Which type of 300 litre hot water cylinder works best with solar PV?

Bif

Hi. I am changing my old hot water cylinder to a 300 litre model. I want to be able to heat with my kerosene boiler but I mainly use the immersion via a MyEnergi Eddi diverter for electricity from my solar PV. Which model should I look for? I was considering a Joule stainless steel version. It is an a vented heating system. All suggestions welcome. Thanks.

darraghsherwin

I have been looking into changing my cylinder too, I think the Joule TCEMVI-0300NFC looks like a good fit

graememk

Parking the " it will be cheaper to heat via kero and export the solar"

What you are looking for is the immersion as low as possible and/or an external Willis style immersion fitted.

Also with the thermostatic mixing valve on the output, so you can store the water at a higher temperature and it gets mixed down with the cold to a safe level.

Or a destratification pump to equal out the tank

bullit_dodger

That's a fair point that Graememk makes above. The location of the immersion in the tank really affects the amount of hot water you get. The lower down it is helps heat a larger amount. The draw back is that unless you have 2x immersions in there, it's difficult them with a low immersion location to only heat a "sink" amount of water.

My 200L tank gives 200L of hot water nearly when heating via the domestic hot water, but I estimate I only get about 120-130L of hot water from the electric immersion coil because the coil internally only goes about half way down into the tank.

slave1

I got the Joule stainless steel 300L last year with twin coil as I have oil and stove also.

As GMK said, my "top" immersion is a Willis (heats from the top down) and my bottom immersion is the usual fixed at the side immersion, I rarely use it as the Willis operates on a syphon principle so eventually heats the whole tank (much hotter at the top obviously), I get a bit of hot/cold mixing but not at a level I'm so concerned to fit a destratification

bullit_dodger

Yeah, I looked at getting one of those Willis heaters installed too (Graememk tipped me off on it). Decided since it was only me in the house to not go that road as it wasn't justifiable, but I like the concept of it.

So when you heat via the lower immersion, how much of your 300L do you reckon you get? Out of curiosity….

Jonathan

https://www.boards.ie/discussion/comment/121973945#Comment_121973945

For horizontal immersions, you heat from that point to the top of the cylinder. So work out the ratio of the heights and you'll have reasonably good approximate.

Source: my cylinder has a horizontal immersion.

bullit_dodger

https://www.boards.ie/discussion/comment/121974039#Comment_121974039

Generally I'd agree with that, but what happens in my experience is that the hotter water circulating up through the center of the tank from the immersion coil creates circulatory flows and hot water does go down "a little" beneath where the coil is. The reason I bring this up is sort of a heads up to people who might be thinking of swapping out their tank and going for a larger one is that you won't necessarily get all that water.

I went from (circa) 120L tank last year to 200L, but in real terms my hot water probably went from 80-90L to 120-130L - when I'm comparing heating with electrics. Just something to be aware of if your thinking that say 300L will solve all your water shortages.

slave1

https://www.boards.ie/discussion/comment/121973945#Comment_121973945

Well two drawbacks if looking to lower immersion

1. It will only heat above itself so maybe 2/3 of a tank, the bottom immersion is annoyingly not at the bottom but I guess my coils occupy that space
2. You cannot heat as much as the Willis, mine is at 85degrees in the tank and temp sensors will peak at 85top and 54bottom (where the sensors are placed)

Jonathan

https://www.boards.ie/discussion/comment/121974167#Comment_121974167

I don't see any mixing below the element. I've got three sensors on the cylinder; two above the immersion element, and one below. There is no change registered on the bottom sensor when heating.

There is a slight issue with calibration of the top two sensors, they should be the same, but the middle one is out by about 1.5°C.

Ha Long Bay

I see the same here on Saturday I use the Eddi to heat the water as I have free electricity on the current tariff.

This is heating gas where the sensor is below the immersion.

Back to the original question I got a Joule 300L single coil single immersion cylinder installed last year and very happy with it especially the heat retention.

Latro

Stainless steel Joule Cyclone 300l. The temperature probe pocket is about 20cm from the top.

14 days:

And 1 day:

It loses about 0.33 degree per hour.

bullit_dodger

I do get a bit of heating (not much) below the bottom of the electric coil.

Before someone says it, the temperatures aren't correct. I know. They are not "proper" probes touching the tank but Govee sensors like.

https://www.amazon.co.uk/Govee-Thermometer-Hygrometer-Temperature-Greenhouse/dp/B08Y8XHNL8/ref%3Dsr_1_3_sspa?crid=QT6LEIAG8KGS&dib=eyJ2IjoiMSJ9.dQVgsIW_AQEVVSzs72dQKGG1mImKbHR5E97Uc-ULMtg4s2nOehhIrjpFiOGdnxZNFKApSZg9OnNE4679U8tr7xc26AbQopAqKzLdhArk6HiKp4k08MNaXKomosmOgAYmmc38FHMrbBbvAx3NWlONkrGPtSkDTiAjdd78A9avHFKGaDSA0wzs4CJM62MmCM214QZswdBhu7I-qNUuorGf0y1Vb2EVGSyftlnMzIrDZ1FltVksjjUm2AjWp9l6oLMMiJ60i0xZ88--3mfKJKxq48lHC_B50qgM2HVD7V0eenU.BWOHFUCaHFbvMUUqb2WNR1cgwFFSe_jYqgk-GgsRfyA&dib_tag=se&keywords=govee+temperature+sensor&qid=1712267626&sprefix=govee+temp%2Caps%2C92&sr=8-3-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

45C is on the upper one is when the water is actually 60C. I could recalibrate the sensors, but decided to leave it. The main thing above is that I get a small amount of heating on the bottom one. The sensor is about 6 inches below where the coil stops (assuming it's actually 36 inches which the spec says). I estimate a temp loss of about 0.5C/hr - or there abouts.

My old cyclinder with 2x lagging jackets was losing about 1c/hr, so these new tanks are pretty good.

Jonathan

https://www.boards.ie/discussion/comment/121977339#Comment_121977339

Is your immersion vertical or horizontal though?

bullit_dodger

https://www.boards.ie/discussion/comment/121977876#Comment_121977876

Vertical. that's why I'm somewhat at the mercy of what the specs say. It's apparently a 36 inch element, which means that my sensor is about 6 inches underneath where the bottom of the coil is, if I read the tape measure right :-)

It's more a curiosity to me to be fair - I like to understand these things.

Big Lar

My element is also 2/3rds the way up the tank and I would really like to put more solar into it if I could, I had considered a wilis but my HW system is pressurized and by all accounts the willis will not work, has anyone ever come up with a cheap pump idea that could circulate water inside the tank ?

graememk

https://www.boards.ie/discussion/comment/121980671#Comment_121980671

A normal circulation pump should be fine, out the top and in the bottom.

I have a kingspan stainless steel tank for the same purpose. The immersion is down at the bottom of the tank. It is designed for a closed system but works fine in my open system.

Haven't yet added the solar but it works fantastically off the kerosine boiler.

Big Lar

https://www.boards.ie/discussion/comment/121978793#Comment_121978793

I don't think it would be that simple at all. Have to be a brass pump for a start, the circulating pump is 1" so that's a mighty flow of water, I was looking for a handy half inch one but cant find one.

I wonder if one was to put a pipe straight up a meter or so from the outlet of the tank an then down back into the bottom would the water naturally circulate. Perhaps an automatic valve on that so that the water only naturally circulates when the immersion is on.

graememk

https://www.boards.ie/discussion/comment/121982647#Comment_121982647

The eddi can have the relay board that can trigger the pump.

Pump doesn't need to run for very long to mix up the tank, immersion reaches max temp, pump kicks in for 5 minutes, and then waits for max temp again

A motorised valve would prevent bypass if your only access is the flow in and out.

Bif

https://www.boards.ie/discussion/comment/121980808#Comment_121980808

thanks for the info. Any idea of model number and price? Thanks.

https://www.boards.ie/discussion/comment/121984475#Comment_121984475

I got mine second hand. Its relatively small but has never left us without hot water. I know they are expensive for the big tanks. They have lots of nice features like a baffle for the inlet cold feed to prevent mixing and the coil is right at the bottom of the tank to maximize the useful capacity.

Big Lar

https://www.boards.ie/discussion/comment/121980792#Comment_121980792

I as thinking of natural circulation loop out top of cylinder and back in the bottom with a motorized valve, where its purpose would be to stop natural circulation when the immersion is off, otherwise when the oil boiler has finished heating the tank it would mix all the water on the tank.

bullit_dodger

https://www.boards.ie/discussion/comment/121987218#Comment_121987218

I like that idea. Not sure there would be enough circulation there but in theory you would get "something", just don't think it would be enough. The water in the pipe might be losing heat with losses etc. What's the point of the motorized valve though? I'd just leave it as a normal valve, or missing. You want it open 99% of the time I would have thought?

Really a low powered pump (5-10 watts) is all your need there at that motorized valve location. Doesn't have to shift much water maybe 1L/min. Power it on the same feed as the immersion. So when the immersion is on the pump is on. Course you'd have to not be using an Eddi.

Rows Grower

I changed my 300lt twin coil vented cylinder before Christmas, did a lot of searching online and MD O Sheas was the best place to purchase the Joule.

graememk

https://www.boards.ie/discussion/comment/121987218#Comment_121987218

Unfortunately that won't work without a pump, there is nothing to make the cold water rise to drive the circulation. There's nothing to drive the natural convection, that setup is almost like a Willis setup, but the Willis heating the water drives the convection.

A standard 5m circulation pump will work, you can set it at the minimum speed which is about 5w

Latro

https://www.boards.ie/discussion/comment/121987218#Comment_121987218

As Graememk mentioned, this would not work. There would be no movement in this design. Also it could create other issues.

steamdave

What I'm about to write applies to all heating systems.

Before changing your tank, it will be beneficial to get a water analysis test to include the Langelier Index. I am having a new cylinder installed and I was given this advice by my heating engineer/plumber. If your LI is not neutral (about 5) it means there is a possibility of early damage to your system, particularly the cylinder.

Joule are a well advertised brand of cylinder, but check their warranty. You will need to have anodes in your system and if the anodes have not been replaced according to the warranty terms and your tank springs a leak, hard luck. I don't know where the anodes are placed but to me, it would be a pain in the backside to have to renew anodes on an ongoing basis.

Just saying, not knocking any brand or recommending any other.

Dave

https://www.boards.ie/discussion/comment/121990142#Comment_121990142

There are almost no municipal supplies that are in the acid range requiring such consideration. Most supplies are quite neutral to basic with quite high hardness.

steamdave

https://www.boards.ie/discussion/comment/121990199#Comment_121990199

I'm on a well and when the filter will be installed, I will ensure the LI is neutral. For mains water the option would be to go for a whole house filtration system, if required. Do you drink your mains water? Yuk.

Kingspan are a good make of cylinder so you shouldn't have any pinhole problems.

Dave

Ubbquittious

https://ecovolt.ie/products/h2o-hot-water-system/

Cylinder with built in heat pump

bullit_dodger

Heat pump makes a lot of sense for a immersion, although you'd probably need ducting as with the door closed in the hot press I guess there's not a lot of "air heat" available without a duct? Not in the market myself, but I couldn't find a price on that (curious)

bunderoon

I've a 250ltr triple coil stainless steel cylinder in since 2010. 3 zoned pumped manifold. One coil for oil, one for boiler stove and the third was planned for solar tubes. Immersion is 2/3s down the tank. Lose about 1c per 1.5 hours due to the feed of the inactive stove pulling the heat from it. Stove when lit, heats house and bedrooms and gives us about 1/2 a tank of hot water - where the coil is located in the tank. Fuel prices have gone up, making it more of a hassle these days.

I was hoping the cost of a 60 tube installation (due to orientation of roof) would go down over time and now that PV is much cheaper, its looking like PV to heat hot water going forward. Have an EV now and need to pull the trigger on an EV Electric rate 2am-5 or 6am for car and immersion. My issue is that the immersion will only heat half the tank at the very most. I have no means to mix the tank or de-stratify the hot and cold water. The bottom of the tank concerns me about the potential of Legionnaires.

I could get plumber to move the oil down to the bottom solar coil as oil seems to be the most efficient way to heat the tank. Later swap out tank for a dual coil and dual immersion tank. But then the massive cost of a house refit to get anything decent out of an A2W or A2A system.

I just dont know. Any advice welcome. Family of 4. 2 kids which will be using lots of hot water in the next couple of years.

graememk

https://www.boards.ie/discussion/comment/121993588#Comment_121993588

Legionella in the bottom section isn't a issue as it's too cold for it.

But I would get the oil connected to it to give you more reserve.

Immersion just above the solar coil?

bunderoon

https://www.boards.ie/discussion/comment/121993636#Comment_121993636

Good to know about the legionella.

I have a cheap temperature sensor with display connected into the top solar sensor tube. Works well for what it is.

I bought an EDDI from one of the boardsies here last year and wired it up over the weekend. The old ATP immersion clock eventually failed. I know it wont pay for itself but wanted to see how it works. Reversed the clamp on the Harvi and can see what I'm importing. Nice bit of kit. (Zappi to be installed very soon). Set the boost to the 3Kw immersion to 11A (2.5Kw) test. No issues. Plenty of space for DIY PV ground mounts, so will see how the above fares out in being utilised.

Yep, Immersion is above the solar. Solar coil at the very bottom. So I know if I move the oil to it, it will heat the entire tank. The way our house is plumbed with the external facing walled off 'outhouse boiler', the tank is about 4meters away from it so minimal heat losses. Boiler house, walk-in pumped shower and hotpress are in a line, think of three 5ft x 5ft cubes in a row.

I guess oil is here to stay for many years to come then..

curioustony

Many years ago I got a dual coil tank. Never made sense to get the tubes on the roof, so just looped the heat through twice. Very quick to heat 330l.

Next upgrade is a willis heater as the immersion is too high. Then I can take full advantage of the cheaper EV rate, and lower the boiler temp.

bunderoon

https://www.boards.ie/discussion/comment/121994078#Comment_121994078

Interesting idea. Means my plumber would only need to move the Boiler return down to the lower coil return and then make up a ~2ft 1" pipe copper joiner from bottom of coil2 to top of coil3. Brilliant.

I installed a Sonoff POW R3 remote relay for controlling the immersion, has a rating of 50amps. This was about €50.00 and I will be able to coordinate the solar PV, night rate and oil boiler to choose the cheapest energy source on the fly using Homeassistant. Bit cheaper than an EDDI and more versatile.

zg3409

I have a standard copper cylinder with an old dual sink bath immersion in from the top. It's a bit taller than standard and comes with basic attached insulation. Like here I find the bottom is not heated at all and I want to use tank as a day before energy store for hot showers at 7am. I know standard elements are available in different lengths

Next time I have a plumber in I intend to have a new element ready. Note the length may be slightly different to height of tank as it may not be exactly at the top and also angled down.

My understanding is it's best to heat sink first, and when hot then heat bath. This way you get hot water initially but a low amount and then longer term a full tank of medium then hot water. One concern is that system will detect when "sink" has reached desired temperature but switching off, if you immediately switch to bath mode then it should also be off as they typically share the exact same thermostat. I do have temperature sensors so I could heat sink to 60, then bath to say 70. The stat would never operate.

bullit_dodger

https://www.boards.ie/discussion/comment/121997897#Comment_121997897

My understanding is it's best to heat sink first, and when hot then heat bath. This way you get hot water initially but a low amount and then longer term a full tank of medium then hot water. One concern is that system will detect when "sink" has reached desired temperature but switching off, if you immediately switch to bath mode then it should also be off as they typically share the exact same thermostat. I do have temperature sensors so I could heat sink to 60, then bath to say 70. The stat would never operate.

Yeah, you correctly described the behavior. They share the 1 thermostat, so if you heat the tank with sink until temperature cutoff, and then move over to bath…..the bath won't work until the tank cools down by 2-3c. Depends on the size of the tank of course, but with 2.9Kw - it will heat most tanks in 60-90 minutes there abouts.

graememk

https://www.boards.ie/discussion/comment/121998020#Comment_121998020

Id even go as far, if heating from solar excess only use the bath element, as you said they share the same thermostat, at the very top. Yeah it may cool by a few degrees, and kick back in eventually, but will still quickly heat up the top bit and trigger the thermostat again.

Then top up with the sink if you need a boost of hot water in the evening.

TheSunIsShining

Hi,

Reading the above with great interest. I have a pretty standard 190l cylinder with gas as the main heating source - then your bog standard dual immersion which is top entry. I'm about to switch to an EV electric plan and was thinking of using the immersion during the EV rate window - cost per KW is cheaper during that window for electricity than for gas with the added bonus, as I understand it, of pretty much 100% efficiency.

However, much like the above discussion, what I'm seeing in practice is that the immersion is having zero impact on the temperature probe which controls the call to the gas boiler. That probe is in a thermostat pocket about 1/4 or 1/3 up from the bottom of the cylinder. So clearly the immersion coil ends above that probe. But if I do use the immersion for the 3 hours of the cheap EV electricity, my expectation is that the gas boiler will still receive a call for hear - that controller is a Sonoff which calls if the cylinder is below 40 degrees between 6.45am and 8.30am.

So I'd imagine I could heat using the immersion from 2 to 5am on the cheap EV rate - but at 6.45am the gas will still be called as the water at the probe level will still be below 40c. So it seems similar to the above discussion and wondering, other than a destrat pump or a willis, does anyone have practical experience of solving the riddle....?

Thanks

graememk

https://www.boards.ie/discussion/comment/122160211#Comment_122160211

You might be able to fit a longer immersion too,

TheSunIsShining

https://www.boards.ie/discussion/comment/122160276#Comment_122160276

That possibility occurred to me. The current tank is 54x18. But was wondering if the immersion needs to stop above the coil that the gas boiler drives?

oaklands

https://www.boards.ie/discussion/comment/121997045#Comment_121997045

can be had for almost half that on Ali…Also rating seems to be 25A (NOT 50A). Also consider others in the range I am using POWR320D (20A rating) to drive immersion during cheaper night EV rate at circa 2.6kW.

TheSunIsShining

https://www.boards.ie/discussion/comment/122160535#Comment_122160535

Do you not get caught for customs and handling fee if you chance Ali?

oaklands

it is included (has been that way for ages - vat is added by AliExpress)…just takes a while to arrive.

Once you are logged in & have IE set, the prices usually show with 23% VAT included.

PS: Alibaba is different

slave1

Not all sellers include VAT from AE, I've had a few caught in Customs so just left them and waited for delivery period to expire for refund

TheSunIsShining

https://www.boards.ie/discussion/comment/122160591#Comment_122160591

Thanks. Didn't know that. By the way - you're happy with the POWR320D driving the immersion - I.e. you're happy with it's 20A rating? I had been looking at the 25A R3 as well - as much for peace of mind etc

oaklands

https://www.boards.ie/discussion/comment/122160629#Comment_122160629

Originally I tried a smaller 16A rated switch(different brand) but that got too warm for my liking. Based on the size I suspect it was just for a light.

The POWR320D is fine I did not detect any issues over the last 6 months…. but my immersion runs at circa 2.6kW (others may be higher). I have it set up to turn on during the cheap rate and can also be controlled via eWelink & Home Assistant.
Note: The terminals on these are somewhat exposed!. (also be careful about connecting up 1, 2 or both elements)

"Not all sellers include VAT from AE"
@slave1 : It has never happened to me since it was introduced on AliExpress, which I use a lot+++. But a good tip if it ever does happen.