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

  • 03-04-2024 03:11PM
    #1
    Registered Users, Registered Users 2 Posts: 728 ✭✭✭


    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.



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Comments

  • Registered Users, Registered Users 2 Posts: 170 ✭✭darraghsherwin


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



  • Moderators, Home & Garden Moderators Posts: 7,102 Mod ✭✭✭✭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

    Post edited by graememk on


  • Registered Users, Registered Users 2 Posts: 2,700 ✭✭✭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.



  • Moderators, Sports Moderators Posts: 18,289 Mod ✭✭✭✭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

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  • Registered Users, Registered Users 2 Posts: 2,700 ✭✭✭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….



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  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,309 Mod ✭✭✭✭Jonathan


    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.



  • Registered Users, Registered Users 2 Posts: 2,700 ✭✭✭bullit_dodger


    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.



  • Moderators, Sports Moderators Posts: 18,289 Mod ✭✭✭✭slave1


    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)

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  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,309 Mod ✭✭✭✭Jonathan


    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.

    Screenshot_20240404-190225.png

    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.



  • Registered Users, Registered Users 2 Posts: 18,848 ✭✭✭✭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.

    1.png

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

    2.png

    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.



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  • Registered Users, Registered Users 2 Posts: 223 ✭✭Latro


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

    14 days:

    Joule1.PNG

    And 1 day:

    image.png

    It loses about 0.33 degree per hour.



  • Registered Users, Registered Users 2 Posts: 2,700 ✭✭✭bullit_dodger


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

    image.png

    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.



  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,309 Mod ✭✭✭✭Jonathan


    Is your immersion vertical or horizontal though?



  • Registered Users, Registered Users 2 Posts: 2,700 ✭✭✭bullit_dodger


    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.



  • Registered Users, Registered Users 2 Posts: 1,444 ✭✭✭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 ?



  • Moderators, Home & Garden Moderators Posts: 7,102 Mod ✭✭✭✭graememk


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



  • Posts: 6,626 ✭✭✭ [Deleted User]


    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.



  • Registered Users, Registered Users 2 Posts: 1,444 ✭✭✭Big Lar


    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.



  • Moderators, Home & Garden Moderators Posts: 7,102 Mod ✭✭✭✭graememk


    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.



  • Registered Users, Registered Users 2 Posts: 728 ✭✭✭Bif


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



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  • Posts: 6,626 ✭✭✭ [Deleted User]


    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.



  • Registered Users, Registered Users 2 Posts: 1,444 ✭✭✭Big Lar


    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.

    image.png


  • Registered Users, Registered Users 2 Posts: 2,700 ✭✭✭bullit_dodger


    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.



  • Registered Users, Registered Users 2 Posts: 8,575 ✭✭✭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.

    "Very soon we are going to Mars. You wouldn't have been going to Mars if my opponent won, that I can tell you. You wouldn't even be thinking about it."

    Donald Trump, March 13th 2018.



  • Moderators, Home & Garden Moderators Posts: 7,102 Mod ✭✭✭✭graememk


    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



  • Registered Users, Registered Users 2 Posts: 223 ✭✭Latro


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



  • Registered Users, Registered Users 2 Posts: 167 ✭✭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



  • Posts: 6,626 ✭✭✭ [Deleted User]


    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.



  • Registered Users, Registered Users 2 Posts: 167 ✭✭steamdave


    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



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  • Registered Users, Registered Users 2 Posts: 6,337 ✭✭✭Ubbquittious




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