Hot water immersion through Eddi - longer immersion element not responding

manatoo

Hi

Tricky one to post this because it touches on electrics and plumbing but I think it's more suited here.

I have recently had solar installed with an Eddi diverter, a new 42inch stainless steel hot cylinder and a 36 inch double element immersion. The Eddi can accommodate two circuits, one for each of the elements in the immersion so sink/bath switchability. The electricians have wired each of the elements to each of the circuits but only the sink portion is heating. It doesn't matter what way I switch it on the Eddi using the device or the app, it just heats the upper portion of the tank. The electricians have tested both circuits of the immersion and say they are both working. The Eddie "sees" both circuits and I have it set so that when one heats to the max thermostat setting, the other should then heat to its setting but this switchover doesn't kick in and when I manually switch it to the second circuit it clicks off in a matter of seconds claiming the max temp is reached.

Does anyone have any ideas? I've had the electricians look at this multiple times and they are coming up with nothing despite speaking with Eddi staff and supposedly testing everything.

Thanks for any help/guidance/wisdom

John.G

Is this the set up you have, with one thermostat?.

pale rider

I have an iboost which does the same job, Also with two circuits, when installed it was set to heat bath, I had it changed to sink.

I don’t know how you have it wired directly to both unless it has a. Auto switch which the iboost does not, has the Eddi an auto switch

My sense is it is set up to sink only hence the trip when you change it.

monseiur

I would guess the issue is with the stat. Get your electrician to wire the bath element on it own (if that's possible) see if it works ok

50HX

Is it switching to tank 2 on the eddi when tank1 is heated?

manatoo

Hi all

Sorry for ghosting this thread. Just to wrap it up, I figured it out and I think it was by coming to the same conclusion John.G was about to tell me above. The issue is that there's only one thermostat at the top of the immersion so when the sink (short) element heats to temperature at the top of the cylinder then switching to the bath (long) element does nothing because it's all the one thermostat. The solution is to just leave it heating the bath element at all times. Presumably there's double-element immersions that have two thermostats which is what the plumbers should have used but believe me, with these guys, that was the least of my problems…

dingding

there is an add on board to the Eddi that you can add extra temperature probes.

I use this but with a Willis heater. Water always hot and excess energy exported.

It gives a lot more control over the tank and water temp.

manatoo

https://www.boards.ie/discussion/comment/123756637#Comment_123756637

How do you add the extra probes to the hot water cylinder?

Lenar3556

https://www.boards.ie/discussion/comment/123755995#Comment_123755995

A good diagnosis and solution.
The ‘sink’ element often brings about more issues than it’s worth, even without a solar diverter involved.

A single long element and a well insulated low loss cylinder is the way to go in my opinion.

dingding

https://www.boards.ie/discussion/comment/123756724#Comment_123756724

My tank was insulated with a green foam. I also then lagged it with a sheeps wool lagging jacket. I pierced a hole through the foam gently till I rubbed against the copper cylinder and then shoved the probe into the hole. Link below is not the actual one I used, but it is similar. Just be careful, there is a PT100 and PT1000 sensor, just check which is the correct spec for the job.

I have mine set to heat the water to 55 Degrees on the night rate, and I top it up to 50 Degrees on the Solar. The actual temperature does not matter, with trial and error just set it up to give you the amount of water you need.

This has worked well for me, and has meant I have exported more Electricity and just used the minimum necessary to heat the tank.

This is the link to the expansion board.

https://www.myenergi.com/product/eddi-relay-sensor-board/

This is a link to the type of sensor.

https://www.amazon.co.uk/dp/B088V55M43

John.G

Where is the PT1000 sensor mounted?

One would think there could/would be a big temperature gradient if a top mounted heating element is controlled by the PT1000 sensor depending on where its installed on the cylinder. If its installed close to the top then a very small temperature gradient but practically the whole cylinder HW contents must be used up before reheating can occur. If its installed say 1/4 way up or so then the reheating will commence when a relatively small vol of HW is drawn off but because of the vertical element there will be very little de stratification so a big temperature gradient IMO.

dingding

I have the sensor mounted about 1/3 way down. I have a Willis heater so it heats from the top down, so the setup works well. Trial and error has given me 2 showers at a 50 degree setting.

So after some water is used the solar (Eddi) heats the water up to 50 degrees.

I have the Eddi set to heat the water to 55 on the night rate and the Eddi keeps it at 50 degrees during the day.

John.G

https://www.boards.ie/discussion/comment/123767101#Comment_123767101

Thats quite interesting, what diameter piping are you using, often the circulation flow rate through the Willis is too low resulting in very high Willis outlet temperatures, have a read through this sometime where a pipe stat was installed to control the (Over) temperature.

https://www.boards.ie/discussion/2058243718/fitting-a-willis-immersion-heater

dingding

https://www.boards.ie/discussion/comment/123767529#Comment_123767529

I think that was the issue I had, before I had the temperature sensor installed, the Eddi used to try to put all the excess solar into the tank. From memory, it caused it to overheat and the hot taps were dangerously hot. At that time I put a valve on the shower which limited the hot temperature. It was a Thermostatic Mixing Valve, with a hot and cold inlet and a warm (Max Temp could be set) outlet.

It now gives me plenty of hot water, but does not overheat the water, or waste the potential to export electricity.

I think with the current set up I have the best balance of having hot water and exporting the most electricity. I am very happy with the setup and the key to it is probably the willis heater as it heats the tank from the top down.

I think the copper pipe from the Willis is 1/2 inch or the nearest metric.

The best solution would be to replace the tank with a larger Stainless Steel factory insulated tank with a top and bottom element, however the current setup will do me another while. The Eddi would work well with the expansion board as 2 elements can be powered from the Eddi and 2 temperature probes can be added.

I tried to put in a Dual Element Immersion heater around that time that the water was over heating, as I felt the solution was probably to heat with the long element, however the plumber 20 years ago installed the plug with boss white or similar and it was stuck solid, was in danger of damaging the tank, thread if I put much more effort into it.

John.G

https://www.boards.ie/discussion/comment/123770315#Comment_123770315

Is the Willis installed with the heating element top at the bottom? what setting is the Willis thermostat set to?. The 1/2 ins dia. outlet pipe seems to be the recommended one but can lead to very high outlet temps, some install 3/4 ins to help get faster circulation through the heater leading to lower outlet temperatures. There are thousands of these (conventionally) installed and I have rarely, if ever, seen any complaints about high temperatures which should be immediately apparent since they heat the cylinder from the top down.

You might post a photo of your set up sometime.

dingding

Hi John, Ill take a picture later and post it up.

The Willis is installed with the element and cable at the bottom. It works by getting very hot water from the top into the tank.

I am not sure what the thermostat setting is, Mine went faulty and I just installed the new one with what ever settings were in it. I dont think the thermostat is really an issue, When I look at the power through the Eddi, The thermostat does not cycle, it is the tank thermostat that controls the temperature.

As the water heats, it leaves the willis heater so it never trips the thermostat. I would expect for the thermostat to trip, the tank would need to heat to the willis termostat temperature all the way to the bottom 1/3 of the tank.

I must try to measure the temperature, I have the pipes insulated, but I would imagine you would burn your hand from the water. When I run a hot tap, the water is initally very hot as it is coming straight from the top of the tank.

dingding

Some photos added, the water exiting the Willis is over 70 C. This circulates to the top of the tank and the water drawn off from the top of the tank can be 70 degrees. The willis heater is installed externally towards the bottom of the tank. The sesnor is installed towards the centre of the tank, the hole I put in the insulation is under the grey duct tape. The sensor is under the top horizontal piece of duct tape.

Hope this explains how my set up works.

John.G

That's excellent, if the input power was 3kW when that photo was taken, then with a present 18C cold mains temperature, the flowrate through the heater is, 3*860/60/(73-18), 0.78LPM, so 5L of HW available after say 6 or 7 minutes?, also, even though you have the cylinder stat set to 50/55C you should still have practically a 1/3rd of a tank of water at around 70C before the probe gets to 50/55C as stratification will mean that hot water only hits that probe when the tank 1/3rd is almost "full" of very hot water.

Or, are you showing it starting at 73C and then when the circulation gets going that its at 53.5C?. in which case its circulating at 1.2LPM.

dingding

When I took the thermal photo, the heater was being powered by the Eddi, I think on one of the Solar Topup sessions. I just checked the MyEnergi app and it looks like the Eddi was applying about 1Kw or less to the element.

I will try to get a thermal image later when it is pushing the full 3KW through the heater. Your calculation above was the example the builder gave me when he was suggesting I get the Willis Heater in. It gives you a few liters of hot water very quickly so you can get a sink full of water very quickly. The way the house is wired, there isa switch at the kitchen sink which supplies power to the Willis Heater, It is just left permanently on now and energises the Eddi.

dingding

The top picture shows the Eddi and the heat from the transistors. The picture above shows the water heated to 55 C on night rate electricity using about 2Kw (2.28KwHr). Then the excess solar about 2Kw(2.13 KwHr) Heats the water to 50 C and makes up for the lost temperature in hot water usage. At the time of taking the pictures in the previous post, at best the Eddi was pushing one Kw through the element.

It gives me a good control on the water heating, giving me 50 C on a sunny day, with the excess exported. In the winter, the coil from the oil fired central heating, heats up the themperature probe, essentially disabling the electric heating of the water.

I use a Tado X system controlling the heating of the radiators and the hot water cylinder through a valve on the hot water circuit. This has allowed me to cut my usage of kerosene to about 800L per year. The Tado X system, with a pumped beads in the wall and attic insulation would have halved by kerosene usage.

dingding

This is the graph for the full day yesterday. So the system gives me constant hot water. Interesting the extra lagging jacket made a big difference when I installed it.

John.G

Just to be clear on this, you are using the Willis for all (electric) HW heating?, if so, at night, assuming you have a 3kW (willis) heating element, how to you control the power, ie kW, through it, or is it all (3kW) or nothing?

dingding

At night when it is not on solar, it heats at 100% i.e. 3Kw.

So I have it timed to come on at 6 for a couple of hours to heat to 55 C.

I also have it set to heat to 50 C on the excess solar, so if it needs heating and it can use reduced power to balance with the excess solar.

So I heat it for about 12c per unit at night and I forfeit 20c per unit in export to heat during the day.

When you look at the full day chart, you can see it max power 3Kw from 6am till its up to temp.

Then during the day, it tops it up with excess solar, with a variable power depending on available energy.

During the winter the Oil heating heats the water above the 55c or 50c so no electricity is used.

John.G

Ok, thanks, what is the Willis outlet temperature then during that period and is that its max, once circulation has started?

dingding

hi John.

I’ll try to measure it with the camera later. I have a laser temperature measurement device which might be more accurate at measuring a point.

manatoo

All very interesting. You guys clearly are on a different level of understanding of all this than I am.

That said, elements do align with how I have set up my system so I'll give you the details.

The smart electricity plan I'm on provides for cheaper KWh rate between 11pm and 8am so I have my Eddi set to power the long element from 5am for 1 hour. I have a 120l factory insulated stainless steel cylinder. Unless someone has used most/all of the available hot water by having a bath after the sun has gone down on the previous day, the 1 hour at constant 2.8kw is enough to heat the water to the immersion thermostat setting which I think is 60 degrees. Generally assuming a full hot tank is in place at sundown, it only takes 15-25 minutes of night rate to get the cylinder back to the max temp setting. Afterward, similar to dingding, the Eddi heats the water back up to the thermostat setting at variable kw depending on what the solar pv is producing. My panel orientation is East/West so on a sunny morning the whole tank is topped up to the max by 9am. Even if it's overcast it will top up by 12 midday. Throughout the day when the water temp drops below the thermostat setting the Eddi cuts back in to top up using whatever KW is available until the max temp is reached again.

I noted dingding heats his water on the night rate from 6am. I had this setting in place rather than 5am also but I was finding at peak summer the solar PV was kicking in as early as 6am as the sun rose so I was still using solar PV and not entirely the night rate so I moved the night rate scheduler back by an hour.

As mentioned above, I now leave the Eddi setup powering the long element only for reasons mentioned.

When I first had the system installed I just let the Eddi handle all water heating from excess solar PV but when I signed up to the smart plan it occurred to me that the night rate (approx 13 KWh) is cheaper than the feed in tariff (19.5c). Hence I set up the 1 hour night rate heating to allow more excess solar PV to be exported and less utilised. I'm pretty sure this is a major hole in the eco-argument for solar PV. I guess it depends on how much of your exported KWh the grid is able to utilise.

One key difference I see to dingding's setup is that during the less sunny months my intention is still to leave the above setup in place rather than use the coil to heat the cylinder. The reason is that I've found that heating the tank electrically using the night rate is cheaper than using the gas to do the same thing. This isn't a guesstimation. I've noted the gas unit usage under identical circumstances (time, ambient temp and cylinder temp and only applying the water heating zone) using both and it's consistently cheaper to use night rate electricity. Since the boiler I have is brand new and was installed at the same time as the solar PV as part of a whole house upgrade I was surprised and a little disappointed at this because the old boiler which was 30 years old and supposedly far less efficient cost more or less the same to do the same job, again using readings to calculate.

John.G

If you have a dual immersion with a short and long heating element then, generally, the rod type thermostat only extends down the length (or maybe a slight bit more) of the short element so only sensing ~ the top 30% of the cylinder vol, in your case around 35L, if you end up with a "full" cylinder of hot water either heated by the Eddi or from the Mains then either practically the total cylinder contents or certainly ~ 75/80% must be used up to make the stat switch in again or say overnight (with no HW draw off) the cylinder must lose ~ 8C (the stat hysteresis) to make it switch back on, this possibly accounts for your 15/25 minute reheat, theoretically, 120*8/860, 1.12kWh, 1.12/2.7*60, 25 minutes. THe problem is that during the day, if say the cylinder had reached its cut out temperature with maybe 3 hours more Eddie available then it can't be utilized unless a huge vol of HW is drawn off. Also the heating element may only reach down 75% or so otherwise it might foul the heating coil. I think this is the or another reason that some go for the Wiilis?.

Buffman

Just on the cost side of things, if your night rate is less than the FIT, which most if not all are, then it would probably work out financially better to heat your water at night on cheap rate and sell all excess solar possible back to the grid for higher FIT. (Depending on usage etc.)

Similarly a lot of people with batteries will charge them at night on cheap rate and then sell back for higher FIT.

manatoo

https://www.boards.ie/discussion/comment/123777761#Comment_123777761

The dual immersion I have extends almost to the bottom of the 120l cylinder. I had to have an argument with the plumber about this because I made it crystal clear before the old smaller cylinder with single immersion was replaced that I wanted the new one to be fully heatable electrically so that I could use excess solar PV to heat it without using the coil/gas. They initially replaced the old cylinder with the new taller 120 litre cylinder and then proceeded to put in an identical single element short immersion to the one that had been in the old cylinder. When I spotted this they tried endlessly to convince me that no longer immersion would fit within the confines of the coil in the new larger cylinder and that I needed to use the coil (gas) to heat the full tank. I'm no plumber but thankfully I stood my ground on this and when they did eventually concede and replace it with a new longer double element immersion I watched it being installed and it did extend to almost the full depth of the cylinder.

You raise an interesting point about the length of the rod thermostat however. I thought that the thermostat must sit just at the top or near the top of the immersion because it was by coming to this conclusion that I diagnosed the initial issue where only the top of the tank was heating when I had it set to heat sink and then bath once sink was showing max temp and switching to bath at that point was doing nothing. I drained off a full tank of hot water and once the cylinder had refilled it then heated it the complete tank without issue. My reading of this was therefore that with the thermostat at the top of the cylinder and the longer element heating, then the cylinder heated more or less uniformly meaning that when the thermostat cut off, the full tank had been heated and not just the top.

However it's working, I am getting a full hot tank, including by Eddi solar PV now. For example, on Sunday night the tank was heated as usual by mains low rate at 5am-6am. As usual it was topped up by solar PV as the sun rose and then maintained until approx 12pm when a household member had a bath. As far as I'm aware a bath draws off more than 60%-75% of the contents of the cylinder, possibly more. I observed on the Eddi app that it began solar PV reheating of the cylinder immediately at 2.5kw+ and took about 90-120 minutes until max temp was reached and later that day, around 7pm, another householder had a bath and again was able to draw off the same amount of hot water from the cylinder without issue.

manatoo

https://www.boards.ie/discussion/comment/123777808#Comment_123777808

Hi Buffman

Yes, correct. I do now heat the water on the night rate for an hour and then sell excess on the FIT using the Eddi only to top up the hot water stock throughout the day.

To be honest, doing the above brings into question the value in having an Eddi at all since if you've a sufficiently large hot water store built up from the FIT rate overnight, the Eddi wouldn't be needed for topping up during the day and all excess solar would just be sold to the FIT. It makes the payoff period of the Eddi very very very long, especially at the ridiculous cost my plumber charged for its installation….unfortunately I didn't fully understand the above when I specced out the system. If I was doing it again I probably wouldn't bother with the Eddi.

Buffman

@manatoo Yes, before FIT was available a solar diverter was possibly worth it but with current rates they just don't justify their high cost.

There is a lot of information over on the renewables section about how to maximise your return if you haven't seen it.

https://www.boards.ie/categories/renewable-energies