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Is a heap pump with an immersion/solar/EDDI a good idea?

  • 05-03-2022 1:50pm
    Registered Users Posts: 1,732 ✭✭✭

    As the title says, is a heap pump with an immersion and solar/EDDI a good idea.

    I'll be retrofitting shortly with a heat pump and solar PV. Is there any point in getting an EDDI coupled to an immersion for hot water? Obviously, most benefit would be achieved during the summer months.


  • Registered Users Posts: 1,456 ✭✭✭Evd-Burner

    From what I have learned, you can wire the Eddi in with the heatpump, so that of a certain excess is reached that the eddi will call on the heatpump to turn on.

    also depending on the output temp of the heatpump you may need an immersion regardless to go to 60c every so often for legionnaires etc.

  • Registered Users Posts: 10,977 ✭✭✭✭the_amazing_raisin

    My one word of warning would be to watch out for the "kit" heat pumps sold by some suppliers, they might make accessing the immersion heaters in the cylinder quite difficult

    Ideally you'd be able to use the heat pump itself as the diverter to take advantage of it's efficiency, but I've yet to find one that integrates properly with solar PV

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost

  • Registered Users Posts: 1,456 ✭✭✭Evd-Burner

    The Eddi can do it.

    See point 14 on their site regarding how to wire it.

    If you had a stratification buffer and how water tank you could even get some house heating out of it. Although you'd need a decent array.

  • Registered Users Posts: 1,732 ✭✭✭podge3

  • Registered Users Posts: 1,123 ✭✭✭The Bull

    What size array would work ok with this set up of an Eddi and heat pump? I am currently looking at a 5KW south facing solar array and do intend to hopeful add a heat pump down the road? The eddi sound like a handy piece of kit but would 5 KW be enough to run the unit on a average day of solar generation or what would a 8kw heat pump need power wise lets say per hour to work with the array ?

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  • Registered Users Posts: 2,466 ✭✭✭bullit_dodger

    I should say from the outset that I don't have a heat pump, so this is a little bit of speculation on my part. However, I think that trying to couple a PV setup to HP, while it sounds like a great idea, in reality (and it's kind of obvious when you think about it) the times of the year that you want heating are the very times of the year that solar is invariably pants. Wintertime.

    For some context, here's the output of my array for Nov-21, Dec-21 and Jan-21.

    I've highlighted the average production. This is for a 5.3kwp installation split in East/West configuration. Sure, if you had a south facing array you'd get a bit more, and of course you could "go large" with say a 8-9Kwp installation - but in reality, I'd say you'd be doing well to break an average of 5-6Kwhr.

    So if this is your average, and your house (probably) needs 10-15Kwhr if your a standard house, there's simply not enough energy to power a Heat Pump after powering your house.

    As Scotty would say, "Ya cannae change the laws of physics Jim!!"

  • Registered Users Posts: 994 ✭✭✭Mr Q

    Some brands of heat pumps can integrate with solar. But you hear very mixed reviews from people with this option.

    I will be adding it to mine but if I get the parts from Poland or similar it would cost around 100 Euro. So even if it doesn't work great I won't be too concerned. This also gives the option not just to heat the water but also to heat and cool the house. This is not just using the electrical element so you are gaining from doing it through the HP.

    As mentioned above you wont have much excess in the winter but for me I already use the HP to cool in the summer so it is a good option if it works well to use up the summer excess.

  • Registered Users Posts: 1,456 ✭✭✭Evd-Burner

    Agree on the heating, you wouldn't get much for the coldest months of the year. But it would be a lot more efficient at heating the water vs the eddi alone.

    If integrating with zappi there would be more excess to push into the car.

  • Registered Users Posts: 2,466 ✭✭✭bullit_dodger

    True - but if we go back to the original question, that being "is a heat pump with solar a good idea"....I'd go back to the fact that there simply isn't enough energy being captured by the panels in wintertime to make it a viable strategy. The concept is great and if you had enough panels, (think 30-40Kwp) your 100% right the HP would indeed be more efficient at heating water than Eddi - but I don't think my Eddi went into "active" mode from Nov1st until end of Feb for the first time.

    Course, I've a bigger load than most, but I fear this situation would be true for many.

    In summertime it's the opposite problem. most people are going around looking for ways to use our excess! :-)

  • Registered Users Posts: 1,732 ✭✭✭podge3

    Looks like there is no simple answer. I think I'm gone off the idea of an EDDI in favour of a battery.

    I had decided against a battery but now I'm thinking a battery might be more cost effective during the summer. By using the heatpump for just DHM running only off the battery might be the best idea. While the battery is more expensive, I don't think the cost of an EDDI will be recuperated.

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  • Registered Users Posts: 2,466 ✭✭✭bullit_dodger

    Leaving aside the whole heat pump efficiency side for a min, the general feeling on the forums, is that it's difficult make your money back on a Eddi. Even if you do the simple math of it, Eddi costs say €500. Your 2.5Kw immersion heater will heat the water in what ... an hour? Less? Let's say an hour to keep the math easy.

    So that's 2.5Kwhr @ €0.20/unit = €0.50 to heat the water in the tank for 1 day.

    (I'll assume a regular sized tank and your using day rate, if you use night rate or a combination, the payback time is worse... let's be generous here)

    So that's 1000 "charges" of the immersion, or basically you heating the immersion each and every day for 3 years. And your fully using the tank every day so that there's no hot water left over from day 1 into day 2.

    That's best cast. If you start to get more realistic, heading the tank on a timer at night rate, and then perhaps only doing a "boost" for 10 mins when you need it, it becomes less favourable.

    All that said, I bought one! I know the math isn't there, but it's nice to have the convience of doing that "once off" payment of €500 and then hopefully having hot water for 7-8 months of the year.

  • Registered Users Posts: 1,732 ✭✭✭podge3

    I've done similar calculations but I'm assuming that I'll have surplus solar for only about 4 months of the year so that's more like 9 years payback!

    Thats at current electricity prices of course. And not including any FIT, small and all as it might be.

  • Registered Users Posts: 2,466 ✭✭✭bullit_dodger

    Yup your dead right podge3 and it's great to see you've thrashed it out mentally. It doesn't factor in a FIT, which would pay for (even meagerly) a few cents for those units you export. Or include the fact that that you have to use every liter, every day, of that tank of water. Or the fact that that there are days (even over the summer!) that there isn't enough sunshine to get the house load covered, battery full and then the tank heated, so you might be turning on the "grid power" anyway.

    Still as mentioned, while the payback isn't there, I really like the concept of hot water on tap half the year or more and I can be a little flippant about using it... or not. I think the main thing of the forums here isn't to tell people what to do, but rather give them the info and let them decide themselves. As long as people are making informed decisions, that's the main thing.

  • Registered Users Posts: 1,599 ✭✭✭THE ALM

    Agree on the payback of the Eddi but to see that solar generation feeding into the Eddi and have piping hot water is one of the small joys in life.

    It is only a handful of days since February that we haven't managed to heat the water using the Eddi, we averaged 2.88kWh/day for the month. We did save a few € by getting the Eddi from the local electrical wholesaler at €400 and fitted it ourselves.

    As we have oil fired heating it meant running this in summer or turning on the immersion to get hot water before.

    Another change for us is not having to use the pumped electric shower which consumed 9000W compared to the pumped shower using 800w as we now have sufficient hot water most of the year.

  • Registered Users Posts: 297 ✭✭spose

    I think the eddi payback can be better. Appreciate its case dependent. We have oil boiler and a 300L tank. From April to October we always have hot water and don’t need to use the boiler at all for a few months a year. The iboost puts ~1.4MWh a year in to the tank. There’s plenty of factors you can take in to account trying to calculate payback but at its simplest take 7c/kWh for the oil or 16c based on my current electricity price I think it’s worth somewhere between 1 and 200 a year to me

  • Registered Users Posts: 2,466 ✭✭✭bullit_dodger

    Yeah, as mentioned I do like the Eddi, and I've always recommended get one (although I always tell people if they are buying one for "payback reasons", to at least go in with eyes open)

    To your point spose about the 1.4MWh into the tank a year. It's a fair point, and it sounds a fair whack doesn't it? However some of diversion could be on days where you weren't even in the house. Ok, the last year is a bad example with us all stuck from home with covid, but on a normal year, you'd be heating the immersion when your living it up on holliers for 2 weeks in spain :-)

    Seems wrong to count times like that as savings, as the logic is that you wouldn't be heating the water with oil/grid if you were doing it manually. Also, the 1.4Mwh assumes you used every single gallon every day, for it to classify it as "savings". In reality you won't empty the tank of all the hot water every day. So of that 1.4MWh, I'd say if you used 600-700Kwhr, I'd be impressed. Since most of that energy could be done at night rate more likely €60-70/year, and of course you could simply just have a timer to come on at 2pm when the solar is out, and sort of "cheat" and do a immersion with a smart plug.

    It's a bit sad really that that payback isn't great - but I love it. Think it's a great addition to a solar installation.

  • Registered Users Posts: 297 ✭✭spose

    if the energy goes in to the tank the only way it comes out is through the tap or heat loss from the tank and the heat loss is pretty minimal. Like if the house was empty and the tank hot on day 1 then it can only take a kw or so the next day to top it back up so I’m pretty comfortable that what ever went in to it we used. We don’t have a day/night meter. Agree though savings isn’t the best benefit. For me it’s not having to use the oil at all and always having plenty of hot water without having to think about it