but seeing as how Grid is positive for exporting (i.e. when your battery is max'd out, all the excess power suddenly switches to going out to the Grid) then negative (below the line) would signify import.

 

The way the red trace slopes down initially looks more than a spike to me. Just before, the battery took on charge while PV briefly rose. Then the Grid spike overlaps the battery discharge and consumption making it look to me as though the battery inverter reached its maximum generation limit (3kW?) and the load was such that a top-up was needed from the grid. That's what it looks like.

[Radian]

On 16/04/2023 at 13:09, JohnMo said:

I put my immersion on to an external thermostat, as I could never get the cylinder hot enough, even replaced the immersion and integrated thermostat, but it made little or no difference.  Max temp I could get to was about 60, even the immersion thermostat set at 75.

I'm also struggling to get more than 58^oC hot water even when the built-in immersion thermostat is dialed all the way up to 70^oC

While I've also contemplated bypassing the immersion thermostat and controlling the heater with an external thermostat, I'm wondering if there's a reason for this apparent 'universal limitation' among like devices?

Do they deliberately underrate them because they'll rapidly fall over if made any hotter? Seems odd that they'd consistently mislead with the temperature dial.

[SteamyTea]

6 minutes ago, Radian said:

I'm wondering if there's a reason for this apparent 'universal limitation' among like devices?

Safety maybe.

 

[JohnMo]

It could be the thermostats in the heating element, it could be seeing local temperatures at the set point, but the cylinder isn't at that temp.  My view it's just a rubbish design that is just copied.

 

No-one ever really looks at the temp, except some on here when they are trying to use excess PV and it doesn't go to plan.

[Radian]

Just now, SteamyTea said:

Safety maybe.

 

Yeah but from what issue? Scalding hot water? Uncontrolled boiling in the cylinder? Electrical wiring or insulation integrity? In which case why promise 70^oC and deliver 58^oC?

In other words, what perils await me and @JohnMo if we bypass the stat?

[SteamyTea]

13 minutes ago, Radian said:

Yeah but from what issue? Scalding hot water? Uncontrolled boiling in the cylinder? Electrical wiring or insulation integrity? In which case why promise 70^oC and deliver 58^oC?

In other words, what perils await me and @JohnMo if we bypass the stat?

Probably all the above.

Our cars (the Ford ones) are capable of 113 MPH, but not for very long.

My usual average speed is around 30 MPH, even though I sometimes go almost to the speed limit.

By driving like I do, I avoid excess expenses (maintenance, fuel and fines) so I have built in reliability.

 

There is also a lot of energy in water at 70°C.  Each gram has 4.2J for every degree above ambient.

So if skin temperature is say 35°C, and a gram of water is at 65°C when it hits your skin, that is 126J.

Now a joule is defined as kg.m^-2.s^-2.

As a gram or water is going to have a tiny surface area, say 5mm² and cool down in say 0.5s once smeared on your arm, it is akin to being hit by a 1 kg hammer travelling at 40m.s^-1.

I think, it will hurt all the same.

 

Edit: Whoops forgot the time element, so 20 m/s.

 

Edited April 17, 2023 by SteamyTea

[Radian]

So perhaps the water right next to the pocket with the sensing element in it does actually reach the setting on the dial, in which case the 70^oC might be the truth. Maybe the difference with the temperature at the top of the tank reflects the physics of the water blending?

The worry here is that bypassing the stat could lead to local boiling. I'm not worrying about catastrophic boiling of the whole cylinder but the consequences of boiling at the element might have a subtle effect on the element - might it push it past some design limit?

Mixer taps get round the problem of storing HW at a wide range of temperatures so it's very tempting to find some way of lifting the limit.

[JohnMo]

Mine is on a thermal store, not sure that really makes much difference, but our our outlet water goes out via a temperature controlled mixing valve. 

 

Safety not sure on that.  If I had mine set at 60 for a so called legionnaires cycle, I would hit the low 50s so that's not good for that safety cycle.

 

Poor design - Or is the PV diverter putting out a smaller kW than the design of 3kW, so the water flow around the immersion not per design intention?

[SteamyTea]

16 minutes ago, JohnMo said:

Safety not sure on that.  If I had mine set at 60 for a so called legionnaires cycle, I would hit the low 50s so that's not good for that safety cycle.

The element may easily be at 150⁰C+, as most of the stored water will pass by it, it should sort out the bacteria.

My cylinder makes quite a noise when it is heating, like a kettle.

[MrTWales]

You've got me questioning everything I thought I knew!

 

I can see what you are saying but it does seem like consumption really is consumption (though how accurate it is is another matter). If I look at the history data it shows the following: it looks like the immersion flicked on and it took a while for the battery to discharge. As far as I can see, the battery can discharge at 4kW at least as I've seen this "pDisCharge" value on other days (I'm fairly sure that this is the limit).

 

The chart uses 5 min incremements so I think some spikes can look bigger than they are. 

 

 

5 hours ago, Radian said:

 

"Consumption" does indeed sound like local power demand - be it supplied by solar PV, battery or grid (or combination thereof) but seeing as how Grid is positive for exporting (i.e. when your battery is max'd out, all the excess power suddenly switches to going out to the Grid) then negative (below the line) would signify import.

 

The way the red trace slopes down initially looks more than a spike to me. Just before, the battery took on charge while PV briefly rose. Then the Grid spike overlaps the battery discharge and consumption making it look to me as though the battery inverter reached its maximum generation limit (3kW?) and the load was such that a top-up was needed from the grid. That's what it looks like.

 

Edited April 17, 2023 by MrTWales
"kW" instead of "kw" to keep Stormytea happy.

[Radian]

17 hours ago, JohnMo said:

  If I had mine set at 60 for a so called legionnaires cycle, I would hit the low 50s so that's not good for that safety cycle.

 

Very good point. 

 

17 hours ago, JohnMo said:

Poor design - Or is the PV diverter putting out a smaller kW than the design of 3kW, so the water flow around the immersion not per design intention?

 

So long as it exceeds the losses, the first law of thermodynamics makes sure that the temperature will rise regardless of reaching the design power.

[PhilT]

15 hours ago, MrTWales said:

As far as I can see, the battery can discharge at 4kW

Your Luxpowertek app says that your system is capable of discharging at up to 180amps = c. 9kW

[MrTWales]

6 minutes ago, PhilT said:

Your Luxpowertek app says that your system is capable of discharging at up to 180amps = c. 9kW

Thanks, that seems like a lot. I think I just assumed 4kW as when I looked at the data there were a few discharge figures around there but it may be concidence. 

[Radian]

Testing the rod thermostat out of the cylinder I found the switching point is around 15^oC lower than shown on the adjustment pointer. Difficult to say exactly because of around 5^oC hysteresis. 15^oC certainly tallies with what I was finding with the dial set to 70^oC and getting water at 55^oC. I took the cap off the thermostat assembly and found the pointer sits on a splined shaft so can be put back on with an offset. Trying that now.

 

[SteamyTea]

1 hour ago, Radian said:

found the pointer sits on a splined shaft so can be put back on with an offset. Trying that now.

I shall get the teapot ready.

[Iceverge]

Meanwhile at @Radians house............

Edited April 18, 2023 by Iceverge

[JohnMo]

All those years inventing rockets, all they needed was an UVC. And a badly set immersion and a relief valve that didn't work.

[SteamyTea]

1 hour ago, JohnMo said:

All those years inventing rockets, all they needed was an UVC. And a badly set immersion and a relief valve that didn't work.

Could have been worse, or better.

 

Operation Plumbbob, at least it has a plumbing term in it.

 

In 1956, Dr Robert Brownlee, from Los Alamos National Laboratory in New Mexico, was asked to examine whether nuclear detonations could be conducted underground. The first subterranean test was the nuclear device known as Pascal A, which was lowered down a 500 ft (150 m) borehole. However, the detonated yield turned out to be 50,000 times greater than anticipated, creating a jet of fire that shot hundreds of feet into the sky.[8] During the Pascal-B nuclear test,[8] of August 1957,[9][8] a 900-kilogram (2,000 lb) steel plate cap (a piece of armor plate) was welded over the borehole to contain the nuclear blast even though Brownlee predicted it would not work.[8] When Pascal-B was detonated, the blast went straight up the test shaft, launching the cap into the atmosphere at a speed of more than 66 km/s (41 mi/s; 240,000 km/h; 150,000 mph). The plate was never found.[10] Scientists believe compression heating caused the cap to vaporize as it sped through the atmosphere.[8] A high-speed camera, which took one frame per millisecond, was focused on the borehole because studying the velocity of the plate was deemed scientifically interesting.[8] After the detonation, the plate appeared in only one frame, but this was enough to make an estimation of its speed. Dr. Brownlee joked the best estimate of the cover's speed from the photographic evidence was it was "going like a bat!".[10] Brownlee estimated that the explosion, combined with the specific design of the shaft, could accelerate the plate to approximately six times Earth's escape velocity.[10] In 2015 Dr. Brownlee said, "I have no idea what happened to the cap, but I always assumed that it was probably vaporized before it went into space."[9][failed verification] Later calculations made during 2019 (although the result cannot be confirmed) are strongly in favor of vaporization

[ProDave]

17 hours ago, Radian said:

Testing the rod thermostat out of the cylinder I found the switching point is around 15^oC lower than shown on the adjustment pointer. Difficult to say exactly because of around 5^oC hysteresis. 15^oC certainly tallies with what I was finding with the dial set to 70^oC and getting water at 55^oC. I took the cap off the thermostat assembly and found the pointer sits on a splined shaft so can be put back on with an offset. Trying that now.

 

In defence of @Radian I did much the same.

 

My immersion (similar design) cur out at I think it was about 62 degrees with the thermostat at max. So I made pretty much the same adjustments.

 

Each time I raised the "thermostat range" I tried it, using the ASHP's probe to measure the new cut off temperature.  I stopped adjusting when it would reach 78 degrees and then cut out.  That is still well below any danger level but allows quite a bit more surplus PV to be stored in the tank.

 

All I would say is if you try such a thing, you need an independant, trusted means to measure  the temperature your thermostat cuts out after being "adjusted"

[dpmiller]

I can't say I've ever thought of accurate calibration as a risk of any kind, moreso when there's a failsafe anyway...

[ProDave]

15 minutes ago, dpmiller said:

I can't say I've ever thought of accurate calibration as a risk of any kind, moreso when there's a failsafe anyway...

Don't under estimate the danger of boiling the water in an UVC, hence why I made a series of small adjustments checking progress after each one.

[dpmiller]

1 minute ago, ProDave said:

Don't under estimate the danger of boiling the water in an UVC, hence why I made a series of small adjustments checking progress after each one.

Absolutely. But it would be *incredibly* bad luck for both the 'stat's redundant overtemp AND the T&P valve to both fail.

[Alan Ambrose]

>>> the detonated yield turned out to be 50,000 times greater than anticipated

 

That's often what happens when you calculate in imperial.